Abstract: Five-axis simultaneous milling can optimize the cutting process and parameters, which is beneficial to reduce tool wear and reduce post-processing. It is the development trend of automotive mold processing technology. It is suitable for machining a convex surface with a small curvature and a shallow concave surface using a ball end mill. It can also be used to machine a free surface on the side of a milling cutter. The 3+2 axis machining method can be used to maximize the speed of the pass. CNC milling has higher precision and less post processing than copy milling. To realize five-axis high-speed milling, it is necessary to continuously strengthen the functions of the computer numerical control system of the machine tool, so that it can directly receive and utilize all the design data, and can process multiple blocks in a forward-looking manner, which is convenient for the user to intervene in the computer-aided manufacturing process to correct the design data.
1 Introduction <br> <br> high-speed cutting applications (HSC) mold manufacturing technique, high cutting efficiency, the motor can be significantly reduced processing time, high machining accuracy, surface quality and therefore can greatly shorten the mechanical processing such as grinding, artificial Post-processing and sampling inspections help with many advantages such as working hours. When manufacturing a certain automobile door stretching mold abroad, the high-speed milling technology after rough milling increases the semi-finishing operation process by about 10 hours compared with the traditional milling process, but the finishing time is shortened from 36h to 30h, and the fitter is evenly saved. The work marks are 20h, the fitter scraper is reduced from 30h to 4h, the fitter polishing is reduced from 20h to 10h, and the total working hours is shortened from 106h to 54h.
Production practice shows that the introduction and application of high-speed milling technology, especially the related five-axis linkage milling, computer-aided design (CAD) / computer-aided manufacturing (CAM) and computer numerical control (CNC) technology, has promoted the manufacture of automotive molds. development of.
2 five-axis milling <br> <br> milling can obtain good approximate curved surface. When using the ball-end tool for three-axis simultaneous milling, the linear feed motion through the x, y, and z3 axes ensures that the tool can be cut to any coordinate point on the workpiece, but the direction of the tool axis cannot be changed. The actual cutting speed at the point on the tool axis is zero, and the chip space in the center of the tool is also small. If these points are involved in cutting, unfavorable cutting conditions can result in reduced surface quality, increased edge wear, and prolonged processing time, resulting in underutilized high-grade tool materials.
Compared to three-axis simultaneous milling, five-axis simultaneous milling has a number of advantages. At this time, the direction of the tool axis can be adjusted at any time by the movement of the two rotating shafts, so that the angle between the milling cutter axis and the workpiece surface and the actual cutting speed remain unchanged. The pass path can be set more flexibly to meet the specified peak-to-valley depth requirements for the workpiece surface. When machining with a ball-end tool, the chip is always separated on the hemisphere regardless of the orientation of the tool relative to the workpiece. Therefore, the chips of the same geometry and size are always cut each time. What has changed is the trajectory of the blade when separating the chips, and the resulting blade contact conditions and cutting geometry movement conditions. In other words, the cutting process and geometric motion parameters can be influenced by purposefully changing and determining the orientation of the tool, and both can be optimized from the aspects of tool wear, surface quality and process stability, as shown in the figure to the right. .
Figure five-axis milling geometry motion of ball-end milling cutter
Of course, the numerical control programming of five-axis simultaneous milling is more complicated, and the calculation ability and speed of the computer numerical control (CNC) system are higher. When the linear feed axes of the machine tool are required to make large compensation movements, it is required to avoid interference collision. Therefore, in the mold manufacturing, only a certain range of workpieces can be processed by the advantages of five-axis simultaneous milling.
Five-axis simultaneous milling can be used satisfactorily for machining shallower parts, such as a die-casting mold for a commercial vehicle roof lining. Five-axis milling can also be applied when mathematically describing complex workpiece surfaces that can be milled sideways. A foreign automobile manufacturing accessory manufacturer uses the five-axis milling pass stroke to simultaneously process the contour of the movable combined mold and the crimping ring. However, molds that are deep and have a complex local shape are generally not capable of normal five-axis milling because the tool may interfere with the workpiece.
Limited to the current level of technological development, the movement speed and acceleration of the two rotating shafts of the five-axis linkage cutting machine are low, which results in the five-axis linkage milling often failing to fully utilize the performance and power of the high-speed cutting machine. At this time, the more appropriate compromise scheme is 3+2 axis machining, which ensures that the geometric motion conditions of the points on the workpiece contour are basically the same when cutting, and the trajectory movement speed and acceleration are relatively high. In practice, the workpiece contour is first divided into different regions, and the orientation of the tool is adjusted as optimally as possible within each region. Subsequently, the three-axis linkage interpolation method is used to cut the contours of each part of the workpiece. Although it is not guaranteed that the cutting conditions are completely unchanged, it is possible to avoid unfavorable situations such as the center of the cutter head participating in the cutting.
Practical experience has shown that the use of cylindrical end mills for five-axis simultaneous milling has a wide distance between the cutters, which has a negative effect on the required manual post-processing, because the peaks on the contour of the workpiece indicate that the post-processing positions are far apart from each other, artificially The possibility of forming a undulating surface after sanding is increased, which is not allowed in automotive cover moulds. In contrast, the use of ball-end cutters provides a much smaller pitch, resulting in a groove contour that is close to the contour, which can be used to specify the orientation of the manually polished mold surface.
The mold industry has put forward special requirements for the machine tool industry. One of the outstanding development trends is the five-axis linkage machine tool. Statistics show that 50% to 80% of all German specialized machine tool manufacturers supply mold manufacturers, of which at least 16% up to 50% to 60% of five-axis linkage control machine tools. There are even manufacturers that mass-produce and provide CNC machines with up to six-axis interpolation, mainly for machining bevels and holes. In addition, there is still a considerable proportion of copy milling machines available to mold manufacturers, but the number is decreasing year by year. General machine tool manufacturers also have a high percentage of products supplied to mold manufacturers, but mainly used to manufacture small and medium molds, such as household appliance molds or toy molds. The proportion of the five-axis linkage machine is not high, only about 3% to 5%.
Every axis of motion of the machine is a source of error. The movement of two rotating shafts on the five-axis linkage bed makes the machining accuracy more difficult to achieve the specified value than the three-axis linkage machine, but the accuracy of the mold manufacturing of the order of 0.1 mm is not difficult to achieve. Machine tool manufacturers believe that the accuracy problem is not decisive, and does not hinder the development trend of investment in the production of five-axis linkage machine tools. The primary factor affecting the motion accuracy and speed of a five-axis linkage machine is the performance of the control system, then the performance of the drive system, and the level of mechanical design.
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