Basic requirements for fixture design
(1) The fixture shall have sufficient strength and rigidity
(2) Clamping reliability
(3) Flexibility of welding operation
(4) Easy to load and unload the weldment
(5) Good processability
Basic Methods and Steps of Fixture Design
(1) Preparation before design
The original materials of fixture design include the following contents: fixture design task list; Workpiece drawings and technical conditions; Assembly process specification of workpiece; Technical conditions for fixture design; Standardized data of fixture and specification, including national standards, factory standards, standardized structure atlas, etc.
(2) Steps of design
Determine the fixture structure scheme; Drawing general drawing of fixture work stage; Drawing the part drawing of assembly welding fixture; Compile design instructions for assembly welding fixture; If necessary, it is also necessary to prepare the instruction manual for the assembly and welding fixture, including the performance of the machine, precautions for use, etc.
(3) Accuracy requirements for fixture manufacturing
The first type is directly in contact with the workpiece and strictly determines the position and shape of the workpiece, mainly including positioning elements such as joint locating pieces, V-shaped blocks, locating pins, etc. The second type is various guide elements, which can determine the position of the first type of elements although they do not directly contact with the positioning workpiece. The third category belongs to the fixture elements in which the internal structural parts of the fixture cooperate with each other, such as the fit dimension tolerance between the components of the clamping device. The fourth type does not affect the position of the workpiece, nor does it match with other components, such as the main framework of the fixture.
(4) Fixture structure manufacturability
Basic requirements for good workmanship of the fixture: ① As far as possible, various standard parts and general parts shall be used for the composition of the overall fixture structure, and the proportion of special parts for manufacturing shall be as small as possible, so as to reduce the amount of manufacturing labor and reduce costs. ② The structural shape of various special parts and components shall be easy to manufacture and measure, and easy to assemble and debug. ③ It is convenient for the maintenance and repair of clamps.
Reasonably select the assembly datum:
① The assembly datum should be an independent datum surface or line on the fixture, and the position of other components should only adjust and repair this surface or line.
② Once the assembly datum is processed, its position and size shall not be changed. Therefore, those surfaces or lines whose positions and dimensions need to be adjusted or repaired during the assembly process cannot be used as the assembly datum.
③ The adjustability of the structure often depends on the way of bolt fastening and pin position. When adjusting and assembling the fixture, it is convenient to repair the size of a certain element. The adjusting washer, adjusting washer or adjusting sleeve can also be set between the components to control the assembly size, compensate the error of other components and improve the accuracy of the fixture.
④ Maintenance technology, when designing the fixture, the problem of convenient maintenance should be considered.