Optimal setting of tool path generation in the hot

2022-08-24
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High speed milling technology is a new processing method in recent years. Because it can effectively process high hardness materials and other excellent characteristics, after continuous development, it has been widely used in aviation, cars, forging dies and other manufacturing fields. During high-speed milling, the spindle speed of the machine tool is as high as 8000 ~ 30000rpm, and the feed speed is about 3 ~ 6m/min. it is very important to keep the machine tool and cutting tool under constant cutting load during machining. Although some CNC machine tools can realize the adaptive cutting load in machining because the in/com of 5502 converter is +24vdc, the unreasonable arrangement of tool path will also produce a large inertial impact on the machine tool and tools, which is also very unfavorable to the spindle of the machine tool and will affect the service life of the spindle and other parts. Therefore, the programming of high-speed milling should be very careful. It requires CAM software to provide a new tool cutting mode, so that the tool can maintain a relatively constant contact state with the material to be cut under different cutting forms. In addition, appropriate parameters such as tool feed and cutting depth should be selected. These process schemes must meet the actual requirements of high-speed cutting

2 several principles that should be paid attention to when programming high-speed milling

high feed, high speed and low cutting volume are the basic principles

screw feed should be used as much as possible for vertical feeding, and vertical cutting should be avoided, because this will reduce the cutting speed and leave a lot of tool marks on the surface of parts

do everything possible to ensure that the tool path is smooth and stable. Do not turn hard when walking the tool in the program. Try to reduce the sudden change of any cutting direction as much as possible, so as to minimize the reduction of cutting speed

try to reduce the full tool width cutting and maintain the stability of metal removal rate

it is best to use forward milling, and when cutting in and out the workpiece, use the arc cutting in and cutting out methods to cut in or leave the workpiece

if the NC system supports, it is best to use NURBS output to reduce the amount of programs and improve the processing speed of the NC system

for safety reasons, careful collision and overcut inspection should be carried out before outputting the program

3 special settings for generating trajectories during high-speed milling

rapid development based on high-speed milling technology 5. Relaxation experimental machine specialized module experimental software exhibition. At present, most CAM software provides support for high-speed milling. The following describes the common functions of each software

when machining three-dimensional curved workpiece with ball end milling cutter, the actual machining diameter of the cutter changes with the axial feed rate or the edge contact point. The high-speed spindle and high feed speed of high-speed milling machine tools require small feed and small cutting depth as much as possible. With the change of three-dimensional surface, the actual contact point of the tool edge is constantly changing. The machining diameter of ball end milling cutter with too large diameter is too different from the nominal straight diameter, the cutting speed is not well matched, and it is not easy to obtain high surface quality. Therefore, in order to maintain the best cutting speed and cutting performance of the tool and obtain the best machined surface, the best way is to use the tool with the smallest diameter when the rigidity of the tool can overcome the cutting force

after selecting the tool, it is the reasonable setting of the tool path. When setting the tool path, we should follow some of the principles mentioned above. The main solution is to add a reasonable arc transfer. Here are several examples to illustrate the special setting of high-speed milling

Figure 1

Figure 2

Figure 3

Figure 4

add a smooth knife path transfer between two adjacent rows of knife paths

as shown in Figure 1, after using the knife path smoothing setting provided by the software, a smooth transfer is automatically added to the inter row tool shift in the adjacent rows of knife paths (shown at ② in Figure 1). In addition, after certain settings, a smooth knife cut in and cut out transfer is added at ① in Figure 1. This not only ensures the smoothness of the tool path, but also effectively avoids the phenomenon of turning hard between the two lines of cutting, so that the tool path can be smoothly transferred to the next line. This transfer method is widely used in various surface milling methods

add smooth tool path transfer between adjacent two-layer cutting paths

when cutting at constant height of curved surface and other conditions involving tool movement between adjacent two-layer cutting paths occur, the most effective method is to add smooth tool transfer. As shown in ② in Figure 2, the arc transfer of the tool path between the two layers not only effectively solves the requirement of smooth tool path, but also meets the problem of spiral cutting to reduce cutting resistance. In addition, as shown in ① in Figure 2, the additional arc makes the workpiece cut in and cut out along the tangent direction, which also plays a role of uniform cutting load

use cycloid cutting to avoid full edge diameter cutting

as shown in ① in Figure 3, in the machining of curved surface grooving, when the spiral cutter is used to cut into the workpiece, the correct method is to use cycloid cutting to swing forward to cut one or two through grooves, rather than straight lines. Therefore, the creation of this series of works began. After the through grooves are cut, the straight-line cutter is used for cutting. This effectively avoids the forward cutting of the full edge diameter, and makes the cutting load of each tool of the whole surface grooving more average. In addition, as shown in ② in Figure 3, cycloid approach and additional arc angle are also added at the turning, making the knife path more smooth

when encountering circular or myopic circular grooves, there will be a lot of empty cutting in the cycloid cutting path. At this time, the spiral cutting path shown in Figure 4 can be used, and the spiral path also effectively avoids cutting with full edge diameter

cut into the workpiece with an effective screw cutter

as shown in ① in Figure 5, when the cutter cuts into the workpiece, use the screw cutter to smoothly cut into the workpiece. In addition, a certain range of change should be set for the screw diameter. When the lower cutter position is not enough for the screw diameter, the system will automatically reduce the diameter of the screw when cutting until it can be cut (② in Figure 5). However, the diameter of the screw cannot be reduced without limitation, which is limited by the lower limit value. When the diameter of the screw is too small, it will be short-sighted to cut in a straight line. At this time, it should be set to solve the problem by cutting in a slope, and it is best to use a slope to cut down to the size. The back and forth slope processing will still look like the new one, resulting in very severe hard turns

Figure 5

these settings above do not exist independently, but often intersect with each other. To effectively realize high-speed milling, we should also consider comprehensively and use them reasonably. The method shown in Figure 1 can be used when the spacing between the tool rows is large. When the spacing between the two rows is too small during fine cutting, even if the additional arc transfer will be short-sighted because the arc diameter is too small. At this time, the cycloid crossing between the rows as shown in Figure 5 ③ should be used, or the milling method should be changed. The method of milling from the middle cycloid and separating the middle to both sides for girdling milling is used to increase the spacing between the two rows. The method shown in Figure 2 will encounter insufficient space distance of additional arcs when milling multi Island surfaces. At this time, it is necessary to change the method, use follow-up milling, and attach curves or straight lines that follow the surface changes along the layers on the relatively flat surface, so that it can also smoothly transition to the next milling layer. In the surface grooving with cycloid grooving and linear milling, when the groove contour is irregular and there are many acute angles, all cycloid milling functions should be used

4 optimization before post output of high-speed milling program

in addition to reasonably setting the tool path, the tool path and cutting parameters should also be optimized before the post output of high-speed milling is used for high-speed milling. Specifically, it includes optimization measures such as feed rate smoothing, turning deceleration, collision overcut detection, and material removal rate homogenization detection

when setting the tool path, the basic cutting feed speed is given. There are many tool paths generated during surface machining, and the tool path of each step has the corresponding cutting speed. Generally, when the change of the feed rate is less than 10%, several adjacent different feed rates are combined into one, so that the cutting process of the machine tool should be relatively stable

when the included angle between the two tool paths before and after turning is an acute angle, it is necessary to set the cutting feed rate at the turning. The cam system will divide the cutting path into several segments within a certain distance before and after turning, and assign different cutting feed rates to each segment, so as to achieve the effect of reducing the normal cutting feed rate to the cutting feed rate set by the turning angle before turning, and gradually accelerating to the normal cutting feed rate after turning

the feed of high-speed milling is very fast, so collision inspection is very important, and the possible collisions prompted by the system should be solved one by one. In addition, because there are too many additional tool paths for high-speed milling, if the setting of machining plane, detection plane, cutting boundary, machining method and other items are not well coordinated, it is easy to have overcut phenomenon. Therefore, careful overcut detection should also be carried out, and the overcut tool path detected by the system should be carefully eliminated before outputting the program

in order to make the tool have a relatively constant cutting load, it is necessary to optimize the material removal rate before postposition. When the removal rate of a certain tool path is high, the cutting feed rate will be appropriately reduced, otherwise, the cutting feed rate will be appropriately increased, and the maximum feed rate of the machine tool will be increased during idle cutting, so that the cutting load can be effectively uniform

5 Conclusion

high speed milling technology solves many processing problems, effectively improves the processing efficiency and the surface and internal quality of the workpiece, and it will develop more and more rapidly. Effective high-speed cutting not only has high requirements for machine tools and cutting tools, but also has high requirements for CAM software, cutting methods and the technical proficiency of operators

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