What are the guidelines for CNC precision parts machining? In the process standard design, the correct selection of positioning data has a crucial impact on ensuring the processing requirements of the part and the reasonable arrangement of the processing sequence.
Positioning datum is divided into fine datum and coarse datum: coarse datum takes the unmachined surface on the blank as the positioning datum. The fine datum takes the machined surface as the positioning datum.
I. Guidelines for selecting a fine reference
1. Baseline overlap criterion: The processed surface design data should be selected as accurately as possible to prevent positioning errors caused by data misalignment.
2. Consistent baseline guidelines: To ensure the relative positioning accuracy between the machined surfaces of the part, as many surfaces on the workpiece as possible should be machined using the same set of fine references.
3. Workpiece processing surface benchmark guidelines for each other: the repeated processing method of two processing surfaces can be used as a mutual reference.
4. Since the benchmark guidelines: some surface finishing process requires small and uniform processing tolerances, often processing the surface itself as the accuracy benchmark.
The above-mentioned four criteria for selecting the excellent benchmark is sometimes impossible to meet at the same time, must be decided according to the actual situation.
Second, the selection of rough benchmark guidelines
1. The first time the workpiece processing should use the coarse datum, coarse datum selection is correct, not only related to the first process of processing, but also has a great impact on the entire process of the workpiece.
2. The standard of reasonable distribution of machining tolerance: the machining allowance of the workpiece surface should be kept evenly, with the important surface as the rough datum.
3. Easy clamping standard: In order to make the workpiece positioning stable and clamping secure, the approximate reference point selected is required to be as smooth and clean as possible, without lightning strike, and the forging cut or other shortcomings are allowed to have a satisfying support area.
