The Huddersfield facility of Cummins Turbo Technologies has installed an Engis SPM single pass, four spindle, superabrasive bore finishing machine to help it reduce cycle times and achieve repeatability on the critical tolerances of two types of important turbocharger bearing housings.

Huddersfield is home to the European turbocharger manufacture and worldwide technical centre of Cummins Turbo Technologies, a company with a proven track record in the automotive sector. Around 1,000 people on site help design and manufacture the full range of Holset turbochargers and related components. These are supplied to various Cummins’ sister plants worldwide, where they breathe life into ever increasing numbers of the world's medium and heavy-duty diesel engines.

Essentially, the turbochargers manufactured at Huddersfield are split into four size ranges: mid-range; heavy-duty; high horsepower; and variable geometry types. To further enhance bore finishing operations (in line with strict tolerances) on its turbocharger bearing housings, the company recently considered the replacement of its conventional reciprocal honing machine, which although reliable was nearing the end of its useful life.

“We actually looked at replacing this machine a while ago and made an enquiry for an Engis machine because we knew it was based on single pass technology,” says operations engineer Howard Earnshaw. “Single pass bore finishing appeared both simpler and faster than conventional reciprocal honing and was therefore of great interest to us. We sent some bearing housings to Engis for bore finishing and the results were spot-on. However, due to funding restraints the project had to be postponed.”

With the recent upturn in the automotive industry, the project has been revived, and Mr Earnshaw insisted once more upon the consideration of single pass bore finishing technology. “We looked at three machines,” he explains. “In the end, the Engis machine was more robust than its rivals and we found the Engis team to be extremely responsive to our needs, which proved to be a major influence in our decision to buy the SPM.

The Engis SPM bore finishing machine supplied to Cummins Turbo Technologies features four spindles and a six station rotary index table that accommodates quick change fixtures for different types of turbocharger bearing housings. The machine uses three, single pass diamond tools to finish the bores with the fourth spindle fitted with an abrasive brush to remove any shards or metal residue.

Manufactured from grey cast iron, bearing housings are a vital turbocharger component. The housings provide locations for a fully floating bearing system for the shaft, turbine and compressor which can rotate at speeds up to 170,000rpm. CNC machinery mills, turns, drills and taps housing faces and connections, after which the bores are finish honed to meet stringent roundness, straightness and surface finish specifications.

Installed at Huddersfield in late 2009, the Engis SPM was subject to a strict testing programme that involved mounting the bearing housings it had processed on actual engine beds to ensure there was no change in performance resulting from the implementation of the new machine. With the tests successfully completed, the machine entered production at the start of 2010.

“The bore that we hone is not a straightforward through bore – it features two pods and the parallelism tolerance between the bores honed in each pod is tight,” Mr Earnshaw states. “However, the capability of the SPM is very adept at meeting these requirements in a repeatable and reliable manner. Bore roundness also features a critical tolerance, while bore surface finish is a further strict requirement.”

The four spindles of the machine are tooled to produce a sequence of: rough; semi-rough; brush; and finish. Programming the Mitsubishi CNC is said to be simple and all spindles come down simultaneously, with the table indexing one station at the completion of each cycle.

“As a result, a completed component emerges every 60 seconds,” says Mr Earnshaw. “Using our previous reciprocal machine the cycle time was in excess of two minutes. While quality was our premier concern, halving the cycle time helped justify the capital expenditure as it means we can achieve a quick return on our investment.”

Engis SPM series machines are designed specifically with small to medium sized parts in mind – internal diameters of primarily 50mm and smaller. Machines are available in four, six, eight and 10 spindle models, with stroke of 457mm offered as standard, although extended stroke options are available.

“The operators are very happy with the new machine,” concludes Mr Earnshaw. “It requires very little adjustment and also uses coolant instead of honing oil. Additionally, while Engis originally suggested that we should get around 10,000 parts out of the tooling, we have currently machined over 23,000 with the same set of tooling.”

Engis
www.engis.com