Editorial Feature

Rapid Prototyping - Photolithography and Stereolithography

In addition to quality and cost, time to market is becoming an increasingly important factor in a product's success.  A major contributor to product development cycles is the time needed to produce prototypes.  Further, in markets where customers are demanding individually tailored components, the cost and time to produce tools or moulds can be considerable. 

Rapid Prototyping (RP), also known as Solid Freeform Fabrication (SFF) processes help to overcome these problems In general the processes build complex shapes through additive processes, producing components without the use of tools.

Photolithography

The use UV or laser light to selectively cure resin is the basis of the Stereolithography Apparatus (SLA), a commercial photolithography RP system.  The SLA machine produces plastic prototypes by photopolymerisation of a liquid monomer.  The 3D computer based component design is divided into 0.25mm thick layers.  The laser is then scanned onto the surface of the monomer, drawing the cross section of the component.  Once this resin is cured, the platform drops 0.25mm into a vat filled with monomer.  The liquid monomer flows over the layer and the second layer is scanned.  The procedure is repeated until the part is finished.

Schematic of a photolithography process.

Figure 1. Schematic of a photolithography process.

Stereolithography Apparatus

The photocured resin can be used as a binder to build ceramics with photolithography.  The ceramic green shape typically consists of 40-55% ceramic powder and 45-60% polymerised binder (typically UV curable acrylamide monomer).  The binder is then burnt out and the body fired to produce a dense ceramic object.  Several ceramic materials, including Al2O3, Si3N4, and SiO2, have been used to make cores or shell moulds for investment casting.  Hydroxyapatite has been processed to make bioceramics. 

In the case of Al2O3 parts, good surface finish and fine detail were produced.  Further, no cracking, distortion or delamination was seen during processing.  The disadvantages are that products require support structures growing in the resin, components may warp and resin handling needs care as some resins are toxic

Source: CERAM Research Ltd

For more information on this source please visit CERAM Research Ltd.

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