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1. Installation of parts and selection of fixtures
(1) Basic principles of positioning and installation
1) The benchmarks for design, process and programming calculations should be uniform
2) Reduce the number of clamping times, and process all the surfaces to be processed after one positioning and clamping
3) Avoid using the manual adjustment processing scheme
(2) Basic principles for selecting fixtures
The characteristics of CNC machining put forward two basic requirements for the fixture: one is to ensure that the coordinate direction of the fixture is relatively fixed with the coordinate direction of the machine tool; the other is to coordinate the dimensional relationship between the part and the machine coordinate system. In addition to this, consider the following four points:
1) When the part processing batch is not large, the combination fixture, adjustable fixture and other common fixtures should be used as much as possible to shorten the production preparation time and save production costs.
2) Consider special fixtures in batch production and strive for simple structure
3) The loading and unloading of parts should be fast, convenient and reliable.
4) The components on the fixture shall not interfere with the machining of the surface of the workpiece by the machine tool, that is, the fixture shall be opened for positioning, and the components of the clamping mechanism shall not affect the machining in the machining (such as collision).
When programming, the position of the "tool point" and "tool change point" should be correctly selected. The “tool point” is the starting point of the tool relative to the workpiece when machining the part on the CNC machine. Since the block is executed from this point, the tool point is also called "program start point" or "start point".
The selection principle for the tool point is:
1. Facilitate digital processing and streamline programming;
2. It is easy to find on the machine tool, and it is easy to check during processing;
3. The resulting machining error is small.
For CNC miling Parts with point control, only the positioning accuracy is high, the positioning process is as fast as possible, and the movement path of the tool relative to the workpiece is irrelevant. Therefore, such machine tools should arrange the route according to the shortest flight time. In addition to this, the axial movement of the tool is determined. The size of the tool is mainly determined by the hole depth of the part to be machined, but some auxiliary dimensions should also be considered.