IR welding technique raises quality and cuts waste

Special-purpose infra-red emitters improve the quality of an inspection chamber assembly production process while eliminating environmental problems.

An infra-red (IR) welding system using special-purpose infra-red emitters from Heraeus Noblelight has helped Hepworth Drainage to improve the quality of an inspection chamber assembly production process at its Lichfield plant, while eliminating any environmental problems associated with a hot melt adhesive technique that was formerly used.

Hepworth Drainage is one of the largest manufacturers of drainage systems and products in the world and for over 150 years has enjoyed a reputation for product quality, technical knowledge and customer support.

One of its major product lines is a polypropylene inspection chamber, which provides access to inspect below ground drainage systems from the surface.

This product consists of a base unit offering multiple connections to clay or plastic drainage systems.

The addition of two or four raising pieces creates the required depth of inspection chamber.

An important step in the manufacturing process is the joining of the raising pieces, first to the base unit of the inspection chamber and then to each other as required.

This was formerly carried out using a hot melt adhesive but increasing demand for Hepworth products stimulated the need for enhanced automation of this part of the process.

Environmental improvements to the process and a reduction in the cost of consumables were key objectives.

As a result, special purpose machine builder, CPR Automation, of Tamworth, was asked to develop an automated joining process.

The solution involved the creation of an enclosed infra-red welding cell, into which the base units are fed by conveyor and the raising pieces are transferred from an adjacent injection moulding machine by an ABB robot.

In operation, the robot takes two 475mm diameter raising pieces from the adjacent injection moulding machine and locates one of the pieces over an annular infra-red heater, which features small custom-designed, short wave emitters, each delivering 15W/mm, distributed around its annular surface.

When switched on, this heater softens the bottom, abutting face of the raising piece.

At the same time, a base unit is brought into the cell by a belt conveyor from another moulding machine and fed into position below a second, similar annular heater.

This infra-red heater is switched on to soften the top abutting face.

The robot then picks up the heated raising piece and positions it above the heated base unit.

The base unit heater is split along its diameter and it is opened pneumatically to allow the robot to locate the raising piece precisely on the base unit and then apply pressure to bond the two parts together and control the finished assembly height of the two abutting faces.

When this is completed, the split heater will index up so that it can heat the top abutting face of the joined raising piece.

Meanwhile, the first heater has been located below the second raising piece by means of a tracked system and the abutting face of this component is heated before the robot returns to pick it up and transfer it to the already welded assembly.

As before, the split heater opens and the robot locates the second raising piece precisely on top of the assembly and applies pressure.

The robot then returns to pick up two more raising pieces from the injection moulding machine and the welding process is repeated until the required height of inspection chamber is achieved and the complete welded assembly is moved along to the packaging and despatch area.

With cycle times of around 22 seconds, the new process is considerably faster than the former, semi-automatic system and significant improvements in quality have been realised.

The infra-red welding has also shown itself to be far superior, environmentally, to the hot melt adhesive technique, as there are few fumes associated with the process and there have been gains in energy efficiency as the high power infra-red emitters are only switched on when necessary in the operating cycle.

Infra red welding is fast gaining acceptance in the plastics sector with CPR Automation, of Tamworth, firmly established as the leading supplier of equipment to satisfy the rising demand.

Being a noncontact method, IR welding suffers none of the disadvantages of hot plate methods, such as plastic adhesion to the heating surface which necessitates frequent tool cleaning.

It is also capable of handling large surface area products, as it is a simple operation to add more emitters to a heating bank.

In addition, as demonstrated at Hepworth, infra-red heaters can be custom-built to match the geometry of the product to be welded.

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