The cutting edge of machine saw design

Edited by the Engineeringtalk editorial team Apr 22, 2002

A variable-speed high-precision rotary saw for cutting plastic extrusions to length, developed and refined by OEM Gatfield Systems, has as its heart a Toshiba inverter.

A variable speed, high precision rotary saw for cutting plastic extrusions to length, developed and refined by OEM Gatfield Systems, has as its heart a Toshiba inverter which optimises the speed so that a clean cut can be achieved with any type of plastic.

The complexities of cutting plastic at the speeds required for commercial production are often under-estimated.

Gatfield has spent the best part of 10 years analysing and quantifying the cutting dynamics, constantly improving its machine designs, to the point where it has now mastered the art entirely and is recognised as the premier supplier to the plastics, rubber and electrical cables industries.

Choosing the right blade is critical: for instance something like a wood saw is used on harder plastics, but a bacon slicer blade works better on soft plastic and rubber - particularly if it contains a wire insert such as used in car door seals.

Gatfield Systems is a father and son partnership, backed up by a fully equipped workshop and production facility: "We run a lean and flexible operation, so that we can adapt to the changing demands of our customer base", says father Arthur.

"To maintain this we need to form strong relationships with our suppliers.

The more supportive they are, the better our company works".

One of its key suppliers is Toshiba's Strategic Partner for automation technology, TM Automation, whose drives expertise often proves invaluable.

"Accurate cutting speed is vital.

Each extrusion has its own optimum speed, depending on the type of plastic used, its profile and size.

With the speed right you get a nice neat cut: but you don't have to be too far out to make a real hash of it! Too slow and you rip the plastic, creating a very untidy edge; too fast and you'll burn it.

During early development trials with new plastics we regularly end up with the extrusion melting and welding itself onto the saw blade!".

In use the Gatfield saws are nearly always used on a range of different extrusions, so Gatfield has worked with TM Automation to develop the fine tuning between the different speeds required.

After trying several others, the Toshiba drive has proved ideal for this job.

Son Graeme takes up the story: "Most of the time our blades run between 2300 and 3750rev/min, but we always have to allow for the rare occasions so design for a low speed of 1000rev/min and a top speed of 5000rev/min.

These typically equate to peripheral cutting speeds of up to 3900m/min.

At the highest speeds we even sometimes water cool and/or lubricate the blade".

Combining the 15 programmable preset speeds with infinite variability the Toshiba drive enables optimum profiles to be quickly and easily set.

These are held in memory and accessed through the machine's operator interface.

Some of Gatfield's machines now have touch screen operator interfaces, although the industry preference is still for more traditional hard-wired push button operation.

Alternatively, the drive communications port can link the saw blade through to a plant wide control system for integrated automation.

Feeding the extrusion through to the workstation and raising and lowering the blade into position are also done with Toshiba drives in some of the Gatfield machines, the onboard PID controllers being used to set up and run these various movements.

The drive also features low level current detection, overcurrent protection, an overload stall function, supply voltage correction, and mains loss ride-through, all of which help keep the Gatfield machine at the sharp end of saw developments.

Graeme offers an interesting insight here: "On some of our special designs, as with high performance machine building in general, servo drives are often used.

But more recently we have begun switching to inverters and induction motors, because their performance is improving and is now challenging the servos".

"We are seeing the march of progress with the controls as well as the drives.

A few years ago there was a hefty PLC behind most of our control panels, now it is a nano controller -which can provide more functionality than a far bigger PLC could five years ago".