Fixture Types and Selection for CNC Milling Processing

1. The basic requirements of CNC milling for fixtures

In CNC milling machining generally does not require very complex fixtures, only requires simple positioning and clamping on it, its numerical control milling design principle is the same as the general milling machine fixture, combined with the characteristics of CNC milling machining, here put forward some basic requirements:

1.1 In order to ensure that all the unfinished surfaces of the workpiece in this process are fully exposed, the fixture should be as open as possible, because the clamping mechanism components and the processing surface should maintain a certain safe distance, while the clamping mechanism components should be as low as possible, to prevent the fixture and milling machine spindle sleeve or knife sleeve, blade interference in the processing process.

1.2 In order to maintain the consistency of the installation orientation of the part with the direction of the machine coordinate system and the programming coordinate system, the fixture should ensure directional installation on the machine, and also require the coordination of the coordinates between the part positioning surface and the machine to maintain a certain coordinate relationship.

1.3 The rigidity and stability of the fixture must be good. CNC milling machining fixture as far as possible do not use in the processing process to replace the clamping point design, when not to change the clamping point in the processing process, pay special attention to not replace the clamping point due to the replacement of the damage to the positioning accuracy of the fixture or workpiece.

2. Types of CNC milling machining commonly used fixture

2.1 Universal combination fixture. Suitable for small and medium-sized workpieces in small batch production or development in CNC milling.

2.2 Special milling fixtures. This is a fixture specially designed for one or several similar workpieces, generally used in large annual production or development. Its structure is fixed and used only in the specific process of a specific part, such fixture design should strive to simplify so that the manufacturing time is as short as possible.

2.3 Multi-station fixture. This tool can clamp multiple workpieces at the same time, which can reduce the number of tool changes. This processing method is convenient for one-side processing and one-side loading and unloading of workpieces, which is beneficial to shorten the auxiliary time and improve productivity and is more suitable for medium-batch production.

2.4 Pneumatic or hydraulic fixtures. Suitable for the production of larger batch occasions, it needs to spend more time and labor because of using other fixtures, can reduce the labor intensity of workers and improve CNC milling machining productivity, but such fixture structure is more complex, the cost is often high, and the manufacturing cycle is longer.

2.5 Universal milling fixture. There are universal adjustable fixtures, tiger pliers, scale head and three-claw chuck, etc.

3. Selection principle of CNC milling machining fixture

In the selection of CNC milling machining fixtures, it is usually necessary to consider the production volume, productivity, quality assurance, and economy of the product, the selection can refer to the following principles:

3.1 In the production of small or developed, should be widely used universal combination fixture, only the combination fixture can not solve the problem then using other fixtures.

3.2 For small batch or mass production, you can use special fixtures, but they should be as simple as possible.

3.3 In the large production volume, you can use multi-position fixtures and pneumatic, hydraulic fixtures.