Resins contribute to living history

Rapid modelling and rapid prototyping materials play an important role in helping the Smithsonian Institute's National Museum of American History "bring history to life".

Rapid modelling and rapid prototyping materials play an important role in helping the Smithsonian Institute's National Museum of American History "bring history to life".

Recent examples include miniatures of a 200-year-old American home and a replica anti-slavery medallion.

"Within these walls", a current Smithsonian exhibition, revolves around a 200 year-old house that was moved from Ipswich, Massachusetts to the second floor of the museum.

The exhibit focuses on how the lives of five families that lived in the house from 1757-1945 reflected the great changes and events spanning American history including colonial times, the American Revolution, slavery and abolition, immigration and industrialisation, and World War II.

As part of that focus protoCAD, a rapid model making and engineering firm in LaPlata, Maryland, was subcontracted to recreate three scale models of the house, suggesting how some of the rooms might have been used in the 1760s, 1840s, and 1940s.

The models protoCAD created were on a scale of 1:24 of the actual house that is on display.

These models are not only on exhibit for the general public, but are embedded with Braille for use by sight-impaired persons.

Scale models were produced in four stages.

First, the Smithsonian provided protoCAD with a set of hand sketches and photographs.

Second, using those documents, protoCAD recreated many of the architectural details using Pro/Engineer (Pro/E) software.

"There was a significant degree of difficulty at this level of the process", says Brian Edwards, Design Director for protoCAD.

"We were faced with the challenge of replicating extensive details at a very small scale.

Moreover, we were committed to the task of being true to historic accuracy, both in cosmetic and functional specifics of the building.

It was necessary to accommodate diverse geometries in modelling not only the main structure but the intricacies of doors, windows and other sub-components of the house".

Third, approved Pro/E electronic 3D CAD files were used by protoCAD's stereolithography machine to create the actual models.

Once the Pro/E files were available it required only several hours to translate the key architectural details into stereolithography parts.

To ensure that proper physical attributes were achieved, protoCAD selected as its rapid modelling material, a DSM Somos 7100 ProtoFunctional resin.

According to Brian Edwards: "Somos ProtoFunctional materials are a leading choice for rapid prototyping applications because they replicate the performance parameters of production materials.

For our purpose in rapid modelling this particular Somos grade was ideal because of its strength.

We knew it would be ideal in its ability to act as a master pattern for tooling".

Fourth, the scale models went through a final step where they were used in a rubber tooling process to create multiple copies.

Brian Edwards summarises the project in these words: "We are very pleased with the results of this effort.

There is nothing that compares with providing museum visitors a realistic visual and hands-on perspective of living history.

The use of rapid modelling and the reliability of the materials used to create these models, helps ensure the preservation of historic accuracy in meaningful three-dimensional forms.

Moreover, new materials and processing technology enabled us to complete our portion of the project within a very short turnaround time".

A second project, also co-ordinated by protoCAD on behalf of the Smithsonian Institute, featured an objective that was opposite from the challenge of producing miniature scale models.

In this instance a small object an antislavery medallion, created circa 1787 was enlarged so that the public could easily see the detail involved and for the sight impaired to touch.

Originally designed as a jasperware cameo made at Josiah Wedgwood's factory in Staffordshire, England, the medallion features a motto adopted by the British Committee to Abolish the Slave Trade in 1787: "Am I Not a Man and a Brother?".

An active abolitionist, Wedgwood sent one of these cameos to Benjamin Franklin in 1788, hoping to promote American support for the antislavery cause.

The medallion is part of the "Protest and conflict" collection, which highlights other items that were used in protest during different parts of American history.

"This piece is approximately the size of a half-dollar", say's protoCAD's Brian Edwards.

" The detail of the medallion is difficult to see locked away behind glass at the Smithsonian.

An enlarged replica needed to be made in order to emphasise its features and for it to be handled by the public.

The medallion was scanned with 3D digitising equipment creating surfaces that could be exported into Pro/E.

The surfaces were converted to a solid in Pro/E and further edited before being scaled up".

In this application, as with the miniature house models, a replica was produced using a stereolithography machine.

DSM Somos 7100 ProtoFunctional resin was again used because of its ability to achieve rigid, undistorted, high-accuracy parts.

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