Alternative cut-off and surface finishing of investment castings

Cashman, Miriam (2015). Alternative cut-off and surface finishing of investment castings. University of Birmingham. M.Sc.

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Abstract

The research investigates the capability of replacing the cut-off and gate-removal processes at DePuy Synthes (Ireland) with a single cutting operation. Abrasive WaterJet Cutting (AWJC), laser cutting, Electrical Discharge Machining (EDM) and plasma cutting were considered as alternatives to the current system. Custom investment castings were produced for use in A WJC experiments to determine the cutting speeds for a range of cut thickness (2 to 30 mm) for the Cobalt-Chrominum-Molybdenum (CoCrMo) alloy. Femoral and tray castings, each with different tree designs, were evaluated post knockout (vibratory shell removal). Femoral parts were undamaged by jet deflection or wear when utilising the correct set up of the A WJC nozzle. Using a traverse speed of 130 mm/min, the surface finish at the bottom of the 16 mm thick femoral gate was visually equivalent to the current surface finish obtained after gate removal (Ra of 9 μm). Thin femoral sections (3.2 mm) cut at 400 mm/min achieved an acceptable Ra of 7 μm with a cycle time of 6 minutes per tree, which was 70% lower than the current processing time of 23 minutes. Tray castings cut with a traverse speed of 60 mm/min achieved a surface roughness Ra of 10 μm. However, the process was unsuitable for trays because jet deflection below the cut caused excessive wear to the machined parts. The use of AWJC for femorals has the ergonomic benefit of eliminating all manual grinding in the foundry, as well as labour savings equivalent to a Return-On-Investment (ROI) of two years. Further development of a 3-dimensional (3-0) vision system however is required to automate the AWJC of femoral castings.

Type of Work:

Thesis (Masters by Research > M.Sc.)

Award Type:

Masters by Research > M.Sc.

Supervisor(s):