CNC machining center machining process, the selection of the positioning datum is reasonable or not to determine the quality of the parts, whether to ensure the dimensional accuracy of the parts and mutual position accuracy requirements, as well as the processing sequence between the surfaces of the parts have a great impact on the arrangement, when the fixture to install the workpiece, the selection of the positioning datum will also affect the complexity of the fixture structure. This requires the fixture to be able to withstand large cutting forces, but also to meet the positioning accuracy requirements. Therefore, the choice of positioning datum is a very important process issue. So when machining parts with CNC machining center, how do we choose the positioning reference? The following is a brief introduction.
1, the selected benchmark should be able to ensure accurate positioning of the workpiece, easy loading and unloading workpiece, can quickly complete the positioning and clamping of the workpiece, clamping reliable, and fixture structure is simple.
2, CNC machining center selected benchmark and each processing part of each size operation simple, minimize the size chain calculation, avoid or reduce the calculation links and calculation errors.
3, to ensure that each processing accuracy. In the specific determination of the positioning datum of the part, the following principles should be followed.
The origin of the workpiece coordinate system, the "programming zero" and the part positioning reference do not have to coincide, but there must be a definite geometric relationship between the two. The choice of the origin of the workpiece coordinate system is mainly considered to facilitate programming and measurement. For each dimensional accuracy requirements of high parts, determine the positioning reference, should consider the CNC machining center coordinates of the origin can be accurately measured through the positioning reference.
When in the CNC machining center both processing benchmark and complete the processing of each station, the selection of its positioning benchmark need to consider the completion of as much processing content. To this end, consider the positioning method that facilitates each surface to be processed, such as for the box, it is best to use the positioning method of two pins on one side, so that the tool can be processed on other surfaces.
Try to choose the design reference on the part as a positioning reference. This requires rough machining, consider how the rough benchmark to the surface of the fine benchmark, that is, the CNC machining center on the use of each positioning benchmark should be in front of the ordinary machine tools or other machine tools to complete the processing, so that it is easy to ensure the accuracy of each station processing surface relationship between each other.
When the positioning datum of the CNC machining center parts and design datum is difficult to overlap, the assembly drawings should be carefully analyzed to determine the design function of the design datum of the part, through the calculation of the dimensional chain, strictly specify the positioning datum and the design datum between the form tolerance range to ensure processing accuracy.
When the CNC machining center can not be completed at the same time, including the design reference station processing, should try to make the positioning reference and design reference overlap. At the same time, we should also consider that after positioning with this datum, one clamping can complete the processing of all key precision parts.