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Increasing engine productivity

Horizontal machining centres help Mahle to cut cycle times by a third

Posted on 07 May 2018 and read 4401 times
Increasing engine productivityMahle Powertrain — an independent company specialising in the design, development, testing and manufacture of ‘combustion engines’ — has installed a second pair of twin-pallet horizontal machining centres (HMCs) at its factory in Booth Drive,Wellingborough.

A four-axis Heller H2000 has joined two identical models in an eight-machine production line dedicated to manufacturing cylinder blocks, while a larger five-axis FP6000 has been added to a flexible machining cell to expand its capabilities.

At the end of 2016, Mahle project manager Geoff Brown and production engineer Bob Price decided that the decade-old line producing aluminium engine blocks for a major British OEM needed to be upgraded. It comprised six HMCs (each performing separate operations) plus two bore-honing machines.

All the HMCs had originally been supplied by a Japanese manufacturer; in early 2017, the first two machines in the line were replaced with Heller H2000s.

Designed at Heller’s German headquarters, they were manufactured at the group’s UK factory in Redditch (www.heller.biz).

Mr Brown said: “We were already familiar with Heller machines, as we have successfully operated 21 of them for more than a decade at our facility in nearby Ryle Drive.

“They were used to make cylinder heads and cylinder blocks for a British manufacturer of off-road plant, although that contract has now ended and the machines have been sold.

“I also had experience of working with Heller horizontal machining centres at another engine manufacturer, which operated more than 20 of them in a transfer line.

22 Heller pic 2“We sent some V8 cylinder blocks to Heller’s Redditch technical centre, where they carried out Op 10 and Op 20 trials on an H2000 HMC.

“Op 20 was particularly successful; with new fixturing, the machine overcame a problem we were having machining a side port in the new model of cylinder block.”

As a result of these trials, the first two machines in the production line at Booth Drive were replaced by Hellers. Mr Price says the benefits were immediately apparent.

“The cycle time for each of the first two operations is one-third faster on the new machines — eight minutes instead of the previous 12.

“Moreover, the 33% time reductions have been achieved despite adding extra routines by including some sections of the Op 40 cycle into Op 10 and parts of Op 30 into Op 20.”

Machine performance

The greater productivity is largely down to the rigidity of the H2000s, the higher speed of the HSK63A spindles (16,000rev.min), and programmable through-tool coolant up to 70 bar — all of which allow the use of higher cutting-feed rates.

Rapid-traverse rates are also faster than before, and further time savings are gained by using integral hydraulics to automatically clamp the engine blocks — along with air-detect to check that components are seated correctly.

St Heller pic 3Furthermore, a probe in the tool magazine for identifying broken cutters shaves off further time by removing that checking function from the machining cycles.

Also key in the decision to buy the Heller machines was their efficient swarf management.

Mahle says this is essential for removing large amounts of aluminium chips efficiently from the machining area and avoiding hours of costly machine stoppage to clear accumulated swarf.

A further feature highlighted by Mahle is the no-scan/no-run safety software, which is run through the Siemens control to prevent a component from being machined unless its bar-code has been scanned.

Linked into Mahle’s new SAP enterprise resource planning (ERP) system, which became operational at the start of 2018, this provides traceability to ensure stock accuracy and has eliminated having to track paperwork manually.

Capital-expenditure approval to replace a third HMC was given by the Mahle board in mid-2017, resulting in another Heller H2000 being ordered. Also built in Redditch and commissioned at the beginning of this year, it took over Op 30 from its predecessor in February.

Again, the previous 12min cycle has been cut to 8min, despite taking some of the load from Op 50 as well; and when the fourth H2000 undertakes responsibility for Op 40, it will carry out some of the Op 60 cutting scheme, as well as delivering a more-efficient Op 40 routine.

By then, the TAKT time for the whole line will be 10min — although undertaking Ops 50 and 60 on Hellers in the future will reduce this time to 8min.

Shopfloor re-organisation

Another on-going project at the Booth Drive facility is the re-organisation of the shopfloor so that all six HMCs — plus the two bore-honing machines — are in a straight line (currently, some zig-zagging is involved).

This will allow two operators to be deployed to other work — one from Ops 50 and 60 and one from the honing section — thereby helping to amortise the investment more quickly.

The overhead gantry facility is being extended and reconfigured so that the existing Dalmec component-handling equipment can be retained for loading and unloading the 45kg aluminium blocks.

St Heller pic 4Another advantage of the re-arrangement will be to slash work-in-progress to two or three components; currently, there can be as many as 100 parts queuing on the shopfloor.

This will provide major savings in tied-up capital, reduce double handling, minimise the risk of component damage, and take up less space on the shopfloor.

The line currently operates 24hr a day, five days a week; previously, it needed to run 24/7.

It also maintains tight tolerances; this includes 50-70µm on the ‘true position’ of some features, and 10-12µm on holes up to 16mm in diameter.

Before honing, each cylinder bore and crank bore is pre-machined to 28µm roundness, 0.15mm for true position and 50µm for squareness.

Five-axis capability

At the start of this year, a Heller FP6000 five-axis HMC (built in Germany) was added to a pre-existing flexible machining line at another location in the factory.

The line already comprised a vertical machining centre and three HMCs of a different make — all five-axis models.

During a recent Open Day at the Wellingborough factory, Mahle explained that the line had been relaunched as a facility for the manufacture of cylinder heads and cylinder blocks for V12 and in-line six-cylinder engines, as well as a wide range of other prismatic parts that could be one-offs or in batches up to 20,000 — for customers in any industry.

Previously, the line was used to produce cylinder heads for a German OEM.

To make it more suited to a diverse range of sub-contract work — and to reduce future fixturing costs — all five machines are being fitted with a zero-point modular plate system for work-holding.

The line will initially machine a variety of components, although it has the potential to produce components for customers in many different sectors.