Emerald Group Publishing Limited
Copyright © 2004, Emerald Group Publishing Limited
Sub-contractor win major contract
Sub-contractor win major contract
Keywords: Contracts, Grinding, Bosworth Tools
Having tendered for a major contract a year or so ago and failed to win the order, precision grinding specialist Bosworth Tools decided it was time to improve its production efficiency. And as a result, when it got another chance to quote for the same job with a new Okamoto IGM 15NC internal grinding machine and an Okamoto ACC 63ST surface grinder supplied by the 600 Centre of Shepshed near Loughborough installed, the Hinckley-based sub-contractor won the day.
According to Managing Director, Mike Fawcett, not only did these new machines help to boost production efficiency and reduce cycle times by 40 per cent on its wear sleeve component contract, but also the company's new found repeatability and consistency of production had such an effect on operational standards that it became a major influence on the business.
Bosworth Tools uses both Okamoto machines to finish grind the 63.5 mm diameter by 31.75 mm long 60 HRC steel wear sleeves. The components feature a 53.97 mm through bore and a 10 mm tolerance recessed section on the front end that originally caused so much disappointment in losing the original order. The IGM 1-5NC internal machine now grinds four features of the sleeve which includes the main bore, recess and two faces in a single chucking operation, while the ACC surface grinder finishes a top flat face. A cylindrical grinder is then used to finish grind the outside diameter.
Previously, when Bosworth quoted for the job and made some sample parts, it used its conventional grinding machines which were capable of automatic cycle. However, these machines required five operations and took around 10min grinding time to produce a part. But now the Okamoto machines are said to be able to reduce the grinding time by some 4min a part and with 200 sleeves required each week, this stacks up to a considerable saving in production lead time.
As well as reducing machining time, the new Okamoto internal grinder has enabled other improvements to this contract, as Mike explained: “The overall quality and accuracy of wear sleeves has been significantly improved and especially the maintenance of the 10 micron tolerance of the recessed section which is now a simple process to achieve. Previous methods meant it was really difficult to hold tolerances on this feature but the IGM has made the complete recessing operation a success due to its inherent accuracy and combined programmable automatic wheel dressing routines. In fact, after we delivered the very first batch of sleeves, produced by the new method, the customer came straight back saying the parts were perfect”.
Set-up in 1974, Bosworth Tools originally produced and reground cutting tools. However, when Mike joined in 1978, the emphasis was changed to providing a subcontract grinding service. The company purchased its first Okamoto microprocessor controlled internal grinder in 1988 and added a second identical machine within 12 months.
Over the following years, the emphasis changed to providing internal, external and centreless grinding capacity resulting in the six-people company now having nine grinding machines installed in its 3,500 ft2 factory. Components such as pins, spindles, sleeves and bushes are regularly produced for industry sectors, such as, aerospace and bearings, in batches as small as 50 parts.
The Okamoto IGM 15NC has a 20,000 rev/min spindle, 4 kW main drive and has a swing of 254 mm. It can handle internal diameters ranging from 6 to 152 mm and has a grinding stroke of 127 mm. Controlled by a two-axis Fanuc 1ST CMC system, it has a very easy-to-use conversational programming system which Bosworth Tools has put to good use over its wide range of ground components.
While predominantly used on the wear sleeve contract, the IGM 15NC has also enabled Bosworth Tools to improve machining efficiency on other projects such as the grinding of a tractor transmission component which looked rather like a brake drum with a central multi-diameter boss and a hollow spigot.
Previously ground involving five separate operations on the microprocessor controlled Okamoto internal machine, this 203 mm diameter by 50 mm wide steel component, with an 89 mm diameter central boss and a 50 mm stepped bore, needed two operators for one of the operations with one permanently required for inspection duties. The company then purchased an older technology CNC machine and was able to produce the part in a single chucking with one operator. But with the latest Okamcto CNC machine the cycle is reduced considerably and the quality and ease of production described by Mike as being “infinitely better!”
When considering the purchase of another internal grinding machine for both wear sleeve and tractor transmission parts, Bosworth Tools initially thought to buy another second-hand CMC machine due to the higher cost of the latest Okamoto model. However, the company had trouble tracking down a suitable machine and eventually contacted the 00 Centre to see if it could help to locate one that was used.
This led to a demonstration of the IGM 15NC, which was put through its paces at the 600 Centre's showroom in Shepshed, when Bosworth's were surprised over what could be achieved with the latest developments and what it could get in improved production for its investment in a new machine. This also led to a casual interest in the Okamoto ACC surface grinder which was installed in the showroom and following detailed discussions, Mike was able to negotiate a package for both, resulting in their installation at Bosworth Tools' works on the Sketchley Lane Industrial Estate in February 2003.
“The IGM 15NC is an unbelievably accurate machine”, added Mike. “It's so easy to program using the conversational system and we consistently produce high precision parts very easily without too much attention to the process once it is set. We also like the automatic in-cycle dressing feature which has enabled us to fine tune and optimise the operational cycle on the 60 HRC wear sleeves where the 50 mm outside by 25 mm long aluminium oxide wheel has to be dressed four times in each component grinding cycle. As well as enabling us to secure this major contract, the Okamoto has significantly improved our ability to offer higher quality internal grinding capacity on a sub-contract basis”, he concludes.