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As a flexible manufacturing technique, Multi-point stretch forming (MPSF) is a suitable method for forming aircraft outer skin part. The traditional solid stretching die is replaced by the discrete multi-point die (MPSD), and the sheet metal is stretch-formed over the MPSD generated by serial adjusting mode or parallel adjusting mode. The MPSF can be used to form the parts of different shape and reduce the cost and leading time of stretching die fabrication for aircraft outer skin part. A series of numerical simulations on typical MPSF processes of aircraft outer skin part were carried out. The thickness of elastic cushion and free length are important factors to influence on the stretch forming results of stretch-formed parts. The numerical simulation results show that the thicker the elastic cushion is, the more valid the dimple will be suppressed .The longer the free length is, the easier the wrinkle will be brought.

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In this paper, the basic theory of multi-point stretching process was introduced, the process of multi-point stretching of saddle part was simulated, the generation and suppression of dimples were studied [1~3]. The results showed that dimple is specific defect in the multi-point stretching process; the dimples can be suppressed effectively by elastic cushion technology. Thicker elastic cushion is more effective to suppress dimples, but the error between formed workpiece and objective shape will get large. By adopting elastic cushion with appropriate thickness, workpiece with smooth surface can be obtained and the forming error is small.