Powder Metallurgy (PM) starts with metals in a powdered form which are then consolidated in a variety of ways to make high-quality parts.
PM is used in the aerospace, automotive, electronics, defense, medical and dental industries, as well as general industrial and consumer applications.
Steel and aluminum powders are the main materials used for powder metallurgy but the relatively expensive titanium is very well suited the the low-waste PM processes.
Examples of what can be made include artificial hip joints, metal plates for implants, gears, nozzles, pump rotors, sports equipment, watch and cell-phone cases and aircraft engine components.
PM allows new products to be made which were not previously possible. New metal alloys can be formed and the manufacturing process is often cheaper and more efficient.
- Precise shapes and sizes can be formed, reducing the need for further machining or manufacturing steps
- Suited to semi-automated processes for low-cost volume production
- Enables many of the latest additive manufacturing (3D printing) processes.
- Computer aided design and toolless 3D printing leads to quicker development times, cheaper development costs and more efficient and lightweight products.
- Enables Metal Injection Molding (MIM) processes.
- Suitable for moderate complexity geometry and smaller parts
- Environmentally responsible manufacturing – low material waste
- Superior material properties (greater than 98% density achievable)
- High quality surface finishes
3D printing: many methods have been developed to consolidate powder into parts in these modern developing processes, some of the commercially developed processes include:
- Selective laser melting (SLM); involves laying down a layer of powder about 30 microns thick and then using a laser to selectively melt the powder in the desired patern to form a layer of the desired object. Layers are built up by sequentially depositing powder and fusing subsequent layers to form the part. The process is conducted in an inert atmosphere to reduce oxidation of the powder.
- Electron Beam Melting (EBM or EBeam); a similar powder bed/layer fusing method to SLM, but the energy source is an electron beam and the process is conducted in a vacuum.
- Powder Bed Binder-jet; another powder bed/layer-by-layer process, which prints binder (“glue/ink”) in a manner similar to an ink-jet printer to temporarily bind each layer of a part to build up the component layer by layer – the polymer bound part refered to as a”green body”. After the printing process the binder is removed from the green body and the metal particals fused in a series of chemical and/or thermal steps to form the final part.
Metal Injection Molding (MIM):
- Metal powder is mixed with polymer which can then be injected into a mould when the polymer is liquified through heating. The process of injecting the metal filled polymer being very similar to conventional plastic injection molding, with the result of the molding step being a polymer/metal mix “green body”. The polymer binder is removed from the green body and the metal particals fused in a series of chemical and/or thermal steps to form the final part.
- One of the first and simplest PM processes. Die pressing involves placing some powder in a die and applying pressure with a punch to compress the powder and cause local adhesion between metal particals. The full component strength and density is then achieved by subsequent furness sintering steps.
Other consolidation methods include:
- hot or cold isostatic pressing,
- screen printing.
- high temperature plasma spraying
- high velocity cold spray and
- various hot working processes i.e. extrusion, rolling and forging.
Some common characteristics of PM processes;
- Material waste is minimal as final geometry can be formed without subtractive manufacturing steps.
- Near net shape parts from automated processes reduces labour costs and complexity.