Scientific selection of relevant processing methods and reasonable numerical control programming of mold processing will significantly improve the product quality of the mold and shorten the manufacturing cycle, and it will also directly benefit the manufacturing cost (such as tool consumption, maintenance of machine tool accuracy, etc.).
The automobile exterior cover mold directly affects the appearance quality of the final automobile product. How to ensure quality and improve quality through reasonable programming and selection of processing methods is a key difficulty in continuous innovation and improvement in mold manufacturing.
The automobile exterior cover mold includes an overall side wall, a door, front and rear fenders, a hood, a top cover, a rear trunk, a side wall mold, etc., wherein the overall side wall mold is more difficult to program and process, and is also the most in the programming process. Representative molds. In this paper, the overall lateral side drawing die is taken as an example to discuss the choice of programming and processing methods for automotive exterior cover molds.
Overall programming ideas
For CNC machining roughing of large drawing dies, the first problem to be considered is to cut off the maximum metal machining allowance in the shortest time, as long as the cutting conditions allow. The reasonable choice of numerical control programming processing parameters (mainly including programming processing methods, matching of spindle rotation speed and feed, stepping, cutting depth, tool selection), especially reasonable crushing rough machining parameters, can not only ensure the processing efficiency, but also It can save the cost of tools and improve processing efficiency. For rough machining, before the programming, it must be combined with the past experience of numerical control processing of small-scale complex molds to perform the partition processing, and a variety of rough machining methods combined with the programming method for rough machining.
The semi-finishing does not involve the issue of the knife mark, so it can only be considered in any partition programming process under the premise of processing feasibility and ensuring processing efficiency. During semi-finishing programming, the algorithm for calculating the tool path is different due to different programming methods. In some programming methods, the residual amount in the local part will be larger. It is necessary to compile the influence on the machining quality and precision during finishing. Local patch program.
The choice of finishing method and processing parameters directly affects the quality of the mold surface and the subsequent product manufacturing cycle. The author believes that it should spend more time in the early programming and processing time to ensure the surface quality of the mold to avoid the mold surface quality due to programming and processing problems can not meet the technical requirements and rely on fitter to repair.
Analysis of the physical structure and processing of the die
Figure 1 shows the entity of an integral side wall punch. Before processing, digital and physical coordinates system, material thickness and direction, the right and left parts of the side of the surrounding information and other confirmation is very important, so as to avoid incalculable losses caused by some low-level errors.
Figure 1 overall side punch
Figure 2 The overall side wall processing model
If the programming software is different from the modeling software, problems may also arise during data transmission. In the process of converting CATIA and DELCAM software to digital dies, we sometimes see inaccurate data conversions such as bad cuts, gaps, crossovers, leaks, and unwanted small scraps. These have no effect on the general mold. However, the influence of the surface quality of the drawing die of the outer cover is rather large. Therefore, a thorough and detailed inspection must be performed before the preparation of the procedure, and some targeted treatments must be performed.
Preparation of roughing procedures
The range of surface processing of the whole side wall drawing die is relatively large, so it is more economical to use a rigid CNC milling machine and a tool with a large diameter, and the machining efficiency can be ensured. In China, due to the limitation of the manufacturing level of casting blanks and the uncertainty of unbalanced blanks, we have not been able to reasonably select the profiling cutter for the rough machining of the profile. According to the current situation, we use the D50mm or D40 ball head tool to program different machining methods for rough machining in different areas, which is still economical in actual production.
1, contour roughing program
The blank at the contour may affect the life of the roughing tool, especially when the tool moves from the top down, there is a tendency of the tool to cut into the blank vertically, so before the roughing, the test procedure is used to ensure that the surface is processed. Under the premise, we must rough outline, or finish machining.
2. Local processing procedures and contour roughing procedures before contour roughing
The punch is relatively steep around the surface, and it is generally processed by the contour roughing method, but there is a relatively flat profile in the part. The local processing program in Fig. 3 and the contour program in Fig. 4 can be seen partially. The software simply handles the flat surface when calculating the contour processing method. If the local processing is not performed, the cutting amount will be due to the local tool. As a result of the abrupt increase in the number of cutters, accidental programming, such as local parallelism and three-dimensional offset before contouring, are particularly necessary.
Figure 3 local processing program
Figure 4 contour program local
The drawback of contour programming is that the number of cutters is large, and the tool path is shown in Fig. 5. However, if you use a fast sweep between the cutters, you can ignore the time lost due to the cutter. The advantage is that each layer can be processed. At the same height, from top to bottom layer by layer, the damage to tools and machine tools is relatively small, and the process is safer and more stable.
Figure 5 Tool path of contour program
3, three-dimensional offset roughing
The three steep areas in the middle are machined in a three-dimensional offset (Figure 6). The disadvantage is that the machining trajectories of each layer cannot be guaranteed at the same height. The advantage is that the number of lifting times is greatly reduced.
Figure 6 Three-dimensional offset roughing
When three-dimensional offsets are used instead of contours, it must be carefully checked whether the three-dimensional offset tool path has a trajectory for the movement of the knives. If it exists, the reference line or boundary must be changed and the program must be recalculated. Otherwise, it is very easy to perform numerical control. Knife blade.
4, parallel roughing
After the completion of the steep area processing, the procedure for programming the top flat surface is started. The parallel roughing method (Fig. 7) can be used, and the flat area can be divided into three layers for pen root removal and line cutting processing according to different retention.
Figure 7 Parallel roughing
Because rough machining uses D50mm ball-end knives for processing and semi-finishing with D30mm ball-end knives, it is necessary to use the D40 tool to clear the roots after rough machining. The method of clearing roots is to select single or multiple strokes according to the degree of depression at the root.
Preparation of semi-finishing programs
Clear root before semi-finishing (Figure 8) is very necessary, in addition, limited by the tool, clear root program according to the extension of the length of the standard tool, while giving the NC process does not collide, but the cutting angle is necessary. Specific steps are as follows: the preparation of D30 ball head knife multiple clear roots; preparation of D30 ball head knife single pen root; preparation of D20 ball head knife multi-pen root; preparation of D30 ball head knife surface semi-finishing process (tool path such as Figure 9).
Figure 8 Clearance procedure
Fig. 9 Tool path of semi-finishing program
Compiling a finishing program
Finishing programming steps are as follows: the preparation of D16 ball head knife single clear root; preparation of D10 ball head knife multi-pen root; preparation of D30 ball head knife before finishing semi-finishing; preparation of D30 ball head knife make up knife program; D30 ball nose knife finishing program (the tool path is shown in Figure 10).
Figure 10 Finished tool path
The side edges of the finishing tools are susceptible to wear and the knives are present during the machining process. The margin of the steep faces is slightly larger. To prevent the finishing inserts from being worn too quickly, a margin adjustment program must be added to the steep faces.
The first solution of the knife making procedure is to use the three-dimensional biasing method to perform the milling method from top to bottom as much as possible. The second scheme is to cut and make up the knife. In the actual processing, if the three-dimensional offset compensating knife program of the first scheme has an up-cut or a local over-cut phenomenon due to the protruding tool being too long, the second set of programs shall be used to cut the complementary cutter.
When using three-dimensional offsets to make up the knife program, special attention should be paid to the following points:
â–¡ Programming as possible with milling milling;
â–¡ The collision must be checked and the tool length must be measured. According to the experience, when the D20 ball nose tool protrudes more than 110mm and the D30 ball nose tool protrudes beyond 145mm, the tool cannot be compensated by the three-dimensional offset method (except for the program without reverse milling);
â–¡ When the clear roots are in place, the three-dimensional offset tool compensation program can be used only after the semi-finishing process before finishing.
The second program of the supplemental knife program may also cause overcutting of the cutting knife. The analysis may be due to:
â–¡ Tool extends too long;
â–¡ The speed and feed do not match (for example, experience parameter: D20 ball head speed 6000r/min, feed rate 6000mm/min is better);
â–¡ The blade is worn. Overcutting occurred when the blade was replaced.
In addition, the side convex die finishing process is the most critical factor affecting the surface quality. For example, the matching of empirical parameters such as tolerance, step, speed, and feed can not be ignored.
Partition processing
From the perspective of improving machining efficiency, protecting machine tool accuracy, saving tool costs, and cutting tool safety during roughing and semi-finishing (without blade play), it is better to perform different procedures for rough and semi-finishing programs in different areas. Partition, to maximize the use of milling milling programming.
For the above punches, the crush milling method is not typical enough, but it is very suitable for most pressing rings and flat concave molds. As shown in Fig. 11, the concave model surface adopts a three-dimensional offset spiral crushing roughing process, and 80% of the area can be programmed and processed by a crest milling method. This piece is divided into four areas for roughing: the smooth surface of the outer profile divides the two areas 1 and 2, the middle flat area is area 3, and the area 4 is the facade area. Area 4 can be machined at the same height, but it is also best to use 3D offset crushing to work from top to bottom.
Figure 11 Rough Machining
Of course, for the first tool path at the tool under the machining program, it is sometimes necessary to first add a single layered tool path to mill the amount of the blank at the lower tool to avoid the cutting edge due to the large amount of cutting in the first turn.
to sum up
The automobile outer cover mold directly affects the appearance quality of the final automobile product, scientifically selects the relevant processing method, and reasonably performs the numerical control programming of the mold, which will obviously improve the mold product quality and shorten the manufacturing cycle, and also the manufacturing cost (such as tooling Consumption, machine tool accuracy, etc.) also have a direct benefit.
For roughing, it must be combined with the previous experience before programming, and a variety of rough machining methods should be used to combine the programming methods; semi-finishing can only consider any partition in the premise of processing feasibility and ensure the processing efficiency Programming and processing, when some local residuals are large, it is necessary to compile the supplementary knife program; the clean heel and knife replacement procedures in the finish machining are very important, and the matching of experience parameters such as tolerance, step, speed, and feed can not be ignored.
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