Ultimate 3D precision modelmakers at www.ultimate3d.co.uk

Ultimate 3D Ltd

18 Towerfield Rd, Shoeburyness, Essex, SS3 9QE UK

Phone Tom Glacken on +44 (0)1702 293030

A prototype is a model suitable for use in the complete evaluation of form, design, performance and material processing.

Ultimate 3d produce CAD/CAM design and development models of aircraft interiors with a particular speciality, prototype seat foams.

When composite prototyping, the expense of plastics tooling and the uncertainties inherent in plastic part design contribute to the extensive use of prototyping and testing sequences while developing plastics applications. Engineering tests are performed on a sufficient number of prototypes to qualify the design.

Prototypes can be prepared by a number of different methods. The basic trade-off is prototype cost versus the reliability of the data obtained during part testing. Less expensive prototypes usually provide less reliable test data.

Invariably, the physical differences between prototypes and production-quality parts result from the physical effects that are induced in plastic parts during processing, which can affect the properties of the finished part. These physical-property differences can lead to uncertainties when evaluating the suitability of a design in an engineering test program.

The three principal mechanisms by which processing can affect part properties are internal stress generation, molecular orientation effects, and weld lines formation.

Internal stress can be induced and retained in plastic parts by machining, flow, or thermal stresses that are applied to the part during processing. These are true stresses, which can influence the behavior of a part by lowering ultimate physical properties, by increasing the susceptibility to deteriorating agents, or by causing the part to warp if the stresses within are not balanced.

CNC machining of composite prototypes.

Plastic prototypes, therefore, may exhibit properties that are different than those of production-quality plastic parts if differences exist in internal stress, orientation or location due to processing.

Prototype parts can often be made rapidly and at little expense by cnc machining from stock, unless the part is of unusual complexity. Machined prototypes help to qualify a design, but the limitations of machining must be recognized. Machined parts exhibit internal stresses that are very different from the internal stresses generated in, say, moulded production parts produced by reaction injection moulding.

Internal stresses may have a profound effect on the ultimate physical properties of a part, such as its impact strength. Machined prototypes often exhibit tooling marks and sharp corners which can act as stress concentrators, decreasing part strength. Reaction injection mouldings may exhibit voids in thick sections (due to excessive shrink) that would not be present in machined prototypes.

Moulded prototypes are preferred to machined prototypes, although they are typically more expensive. The preferred prototyping method uses production of preproduction tooling, which is made of tool steel but may not be hardened. This allows the very representative of production parts. Such prototypes can be tested with a high degree of confidence that test results will be mirrored in production parts.

The drawback of this approach is that not only is the tooling relatively expensive, initially, but if it is determined during testing that the part must be significantly redesigned, the tooling investment may be lost.

Prototyping and testing new designs of plastic parts is absolutely essential for all but the most trivial applications. A major goal is to obtain prototypes for testing that are as similar as possible to production parts. If the production parts are to be reaction injection mouldings, moulded prototypes are preferred over machined prototypes.