Rapid manufacturing of patterns for investment casting: improvement of quality and success rate

Abstract

PurposeThe main objective of this paper is to analyse all stages of the CastForm™ polystyrene (CF) pattern fabrication process, identify the reasons leading to inferior quality, and outline techniques for its improvement and reduction of failures.Design/methodology/approachThis paper describes rapid manufacturing of patterns for shell or flask investment casting using the laser sintering (LS) technique with CF material. The process involves data preparation, LS fabrication of a “green” part, cleaning, and wax infiltration. All process stages are equally important for successful project completion in terms of pattern quality and delivery time. A failure at any stage requires a part or pattern to be produced again, which would incur additional time and cost.FindingsThe conducted experiments show how the CF material strength varies at different process stages and temperatures. Cleaning and wax infiltration are considered the main reasons for part distortion and breakage.Originality/valueThe paper proposes a new approach for wax infiltration. Deformation and breaking of unsupported features could be reduced or eliminated by introducing a supporting structure under these features.

A Review of Fused Deposition Modeled Sacrificial Patterns in Investment Casting

“…Dotchev and Soe [5] investigated CastForm using SLS technologies, Yao [6] studied SLA technology during his doctoral research, and Qingbin et al [7] developed a novel technology investigating rapid freeze prototyping. FDM technology has also been heavily researched by Blake and Gouldsen [8], Grimm [9], Cheah et al [2], Harun et al [10], and Singh et al [11].…”

“…Dotchev and Soe [5], for example, concluded that the weakest link of the CastForm process involved the infiltration of wax into the green part. Since the green part is so fragile, cleaning and movement should be limited and performed with extreme care.…”

“…Since the green part is so fragile, cleaning and movement should be limited and performed with extreme care. The main principle is not to move or touch the green part during wax infiltration when the material strength is minimal [5]. Current practices of wax infiltration involve manual processes, where, the green part is submerged into a vat of wax or the wax in poured over the part.…”

Selective laser sintering of HIPS and investment casting technology

“…Despite the PC is a high-performance, versatile thermoplastic, it is found that PS shown to be more suitable for (Ho et al, 1999;Dotchev et al, 2007a;Hock et al, 2003). However, PS is not suitable for making thin-walled parts or delicate structure parts due to its poor mechanical properties (Xu et al, 2005;Shi et al, 2004;Dotchev and Soe, 2006). In this study, a type of high impact polystyrene (HIPS), a polymer blend of PS toughened with polybutadiene rubber, is adopted as an SLS material to make the parts with good mechanical properties as well as with good laser sintering properties.…”

Effect of thermophysical property and coating thickness on microstructure and characteristics of a casting

“…SLS has been used to produce a small number of wax-like patterns with CastForm polystyrene (CF) material for shell IC. FDM machines extrude molten plastic to build an expendable pattern, usually using acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) [16] . However, a plastic pattern made of the above materials easily cracks the ceramic shell due to its large expansion stress, and it is very difficult to demould after the ceramic shell has dried.…”