Compact valve terminals facilitate innovative distributed control system that reduces industrial IC engine circlip insertion machine cycle time by at least 20% and raising output by nearly a third.
When the Cummins Engine Company sought a new control system for an automated circlip insertion machine on one of its engine assembly lines, it commissioned automation specialist Wearside Pneumatics, a member of the Festo Premier Stockist network, to handle the project. Wearside had previously developed a number of electro-pneumatic control systems for the engine load testing cells at Cummins' Darlington engine plant, as part of a highly successful system upgrade. The circlip insertion machine is installed on the B series diesel engine assembly line at Darlington.

These engines are produced in 3.9L four-cylinder and 5.9L six-cylinder versions, and are widely regarded as industry workhorses, being used in applications as diverse as medium-sized trucks, fire pumps and generator sets.

Designed to fully automate a complex assembly operation, the insertion machine takes partly-built sub assemblies containing pistons and con-rods with loose gudgeon pins, and applies circlips to either side of the piston.

Part of the process involves removing pre-fitted bolts from each conrod before the circlips are fitted.

The machine is a dual-stage system - using a total of 16 pneumatic actuators - with fully replicated functions, enabling one half to be loaded with new components while the other half is handling assembly operations, to maximise throughput.

The machine performs six assembly operations on each 6 cylinder engine, and with its original control system had a cycle time of 200 seconds, giving a throughput of just over 18 engines per hour.

The circlip insertion machine has performed impeccably ever since it was installed.

However, after some 18 years, its control system was showing signs of age and presenting Cummins with a variety of problems.

The pneumatic valves were early-generation models that were now obsolete and unreliable.

Increased machine downtime was impacting production throughput and maintenance costs were rising.

Also, the control system was very large by today's standards - occupying a 0.6m deep panel measuring some 2 x 1.5m - and was becoming extremely noisy in operation.

According to Garry Price, Manufacturing Systems Support Leader at Darlington, 'The control system was really no longer suitable for a modern manufacturing environment.

Apart from its size, which was preventing us installing further automation because of limited space on the production floor, downtime was becoming a big issue.

It wasn't unusual to experience two to three breakdowns a week, which would typically take between 10 and 30 minutes to fix - during which time of course, production was halted.

Manual override wasn't an option either, because the control valves didn't allow for it.' When it awarded the development contract to Wearside, Cummins specified that Festo compact valve terminals must be used for the new control system, because previous experience had proved these to be highly reliable, small form factor components.

They also offer Profibus communication facilities, which is the protocol Cummins is adopting for all future automation control.

After analysing the existing set-up, Wearside was convinced it could create a control system that would not only overcome all the problems of the existing installation, but also reduce circlip insertion cycle time to help speed up the line.

By basing the new control system on compact valve technology, the company knew it could design a highly reliable, small footprint solution that could easily be housed next to the machine on the production floor.

In fact, during development, it became clear that an even more innovative control architecture was feasible.

Instead of a single, centralised control system, a distributed approach would allow even greater space savings.

As Darren Barnes, Fluid Power Consultant for Wearside Pneumatics, points out, 'We realised that the exceptionally compact dimensions of Festo CPV valve terminals combined with the fact that we were effectively producing two identical control systems - one for each half of the insertion machine - would enable us to use two small cabinets instead of one larger one.

This would allow the entire control system to be accommodated beneath the machine, taking up no extra floor space, with the added advantage that the valve terminals could be connected to the machine's pneumatic cylinders via much shorter air supply tubes, to maximise dynamic performance.' Wearside chose to base the control system on Festo CPV18 valve terminals because it wanted high flow rates to achieve fast switching - and these latest models can handle flow rates up 1600 litres per minute.

They are also the only compact 18mm valves on the market which offer a broad choice of electrical/pneumatic connections and different pressure ranges, to help speed design-in.

Like all Festo CPV valves, the CPV18 are IP65-rated - making them ideal for decentralised control applications such as this - and feature generously dimensioned flow ducts and powerful surface-mounted silencers to accommodate the high flow rates needed for relatively large pneumatic cylinders.

The final system comprises two 0.5m2 cabinets - each with a depth of just 0.3m - containing a CPV18 valve terminal and an air preparation system.

The cabinets are mounted beneath either end of the machine, rather than next to it, saving approximately 1m2 of floor space compared to the previous system.

The control system was installed at Cummins' Darlington plant at the end of July, 2004 - just five weeks after Wearside was awarded the development contract.

It has performed flawlessly ever since.

To quote Price again, 'We are extremely pleased with the new system, which has a performance that significantly exceeds the original design specification.

It has enabled us to reduce the cycle time of the insertion machine by at least 20%.

To put this in perspective, trimming some 20 seconds off each complete assembly operation means that we now achieve a throughput of 22 engines per hour, compared to the previous figure of 18.

What's more, the control system is virtually silent in operation, making working conditions more pleasurable, and because it is effectively integrated with the insertion machine and takes up no extra space, we have since been able to install further much-needed machinery on the production floor.