Experimental study and numerical modelling of injection stretch blow moulding of angioplasty balloons

Angioplasty balloons are a class of medical device used to clear clogged arteries. They are manufactured via a process similar to that of injection stretch blow moulding. At present the forming of angioplasty balloons is something of a black art. When a new balloon is being developed, the process parameters and tube dimensions are determined through a mixture of trial and error and experience. The present paper describes the first phase in the development of a finite element simulation of the process which will ultimately be used to optimise the design and manufacture of these devices. A data acquisition system has been developed that measures the temperature and the tension/force in the tube during forming as well as the displacement applied to the tubing to initiate the forming process. Additionally a high speed video camera has been used to visualise the process. The balloon can be seen to form within 0·03 s with an average strain rate of 2000 s−1. Based on the data supplied from the data acquisition system a process simulation has been developed which replicates the formation of the balloon as seen on the high speed video camera. A series of biaxial tests of Nylon 12 in the temperature range between 60 and 120°C and strain rates between 1 and 32 s−1 show that the behaviour of the material is sensitive to temperature but is not dependent on strain rate. Further work is required in terms of the development of a suitable material model capable of capturing this behaviour.