Fused Deposition Modelling (FDM)

Question 1

What is fused Deposition Modelling (FDM)?

Answer 1

• Forms 3D objects from CAD generated solid or surface models wihout the need of tooling (most widely used FDM technology)
• A temperature-controlled head extrudes thermoplastic material layer by layer
• Object is created by depositing melted material in a pre-determined path layer-by-layer

Question 2

Explain the basic process of FDM (6 steps)

Answer 2

1. Filament of thermoplastic build material (1.5mm diameter) is unwouind from a spool and fed into deposition head.
2. In the head, it is heated to just above its melting point and a precision volumetric pump is used to extrude a bead of semi-molten polymer through a nozzle tip.
3. Deposition head can be moved in the X-Y plane to deposit a thin bead of thermoplastic in the required layer geometry
4. A single deposited bead of thermoplastic is calld “a road”
5. Thermoplastic solidifies immediately after being extruded from the nozzle tip (bonded to the layer below)
6. Build platform is then stepped down in the Z direction by one layer thickness and the process is repreated.

Question 3

What are potential control issues concerning FDM?

Answer 3

• Maintaining semi-liquid modeling material just above the solidifcation point is fundamental.
• Temperature of thermoplastic extrusion is controllled to 0.5°C above its solidification temperature
• It solidifies quickly enough upon extrusion to generate “roads” that are : 1. strong enough to be depositied in a controlled way. 2. Able to bond to the previous layer through thermal fusion.
• Entire system is contained within an “oven chamber” which is held at a temperature just below the melting point of the polymer.
• Only a small amount of additional thermal energy needs to be supplied by the extrusion nozzle to casue the plastic to melt (provides much better control of process)

Question 4

What are the three key FDM process variables?

Answer 4

1. Nozzle tip diameter - 0.3,0.4,0.5 and 0.6mm diameter
2. Feed rate of filament material - 5mm/s to 15 mm/s
3. Nozzle transverse velocity - range not published

Question 5

Why are support structures needed in FDM and what are adv/disadv?

Answer 5

• FDM processes require support material to support the geomerty as it gets printed layer by layer (due to orientation)

Adv: prevent the part breaking during printing

disadvantage: increased material cost, increased printing duration, added post processing work, risk of damaging model upon removal.

Question 6

What are the two types of support structures?

Answer 6

1. Break away- supports made from polyester, join the part during the build process, manually broken away during post processing
2. WaterWorks soluble - dissolved in a water based solution in a special unit, allows much finer geometries to be built and finished without damage

Question 7

What are some advantages of FDM?

Answer 7

• Good variety of functional materials available (non-toxic and easy to handle)
• extremely time and cost effective for thin-walled parts
• Material shrinkage is predictable and relatively low (0.13-2mm, good process control)
• clean safe to operate in office environment
• relatively low purchase cost compared to SLA
• low operating costs (low temperature and power)
• low mainteneance costs

Question 8

What are some disadvantages of FDM?

Answer 8

• Process tolerance over entire part is 0.2mm compared to 0.05-0.1 mm for SLA)
• wall thicknesses of 0.8mm or less may not produce good parts
• Temperature fluctuations during production could lead to poor bonding (delamination)
• Part strength is weak perpendicular to build axis (layers effect)
• Increase in part solid volume (layer area) which significantly increases build time

Question 9

Explain FDM vs SLA?

Answer 9

• In FDM, resolution is a factor of nozzle size and the precision of deposition head X-Y movements. In SLA the resolution is primarily determined by optical spot size of laser.
• SLA printers higher resolution and more accurate than FDM printers
• In FDM, weight of upper layers may squeeze layers below, in SLA, parts printed upside down on build platform so no risk to layer squeezing.
• FDM 2-4 times faster and 25% cheaper than SLA
• SLA needs environmentally controlled lab, FDm can operated in office
• FDM is a very simple/robust apparatus, SLA is a laser device with precision optics.