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From Basic Machining To Proficiency, The Fixture Requirements Of Typical CNC Machine Tools

May 28, 2020

The CNC machine tool fixture should be conducive to the concentration of the machining process, that is, the workpiece can be processed on multiple surfaces after one clamping, so as to reduce the number of workpiece clamping.


The clamping of the CNC machine tool fixture should be firm and reliable, and the operation is convenient; the position of the clamping element should be fixed and unchanged to prevent the element from touching the tool during the automatic processing.


Each CNC machine tool has its own coordinate system and coordinate origin, which is one of the important basis for programming.


1. Basic requirements of CNC milling machine fixtures

Prevent tool from colliding with fixture components


1. In order to maintain the consistency of the installation orientation of the parts and the direction of the machine tool coordinate system and the programming coordinate system, the fixture should be able to ensure the directional installation on the machine tool, and it is also necessary to coordinate the coordinate positioning between the part positioning surface and the machine tool.


2. In order to keep the workpiece to be fully exposed in the process, the fixture should be opened as much as possible, so a certain safety distance should be maintained between the clamping mechanism components and the processing surface, and clamping is required The mechanism components can be as low as possible, thereby preventing the collision between the fixture and the milling machine spindle sleeve or tool sleeve and tool during the machining process.


3. The rigidity and stability of the fixture are better.


Second, the types of commonly used CNC milling machine fixtures


1. Combined fixture: It is suitable for milling of small and medium-sized workpieces in small batch production or development on a CNC milling machine.


2. Special milling fixture: It is a fixture specially designed and manufactured for a certain item or similar items. It is generally used when mass production or development is necessary.


3. Multi-station fixture: it can clamp multiple workpieces at the same time, which can reduce the number of tool changes, and it is also convenient to process and load and unload the workpieces at the same time.


4. Pneumatic or hydraulic fixture:

5. Vacuum fixture: suitable for workpieces with large positioning planes or large sealable areas.


Three, CNC drilling machine fixture


The CNC drilling machine is a numerically controlled hole processing machine tool mainly for drilling. In the development process of CNC machine tools, the emergence of CNC drilling machines is early, and the design principle of its fixture is the same as that of general-purpose drilling machines. Combined with the characteristics of CNC drilling, the following issues should be noted in the selection of fixtures:


1. Preference is given to combined fixtures.


2. Under the condition of ensuring the machining accuracy of the parts and the rigidity of the fixture, try to reduce the clamping deformation and select a reasonable positioning point and clamping point.


3. For small and medium-sized parts with short working hours, the loading and unloading clamping time should be reduced as much as possible. Various air pressure, hydraulic clamps and fast linkage clamping methods are used to improve production efficiency.


4. Machine Center Fixture


The machining center machine tool is a CNC machine tool with more complete functions. In the machining center, the task of the fixture is not only to clamp the workpiece, but also to determine the zero point of the workpiece programming with the positioning surfaces in all directions as the reference datum. The parts processed on the machining center are generally more complicated. In one clamping, the parts require rough milling, rough boring, fine milling, and fine boring. A variety of tools are required, which requires the fixture to withstand large The cutting force must meet the positioning accuracy requirements. The automatic tool change (ATC) function of the machining center also determines that fixture components such as brackets, position detection and tool setting cannot be used during machining. The high flexibility of the machining center requires that its fixture is more compact and simpler than the ordinary machine tool, and the clamping action is quick and accurate. The auxiliary time is reduced as much as possible. The operation is convenient, labor-saving and safe, and it must be sufficiently rigid and flexible. According to the machine tool characteristics and processing needs of the machining center, the commonly used fixture structure types include special fixtures, combination fixtures, adjustable fixtures and group fixtures.