Technical application guide for high-speed machining of metal molds

The main goal of metal mold rough machining is to pursue the material removal rate per unit time and prepare the geometric contour of the workpiece for semi-finish machining. During the cutting process, the metal area of ​​the cutting layer changes, which causes the load on the hardware tool to change, which makes the cutting process unstable, the hardware tool wear rate is uneven, and the quality of the processed surface decreases.
Many CAM software developed at present can keep the cutting conditions constant through the following measures, so as to obtain good machining quality. Constant cutting load. Through calculation, a constant cutting layer area and material removal rate are obtained, so that the cutting load and the tool wear rate are kept in balance to improve tool life and processing quality. Avoid sudden changes to the tool feed direction. Avoid burying the tool in the workpiece. For example, when processing the mold cavity, avoid inserting the tool vertically into the workpiece, and use the inclined cutting method (usually the inclined angle is 20°~30°). It is best to use the spiral cutting tool to reduce the tool load; when processing the mold core , Should try to cut from the outside of the workpiece and then cut into the workpiece horizontally. When the tool cuts in and cuts out the workpiece, the inclined (or arc type) cut in and out should be used as much as possible, and vertical cut in and out should be avoided. Climb cutting can reduce cutting heat, reduce tool stress and work hardening, and improve machining quality. The main goal of semi-finishing mold semi-finishing is to make the contour of the workpiece flat, and the surface finishing allowance is uniform. This is especially important for tool steel molds, because it will affect the change of the cutting layer area of ​​the tool and the change of the tool load during finishing. , Thereby affecting the stability of the cutting process and the quality of the finished surface. Rough machining is based on the volume model, and finishing is based on the surface model. The previously developed CAD/CAM system does not describe the geometry of the part continuously. Since there is no intermediate information describing the machining model after rough machining and before finishing, the remaining machining allowance distribution and maximum remaining machining allowance of the rough machining surface All are unknown. Therefore, the semi-finishing strategy should be optimized to ensure that the surface of the workpiece after semi-finishing has a uniform remaining machining allowance.
The high-speed finishing strategy of finishing molds depends on the contact point between the tool and the workpiece, and the contact point between the tool and the workpiece changes with the slope of the machined surface and the effective radius of the tool. For complex curved surface processing composed of multiple curved surfaces, continuous processing should be carried out in one process as much as possible, instead of processing each surface separately, in order to reduce the number of times of raising and lowering the knife. However, due to the change of the surface slope during processing, if only the stepover is defined for processing, the actual step distance may be uneven on the surface with different slopes, thereby affecting the processing quality. Pro/Engineer’s solution to the above problems is to define the amount of side-grabbing and at the same time define the high residual area of ​​the machining surface (Scallopmachine); HyperMill provides an equal step machining (Equidistantmachine) method to ensure uniform cutting paths The side-grabbing amount is not limited by the surface slope and curvature, ensuring that the tool always bears a uniform load during the cutting process.
The optimization process includes: the calculation of the contour after rough machining, the calculation of the maximum remaining machining allowance, the determination of the maximum allowable machining allowance, and the division of the profile with the remaining machining allowance greater than the maximum allowable machining allowance (such as transitions such as grooves and corners) The radius is smaller than the area of ​​the roughing tool radius) and the calculation of the tool center path during semi-finishing. Most of the existing CAD/CAM software for high-speed machining of molds has the remaining machining allowance analysis function, and can adopt reasonable semi-finishing machining strategies according to the size and distribution of the remaining machining allowance. For example, OpenMind’s HyperMill and HyperForm software provides methods such as Pencilmilling and Restmilling to remove the corners with a large remaining machining allowance after rough machining to ensure a uniform machining allowance for subsequent processes. The local milling (Localmilling) of PRO/ENGINEER software has similar functions. For example, the remaining machining allowance of the local milling process is equal to the roughing. This process only uses a small diameter milling cutter to remove the corners that have not been cut by the roughing. , And then perform semi-finishing; if the remaining machining allowance value of the partial milling process is taken as the remaining machining allowance of semi-finishing, this process can not only remove the corners not cut by rough machining, but also complete semi-finishing.
In general, the radius of curvature of the finishing surface should be greater than 1.5 times the radius of the tool to avoid sudden changes in the feed direction. In the high-speed precision machining of the mold, each time the workpiece is cut in or out, the feed direction should be changed by arc or curve as far as possible, and straight line should be avoided to maintain the smoothness of the cutting process. Feed rate optimization At present, many CAM software have the function of optimizing and adjusting the feed rate: in the semi-finishing process, when the cutting layer area is large, the feed speed is reduced, and the cutting layer area is small to increase the feed speed. The optimized adjustment of the feed speed can make the cutting process smooth and improve the quality of the machined surface. The size of the cutting layer area is automatically calculated by the CAM software, and the adjustment of the feed speed can be set by the user according to the processing requirements.
Mold high-speed machining technology is the integration of a variety of advanced machining technologies, not only involving high-speed machining technology, but also including high-speed machining machine tools, CNC systems, high-speed cutting tools and CAD/CAM technology.
Mold high-speed processing technology has been widely used in the mold manufacturing industry in developed countries, but the application scope and application level in my country still need to be improved. Vigorously developing and popularizing mold high-speed processing technology will promote the overall technical level and economy of my country’s mold manufacturing industry The improvement of efficiency is of great significance.