Shopping Basket
PDF's from PIM International
Contribution to the development of 18 carat gold alloy shaped by MIM
Technical Paper: PIM International, Vol.5 No.2 June 2011, pages 66-70, 2880 words
[1] Arts et Métiers ParisTech, LaBoMaP, Porte de Paris 71230 Cluny, France
[2] Ecole Catholique d’Arts et Métiers, Laboratoire de Sciences des Matériaux, 69321 Lyon 03, France
[3] ALLIANCE MIM, ZA des belles ouvrières, 23210 Saint-Vit, France
Abstract
Metal Injection moulding (MIM) is an appropriate manufacturing process for small complex-shaped components with good surface finish. In comparison to parts manufactured by traditional processes, such as investment casting or forging, parts with better tolerances can be achieved. Hence MIM is a viable manufacturing method for the jewellery industry, which additionally desires strong aesthetic criteria (brightness, colour, surface finish, smooth appearance etc.). Nevertheless due to the specific properties of precious alloys, such as low temperature sintering, the MIM process for conventionally used materials (low alloys steels, stainless steels etc.) is not easily transposed to precious metals. This paper will focus on parts made of 18-carat gold alloy. The study, supported by an industrial partner, highlights the technical difficulties encountered at the sintering step and their consequences. In addition, post treatment effects (HIP) are investigated.
Keywords: MIM, gold, sintering, HIP, grain growth, porosity
Introduction
Today, MIM is a well-known mass production process derived from plastic injection moulding. MIM combines plastic injection moulding and powder metallurgy to obtain dense components. With only ten publications before 1970, and more than one thousand by 1999, MIM still stimulates the interest of researchers and manufacturers [1].Among the diverse range of powders used (standard and low alloy steels, stainless steels, high speed steels, carbonyl iron and nickel, copper based alloys, nickel and cobalt based superalloys, titanium, magnetic alloys, refractory metals and hardmetals), precious metal alloy powder could also be successfully processed, not only for luxury industry but also for additional applications.
As J.T. Strauss stated, “The jewellery manufacturing industry is in a unique position to adopt MIM technology as many of its general advantages are greatly amplified in jewellery manufacturing due to the high cost of precious metal alloys” [2]. In reality, the development of the MIM process based on different gold alloys could enable new means of more efficient and less expensive production for the luxury products industry, especially jewellery. Usual tolerances reported for MIM are between +/- 0.1% (+/- 0.001 in/in) and +/- 0.3% (+/- 0.003 in/in). Density reaches 93% to 100% [2-3]. Not only could new designs with much more complexity or with different coloured alloys be produced, but also a perfect guaranteed microstructure [4].
Moreover, the material losses are minimised. With MIM, only a polishing step is necessary, and in contrast to other processes widely used today, like casting, investment casting or forming, no machining operation needed. For instance, it can be noticed that machining has a global yield of 10% with gold alloys. Without re-melting, it can be possible with MIM to reduce the recycling loop using, for instance, re-ground feedstock [2].
Primary tests with the MIM process were conducted with an 18-carat yellow gold alloy; they showed that it is possible to obtain samples with very good properties. For example the microstructure presented in Fig. 1c shows that the grain size of a MIM part is the same or smaller compared to the other processes (cast Fig. 1a and stamped (Fig. 1b) without addition of a grain refiner.........
Further sections of this paper include:
- Materials and Experimental section
- Materials section
- Part Characterisation - Results and Discussion
- Heterogeneous grain growth
- Non-sintered areas (NSA) - Conclusion
- References
Figures and Tables:
Fig. 1 (a) Gold 18 carat (75Au-15Ag-9Cu-1Zn) with 0.01% Ir added as a grain refiner cast [5]; (b) Gold 18 carat stamped (CETEHOR); (c) Gold 18 carat MIM
Fig. 2 Schematic view of the reference cycle
Fig. 3 Defects encountered on injected parts after sintering
Fig. 4 Gold powder cold pressed without binder or lubricant and sintered with an atmosphere (80% Ar + 20% H2)
Fig. 5: Injected part at the beginning of sintering cycle (step C)
Fig. 6: Gold powder with additional Al203 particles. Pastille cold pressed and sintered with reference cycle
Fig. 7 Effect of Hot Isostatic Pressing (HIP) on injected parts
Fig. 8 NSA evolution with compaction pressure
Fig. 9 SEM and EDS analysis of a NSA
Table 1 Differences in disc preparation
Search all documents in the PDF Store
Please note that this search only covers document title, introduction / abstract, table / figure captions and author details, as available to view on each document preview page.Or view by topic
