Measurement machine eases shift to aerospace

What is believed to be one of the largest co-ordinate measuring machines (CMM) in the north of England is the LK G80 installed at contract machinist, CTL Engineering.

What is believed to be one of the largest co-ordinate measuring machines (CMM) in the north of England is the LK G80 installed at contract machinist, CTL Engineering.

Ever since the machine was installed for inspecting mining equipment components for British Coal in 1988, the company has not only used it for internal quality control but has also offered its 3 metre x 1.5 metre x 1.5 metre high measuring volume for subcontract inspection work.

On the back of that, many new contracts for machining have been won said the system's manufacturers LK.

Traditionally an oil industry subcontractor, CTL has halved that sector's contribution to turnover to around 35 per cent, and moved into aerospace, which now accounts for 25 per cent of business.

Typical jobs going through the shop in September, for example, were Airbus landing gear components for Messier-Dowty, training bombs for Harrier jump jets, escalator winding mechanisms for London Underground and an aluminium-bronze submarine propeller requiring five-axis machining that the company completed by repeated repositioning on a four-axis machining centre.

CTL has also had a contract to inspect Eurofighter parts for BAE Samlesbury, which involved measuring the aircraft's fuselage frame.

The latter is 1.8 metres high, however, so the subcontractor asked LK to extend the G80's Z-axis by 300mm to accommodate the component.

To ensure that the machine was accurate over the extended volume, LK's customer support department carried out full error mapping and correction.

At the same time, as BAE supplied to CTL inspection programs written in Valisys DMIS (Dimensional Measuring Interface Standard), whereas the G80's control used the older CMES protocol which was retrofitted on a PC platform 10 years ago by LK to replace the orginal DEC VAX computer, together with new scales and drives.

This time LK was also asked to upgrade the machine with a modern PC running DMIS.

Despite the machine's age and it having been operated virtually round the clock since it was installed, it still measures very accurately, testament to the original build quality and the six-monthly calibration carried out by LK to ISO 10360-2 said the company.

The latest calibration certificate shows that the machine's original accuracy specification of MPEE (maximum permissible error when measuring length) of 14 + L/125 microns is still achieved.

CTL was one of the first subcontractors in the UK to obtain ISO 9001:2000 and earlier this year it received the SAE AS 9100 Revision B, which is the latest approval required by the international aerospace industry.

Both the G80 and the smaller G-90C CMM from LK underpin those approvals said LK.

According to Simon Walker, quality assurance manager at CTL, the new work came from all industry sectors and also from neighbouring sister company, TDA Solutions, which assembles clean rooms for mass spectrometry and manufactures sterilising equipment for hospitals and food factories.

Inspecting bought-in parts for the latter operation now accounts for eight hours' CMM time per week.

Commented Walker: "Aerospace customers have always demanded comprehensive CMM inspection of their components backed by full reports.

However, over the past few years, companies operating in other sectors have increasingly been demanding a similar service, including the oil industry where component failure can be catastrophic.

It has lead to a big increase in quality control workload and, together with the general upturn in business, meant that we needed a second CMM.

The G-90C is a quick machine, capable of inspecting any given part around three times faster than the G80, not surprisingly as the latter's bridge alone weighs seven tonnes." The measuring envelope of the new CMM is nominally 2,000mm x 1,200mm x 1,000mm and, owing to the complexity of many of the parts being inspected, has been fitted with a six-position stylus changer to avoid manual change and resets.

Walker estimated that automated stylus exchange saves eight hours of CMM time per week.

He continued: "When it came to invest in a second machine, we reviewed what was available on the market and decided that, in terms of speed and build quality, there was not much to choose between the different CMMs; they would all have been able to inspect our parts.

Where the LK machine scored was its ease of operation and programming.

The latter is particularly important here as eight-off is a big batch for us and we often inspect one-offs.

We were also happy with the support we have received from the supplier over the years." A general observation he made on the use of CMMs is that they make sure the machine tools are performing correctly, which he describes as a 'huge advantage' as it is possible to see if a series of components is drifting out of tolerance.

It allows timely investigation as to the cause and in addition helps in choosing the best machine to deploy on any particular job he added.

In 2005, CTL intends to upgrade both its CMMs by having LK fit its latest AIM controller and installing the manufacturer's proprietary Camio Studio software.

That would allow measuring programs to be prepared directly from a CAD model of the component, instead of having to program the CMM by the teach-in method.

More complex jobs such as a rotor blade currently take a day to program this way, whereas demonstrations given by LK engineers show that the same program could be produced in a couple of hours using Camio Studio.

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