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Horizontal Machining Centre Installed at Gretone

Horizontal Machining Centre Installed at Gretone

Added to MTDCNC by MTDCNC on 05 January 2012

Sometimes you need luck, said Ian Hawkins, managing director of precision subcontractor Gretone Engineering. Within weeks of him and fellow director Kevin Owen leading a successful management buyout in April 2010, the company, which had specialised in aerospace component machining, quoted for and won an important contract to supply 100 machined cast iron housings a week which required very close tolerances for size, position, flatness and surface finish.

Said Mr Hawkins: While our existing installed machines were capable of producing the part it was very clear we needed a high quality machining centre to achieve the levels of production consistency in cast iron the customer was looking for.&rdquo

The company already had an existing Toyoda FH60 horizontal machining centre installed in 1989 engaged on aircraft component machining in the 30,000 ft2 machine shop based in Lytham St Annes. Said Mr Hawkins: Even with 21 years of constant service its production capability and achieved quality levels had never been questioned. While we looked at and dismissed other machines, it was really an open and shut case that this was the level of machine tool quality that we needed for parts of this type and we decided to contact the UK sole agent 2D CNC of Rushden, Northants which resulted in the installation of a Toyoda FH630SX four-axis horizontal spindle machine with twin pallets.

The machine which has a working envelope of 1,000 mm in X, 800 mm in Y and 850 mm in Z with a positioning accuracy of + 0.003 mm and a repeatability of 0.002 mm. It was Gretone's first installation following the buyout and with growing success in the next 18 months, four other machine tools worth over £750,000 were also installed. From day one, despite the uncertain market conditions, the company has expanded from a previous £3.4 million to £4.8 million turnover and is well on target to hit £6 million this financial year.

The original workforce of 61 has been progressively expanded to 69, largely to meet demands from its diversification that now adds general engineering customers to its aerospace business, which for the previous 30 years of its production history dominated the order books. However, while aerospace currently accounts for around 40 per cent of sales, with future contract potential this should again expand to account for around half of production. Around 20 per cent of components produced are exported into Europe.

Gretone Engineering operates around the clock with batch sizes, due to the type and complexity of work produced that varies between just four and 30 parts. As most components supplied to the civil aerospace sector are largely airframe and flight control parts up to 5 m by 2.5 m in size, a batch of 30 involves considerable machining demands. However, with many of the orders being repeats of proven production methods, there is a growing need for prototype and new component development with customers.

Materials processed include aluminium, aircraft grade stainless steel, AMS forged steel, titanium and cast iron with cycle times that vary between 55 hours to just two minutes on small turned parts. As the business is developing Gretone is also responding to customer requirements to produce sub assemblies to accompany machining which Mr Hawkins feels will become another growth area and an important element in the company portfolio of services.

Mr Hawkins reckons the installation of Catia V5 CADCAM software revolutionised programming for its 4- and 5-axis machining and as part of the company's quality regime, every single component produced is subjected to a critical feature report which is logged against an individual serial number for traceability.

In order to meet this quality audit trail requirement, stability of the machine and its ability to perform in a consistent manner over extended production periods was the key factor in the decision to purchase the Toyoda FH630SX. In particular, the use of dual ballscrews mounted on both the Y- and Z-axes, linear scales and Toyoda's low-friction roller bearing based linear guideways that provide twice the rigidity and three times the vibration damping of traditional ball bearings, these were important factors in the machine build specification for the subcontract company.

The 18 tonne machine has two pallets each 630 mm square with a 60 tool magazine. It has a rapid traverse rate of 60 m/min with an acceleration of 1G which is a significant aid to productivity when positioning. The spindle is 18kW. To illustrate the complexity involving the machining of the 400 mm by 200 mm by 85 mm cast iron housings, 57 tools are in use. Mounted on each pallet is a cube for which three faces are used to enable the part to be progressively sequenced from face to face of the cube to process the finished part in three operations.

The initial cycle enables the raw casting to be skimmed in order to create a datum face with process relocation holes. When the part is relocated to position two, the outside sealing face is machined, a series of bores and counter bores of 75 mm, 90 mm and 100 mm as well as features on the edge of the component that include slots and angled deep holes to break into the bores are machined.

When the part is relocated for the final machining process the original datum face is re-skimmed to provide a seal with further bores and counter bores finished to size. All faces must be square and flat within 15 microns and certain key features have positional tolerances within 12 microns. Altogether some 17 holes are drilled and tapped around the housing.

As Mr Hawkins maintains, with the equipment installed and being able to apply aerospace production disciplines and capabilities to the general machining sector to provide high orders of quality on the more complex components the risk from all eggs in one basket' is significantly reduced. Commenting on skills, Mr Hawkins maintains the company is investing heavily in providing training for its three apprentices and plans to recruit a new apprentice every year to ensure continuous development of a capability to meet customer demands.

 


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