Sometimes you need luck,” says Ian Hawkins, managing director of the precision sub-contractor Gretone Engineering. Within weeks of him and fellow director Kevin Owen leading a successful management buy-out in April 2010, the company, which had special-ised in aerospace component machining, quoted for and won an important contract to supply 100 machined cast-iron housings a week.
The parts required very close tolerances for size, position, flatness and surface finish; and while Gretone’s existing machines were capable of producing the part, it was clear that the company needed a high-quality machining centre to achieve the levels of production consistency in cast iron the customer was looking for.
The company already had a Toyoda FH60 horizontal machining centre — bought in 1989 and used for machining aircraft components — in its 30,000ft2 machine shop in Lytham St Annes. Mr Hawkins says: “Even with 21 years of constant service, its production capability and the quality levels it achieved had never been questioned; and while we looked at other machines, it was really an open and shut case that the Toyoda offered the level of machine tool quality that we needed for parts of this type. We subsequently installed a Toyoda FH630SX four-axis horizontal machining centre with twin pallets.”
The machine — supplied by Rushden-based 2D CNC Machinery Ltd (Tel: 0844 871 8584 – www.2DCNC.co.uk) — has a working envelope of 1,000 ¥ 800 ¥ 850mm, a positioning accuracy of ±0.003mm and a repeatability of 0.002mm. It was Gretone’s first machine installation following the buy-out; and with increasing success in the next 18 months, four other machine tools worth over £750,000 were also installed.
Despite uncertain market conditions, the company has increased its turnover following the buy-out, from £3.4 million to £4.8 million — and it is well on target to hit £6 million this financial year.
Diversification
The workforce numbered 61 at the time of the buy-out but has grown to 69, largely to meet the demands of Gretone’s diversification, which has seen the company add machining for the general-engineering sector to its aerospace work — the mainstay of the business for the previous 30 years. Aerospace currently accounts for around 40% of sales.
Batch sizes vary between four and 30 parts; and because most of the components supplied to the civil-aerospace sector are largely airframe and flight control parts up to 5 x 2.5m, a batch of 30 involves a considerable amount of machining.
Materials processed include aluminium, aircraft-grade stainless steel, AMS forged steel, titanium and cast iron. Cycle times can be as long as 55hr, or as short as just 2min (for small turned parts). Increasingly, Gretone is producing sub-assemblies to accompany machining, and Mr Hawkins feels this addition will become an important factor in expanding the company.
With regard to programming, Mr Hawkins says the installation of Catia V5 CAD/CAM software revolutionised this for Gretone’s four- and five-axis machining; and as part of the company’s quality regime, every component produced is subjected to a ‘critical feature’ report and logged against an individual serial number for traceability.
Consistent performance
In order to meet ‘quality audit trail requirements’, the ability of the Toyoda FH630SX to perform in a consistent manner over extended production periods was the key factor in the purchase decision. Contributing to the machine’s performance is the use of dual ballscrews on both the Y and Z axes, linear scales and Toyoda’s low-friction roller-bearing linear guideways (these provide twice the rigidity and three-times the vibration damping of traditional ball bearings). The 18-tonne machine has two pallets (each 630mm square), a 60-tool magazine, a rapid-traverse rate of 60m/min, an acceleration rate of 1g and an 18kW spindle.
Typical of the type of component machined is a cast-iron housing that measures 400 x 200 x 85mm and requires the use of 57 tools. Each pallet is fitted with a cube fixture, and three faces are used (the part is sequenced from face to face of the cube and finished in three operations).
The initial cycle sees the raw casting skimmed to create a datum face and the machining of process location holes. At the second position, the outside sealing face is machined, as are a series of bores and counter-bores, as well as features on the edge of the component (these include slots and angled deep holes that break into the bores). At the final machining position, the original datum face is re-skimmed to provide a seal, and additional bores and counter-bores are machined to finished size. All faces have to be square and flat within 15µm, and certain key features have to be within a positional tolerance of 12µm.
To ensure that Gretone can maintain the skill levels it requires, Mr Hawkins is investing heavily in providing training for the company’s three apprentices; he also plans to recruit one apprentice every year.