SilverPowder Bed FusionDMLSJewelry, Medical Gauze, Implants925 Sterling SilverContact Us
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Platinum/RutheniumPowder Bed FusionDMLSJewelry950 PlatinumContact Us
Precious Metal Additive Manufacturing
Precious Metal Additive Manufacturing (PMAM) presents unique opportunities to a whole host of industries but mainly jewelery, healthcare and electronics. In total there are sixteen different precious metal, in this article we will focus on Gold, Silver and Platinum / Ruthenium.
Direct versus Indirect
There are two main approaches for 3D printing precious metal. You can either use direct manufacturing or indirect manufacturing. Direct manufacturing refers to the creation of an object straight from the 3D design while indirect manufacturing means that the object (pattern) that is 3D printed eventually is used to create a mold for investment casting.
The most used direct manufacturing process used for precious metal is Powder Bed Fusion (DMLS). The printing of patterns for indirect manufacturing processes can be done via many different 3D printing processes, but mainly Vat Photo (DLP/SLA), 3D Inkjet (Material Jetting) and Material Extrusion (FFF/FDM).
With Powder Bed Fusion, precious metal powder is solidified by a laser, layer-by-layer. When a print is done, the finished object is extracted from the powder bed. Most of the left over powder can be reused. Post-processing is necessary to give the object an end-product finish. This will give the it a clean, glossy look or a polished shine.
Direct manufacturing of precious metal allows you to create highly detailed and complex geometric designs that can not be made using traditional subtractive processes. It’s most suited for low-volume production as it eliminates time-consuming tooling.
Within the realm of indirect precious metal manufacturing there are a few different approaches due to different print technologies. In the end it all comes down to creating an object (pattern) with a castable 3D printing material. This is the ‘indirect part’. In order to make a successful cast, first there are one or more wax sprues attached to the object. The object is then covered with plaster. The solidified plaster forms the mold that can be used for casting precious metal. Before you can start pouring metal in the mold, the object inside needs to be burned out. This can be done by putting it in an industrial oven for several hours. Then you are ready to pour the precious metal. Once the metal is cooled and solidified, the plaster can be removed. With some post-processing like sanding, polishing and sandblasting, the final object can get a clean and shiny finish.
Which precious metals are most used in AM?
Not all precious metal is suitable for additive manufacturing, below we’ll go through the most popular ones and describes their properties and applications.
Silver has more uses than one would assume, with some obvious and others more obscure. Besides jewelry, it’s also widely used in the photographic industry due to its great light reflection properties. But more important for the additive manufacturing industry is its use in dental alloys, electrical contacts and high capacity batteries.
Silver is particularly useful for products that need the ability to resist the corrosive effects of oxygen and moisture, making it a staple for dentistry and silverware.
Silver is soft, ductile and malleable. It has the highest electrical and thermal conductivity of all metals. It is also stable in oxygen but does not do well against sulphurs. It’s slightly harder than gold but has the lower contact resistance of all metals.
Gold has multiple use cases, from electronics to jewelry. Being such a diverse metal, it crops up in a plethora of industries with unique needs. Its balance of relative malleability and excellent electrical conductivity makes it so widely used.
Platinum is malleable, ductile, heavy and dense yet soft at the same time. It has the third highest density, behind Osmium and Iridium. Platinum is unaffected by air and water, but will dissolve in hot aqua regia, hot concentrated phosphoric and sulphuric acids and molten bases. It is as resistant as gold to corrosion and tarnishing and will not oxidize in air no matter how high one raises its temperature.
Aside from jewelry, which is the most prominent use of the metal, platinum is also used for surgical tools, laboratory utensils, electrical resistance wires, and electrical contact points. It is also present in automobile exhaust systems, glass fibre, optical displays and LCD screens.
Ruthenium, like the other platinum group metals, commercially procured as a by-product from nickel, and copper, and platinum metals ore processing. It is a hard, white metal with varying properties in different oxidation states. Small amounts of Ruthenium present in both palladium and platinum can increase their hardness.
While it does not tarnish at room temperatures, it can oxidise in air at about 800°C. The metal is not affected by hot or cold acids or aqua regia, but when potassium chlorate is added to the solution, it oxidises explosively. It also dissolves in molten alkalis. The primary demand for Ruthenium comes from the electronics industry (50%) and the chemical industry (40%), with smaller amounts being used in alloying.