According to the larger tool size and higher processing efficiency, multi-tool combination machining is also an effective way to improve the overall machining efficiency of large surfaces for large-area complex surfaces. The larger the size of the tool, the higher the machining efficiency in the area that can be processed, but the larger the area of ​​the surface that does not meet the conditions on the curved surface. These undercut areas need to be processed by small tools with low machining efficiency. Therefore, the overall processing efficiency of the curved surface may be reduced. Theoretically, there is a certain correspondence between the large tool size and the overall machining efficiency of the curved surface after the small tool size is determined. As shown
The relationship between the size of the large tool and the machining efficiency. In the stage, as the size of the large tool increases, the overall machining efficiency of the surface increases, reaching the maximum at the point; at the stage, as the size of the large tool increases, the surface is curved. The overall machining efficiency is gradually reduced, and the minimum machining point is reached. At this time, the selected large tool size is not satisfied on the entire surface, which is equivalent to using only a small tool that satisfies the condition on the entire surface for surface machining, so the surface is curved. The overall processing efficiency is the same as the point. Establish a functional relationship between large tool size and surface machining efficiency, and choose an effective way to achieve large-size complex surfaces to achieve processing efficiency.
The relationship between large tool size and machining efficiency for combined tool selection for large-scale complex surface machining In addition to the above methods, there is theoretically another tool selection method: manual selection of tool combinations of different sizes and tool path planning, and then adoption The simulation program performs simulation cutting, and then the machining efficiency is compared, and finally the optimized tool combination can be obtained. However, since this method is too time consuming, it is difficult to obtain practical applications. Optimal Small Tool Selection The optimal small tool for surface machining is the largest tool that can machine the entire surface without interference. Interference feature points are the surface points that are most likely to interfere with the tool. For a free-form surface with a machining constraint surface, the interference feature points are very clear, so the position of the interference feature point can be directly determined according to the characteristics of the constraint surface. For a free-form surface without a machining constraint surface, the area on the surface where interference is most likely to occur is the surface point with the largest principal curvature and its neighborhood. Therefore, the determination of the interference feature point depends on the calculation of the maximum principal curvature of the surface.
The selection surface of the small tool is processed to obtain one or several surface points with the largest principal curvature. The local geometric properties of these surface points determine the type and size of the small tool.
Tool type selection Regarding the choice of tool type, although the application of ball end milling cutter in CNC machining is quite common, it has been proved that the flat end mill has obvious advantages over the ball end mill: First, the machining efficiency is high. Under the same processing conditions, the flat cutter can obtain a large effective cutting radius by changing the inclination angle of the cutter shaft, and improve the closeness of the effective cutting edge of the tool to the surface to be machined. Under the premise of satisfying the same residual height, the flat head milling Knife processing can use a larger line spacing and thus has higher processing efficiency. Second, the cutting performance is good. The cutting edge of the ball-end knife has different cutting speeds at different positions, and the cutting speed near the end of the ball is almost zero; and the cutting speed of the cutting blade at different positions on the cutting edge is the same, so that the cutting performance is good. .
The above shows that in the multi-axis machining of the free-form surface, the flat-end milling cutter has obvious advantages in terms of the processing efficiency and precision of the curved surface relative to the ball-end cutter, so the flat-blade cutter should be preferred when possible.
After the tool size selection interference feature point and tool type are determined, the tool size can be selected. For the ball-end knife, since the projection of the cutting edge on the curved section of the curved surface is an arc of the same radius, the optimal small tool radius of the ball-shaped shape can determine the optimal small shape of the ball or the flat head. The tool size of the tool satisfies the requirement of the tool without curvature interference machining in the entire surface, but the tool bottom interference and the tool bar interference need further testing. After the interference avoidance algorithm is applied to the determined feature of the surface to verify and adjust the determined tool, the final determined tool radius is the final optimized small tool size.
The choice of combination tool The selection method of the large tool is the same as that of the small tool, but the size selection is closely related to the area of ​​the area that can be processed: the larger the size of the tool, the higher the machining efficiency in the area that can be processed. The smaller the interference-free cutting area that can be performed.
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