Small is the new big

There’s an obvious attraction in 3D printing small objects – because you can print a lot of them without having to have a huge build space. And a high productivity rate helps to justify the cost of the machine in the first place. But it’s not so easy to produce really small and highly detailed metal parts, which is exactly the area that the Swedish company Digital Metal specialises in.

Nut and bolt, printed on a Digital Metal DM P2500 3D metal printer. Shown with a new £1 coin for scale.

I met with Digital Metal’s managing director, Ralf Carlstrom, at the TCT show in the UK. The company is part of the Höganäs Group, which specialises in working with metal powders, with Digital Metal giving the group a 3D metal printing capability. For the last four years this has meant offering a manufacturing service using Digital Metal’s proprietary metal printer but the company recently announced that it would also offer to build and sell its DM P2500 printer to interested customers.

Carlstrom explains: “We came to the conclusion that to ensure the growth of our technology we need to have more users.” He says that the company has gained a lot of experience from its internal production, adding: “We have supported an external machine for two years so we feel confident in offering this machine to the market.”

The Digital Metal process has been specifically designed for producing small intricate components. Carlstrom explains: “We use a metal powder bed process and build it layer by layer. With each metal powder layer we jet our binder just in the right place to form the component. Then we add the next metal powder layer and jet the binder again. All the time the bottom of the build is lowered so the parts are hidden in powder the whole time.” This means that there’s no need for any support material because the powder on the bed offers enough support. Each layer is a 42 micron slice. The printer works at room temperature and there’s no need for a protective atmosphere.

The printhead is a thermal head. Carlstrom adds: “The binder is a water-based binder that we developed. In Hoganas we have a lot of know-how in binder development because of the metal powder mixes that we supply for the automotive industry. We have used binders since the mid 80s to ensure that we have consistent components and that technology has been fine-tuned over the years.”

The parts can then be cleaned and the loose powder recirculated back into the machine for re-use. The parts are then sintered, which removes the binder and bonds the powder particles together giving them high density and strength. Separating the printing and the sintering stages also means that each step can be optimised for the material in use.

Carlstrom says: “The parts are not used in stressed applications but the parts that we provide would withstand highly loaded applications because we follow a standard that the metal injection moulding industry has. So we apply this standard and get the same structure and same performance.”

The process is capable of producing very small, highly detailed parts, though this is partly down to the finishing, as Carlstrom explains: “We blast the parts to take the surface finish from six to three microns. Then we can add a further finishing process to get down to one micron.”

He says that this machine is designed for “high volume serial production” with the target markets including Industrial, dental and luxury applications, as well as prototyping for the medical, automotive and aerospace markets .

The machine has a large build area of 3x1x1.8 metres. However, it takes roughly 15-20 minutes to change from one job to the next assuming the same material, which can rise to a few hours if the material also has to be changed. Clearly it’s best to batch jobs together that use the same materials and change materials at the shift changes to maximise the productivity.

Ralf Carlstrom, general manager of Digital Metal

Carlstrom seems a little nervous talking about the price of the machine, pointing out that it’s not cheap. He wouldn’t name a figure but it doesn’t seem as if there would be much change from half a million euros, which does not seem expensive for a high volume metal printer.

He adds: “There is a standard configuration and we make some ancillary products like cleaning boxes to help people with different materials. So, for example, there is a down draft table for materials handling, which has an advanced filter system so you can draw the powder down through the mesh in the table.”

Carlstrom says that the company is still working on refining the process further, explaining: “Today we have several metal processes, like separating the powder and the printed parts but we want to automate these. It should be possible to have a no-hands process.”

There’s a YouTube video that explains the process and shows the machine itself. The process is best suited to producing small parts, which also allows the bed to be optimised to produce in high volume, reducing the cost per part to be competitive against more traditional methods. The actual parts are extremely impressive, having a great deal of detail but without requiring excessive and costly finishing. No doubt once the first machines are completed and installed we’ll hear more about this process as customers start to explore different applications.


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