Electrohydraulic Crimping of Tubes within Rings

Abstract

Crimping processes are commonly used in industry to join two tubular parts together. In the case of positive clearance crimping, one of the two parts must be plastically deformed to fill the initial clearance and block elastic deformations in the second one. The strength of the assembly will then depends on the residual contact pressure established at the interface. Quasi-static processes are the most commonly used to perform these operations, but over the past two decades, there has been a growing interest in the use of dynamic crimping by magnetic pulse. Processes that generate high-strain rate allow to reduce the springback, which is of great interest for crimping. However, its use is limited if the part to be deformed is made of a poor electrical conductor material or if its dimensions are too small. This paper presents an alternative for dynamically crimping tubes within rings using electrohydraulic process. An experimental equipment has been designed to guide and amplify pressure waves to the area to be deformed. Two amplifiers called acoustic and mechanical pulse shapers (APS and MPS) have been tested and allow to reach hoop strain rate at about 1000 and 100 s−1 respectively. An analytical model was also built allowing to define the stored energy and the inter-electrodes distance to maximize the pressure. Results of push-out tests are also presented and demonstrate the ability of the electrohydraulic crimping process coupled with the MPS to crimp small 316L tubes into rings made of the same material, but achieving crimping successfully with the APS still require further work.

Keywords

• electrohydraulic crimping
• waves propagation
• acoustic and mechanical pulse shapers
• positive initial clearance
• three-stage crimping equipment