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Basic Methods and Steps of Jig and Fixture Design

Ⅰ. Preparation before the jig and fixture design

The original materials for jig and fixture design include the following:

(1) The task list for jig and fixture design;

(2) Workpiece drawings and technical conditions;

(3) Assembly process regulations of the workpiece;

(4) Technical conditions for assembly jig and fixture design;

(5) Standardization data and specifications of fixtures, including national standards, factory standards and photo album for standardized structure, etc.

Ⅱ. The steps of jig and fixture design

(1) Determine the structure plan;

(2) Finish the general drawing about how the fixtures work;

(3) Finish the parts drawing for assembly and welding fixtures;

(4) Compile the design instruction of assembly and welding fixtures;

(5) If necessary, an operation instruction for the assembly and welding fixtures should be written, including the performance of the machines and tools and the precautions for use.

Ⅲ. The precision requirements for the jig design and manufacture

The first type is to directly contact the workpiece and strictly determine the position and shape of the workpiece, mainly including the positioning parts of the joint, the V-shaped block, the positioning pin and other positioning elements.

The second type is a variety of guides, although this type of component does not directly contact the positioning workpiece, but it can determine the position of the first type of component.

The third type belongs to the fixture components, for which the internal structural parts are matched with each other in jig and fixture design, such as the fit dimensional tolerances between the components of the clamping equipment.

The fourth type does not affect the position of the workpiece, nor does it cooperate with other components, such as the main frame of the fixture.

Ⅳ. The manufacturability of structure in the jig and fixture design

1. Basic requirements for good manufacturability of fixtures:

(1) For the composition of the overall fixture structure, various standard parts and general parts should be used as much as possible, and the proportion of special milling small parts should be as small as possible to reduce the amount of manufacturing labor and reduce costs.

(2) The structure and shape of various special parts and components should be easy to manufacture and measure, and convenient to assemble and debug.

(3) It should be convenient to maintain and repair the fixture.

2. Reasonable selection of assembly datum from the cnc parts supplier:

(1) The assembly datum should be an independent datum surface or line on the fixture, and the positions of other components can only be adjusted and repaired on this surface or line.

(2) Once the assembly datum is processed, its position and size should not be changed. Therefore, those surfaces or lines whose position and size need to be adjusted or repaired during the assembly process cannot be used as the assembly datum.

(3) The adjustability of structure in the jig and fixture design is often achieved by means of bolt fastening and pin positioning. When adjusting and assembling the fixture, it is convenient to grind a certain component size. It is also possible to use adjusting washers, adjusting shim or adjusting sleeves between components and parts to control the assembly size, compensate for the errors of other components, and improve the accuracy of the fixture.

(4) The manufacturability of maintenance. The convenience of maintenance should be taken into consideration when designing fixtures.

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