Stereolithography progresses beyond prototypes

Richard Wooldridge of Ford Europe and Ali Siblani of Sibco comment on the existing benefits and future possibilities of rapid manufacturing.

Over the past 25 years, the Ford Technical Centre (Dunton, United Kingdom) has acquired a central role in the production of prototypes for Ford's global R and D network.

The multi-billion dollar centre houses the complete spectrum of free from fabrication technologies, including metal, sand and plastic selective laser sintering, fused deposition modelling (FDM) and layer object manufacturing (LOM).

The first free from fabrication stereolithography (SL) machine was installed in the late1980s.

Stereolithography is a layer additive prototyping technology based on the use of photopolymer liquid resins which solidify when exposed to UV light.

Fast and accurate, the window of opportunity allowed by stereolithography, as with most manufacturing technologies, was limited mainly by the materials.

Many engineers may recall the processing deficiencies of the first generation of acrylic based resins as well as the fragility and lack of long-term dimensional stability of the finished parts.

Recent advances in materials technology, most significantly the launch of the Somos range of ProtoFunctional resins, have helped to dramatically expand the process' range and utility.

Throughout these developments, engineers at Ford Dunton have been advised and supported by Sibco Incorporated, one of the world's leading rapid prototyping materials suppliers and value-added maintenance and service providers.

The Sibco partnership provides one-stop expert solutions for Ford's complete range of free from fabrication needs, including on-site technical support, and just-in-time delivery of materials.

With Sibco's support, Ford has been able to successfully address the two key challenges faced by prototyping departments: the optimisation of machine performance and the identification of materials which provide the characteristics essential to a range of both aesthetic and functional prototypes.

As a result, Ford engineers now benefit from a more economic utilisation of Dunton's in-house free from fabrication capabilities.

The company as a whole benefits from a range of functional, high quality, accurate and dimensionally stable prototypes which can be produced and shipped at short notice for both aesthetic evaluation and dynamic testing.

Alongside low viscosity, high humidity and temperature tolerance, each family or series of Somos resins currently used by Ford engineers at Dunton offers a distinct set of mechanical and materials properties, closely mimicking those of key engineering plastics.

Launched in December 2000, Somos 9120, a particularly resilient and stable resin which replicates polypropylene's tensile strength, elongation at yield and appearance has been selected by Ford engineers at Dunton for a range of prototypes, including a series of particularly complex and filigree air intake grills as well as clips and fittings, brackets and interior trim panels.

Large single-piece component prototypes such as dashboards, which would normally break under their own weight when made from alternative stereolithography resins, have also been successfully produced using Somos 9120.

The resin's physical characteristics, chemical resistance and humidity tolerance make a significant contribution to the level of accuracy which can be achieved, as well as to the long-term dimensional stability of the finished component.

In addition to Somos 9120, Ford engineers at Dunton have also installed the Somos 10120 WaterClear resin, first introduced Autumn 2001.

The glass-clear optics of WaterClear facilitate all forms of fluid and gas-flow analysis, including engine related development work and dynamic testing, frequently at elevated temperatures.

Alongside optical clarity, which also makes the resin suitable for a range of transparent components and complex assemblies, WaterClear mimics a range of key engineering plastic properties, including the flexural strength and modulus of polycarbonate, the notched strength of nylon 66 and the tensile strength of ABS.

The transparent appearance of WaterClear may be modified in a secondary step for colour tint.

The potential for free-from fabrication technologies is essentially unlimited, albeit dependent upon customer focus and close co-operation along the development chain.

The partnership with Sibco Incorporated has already enabled Ford engineers at Dunton to make many significant advances in free-from fabrication technologies, including the optimisation of SL processes, not only for prototypes but also for direct tooling.

In what many choose to refer to as the "third industrial revolution", many believe that stereolithography is now ready to graduate from rapid-prototyping to full "rapid manufacturing" status.

Stereolithography is a layer additive rapid-prototyping process based on the use of photopolymer liquid resins which solidify when exposed to UV light.

A software program transfers the designer's 3D CAD model into an electronic file for stereolithography machines (STL format), composing the information into thin cross sections or layers.

A laser beam then traces each layer onto the surface of a vat of photopolymer resin, building the part in repeated layers until a solid replica of the original CAD model is completed.

DSM Somos has commercialised an entire range of ProtoFunctional resins to respond to the needs of new product development and industrial design.

Among the newest ProtoFunctional materials to be launched is the Raven 7600 series which creates dark colored, rigid prototypes with high humidity and mechanical resistance; WaterClear 10100 series, the industry's first transparent, tough and durable resins; and the Somos 9100 series which allows material properties similar to polypropylene, with superior mechanical memory.

Each family of Somos photopolymer epoxy resins is comprised of materials specially formulated and optimised for the variety of stereolithography platforms commercially available: Somos XX00 resins are for use in argon ion laser systems; Somos XX10 for helium cadmium laser systems; Somos XX20 resins for platforms utilising solid-state laser systems.

DSM Somos also offers materials for selective laser sintering and is the first manufacturer of powder elastomeric polymer (Somos 201) that can be sintered to produce highly flexible parts with "rubber like" characteristics.

Product datasheets for the entire line of DSM Somos material technologies are available on the company website under "downloads, product datasheets".

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