19-05-2012, 05:05 PM
DIRECT METAL DEPOSITION
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With new technologies evolving almost every week, it was just a matter of time before
someone would experiment by blending a number of technologies to come up with something
new. POM, Inc., (Precision Optical Manufacturing) of Auburn Hills MI combined CAD, CAM,
lasers, sensors, and powder metallurgy to develop the Direct Metal Deposition (DMD) process. It
might well be the PUT-ON tool many of us wished we had after making machining errors during
our early years in the trade.
Direct Metal Deposition (DMD)™
DMD is a form of rapid tooling process that makes parts and molds from metal powder
that is melted by a laser, and then solidified in place. This process closely resembles
conventional rapid prototyping processes (material processed by laser under computer control)
but differs in that metal powder, and even tool steel, can be melted rather than plastic polymers.
DMD allows the production or reconfiguration of parts, molds and dies that are made out of the
actual end material, such as tool steel or aluminum. It always produces a new part or part
reconfiguration directly from a CAD drawing.
DMD is the blending of five common technologies: lasers, computer-aided design
(CAD), computer-aided manufacturing (CAM), sensors, and powder metallurgy. The resulting
process creates parts by focusing an industrial CO2 laser beam onto a flat tool-steel workpiece or
preformed shape to create a molten pool of metal.
• A small stream of powdered tool steel is then injected into the melt pool to increase the
size of the molten pool.
• By moving the laser beam back and forth, under CNC control, and tracing out a pattern
controlled by a computerized CAD design, the solid metal part is built one layer at a time.
• With this process, the molten pool cools and solidifies rapidly producing metal parts of
superior quality and strength with no material waste as in conventional machining.
• The parts have consistent, fine microstructures, with superior quality and tool strength.
• More importantly, with DMD, the metallic composition can be altered by injecting
different types of metal powders into the melt pool.
FROM CAD to STEEL
A typical job starts on POM's secure FTP Web site (www.pom.net), where customers
post CAD files.
• Engineers download and edit the CAD file, adding machining stock or hard-face surface
geometry. The updated solid CAD model is then sliced and tool paths, identical to that
used for CNC machining, are generated.
• Information is downloaded to the overhead three-axis gantry machine similar to a CNC
setup with travel in the X, Y and Z axes.
• The process uses a variety of metal powders and metal matrix composite materials,
including conventional tool steel alloys and special metals.
• Cooling rates are fast, resulting in a very fine-grain microstructure.
• Hard faces are applied within an inert-atmosphere box, filled with pure argon, that
surrounds the workpiece and the machine nozzle.
The Big Three of Manufacturing
DMD for the processing of molds, dies and prototype parts provides is thought be the Big
Three of Manufacturing:
• Speed - as in faster product to market. A study performed by the National Center of
Manufacturing Science indicates die production time can be reduced by 40% with DMD.
• Economy - lower tooling costs due to factors including the reduction of labor and capital
equipment costs.
• Quality - the parts produced are generally .001 in. oversized for a quick clean-up.
The DMD Process
A CNC-controlled overhead gantry is used to control a nozzle and focusing optics
associated with a C02 laser according to CAM tool path data associated with the CAD model
geometry.