Study Of Combined Fixture For Micro Parts Assembly Of Micro Parts With High-performances

Because of advantages of small volume, low energy consumption and reliable performance, precise and miniature electromechanical products, this kind of products are not always manufactured for one time, but always are combined by miniature parts. Assembly is an important link in the manufacturing of this kind of products. The precision automatic assembly system for micro parts is widely used in the variety of fields. The importance of fixturing is often underestimated in the development of precision assembly system for miniature products. Emphasis is usually laid on high accuracy sensing, measurement and positioning techniques. In practice, the detail in fixture design, which tends to be ignored, frequently determines the success or failure of the assembly quality and the device performance.The precision assembling fixture used in the precision automatic assembly system was designed to assist the automatic assembly of micro parts in the paper. Small parts, after mounted in place, are easily to be influenced by disturbance while being fastened or locked. Small screws with tipped end are often used in fastening miniature parts, but one screw has only one contacted point and the rotational movement of the tip disturbs the part. A fixture with flexible fastening mechanism was designed for assembly of a set of miniature parts, as shown. The characteristic of the flexible alignment fastening structure is that it will convert the rotational moment of the fastening bolt into the linear fastening force of the flexible part. There are two contacting points on the flexible part, which reduce effectively the disturbance of parts and improve the assembly accuracy. The FEA was used for stress analysis and the fastening force of the flexible part.The assembly sequence and strategy decide the base plane and parts’fastening mode employed in the assembly procedure. The fact that the base plane and parts’fastening mode affect the quality of the assembled devices is often ignored. To a great extent, the deterioration of quality is due to the micro stress generated in the sensitive part of the device during assembly procedure. The stress worsens the stability and other performance of the device. The causes of stress generation were analyzed in this paper as well as the assembly sequence and strategy was optimized. With different assembly sequences and parts’fastening modes, the causes were analyzed and explained, including machining error of the parts, adhesive hardening, and different temperature coefficients of the parts made of different materials. The results showed that the stress of critical part was reduced about30%under the same assembly condition. At last, the assembling fixture was designed according to the improved assembly strategy.