Control package aids fence pale production

The latest generation of fence pale production machines from Metform incorporates advanced Rexroth servo drive, hydraulics and control architecture.

The latest generation of fence pale production machines from Metform, recognised as one of the world's leading authorities on roll form engineering and technology, incorporates advanced Rexroth servo drive, hydraulics and control architecture, which has helped triple output from 15 to 45m/min, at the same time enhancing accuracy and quality.

A Rexroth compact, industrialised PLC (programmable logic controller) provides combined hydraulic, motor and motion control, precisely synchronising key functions within the production process and facilitating critical time savings, in addition to ensuring complete ease of operation.

So impressed was Metform with the performance of Rexroth's electrohydraulic drive and control solution that it is now incorporating the technology into its 60m long purlin lines and other punching equipment, being exported to the USA, Canada, South Africa and elsewhere.

Apart from the synergy of adopting components from a single manufacturer, Metform can offer its customers a system supported in the field by the global Rexroth Service Automation network.

A market leading manufacturer of roll forming machinery, coil handling equipment, cut-to-length and slitting lines, and other engineering products, Metform is based in Dudley, West Midlands, with its international division in Ontario, Canada.

Its latest fence pale machinery produces profiled steel uprights for palisade fencing, used for railway sidings, electricity stations and similar perimeter security installations.

Operating at line speeds up to 45m/min, it produces 1-4m long, cut-to-length profiles with one square end and a choice of round, round and notched, pointed or splayed tops, the latter with rather fearsome sharp prongs.

In process, the strip metal is fed from an unpowered decoiler unit into a roll former, where the longitudinal profile is formed.

The profiled strip is then fed into a flying shear or traversing pre-punch mechanism, which cuts the metal to length, punches top and bottom holes, and removes slugs of metal to create the differently shaped tops.

The precut lengths are next discharged to a magnetic stacker, where there is the further option of splaying two posts at a time, before being stacked in up to 20 layers of 10 pales.

Whereas the previous machine had employed individual analogue hydraulic control cards and limit switches, the new model is PLC-controlled throughout the main manufacturing sequence.

In addition to an MTS-R plug-in PLC module, Rexroth supplied a dedicated CLM flying shear positioning controller, a DKC analogue drive controller and linked MKD synchronous servo motor, which is coupled directly to the high performance ballscrew that powers the flying shear back and forth, as well as peripheral digital and analogue slot-in I/O cards.

The Rexroth hydraulic content comprises five 4WRSE high response proportional valves, for controlling the cylinders that perform the various cutting/punching operations, which are all powered by a medium pressure 10VSO axial piston pump.

Total Rexroth content is valued at around GBP 15,000, although the sophisticated drive and control solution has given Metform a distinct competitive edge.

To eliminate the individual hydraulic control cards, Rexroth and Metform's in-house software engineers developed a high priority timed task program within the PLC, to control the proportional valves and the movement of their associated hydraulic cylinders.

A transducer on each cylinder supplies the PLC with a signal via an RMC analogue I/O card, which indicates the position of the cylinder stroke and is checked and updated every 10ms.

Also incorporated into this program is a 'material clear' sequence, which allows the flying shear to return to its start point before the cylinders return to their home positions, enabling a three-fold increase in line speed.

The CLM unit is a dedicated, intelligent flying shear controller, which uses an encoder signal from a measuring wheel at the exit of the roll former to detect the current line speed and amount of material passed.

When the required length is indicated, the controller causes the DKC drive and servo motor to accelerate the shear and synchronise with line speed.

The flying shear itself comprises a ballscrew-mounted traversing bolster, carrying one cut-off and two punching tools and their associated cylinders/valves, and once this is running at the required speed, the CLM outputs a signal to the PLC to indicate readiness and the PLC activates the firing sequence, all within milliseconds.

So as to exploit the increased upstream line speed and preserve the output gains, the penultimate online sequence of splaying the heads is now performed two products at a time.

Again Rexroth proportional valves control the hydraulic cylinders that operate the twin splay heads, with this optional process also programmed into the PLC.

Previously, cut-to-length product was manually stacked, then fed into a manual press for splaying, before being re-stacked and banded, so significant time and labour savings have been introduced here.

"This advanced electrohydraulic solution means we can offer significant customer benefits on the latest generation of this machine, whilst having a totally Rexroth system of controls, servo motors, hydraulic valves and pumps means that it's supported worldwide by the Bosch Rexroth Group", says Metform's Engineering Director, Steve Cant.

"We are already applying the same Rexroth technology to other machines, where we are achieving similarly impressive advantages".

Back to top