The main goal of roughing mold roughing is to pursue the material removal rate per unit time, and to prepare the geometric outline of the workpiece for semi-finishing. In the cutting process, due to the change of the metal area of ​​the cutting layer, the load that the tool bears is changed, the cutting process is unstable, the tool wear speed is uneven, and the quality of the machining surface is reduced.
Many CAM softwares currently developed can maintain a constant cutting condition by the following measures, thereby obtaining good processing quality. Constant cutting load. By calculating the constant cutting area and material removal rate, the cutting load and the tool wear rate are kept in balance to improve the tool life and processing quality. Avoid sudden changes in the tool feed direction. Avoid burying the tool in the workpiece. Such as the processing of mold cavity, the tool should be avoided vertical insertion into the workpiece, but should be used to tilt the knife way (common tilt angle of 20 ° ~ 30 °), it is best to use spiral knife to reduce tool load; processing mold core , should try to cut from the outside of the workpiece and then cut into the workpiece horizontally. When the tool cuts in or cuts out the workpiece, it should be inclined or arc-shaped as far as possible to cut in and cut out, so as to avoid vertical cut-in and cut-out. The use of climbing cutting (Climbcutting) can reduce the cutting heat, reduce the tool force and work hardening degree, improve the processing quality. The main goal of semi-finishing tool semi-finishing is to make the contour of the workpiece flat and the surface finishing allowance is even. This is especially important for tool steel molds, because it will affect the cutting surface area of ​​the tool and the change of tool load during finishing. This affects the stability of the cutting process and the quality of the finished surface. Roughing is based on the volume model, and finishing is based on the surface model. The CAD/CAM system developed previously does not have continuous geometric description of parts. Since there is no description of the intermediate information of the rough machining model and the pre-finishing machining model, the remaining machining allowance distribution and the maximum remaining machining allowance of the rough machining surface are not described. Both are unknown. Therefore, the semi-finishing strategy should be optimized to ensure a uniform residual machining allowance on the workpiece surface after semi-finishing.
The optimization process includes: calculation of the profile after rough machining, calculation of the maximum remaining machining allowance, determination of the maximum allowable machining allowance, and division of the model surface where the remaining machining allowance is greater than the maximum allowable machining allowance (such as the transition of grooves, corners, etc.) The radius is smaller than the area of ​​the roughing tool radius) and the calculation of the trajectory of the shank during semi-finishing. The existing mold high-speed machining CAD/CAM software mostly has the residual machining allowance analysis function, and can adopt a reasonable semi-finishing strategy according to the size and distribution of the remaining machining allowance. For example, OpenMill's HyperMill and HyperForm software provide methods such as Pencilmilling and Restmilling to remove the remaining corners after rough machining to ensure a uniform machining allowance in subsequent operations. The Local Milling of the Pro/Engineer software has similar functions. For example, the remaining machining allowance in the local milling process is equal to the roughing process. This process uses only a small-diameter milling cutter to clear the uncut corners of rough machining. Then, semi-finishing is performed; if the remaining machining allowance value of the local milling operation is used as the remaining machining allowance of semi-finishing, this step can not only clear the corners that are not cut by rough machining, but also complete semi-finishing.
The high-speed finishing strategy of the finishing tool depends on the point of contact between the tool and the workpiece, and the point of contact between the tool and the workpiece changes as the surface slope of the machined surface and the effective radius of the tool change. For complex surface machining that consists of a combination of multiple surfaces, continuous machining should be performed in one process as much as possible, instead of machining each surface individually to reduce the number of times the tool is lifted or dropped. However, due to the change of the surface slope during machining, if only the amount of side-stepping of the machining is defined, the actual step distance on the surfaces with different slopes may be uneven, which may affect the machining quality. Pro/Engineer solves this problem by defining the Scallop machine at the same time as the blade at the defined side, and HyperMill provides the Equidistant machine method to ensure a uniform path between the passes. The amount of knife on the side is not limited by the surface slope and curvature, so as to ensure that the tool always bears a uniform load during the cutting process.
Under normal circumstances, the radius of curvature of the finished surface should be greater than 1.5 times the radius of the tool to avoid abrupt changes in the feed direction. In the high-speed finishing of the die, each time the workpiece is cut in or cut out, the feed direction should be changed as much as possible using arcs or curves to avoid the use of straight line transfer to maintain the smoothness of the cutting process. Optimization of feed rate Many CAM softwares currently have the optimal adjustment function of feed speed: In the semi-finishing process, the feed speed is reduced when the cutting layer area is large, and the feed speed is increased when the area of ​​the cutting layer is small. The optimal adjustment of the application feedrate speeds the cutting process and improves the quality of the machined surface. The size of the cutting layer is completely calculated by the CAM software. The adjustment of the feed rate can be set by the user according to the machining requirements.
Conclusion
The high-speed mold processing technology is an integration of various advanced processing technologies, not only involving high-speed machining processes, but also high-speed machining tools, numerical control systems, high-speed cutting tools, and CAD/CAM technology.
Mould high-speed machining technology has been widely used in the mold manufacturing industry in developed countries. However, the application scope and application level in China still need to be improved. The rapid development and promotion of the application of high-speed mold processing technology to promote the overall technical level and economy of China's mold manufacturing industry. The improvement of benefits is of great significance.
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