CNC
Machining Center in the process of machining the workpiece, the selection of positioning reference is reasonable or not to determine the quality of the parts, can ensure the dimensional accuracy of the parts and mutual position accuracy requirements, as well as the processing sequence arrangement between the surfaces of the parts have a great impact, when the fixture installation of the workpiece, the selection of positioning reference will also affect the complexity of the fixture structure. This requires the fixture to withstand large cutting forces, but also to meet the positioning accuracy requirements. Therefore, the selection of positioning datum is a very important process problem. So when machining parts with CNC machining center, how do we choose the positioning benchmark? Here is a brief introduction:
1, the selected benchmark should be able to ensure that the positioning of the workpiece is accurate, the loading and unloading of the workpiece is convenient, the positioning and clamping of the workpiece can be quickly completed, the clamping is reliable, and the fixture structure is simple.
2, numerical control machining center selected the benchmark and each processing parts of the size of the calculation is simple, as far as possible to reduce the size chain calculation, to avoid or reduce calculation links and calculation errors.
3, ensure the processing accuracy. When specifically determining the positioning basis of the parts, the following principles should be followed:
1) The origin of the workpiece coordinate system, that is, "programming zero", does not necessarily coincide with the part positioning reference, but there must be a definite geometric relationship between the two. The selection of the origin of the workpiece coordinate system is mainly considered to facilitate programming and measurement. For the parts with high dimensional accuracy requirements, when determining the positioning datum, it should be considered whether the coordinate origin of the CNC machining center can be accurately measured by the positioning datum.
2) When machining the basis and completing the processing of each station on the CNC machining center, the selection of the positioning basis should consider completing as much processing content as possible. To this end, it is necessary to consider the positioning method that facilitates the processing of each surface, such as for the box, it is best to use a one-side two-pin positioning method in order to process the tool on other surfaces.
3) Try to choose the design benchmark on the part as the positioning benchmark. This requires that when roughing, consider what kind of rough benchmark to the surface of the fine benchmark machining out, that is, the various positioning benchmarks used in the CNC machining center should be processed in the front ordinary machine tools or other machine tools, so that it is easy to ensure the precision relationship between the machining surfaces of each station.
4) When the positioning datums of CNC machining center parts are difficult to coincide with the design datums, the assembly drawings should be carefully analyzed to determine the design function of the design datums of the parts, and the form and position tolerance range between the positioning datums and the design datums should be strictly stipulated through the calculation of the size chain to ensure the machining accuracy.
5) When the CNC machining center can not be completed at the same time, including the design base, the positioning base should be as far as possible to coincide with the design base. At the same time, it is also considered that after positioning with the reference, the processing of all key precision parts can be completed at one time.
