Rapid production tools through E-beam technology
March 1, 2003
This is not your father’s way of making tools: layer by layer, using an electron beam that fuses powdered metal. Sound like RT? It is—but the parts molded from these tools are not necessarily prototypes. They’re the real thing.
Figure 1. The cooling cycle for this Volvo camshaft sensor cover made of reinforced PBT was reduced from 25 to 15 seconds using conformal cooling channels, created as Arcam’s EBM technology made the core and cavity inserts. |
For many molders and moldmakers, the term rapid tooling (RT) has become associated with tooling for prototypes or short runs. One company is attempting to redefine RT to mean, simply, production tools made very quickly.
Arcam AB calls itself a provider of equipment for free-form fabrication (FFF) of parts in steel, or, in other words, direct production from CAD file to metal. Tooling for injection molding is one of its principal markets, and as managing director Magnus René put it, the benefits of electron beam melting (EBM) technology are gaining acceptance.
What Arcam’s EBM system creates is production tooling made of tool steel suitable for the number of impressions and quality level considered normal for tool steel. But EBM technology can do it faster than normal machining and offers the ability to put features within the mold that defy normal machining and erosion technology.
If, for instance, you want a completely closed space within a piece of steel, FFF lets you have it. Why would you want it? One reason could be conformal cooling channels, and a recent verification project done in Sweden for a Volvo engine component showed very clearly how this works and what the benefits can be.
Figure 2. A psychedelic pretzel? No, this is the shape of the conformal cooling channels within the mold for the Volvo part created in the normal course of the structural building process from CAD to metal. |
EBM Put to the Test
The Volvo component used for this evaluation is a fairly complex camshaft sensor housing (Figure 1) molded of PBT filled with 15 percent glass fiber and 15 percent mineral. The molder, Nolato Gota AB (Götene, Sweden), is a long-term Volvo supplier. For this verification project, Arcam made core and cavity inserts of HR-13 tool steel using its EBM system, and the rest of the mold was made by CL-Verktyg AB (Lidköping, Sweden). To enable a fair comparison, CL-Verktyg also made an identical tool using traditional methods.
are created in the normal course of building the pieces from powdered tool steel—no special steps required—while the other tool has straight drilled cooling channels. The two tools run side by side to enable continuous benchmarking.
For the toolmaker, the production lead time was reduced by a third, from 15 weeks to 10. For the molder, the conformal cooling channels yielded a productivity increase of 25 percent. Compared with the traditionally made tool, the cooling time of the Arcam tool is reduced 40 percent, from 25 to 15 seconds. This translates to a reduction of 20 percent, from 50 to 40 seconds, in the overall cycle time, and on the bottom line it means a cost reduction of about 5 percent—an amount deemed significant by all participants.
Flying Colors
Lars Staaf, a senior purchaser at Volvo, says that the technology can make a real difference in quality and throughput at an established, cost-driven supplier like Nolato. “The benefits in production rates and accuracy are real, and this method will now be taken in consideration in production of injection molded parts,†he says. Jan Wedebrandt, the project manager at Nolato, adds, “The project clearly demonstrates that Arcam’s CAD-to-metal technology produces tools in first-class tool steel. It brings exciting opportunities for the near future.â€
The project also clearly demonstrates that, as Morgan Larsson, Arcam’s head of R&D, notes, “Conformal cooling in molds adds some very significant value.†He was also pleased that the side-by-side evaluation showed how Arcam’s EBM technology is suitable for production tooling and that it yields benefits in both lead time and cost. The quantity specification for the Volvo parts was 500,000 pieces minimum, which hardly sounds like prototype or short-run parts. The mold’s AISI H-13 steel rings in at 48 to 52 Rockwell C hardness, which certainly sounds like tool steel and not a soft metal or composite.
Arcam’s EBM S-12 System starts with a CAD file of the part or mold received via a standard STL interface. The part is then built up in layers using the powerful electron beam to fuse the powdered metal. The layer thickness is .1 mm and the melting speed is .3 to .5 m/sec, both material dependent. Accuracy is ±.4 mm and the maximum build size is 200 by 200 by 160 mm. The process computer is a PC running Windows 2000 or XP Professional; the physical interface is via Ethernet 10/100.
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