The installation of a fixed-head twin-spindle twin-turret turning centre at Coleshill-based electrical-wiring conduit manufacturer ABB Cable Management Products Ltd brought about a fundamental change in the way the company turn-mills its cable end fittings.

The resulting benefits include: cycle time savings of up to 70% (with more to come), reductions in manufacturing cost, scrap and returns; and eliminating the need to outsource 10% of production to sub-contractors.

These benefits will combine to amortise the cost of the Miyano BNE51-MSY — supplied by Bushey-based Citizen Machinery UK Ltd (www.citizenmachinery.co.uk) — well within 18 months of its installation at the beginning of this year.

Manufacturing-unit manager Andrew Fellows describes this payback time on a major item of capital expenditure as “brilliant”.

Every week, 100,000m of ABB flexible metal conduit and 65,000m of nylon conduit find their way into industry (predominantly the automotive, rail and mining sectors) in Europe, the Middle East and China — and even as far afield as Australia.

Some is also destined for use in the parent group’s robot systems. With these volumes of conduit, there is a correspondingly high demand for the fittings required at both ends of every length of conduit.

Most of these fittings are made of brass, although some stainless steel, aluminium and plastic varieties are also used.

Fittings needed in large volumes are produced in-house on six cam-type multi-spindle autos, while the shorter runs are completed on four single-spindle single-turret CNC lathes — and now the Miyano twin-spindle twin-turret turning centre, which replaced a similarly specified but ageing model on which one of the turrets was defective.

‘Simultaneous benefits’

Comparing the performance of the latter two lathes, Mr Fellows said: “In the first two weeks of the Miyano being installed, we transferred the manufacture of four fast-moving products onto it; all these benefitted from drilling on both end faces simultaneously, at the main spindle and counter-spindle.

“The average cycle time saving was 59%. The largest reduction was 70%, with the turn-mill cycle now taking 40sec to complete on the Miyano.”

Senior operator Dan Gardner added: “So far, we have only taken advantage of cutting with two tools at a time, but the superimposition function in the Mitsubishi M730VS control, coupled with Y-axis movement of the upper turret and X-axis travel of the counter-spindle, allows three tools to be in cut at the same time. Moreover, after five days’ training from Citizen — both on- and off-site — we carried out a time study on a complex fitting that will see an 80% reduction in cycle time from 230 to 46sec.”

He went on to describe a further benefit that comes from the ability to have 6,000rev/min live tools with 20Nm of torque at all stations in both turrets (a total of 24 positions); and whereas 85% of production on the single-spindle lathes is currently from hexagonal bar, the plan is to reduce this to zero in favour of round bar over the coming years, as machines are upgraded and powerful driven cutters can mill the flats economically.

This process is starting with the Miyano.

The main advantage will be the longer service life of the lathes — and of the bar magazines feeding them — due to the absence of interrupted cutting of hexagonal stock (and hence lower vibration levels).

In the case of the Miyano, it will also allow round bar at the full 51mm-diameter capacity to be rotated in both spindles at the maximum speed of 5,000rev/min, whereas it would need to be backed off by 75% to run the largest possible size of hexagonal stock.

For this reason, hexagonal stock currently machined on the BNE51-MSY at Coleshill is restricted to 38mm, so that it can be rotated at full speed.

Machine rigidity

Mr Gardner says that despite currently using mainly hexagonal stock, the rigidity provided by the Miyano’s bed, hand-scraped box slideways, spindles and turrets is sufficient to allow total tolerances down to 30µm to be held on fittings; this is the level of accuracy needed for explosion-proof and watertight conduits.

Data collection and display on ‘dashboards’ of overall equipment effectiveness has been instigated by Mr Fellows since he started at the factory in July 2018.

Optimisation of every aspect of round-the-clock production has resulted in 24% more output in five days than was previously achieved in seven days, reducing manufacturing cost by 17% and boosting competitiveness.

Installation of the Miyano, with its higher levels of productivity, will improve these figures further, as will a new off-line tool pre-setter, which will cut the present 60min change-over time for the next batch run by up to three quarters; batch sizes can be as low as 50-off.

In conclusion, Mr Fellows said that selection of the Citizen Miyano BNE51-MSY was down to its cost being 30-40% less than two alternatives considered and the lead time from order to delivery being the shortest — just 12 weeks.