Archive for the ‘Powder’ Category

Laser Engineered Net Shaping (LENS) / Direct Metal Deposition (DMD)

05/20/2009

LENS and DMD are the same technology. LENS/DMD is used to print parts out of metal using a print head (as opposed to the DMLS process). The print head moves in all three axes. A laser is focused through the print head and metal powder is injected into it. The powder is sintered as it exits the head and is put down on the model.

An inert shroud gas is used inside of the print head to shield the metal from oxygen (so that it sinters correctly and can be controlled more accurately).

from http://home.att.net/~castleisland/lens.htm:

These technologies have been utilized to fabricate and repair injection molding machines, and to create specialized parts for aerospace applications.

LENS/DMD is limited at the moment because support structures would have to be made out of the same material as the model, which makes them difficult to remove afterwards.

Advantages?
• The printed objects usually have desirable metallurgical properties and are completely dense.
• Can be used not only to fabricate but to repair parts (something DMLS is not capable of doing).

Disadvantages?
• Severe overhangs are an issue because of a lack of a different material for support structures.
• Objects usually require some post-print machining.

Direct Metal Laser Sintering (DMLS)

05/20/2009

DMLS is identical to SLS, except that the machine sinters metal powder instead of plastic powder. The model does not require a finishing stage.

According to custompart.net, DMLS is capable of printing steel alloys, stainless steel, tool steel, aluminum, bronze, cobalt-chrome, titanium, and ceramics.

One of the most common uses for DMLS is “rapid tooling,” which is the production of specialized tools that go in machines; these tools may be specific to one application in one machine and therefore aren’t produced in mass quantities. The cost of traditionally producing one of these pieces (by CNCing, casting, etc.) is extremely expensive and wasteful in comparison to printing it. DMLS has proven successful for making these sorts of parts.

Moldmakingtechnology.com has an excellent article on a 2003 collaboration between two companies (Morris Technologies and Extreme Tool & Engineering) testing the pros and cons of using DMLS to make molds. They were somewhat disappointed with the results.

Advantages?
• No waste is generated and little energy is used, as compared to traditionally machining an object. This is great for prototypes and one-offs.

Disadvantages?
• In Morris and ET&E’s test, the mold they printed had a considerable amount of warpage and required additional machining, as well as polishing. Bottom line: not a good solution for moldmaking.

Three Dimensional Printing (3DP)

05/20/2009

The name is a bit confusing, since it doesn’t give any insight into the process, but 3DP is the term used to describe  Z Corp’s technology, which they employ in their line of ZPrinters.

The machine uses a bed of powder and a print head. The print head dispenses a plastic resin which binds to the powder and solidifies it. It spreads on a layer of powder with each new print layer.

Like SLS, the unsolidified powder stays in the workable area so support structures are unnecessary.

Z Corp’s claim to fame on their printers, though, is their ability to color the resin as the machine prints. This means that one model can be printed in any combination of colors; it is even precise enough to print text into an object. Taken from the Z Corp website:

In addition, it can print moving parts the same way that FDM can. The quality of the finished models is rough compared to other technologies, though the parts can be machined afterwards.

Advantages?
• 24-bit color system…
• Prints moving parts.
• No supports necessary.
• Relatively fast printing time.

Disadvantages?
• Rough finish.

Selective Laser Sintering (SLS)

05/20/2009

Selective laser sintering is similar to SLA. It uses a laser, but instead of photosensitive liquid, the laser heats a bed of thermoplastic powder. It sinters the powder, fusing it into larger chunks, again in a layer by layer process.

A roller first rolls a thin layer of powder onto the bed; the laser traces a cross section of the model, and when it finishes the bed moves down one layer and the roller rolls another layer of powder on.

From custompart.net:

To speed up the sintering process, the whole workable area inside the machine is heated up to just below the melting point of the plastic. This way the laser does not need to be as powerful and can move quicker through each layer.

Advantages?
• This method uses material similar to thermoplastic, so the models are rigid upon completion.
• A major advantage is that support structures are unnecessary; since the unsintered powder isn’t removed until the model is finished, it provides support.

Disadvantages?
• This process is not as accurate as SLA. Since it is difficult to control exactly how much powder gets sintered, models often come out grainy or with excess plastic on them.
• The models are also porous, so some sort of varnish is necessary to seal and strengthen them.
• The workable area must be cooled down when the model is finished, which, according to some companies that use SLS technology, can take up to two days.