Single-hit production solutions are known to produce significant reductions in cycle times compared with multiple set-ups on several machine tools.

However, few applications result in a time saving as great as that being achieved by the Plymouth-based sub-contractor Morris Engineering, when producing a military-aircraft gyroscope part from S420 stainless-steel bar.

A 36mm-capacity Biglia B436-Y2 twin-spindle lathe with two Y-axis turrets — supplied by Kenilworth-based Whitehouse Machine Tools Ltd (www.wmtcnc.com) — is now used to turn and mill the component in a 7.5min cycle.

Previously, it took 10-times longer to machine the part on three separate machines: a three-axis CNC lathe, a CNC mill with a fourth axis, and finally a manual lathe (this was needed to achieve the required surface finish in a face groove). The 10-fold improvement mentioned is in cycle time alone; the former production route also required inter-machine handling, so the costs associated with extra labour and administering work-in-progress are also saved.

Morris Engineering’s production director, Antony Dyer, says: “The main problem previously was the limited spindle speed of our three-axis CNC lathe. With the higher speed of the Biglia lathe and the ability to produce the part in one hit, not only is the overall cycle time massively faster, we have also raised the yield of good parts by a fifth — from 80 to over 95%.”

Managing director Tim Winzer said: “The one-hit machining capability of the Biglia lathe has already resulted in our receiving an additional aerospace contract to produce another complex stainless-steel part for a military aircraft. We would not have won the job if we had quoted based on a multi-hit machining approach; in fact, it would have been pointless quoting at all.

“Now we intend to leverage our economical one-hit turn-milling capability and our AS9100 accreditation — together with our bronze award in SC21 supply chain management — to pursue civil aerospace work at Tier One or Tier Two level, which we are actively seeking.

The machine will also be ideal for fulfilling oil and gas contracts, which used to account for a quarter of our turnover before the latest downturn in that market. So when normal volumes return, we are well placed to offer extra highly capable capacity coupled with short lead times.”

Two-machine strategy

The B436-Y2, delivered in March this year, is the second of two Italian-built Biglia turn-mill centres purchased from Whitehouse Machine Tools. In January, a twin-spindle B465-T3Y3 with three Y-axis turrets was installed after Morris Engineering discovered that it could purchase both machines for the price of a single lathe offered by a shortlisted competitive supplier.

So instead of having one big lathe producing components from 6 to 65mm in diameter, smaller parts up to 36mm diameter are machined on the ‘nimble’ B436-Y2, while larger parts go onto the B465-T3Y3. Deploying two machines rather than one not only doubles output but also provides cover in case of down-time on one of the machines.

Both Biglia lathes are used for the production of a family of five stainless steel gyroscope parts in batches of around 200, the previously mentioned component being one of them. Three are turn-milled on the smaller lathe, one on the larger machine, and the fifth can be produced economically on either.

LNS Quick Load Servo 80 magazines for 1m-long bars were supplied by Whitehouse Machine Tools for feeding both turning centres as part of the turn-key packages.

Furthermore, a twin conveyor arrangement on the output side of each lathe directs machined components onto a second conveyor at right angles to the first, carrying them into a container at the front. However, by the time a bar remnant arrives on the first conveyor, the control has already told the second conveyor to reverse direction so that the bar end is routed to a container at the rear.

The extensive milling and drilling capability of both lathes has resulted in a dramatic lowering of the workload on the milling section at Morris Engineering, freeing up a lot of capacity — so much so that the company recently sold an ageing vertical machining centre and did not replace it.

Novel machine design

A particular feature of the compact B436-Y2 (it has a 3.7 x 1.5m footprint, without peripherals) is that the counter-spindle has two degrees of freedom; it can move in both the X axis and the Z axis, allowing it to be offset by up to 170mm from the centre-line of the main spindle.

This arrangement eliminates interference between the turrets when simultaneously machining the front and reverse ends of complex components; it also allows an unusual arrangement where a tailstock can be advanced in the space vacated by the offset counter-spindle to enable turn-milling between centres (using the main spindle) and simultaneous reverse-end machining (using the counter-spindle and second turret).

The machine’s speed and capability are derived from 11kW 7,000rev/ min (62Nm of torque) opposed spindles and 4.6kW 6,000rev/min (22Nm of torque) tool drives in the 12-station turrets, which offer a station-to-station indexing time of 150msec. The rapid traverse rate is 30m/min in Z and half that figure in X and in the ±25mm Y axes.