Rapid metal

Manufacturing Engineering, Nov 2003 by Waurzyniak, Patrick

Rapid manufacturing and rapid tooling for metal parts gain support

Speeding manufacturers' time-to-market with rapid manufacturing and rapid tooling techniques remains an elusive goal. Originally a tool for designers and a replacement for the model shop, rapid technology today is producing larger, stronger parts from metal alloys and plastics.

As manufacturers get better at making parts and tools quickly, rapid technology has enabled production of metal and plastic parts in small quantities, as well as producing larger components than were possible a few years ago. Recent advances in approaches for rapid manufacturing, tooling, and rapid prototyping with metal-based materials show promise that may eventually have an impact on the rapid prototyping industry.

Defining rapid manufacturing can be difficult, and some longtime rapid prototyping industry observers contend that rapid manufacturing hasn't taken off yet. But that may be about to change, as many rapid prototyping systems are being used successfully in rapid production of end-use parts.

To date, some rapid tooling techniques have been successfully deployed in the automotive industry, such as the process developed by the Manufacturing Systems department of Ford Motor Co.'s (Dearborn, MI) Scientific Research Laboratory (see the article "Rapid Tooling Technology From Ford Country" in the November 2001 issue of Manufacturing Engineering.) Ford has been licensing the technology to companies for producing dies, punches, and other tools by a thermalspray process it developed by which a ceramic master of the working die surface is spray coated with molten metal, then backfilled with epoxy to create a working die.

Traditional rapid prototyping approaches employ several additive prototyping processes, such as stereolithography (SLA), selective laser sintering (SLS), fused deposition modeling (FDM), laminated object manufacturing (LOM), and 3-D printing, that all typically produce rapid prototypes created from various types of plastics, thermoplastics, photopolymers, and liquid resins. Most additive technologies used in rapid prototyping, rapid manufacturing, or rapid tooling are layer-based processes that create plastic or metal prototypes and small-run production parts directly from 3-D CAD models. They offer an alternative to subtractive processes for parts production with metal-removal methods using CNC metalcutting.

Direct metal technologies that generally use powdered metals for rapid tooling and manufacturing have recently gained favor among manufacturers. In August, several metal-based rapid technologies were outlined in papers presented at the Direct Metal Systems in Manufacturing technical forum sponsored by the Rapid Prototyping Association of SME (RPA/SME). The program detailed several metal-based rapid technology efforts either currently offered or under development at companies including ArCam AB (Molndal, Sweden), EOS GmbH (Munich, Germany), POM Group Inc. (Auburn Hills, MI), the ProMetal division of Extrude Hone (Irwin, PA), Solidica Inc. (Ann Arbor, MI), 3D Systems (Valencia, CA), and the US Army's Tank-automotive and Armaments Command (TACOM, Warren, MI).

In contrast to the plastics, thermoplastics, and resins used in rapid prototyping processes, most of the metalbased rapid processes involve powdered metals and other metallic feedstock, including binder-coated powder, wire, flat wire, ribbon, foil, sheetmetal, and atomized spray, according to Vito Gervasi, Milwaukee School of Engineering, who presented at the Direct Metal Systems forum. Gervasi notes that the list of creative direct metal processes continues to advance, with a growing list of players and machines in service. Capable of producing metal parts to more than one meter in size, Gervasi says that a number of the processes are no longer lab curiosities, and are in use by industry.

Among these technologies, the POM Group's patented Direct Metal Deposition (DMD) process features a laser-based additive metal process in which POM claims to produce fully dense metal parts of 99.8% density, which is slightly better than the 99.6% density of 'handbook grade' metals from castings manufacturers, according to Dwight Morgan, president of The POM Group Inc. (Auburn Hills, MI). Originally developed at the University of Michigan (Ann Arbor, MI) by POM co-founder and CEO Jyoti Mazumder, the DMD process isn't considered rapid manufacturing by Morgan, who instead refers to the process as "direct manufacturing," because DMD makes parts directly from powdered metal.

"If we were to take 10 of the most prominent names in rapid prototyping and ask us all to write down the definition of rapid manufacturing, I'm not sure that you'd get a consensus, but I'm sure if you asked what rapid prototyping is, you would get a consensus," says Morgan. "That has to do with the maturity of that particular industry, and the fact that people know what rapid prototyping is.

"My definition of rapid manufacturing is using a rapid prototyping technology as the precursor to a pattern used to build something in the future," Morgan adds. "In other words, an SLA, SLS, or LOM model is used to create a seed part, which you would then use to make tools. Using that definition, I would definitely concur that, on a commercial perspective, no one is out there using rapid manufacturing, because it's not yet an economically viable process. If you think about rapid prototyping as a process that is quite cost-effective when used to make a rapid prototyping part, and to then convert that into the pattern, you need to put a lot of time into it to perfect it, and then you begin the manufacturing process. The time and cost penalty is one of the drawbacks involved in using rapid manufacturing.