In the numerical control processing, the process route arrangement, processing strategy and tool selection have a great influence on the processing efficiency, processing quality and processing cost. In the past few years, we have been devoting ourselves to research and experiments in this area. We have achieved certain results in improving processing efficiency and reducing tooling costs. The following takes the car crankshaft type forging die and PowerMILL as the programming software as an example to discuss some of its CNC machining strategies and tool selection.
Structural analysis and processing technology
Structural analysis
The structure of the car crankshaft forging model cavity (see Figure 1) is characterized by deep and narrow crank parts, small concave round corners, crank depth of about 58mm, crank width generally less than 16mm, minimum draft angle of 1°, cavity concave circle Most of the corners are R3. The connecting rod diameter of the crankshaft and the rounded corner of the crankshaft are R2. There are annular grooves on both sides of the middle spindle diameter. The dimensions of this type of die (forging die) are approximately 600mm x 330mm x 160mm, the die material is H11, the die hardness is dB = 2.9-3.1, the groove dimension accuracy is ± 0.10mm, and the surface roughness Ra1.6.
Die processing technology for the shape processing - hole processing - cavity NC roughing - heat treatment - contouring - cavity cavity CNC finishing - bench polishing. The current tooling technology is fully capable of machining hardened tool steels. The roughing and finishing of the cavity here are mainly considered from the aspect of saving the tool cost. Before the heat treatment, most of the margin is removed. After the heat treatment, the finishing process can reduce the tool consumption.
The rough machining, semi-finishing and finishing machining should be performed in the cavity NC machining process to obtain better surface quality and dimensional accuracy. In the semi-finishing before finishing, first remove the excess, especially the corner, leaving a margin of about 0.1 mm for finishing, and the balance is even, so that the finishing cutting is smooth and the tool life is improved. Ensure dimensional accuracy and surface roughness.
Processing strategy analysis
1. Roughing strategy and tool selection
For the structural characteristics of car crankshaft forging model cavity, two cutters can be selected to complete the roughing process of the cavity with the offset area removal strategy and the contour processing strategy.
The first knife selects the bias region removal strategy. The tool processes the contour section contours from the top contour of the trough, one cut surface and one cut surface to the cut plane of the cut surface. In the forging die machining, the first blade generally selects the bias region elimination strategy, which is not discussed here.
The second tool selects the contour machining. There is no choice for residual machining and contouring because there are so many tools available for these two machining methods. In actual machining, the number of pick-ups has a great influence on the actual machining time, which is several times the simulation time. With the same cutting parameters, there are fewer high-speed machining operations and high efficiency. The comparison of knife mention is shown in Figure 2.
The second is to use indexable inserts as much as possible to reduce the cost of tools.
Third, the tool can be processed to the deepest and narrowest part of the cavity, such as the crankshaft crank parts, to remove as much of the headroom as possible, so that the less the fine processing after heat treatment, the better.
Fourth, tool selection must be considered in conjunction with processing strategies. If the second machining strategy is equal height machining, the second tool diameter should be larger than the first tool radius, so as to ensure that the tool path covers the last machining path of a tool and does not leave a local convexity. Bags make it difficult to finish.
2. Finishing strategy and tool selection
PowerMILL software (see Figure 4) provides a very rich processing strategy for finishing. Here we use the contour finishing and parallel processing (beach) strategy to complete the cavity finishing. The boundary R2 is also determined by contouring.
in conclusion
Practice has verified that the above strategy is very effective for further improving the CNC machining efficiency of car crankshaft forging dies. According to the above processing strategy and tool selection principle, we performed actual tracking test on a car crankshaft forging die (see Fig. 7), completed roughing, semi-finishing and finishing machining of the cavity with five tools and six tool paths. The results showed that the machining efficiency was increased by more than 30% compared with the previous time. The processing time of each pair of mold cavities did not exceed 32 hours, the machining accuracy was ±±0.05 mm, the surface roughness reached Ra1.6, and the tool cost was reduced by 15%.
1. The contour finishing machining process is stable, with little lifting and high efficiency. It is not only suitable for precision machining, but also suitable for semi-finishing and root cleaning. Therefore, in the actual programming process, various processing strategies should be applied flexibly.
2. NC programmers must not only be fluent in programming software, but also have knowledge of machining technology, cutting principles and tools, and also have rich field experience.
3. The numerical control program must not only be simulated on the computer repeatedly, the numerical control programmer must often observe and observe the actual processing situation on the spot at the same time, optimize the procedure, improve the processing precision and efficiency.
4. CNC programmers should fully communicate with the CNC machine operators and let the operators understand the programmer's ideas so as to obtain the best results.
5. In order to reduce the cost of mold manufacturing, the molds that fail in general are either refurbished or refurbished. Therefore, when we compile a new mold program, we must fully consider the processing of the refurbished mold, and the procedure is the best. We can process new molds and process refurbishment molds to facilitate the use of the production department and also save programming time.
Structural analysis and processing technology
Structural analysis
The structure of the car crankshaft forging model cavity (see Figure 1) is characterized by deep and narrow crank parts, small concave round corners, crank depth of about 58mm, crank width generally less than 16mm, minimum draft angle of 1°, cavity concave circle Most of the corners are R3. The connecting rod diameter of the crankshaft and the rounded corner of the crankshaft are R2. There are annular grooves on both sides of the middle spindle diameter. The dimensions of this type of die (forging die) are approximately 600mm x 330mm x 160mm, the die material is H11, the die hardness is dB = 2.9-3.1, the groove dimension accuracy is ± 0.10mm, and the surface roughness Ra1.6.
Fig.1 Schematic diagram of car crankshaft forging model cavity
Die processing technology for the shape processing - hole processing - cavity NC roughing - heat treatment - contouring - cavity cavity CNC finishing - bench polishing. The current tooling technology is fully capable of machining hardened tool steels. The roughing and finishing of the cavity here are mainly considered from the aspect of saving the tool cost. Before the heat treatment, most of the margin is removed. After the heat treatment, the finishing process can reduce the tool consumption.
The rough machining, semi-finishing and finishing machining should be performed in the cavity NC machining process to obtain better surface quality and dimensional accuracy. In the semi-finishing before finishing, first remove the excess, especially the corner, leaving a margin of about 0.1 mm for finishing, and the balance is even, so that the finishing cutting is smooth and the tool life is improved. Ensure dimensional accuracy and surface roughness.
Processing strategy analysis
1. Roughing strategy and tool selection
For the structural characteristics of car crankshaft forging model cavity, two cutters can be selected to complete the roughing process of the cavity with the offset area removal strategy and the contour processing strategy.
The first knife selects the bias region removal strategy. The tool processes the contour section contours from the top contour of the trough, one cut surface and one cut surface to the cut plane of the cut surface. In the forging die machining, the first blade generally selects the bias region elimination strategy, which is not discussed here.
The second tool selects the contour machining. There is no choice for residual machining and contouring because there are so many tools available for these two machining methods. In actual machining, the number of pick-ups has a great influence on the actual machining time, which is several times the simulation time. With the same cutting parameters, there are fewer high-speed machining operations and high efficiency. The comparison of knife mention is shown in Figure 2.
Figure 2 Comparison of knife mention
Figure 3 Roughing tool
The second is to use indexable inserts as much as possible to reduce the cost of tools.
Third, the tool can be processed to the deepest and narrowest part of the cavity, such as the crankshaft crank parts, to remove as much of the headroom as possible, so that the less the fine processing after heat treatment, the better.
Fourth, tool selection must be considered in conjunction with processing strategies. If the second machining strategy is equal height machining, the second tool diameter should be larger than the first tool radius, so as to ensure that the tool path covers the last machining path of a tool and does not leave a local convexity. Bags make it difficult to finish.
2. Finishing strategy and tool selection
PowerMILL software (see Figure 4) provides a very rich processing strategy for finishing. Here we use the contour finishing and parallel processing (beach) strategy to complete the cavity finishing. The boundary R2 is also determined by contouring.
Figure 4 PowerMILL software interface
Figure 5 Contour Road (left) and Shoal Knife Road (right)
Figure 6 Finishing tool
in conclusion
Practice has verified that the above strategy is very effective for further improving the CNC machining efficiency of car crankshaft forging dies. According to the above processing strategy and tool selection principle, we performed actual tracking test on a car crankshaft forging die (see Fig. 7), completed roughing, semi-finishing and finishing machining of the cavity with five tools and six tool paths. The results showed that the machining efficiency was increased by more than 30% compared with the previous time. The processing time of each pair of mold cavities did not exceed 32 hours, the machining accuracy was ±±0.05 mm, the surface roughness reached Ra1.6, and the tool cost was reduced by 15%.
Figure 7 Crankshaft forging die of a car
1. The contour finishing machining process is stable, with little lifting and high efficiency. It is not only suitable for precision machining, but also suitable for semi-finishing and root cleaning. Therefore, in the actual programming process, various processing strategies should be applied flexibly.
2. NC programmers must not only be fluent in programming software, but also have knowledge of machining technology, cutting principles and tools, and also have rich field experience.
3. The numerical control program must not only be simulated on the computer repeatedly, the numerical control programmer must often observe and observe the actual processing situation on the spot at the same time, optimize the procedure, improve the processing precision and efficiency.
4. CNC programmers should fully communicate with the CNC machine operators and let the operators understand the programmer's ideas so as to obtain the best results.
5. In order to reduce the cost of mold manufacturing, the molds that fail in general are either refurbished or refurbished. Therefore, when we compile a new mold program, we must fully consider the processing of the refurbished mold, and the procedure is the best. We can process new molds and process refurbishment molds to facilitate the use of the production department and also save programming time.
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