Characteristics of fixtures for large CNC machining centers
The precise positioning accuracy controlled by the program on large CNC machining centers can achieve the tool guiding function in fixtures. Therefore, fixtures in CNC machining generally do not require guiding and tool setting functions, but only need to have positioning and clamping functions to meet usage requirements, thus simplifying the structure of the fixture. Traditional special-purpose fixtures have four functions: positioning, clamping, guiding, and tool setting. However, CNC machines are usually equipped with devices such as contact probing heads, tool pre-setting instruments, and tool setting components, which can solve the tool setting problem.
CNC machining is suitable for multi-variety, medium and small batch production. To be able to clamp different sizes and shapes of multi-variety workpieces, CNC machining fixtures should have flexibility and can hold various shapes and sizes of workpieces after appropriate adjustments. As machine tool fixtures, they must first meet the clamping requirements during mechanical processing. At the same time, fixtures for large CNC machining also have their own characteristics. These characteristics include:
a) For workpieces with low stiffness, the minimum clamping deformation should be ensured. For example, the clamping point should be close to the support point, avoiding applying clamping force on the hollow area of the workpiece, etc. When roughing and finishing are completed within the same process, if the above measures cannot control the workpiece deformation within the range required by machining accuracy, the program should be paused before finishing, allowing the operator to change the clamping force (appropriately reduce it) between roughing and finishing, thereby reducing the impact of clamping deformation on machining accuracy.
b) To adapt to the high efficiency of CNC machining, CNC machining fixtures should use pneumatic, hydraulic, electric, or other automatic clamping devices as much as possible to achieve quick clamping and shorten auxiliary time.
c) To adapt to multi-aspect CNC machining, interference between the fixture structure (including components on the fixture) and the tool motion trajectory should be avoided, and the fixture structure should not hinder multi-surface machining of all parts of the workpiece by the tool.
d) The fixture itself should have sufficient rigidity to adapt to high cutting volume machining. CNC machining has the characteristic of concentrated processes, where both heavy roughing with large cutting forces and finishing that meets the final accuracy requirements of the workpiece need to be performed in one clamping operation. Therefore, the rigidity of the fixture and the clamping force must meet the requirements of high cutting forces.
e) The positioning of the fixture should be reliable, the positioning elements should have high positioning accuracy, and the positioning areas should be easy to clean chips without chip accumulation. If the workpiece's positioning surface is too small, consider adding a process boss or auxiliary datum.
Dongguan Wanjun Large CNC Machining Center (http://www.dgwanjun.com) specializes in providing large CNC machining, large computerized milling machining, China material recycling network, large aluminum plate machining, large precision part machining, machinery equipment panel machining, precision sand casting, and large mold machining.