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

In the process of machining work-pieces 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, as well as the processing sequence arrangement between the surfaces of the parts. When the work-piece 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 work piece, convenient loading and unloading of the work-piece, quickly complete the positioning and clamping of the work-piece, reliable clamping, and simple fixture structure.

2.The datum selected by the CNC machining center and the various dimensions of each processing part are simple to calculate, and the calculation of the dimension chain is minimized to avoid or reduce the calculation links and calculation errors.

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

1)The origin of the work-piece coordinate system, that is, the “programming zero point”, does not necessarily have to coincide with the part positioning datum, but there must be a definite geometric relationship between the two. The selection of the origin of the work-piece 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 work-piece 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 the machining of the stations including the design datum cannot be completed at the same time on the CNC machining center, the positioning datum and the design datum should be overlapped as much as possible. 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.

Want to know more about the process of the product? ANTISHI has a mature team of engineers who are very familiar with heat treatment processing and can handle product processing problems including packaging technical problems. In addition, during the installation and design process, our engineer team can be assigned to solve problems on the spot, to the greatest extent possible. Helping producers to carry out convenient and efficient production has always been the goal of our company. Customers can visit the official website, or send questions to our email: consult

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