The influence of temperature on the machining accuracy of the machine tool

Thermal deformation is one of the reasons that affect the machining accuracy, the machine tool is affected by the change of the ambient temperature of the workshop, the heating of the motor and the friction of mechanical movement, the heat of cutting and the cooling medium, resulting in the uneven temperature rise of each part of the machine tool, resulting in the change of the shape accuracy and machining accuracy of the machine tool. For example, if a 70mm×1650mm screw is machined on a CNC milling machine with ordinary precision, the cumulative error of the milled workpiece from 7:30 a.m. to 9:00 a.m. can vary by up to 85m compared with the workpiece processed from 2:00 p.m. to 3:30 p.m. At constant temperature, the error can be reduced to 40m.

For another example, a precision double-end grinding machine for double-end grinding of 0.6~3.5mm thick thin steel sheet workpieces, processing 200mm×25mm×1.08mm steel sheet workpieces can achieve mm dimensional accuracy, and the bending degree is less than 5m in the full length. However, after continuous automatic grinding for 1 hour, the size change range increased to 12m, and the coolant temperature increased from 17°C at start-up to 45°C. Due to the influence of grinding heat, the spindle journal elongates and the front bearing clearance of the spindle increases. Accordingly, the addition of a 5.5 kW chiller to the machine’s coolant tank was a perfect result.

Practice has proved that the deformation of the machine tool after heating is an important reason affecting the machining accuracy. However, the machine tool is in an environment where the temperature changes everywhere at any time; The machine tool itself will inevitably consume energy when working, and a considerable part of these energy will be converted into heat in various ways, causing physical changes in the components of the machine tool, which are very different because of the different structural forms, the differences in materials and other reasons. Machine tool designers should grasp the formation mechanism of heat and the law of temperature distribution, and take corresponding measures to minimize the impact of thermal deformation on machining accuracy.

Temperature rise and temperature distribution of the machine tool

  1. Natural climate influences

China has a vast territory, most of which is in the subtropics, and the temperature varies greatly throughout the year, and the temperature difference varies differently in one day. As a result, people intervene in different ways and degrees of temperature in the room (e.g. on the shop floor), and the temperature atmosphere around the machine can vary greatly. For example, the seasonal temperature change range in the Yangtze River Delta region is about 45 °C, and the diurnal temperature change is about 5~12 °C. The machining workshop generally has no heating in winter and no air conditioning in summer, but as long as the workshop is well ventilated, the temperature gradient in the machining workshop does not change much. In the Northeast, the seasonal temperature difference can reach 60 °C, and the diurnal variation is about 8~15 °C. The heating period is from late October to early April of the following year, and the design of the machine shop is heated, and the air circulation is insufficient. The temperature difference between the inside and outside of the workshop can reach 50°C. Therefore, the temperature gradient in the workshop in winter is very complex, the outdoor temperature is 1.5 °C when the measurement is timed, the time is 8:15-8:35 in the morning, and the temperature change in the workshop is about 3.5 °C. The machining accuracy of precision machine tools will be greatly affected by the ambient temperature in such a workshop.

  1. The influence of the surrounding environment

The surrounding environment of the machine tool refers to the thermal environment formed by various layouts within the close range of the machine tool. They include the following 4 aspects.

(1) Workshop microclimate: such as the distribution of temperature in the workshop (vertical direction, horizontal direction). When day and night alternate or when the climate and ventilation change, the temperature of the workshop changes slowly.

(2) Workshop heat source: such as sun exposure, heating equipment and high-power lighting radiation, etc., they can directly affect the temperature rise of the whole or part of the machine tool for a long time when they are close to the machine tool. The heat generated by adjacent equipment during operation can affect the temperature rise of the machine in the form of radiation or air movement.

(3) Heat dissipation: the foundation has a good heat dissipation effect, especially the foundation of the precision machine tool should not be close to the underground heating pipeline, once it is ruptured and leaked, it may become a heat source that is difficult to find the cause; An open workshop will be a good “radiator”, which is conducive to the temperature equalization of the workshop.

(4) Constant temperature: It is very effective for the workshop to maintain the accuracy and machining accuracy of precision machine tools by adopting constant temperature facilities, but the energy consumption is large.

  1. Thermal influencing factors inside the machine tool

1) Structural heat source of machine tool. Electric motor heating, such as spindle motors, feed servo motors, cooling and lubrication pump motors, electric control boxes, etc., can generate heat. These conditions are permissible for the motor itself, but have a significant adverse effect on components such as spindles and ball screws, and measures should be taken to isolate them. When the input electric energy drives the motor to run, except for a small part (about 20%), it is converted into the heat energy of the motor, and most of it will be converted into kinetic energy by the moving mechanism, such as spindle rotation, worktable movement, etc.; However, it is inevitable that a considerable part of it is still converted into friction heat during movement, such as the heat generation of bearings, guide rails, ball screws and gearboxes.

2) Cutting heat of the process. In the cutting process, part of the kinetic energy of the tool or workpiece is consumed by the cutting work, and a considerable part is converted into the deformation energy of cutting and the friction heat between the chip and the tool, forming the heating of the tool, the spindle and the workpiece, and the heat of a large number of chips is transmitted to the workbench fixture and other components of the machine tool. They will have a direct impact on the relative position of the tool and the workpiece.

3) Cooling. Cooling is a countermeasure to the temperature increase of the machine tool, such as the cooling of the electric motor, the cooling of the spindle components, and the cooling of the basic structural parts. High-end machine tools often equip the electric control box with a chiller and force cooling.

  1. The influence of the structural form of the machine tool on the temperature rise

In the field of thermal deformation of machine tools, the structural form of machine tools is discussed, usually referring to the structural form, mass distribution, material properties and heat source distribution. The structural shape affects the temperature distribution of the machine tool, the direction of heat conduction, the direction of thermal deformation and matching, etc.

1) The structural form of the machine tool. In terms of overall structure, the machine tool has vertical, horizontal, gantry and cantilever type, etc., and the thermal response and stability are quite different. For example, the temperature rise of the headstock of the lathe with variable gear speed can be as high as 35°C, so that the spindle end is raised, and the thermal equilibrium time is about 2h. In the case of the inclined bed-type precision turning and milling machining center, the machine tool has a stable base. The rigidity of the whole machine is significantly improved, the spindle is driven by a servo motor, and the gear transmission part is removed, and its temperature rise is generally less than 15 °C.

2) The influence of heat source distribution. On machine tools, the heat source is often thought of as an electric motor. Such as spindle motors, feed motors and hydraulic systems, etc., are actually incomplete. The heat generation of the motor is only the energy consumed by the current on the armature impedance when bearing the load, and a considerable part of the energy is consumed by the friction work of the bearing, screw nut and guide rail. Therefore, the motor can be called the primary heat source, and the bearing, nut, guide rail and chips can be called the secondary heat source. Thermal distortion is the result of the combined influence of all these heat sources. The temperature rise and deformation of a column mobile vertical machining center in the Y-direction feed movement. The table does not move during the Y-direction feed, so it has little effect on the thermal deformation in the X-direction. On the column, the farther the point from the guide screw of the Y-axis, the smaller its temperature rise. The effect of heat source distribution on thermal deformation is further illustrated when the machine is moved in the Z-axis. The Z-axis feed is farther away from the X-direction, so the influence of thermal deformation is smaller, and the closer the column is to the Z-axis motor nut, the greater the temperature rise and deformation.

3) The influence of mass distribution. There are three aspects of the influence of mass distribution on the thermal deformation of machine tools. First, it refers to the mass size and concentration, which usually refers to changing the heat capacity and the speed of heat transfer, and changing the time to reach thermal equilibrium; Second, by changing the layout form of the mass, such as the arrangement of various ribs, the thermal stiffness of the structure is improved, and the influence of thermal deformation is reduced or the relative deformation is kept small under the same temperature rise; Third, it refers to changing the form of mass arrangement, such as arranging heat dissipation ribs outside the structure, to reduce the temperature rise of machine tool components.

4) Influence of material properties: Different materials have different thermal performance parameters (specific heat, thermal conductivity and linear expansion coefficient), and under the influence of the same heat, their temperature rise and deformation are different.

Testing of the thermal performance of machine tools

  1. The purpose of the thermal performance test of the machine tool

The key to controlling the thermal deformation of the machine tool is to fully understand the changes in the ambient temperature of the machine tool, the heat source and temperature changes of the machine itself, and the response (deformation displacement) of the key points through the thermal characteristics test. Test data or curves describe the thermal characteristics of a machine tool in order to take countermeasures, control thermal deformation, and improve the machining accuracy and efficiency of the machine tool. Specifically, the following objectives should be achieved:

1) Test the surrounding environment of the machine tool. Measure the temperature environment in the workshop, its spatial temperature gradient, changes in the temperature distribution during the alternation of day and night, and even the influence of seasonal changes on the temperature distribution around the machine tool.

2) Test the thermal characteristics of the machine tool itself. Under the condition of eliminating environmental interference as much as possible, let the machine tool be in various operating states to measure the temperature change and displacement change of the important points of the machine tool itself, record the temperature change and the displacement of key points in a long enough period of time, and also use the infrared thermal phase to record the heat distribution in each time period.

3) Test the temperature rise thermal deformation in the machining process to judge the influence of the thermal deformation of the machine tool on the accuracy of the machining process.

4) The above test can accumulate a large amount of data and curves, which will provide a reliable criterion for the design of machine tools and the control of thermal deformation by users, and point out the direction of effective measures.

  1. The principle of thermal deformation test of machine tools

Thermal deflection testing begins with the measurement of temperature at several relevant points, including the following:

1) Heat source: including feed motor, spindle motor, ball screw transmission pair, guide rail, spindle bearing.

2) Auxiliary devices: including hydraulic system, refrigerator, cooling and lubrication displacement detection system.

3) Mechanical structure: including bed, base, slide plate, column, milling head box and spindle. An indium steel probe is held between the spindle and the rotary table, and five contact sensors are configured in the X, Y, and Z directions to measure the comprehensive deformation in various states to simulate the relative displacement between the tool and the workpiece.

  1. Test data processing and analysis

The thermal deformation test of the machine tool should be carried out in a long continuous time, continuous data recording, and after analysis and processing, the thermal deformation characteristics reflected are highly reliable. If error culling is carried out through multiple trials, the regularity shown is credible.

A total of 5 measuring points are set up in the thermal deformation test of the spindle system, among which points 1 and 2 are at the end of the spindle and close to the spindle bearing, and points 4 and 5 are respectively at the milling head housing near the Z guide rail. The test time lasted for 14 hours, of which the spindle speed in the first 10 hours was alternately changed in the range of 0~9000r/min, and from the 10th hour, the spindle continued to rotate at a high speed of 9000r/min. The following conclusions can be drawn:

1) The thermal equilibrium time of the spindle is about 1h, and the temperature rise after equilibrium changes in the range of 1.5°C;

2) The temperature rise mainly comes from the spindle bearing and the spindle motor, and the thermal performance of the bearing is good in the normal speed range;

3) The effect of thermal deformation in the X direction is very small;

4) The Z-direction expansion and contraction deformation is large, about 10m, which is caused by the thermal elongation of the spindle and the increase of the bearing clearance;

5) When the speed continues at 9000r/min, the temperature rise rises sharply, rises sharply about 7°C within 2.5h, and there is a tendency to continue to rise, and the deformation in the Y and Z directions reaches 29m and 37m, indicating that the spindle can not run stably when the speed is 9000r/min, but it can run in a short time (20min).

Control of thermal deformation of machine tools

From the above analysis and discussion, the temperature rise and thermal deformation of the machine tool have a variety of influencing factors on the machining accuracy, when taking control measures, the main contradiction should be grasped, and one or two measures should be taken to achieve twice the result with half the effort. In the design, we should start from four directions: reduce heat generation, reduce temperature rise, balance structure, and reasonable cooling.  

  1. Reduce fever

Controlling the heat source is a fundamental measure. In the design, measures should be taken to effectively reduce the heat generation of the heat source.

1) Reasonably select the rated power of the motor. The output power P of the motor is equal to the product of voltage V and current I, in general, the voltage V is constant, therefore, the increase of load, means that the output power of the motor increases, that is, the corresponding current I also increases, then the heat dissipated in the armature impedance increases. If the motor we designed and selected works close to or greatly exceeds the rated power for a long time, the temperature rise of the motor will increase significantly. To this end, a comparative test was carried out on the milling head of BK50 CNC needle groove milling machine (motor speed: 960r/min; Ambient temperature: 12°C).

The following concepts are obtained from the above test: from the heat source performance consideration, whether the spindle motor or the feed motor, when selecting the rated power, it is best to choose about 25% greater than the calculated power, in the actual operation, the output power of the motor matches the load, and the impact of increasing the rated power of the motor on energy consumption is very small. However, it can effectively reduce the temperature rise of the motor.

2) Appropriate measures should be taken to reduce the heat generation of the secondary heat source and reduce the temperature rise. For example, when designing the spindle structure, the coaxiality of the front and rear bearings should be improved, and high-precision bearings should be used. Where possible, change the sliding guide to a linear rolling guide, or use a linear motor. These new technologies can effectively reduce friction, reduce heat generation, and reduce temperature rise. Metal processing WeChat, the content is good, it is worth paying attention to!

3) In terms of process, high-speed cutting is adopted. Based on the mechanism of high-speed cutting. When the linear velocity of metal cutting is higher than a certain range, the metal to be cut has no time to produce plastic deformation, no deformation heat is generated on the chip, and most of the cutting energy is converted into chip kinetic energy and is taken away.

  1. Structural balance to reduce thermal deformation

In machine tools, where the heat source is always present, further attention needs to be paid to how the direction and speed of heat transfer can help reduce heat distortion. Or the structure has good symmetry, so that the heat transfer is along the symmetrical direction, so that the temperature distribution is uniform, and the deformation cancels each other out, becoming a thermal affinity structure.

1) Prestress and thermal deformation. In the higher-speed feed system, the ball screw is often fixed axially at both ends to form a pre-tensile stress. This structure has an obvious effect on reducing the thermal deformation error in addition to improving the dynamic and static stability of high-speed feed.

The axial fixed structure with a total length of 600 mm pre-stretched for 35 m is relatively close to the temperature rise under different feed rates. The cumulative error of the fixed pre-tensioned structure at both ends is significantly smaller than that of the structure with a single end fixed and the free elongation of the other end. In the axially fixed pre-tension structure at both ends, the temperature rise caused by heat generation mainly changes the stress state inside the screw from tensile stress to zero stress or compressive stress. Therefore, it has little effect on the displacement accuracy.

2) Change the structure and change the direction of thermal deformation. The Z-axis spindle slide of the CNC needle groove milling machine with different ball screw axial fixed structures requires a milling groove depth error of 5m in the machining. The axial floating structure at the lower end of the lead screw is adopted, and the groove depth is gradually deepened from 0 to 0.045mm within 2 hours of processing. On the contrary, the structure of floating at the upper end of the lead screw can ensure that the groove depth changes.

3) The symmetry of the geometry of the machine tool structure can make the thermal deformation trend consistent, so that the drift of the tool tip point can be reduced as much as possible. For example, the YMC430 micromachining center launched by Yasda Precision Tools in Japan is a sub-micron high-speed machining machine, and the design of the machine tool is fully considered for thermal performance.

First of all, a completely symmetrical layout is adopted in the structure of the machine tool, and the column and beam are integrated structures, which are H-shaped, which is equivalent to a double column structure and has good symmetry. The approximately circular spindle slides are also symmetrical both longitudinally and transversely.

The feed drive of the three moving axes adopts linear motors, which makes it easier to achieve symmetry in the structure, and the two rotary axes are directly driven to minimize the friction loss of mechanical transmission.

  1. Reasonable cooling measures

1) The influence of coolant in machining on machining accuracy is direct. A comparative test was carried out on the GRV450C-type double-end grinding machine. The test shows that the heat exchange treatment of the coolant with the help of the refrigerator is very effective in improving the machining accuracy.

With the traditional coolant supply method, after 30 minutes, the size of the workpiece is out of tolerance. After using the refrigerator, it can be processed normally to more than 70min. The main reason for the deviation of the workpiece size at 80 minutes is that the grinding wheel needs to be trimmed (to remove metal chips on the grinding wheel face), and the original machining accuracy can be restored immediately after trimming. The effect is very noticeable. Similarly, very good results can be expected for forced cooling of the spindle.

2) Increase the natural cooling area. For example, adding a natural air cooling area to the spindle box structure can also have a good heat dissipation effect in the workshop with good air circulation.

3) Automatic chip removal in time. Timely or real-time evacuation of high-temperature chips out of the workpiece, table and tool section will be very beneficial in reducing the temperature rise and thermal distortion of critical parts. 

Vision & Vision

Controlling the thermal deformation of machine tools is an important topic in the field of modern precision machining, and the factors affecting the thermal deformation of machine tools are very complex. In addition, the simultaneous development of high speed, high efficiency and precision in modern cutting makes the thermal deformation problem of machine tools more prominent. It has attracted wide attention from the machine tool manufacturing community. Scholars in the machine tool industry at home and abroad have done a lot of research on this and have made considerable progress in theory. The problem of thermal deformation of machine tools has become one of the basic theories in machine tool research.

From the perspective of machine tool design and application, this paper analyzes the influencing factors, measurement and analysis methods of machine tool thermal performance, and proposes improvement design measures. Therefore, we believe that the optimal design of the thermal performance of the machine tool should start from the following aspects:

1) In the design stage of modern high-end machine tools, attention should be paid to the environmental conditions of the future application of the designed machine tools.

2) Controlling and configuring the heat source is key. Controlling the heat source mainly refers to the matching of the control energy consumption and the power source, adopting a new structure, reducing the secondary friction heat source, and improving the utilization rate of energy.  

3) Change the traditional thinking, and promote the cooling, heat dissipation, lubrication, chip removal and other devices from the status of “auxiliary” components of the machine tool to the status of “important” components, which cannot be underestimated.

4) Pay attention to the symmetry of the structure and the design of the direction of thermal deformation, so that the influence of thermal deformation on the accuracy is minimized, especially the research and application of the mathematical model of thermal deformation of structural parts, so as to provide qualitative and quantitative instructions for the design of thermal deformation control. 

Rationalization of milling cutter selection

1. Reasonable choice of milling tool applications with different tooth counts

Sparse-tooth milling cutters are unequal-pitch milling cutters. Because of the wide chip-bearing groove, they are suitable for milling long-chip metals such as stainless steel and aluminum alloy; and because the milling cutter has a small number of teeth milling metal at the same time, the cutting force generated is small, which is suitable for low-power spindle machine tools or workpieces with weak workpiece clamping.

Dense-tooth milling cutters are milling cutters with moderate number of teeth and have a wide range of versatility. They are usually recommended as the first choice.When the milling cutting force is required to be small, the method of reducing the number of blades is usually adopted, but the adjacent positions must be removed evenly.

Special dense tooth milling cutters are used in machine tools with sufficient spindle power. When the workpiece is clamped enough, the high-efficiency metal removal rate of large cutting depth and large tool walking can be obtained.It is also suitable for milling metals such as gray cast iron that require low chip capacity.

2. Reasonable choice of tool diameter

The choice of milling cutter diameter is usually based on the width of the workpiece and the effective power of the machine tool. By convention, the diameter of the milling cutter is selected according to the size of the workpiece, especially the milling width of the workpiece, but for a given face milling cutter, its optimal milling width is 70-80% of the nominal diameter of the milling cutter.So that the milling width is approximately equal to 2/3 of the diameter of the milling cutter, it can ensure that the blade cuts into the workpiece immediately from the beginning, with almost no friction. The milling width is less than 1/2 of the diameter of the milling cutter, and the blade begins to “rub” the workpiece. During rough milling, if the radial cutting width is less than 2/3 of the diameter of the milling cutter, the amount of tool travel will be increased, and the tool life will be improved.

3. Reasonable choice of the main declination angle of the tool

The main declination angle is the angle formed by the tool body and the front edge of the blade. The main declination angle will affect the chip thickness, cutting force and tool life. If the main declination angle is reduced at a given feed rate, the cutting thickness will be reduced. This is due to the fact that the cutting edge contacts the workpiece in a wider range. Reducing the main declination angle allows the blade to gradually cut into or exit the surface of the workpiece, which helps to reduce the radial pressure, protect the cutting edge of the blade, and reduce the chance of damage to the cutting edge, but its negative impact is that it will lead to an increase in axial pressure, which increases the possibility of vibration when machining thin-section workpieces and causes deviations on the machining surface.

Fourth, the reasonable choice of milling blades

It is best to use pressed blades for roughing, which can reduce processing costs.The dimensional accuracy and sharpness of the pressed blade are worse than that of the ground blade, but the edge strength of the pressed blade is better, it is resistant to impact during roughing and can withstand a larger depth of cut and feed.Sometimes the pressed blade has a chip rolling groove on the front tool surface, which can reduce the cutting force, but also reduce the friction with the workpiece and chips, and reduce the power requirement.However, the surface of the pressed blade is not as tight as that of the ground blade, the dimensional accuracy is poor, and the height of each tip on the milling cutter body differs a lot.Because the pressing blade is cheap, it is widely used in production.

For precision milling, it is best to choose a grinding blade.This kind of blade has good dimensional accuracy, so the positioning accuracy of the blade in milling is high, and good machining accuracy and surface roughness can be obtained.In addition, the development trend of grinding and milling blades used in finishing is to grind out the chip rolling groove to form a large positive front angle cutting edge, allowing the blade to cut on a small feed and a small depth of cut.For cemented carbide blades without sharp front corners, when small-feed and small-cut deep processing is used, the tip of the blade will rub against the workpiece and the tool life is short.

Five key issues in drilling and processing

As the most common tool in hole processing, drill bits are widely used in machinery manufacturing, especially for the processing of holes in parts such as cooling devices, power generation equipment, pipe plates, and steam generators. The application surface is particularly extensive and important.
1. The characteristics of drilling. Drill bits usually have two main cutting edges. During processing, the drill bits are rotated and cut at the same time.The front angle of the drill bit is getting larger and larger from the central axis to the outer edge. The closer it is to the outer circle, the higher the cutting speed of the drill bit, and the cutting speed decreases to the center, and the cutting speed of the drill bit at the center of rotation is zero.The horizontal edge of the drill bit is located near the central axis of rotation. The sub-front angle of the horizontal edge is large, there is no chip space, and the cutting speed is low, which will produce greater axial resistance.If the edge of the horizontal edge is sharpened into type A or type C in DIN1414, and the cutting edge near the central axis is a positive front angle, the cutting resistance can be reduced and the cutting performance can be significantly improved.
Depending on the shape, material, structure, function, etc. of the workpiece, drill bits can be divided into many types, such as high-speed steel drill bits (twist drills, group drills, flat drills), integral cemented carbide drill bits, indexable shallow hole drills, deep hole drills, nesting drills and interchangeable head drill bits.

2. The cutting of the chip breaking and chip removal drill bit is carried out in a hole with a narrow space, and the chips must be discharged through the edge groove of the drill bit, so the shape of the chips has a great impact on the cutting performance of the drill bit.Common chip shapes are flaky chip, tubular chip, needle chip, tapered spiral chip, ribbon chip, fan-shaped chip, powdery chip and so on.The key to drilling-chip control
When the shape of the chips is not appropriate, the following problems will arise: ① Fine chips block the edge groove, affect the drilling accuracy, reduce the life of the drill bit, and even break the drill bit (such as powdery chips, fan-shaped chips, etc.).②The long chips wrap around the drill bit, which hinders the operation, causes the drill bit to break or prevents the cutting fluid from entering the hole (such as spiral chips, ribbon chips, etc.).
How to solve the problem of improper chip shape:
①the methods of increasing the feed volume, intermittent feed, sharpening the horizontal edge, and installing a chip breaker can be used separately or in combination to improve the chip breaking and chip removal effect, and eliminate the problems caused by chips.
② You can use a professional chip breaking drill bit to punch holes.For example: adding a designed chip breaking blade to the groove of the drill bit will break the chips into debris that is easier to remove.Debris is removed smoothly along the groove, and no clogging in the groove will occur.Therefore, the new type of chip breaking drill has obtained a much smoother cutting effect than the traditional drill bit.At the same time, the short-broken iron shavings make it easier for the coolant to flow to the drill tip, further improving the heat dissipation effect and cutting performance during processing.Moreover, because the new chip-breaking blade penetrates the entire groove of the drill bit, its shape and function can still be maintained after multiple grinding.In addition to the above functional improvements, it is worth mentioning that the design strengthens the rigidity of the drill body and significantly increases the number of drilling holes before a single grinding.

3. Drilling accuracy

The accuracy of the hole is mainly composed of factors such as aperture size, position accuracy, coaxiality, roundness, surface roughness, and orifice burrs.
Factors that affect the accuracy of the hole to be machined during drilling:
①the clamping accuracy and cutting conditions of the drill bit, such as tool clamp, cutting speed, feed volume, cutting fluid, etc.
②The size and shape of the drill bit, such as the length of the drill bit, the shape of the blade, the shape of the drill core, etc.③The shape of the workpiece, such as the shape of the side of the orifice, the shape of the orifice, the thickness, the state of the card, etc.

Reaming
Reaming is caused by the swing of the drill bit during processing.The swing of the cutter clamp has a great impact on the aperture and the positioning accuracy of the hole, so when the cutter clamp is severely worn, a new cutter clamp should be replaced in time.When drilling small holes, it is more difficult to measure and adjust the swing, so it is best to use a coarse-shank small-blade drill bit with a good coaxiality between the blade and the shank.When using a re-grinding drill bit for processing, the reason for the decrease in hole accuracy is mostly due to the asymmetry of the shape behind it.Controlling the blade height difference can effectively suppress the cutting and expansion of the hole.
Roundness of the hole

Due to the vibration of the drill bit, the drilled hole shape can easily be polygonal, and lines like repeating lines appear on the hole wall.Common polygonal holes are mostly triangles or pentagons.The reason for the triangular hole is that the drill bit has two centers of rotation when drilling, and they vibrate at a frequency of 600 exchanges every interval. The main reason for the vibration is the unbalanced cutting resistance. When the drill bit rotates for one turn, due to the poor roundness of the processed hole, the resistance is unbalanced during the second turn of cutting, and the last vibration is repeated again, but the vibration phase is offset to a certain extent, resulting in the appearance of repeating lines on the hole wall.When the drilling depth reaches a certain level, the friction between the edge surface of the drill bit and the hole wall increases, the vibration attenuates, the reciprocating line disappears, and the roundness becomes better.This hole type is funnel-shaped from the longitudinal profile.For the same reason, pentagonal and heptagonal holes may also appear in cutting.In order to eliminate this phenomenon, in addition to controlling the vibration of the chuck, the height difference of the cutting edge, the asymmetry of the shape of the back and the blade, measures such as improving the rigidity of the drill bit, increasing the feed per revolution, reducing the rear angle, and sharpening the horizontal edge should also be taken.

Drilling holes on bevels and curved surfaces

When the knife-eating surface or drill-through surface of the drill bit is inclined, curved or stepped, the positioning accuracy is poor. Since the drill bit is radial and single-sided at this time, the tool life is reduced.In order to improve the positioning accuracy, the following measures can be taken:
① Drill the center hole first.
②.Use an end mill to mill the hole seat.③Choose a drill bit with good cut-in and rigidity.④Reduce the feed speed.

Treatment of burrs
During drilling, burrs will appear at the inlet and outlet of the hole, especially when processing materials and thin plates with high toughness.The reason is that when the drill bit is about to drill through, the processed material is plasticly deformed. At this time, the triangular part that should have been cut by the edge of the drill bit near the outer edge is deformed and bent to the outside by the axial cutting force, and it is further curled under the action of the chamfering of the outer edge of the drill bit and the edge surface of the edge belt, forming crimping or burrs.
Fourth, the processing conditions of drilling
In the general drill bit product sample book catalog, there is a “Basic Cutting Dosage Reference Table” arranged by the processing material. Users can refer to the cutting dosage provided to select the cutting conditions for drilling.Whether the selection of cutting conditions is appropriate, trial cutting should be passed, and a comprehensive judgment based on factors such as machining accuracy, processing efficiency, and drill bit life should be made.
1 Drill bit life and processing efficiency

Under the premise of meeting the technical requirements of the workpiece to be processed, whether the drill bit is used properly should be comprehensively measured based on the service life and processing efficiency of the drill bit.The evaluation index of the service life of the drill bit can choose the cutting distance; the evaluation index of the processing efficiency can choose the feed speed.For high-speed steel drill bits, the service life of the drill bit is greatly affected by the rotation speed and less affected by the feed per revolution. Therefore, the processing efficiency can be improved by increasing the feed per revolution, while ensuring a longer drill life.

However, it should be noted: if the feed per revolution is too large, the chips will thicken, making it difficult to break the chips. Therefore, the feed range per revolution that can break the chips smoothly must be determined through trial cutting.For cemented carbide drill bits, the cutting edge has a larger chamfer in the direction of the negative front angle, and the optional range of feed per revolution is smaller than that of high-speed steel drill bits. If the feed per revolution during processing exceeds this range, the service life of the drill bit will be reduced.Since the heat resistance of cemented carbide drill bits is higher than that of high-speed steel drill bits, the rotation speed has little effect on the life of the drill bit, so the method of increasing the rotation speed can be used to improve the processing efficiency of cemented carbide drill bits, while ensuring the life of the drill bit.

2 Rational use of cutting fluid
The cutting of the drill bit is carried out in a hole with a narrow space, so the type of cutting fluid and the injection method have a great impact on the life of the drill bit and the machining accuracy of the hole.Cutting fluid can be divided into two categories: water-soluble and non-water-soluble.The non-water-soluble cutting fluid has good lubricity, wettability and adhesion resistance, and it also has anti-rust effect.The water-soluble cutting fluid has good cooling properties, non-fuming and non-flammable properties.Due to the consideration of environmental protection, the use of water-soluble cutting fluid has increased in recent years.However, if the dilution magnification of the water-soluble cutting fluid is improper or the cutting fluid deteriorates, the service life of the tool will be greatly shortened, so attention must be paid in use.Whether it is a water-soluble or non-water-soluble cutting fluid, the cutting fluid must be fully reached at the cutting point in use, and the flow rate, pressure, number of nozzles, and cooling method (internal cooling or external cooling) of the cutting fluid must be strictly controlled.
5. Re-sharpening of the drill bit
Drill bit re-grinding discrimination
The criteria for determining whether the drill bit needs to be re-sharpened are:
①The amount of wear on the edge, horizontal edge, and edge surface of the cutting edge;
②The dimensional accuracy and surface roughness of the processed hole;

③The color and shape of the chips;

④Cutting resistance (indirect values such as spindle current, noise, vibration, etc.) ;

⑤Processing quantity, etc.In actual use, according to specific circumstances, accurate and convenient discrimination criteria should be determined from the above indicators.

Using the amount of wear as the criterion for determining, the best re-wear period with the best economy should be found.Since the main sharpening parts are the back of the head and the horizontal edge, if the drill bit wears too much, the sharpening time is too much, and the grinding amount is large, the number of times it can be re-ground is reduced (the total service life of the tool = the tool life after re-grinding × the number of times it can be re-ground), on the contrary, the total service life of the drill bit will be shortened; the dimensional accuracy of the processed hole is used as the discrimination standard, and the column gauge or limit gauge is used to check the hole’s cutting expansion, non-straightness, etc., once the control value is exceeded, it should be re-sharpened immediately; the cutting resistance is used as the discrimination standard, and the set limit value (such as spindle current) can be used immediately. Automatic shutdown and other methods; when using the management of processing quantity limits, the above-mentioned discrimination content should be integrated and the discrimination criteria should be set.
How to sharpen the drill bit
When re-sharpening the drill bit, it is best to use a special machine tool for sharpening the drill bit or a universal tool grinder, which is very important to ensure the service life and machining accuracy of the drill bit.If the original drill type is in good processing condition, it can be re-ground according to the original drill type; if the original drill type is defective, the back shape and horizontal edge grinding can be appropriately improved according to the purpose of use.
The following points should be paid attention to when sharpening:

①.Prevent overheating and avoid reducing the hardness of the drill bit.② All the damage on the drill bit (especially the damage to the edge of the blade) should be removed.③The drill type should be symmetrical.④Be careful not to touch the edge during sharpening, and the burrs after sharpening should be removed.⑤ For cemented carbide drill bits, the sharpening shape has a great impact on the performance of the drill bit. The drill type at the factory is the best drill type obtained by scientific design and trial and error. Therefore, the original blade type should generally be maintained when re-sharpening.

Various thread processing methods

1. Thread cutting

Generally refers to the method of machining threads on the workpiece with forming tools or abrasives, mainly turning, milling, tapping, threading, grinding, grinding and cyclone cutting.When turning, milling, and grinding threads, the transmission chain of the machine tool ensures that the turning tool, milling cutter, or grinding wheel moves a lead accurately and evenly along the axial direction of the workpiece for each revolution of the workpiece.When tapping or threading, the tool (tap or tooth) rotates relative to the workpiece, and the threaded groove formed first guides the tool (or workpiece) to move axially.

For turning threads on a lathe, forming turning tools or thread combing tools can be used (see thread processing tools).Turning threads with a forming turning tool, due to the simple structure of the tool, is a common method for single-piece and small-batch production of threaded workpieces; turning threads with a thread comb tool has high production efficiency, but the tool structure is complex and is only suitable for medium and large-scale production of short threaded workpieces with fine teeth.The pitch accuracy of turning trapezoidal threads on ordinary lathes can generally only reach 8~9 levels (JB2886-81, the same below); processing threads on specialized thread lathes, productivity or accuracy can be significantly improved.

2. Thread milling

Use a disc milling cutter or comb milling cutter for milling on a thread milling machine.Disc milling cutters are mainly used for milling trapezoidal external threads on workpieces such as screws and worms.Comb milling cutters are used for milling internal and external ordinary threads and tapered threads, and multi-edged milling cutters are used for milling. The length of the working part is greater than the length of the thread to be processed, so the workpiece only needs to be rotated 1.25~1.5 revolutions to complete the processing, and the productivity is very high.The pitch accuracy of thread milling can generally reach 8~9 levels, and the surface roughness is R5~0.63 microns.This method is suitable for batch production of thread work with general accuracy or roughing before grinding.

3. Thread grinding

It is mainly used for machining precision threads of hardened workpieces on thread grinders.

Thread grinding is divided into two types of single-line grinding wheels and multi-line grinding wheels according to the different cross-section shapes of the grinding wheels.The pitch accuracy that can be achieved by single-line grinding wheel grinding is 5~6 levels, and the surface roughness is R1.25~0.08 microns, which makes grinding wheel dressing more convenient.

This method is suitable for grinding precision screws, thread gauges, worms, small batches of threaded workpieces and shoveling precision hob.Multi-line grinding wheel grinding is divided into two types: longitudinal grinding method and cut-in grinding method.The width of the grinding wheel of the longitudinal grinding method is less than the length of the thread being ground, and the grinding wheel can be moved vertically once or several times to grind the thread to the final size.The width of the grinding wheel of the cut-in grinding method is greater than the length of the thread being ground. The grinding wheel cuts radially into the surface of the workpiece, and the workpiece can be ground at about 1.25 revolutions. The productivity is higher, but the accuracy is slightly lower, and the grinding wheel trimming is more complicated.The cut-in grinding method is suitable for shoveling large batches of taps and grinding certain threads for fastening.

4. Thread grinding

Nut-type or screw-type thread grinding tools are made of softer materials such as cast iron, and the parts of the processed thread with pitch errors on the workpiece are rotated and ground forward and reverse to improve the pitch accuracy.Hardened internal threads are usually ground to eliminate changes and improve accuracy.

5. Tapping and threading

Tapping is to use a certain torque to screw the tap into the pre-drilled bottom hole on the workpiece to process the internal thread.

Threading is the use of plate teeth to cut out external threads on the bar (or pipe) workpiece.The machining accuracy of tapping or threading depends on the accuracy of the taps or teeth.Although there are many methods for processing internal and external threads, small-diameter internal threads can only be processed by taps.Tapping and threading can be operated manually, as well as lathes, drilling machines, tapping machines and threading machines.

6. Thread rolling

A processing method for plastic deformation of the workpiece by forming and rolling a mold to obtain a thread.Thread rolling is generally in a wire rolling machine.The wire rubbing machine may be carried out on an automatic lathe with an automatic opening and closing thread rolling head, which is suitable for mass production of standard fasteners and other external threads of threaded joints.

The outer diameter of the rolling thread generally does not exceed 25 mm, the length is not greater than 100 mm, and the thread accuracy can reach Level 2 (GB197-63). The diameter of all blanks is roughly equal to the middle diameter of the thread being processed.Rolling generally cannot process internal threads, but for workpieces with softer materials, slotted extrusion taps can be used to cold squeeze internal threads (the maximum diameter can reach about 30 mm). The working principle is similar to tapping.The torque required for cold extrusion of internal threads is about 1 times larger than that of tapping, and the machining accuracy and surface quality are slightly higher than that of tapping.

 

External thread rolling processing!

The advantages of thread rolling are:

1. The surface roughness is less than that of turning, milling and grinding;

2. The surface of the thread after rolling can improve its strength and hardness due to cold work hardening.;

3. High material utilization rate; productivity is exponentially higher than that of cutting, and it is easy to realize automation.;

4. The rolling mold has a long life.However, rolling threads require that the hardness of the workpiece material does not exceed HRC40;

5. High requirements for the dimensional accuracy of the blank;

6. The accuracy and hardness requirements of rolling molds are also high, and it is more difficult to manufacture molds.;

7. It is not suitable for rolling threads with asymmetric tooth shape.

According to the different rolling molds, thread rolling can be divided into two types: wire rubbing and wire rolling.

Rub silk

The two threaded toothed wire rubbing plates are staggered and arranged at a pitch of 1/2. The static plate is fixed, and the moving plate moves in a reciprocating linear motion parallel to the static plate.When the workpiece is fed between the two plates, the moving plate advances and rubs the workpiece, causing its surface to plasticize and deform into a thread.

Rolling wire

There are three types of radial wire rolling, tangential wire rolling and rolling head wire rolling.Radial wire rolling: 2 (or 3) threaded toothed wire rolling wheels are mounted on shafts parallel to each other, the workpiece is placed on the support between the two wheels, and the two wheels rotate at the same speed in the same direction.

One round also made radial feed movement.The workpiece rotates under the drive of the wire roller, and the surface is radially squeezed to form a thread.For some screws with low precision requirements, a similar method can be used for rolling and forming.Tangential wire rolling: Also known as planetary wire rolling, the rolling tool consists of a rotating central wire rolling wheel and 3 fixed curved wire plates.

When rolling wire, the workpiece can be continuously fed, so the productivity is higher than that of rubbing wire and radial rolling wire.Wire rolling head wire rolling: Carried out on an automatic lathe, generally used to process short threads on workpieces.The rolling head has 3 to 4 wire rolling wheels that are distributed on the periphery of the workpiece.

When rolling the wire, the workpiece rotates, and the rolling head feeds axially, rolling the workpiece out of the thread.

Industrial mother machine-CNC machine tool

Machine tools, known as “industrial mother machines” and “the heart of modern industry”, are the foundation of the manufacturing industry and the key area of high-end breakthroughs in the manufacturing industry, especially for the automotive industry, rail transit, electronic information equipment, shipbuilding, aerospace and other high-end equipment manufacturing fields provide important support.The technical level of high-end CNC machine tools is one of the standards for measuring a country’s core manufacturing capabilities.

 

History of machine tool development

A machine tool refers to a machine that makes a machine.Machine tools play an irreplaceable and important role in the modernization of the national economy.

Machine tools took shape in the early 15th century. They were originally designed to make clocks and weapons. Thread lathes and gear processing machine tools appeared, as well as hydraulically driven barrel boring machines.The “Heavenly Work” published in the Ming Dynasty of China also contains the structure of a grinder, which rotates the iron circle by stepping on it, and adds sand and water to cut the jade.

The industrial revolution has triggered the production and improvement of various machine tools, including gantry planers, horizontal milling machines, cylindrical grinders, coordinate boring machines and thread grinders.

From the end of the 19th century to the beginning of the 20th century, a single lathe has gradually evolved into milling machines, planers, grinding machines, drilling machines, etc. These main machine tools have been basically shaped, which created conditions for the mechanization and semi-automation of production in the early 20th century.

In the 30 years after 1920, mechanical manufacturing technology entered a period of semi-automation, and hydraulic and electrical components were gradually applied to machine tools and other machinery.

In 1950, the development of machine tools began to enter a period of automation, and in 1951, the first CNC machine tool appeared.

 

CNC machine tools

CNC machine tools are short for Digital control machine tools (Computer numerical control machine tools), which are automated machine tools equipped with a program control system.The control system can logically process programs with control codes or other symbolic instructions, decode them, represent them in coded numbers, and input them to the CNC device through the information carrier.After calculation and processing, various control signals are sent by the CNC device to control the action of the machine tool, and the parts are automatically processed according to the shape and size required by the drawings.

 

CNC machine tools mainly contain the following parts:

The main body of the machine tool: The main body of the machine tool is the main component of the machine tool and an important mechanical accessory part. It is the part that is easiest to see intuitively with the naked eye. As the hardware of the machine tool, it also includes the bed and base castings, the spindle and the gearbox, the guide rail and the slide table, lubrication, chip removal and cooling and other parts.

 

Transmission system: The transmission system is an important “context” of CNC machine tools, which leads the orderly progress of all parts of the machine tool and completes the work mission of the machine tool, including tools, transmission machinery and auxiliary power systems.

 

Tool part: including protection device, tool magazine and tool changer;

 

Transmission machinery: it includes two parts: ball screw, linear guide rail and worm;

 

Auxiliary power system: it includes two parts: hydraulic system and starting system, which is also the power of CNC machine tools.

 

CNC system: The CNC system can be said to be the soul of the CNC machine tool, and it is also the most emotional part of the entire machine tool. It is the essence of the machine tool to complete various functions and operations.CNC systems are basically divided into two categories:

 

Drive device: it includes high-speed spindle, torque motor, linear motor, ordinary motor and stepper motor;

 

Control and detection equipment: including CNC system, programmable controller, feed servo control module, position detection module, etc.

 

CNC machine tools can better solve the problems of complex, precise, small-batch, and multi-variety parts processing. They are a flexible and high-performance automated machine tool that represents the development direction of modern machine tool control technology and is a typical mechatronics product.

CNC machine tools are one of the 16 major national science and technology projects in our country.

 

High-end CNC machine tools

High-end CNC machine tools have functions such as high-speed, precision, intelligence, composite, multi-axis linkage, and network communication. Their development symbolizes that the country’s current machine tool manufacturing industry accounts for the advanced stage of the development of the world’s machine tool industry.Multi-axis linkage technology is one of the core technologies of high-end CNC machine tools.Multi-axis linkage refers to the simultaneous movement of each feed axis of the CNC machine tool (including the linear coordinate feed axis and the rotary coordinate feed axis) under the control of the CNC device in accordance with the program instructions.High-end CNC machine tools generally have 3-axis or more linkage control functions, mostly 4-axis linkage or 5-axis linkage.

Internationally, high-end machine tool technologies such as five-axis linkage CNC machine tools are regarded as an important symbol of a country’s industrialization.Five-axis linkage CNC machine tools refer to machine tools specially used to process complex curved surfaces, which have the advantages of wide application range, high work efficiency, improved machining accuracy, and increased tool life.With the rapid development of advanced manufacturing, five-axis linkage CNC machine tools, as an important symbol of the country’s industrialization level, have gained broad prospects for development.

There are many types of five-axis linkage CNC machine tools.According to different styles, five-axis linkage CNC machine tools can be divided into two types: vertical spindle double swing head and horizontal spindle double swing head; according to different structures, five-axis linkage CNC machine tools can be divided into double turntable form, one swing and one turn form, vertical swing head type, vertical workbench type and so on.At present, vertical spindle double pendulum head five-axis linkage CNC machine tools are the mainstream products in the market. In 2021, the global vertical spindle double pendulum head five-axis linkage CNC machine tool revenue will reach US44.41 billion, accounting for nearly 60% of the global CNC machine tool market share.

Five-axis linkage CNC machine tools are widely used in a wide range of fields, including military industry, precision equipment, aerospace, urban rail transit, new energy vehicles, medical and health care, etc.The aerospace field is the largest demand end for five-axis linkage CNC machine tools, accounting for 40.0% of the demand.Five-axis linkage CNC machine tools can cut and process aircraft engine blades, blades, impellers, and structural parts of large, medium and small aircraft, which have an irreplaceable role in the aerospace field.

High-precision CNC gear grinding machine

Gear grinding machine is a kind of gear processing equipment widely used in the machinery manufacturing industry. Its main function is to grind gears made of various metal materials to improve their accuracy, surface quality and service life.This article will introduce in detail the structure, working principle, classification and application fields of gear grinding machines.

1. The structure and working principle of the gear grinding machine
Gear grinding machines are usually composed of the following parts: host, workbench, grinding head, cooling system, control system, etc.Among them, the main machine is the main body of the gear grinding machine, which is responsible for supporting and fixing other components; the workbench is used to place and fix the gears to be processed; the grinding head is an important part of the gear grinding machine, which is internally equipped with abrasive and coolant for grinding the gears; the cooling system is responsible for providing coolant to reduce the temperature during the grinding process; the control system is used to control the operation of the entire gear grinding machine.

The working principle of the gear grinding machine is mainly based on the principle of grinding.During the working process of the gear grinding machine, the abrasive inside the grinding head rubs against the surface of the gear to be processed, grinding down the metal on the surface of the gear, making it gradually approach the ideal shape.At the same time, the scouring effect of the coolant can take away the heat generated by grinding, reduce the temperature of the gear, and prevent thermal damage.

2. Classification of gear grinding machines
According to different classification criteria, gear grinding machines can be divided into many types.According to the different grinding principles, gear grinding machines can be divided into gear grinding machines by development method and gear grinding machines by forming method.Zhancheng gear grinding machine uses the meshing movement of a pair of gears for grinding, and its machining accuracy is high, which is suitable for the processing of high-precision gears; forming gear grinding machine is based on the shape of the gear to be processed to make a corresponding grinding wheel for grinding, its processing efficiency is high, but the accuracy is relatively low.

In addition, depending on the number of grinding shafts and the number of grinding wheels, gear grinding machines can be divided into single-axis, dual-axis and multi-axis types.Single-axis gear grinding machine has only one grinding wheel shaft, which is mainly used for roughing; dual-axis gear grinding machine has two grinding wheel shafts, which can be roughed and finished; multi-axis gear grinding machine has multiple grinding wheel shafts, which can be used for efficient multi-faceted grinding.

Third, the application field of gear grinding machine
Because the gear grinding machine has the characteristics of high precision and high efficiency, its application fields are very wide.In the field of automobile manufacturing, various gear parts need to be ground to improve accuracy and wear resistance; in the field of wind power, large-scale gears need to be processed to ensure the stable operation of wind turbines; in the field of shipbuilding, large gear parts need to be ground to improve their carrying capacity and stability.

In addition, in the fields of mining machinery, aerospace, medical equipment, etc., gear parts made of various metal and non-metallic materials also need to be ground to improve their performance and service life.Therefore, with the development of the machinery manufacturing industry and the continuous progress of technology, the application prospects of gear grinding machines will be broader.

In short, this article introduces the structure, working principle, classification and application fields of gear grinding machine in detail.Understanding and mastering this knowledge is of great significance to improve the production efficiency and product quality of the machinery manufacturing industry.In the future, with the continuous progress of technology and the expansion of application fields, gear grinding machines will be applied and developed in more fields.

Three methods of machining threads in CNC machining centers

Everyone has an in-depth understanding of the benefits of using CNC machining centers to process workpieces. There is still a layer of mystery about the operation and programming of CNC machining centers.Today I will share with you the thread processing method.There are three methods of CNC machining: thread milling method, tap machining, and buckle machining method.:
1. Thread milling method Thread milling is the use of thread milling tools for the processing of large-hole threads, as well as the processing of threaded holes of more difficult-to-process materials, which have the following characteristics:

1.The tool is generally made of cemented carbide material, with fast speed, high thread milling accuracy and high processing efficiency.;

2.The same pitch, whether it is a left-handed thread or a right-handed thread, can use a tool to reduce the cost of the tool;

3.Thread milling method is particularly suitable for thread processing of more difficult materials such as stainless steel and copper. It is easy to remove chips and cool down, and can ensure the quality and safety of processing.;

4.There is no guide at the front end of the tool, which is more convenient to process blind holes with short threaded bottom holes or holes without tool retreat grooves.

Thread milling tools are divided into two types: machine-clamped cemented carbide blade milling cutters and integral cemented carbide milling cutters. Machine-clamped tools can process holes with thread depth less than the length of the blade, as well as holes with thread depth greater than the length of the blade; and integral cemented carbide milling cutters are used to process holes with thread depth less than the length of the tool.;

Precautions for thread milling CNC programming: So as not to cause tool damage or machining errors.

1.After the threaded bottom hole is processed first, the small diameter hole is processed with a drill bit, and the larger hole is processed with boring to ensure the accuracy of the threaded bottom hole.;

2.The tool generally adopts an arc trajectory of 1/2 circle to cut in and out to ensure the shape of the thread. The tool radius compensation value should be brought in at this time.

2. The tap processing method of CNC machining centers is suitable for threaded holes with small diameters or low hole position accuracy requirements. Under normal circumstances, the diameter of the threaded bottom hole drill bit is selected close to the upper limit of the diameter tolerance of the threaded bottom hole, which can reduce the processing margin of the tap, reduce the load on the tap, and at the same time improve the service life of the tap.

Everyone should choose the appropriate tap according to the material being processed. The tap is relative to the milling cutter and boring cutter.;

It is very sensitive to the material to be processed; taps are divided into through-hole taps and blind-hole taps. The front end of the through-hole tap is guided long, which is the front chip removal. The processing depth of the thread cannot be guaranteed when processing the blind hole, and the front end of the blind hole is guided short, which is the rear chip removal, so pay attention to the difference between the two; the use of flexible tapping chucks should pay attention to the diameter of the tap shank and the width of the square should be the same as the tapping chuck; the diameter of the tap shank for rigid tapping should be the same as the diameter of the spring jacket.

The programming of the tap processing method is relatively simple. It is all in a fixed mode. Just add the parameter values. It should be noted that the CNC system is different and the format of the subroutine is different, so the representative meaning of the parameter values is different.

Third, the buckle processing method

The buckle processing method is suitable for the processing of large threaded holes on box parts, or this method is used without taps and thread milling cutters, and thread turning tools are installed on the boring tool bar for boring threads.There are the following precautions for the implementation of the buckle processing method:

1.There must be a delay time to start the spindle to ensure that the spindle reaches the rated speed;

2.The sharpening of hand-ground threaded tools cannot be symmetrical, and reverse tool retreat cannot be used. The spindle must be used to orient the tool to move radially, and then retreat.;

3.The tool holder must be precise and consistent with the position of the tool slot, otherwise multiple tool holders cannot be used for processing, resulting in random buckles.;

4.When picking the buckle, be careful not to pick it with one knife, even if it is a very fine buckle, otherwise it will cause tooth loss and poor surface roughness. Multiple knives should be used to pick the buckle.;

5.The buckle processing method is only applicable to single-piece, small batches, special pitch threads and situations where there is no corresponding tool, and the processing efficiency is low.

The buckle processing method of CNC machining centers is only a temporary emergency method. It is recommended that everyone process tools by thread processing methods in order to effectively improve the thread processing efficiency and quality, reduce processing costs and improve the efficiency of machining centers. Efficiency.

Seven ways to detect the positioning accuracy of CNC machine tools

The positioning accuracy of a CNC machine tool refers to the position accuracy that can be achieved by the movement of each axis of the machine tool under the control of a CNC device.The positioning accuracy of CNC machine tools can also be understood as the motion accuracy of machine tools.Ordinary machine tools are fed manually, and the positioning accuracy is mainly determined by the reading error, while the movement of CNC machine tools is achieved by digital program instructions, so the positioning accuracy is determined by the CNC system and the mechanical transmission error.
CNC machine tool is the abbreviation of digital control machine tool, which is an automated machine tool equipped with a program control system.The control system can logically process programs with control codes or other symbolic instructions, and decodes them, represented by coded numbers, and Nanjing No. 4 Machine Tool Co., Ltd. enters the CNC device through the information carrier.After calculation and processing, various control signals are sent by the CNC device to control the action of the machine tool, and the parts are automatically processed according to the shape and size required by the drawings.

The movement of each moving part of the machine tool is completed under the control of a CNC device. The accuracy that each moving part can achieve under the control of program instructions directly reflects the accuracy that the processed part can achieve. Therefore, positioning accuracy is a very important test content.

1. Linear motion positioning accuracy detection Linear motion positioning accuracy is generally carried out under no-load conditions of machine tools and workstations.According to national standards and the regulations of the International Organization for Standardization (ISO standards), laser measurement shall prevail for the testing of CNC machine tools.In the absence of a laser interferometer, for ordinary users, a standard scale can also be used with an optical reading microscope for comparative measurements.However, the accuracy of the measuring instrument must be 1~2 levels higher than the measured accuracy.In order to reflect all the errors in multiple positioning, the ISO standard stipulates that each positioning point calculates the average value and dispersion according to the five measurement data, and the dispersion band of the positioning point composed of the dispersion band.

2. The instrument used for detecting the repeated positioning accuracy of linear motion is the same as that used to detect the positioning accuracy.The general detection method is to measure at any three positions close to the midpoint and both ends of the stroke of each coordinate. Each position is positioned with rapid movement, and the positioning is repeated 7 times under the same conditions. The stop position value is measured and the maximum difference in reading is obtained.Take one-half of the difference between the largest of the three positions and attach a positive and negative symbol as the repeated positioning accuracy of the coordinate. It is the most basic index that reflects the accuracy and stability of the axis movement.

3. The return accuracy of the origin of linear motion detects the return accuracy of the origin, which is essentially the repeated positioning accuracy of a special point on the coordinate axis, so its detection method is completely the same as the repeated positioning accuracy.

4. The reverse error of linear motion detects the reverse error of linear motion, also known as the loss of momentum. It includes the reverse dead zone of the drive parts (such as servo motors, servo hydraulic motors, and stepper motors) on the axis feed transmission chain, and the comprehensive reflection of the errors such as the reverse gap and elastic deformation of each mechanical motion transmission pair.

The greater the error, the lower the positioning accuracy and repeated positioning accuracy.The detection method of reverse error is to move a distance forward or reverse in advance within the stroke of the measured axis and use this stop position as a reference, and then give a certain movement command value in the same direction to move it for a certain distance, and then move the same distance in the opposite direction to measure the difference between the stop position and the reference position.Multiple measurements (generally 7 times) were made at three positions near the midpoint of the stroke and at both ends, and the average value at each position was obtained, and the maximum value in the resulting average value was used as the reverse error value.

5. The positioning accuracy detection and measurement tools of the rotary table include standard turntable, angle polyhedron, circular grating and parallel light tube (collimator), etc., which can be selected according to specific circumstances.The measurement method is to turn the workbench forward (or reverse) at an angle and stop, lock, and position it. This position is used as a reference, and then quickly rotate the workbench in the same direction, locking and positioning every 30 seconds for measurement.Forward and reverse turns are measured for one week each, and the maximum value of the difference between the actual angle of each positioning position and the theoretical value (instruction value) is the indexing error.

If it is a CNC rotary table, every 30 should be used as a target position, and each target position should be quickly positioned 7 times from the positive and negative directions. The difference between the actual position and the target position is the position deviation, and then the average position deviation and standard deviation are calculated according to the method specified in GB10931-89 “Evaluation Method for the Position Accuracy of Digital Control Machine Tools”. The maximum value of all average position deviations and standard deviations and the sum of the minimum values of all average position deviations and standard deviations is the positioning accuracy error of the CNC rotary table.Considering the actual use requirements of dry transformers, key measurements are generally made at several right-angle points such as 0, 90, 180, and 270, and the accuracy of these points is required to be one level higher than that of other angular positions.

6. Detection of repeated indexing accuracy of rotary table
The measurement method is to repeat the positioning 3 times in any three positions within a week of the rotary table, and to detect the rotation in the positive and negative directions respectively.The maximum indexing accuracy of the difference between all reading values and the theoretical values of the corresponding position.If it is a CNC rotary table, take a measurement point every 30 as the target position, and quickly locate each target position 5 times from the positive and negative directions, and measure the difference between the actual reached position and the target position, that is, the position deviation, and then calculate the standard deviation according to the method specified in GB10931-89. The standard deviation of each measurement point is 6 times the maximum value, which is the repeatability of the CNC rotary table. Indexing accuracy.

7. The detection and measurement method of the origin return accuracy of the rotary table is to perform an origin return from any of the 7 positions, determine its stop position, and take the maximum difference read out as the origin return accuracy.

It should be pointed out that the detection of existing positioning accuracy is measured in the case of fast and positioning. For some CNC machine tools with poor feed system demeanor, different positioning accuracy values will be obtained when positioning at different feed speeds.In addition, the measurement results of positioning accuracy are related to the ambient temperature and the working state of the axis. At present,

Application of machine tool thermal compensation technology in industrial processing

With the continuous development of modern industry, CNC machine tools are more and more widely used in the manufacturing industry.CNC machine tools mainly control the processing process through computer programs, which can achieve high-precision and high-efficiency processing operations.However, during the operation of the machine tool, due to the influence of temperature, the structure of the machine tool will be deformed, which will affect the machining accuracy.Therefore, in order to solve this problem, the thermal compensation technology of CNC machine tools came into being.

The thermal compensation technology of CNC machine tools refers to a technical means of using temperature sensors and other measuring equipment to monitor the temperature of machine tools in real time, and to compensate for errors in the processing process in real time through a computer control system.There are mainly the following commonly used thermal compensation methods for machine tools:

Thermal error compensation method based on empirical model: Based on the historical data of machine tool processing, this method establishes an empirical model to predict the temperature change of the machine tool in the current environment, and automatically adjusts the processing parameters through a computer control system to achieve the purpose of precise processing.

Thermal error compensation method based on neural network: This method learns and trains the input temperature and output error of the machine tool by establishing a neural network model, so as to compensate for the thermal error in the machining process of the machine tool.

Thermal error compensation method based on finite element analysis: This method uses finite element analysis software to model the structure of the machine tool, the deformation of the computer bed under different temperature conditions, and the processing program is adjusted in real time through a computer control system to eliminate the impact of temperature changes on machining accuracy.

Thermal error compensation method based on thermal sensor: This method monitors the temperature change of the machine tool in real time by installing a temperature sensor on the surface or key parts of the machine tool, and adjusts the processing parameters in real time through a computer control system to achieve the purpose of precise processing.

In practical applications, different thermal compensation methods for CNC machine tools have their unique application scenarios, advantages and disadvantages.For example, the thermal error compensation method based on empirical models is relatively simple in terms of data collection and processing, but requires a large amount of historical data for modeling, and cannot consider the thermal error in the new environment.In contrast, the thermal error compensation method based on neural networks can adapt to thermal errors in various environments, but it takes a long time for model training.The thermal error compensation method based on finite element analysis can consider the deformation of the machine tool structure, but it requires a complex modeling process and high-performance computer support.The thermal error compensation law based on the thermal sensor requires the installation of temperature sensors on the surface or key parts of the machine tool, which increases the equipment cost and the difficulty of implementation.

Overall, the thermal compensation technology of CNC machine tools provides an important solution for modern manufacturing.By selecting a suitable thermal compensation method and optimizing it in combination with the actual production environment, the machining accuracy and overall efficiency of the machine tool can be significantly improved.

The thermal compensation technology of CNC machine tools mainly includes the following methods:

Thermal error compensation method based on empirical model: This method establishes a certain mathematical model through the analysis of historical data of machine tool processing.During the processing process, the temperature change of the machine tool is monitored in real time, and the temperature change trend of the machine tool in the environment is predicted based on the empirical model. The computer control system will automatically adjust the processing parameters to eliminate thermal errors, thereby improving the machining accuracy.

Thermal error compensation method based on neural network: This method adopts the method of neural network. By learning and training the input temperature and output error of the machine tool, the relationship between temperature change and machining error is identified, so as to realize the thermal error compensation in the machining process of the machine tool.

Thermal error compensation method based on finite element analysis: This method uses finite element analysis software to model the machine tool, the deformation of the computer bed under different temperature conditions, and the law of processing error with temperature, and the processing program is adjusted in real time through a computer control system to eliminate the impact of temperature changes on machining accuracy.

Thermal error compensation method based on thermal sensor: This method is to install a temperature sensor on the surface or key parts of the machine tool to monitor the temperature change of the machine tool in real time and establish an correlation model with the machining error.At the same time, the computer control system is used to adjust the processing parameters in real time to achieve the purpose of precise processing.

These thermal compensation methods have their own advantages and disadvantages.For example, the thermal error compensation method based on empirical models requires a large amount of historical data as the basis, and cannot consider the thermal error in the new environment; the thermal error compensation method based on neural networks can adapt to the thermal error in various environments, but it takes a long time to train the model; the thermal error compensation method based on finite element analysis can consider the deformation of the machine tool structure, but requires a complex modeling process and high-performance computer support; the thermal error compensation method based on thermal sensors requires the installation of temperature sensors on the surface of the machine tool or key parts, which increases equipment costs and implementation difficulties.Therefore, in practical applications, choices and adjustments need to be made according to specific circumstances.

The difference between CNC machining and traditional machining

CNC processing technology is derived from conventional processing technology and is an organic combination of conventional processing technology, computer numerical control technology, computer-aided design and auxiliary manufacturing technology.Due to the continuous development of technology, more and more parts need to be precision machined in the modern manufacturing industry, and the machining accuracy and surface complexity requirements of the workpiece are also getting higher and higher.Therefore, CNC machining has received widespread attention, but in terms of cost savings, CNC machining is still higher than traditional processing costs.Below we will specifically introduce the difference between CNC machining and traditional machining technology.

1. Processing technology

In ordinary machining processes, whether it is positioning reference, clamping method, tool, cutting method, etc., can be simplified, but the data processing technology is more complex, and these factors need to be fully considered, and even if the same processing task, CNC machining technology can have multiple programs, multiple machining parts and machining tools can be used as the main line to arrange the process, and the process has diversified characteristics, which is the difference between CNC machining technology and traditional machining technology.

2. Clamping and fixture

In the CNC machining process, it is not only necessary to ensure that the coordinate directions of the fixture and the machine tool are relatively fixed, but also to coordinate the dimensional relationship between the parts and the machine tool coordinate system.Moreover, the two steps of positioning and clamping need to be effectively controlled during the clamping process.Moreover, under the traditional machining technology, due to the limited processing capacity of the machine tool itself, it is necessary to perform multiple clamping during the processing process.Moreover, special fixtures need to be used, which leads to higher costs in the design and manufacture of fixtures, which virtually increases the production cost of the product.The positioning of CNC machining technology can be debugged using instruments, and in most cases there is no need to design special fixtures, so its cost is relatively low.

3. Knives

In the processing process, the choice of tool needs to be determined according to the different processing techniques and processing methods.Especially in CNC machining, the use of high-speed cutting is not only conducive to the improvement of processing efficiency, but also the processing quality can be guaranteed, effectively reducing the chance of cutting deformation and shortening the processing cycle, so the demand for cutting tools under high-speed cutting has further increased.

At present, there is also a dry cutting method, which is used for cutting without cutting fluid or with only a small amount of cutting fluid, so the tool needs to have good heat resistance.Compared with ordinary machining technology, CNC machining technology has high requirements for tool performance.

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