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September 16, 1998

5 Min Read
Toying With Model Car Designs

At Testor, scale-model cars require both art and technology. A switch to computer-aided design is saving production time and tooling costs. Ken Stark, mechanical designer, explains why Testor opted for CAD. Prior to 1975, the year Atari introduced the first video game, most customers for scale car models ranked in the under-15 age group. Today, more than half of the hobbyists purchasing model kits are adults who grew up building models and remain loyal to the pastime. For Testor Corp. (Rockford, IL), a leading manufacturer in this field, the demographic shift created a need to improve design sophistication, kit quality, and realism without increasing production costs.

"We turned to the same computer-aided technologies designers use to create real vehicles," says Stark. "CAD allows us to produce highly detailed, top-quality scale models of planes, automobiles, and space ships while keeping moldability and mold costs in check."

"When a hobbyist first breaks open the box of a new scale model, there are hundreds of components linked together in groups via plastic runners," explains Stark. "As the hobbyist requires a specific piece, the component can be cut off as needed. This is no small feat. We have to design many groupings and configurations of incredibly small parts to fit in a certain size box. The placement of gates and runners must follow moldability rules as well as not detract from the aesthetics of the component. Draft angles must also be added to each piece of the model for automatic ejection from the mold."

Besides aiding realism, CAD provides other advantages for scale-model cars. "We can digitally prototype intricate designs in 3-D and render them on a computer," says Stark, "to save time in the conceptual phase." As a result, designers can try many design iterations and visualize what the model will look like without incurring tooling costs. Once a design is approved, Testor's design team creates assembly layouts from the 3-D models to facilitate the moldmaking process, and uses data from the 2-D drawings to generate assembly instructions for each model.

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Testor used 3-D CAD to reduce tooling cost and speed time to market when creating this scale model of the actual CheZoom Car, designed and built by Boyd Coddington of Hot Rods by Boyd.

Scaling Down
"The first step in transforming a vehicle from full size into a model (anywhere from 1/20 to 1/72 scale) is to photograph it from all angles and measure the critical dimensions by hand," explains Stark. "The entire subject is then created component by component in 3-D using Cadkey. The components required to make the kit, which can range from 90 to 130 pieces per model, are designed in the assembled state, just like a full-size car is designed." After the entire assembled car or plane is approved in computer-aided form, the tooling process can begin. Prior to tool cutting, designers can output the 3-D file as an SLA file for rapid prototyping. This allows a final design verification before significant tooling investments begin.

Tooling is the main factor in production costs, according to Stark. Most scale-model components are injection molded, and while the plastic used in a scale kit may cost less than $10, tooling cost can reach $150,000. "Using the injection molding process, very minute details can be duplicated in the plastic," he says. "We can also produce SLA parts at a larger scale with the proper detail, then use them to trace a reduced cavity into the tool steel."

Stark believes that as technology progresses in rapid prototyping--meeting dimensional and tolerance requirements--art-to-part generation will be the next level of tool design. "Right now, because of the scale of parts and the intricate detail, a complete detailed part may not be able to be designed on a computer, then cut on a CNC machine. There still has to be a secondary operation to achieve the fine lines needed to represent certain features distinguishable on the full-size subject."

Models for miniature replicas are often produced at the same time the actual full-sized equivalent is introduced to the public. Getting to market quickly is another reason Testor now designs in 3-D. "CAD has helped knock months off a typical product run, not to mention tooling savings of $20,000 to $40,000 per kit," notes Stark.

Also, in the past, hobby companies might commission three or four models per year, with the average manufactured kit going through two to four versions in its product design cycle. With reduced design cycle times afforded by CAD, Testor can now order five or six models for a retail year.

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Testor's design team creates assembly layouts from 3-D CAD models to facilitate the moldmaking process, then uses data from the associated 2-D drawings to generate assembly instructions for each model.

Although much of the design process is now automated by CAD, the artistry of creating scale models remains intact. Creativity must be exercised at a number of different levels. A scale model of a car, boat, or plane does not have a 1:1 ratio of size compared to the real thing. For instance, it is virtually impossible to reduce the sheet metal thickness of a full-size car to the right proportion for a replica 1/24 the size.

Testor has the expertise to design kits with the consumer and the mold manufacturer in mind. "Our designers must constantly be aware of the parting lines on single plastic parts that typically represent an assembly of parts used in the full-size subject," adds Stark. "It is one thing to create a part that resembles something, but quite another to be able to do that and make sure it is moldable. We try to strike a balance between saving money in the tooling, making the process logical, and creating realism for the consumer."

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