3D CAD helps designers of vandal resistant switches

Dave Wilson went to see the design team at Bulgin Components to hear how 3D solid modelling and rapid prototyping techniques had been employed in the design of a new range of vandal resistant stainless steel switches.

Bulgin’s original range of vandal resistant switches has been in the marketplace for over 10 years. Recently, due to market pressures, it became obvious that it was time to expand and redesign the range. The existing designs for example, were only available in two different sizes – 22mm and 28mm – and two different styles: a microswitch style and a terminal block style. The new range had to include many different sizes as well as different profiles and termination options. The company also believed that a market existed for an illuminated version of the switch.

The new switches had to be more tactile too – the designers wanted a positive resist from the switch when pressed. To improve the tactile feel, it was necessary to redesign the contact plate as well as make other design changes too. A further upgrade in the design plan was to enhance the environmental sealing capability.

In the design of the new range of vandal-resistant switches. Bulgin’s design team made extensive use of 3D CAD and stereolithography. But the use of such systems at the company has been relatively recent. When Robin Masterson, the technical director at Bulgin joined the company eight years ago, there was no CAD system in place at the company at all.

At that time, the designers working at Bulgin particularly liked RoboCAD, and for that reason, Masterson’s first foray into the world of CAD was to equip the entire design office with that software.

The results were useful, but could have been better. `Although we were shrinking the design time, we were getting to the tooling stage before anyone else knew what the product looked like,’ he says. `We weren’t really getting the vision of what we had designed to the marketing and manufacturing people or the board of directors – predominantly because it was a 2D system. Although by that time, a 2D file could be translated into a stereolithographic part, it was cost prohibitive. A small part could cost £2000.’

So about three years ago, Bulgin set about evaluating a more sophisticated CAD system. The result was that the company bought PT/Modeller (which has now been upgraded to Pro/Engineer, from Definitive Applications) in March 1998 and all the engineers working on new projects, such as the new vandal-resistant switches, moved over to it.

At the same time, project teams were set up to address the whole issue of design to manufacture and marketing – a concept that was new to the company.

`One of the good things about the Parametric design software is that you create the design in 3D. I thought that this would slow people down but it proved to be no problem at all. The excitement of creating a design this way overcame the differences between the system and its predecessor,’ says Masterson.

Since then, the design team has been able to show others on the project team within the organisation what the design might look like long before the part is made. `Because we can now show the entire team a 3D solid model, they can pick up hundreds of potential problems before they reach manufacturing,’ says Masterson.

Tony Cummings, one of the product design engineers at Bulgin, adds that it is now a lot easier for production engineers to envisage how the switches will fit together once in production. In certain instances, being able to explode the product in 3D on screen while at the design stage, he can ask the production engineer for his input before the part reaches tooling.

Also of importance to both Masterson and the design team was the CAD system’s extensive facility for mathematical checking of tolerances. `The CAD allows you to do check the amount of clearance or interference that you have between components, so before you go into tooling you can check that there is no clashing of parts. Also, because the system is associative, you can see the effect of one small change on the entire design,’ says Cummings.

There have been reductions in the time taken to produce prototypes and toolmaking too. 3D data can be emailed to prototyping bureaux and stereolithographic prototypes produced very quickly. And inexpensively too. Masterson claims that for just £2000, one bureau has produced 14 stereolithographic parts for Bulgin as well as the silicon moulds for cold moulding to enable Bulgin to create parts in a number of different materials. That has allowed prototypes to be demonstrated quickly to customers all over the world.

And it has proven useful too. In the design of the push button illuminated switches for example, Cummings found that once the design was completed and costed, the cost was slightly higher than required. So he revisited the initial design after viewing the first rapid prototyping model, performed some value engineering, and reduced the cost of the design.

In the future, Bulgin is actively examining the possibility of using the 3D data to create the tooling as well. `At the present time, our toolmakers use a compatible CIM system. They have to manipulate the file slightly in order to compensate for material shrinkage, but it can be done. The links are in place so that we can use it,’ says Cummings.

A sheet metal option on the CAD system has also proved important. Typically, the company designs moulded parts, but there are a few instances where parts must be stamped from sheet steel. In those instances, it is important to be able to create a flat projection from a 3D part and then examine the clearances of a part as it is formed into shape.

For the future, the design team is also looking at animation too. `There are a couple of moving parts within the switch and animation software will allow us to watch what happens as a button is depressed,` says Masterson.

‘At the moment, it is possible to create a 3D model in the pushed position or unpushed position, but you cannot see what happens during the transition period,` adds Cummings. ‘So the spring for example has to be modelled in two positions: one where it is compressed, the other where it is uncompressed. With the animation software, we will actually be able view the assembly as it moves.`

Both Masterson and the design team are optimistic of the benefits that the integration of CAD and CIM will bring. ‘Very soon, we will be able to produce new product designs virtually on demand,` concludes Masterson.

There have been significant reductions in the time taken to produce prototypes. 3D data can be emailed to prototyping bureaux, and stereolithographic prototypes produced very quickly and inexpensively. One bureau produced 14 stereolithographic parts for just £2000 as well as silicon moulds for cold moulding

Bulgin Tel: 0181 594 5588