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Benefits of Investment/Lost Wax Casting
The benefits of the investment casting process may be summed up by the four words accuracy, versatility, integrity and finish. Few if any alternative metal forming methods can offer such a unique and broad spectrum of advantages. Accuracy and versatility stem from the use of a one piece mould without a joint line or the need for draft angles. These features not only give rise to a component shape that is aesthetic and uniform; they also allow the process to give, on a regular basis, consistent and repetitive close tolerances, intricate and re-entrant contours (many impossible to create economically by alternative manufacturing techniques) and competitive cost ratios. Versatility extends to the choice of materials since virtually all alloys can be investment cast.

Utilising the aluminium die form ensures tooling is relatively cheap and is adaptable should design changes be necessary. It also enables relatively small quantities, typically for research and development trials, to be produced prior to commitment to production quantities.

Casting integrity is an important feature of the process and investment casting has a long history of serving the most demanding sectors of industry. This has promoted a tradition of quality and reliability, an aspect that by recent work to develop production methods of guaranteed integrity has resulted in fatigue performances equal to that given by forgings measured longitudinally. Based on this work, investment castings are now beginning to replace forgings and machined components in fatigue related environments.
Other advantages arise from the high degree of dimensional accuracy, + or - 0.13mm per 25mm with improvements up to + or - 0.08mm per 25mm and the excellent surface finish that can be routinely achieved, typically 1.5 to 3.2 microns with improvements up to 0.8 microns.

Typical minimum wall thickness of 1.5mm with thinner sections of 1mm are possible. Tolerances quoted should be taken as a guide, as they may vary depending on the complexity and configuration of the component. Consistency from casting to casting will generally be within the tolerances indicated with individual foundries being able to advise on this point. These characteristics minimise the requirements for machining, in some cases eliminating it entirely, and this leads to substantial savings in raw materials, labour costs and capital expenditure, reduces and simplifies production control and simplifies assembly operations.
These benefits individually offer great competitive advantages; collectively they suggest an overwhelming case for the consideration of investment casting as the most economic method of forming for a wide range of metal components.

Process Characteristics
  • FREEDOM OF DESIGN
  • HIGH PRODUCTION RATES
  • HIGH DIMENSIONAL ACCURACY
  • HIGH DIMENSIONAL CONSISTENCY
  • HIGH INTEGRITY CASTINGS
  • EXTREMELY GOOD SURFACE FINISH CAN BE OBTAINED
  • COMPLEX SHAPES CAN BE CAST
  • LONG/SHORT RUNS CAN BE ACCOMMODATED
  • MACHINING CAN BE REDUCED OR ELIMINATED
  • MINIMUM FINISHING OF CASTINGS REQUIRED
  • ALMOST ANY ALLOY CAN BE CAST
  • ENVIRONMENTALLY FRIENDLY PROCESS

Most industries requiring castings are catered for but investment castings are admirably suited for high technology, high volume orders especially in respect of the aeronautical industry. The petroleum, chemical, electronic, defence, prosthetic and automobile industries are also large users of castings produced by the process.

Contributors include BICTA, with special thanks to Mr David Critchley