Additive Manufacturing - Arrived in the Mainstream
Additive manufacturing technologies are becoming a versatile production method for series production. However, you should be aware of its advantages and disadvantages if you want to use this technology efficiently.
Since man has first worked with materials, he has done it by removing parts of a blank. From stone-age man, who carved works of art from mammoth tusks in the caves of the Swabian Alb, to today's computer-controlled multi-axis milling/turning machines: the principle has always been the same: material is removed from a blank until only the desired geometry remains —be it a lion-man or a complex technical component.
These processes are quite flexible, as each part is manufactured individually. In mass production, however, automated processes are applied frequently and individually formed parts are considerably more expensive than identical serial parts. A further disadvantage of ablating processes is that the more complex the component is, the more expensive the production process becomes, and the more material is lost. For example, 98 % of the huge raw part made from the finest special aluminium that is used in the production of the wing frames of the Airbus A380 is transformed into inferior shavings, which can only be used to a limited extent.
Last limitation: The blank can only be machined from the outside. Although modern five-axis milling machines can move their tool very freely, the milling cutter must still be able to reach the point where it is removed — the inside of a workpiece can only be machined to a very limited extent.
Complexity is for Free
Additive processes — however different they may be in detail — are based on the principle that a material is applied layer by layer to create the component. Since the material is not removed, but added at the places where it is needed, hardly any waste is produced. In addition, the printer doesn't care how complex the form is — a cube is created just as quickly as a complex component: "Complexity is for free" is the motto. Equally, the printer doesn't care if each part has a different shape, since there is no shape to follow. In this way, individualized components can be produced just as quickly as identical parts.
Completely new possibilities are offered by the layered construction for the interior design of the component. Since the part is created layer by layer, the inside of the workpiece can also be designed as desired — with some restrictions. For example, multi-part moving parts such as ball bearings can be manufactured in a single production step.
In almost every case, additive manufacturing processes are slower and more expensive than established technologies. Nevertheless, there are cases in mass production where the additive approach is superior to conventional methods. The points mentioned show where: Whenever it is about
- individualized parts
- very complex parts
- parts with a very high metal removal rate and expensive raw material, or
- where a free interior design offers advantages,
additive manufacturing is worth considering.
The Advantages Outweigh the Disadvantages
There are a number of interesting examples for the benefits of additive production, even in the field of conventional manufacturing. Cooling channels in injection molds can only be produced by drilling the parts in the conventional process. Therefore, the manufacturer is limited to drilling straight holes into the block behind the mold cavity; if it is to be around the corner, several holes must be drilled in such a way that they merge with each other and the superfluous parts of the hole are plugged. This is complex and results in a very unfavorable flow shape of the channels.
If, on the other hand, a mold is produced in 3D printing, the channels in the mold block can be designed as desired, i. e. they can run directly underneath the surface of the cavity, allowing the mold to be cooled extremely efficiently and quickly, thus dramatically reducing cycle times.
One of the best-known examples of additive metal fabrication is the fuel injector of the new GE jet engines installed in the A320 Neo or Boeing 737 MAX. The internal design of the nozzles is crucial for optimum fuel distribution — the better the atomization process, the less fuel is consumed by the engine. GE's engineers have known for a long time how the optimum nozzle should look like on the inside, but this complex shape could not be produced and so far, these nozzles have been made up of more than 20 parts that were welded together. This was laborious, expensive and inaccurate.
Today, GE is printing these nozzles with an optimum geometry and, based on its experience, is embarking on additive metal production. GE plans to produce 40,000 of these nozzles per year by 2020 — 19 of these nozzles are installed per engine. In addition to the significant fuel savings enabled by the optimum design, GE saves 435 kg per engine. GE has now acquired the German supplier Concept Laser and the Swedish company Arcam, both of which are operating in metal 3D printing.
AM Facilitates Refitting
For more than three years now, Siemens Mobility has been using a Stratasys plastic-processing additive manufacturing system and is showing how additive production can help in the spare parts and refitting sectors. The trams and other rail vehicles built by Siemens Mobility are often in operation for more than 30 years, so spare parts for very old vehicles are required again and again. On the other hand, trams are very individually adapted to the requirements of the respective customer, i.e. the transport companies, so that many parts were installed in very small quantities and in the spare parts business any storage would be uneconomical.
Modelling Spare Arts
In addition, modified spare parts are frequently requested, such as armrests for the driver's seat, which contain various operating elements. If, for example, a new safety system is retrofitted, Siemens Mobility will be able to model the old armrest and supplement it with adaptors for the new controls. The 3D model is then printed on the Stratasys Fortus 900 press and the "new old" armrest is delivered to the customer. Siemens Mobility calls this "saving innovation" (artificial word from spare part and innovation). The materials that can be processed in the Fortus facility even comply with the strict fire protection regulations for public transport.
Larger components are also produced in the 3D printing process, so it became apparent that the one-piece clutch skirts at the front of the trams that were originally used, were not an ideal solution, as the entire skirt had to be replaced with a small Rempler on one side. Now, Siemens Mobility has developed a three-part apron, the parts of which can be replaced individually and into which daytime running lights are integrated. These spare parts are also produced at the additive manufacturing plant.
Volvo Trucks has launched a pilot project to explore the potential of additive manufacturing and, above all, the structural freedom offered by these technologies. The engineers revised an existing truck engine and consistently used the possibilities of lightweight construction and functional integration that AM makes possible. In this way, they were able to make the engine 25 % lighter — 120 kg were saved in absolute terms — and 200 individual parts could be saved. In the engine block alone, 80 parts could be integrated; in the cylinder head, the function of 40 parts was taken over by other parts. The savings achieved in assembly, spare parts stock and other areas are significant.
These examples show the advantages of additive manufacturing: when it comes to complex geometries that cannot be produced conventionally or when small quantities and customized spare parts are produced on demand. Additive technologies open up completely new possibilities for the designer to integrate functions into a component or to optimize geometries regardless of complexity. In this way, the higher unit costs are by far compensated for. AM offers completely new possibilities — you just have to find them.
Excursus: Casting is Only Part of the Solution
Mass production involves a whole range of casting processes, from sand casting to injection molding and metal die casting. They make it possible to produce a large number of identical components at low cost. However, changes to the geometry cost a lot of money because an expensive shape has to be changed or even re-manufactured. In most cases, the molds are created by milling material from a blank. In this case, hardly any waste accrues.
This article was first published by konstruktionspraxis.
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