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Development of Foundry Casting Methods for Cost-Effective Manufacture of Medical Implants

Final Report Summary - MEDCAST (Development of Foundry Casting Methods for Cost-Effective Manufacture of Medical Implants)

Orthopaedic implants designed to withstand high mechanical stress, such as knees and shoulders, require the use of metals with high strength. The most commonly used manufacturing method used is investment casting. Improvements in investment casting can therefore enable significant cost reductions and improved reliability when manufacturing complex orthopaedic components. MEDCAST focuses on the improvement of manufacturing processes for investment casting that will result in reduced production costs. This will make implants more affordable and therefore more available to European citizens. Moreover, a reduction of production costs will make the investment casting industry in Europe more competitive worldwide. MEDCAST’s goals will be achieved by gaining a better understanding of most of the processes involved in investment casting, which will enable a reduction of cycle time, increases in quality and yield with a minimisation of human intervention and waste. The objectives of this project are to optimise the investment casting process currently used in DePuy to improve cycle times and resource (materials, energy and water) usage. This will be achieved by researching all the steps involved in investment casting, including the pattern manufacture, casting and shell technology, finishing methods and process modelling and automation. This project aims to advance the state of art in investment casting processes for medical devices by intersectoral cooperation between DePuy Ireland, the University of Birmingham and the University of Limerick to develop the concept of the “Foundry of the Future”. The partners have complementary skills and facilities. University of Birmingham (UoB) Mechanical Engineering Department is a leading Centre of Expertise in casting processes. DePuy (Ireland) is part of the DePuy Corporation, a $4.5 billion global entity in medical orthopaedic implants. DePuy employs 6000 people worldwide of which some 900 are employed in DePuy (Ireland). It is a company of Johnson and Johnson. New innovative concepts developed in UoB and UL’s laboratories can be tested under scaled up and automated conditions in DePuy Ireland’s medical device foundry. The University of Limerick has focused on the development of casting models to predict residual stress. The MSSI, within the University of Limerick (UL), contains sate-of-the-art technologies for mechanical testing which are essential for the successful evaluation of the process improvements carried out during the MEDCAST program. The project is estimated to take 48 months to complete and is based exclusively on secondments with 16 researchers being seconded from UoB and UL to DePuy and 11 researches from DePuy to UoB. During this time, the MEDCAST team have been working on:
- the development of robust process models that accurately describe the flow of molten metal in the mould during the casting process. This can be applied to the evaluation of different tree configurations while minimising the number of required tests. In addition to the mould filling and tree design, the solidification and cooling of the molten metal was also modelled. This allowed the prediction of casting defects such as macro and micro-porosity and distortion. The MEDCAST team have achieved very encouraging results in the development of robust process models using specialised Computational Fluid Dynamics software packages. The molten metal flow has been successfully modelled and the prediction of defects, from entrapment of air bubbles into the fluid stream to the formation of oxides and non-metallic inclusions, using this model has been remarkably accurate. Additionally, this model has been used to redesign the tree configuration and a significant reduction of defects in the parts produced with the new tree was observed.
- the development of pattern wax process simulations that describe the wax flow in the mould, their cooling patterns and shrinkage for different types of wax. One source of waste in investment casting is the wax in the scrap wax parts that are discarded before going onto the next process stage. MEDCAST also investigated the possibility of re-using the different types of wax used in these parts. With this aim, the main mechanical and physical parameters of the new and re-used wax were studied and compared.
- The ceramic shell used to create the mould which the metal will fill is one of the most time consuming steps in the investment casting process. New materials for shell systems that can dry faster would greatly reduce the lead-time of the casting process. With this aim, the MEDCAST team investigated new shell formulations, and the mechanical properties of the resulting material were studied and compared with currently used materials. Encouraging results have been obtained in the development of an ultrafast-drying ceramic shell for investment casting. The MEDCAST team are applying a novel shell formulation that dries in a fraction of the time required for conventional shells. While the toughness of this new ceramic material has been reduced in approximately 4%, the cycle time has been reduced from an average of 4h per layer to 30 min.
- The feasibility study of novel dimensional inspection technologies. Currently, there is a lot of manual dimensional measurements in the foundry, some using go/no-go gauges. Novel CMM technologies have been evaluated as they would be an enabler for automation of the dimensional inspection, they would provide objective data and the output would be compatible with SPC.