CNC improves electrofusion welding of pipe

A novel application of CNC technology is making the production of plastics pipe fittings for gas and water pipelines more reliable and easier to undertake.

A novel application of Siemens CNC technology is making the production of plastic pipe fittings for gas and water pipelines more reliable and easier to undertake.

This is having a vital impact in China, where recent legislation has demanded that domestic gas pipelines should be installed throughout to encourage the use of gas over the burning of fuel.

Leakage in mains water pipes has always been an important issue.

Apart from the problems associated with locating and isolating leaks, repairing and rejoining pipes can be both time consuming and costly.

Electrofusion fittings are used to join pieces of pipeline together.

The fittings utilise a small conductor wire, which is normally embedded in a pipe joint during injection moulding.

Once the fitting has been clamped joining the pipes together, an electric current passes through the coil of wire causing the polyethylene pipes to fuse to the jointing sleeve.

All very interesting for plastic pipe users, you may think.

But what does this have to do with machine tools and China? The connection can be found at MSA Engineering Systems, who manufacture machinery at their Leicester site used in the production of electro-fusion fittings.

The company specialises in designing and building special purpose machinery for a variety of industrial sectors.

For the past fifteen years they have achieved great success with polyethylene pipe manufacturers through the development of a range of wire-laying equipment.

This technology differs from conventional electro-fusion, which normally requires the use of a special mandrel, wound with a helical copper wire.

The mandrel is inserted into the injection-moulding tool and the fitting moulded around the wire coil.

What makes MSA's patented system very different is that the wire used to form the plastic weld is laid into a groove cut inside the pipe or fitting by a special wire-laying tool.

The displaced plastic is then used to enclose the wire in the cut groove.

The system provides numerous advantages over conventional methods of electro-fusion fitting.

However, this method makes accurate control of the boring and wire-laying process crucial.

MSA solved these machinery control challenges by adopting a CNC solution, provided by Siemens Automation and Drives.

Morgan Jones, Operations Manager of MSA, explains why the company's requirements for a CNC controller were particularly demanding: "The wire laying process has a number of advantages over conventional electro-fusion fitting manufacture, mainly because the wire is placed into the fittings after injection moulding.

This means machining can be carried out on a variety of pipe diameters, simply by changing the CNC machining parameters and patented tooling." However, unlike most conventional machine tool applications, the polyethylene pipe manufacturing industry is not familiar with x y z programming.

Because of this, MSA was anxious to develop a CNC solution capable of being operated in a tailored software mode which pipe manufacturers could use more easily..

Siemens suggested the Sinumerik 810D digital CNC system with its integrated PLC and motor drive controller configured to suit the MSA wire laying machines.

The Sinumerik 810D provided MSA with two major benefits.

Firstly, the operator interface could be configured to suit machinists who knew very little about CNC control.

Secondly, as the CNC, PLC and drive are packaged on the same board a more compact solution, without the need for a separate drive interface is provided.

Siemens also started development on a front end that accepted commands based on data that pipe manufacturers could interpret.

An 810D user interface was proposed, which displayed pipe diagrams and drawings with boxes left blank for the operator to complete details about variables such as pipe diameter.

The equipment's ability to machine pipes with diameters up to 710mm and switch from straight couplings to T pieces and other specialised fittings, reduced manufacturing costs significantly.

Over the last two years MSA has continued to develop its technology in the market.

World- wide patents on the equipment have been issued and this has led to major UK companies consulting MSA for individual development work and converting from the traditional method of production.

MSA has also been able to take advantage of Chinese legislation, which has instigated major projects to install domestic gas pipelines throughout China.

Currently the majority of domestic properties use burning fuel for cooking/heating etc, so the main reason for building gas pipelines is to cut down pollution levels.

This has seen many manufacturers in China, who currently only produce extruded pipes, move towards the manufacturing of Polyethylene (PE) Electro-fusion fittings.

After looking at different methods of production (i.e the traditional method of inserting a mandrel in the injection mould, and wire laying) many manufacturers have chosen MSA's patented wire laying technology.

The result has been an increase in MSA's sales by approximately 200 percent.

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