Launched in 1997, the latest versions of the Morgan +8, +4 and 4/4 sports cars have a more curved body shape, a better hood line, improved head and legroom and increased visibility. More intriguingly from a materials engineering viewpoint, they will also feature one piece wings made from superplastically formed (SPF) aluminium (figure 1), the first time the classic Malvern marque has incorporated such an advanced forming process into its world-renowned coach building tradition.
Figure 1. The forming tool for manufacturing Morgan’s SPF wings.
Advantages of using Superplastic Forming
Produced via the cavity forming method from 2.00 mm starting gauge 5083 SPF aluminium, using a blank 3.2 m long by 1.5 m wide, the new wings retain their distinctive shape while being substantially lighter than the three piece steel components they replace, with superior corrosion resistance and reduced paint protection costs.
The two-part cast iron tool (weighing some 7.5 tonnes), as well as being the biggest yet employed by Superform, also represents the largest ever reverse engineering project for Birmingham toolmakers, Survirn Engineering. The reason for this was that a CAD model existed of the car body, but not the wings. They therefore had to be digitised in situ, as the weld assembly of the old wings from three components made them inexact. Using a Faro six axis digitising and measuring arm, data points were collected across the full width and length of each wing, from which sections were created to facilitate the process of CAD model generation.
The information was then used to construct a full CAD model on CATIA workstations, more usually employed for aerospace applications, from which Survirn’s in-house CADCAM facility, CAMCraft Design, was able to design the tooling in conjunction with Superform.
A small-scale model of the new computer generated wing was then manufactured and delivered to Morgan for approval. Modifications were thus highlighted at this stage, before the large scale castings required were produced. From the production angle, the new wings also dramatically improve the quality of fit and surface finish. Although the finishing of each wing is still a job for craftsmen, the new process provides much more accurate blanks to work from, guaranteed repeatability and a very good surface finish.
Benefits of Using Aluminium
Gauge for gauge, aluminium is of course approximately 60% lighter than steel, with higher impact absorption properties, better strength to weight ratios and superior corrosion resistance. Given the multiple challenges of reducing weight and increasing fuel efficiency, in addition to purely environmental factors such as the need to improve the recyclability of materials, it is not surprising that aluminium structures and components remain the subject of massive research and development by the automotive industry. In the case of SPF aluminium, there are the added benefits of low cost tooling (typically around only 10% of those required for matched die stamping, for example), shorter lead times, rapid prototyping, and above all, enhanced design freedom.
As one would expect, then, Morgan are far from being the only carmakers to discover the benefits of SPF aluminium. Among a growing range of users, the process has already been employed for body and door panels for several projects in the US and Europe. Other applications to date include Volvo utility vehicle conversions in Sweden, as well as smaller, more complex components such as the rear wing inner stiffeners for Bugatti in Italy.
In short, the prospects for superplastic aluminium within the automotive industry would appear to be brighter than ever and are limited only by the designer’s imagination.