The production of one-off prototype components is an important part of new model development but the manufacturing and the assembly of complete sub-assemblies for small batch series production has become an increasingly important part of the model building business. The time taken to develop new vehicles is getting shorter and shorter; rapid prototyping is now a key element of the process and helps to deliver projects on time, in full, and on budget. The company Robert Hofmann was integrally involved in the development and production of VW’s perennial best-seller.
The new Golf VII is the latest version of one of the world’s most popular cars. While it has changed a great deal since it was first launched, certain characteristics of the best-selling hatchback remain constant, and quality is right at the top of the list. Among the challenges are time and cost pressures. The planning for a new model’s introduction takes place during its predecessor’s active market period – perhaps even when sales are at their peak. Concept vehicles of upcoming pre-series prototypes have to be made, adapted during the development phase and are subjected to trials and tests. Pre-series production vehicles then have to be made available for pre-launch marketing activities. Individual components have to be provided for concept vehicles; around 100 prototypes then have to be equipped and, finally, 50-100 pre-series production cars are built.
Hofmann‘s model-building personnel applied different strategies to each of these three phases. These included moulding processes, rapid prototyping technologies and highly specialised finishing techniques. In the case of series production vehicles such as the VW Golf VII, rapid prototyping is quickly followed up with industrial prototyping, with batches of 100 to 120 parts for limited series production. Once the main models have been launched, work begins on special versions such as the GTI and limited editions.
Once design was clarified with Volkswagen, Hofmann started preparing the moulds and deployed rapid prototyping technologies, such as LaserCusing (melting metals with laser beams) for individual components including halogen headlights, fog lights, reflectors, rear lights, boot door covers, side panels for seat covers and the dashboard. Finishing methods such as metallisation for lighting components are essential, as is assembly work right up to producing complete sub-assemblies. Process combinations and strategies necessary to produce complex sub-assemblies such as dashboards are standard practice. Their look, feel, finishing, materials and functionality are just as good as typical series production parts – the concept vehicle has to look and feel like the “real thing” as early as possible during development. Traditional development methods typically require lead times of 25 weeks but model building utilising modern technologies can deliver pre-production parts in as little as half this time, and cost-effectively. Functional tests such as leak tests are part of the model builder’s service portfolio.
Big is beautiful
According to Michael Mayer, Project Manager for aluminium tools for model building at Robert Hofmann, the sheer scale of the Golf VII set the project apart, including halogen headlights, fog lights, reflectors, rear lights, boot door covers, seat panelling and the dashboard.
“This range of work involved a wide variety of model building tasks with special finishing processes, such as metallisation, flocking, laminating and painting. We even did the leak tests for our customer,” he said. Timing was also challenging. “The test vehicles and prototypes had to be made available and production line tooling had to be delivered some ten to twelve weeks prior to the start of series production. What was new for us was the possibility to agree on the specifications of most of the parts directly with Volkswagen at their headquarters in Wolfsburg, Germany.” Hofmann generally uses moulding processes using aluminium tools, moulding with resin-based tools or silicon moulding and other non-moulding processes such as laser sintering, which “prints” with a special polymer layer by layer.
“Laser sintering can be used up the size of a dashboard,” said Mayer. “Afterwards, various finishing techniques are used, such as the metallisation of headlight reflectors.” The technique is economically viable for producing up to five large components, batches of up to 50 small components or up to 500 very small parts. “Larger batches call for a move to aluminium tooling for parts that are found in non-visible areas. If we are dealing with high temperature polycarbonate or thermoset material, or where moulding systems are demanded, hardened steel moulds are deployed, just like in series production.”
Hofmann’s model building team is incorporated into the company’s toolmaking division and the company supplied 30 injection moulding tools for the seventh generation VW Golf – within a lead time of only ten weeks. Hofmann says that a development partner who is also a tool supplier means that the prototyping solutions are capable of producing large batches of parts that exactly meet project demands. It also states that having one supplier for prototypes and series production tooling raises quality and improves meeting the project’s lead time challenges. The company can supply, from group resources, milled parts directly from its milling facility in Dresden, as well as low-cost milled components from its factory in China. It also provides support with maintenance and implementing preventive measures.
Industrial prototyping for the Golf VII meant producing 100 to 120 parts of various sub-assemblies, which was a significant volume, but the series production start up for the new Golf VII went completely to plan.