When close enough isn't good enough
When close enough isn't good enough
Keywords: Manufacturing, Automation
Precision and innovation are two words that recur throughout the history of Lancashire-based engineering company, Holroyd. By the end of the nineteenth century, the business had established an enviable reputation at the forefront of industrial gears and machinery production and had already invented the principles of thread milling that are still used today by manufacturing industry world-wide. Later, it pioneered the development of worm gear technology and the production of close tolerance rotors for screw compressors. This is a field where Holroyd regularly works to microns.
Still occupying the site in Rochdale it moved to in 1897, Holroyd is today part of the world-wide Reynold engineering group. The 280-strong company has come a long way since producing its first textile machine in the mid 1800s. It is a recognised leader in helical thread form technology, being the world's largest producer of helical screws from 6mm to 800mm diameter. It is also the UK's largest producer of worm gears and a further substantial part of the company's business is devoted to the development and production of helical milling and grinding machines, chiefly for the manufacture of screw compressor rotors.
Two Queen's Awards for Technical Achievement reflect the company's position at the leading edge of technology. The company also won first prize for "measurement and manufacturing excellence" in the recent Metrology for World Class Manufacturing Awards and has achieved "Millennium product" status for its advanced rotor production centres.
The latest generation of Holroyd thread milling and grinding equipment takes worm gear and helical screw manufacture to new levels of accuracy and productivity. So when the company came to create a state-of-the-art automated manufacturing cell for compressor rotors, these machines would clearly be at its heart. However, a major element governing the success of the venture would be the ability to control the handling of process parts to the same level of precision and reliability as the machine tools themselves.
At 68 metres in length, the new cell is believed to be the worlds' largest. Its layout is split into two separate lines, allowing buffer stocks to be maintained within the cell to smooth out variations in machining cycles. It also incorporates a number of novel features to enable six diameters of rotors to be produced around the clock to the highest quality standards.
After initial turning operations, the rotor billets are profile milled to within 0.4mm of finished size. They then progress for further turning and cylindrical grinding operations, before being transferred to a Holroyd TG 150E machine for finish grinding. This is the most intricate and carefully controlled part of the manufacturing process, with each flute first being ground to within 40 microns of finished size, before an in-built CMM probe monitors the component ahead of the finishing pass. A feed back loop to the control system –coupled with in-process form dressing of the grinding wheel – then ensures that each component is produced, and 100 per cent inspected, to the most rigorous quality standards.
Finally, the finished machined rotors are transferred to a Holroyd Conturo deburring unit prior to delivery to the unload position.
"Yet, the manufacturing capabilities of each of the machine tools represent just part of the total solution", says Mr Hannah, Holroyd's sales director. "From day one, it was clear that the ability to meet the necessary throughput targets for the cell would hinge on the development of a parts loading system to enable the full potential of the production equipment to be realised."
The resultant solution is based on the proven capabilities of a Güdel high precision gantry positioning system which is capable of consistently delivering components weighing up to 110kg each to a few tenths of a millimetre at any of the machine tools in the cell.
With locational accuracy such a key issue, special attention was paid to the gripping mechanism, as well as the transfer of the process parts. Typically,each of the machine tools locates the components at their end faces, which means that the parts handling mechanism has to operate on the body of each rotor.
"This is relatively straightforward while they are at the rough turned state", explains Güdel's joint managing director, Gary Ottley. "But once the spiral form has been generated, this configuration causes severe problems for conventional gripping systems – especially as the system must be capable of accommodating a range of component diameters from 109mm to 160mm.
To overcome this, Güdel and Holroyd devised a solution in conjunction with Eclipse of Sheffield, which utilises a magnetic gripping principle (see Plate 8).
A further requirement of the parts transfer system is that some of the intermediate grinding operations call for the workpiece to be rotated through 180 degrees to enable each end of the rotor to be processed. This has been achieved by incorporating a high accuracy indexing mechanism from Manifold– another Reynold company – within the final installation.
Plate 8 Güdel and Holroyd devised a purpose-designed magnetic gripping system in conjunction with Eclipse Sheffield in order to ensure accurate location of compressor rotors ranging from 109mm to 160mm diameter at each stage in the manufacturing process
The resultant Güdel system combines the benefits of high accuracy –to match the precision of each of the Holroyd machine tools within the cell– with rapid traversing to ensure maximum production throughput.
For further information please contact: Gary Ottley at Güdel UK Ltd. Tel: 024 76 635977; Web site: http://www.gudel.com
