The process of sintering has been around for thousands of years and some of the first ever products produced by sintering were bricks which were heated in open fires in order to increase their strength. In fact, the sintering process is still used today to make bricks, and also porcelain, abrasives, cutting tools, whitewares, and construction materials.
Sintering, also known as frittage, is the process of compacting and forming a solid mass of material by using either heat or pressure without melting it to the point where it becomes liquid. An example of pressure sintering is when snow is compacted into a glacier. Another example is when the ice cubes in your glass of gin and tonic stick together, which is caused by the difference in temperature between the ice and your G&T.
An example of sintering in the early 19th century was when William D Coolidge sintered tungsten powder in order to produce a lamp filament for Thomas Edison. By the 1930’s, sintering was being used to produce cutting tools, spark plugs, bearings, electrical insulators, and electrical contacts. Ten years later, sintering was producing nuclear fuel elements and auto parts.
Today, sintering is used to produce a wide range of products including turbochargers, semiconductor substrates, aircraft wing weights, golf clubs, ultrasonic transducers, and dental implants, among others. At London 3D Printing we use the selective laser sintering process to create objects from nylon powder which is an exceptionally strong and versatile material that can be used to create very fine detail when compared with other types of 3D printing using, for instance, ABS thermoplastics.
The sls 3D printing machines that we use are very expensive and require highly trained and skilled operators to work them. The way that they work is by depositing a fine layer of the nylon powder, usually sls PA11, which we selectively sinter with a laser. This process is repeated layer by layer, solidifying the powder as it goes, to produce the finished object.
SLS 3D printing is moving forward rapidly with new techniques being invented all the time, and they often have almost immediate commercial potential. For instance, Joseph DeSimone who is a research scientist and chemist at the University of Carolina at Chapel Hill, produced a paper demonstrating his advances at a TED talk in Vancouver, Canada, in 2015 and on the same day launched his start-up company Carbon 3D in Redwood, California, although he had quietly registered it two years earlier. Today it is one of the biggest start-ups in 3D printing, having raised $680 million in publicly available funding rounds, and is apparently valued at $2.4 billion. It has a contract with sportswear company Riddell to make padding for helmets for American football players, and another with Adidas to manufacture rubber-like midsoles for sports shoes.
Aircraft companies like Rolls Royce, Pratt & Whitney, and Boeing are using 3D printing techniques to make metal parts for aircraft engines because the complicated components are lighter than parts made the conventional way, and they are cheaper than milling metal blocks.
Scientists are also beginning to improve the strength of printed metals by controlling the microstructure. As an example, back in 2017 a team in the US found that when 3D printing stainless steel, using intense heat and rapid cooling altered it so that it was stronger than products cast in the usual manner. Even more recently, researchers in Australia found that the same thing applied to a titanium-copper alloy, with the copper helping to speed up the solidification process. One of the leaders of this team has already been in contact with aerospace companies who are interested in using it for parts, and it can also be used for things such as hip replacements.
Today, researchers are moving forward and exploring 4D printing – making 3D printed objects that can also perform some sort of mechanical action in a similar way to artificial muscles. A team at the California Institute of Technology has already printed a submarine with paddles that snap backwards when placed in warm water, thus propelling the submarine forwards. At the moment, they have to be reset each time, but they could be reset after each stroke by using battery power. Who knows what the future holds?