The main contents of NC grinding machine programming include: part drawing analysis, process processing, mathematical processing, programming, control medium preparation, program verification and trial cutting. The specific steps and requirements are as follows:
1. Part drawing analysis
After getting the part drawings, first analyze the NC processing technology, determine a reasonable processing scheme according to the material, blank type, shape, size, precision, surface quality and heat treatment requirements of the parts, and select the appropriate NC machine tool.
2. Process treatment
The process treatment involves many contents, mainly including the following:
(1) The determination of processing method and process route shall be based on the principle of giving full play to the functions of CNC machine tools, and the reasonable processing method and process route shall be determined.
(2) The design of tools and fixtures and the selection of NC machining tools shall comprehensively consider the processing method, cutting parameters, workpiece materials and other factors to meet the requirements of convenient adjustment, good rigidity, high accuracy, and good durability. When designing and selecting the NC machining fixture, it shall be able to quickly complete the positioning and clamping process of the workpiece to reduce the auxiliary time. And try to use modular fixture to shorten the production preparation cycle. In addition, the fixture used shall be easy to install on the machine tool to coordinate the dimensional relationship between the workpiece and the coordinate system of the machine tool.
(3) The selection of tool setting point is the starting point of program execution. The selection shall be based on the principles of simplifying programming, easy alignment, easy inspection during processing, and reducing processing error.
The tool setting point can be set on the workpiece to be processed, or on the fixture or machine tool. In order to improve the machining accuracy of parts, the tool setting point should be set on the design basis or process basis of parts as far as possible.
(4) The determination of the processing route The requirements for the precision and surface roughness of the parts to be processed shall be guaranteed when the processing route is determined; Shorten the tool path as much as possible and reduce the empty tool travel; It is beneficial to simplify numerical calculation, reduce the number of program segments and programming workload.
(5) The determination of cutting parameters includes cutting depth, spindle speed and feed speed. The specific value of cutting parameters shall be comprehensively considered according to the provisions of the NC machine tool instruction manual, the material of the workpiece to be processed, the processing content and other process requirements, and in combination with empirical data.
The detailed content and analysis process of process treatment will be further described in Section 2.3.
3. Mathematical processing
Mathematic processing is to calculate the input data required for NC machining according to the geometric dimensions of the part and the determined processing route. General CNC systems have linear interpolation, circular interpolation and tool compensation functions. Therefore, for a simple two-dimensional contour part composed of straight lines and arcs, it is only necessary to calculate the coordinates of the intersection or tangent point (called the base point) of adjacent geometric elements on the part contour. When the geometric shape of a more complex part or part is inconsistent with the interpolation function of the CNC system, a more complex numerical calculation is required. For example, for a non-circular curve, it is necessary to use a straight line segment or an arc segment for approximation. Under the condition of meeting the accuracy, the coordinates of the intersection point or tangent point (called the node) of adjacent approximation line segments or arcs can be calculated. For the programming of free curves, free surfaces and composite surfaces, their mathematical processing is more complex. Generally, they need to be fitted and approximated by automatic programming software to obtain the coordinates of straight lines or arcs.
After the completion of process and mathematical processing, the part processing program shall be compiled section by section according to the instructions and program segment format of the NC system of the machine tool used. Before programming, programmers should understand the performance, functions and program instructions of CNC machine tools, so as to write correct CNC machining programs.
5. Preparation of control medium
After the programming, the control medium shall be made as the carrier of the input information of the NC system. At present, it mainly includes disk, U disk, mobile hard disk, etc. Perforated paper tape and magnetic tape used in the early stage have been basically eliminated. The NC processing program can also be manually input to the memory directly through the CNC system operation keyboard, or through RS232C, DNC interfaces.
6. Program verification and test cutting
NC training and processing program can be used for formal processing only after verification and trial cutting. The correctness of the machine tool motion track and action can be checked by means of idling cutter, idling drawing, etc. It is more convenient to use the method of graphic simulation tool cutting workpiece on CNC machine tools with graphic display function and dynamic simulation function or in CAD/CAM software. But these methods can only check whether the motion track is correct, and can not check the machining accuracy of the machined parts. Therefore, trial cutting of parts is generally required before formal machining. When machining errors are found, the causes of errors shall be analyzed and timely measures shall be taken to correct them.