66.6 FUSED DEPOSITION MODELLING (FDM)

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Developed by Scott Crump, and Stratasys has been selling the machine since 1991.

The concept is that material is heated and then in controlled quantities deposited directly on previous layers. Eventually layers are built up to complete the entire part.

The materials are available on spools of 1/2 mile in length, at costs from $175(US) to $260(US). The filaments are 0.05"

As usual the .STL file is sliced into layers, and the slices are used to drive the machine.

The key to this method is an extrusion head,

- the material is fed into the head

- the material is heated until melting

- the material is then extruded from the tip in controlled quantities

- the material is wiped on the previous layer

The extrusion head is moved about the table with an x-y positioning system to deposit material on each layer

The platform the part is on drops when a layer is complete to allow the addition of a new layer.

materials include

investment casting wax

ABS

polyester

elastomer

slice thickness is 0.002" to 0.03"

material changeover requires a few minutes of "flushing-out'

Advantages,

- a good variety of materials available

- easy material change

- low maintenance costs

- thin parts produced fast

- tolerance of +/- 0.005" overall

- no supervision required

- no toxic materials

- very compact size

- low temperature operation.

Disadvantages,

- seam line between layers

- the extrusion head must continue moving, or else material bumps up

- supports may be required

- part strength is weak perpendicular to build axis.

- more area in slices requires longer build times

- temperature fluctuations during production could lead to delamination

selected specifications for the FDM1000 are,

Approximate costs are,