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In a broad sense, any device used to quickly, conveniently, and safely install workpieces in any process can be referred to as a fixture.
In a broad sense, any device used to quickly, conveniently, and safely install workpieces in any process can be referred to as a fixture. A device used in mechanical manufacturing to fix objects in the correct position for construction or testing. In order to ensure that the surface of the workpiece can meet the technical requirements of dimensions, geometric shapes, and positional accuracy with other surfaces specified in the drawings on the machine tool. Fixtures are usually composed of positioning components, clamping devices, tool guide components, indexing devices, connecting components, and clamp specific components. Below is a brief explanation of the selection method for CNC fixtures:
(1) CNC is capable of clamping multiple types of workpieces of different scales and shapes. The fixture used for CNC machining should be flexible and can hold workpieces of various shapes and sizes through appropriate adjustment.
(2) Traditional specialized fixtures have four functions: positioning, clamping, guiding, and tool setting, while CNC machine tools are usually equipped with touch test heads, tool presetters, and tool setting components, which can be processed by the machine tool for tool setting. The correct positioning accuracy controlled by CNC machine tools can complete the tool guidance function in the fixture. Therefore, CNC fixtures usually do not require guidance and tool setting functions, but only require positioning and clamping functions to meet the application requirements, which can simplify the layout of the fixture.
(3) To get used to the high efficiency of CNC machining, CNC machining fixtures should use active clamping equipment such as pneumatic, hydraulic, and electric to quickly clamp, in order to shorten the auxiliary time.
(4) The fixture itself should have satisfactory stiffness to adapt to large cutting amounts. CNC machining has the characteristic of process convergence. In the clamping process of the workpiece, both coarse processes with high cutting force and precision processes that meet the accuracy requirements of the workpiece end need to be carried out. Therefore, the stiffness and clamping force of the fixture must meet the requirements of high cutting force.
(5) The CNC milling machine model is used for CNC machining in multiple aspects. To prevent the interference of the components on the fixture with the tool movement track, the fixture layout should not hinder the tool from affecting various parts of the workpiece.
(6) The positioning of the fixture should be reliable, the positioning components should have high positioning accuracy, and the positioning position should be easy to clean chips without chip accumulation. If the positioning surface of the workpiece is too small, it can be considered to add technical bosses or auxiliary benchmarks.
(7) CNC milling machine models should ensure minimal clamping deformation for workpieces with low stiffness, such as making the clamping point close to the support point, and preventing the clamping force from being applied to the hollow area of the workpiece. If the above methods cannot control the deformation of the workpiece within the range of accuracy requirements, the program should be paused before finishing to reduce the impact of clamping deformation on accuracy.
