Archive for the ‘Deposition’ 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.

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Jetted Photopolymer (JP)

05/20/2009

JP printing is identical to InkJet printing, but instead of using thermoplastic, it dispenses photosensitive liquid. The print head contains a UV light; after a layer is put down, it is cured with the UV light. This eliminates the need for a separate curing process and is very accurate.

Advantages and disadvantages are similar to Inkjet printing.

Inkjet and MultiJet Printing

05/20/2009

Inkjet printing is almost identical to FDM, however the plastic is held in a liquid state inside of the machine before being dispensed. As soon as the print head dispenses the liquid plastic, it cools and solidifies on the model. This process makes for very smooth finishes, however the print time is slow.

The print head on most inkjet printing machines consists of two dispensers; one for the thermoplastic, and the other for wax that acts as a support material.

Another feature typically included in this technology is a plane milling stage. Between each layer a plane is rolled over the model, cutting extraneous material off of the top layer. This ensures that the layer is precisely flat. This has something to do with the slow print speed.

This method sees some of the smallest layer thicknesses of any of the technologies: as small as 0.0005 inches per layer.

MultiJet is indentical to inkjet, but with many print heads simultaneously dispensing plastic. 3D Systems manufactures MultiJet machines (though they call them Pro-Jet) which have several hundred nozzles.

Advantages?
• Very accurate.
• Smooth surface finish.
• Supports are wax and can therefore be melted away.
• Quick print time for MultiJet.
• Milling stage means better accuracy.

Disadvantages?
• Slow print time for Inkjet.
• Supports must be melted– a separate process in itself.

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.

Fused Deposition Modeling (FDM)

05/20/2009

FDM is gaining ground in the printing world. It is arguably the most “printer-like” of all methods; it consists of a moving bed (Z-axis) and a print head (X-axis and Y-axis). The print head has a heating element in it; thermoplastic is forced into the print head, melts, and is squeezed out, not unlike toothpaste. The bed is usually cooled so that the plastic hardens soon after being placed down. Again, this is a layer by layer process; some systems can print layers as small as 0.178 mm.

From custompart.net:

Since it is squeezing out spools of plastic filament, there are different types of plastic available to print with. ABS is the most popular; if you are not familiar, ABS plastic is what LEGOs are made of. It can also print PPSF and PC plastics.

Stratasys, the developer and leading manufacturer of FDM technology, offers FDM systems that not only print parts as large as 36x24x36, but print moving parts. The machine can differentiate between separate objects within a CAD file, allowing you to print, for example, a system of gears that works right out of the machine. You can print objects within other objects, etc.

Support structures are necessary, but the print head contains a second element for extruding support material. Stratasys’ FORTUS systems (expensive) contain a bed of water soluble liquid that you place the models in after they print; the liquid disintegrates all support material from the model.

Advantages?
• ABS plastic means durable and functional models.
• Several different material options.
• Prints moving parts.
• Separate support material with removal system.

Disadvantages?
• Slow print time compared to some other methods.
• Rougher surface finish than SLA.