Rapid modelling materials: from track racers to the city

Paul Boughton

The latest rapid modelling materials are helping automotive engineers design everything from super cars to city cars! Gino Ceccopieri reports on the latest material applications.

Time to market schedules are increasingly tight for design engineers in all the world's manufacturing industries, but nowhere more so than in global automotive industry.

Here time is money and it is critical to be first to market with the latest design innovation or the latest model. Concept modelling and styling materials play a crucial role in achieving this and the latest materials are even more versatile, durable and totally compatible with CAD technology and CNC milling techniques. This is all helping to further reduce design and development cycle times from several months to just weeks.

Materials that are now widely used by automotive engineers because of their diverse physical properties and characteristics are modelling pastes and tooling boards. In fact, the use of Epoxy boards in modelling vehicles is now so widespread that one of the leading suppliers, Huntsman Advanced Materials has decided to invest in new production facilities within Europe. The new plant will be based in Germany and is expected to start supplying the market by end 2005. Once fully operational it will more than double Huntsman's current epoxy board production capacity.

Tooling boards and modeling pastes have both recently been used in the development of new concept models for two very different automotive markets – a racing car for the international GT circuit and a micro car for the city dweller.

Two-seater sports car

RenPaste Seamless Modelling Paste (SMP) from Huntsman Advanced Materials has proved instrumental in the design and development of the latest model for race and GT car specialists, Picchio, in Italy.

Based near Teramo in Central Italy, Picchio design and manufacture highly specialised racing cars for the European and US super-car circuits. Picchio previously used SMP on their highly successful Daytona Prototype racecar in 2003.

The company’s latest model – the highly innovative CN2 Light – is a two seat open top vehicle that combines super streamlined design with a range of new safety features. The CN2 Light is the first car in the Prototype Sports vehicle category to comply with the latest FIA safety regulations for crash tests.

When developing the CN2 Light prototype, Picchio's engineers tested a range of rapid prototyping materials. They eventually specified the SMP RenPaste SV/HV 4503 epoxy paste from Huntsman Advanced Materials as the most suitable for this demanding application. This brown paste is machine applied in layers up to 40mm thick. It has a density of 0.8g/cm3, a Shore Hardness of 60D and a coefficient of thermal expansion of 55-60 10-6  K-1 .

The SMP was used to make the model of the car body. This comprised a range of separate complex, highly styled components including all the front, rear and side panels and front and rear spoilers, which provide the critical streamlined balance for the car.

To produce the full sized prototype, a slightly undersized model of the car was milled, using CAD design data, from an expanded polystyrene block. Each individual component part was then covered in a 30mm–40mm thick layer of the paste, dispensed through a meter/mix machine.

These SMP models were all cured at room temperature for two days but those with the most irregular contour were also post-cured at 50°C for 4–6 hours as an extra precaution.

The SMP models were then CNC machined to the exact dimensions for the car body parts, with just minimal hand finishing required. These models were subsequently used to build the fibreglass moulds from which the GRP prototype parts were produced.

“In this new project, we capitalised on the experience gained with the original Daytona Prototype SMP model,” explained Guido Pandoli, Head of Project Design at Picchio. “This enabled us to improve the whole building and production process.

“This mainly affected the milling procedures, paste application and the post-curing of the models. By maximising resources, we were able to produce the first CN2 Light car body, from CAD data in just 12 weeks.”

“We have also achieved an unprecedented surface quality finish and level of design accuracy with this model,” added Mr Di Pietrantonio, Managing Director at Picchio. “With this vehicle we not only wanted to produce the prototype of a radical new racing car range but also make a definitive style statement which will be reflected in the road car version, in 2006.  This will be the first road car designed by Picchio.”

Tooling boards

Huntsman Advanced Materials tooling boards have recently been used in the development of a new Italian micro-car – the k200.

The ATR Group, an Italian consortium comprising nine leading companies involved in the research and production of carbon fibre advanced composite structural parts and components, is behind the k200 project
SLC, part of ATR Group, worked on the k200 model, specifically designed for the niche micro-car market. Made entirely from composite materials, as a result, the k200 is a super-light vehicle.

Drawing on their wide expertise in composite materials, ATR Group technicians specified Huntsman Advanced Materials’ RenShape BM 5055 epoxy tooling board to build the models for ten carbon fibre moulds of the chassis, all the bodywork and interior components of the k200.

RenShape BM 5055 epoxy tooling board is ideal for hand laminating pre-preg moulds and vacuum forming. It offers high dimensional stability, good temperature resistance, a smooth surface finish, Shore strength of 75D, density ranging between 0.72-0.75 g/cm3, compressive strength of 50-55 MPa.

Once all the models of the k200 chassis and bodywork components were milled from CAD data, several layers of carbon fibre and epoxy resin pre-impregnated tissue were manually laid on top of the models, making sure that the resulting composite structure was void-less.

An autoclave cure was then undertaken to provide the extra strength and resistance the models required. The temperature ranged from 60ºC to 190ºC to cure the resin and make the tissue tough and strong enough. The whole composite structure was then placed in a nylon vacuum bag and put in the autoclave again to compress all the tissue layers evenly.

“The physical properties of this tooling board were particularly suitable for our technological process,” said Mr Giulio Strambi, Technical and Operational Manager at ATR Group, “especially the high temperature and pressure stability which are key requirements for the curing process of the resin. Also, we appreciated the ease of machining BM 5055 tooling board and its' good surface finish after CNC milling. This enabled us to drastically reduce the final hand polishing operations and, subsequently, to speed up the entire manufacturing process. Just to give an idea, it took about six weeks to build the mould for the largest of the bodywork components measuring 1.7m x 1.0m x 0.8m.

“A series of tests carried out on the tooling board models allowed us to assess the expansion and the thermal conductivity of this material as well as its workability with our work-station,” added Mr Strambi. “We were really pleased with the results and we decided to include this board material in the k200 manufacturing process.”

Mr Abramo Levato, R&D Manager at ATR Group added: “The stability of the board material has certainly contributed to enhancing our production runs and helped us avoid additional cost and time-consuming modifications to the model.”

Enquiry etails

Gino Ceccopieri is with Huntsman Advanced Materials (Switzerland) GmbH, Basel

http://www.huntsman.com   www.atrgroup.it    http://www.superlightcars.it



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