When machining small and medium batches of precision parts, the combined fixture can be used for clamping. Modular fixture has the characteristics of disassembly and reassembly, so modular fixture is a special fixture system that can be reused. However, there are many connections between the various components of the modular fixture, and the stiffness and accuracy of the fixture are not as good as other fixtures. Generally, when using modular fixtures, the machining dimensional accuracy can only reach the IT8-IT9 level. Secondly, the use of modular fixtures requires a large investment for the first time, which is bulky and inconvenient to remove chips.
At present, the commonly used modular fixture systems include slot modular fixture systems and hole modular fixture systems.
- Groove combination fixture: Groove combination fixture refers to components made of T-shaped grooves or keyways with standard spacing parallel and vertical. Through the positioning of the key in the keyway, the exact position of each component in the fixing device can be accurately determined, and these components are connected or tightened by threads. Since the mutual position of the various components of the slot combination fixing device can be determined by the key that can slide along the slot or the position of the key in the slot, it has good adjustability.
- Hole combination fixture: precision parts processing hole combination fixture means that the mutual position of the fixture components is determined by the hole and the positioning pin, and the connection between the components is still fastened by screw connections. Compared with the slot combination fixture, the hole system combination fixture has the advantages of good rigidity, low manufacturing cost, short assembly time and reliable positioning. The disadvantage is that the flexibility of assembly is poor, and the position of the components on the fixed part is not convenient for stepless adjustment.
When large quantities of precision parts are processed, special fixtures or group fixtures are usually used for clamping, but because the machining center is more suitable for single-piece and small-batch workpiece processing. Therefore, there are not many applications of this fixture on CNC machine tools.
In short, according to the accuracy of the part, the structural characteristics of the part, the batch of the product and the accuracy of the machine tool, comprehensive consideration should be given to the selection of the fixture of the part on the machining center. The order of selection is: first consider general fixtures, second, consider modular fixtures, it is best to consider special fixtures and group fixtures.