How To Select Positioning Reference When Machining Parts?

During the machining process of the CNC machining center, whether the selection of the positioning reference is reasonable determines the quality of the parts, which has a great influence on whether the dimensional accuracy and mutual position accuracy of the parts can be guaranteed, and the processing sequence arrangement between the surfaces of the parts.

When the fixture is used to install the workpiece, the selection of positioning reference will also affect the complexity of the fixture structure. This requires that the fixture can not only withstand large cutting forces, but also meet the positioning accuracy requirements.

Therefore, the selection of positioning reference is a very important technological issue. Then how do we select the positioning reference? Here is a brief introduction:

1. The selected reference should ensure accurate positioning of the workpiece, convenient loading and unloading of the workpiece, can quickly complete the positioning and clamping of the workpiece, and the fixture structure is simple.

2. The referenceselected by the CNC machining center and the calculation of each size of each processing part are simple, minimize the calculation of the size chain, and avoid or reduce the calculation links and calculation errors.

3. Ensure the accuracy of various processing. When specifically determining the positioning reference of the parts, the following principles should be followed:

A. The origin of the workpiece coordinate system, that is, the “programming zero point” and the positioning reference of the part do not have to coincide, but there must be a certain geometric relationship between them.The selection of the origin of the workpiece coordinate system is mainly for ease of programming and measurement. For parts requiring high dimensional accuracy, when determining the positioning reference, it should be considered whether the origin of the coordinates of the CNC machining center can be accurately measured by the positioning reference.

B. When both the processing reference and the processing of each station are completed on the CNC machining center, the selection of the positioning reference needs to consider completing as much processing content as possible. For this reason, it is necessary to consider the positioning method that facilitates the processing of each surface. For example, for the box, it is best to use the positioning method of one side and two cuts, so that the tool can process other surfaces.

C. Try to choose the design referenceon the part as the positioning reference. This requires that when roughing, what kind of rough reference should be used to process each surface of the fine reference, so that it is easy to ensure the accuracy relationship between the surfaces processed by each station.

D. When the positioning reference and design referenceof the CNC machining center parts are difficult to coincide, the assembly drawings should be carefully analyzed to determine the design function of the design reference of the part. Through the calculation of the dimensional chain, the geometric tolerance range between the positioning reference and the design reference is strictly specified to ensure processing accuracy.

E. When it is impossible to complete the position processing including design reference at the same time on the CNC machining center, try to make the positioning reference coincide with the design reference. At the same time, it is also necessary to consider that after positioning with this reference, all key precision areas can be processed in one clamping.