Materials add new options in prototyping

Somos continues to drive the stereolithography market forward with the commercialisation of four new products designed to expand the capabilities of the RP industry.

Somos continues to drive the stereolithography market forward with the commercialisation of four new products designed to expand the capabilities of the RP industry: ProtoGen O-XT 18120, ProtoGen O-XT White 18420, ProtoCast AF 19120 and NanoTool.

The first three of these products, all based on the Somos Oxetane Advantage, expand the range of material offerings for low water-absorbing SL resins designed to perform like ABS - the most widely used engineered plastic in the world.

ProtoGen O-XT translucent (18120) and white (18420) materials deliver extremely high accuracy during builds due to very low differential shrink.

The linear shrinkage for typical unfilled resins ranges in the order of 0.002-0.0035in.

ProtoGen resins, however, exhibit linear shrinkage of less than 0.001in - a value typically only seen in highly filled composite resins.

ProtoGen materials provide considerable processing latitude on both large frame machines and in applications such as master patterns and fit-and-function models.

In addition, ProtoGen parts can be drilled and tapped without breakage, making further improvements in accuracy and design flexibility possible during post-machining.

Because ProtoGen materials produce excellent sidewall quality, less secondary finishing is required to remove layer lines - an extremely valuable cost-savings benefit.

In addition, ProtoGen parts are very easy to sand, making them the material of choice for parts finishers.

Finally, with a heat deflection temperature of 68-74C (standard ABS-like resin values: 45-55C) ProtoGen materials deliver a reduced risk of part warpage in high heat environments, including storage or shipping.

This makes them particularly suitable for producing master patterns for silicone moulding - where their ability to retain a high degree of stiffness in thin sections, or above room temperature, creates more accurately finished cast urethane parts.

ProtoCast AF is another exciting Oxetane Advantage material born out of Somos' effort to help select industries improve their processes via optimised SL resins.

Although WaterShed 11120 has long been an SL material of choice for investment casting applications, Somos research recently revealed that the ash from burnout of typical SL investment cast patterns - which can negatively affect metal castings by leaving pit marks - is largely due to antimony oxide formation which comes from the photoinitiator used in almost all epoxy and hybrid SL resins on the market today.

As a solution, the fully antimony-free ProtoCast AF was formulated.

As an oxetane resin, ProtoCast exhibits low water absorption for high dimensional stability and high green strength for reduced warpage during the resin draining process.

But it is the absence of antimony that gives ProtoCast its most significant advantage for investment casting.

Studies with Express Pattern and foundries have shown the residual ash of ProtoCast AF to be less than 0.01% at 815C, compared with less than 0.3% for WaterShed at the same temperature.

Initial casting trials were conducted by Express Pattern in conjunction with Somos and reported at this year's ICI conference in Milwaukee, Wisconsin.

Markets that will benefit most from this material are those requiring large investment cast patterns such as aerospace, automotive, Formula 1 and other motor sports industries.

Heavily filled with noncrystalline nanoparticles, NanoForm is a composite resin with a flexural modulus of 10,500MPa, a heat deflection temperature of 260C (after thermal post-cure) and linear shrinkage of less than 0.001in.

NanoTool's high modulus and superior sidewall quality make it extremely attractive for applications that require smooth, highly finished parts-such as in wind tunnel testing for Formula 1, rapid tooling for injection moulding, and metal plating for prototyping metal cast parts.

Unlike other composite resins which require more extensive time and care to remove residue, NanoTool parts are extremely easy to clean and finish.

NanoTool's properties also make it an excellent resin for metal plating - a growing application which saves time and money as an alternative to fully metal prototypes.

"The issue of part cleanliness becomes extremely important when plating composite resins, because the RP parts will not metallise completely if residue is present", says Sean Wise, President of RepliForm.

DSM Somos, in conjunction with RepliForm, is currently studying the metal plated strength improvements achievable with NanoTool.

To date, flexural modulus values of better than 55GPa have been reached based on a metal-to-resin volume ratio of 1:4.

The technology, coined MC2, is sure to make life easier for prototyping metal parts.

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