The strategic value of five-axis linkage CNC machine tools

The equipment manufacturing industry is the cornerstone of a country’s industry. It provides an important means for the development of new technologies, new products and modern industrial production. It is an indispensable strategic industry. Even developed industrialized countries all attach great importance to it. In recent years, with the rapid development of our country’s national economy and the needs of national defense construction, there has been an urgent and large demand for high-end CNC machine tools. Machine tools are a symbol of a country’s manufacturing level. The five-axis linkage CNC machine tool system represents the highest level of machine tool manufacturing. In a sense, it reflects the level of industrial development of a country.

For a long time, Western industrialized countries, led by the United States, have regarded five-axis CNC machine tool systems as important strategic materials and implemented an export license system. Especially during the Cold War, blockades and embargoes were implemented against China, the former Soviet Union and other socialist camps. Military-loving friends may know the famous “Toshiba Incident”: At the end of the last century, Japan’s Toshiba Company sold several five-axis linkage CNC milling machines to the former Soviet Union. As a result, the propellers used by the former Soviet Union to manufacture submarines were upgraded several grades. The sonar of the American butterfly ship cannot detect the sound of the submarine, so the United States wants to punish Toshiba for violating the strategic material embargo policy.

It can be seen that the five-axis linkage CNC machine tool system has a decisive influence on a country’s aviation, aerospace, military, scientific research, precision equipment, high-precision medical equipment and other industries. Nowadays, it is generally believed that the five-axis linkage CNC machine tool system is the only means to solve the processing of impellers, blades, marine propellers, heavy-duty generator rotors, steam turbine rotors, large diesel engine crankshafts, etc. Therefore, whenever people encounter unsolvable problems in designing and developing complex curved surfaces, they often turn to five-axis CNC systems for help. Because the five-axis linkage CNC machine tool system is very expensive, and it is difficult to create NC programs, it is difficult for the five-axis system to be applied to “civilians”.

However, in recent years, with the breakthrough development of computer-aided design (CAD) and computer-aided manufacturing (CAM) systems, many Chinese CNC companies such as Shanxing Company have launched five-axis linkage CNC machine tool systems, breaking through foreign technology. The blockade has occupied the highest point of this strategic industry and greatly reduced its application costs, thus ushering in a new era for China’s equipment manufacturing industry! The development of modern science represented by information technology has injected an influx into the equipment manufacturing industry. The strong driving force also puts forward stronger requirements for it, which further highlights the irreplaceable basic role of the machinery and equipment manufacturing industry as a carrier of high-tech industrialization in promoting technological progress and industrial upgrading of the entire society.

As the driving force behind national economic growth and technological upgrading, the mechanical equipment manufacturing industry represented by five-axis linkage will progress together with the development of high-tech and emerging industries. China not only wants to be a major manufacturing country in the world, but also a powerful manufacturing country in the world! It is expected that in the near future, with the popularization and promotion of five-axis linkage CNC machine tool systems, it will surely lay a solid foundation for China to become the most powerful country in the world!

Difficulties in five-axis machining

Five-axis machining methods and machine tools have been used by the foreign aviation industry as early as the 1960s in order to process some large parts with continuous smooth and complex free-form surfaces, but they have not been adopted in more industries. It is widely used and has developed rapidly only in the past 10 years. The reason is mainly that there are many difficulties in five-axis machining, such as:

1. Programming is complex and difficult.

Because five-axis machining is different from three-axis machining, in addition to three linear motions, there are also two rotational motions involved. The spatial trajectory of the resulting synthetic motion is very complex and abstract, and is generally difficult to imagine and understand. For example, in order to process the required spatial free-form surface, it is often necessary to go through multiple coordinate transformations and complex spatial geometric operations. At the same time, the coordination of the motion of each axis must be considered to avoid interference and collision, and the interpolation motion must be timely and appropriate, etc. In order to ensure the required machining accuracy and surface quality, programming is even more difficult.

2. High requirements for CNC and servo control systems.

Since five-axis machining requires five-axis simultaneous coordinated motion, this requires that the CNC system must first have at least five-axis linkage control functions; in addition, since rotational motion is added to the synthetic motion, this not only increases the workload of interpolation operations, but also increases the workload of interpolation operations. And because small errors in rotation may be amplified and greatly affect the accuracy of machining, the CNC system is required to have higher operating speed (i.e. shorter processing time for a single program segment) and accuracy. All of this means that the CNC system must increase the processor of the RISC chip for processing (ie, use multiple high-bit CPU structures). In addition, as mentioned before, the mechanical configuration of the five-axis machining machine tool includes tool rotation mode, workpiece rotation mode and a mixture of the two. The CNC system must also be able to meet the requirements of different configurations. Finally, in order to achieve high-speed, high-precision five-axis machining, the CNC system must also have a look-ahead function and a large buffer storage capacity, so that motion data can be calculated and processed in advance and multi-stage buffering can be performed before program execution. Storage to ensure that the error remains small when the tool is running at high speed. All these requirements will undoubtedly increase the complexity of the CNC system structure and the difficulty of development.

The mechanical structure design and manufacturing of three- and five-axis machine tools are also more complex and difficult than those of three-axis machine tools.

Because the machine tool needs to add two rotation axis coordinates, it must use a worktable that can tilt and rotate or a spindle head component that can rotate and swing. The two added components require not only a compact structure, but also sufficient torque, motion sensitivity and precision, which is obviously much more difficult than designing and manufacturing ordinary three-axis processing machine tools.

The development trend of five-axis machine tools

首先是采用直线电机驱动技术(图1)。经过十多年的发展,直线电机技术已经非常成熟。直线电机易受干扰、产生大量热量的问题在最初开发时就已得到解决。直线电机的定位技术可以在高速运动时快速停止,一些机床制造商采用阻尼技术来解决这个问题。

直线电机的优点是直线驱动、无传动链、无磨损、无背隙,因此能达到最佳的定位精度。直线电机具有高动态性,可实现超过 2g 的加速度。采用直线电机驱动还具有可靠性高、免维护的特点。

二是采用双驱动技术(图2)。对于较宽的工作台或龙门类型,如果采用中间驱动,实际上无法保证驱动力位于中心,而且很容易引起倾斜,导致动态性能较差。采用双驱动、双光栅尺、一个驱动模块即可实现完美的动态性能。一条驱动指令,双驱动同时工作,光栅尺检测两点是否平衡。如果不平衡,则使用不同的命令来实现平衡。当然,五轴机床技术的发展远不止于此,很多技术都会体现在DMG的机床产品中。

Advantages of five-axis linkage machine tools

这里所谓的五轴加工是指机床至少有五个坐标轴(三个直线坐标和两个旋转坐标),在计算机数控(CNC)系统的控制下可以同时协调运动进行加工。 。与普通三轴联动数控加工相比,此类五轴联动数控加工具有以下主要优点:

1、可加工普通三轴数控机床无法加工或一次装夹难以加工的连续、光滑的自由曲面。如航空发动机和汽轮机的叶片、船舶的螺旋桨以及许多具有特殊曲面和复杂型腔、孔位的壳体和模具。如果用普通三轴数控机床加工,由于它们的刀具相对加工过程中不能改变工件的姿态角度。在加工一些复杂的自由曲面时,可能会出现干涉或加工不足(即加工失败)的情况。用五轴联动机床加工时,由于加工过程中可以随时调整刀具/工件的姿态角度,可以避免刀具与工件的干涉,一次装夹即可完成所有加工;

2、提高空间自由曲面的加工精度、质量和效率。例如,三轴机床加工复杂曲面时,常使用球头铣刀。球头铣刀采用点接触形成,切削效率低。而且加工过程中刀具/工件位姿角无法调整,一般难以保证使用球头立铣刀上的最佳切削点(即在线速度最高的球头上的最高点)进行切削,有可能切削点落在线速度为零的球头铣刀的旋转中心线上,如图1a所示的刀位。此时,不仅切削效率极低,而且加工表面质量严重恶化,往往需要人工修复,因此可能会损失精度。如果采用五轴机床进行加工,由于可以随时调整刀具/工件姿态角度,不仅可以避免这种情况,而且还可以充分利用刀具的最佳切削点进行切削或加工。线接触成型。螺旋立铣刀可用于替代点接触成形球头立铣刀。甚至可以通过进一步优化刀具/工件的姿态角来进行铣削,从而获得更高的切削速度和切削线宽度,即更高的切削速度。效率和更好的加工表面质量。图3给出了以恒定姿态角和优化姿态角铣削同一自由曲面的效果对比示例。不难看出,采用恒定姿态角(Sturz法)铣削的刀片表面粗糙度比采用优化姿态角(P铣削法——斯达拉格的专利)铣削的刀片低一级,且时间使用量,前者比后者多30%~130%;

表面质量等级平均Ra值

N8 1.6-3.2μm

N7 0.8-1.6μm

N6 0.4-0.8μm

N5 0.2-0.4μm

3、一次装夹即可完成工件全部或大部分加工,符合机床的发展方向。因为随着科学技术的发展和人们物质生活水平的提高,人们对产品的性能和质量有了更高的要求,形式更加多样化和个性化。为了进一步提高产品的性能和质量,充分满足用户节能、节材、轻便、美观、舒适等各种要求,现代产品不仅仅是航空航天产品和车辆(如如汽车、轮船、轮船等),还包括精密仪器、仪表、医疗和运动器材,以及家用和办公电器、儿童玩具等产品的零部件,越来越多地采用铣削加工的整体材料制成并铣削。复杂曲面及斜孔、斜面等种类较多,这些零件如果用传统机床或三轴数控机床加工,必须使用多台机床,才能完成多次定位和安装。这不仅需要大量的设备投资,占用大量的生产面积,生产加工周期长,而且精度和质量也难以保证。为了解决这些问题,需要开发能够集中工序进行高精度、高效率、复合加工的机床,以实现工件的全部或大部分加工能够在一台机器上完成。夹紧。这已经成为当今机床发展的一大趋势,而配备高速加工能力的五轴机床完全符合这一趋势的发展要求,也可能是最好的解决方案选择。因为它不仅具备现代生产加工设备所需的主要功能,而且一台五轴机床的效率约相当于两台三轴加工机床的效率,甚至可以节省更多的机床。

4、模具加工的优点。

在传统模具加工中,一般采用立式加工中心来完成工件的铣削加工。随着模具制造技术的不断发展,立式加工中心本身的一些弱点也越来越明显。现代模具加工中常用球头铣刀。球头铣刀在模具加工中带来明显的好处。但如果采用立式加工中心,底面线速度为零,因此底面光洁度很差。如果采用四轴或五轴联动机床加工技术来加工模具,则可以克服上述缺点。
由于使用五轴联动机床,工件的装夹变得容易(图1)。加工时无需专用夹具,降低了夹具成本,避免了多次装夹,提高了模具加工精度。采用五轴技术加工模具可以减少夹具的使用数量。另外,由于五轴机床在加工过程中可以省去许多专用刀具,从而降低了刀具成本。五轴机床可以增加刀具在加工过程中的有效切削刃长度,减小切削力(图2),增加刀具的使用寿命,降低成本。使用五轴联动机床加工模具可以快速完成模具加工,交货快捷,更好地保证模具的加工质量,让模具加工更简单,让模具修改更容易。

The meaning of five-axis milling

五轴加工是五面加工技术和五轴联动加工技术的总称。

五面加工技术用于复杂的多面体零件。附加机床回转轴在一次装夹的情况下,可轻松完成除安装基面外的所有平面的铣、钻镗床等加工;不仅如此,在加工斜面时,通过刀具或工件的旋转,可以使刀具更加接近加工表面,头部延长长度,有利于提高切削能力和刀具刀具;另外,还可以解决直线轴运动无法解决的凹面加工。

五面加工的另一个特点是回转轴只进行分度定位,不参与切削路径插补运动。例如,对于V形发动机缸体,采用带A/B轴双摆动工作台的式卧式加工中心。A轴移动可以完成V形斜面和缸孔的加工,然后B轴分度可以完成曲轴轴承孔和缸孔的加工。其推力面等进行处理。

五轴联动加工技术是指复杂形状表面需要五个轴共同进行数控插补运动,注意光滑表面的加工技术。虽然理论上任何复杂曲面都可以用2D方向独立上的表面。与三轴联动相比,五轴联动可将加工工件和表面粗糙度降低至1/3~1/6。

五轴联动加工的轴数是指加工同一曲面时需要独立运动的轴数,而不是CNC拥有的可控轴数。例如,龙门铣床为了保证横向梁升降的直线度,需要左右两根驱动轴W1、 W2同步运动,即W​​​​1为驱动轴,W2轴为驱动轴​​​​。此时同步。因此,它们只能用于独立的运动轴。另外,如果复杂的雕塑具有表面旋转体的特性,则不需要Y轴运动,可以在数控车床或车削中心上实现。最大联动轴数多为四个独立轴。

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