1. There are 6 principles for selecting the positioning datum:
(1) Try to choose the design datum as the positioning datum;
(2) When the positioning datum and the design datum cannot be unified, the positioning error should be strictly controlled to ensure the machining accuracy;
(3) The workpiece needs to be clamped more than twice During processing, the selected datum can complete the processing of all key precision parts in one clamping and positioning;
(4) The selected datum should ensure that as many processing contents as possible can be completed;
(5) During batch processing, the part positioning datum should be as close as possible to the established one. The tool setting benchmarks of the workpiece coordinate system are coincident;
(6) When multiple clampings are required, the benchmarks should be unified before and after.
2. There are three basic requirements for selecting a datum:
(1) The selection of a datum should ensure accurate positioning of the workpiece, convenient, convenient and reliable loading and unloading.
(2) The selection criteria and the dimension calculation of each machining part are simple.
(3) Ensure machining accuracy.
Determination of the fixture of the machining center:
1. The basic requirements for the fixture:
(1) The clamping mechanism should not affect the feed, and the processing part should be open;
(2) The fixture can be installed in a direction on the machine tool;
(3) The rigidity and stability of the fixture should be good.
2. Common fixture types:
(1) General fixture: such as vice, indexing head, chuck, etc.;
(2) Combination fixture: Combination fixture is composed of a set of general component combination components whose structure has been standardized and dimensions have been standardized;
(3) Special fixture: a fixture designed and manufactured for a certain or similar processing;
(4) Adjustable fixture: the combination of a combination fixture and a special fixture can not only ensure the machining accuracy, but also provide more flexibility in clamping;
(5) Multi-station fixture: a fixture that can clamp multiple workpieces at the same time;
(6) Group fixture: It is specially used for the clamping of workpieces with similar shapes, similar dimensions, and the same or similar positioning, clamping, and processing methods.
3. Selection principles of fixtures for machining centers:
(1) Under the premise of ensuring machining accuracy and production efficiency, general fixtures are preferred;
(2) Simple special fixtures can be considered for batch processing;
(3) Multi-station can be considered for large-scale processing Fixtures and high-efficiency air pressure, hydraulic and other special fixtures; (4) Group fixtures should be used when group technology is used;
4. The best clamping position of the workpiece on the machine tool table:
The workpiece clamping position should ensure that the workpiece is within the processing stroke range of each axis of the machine tool, and the length of the tool should be shortened as much as possible to improve the machining rigidity of the tool.