Through the programming examples of CNC machining, the operators can improve their programming experience and level. Cam is one of the typical mechanical parts. Due to its complex contour, it is difficult to ensure the machining accuracy when processed on ordinary machine tools. However, machining with a machining center can not only ensure accuracy but also improve efficiency. Figure 6-20 shows the heart-shaped cam part. The material is TH200, and the blank machining allowance is 5mm.
In the process analysis of CNC machining, two aspects are considered: accuracy and efficiency. Theoretical processing technology
Must meet the drawing requirements, and at the same time can fully and reasonably perform the functions of the machine tool.
① Drawing analysis
The drawing analysis mainly includes the contour shape of the part, dimensional accuracy, technical requirements and positioning datum, etc.
It can be seen from the part drawing that the contour shape of the part is a circular arc transition. Figures with high requirements for dimensional accuracy and surface roughness
It is the cam outer contour, installation hole and positioning hole. The higher position accuracy is the parallelism between the bottom surface and the reference axis.
In the process of processing, these items should be ensured in the process of processing.
② Determine the positioning reference
According to the six-point positioning principle when processing the workpiece on the machining center, the positioning of the workpiece still follows the six-point positioning principle.
When selecting the positioning reference, it is necessary to fully consider the processing conditions of each workpiece to ensure that the workpiece is accurately positioned, easy to load and unload, and can quickly complete the positioning and clamping of the workpiece to ensure the accuracy of various processing. The design reference on the workpiece should be selected as the positioning reference as much as possible . According to the above principles and drawing analysis, the processing first uses the top as the reference to process the bottom surface, mounting holes and positioning holes, and then locates the bottom surface and two holes, and installs the card at one time. All surfaces and contours are processed to ensure the dimensional accuracy required by the drawings. And location accuracy.
③ Workpiece clamping
According to process analysis, we mainly process the cam profile, and use flat vise for clamping when processing the bottom mounting holes and positioning holes. When clamping a workpiece with a flat vise, you should first align the fixed jaw of the vise. Note that the workpiece should be installed in the middle of the jaw, and the processed part of the workpiece should be higher than the jaw to avoid interference between the tool and the jaw. When clamping the workpiece , Pay attention to the floating of the workpiece. When machining contours and other surfaces, clamp with pressure plates and bolts. At this time, avoid interference with the processed surface.
④ Determine the programming origin, programming coordinate system, tool setting position and tool setting method. According to process analysis, the workpiece coordinate origin X0Y0 is set on the center of the datum, and the Z0 point is set on the upper surface. After the programming origin is determined, the programming coordinates and tool setting position coincide with the workpiece coordinate origin. The tool setting method can be selected according to the machine tool. We choose manual tool setting.
(2) Determine various process parameters used in processing
The quality of the cutting conditions directly affects the efficiency and economy of the processing, which mainly depends on the experience of the programmer, the workpiece
The material and properties of the tool, the material and shape of the tool, the rigidity of the machine tool, the tool, the workpiece, the machining accuracy, the surface quality requirements, the cooling system, etc.
(3) Numerical calculation
According to the part drawing, according to the determined processing route and allowable program, the error is guaranteed, and the numerical control system needs to be calculated
Numerical value. Numerical calculation includes the coordinates of base point and node, and calculation of tool position point trajectory.
Due to the relatively large workload of the above calculations, it is now mainly done by computers. According to the part drawing and workpiece coordinate system, convex
The coordinates of each intersection point (X, Y) of the wheel profile are as follows.
(4) Write processing program
The program written below is for the TH5660A vertical machining center, the machine tool control system is FAGOR 8055M,
The feature of FAGOR 8055M is that it has advanced programming functions, which can easily set the tool value R (tool radius), L (tool radius)
Tool length), I (tool radius wear), K (tool length wear) are loaded by variables TOR, TOL, TOI, TOK, etc. at the beginning of the program.