Pressing ahead
November 1st 2006

Clamason's precision metal pressings are now fighting back in all sorts of ways against plastics, providing superior solutions in many so-called 'traditional' plastics applications

Our further education system teaches engineering design students a great deal about the myriad choices of 'modern' plastics but far less about metals, so that young people don't feel confident enough to specify metals over plastics when they proceed to join design and project teams and consultancies later, or indeed they go back into lecturing to enthuse the next generation about plastics.

What is more, the many state-of-the-art solid modelling CAD systems are for plastics not for pressed metal parts.

Often comparing very poorly to metal pressings, says Clamason, plastics may suffer from shrinkage, joint line and RFI / EMI shielding problems, be degraded over time by heat, light and ultraviolet rays and hold lower dimensional tolerances.

Plastics are hydroscopic (absorb water) and are gradually getting more expensive because of their oil content. Then, unlike plastics, Clamason presswork is recyclable in 95% of cases. What is more, plastic mouldings have a lower perceived value than metals owing to less weight and their look and feel. Indeed, for marketing purposes, many hand-held devices, although encased in plastics, are required to be coated to simulate metal and would be enclosed better by an actual metal pressing.

The metallising of plastics for mobile phone housings is a very expensive process.

But the modern stamping technology employed by Clamason is fighting back equally against the sometimes competing metalworking processes of casting, diecasting and machining. Clamason's presses either minimise carry strip or use precut blanks and give unmatchable consistency of material, tolerances and surface finish over a million batch produced at high speed.

The practical advantages of pressing are many and varied. The variable of heat, often problematical to casters and moulders, is absent from the process.

Diecasters and moulders of small precision components cannot create the thinwall sections down to 0.1mm possible with pressing. Subtle changes are easy to make to the characteristics of pressed materials to suit the application – there are 500 to 600 grades of stainless steel alone – whereas a diecaster has a restricted choice of a handful of alloys only.

Furthermore, prototypes are cheaper, quicker and easier to make with the stamping process (in 10–14 days) and are a closer representation of what the final production component would be.

Individual pressings can be produced from materials ranging from cold-rolled and stainless steels to copper based alloys, aluminium and bimetallic combinations – selecting from hundreds if not thousands of grades to comply with the characteristics required and conditions of use specified, so the choice can be extremely daunting to the uninitiated.

Just in time Clamason's JIT automotive experience and related technologies represent a substantial benefit when it comes to markets which are less demanding. Those characteristics of: the automotive supply chain are for instance

- Just-in-Time or Kanban supply onto a production line ; the strictest production and quality control through dedicated cellular manufacturing ; the need for high-speed machines with quick-change tooling ; and zero defects to keep customers' assembly lines running and avoid the damage and cost of warranty claims on the manufacturer, vehicle recalls or US-style product liability litigation. Clamason's in-house technologies include the following.

Clamason operates a Chin Fong Worcester transfer press line of six presses located together, with rapid transfer of individual pressings between stations by pick-and-place robots. This system allows the manufacture of highly complex parts with no carry strip and the automatic insertion of other components (such as other precision pressings, machined parts, zinc, aluminium or magnesium diecastings, or even plastic mouldings) and has the facility to reverse the burr side automatically within the process.

Clamason has a three-axis, plccontrolled, robotic spot welding facility from Stäubli Unimation.

A £40,000 Simac Masic 3D realtime vision system measures and monitors in 3D 100% of thin and intricate healthcare components fed in a continuous strip and requiring measurement of four key features to a 50-micron tolerance. The strip feeds from Clamason's new, state-of-theart, £200,000 Bruderer press that runs in a dedicated cell at high speeds of up to 800 blows per minute. The 25-tonne, PLCcontrolled, Bruderer BSTA Series press has a bed length of 750mm and features quick-change tooling for JIT manufacture.

Over in the Metrology Department at Clamason, a Nikon Nexiv 3020 noncontact, CNC video measuring system featuring a through-the-lens laser autofocus facility ensures the repeatability of small, complex and highly toleranced parts from large batch production. The system typically measures 60 sample metal pressings in a 30,000 batch. Lots of 30 are placed on a jig, and the Nexiv measures the programmed dimensions in a few moments using automatic component recognition. The data generated is stored in the Nexiv's data management system for quality audit and exported as an Excel spreadsheet for analysis. Such monitoring of key dimensions enables Clamason to anticipate when and where adjustments need to be made to the process. A specific example would be tool wear, especially when processing hard stainless steels. The Nikon Nexiv provides progressive data so that trends in key features can be identified and monitored, allowing the appropriate adjustments to be effected well before a dimension moves out of tolerance.

The Metrology Department also operates a hardness tester and a £60,000 Brown & Sharpe Mistral CNC co-ordinate measuring machine (CMM). The latter features "slant bridge technology" and a Renishaw PH10M contact probe. This CMM is used for the checking of high-tolerance parts with complex 3D forms and the preparation of associated reports. The machine utilises PCDMIS for Windows software (a major advantage) for reading data and is regularly used for measuring and recording points on say complex airbag inflator housings (four per car – two nearside & two offside) as well as on all kinds of prototype components.