The desire to constantly cut lead times is as relevant for toy makers as it is for the rest of industry. And for Hornby Hobbies, maker of Scalextric, getting a model of the latest car into the market is as crucial as the launch for the ‘real’ car manufacturer.
With its Vauxhall/Opel Vectra, introduced earlier this year, Hornby slashed its lead times by basing its model directly on the manufacturer’s CAD files.
With Hornby’s youthful clientele becoming increasingly sophisticated, and the lifespan of car designs getting shorter, particularly in Formula One, the improved response times and greater accuracy resulting from computer modelling promises to give Hornby an important competitive edge.
Traditionally, the initial drawing phase would take around 10 weeks, patterning 12 weeks, and tooling a further 12 weeks. But the Vectra, modelled on Parametric Technology’s ProEngineer and tooled concurrently, transformed this process to about 20 weeks in total.
Hornby’s operation is unexpectedly high-tech: its six-strong engineering department runs two ProEngineer seats to which it has recently added a ProDesigner seat.
The migration to ProEngineer is recent, and the Vectra is only the second car to be modelled on it. The first was a generic Formula One car for the Scalextric entry level Grand Prix set.
Previously, development of a new Scalextric car was laborious, says Jamie Buchanan, Scalextric design engineer. Depending on the manufacturer and how much information it supplied, designers worked from isometric views and photographs and inspections of competition cars at dealers and race meetings.
The design department would prepare two-dimensional drawings and sections at intervals through the car body which would be issued to a pattern maker. A 1:16 scale model – twice the size of the intended 1:32 finished product – would have been cut in plastic, and the model built up by carving wood to the correct profile between the sections. The pattern maker would also indicate where the mould tool should be split: there would typically be six sections to the mould – two sides, front, back and top and bottom.
By masking off sections of the wooden model and suspending it in a resin bath, the pattern maker would produce a resin pattern for each section of the mould.
These, and the wooden model, were sent to the mould tool manufacturer, where the resin pattern was used to create a 1:32 mould from steel by electric discharge machining. A ‘proving model’ would also be made for internal marketing approval within the company and to check for component fit and any clashes.
But all this has changed. ‘We received the Vectra details as an Iges 3D data file direct from Vauxhall,’ says Buchanan. Until recently it was rare for manufacturers to have a single Cad model for the whole car.
‘We couldn’t use it straight off,’ he adds. ‘It was a huge file in terms of memory, and it was actual size.’
Buchanan also realised that the Cad file would need modifying to join together separate components such as the bonnet and front wings, to produce a one-piece moulding for the scale model.
Buchanan used ProEngineer’s Units tool to reduce the computer model to 1:32 scale. A simplified model of the whole car was then recreated in the software by copying critical curves, such as the edge of the roof, in three dimensions from the original data. This was superimposed on the original.
‘We coloured the imported Iges model bright red and our model white, and overlaid the two so we could see if the shape was right,’ says Buchanan.
Where the two surfaces did not match, high points would stand out in a different colour. The surface could be manipulated until an almost uniform mixture of red and white was achieved, indicating that the model surface closely matched the shape of the original.
Next, the rest of the parts of the Scalextric model – the window moulding, seats, lights and roll cage – had to be created. These are all snap fits, needing no adhesive.
One moulding for all the windows fits within the roof of the body. Modelling the part in the software made it possible to be sure that the outside window surfaces followed the profile of the body more smoothly than would have been possible traditionally; where the moulding fitted within the car’s roof and side pillars, it was designed to be an exact match with the inside surface of the body moulding, with an offset of just 0.15mm to allow for tolerances.
Where the bottom edge of the window unit rests on the seat unit, ‘zero clearance’ was specified to give an exact fit.
Front and rear lights are made from a single piece of plastic or ‘light optic’ illuminated by a bulb in the centre of the car. This was created in ProEngineer to check for clashes with the other parts.
Parts not included in the Iges file, such as the roll cage and wheels, were created directly in the software.
The finished product was sent by DAT tape to rapid prototyping bureau Formation, which in five days produced a stereolithography model to a standard good enough to be approved by Hornby’s marketing department.
In theory, one would expect that the model data could be turned directly into a mould tool via CNC machining. In fact a two-stage process took place: first a 2D file was sent to a tool designer who, working in Autocad, specified where the mould should be split, and where feed and ejection points should go, as well as devising a mould layout to accommodate all the components.
An Iges file for each component was sent to the tool maker along with the data from the tool designer, which was recalculated into 3D in the tool maker’s software, before CNC machining the mould tool.
Buchanan is enthusiastic about the process, although it is not clear to what extent other manufacturers will be able or willing to supply Cad data.
‘We’ve effectively knocked 14 weeks off the process,’ says Buchanan: patterning has been eliminated entirely and drawing cut to six to eight weeks instead of 10 previously.
‘We’ve eliminated clashes, which are common especially with the seat unit. Now we can make sure everything is tight and fits really well.’