Rapid prototyping – spare parts via 3D-printing

Expensive warehousing and lack of spare parts could soon be a thing of the past – thanks to rapid prototyping. Many manufacturers already scope for this 3D technology based on CAD-models, and thus, they rebuild the respective workpiece.

By means of rapid prototyping, it will be possible to rebuild spare parts directly in the workshop. Photo: Fotolia - Patrick Daxenbichler

By means of rapid prototyping, it will be possible to rebuild spare parts directly in the workshop. Photo: Fotolia – Patrick Daxenbichler

That is why, with 3D-printing, it doesn’t matter how long the series hasn’t been manufactured anymore. Single-unit productions aren’t a problem, either. Apart from the printer, expensive special tools aren’t necessary. Furthermore, such spare parts can be made locally, theoretically directly in the workshop.

Different methods are categorized under rapid prototyping, depending on the material. Daimler recently started manufacturing metal spare parts for the Unimog, based on selective laser melting (SLM). To produce a part, the machine first applies a layer of the pulverized material, in this case an aluminum-silicon alloy. Lasers specifically melt the areas responsible for forming the spare part. Afterwards, the lasered material solidifies and the process continues with a new layer of powder. The part grows higher, layer by layer. When finished, Daimler claims it is denser and purer than a comparable cast part and just as durable.

The view into the interior of the 3D printer shows the first printed thermostat covers, which are still connected to the work platform. Photo Daimler

The view into the interior of the 3D printer shows the first printed thermostat covers, which are still connected to the work platform. Photo Daimler

3D-printing also possible using plastic

Spare parts can even be made from plastic in the same way, which is then called selective laser sintering (SLS). An easier, powder-free method has caught on mostly for domestic use. A movable button set on three axles liquefies a plastic thread and injects it through a nozzle onto the work surface. This version produces no excess powder. On the other hand, parts manufactured in this way don’t reach the surface quality that develops with laser sintering, and therefore have only limited suitability as spare parts in the automotive field. While plastic and nowadays even metal can be handled fairly well with 3D-printers, glass still poses a great challenge to manufacturers.

Iris Gomeringer, Manager Digital Plant Powertrain, displaying a 3D-printed casting core of a cylinder head. Photo: Daimler

Iris Gomeringer, Manager Digital Plant Powertrain, displaying a 3D-printed casting core of a cylinder head. Photo: Daimler

So far, the only way to print glass is the application through a nozzle. But glass poses similar problems as plastic. The surface is rough, the parts porous and full of cavities. The Karlsruhe Institut for Technology (KIT) wants to remedy this. The institute uses the principals of stereolithography. In general, the model is formed out of liquid, light-sensitive plastic. Precise light pulses harden the liquid selectively. To print glass in this way, scientists mix nano particles made of highly purified quartz glass with a small amount of the fluid plastic. Little by little, this compound forms a part. Solvents wash off the superfluous material. Afterwards, scientists heat the part and thereby remove the plastic still mixed in. “The shape first resembles a sand cake. It may hold its form, but it’s unstable, which is why the glass is sintered in a last step, heating it so far as to let the glass particles melt and fuse with each other,” Dr. Bastian E. Rapp, project team leader, explains.

Complicated high-precision structures made of glass can be manufactured with a 3D-printing method developed at the KIT. Photo: KIT The Karlsruhe Institut for Technology uses stereolithography for 3D-printing with glass. Photo: KIT Out of a compound consisting of highly purified quartz glass and fluid plastic, a workpiece grows. Photo: KIT At the end, solvents wash off the superfluous material from the workpiece. By heating it up, the researchers remove the plastic still mixed in. Photo: KIT

3D-printing with glass: numerous inquiries from manufacturers

Centimeter-sized parts can be formed with 3D-printing. At first glance, metal- and plastic spare parts are primarily considered for use in vehicles. But according to Rapp, the automotive industry has also started numerous inquiries into glass printing, especially in the field of lighting, for example for integrated headlight lenses. Meanwhile, logistics providers haven’t been idle. Panalpina are considering installing 3D-printers in their logistics centers. Amazon takes it a step further and takes the term “just in time” literally. Almost three years ago, a patent for mobile 3D-printing inside delivery vans popped up, registered by the online giant.

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