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Application of five-axis high-speed machining center in automobile panel mold

High-speed cutting theory is increasingly accepted with the development of CNC machining equipment and high-speed machining tool technology; high-speed cutting is a comprehensive concept that involves many different technical fields. Its emergence has caused the traditional machining concept to change. Fundamental changes. Faced with such a new processing technology, how to effectively use it is a new challenge for the automotive mold manufacturing process.

1. Automobile panel molds have their own manufacturing characteristics, which are mainly reflected in:

The shape of the working part of the mold is composed of non-mathematical curved surfaces. The surface is required to be smooth, smooth, without ripples, and with clear ridges. Because an automobile panel part usually requires several sets of molds to complete, and each working surface must conform to the same requirements. A mathematical model, therefore, its surface roughness and shape accuracy requirements are very high. There are multiple different punching directions in the wedge type mold, which requires the manufacturing equipment to have the function of any rotation angle.

2. Performance of high-speed milling equipment

The main process performance of our company’s five-axis high-speed milling equipment: the maximum spindle speed is 18000r/min, the maximum spindle feed speed is 25m/min, the A-axis rotation angle is ±110 degrees, the C-axis rotation angle is ±360 degrees, axial and radial directions Depth of cut ≤ 0.3 mm, the length of the installed tool should not be greater than 300mm, the weight should not exceed 5kg, and five-axis linkage is possible

Features of high-speed milling: Due to high speed, fast feed, and small cutting volume, the cutting force is small, the cutting temperature is low, and the tool deflection is small. It can obtain a high processing surface finish and high processing efficiency; but it requires uniform cutting load.

3. Design of high-speed milling process

The processing of automobile panel mold parts is mainly based on the profile, and is divided into three stages: rough machining, semi-finishing and finishing according to different processing purposes.

1. Rough machining

Aiming at the maximum amount of material removal per unit time, the surface quality and shape accuracy requirements are not high. Since most of the workpieces are castings, the machined surface layer has many hard points and is uneven, and the company has few high-speed milling equipment. We use powerful milling CNC equipment for rough machining, and choose Φ63R8 ring milling cutter for contour cutting.

2. Semi-finishing

Eliminate the errors left by rough machining, achieve a certain degree of accuracy in shape, make the finishing allowance more uniform, and prepare for high-speed finishing. Since the margin left after rough machining is a zigzag shape, especially the margin at the corners, conventional CNC equipment is still used and a Φ30 ball end milling cutter is selected for semi-finishing. The process method is: first use a small-diameter ball-end milling cutter to evenly clean the margin at the corner, and then use a Φ30 ball-end milling cutter to perform combined processing on large surfaces.

3. Finishing

Remove the semi-finishing allowance to make the surface accuracy meet the technical requirements. High-speed milling equipment is used for finishing, and a Φ20 ball-end milling cutter is selected for parallel line cutting to obtain a high-quality working surface and reduce the amount of grinding and preparation required by the fitter.

The choice between three-axis linkage milling and five-axis linkage milling in finishing: Since curved surface processing is a point contact milling method, and the curvature of the mold surface changes greatly, when using a ball-end milling cutter for three-axis linkage milling, the tool and the workpiece The contact point changes with the change of curvature. The cutting speed at the tool tip point is zero and the cutting force is minimum. The participation of this point in cutting will reduce the quality of the machined surface and increase the wear of the blade. At the same time, the Z-direction stress on the machine tool spindle will increase. . The cutting speed is the largest at the radial point of the tool, and its cutting force is the largest. Participating in cutting at this point will also accelerate the wear of the blade there. (The picture shows the failure mode of the blade during three-axis linked cutting) In other words, the cutting force is constantly changing during the entire cutting process. The larger the tool diameter, the greater the change in cutting force. Therefore, small-diameter ball-nose tools should be selected as much as possible to reduce changes in cutting force. However, for steep wall machining, small diameter and long tool shank are not conducive to high-speed machining.

Compared with three-axis linked milling, five-axis linked milling has certain advantages. It can always maintain a certain angle (or a certain range) between the tool axis and the workpiece surface through the movement of the two rotating axes, avoiding the maximum cutting speed point and the cutting speed zero point, so that the cutting force can maintain a certain stability, and the machining of steep walls can be maintained. There is no need to lengthen the tool holder. For contour surfaces and holes with multiple different punching directions on the mold, using five-axis linkage milling can also simplify the processing process and reduce auxiliary time such as tool alignment. However, the spindle of the five-axis linkage equipment is too large, and the diameter of the clamped tool is small and short, which may interfere with the workpiece during processing, which limits its rotation angle. It is difficult to process parts such as narrow and deep valleys and deep cavities. .

Therefore, the five-axis linkage milling method in the manufacturing of automobile exterior panel molds is currently mainly used in mold parts with relatively flat surfaces, small curvature and little change, such as automobile exterior panel molds. However, many automobile exterior cover parts have complex shapes and large changes in curvature.

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