Additive Manufacturing (AM), aka 3D printing, is the fastest growing manufacturing process in the world today. One of its many advantages is the ability to quickly manufacture a custom product without the expensive set-up costs required for tooling for mass production. Another is the ability to produce more complex, high strength, custom parts, often without sub-assembly or subsequent machining operations.
AM is made up of many different types of operations which range from simple overlay printing, with liquid or filament plastic feed material, for example, to particulate feed ranging from plastics to ceramics to metal powders. Metal Powder AM is commonly known as laser welding or laser melting. Laser welding is now of great interest to, and investment by, the US Department of Defense (DOD). Their motivation is to achieve the ability to manufacture custom replacement repair parts for damaged military equipment, on immediate demand, as close to the point of need, often near the front lines of combat, as possible. This capability would lower the expense of manufacturing large quantities of spare parts, and shipping them to be inventoried at various sites around the world.
The Laser Welding Process
A rotating mirror follows a CAD pattern directing a laser beam onto the top powder layer, melting the powder layer on top of the previous layer of the part. All particles not melted onto the part are scraped off while the next layer is loaded. Attempts are made to successfully re-use the un-melted particles for as many cycles as possible before they show too much wear to meet size and shape criteria. It can take 10 pounds of metal powder to produce a 1-pound part if the left-behind powder can’t be recycled.
Parts can be extremely durable as well as complex. Parts are made in one structural piece requiring no sub-assembly. They are also much more customizable on demand. One machine supplied with a number of different available CAD programs can be used to make individual custom parts on demand. This helps manufacturers save the large expense of tooling to mass produce, ship and inventory a single part type.
Metal powders are used as feed material to laser welding, which need to meet tighter specification tolerances then most other metal powder applications do. The laser melting process is less tolerant of broad size distributions, less than perfectly spherical shapes, and contaminants, than the more traditional powder metallurgy compaction and sintering processes are. Only atomized metal powders, rather than direct-reduced powders, can be used because of their much more spherical shape.
Controlling the Quality of Metal Powders
The metal powders industry and users of metal powders in the powder metallurgy industry have historically controlled size distributions and met quality requirements as measured by laser diffraction particle characterization technology. The additional demand to measure powder sphericity and identify contaminants of atomized metal powders for laser welding requires image analysis technology in addition to laser diffraction, to meet these additional specifications.
There is one commercially available analyzer system which measures particulate samples using both laser diffraction and image analysis technologies, simultaneously on the same sample. Microtrac’s PartAn 3D uses size distribution measurement technology for metal powders. The PartAn reports sphericity and identification of contaminants useful in laser welding process quality control. Want to learn more about this instrument?
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