Selection of machining center positioning datum:
There are three basic requirements for selecting benchmarks
(1) The selected datum should be able to ensure the accuracy of workpiece positioning, convenient and reliable loading and unloading.
(2) The calculation of the selected datum and the size of each processing part is simple.
(3) Ensure the machining accuracy.
6 principles for selecting positioning datum:
(1) Try to choose the design datum as the positioning datum;
(2) When the positioning datum and design datum cannot be unified, the positioning error should be strictly controlled to ensure the machining accuracy;
(3) When the workpiece needs to be clamped for more than two times, the selected datum can complete the machining of all key precision parts in one clamping and positioning;
(4) The selected benchmark should ensure the completion of as many processing contents as possible;
(5) In batch machining, the positioning datum of parts should coincide with the tool setting datum of workpiece coordinate system as far as possible;
(6) When multiple clamping is needed, the datum should be consistent.
Determination of machining center fixture:
Basic requirements for fixtures:
(1) The clamping mechanism shall not affect the feed, and the processing part shall be open;
(2) The fixture can be installed directionally on the machine tool;
(3) The rigidity and stability of the fixture are better.
Common fixture types:
(1) General fixture: such as vice, dividing head, chuck, etc;
(2) Modular fixture: modular fixture is composed of a set of general components with standardized structure and standardized size;
(3) Special fixture: fixture designed and manufactured for one or several similar processing items;
(4) Adjustable fixture: the combination of modular fixture and special fixture can ensure the machining accuracy and more flexible clamping;
(5) Multi position fixture: it can clamp multiple workpieces at the same time;
(6) Group Fixture: it is specially used for clamping workpieces with similar shape, size, positioning, clamping and processing methods.
Selection principle of machining center fixture:
(1) On the premise of ensuring machining accuracy and production efficiency, general fixture is preferred;
(2) Simple special fixture can be used for batch processing;
(3) Multi position fixture and high efficient special fixture for air pressure and hydraulic pressure can be considered for mass processing;
(4) When group process is used, group fixture should be used;
The best clamping position of the workpiece on the worktable of the machine tool: the clamping position of the workpiece should ensure that the workpiece is within the processing stroke range of each axis of the machine tool, and make the length of the tool as short as possible to improve the processing rigidity of the tool
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