A CNC punch press is now producing some 80% of all sheet metal components, replacing an older machine that required a higher number of tool changes to do the work.

Building a nuclear submarine is a complicated business - not least when it comes to the sheet metal components The confined space and curved walls of the interior mean that many items, such as lockers, bunks, kitchen equipment and ducting for heating and ventilation have to be made as one-offs to fit the space available The BAE Systems shipyard at Barrow has just launched HMS Astute, the first of a new class of nuclear-powered hunter-killer submarines for the Royal Navy, and is now building the next two boats, with a fourth on order.

An LVD Global 20 CNC punch press is providing the capability and flexibility to ensure that all the sheet metal requirements for these vessels are met in a timely and cost-effective way.

Colin Taylor, Outfit Manufacturing manager at the Devonshire Dock Hall in the Barrow yard, is in charge of the sheet metal shop and explained how complex the job is.

"There are something like 8,000 different bits of equipment on every submarine that have to be fabricated from sheet metal - as well as about 1000m of heating and ventilation ductwork.

For items such as the lockers we have to design and manufacture units of the right size and shape to fit into the available space.

It isn't like a surface ship where you can use standard units.

And it is the same on the ducting.

Whereas on a normal contract you would expect to have long straight runs, on a submarine every ventilation spool is different." Even if the submarine needs a number of similar components it is unlikely that Colin will be able to schedule them to all be made at the same time.

Everything has to be delivered just in time for installation as the boat is constructed - deck by deck and module by module.

"You have to make what they need when they need it," he said.

"We make a wide diversity of parts and use a lot of different materials - aluminium, stainless steels, mild steel and galvanised steel - in thicknesses up to 3mm on steel and 6mm on aluminium.

And while somebody making PC cabinets or washing machines is making thousands of the same part, we might make a single locker in mild steel, then run half a sheet of aluminium and then move on to something else.

It can literally be one-off after one-off after one-off.

And although we try to plan like with like, we may change the material on the machine eight times a day," said Taylor.

This requirement for total flexibility was the driving force behind the decision to replace an existing punch press with the new LVD Global machine.

The Global installed at Barrow is a 200kN (20 tonf) hydraulic, thick-turret machine with 30 tool stations.

The tool capacity is expanded by the use of multi-tools in two of the three rotary stations.

These hold eight tools and three tools respectively, with each tool able to be individually rotated.

Overall, this gives a total of 39 tools in the turret at any one time, of which twelve are fully indexable.

"Around 80% of what we produce in the sheet metal shop goes through the punch press; it is at the heart of our production so it has to be very productive.

And to be productive it has to be very flexible.

"We were doing massive numbers of tool changes on our old machine because of the variety of materials we are using.

Now we have a bigger turret with more tools so we have been able to optimise the tooling configuration for the type of work we are doing.

For example, we have some common tools duplicated around the turret, but set up with different die clearances for different materials.

This new flexibility means that we only have to change the turret configuration a couple of times a day." The Global has also allowed BAe Systems to use new manufacturing approaches to refine its designs.

Form-working, in particular, has allowed it to reduce secondary operations and assembly time.

As Taylor emphasised, "We aren't a first generation user going from making a locker by hand to using CNC.

We are going from one CNC process to a more sophisticated one.

Now we want to explore how we can refine our designs to such an extent that we are really using the machine's capabilities." At its simplest level this is represented by the use of a centre-dot marking tool to identify every part with a unique product number - previously this was done by hand using a marker pen.

At a more sophisticated level, the use of semi-shear tool allows parts to be snapped together without rivets, and a hinge-making tool can form the hinge from the sheet - whereas before the hinges were also riveted on.

"We have made a lot of modifications to the locker doors, for example," sais Taylor.

"We used to rivet the outer and inner skins of the door together, now the semi-shear tool means we can just snap the parts together.

And with the hinge-making tool, the only secondary operation required is to slide the hinge-pin into place.

We are saving a lot of time by not using rivets.

By using technology to take out manual second operations the standard manufacturing time for a finished locker has been cut from eight hours to five hours.

And if we have to we can manufacture a locker from start to finish in about 2.1/2 hours rather than the seven hours it would have taken us".

Finally, in making the switch to another machinery supplier Taylor said: "Whilst there was the normal learning curve that you would expect with implementing any new technology into the workshop, LVD's back up and response has been excellent, when we have needed help either on the phone or a visit to site the response has been first class.". 


http://www.manufacturingtalk.com/news/lvd/lvd171.html