01 Mar 3D Printing Technology
There are three major rapid prototyping techniques for making plastic parts fast; layer building, low-pressure molding/casting, and machining. Each has its advantages and drawbacks, depending on how you intend to use the part. Let’s start with the various layer-building processes.
Layer built processes create a single part by building up a series of 2D cross-sections. Different methods require different layer heights and have different means of supporting the layers that are hollow underneath. Of course, one advantage of this process is that parts can be made that could never be fabricated by traditional production methods, such as hollow spheres or even an assembly of multiple integrated parts in a single build that come out of the machine assembled (such as the links of a chain).
| Type |
Layer Thickness |
Pros |
Cons |
| SLA – UV laser and resin | 0.001 – 0.006″ | High resolution, optically clear parts, easy to finish | Can be brittle |
| SLS – Laser and powder | 0.004 – 0.006″ | Strong parts, real materials(nylon, Al) | Rough surface finish |
| FDM – hot glue gun | 0.005 – 0.010″ | Strong parts, real materials (ABS, PC) | Resolution is only okay, difficult to finish |
| Polyjet – 3D inkjet printer | 0.0006 – 0.001″ | Very high resolution, fastest process, flexible parts | most brittle/poorest material properties, limited part size |
SLA (Stereolithography) – Liquid photopolymer (resin) is cured with a laser in layers. After each layer is laid down, the platform lowers further into the resin by the layer thickness, and the laser cures the next layer of material. The part is then post cured with UV light. SLA was one of the first additive rapid prototyping technologies and is still the gold standard. It is good for general pupose form and fit protoypes and when parts require high resolution, smooth surface finish, or optical clarity.
A part manufactured by SLA (Photo Credit: Key Tech)
SLS (Selective Laser Sintering) – SLS builds layers similar to SLA, except instead of using UV light and a liquid photopolymer, a powdered material (real plastic or metal) is heated and fused together by a laser as a series of 2D cross-sections. SLS is a good choice for functional testing with real materials when smooth surface finish and fine resolution are not required.
A part manufactured through SLS (Photo Credit: Key Tech)
FDM (Fused Deposition Modeling) – Similar to a precision hot glue gun, long strands of real plastic material (ABS, PC, and others) are fed into the nozzle, melted, and deposited in a series of 2D cross-section layers. FDM layers are generally the thickest of the various processes, which limits feature size, but it usually provides better strength and robustness in comparison. FDM is good for prototyping functional parts without small features where surface finish is not important.
A part manufactured through FDM (Photo Credit: Key Tech)
Polyjet – Using inkjet printing technologies, UV-curable materials are effectively “printed” on top of the previous layer to create a 3-dimensional part. Polyjet can produce high resolution parts with decent surface finish, is generally cheaper and faster than most other processes, and is one of the only additive prototyping processes that can produce flexible parts. It is a good process for small parts requiring good resolution and a decent surface finish, or when flexible parts need to be prototyped.
A part manufactured through Polyjet (Photo Credit: Key Tech)
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