CNC machining center machining workpiece

How to choose the positioning datum in the process of machining parts in the machining center

In the process of machining workpieces in CNC machining centers, whether the selection of the positioning datum is reasonable or not determines the quality of the parts, whether the dimensional accuracy and mutual position accuracy of the parts can be guaranteed, and the arrangement of the processing sequence between the surfaces of the parts. When the workpiece is installed with a fixture, the selection of the positioning datum will also affect the complexity of the fixture structure. This requires the fixture to not only withstand large cutting forces, but also meet the positioning accuracy requirements. Therefore, the choice of positioning datum is a very important process issue. So how do we choose the positioning datum when machining parts with CNC machining centers? Here’s a brief introduction:

1. The selected datum should be able to ensure accurate positioning of the workpiece, convenient loading and unloading of the workpiece, rapid positioning and clamping of the workpiece, reliable clamping, and simple fixture structure.

2. The datum selected by the CNC machining center and each dimension of each processing part are simple to calculate, minimize the calculation of the dimension chain, and avoid or reduce the calculation link and calculation error.

3. Ensure the machining accuracy. When determining the positioning datum of the part, the following principles should be followed:

1) The origin of the workpiece coordinate system, that is, the “programming zero point” and the part positioning datum need not necessarily coincide, but there must be a definite geometric relationship between the two. The selection of the origin of the workpiece coordinate system mainly considers the convenience of programming and measurement. For parts with high dimensional accuracy requirements, when determining the positioning datum, it should be considered whether the origin of the coordinates of the CNC machining center can be accurately measured through the positioning datum.

2) When both the datum and the processing of each station are processed on the CNC machining center, the selection of the positioning datum needs to consider the completion of as many processing contents as possible. To this end, it is necessary to consider the positioning method that is convenient for all surfaces to be processed. For example, for the box, it is best to use the positioning method of two pins on one side, so that the tool can process other surfaces.

3) Try to select the design datum on the part as the positioning datum. This requires that during rough machining, consider what kind of rough datum is used to process all sides of the fine datum, that is, each positioning datum used in the CNC machining center should be processed in the previous ordinary machine tool or other machine tools, so that it is easy to ensure that each workpiece is processed. The precision relationship between the machined surfaces.

4) When the positioning datum and design datum of CNC machining center parts are difficult to coincide, the assembly drawings should be carefully analyzed to determine the design function of the part’s design datum, and the geometric tolerance between the positioning datum and the design datum should be strictly specified through the calculation of the dimension chain. range to ensure machining accuracy.

5) When it is not possible to complete the station processing including the design datum on the CNC machining center at the same time, try to make the positioning datum coincide with the design datum. At the same time, it should also be considered that after using the reference positioning, the processing of all key precision parts can be completed in one clamping.