CMMs keep latest Astons in shape

The factory for the forthcoming Aston Martin DB9 GT includes a new metrology facility to check the quality of the lightweight aluminium-bonded frame structure before the car is hand built around it.

The body of the Aston Martin DB9 GT, launched at last month's Frankfurt Motor Show, has an aluminium-bonded frame that is 25% lighter than that of the DB7 that it replaces, yet has double the torsional rigidity.

To check the quality of this structure before the car is hand built around it, a new metrology facility has been established at the company's recently opened factory in Gaydon, Warwickshire.

Central to its operation is a pair of LK computer-controlled LY90S horizontal-arm, co-ordinate measuring machines (CMMs) for inspecting external features on both sides of the vehicle simultaneously in fully automatic, mirror-image cycles that take around two hours.

Together the CMMs provide a measuring volume of 6000 x 3000 x 2500mm, sufficient to contain the whole vehicle, which is held in "car line" by bespoke fixturing during measurement.

Results are accurate to better than 10um over the length of the car.

A further key feature of the installation is LK's Camio interface software, which enables the data within Aston Martin's CAD files to be downloaded to the CMM environment and used to create measuring programs directly from the models.

When the DB9 enters full production early next year, every day a body fitted with doors, bonnet and boot lid, a so-called "body complete", will be taken out of production at random and checked for each of four car variants (left- and right-hand drive versions of the coupe and the convertible).

In addition, the LK LY90S cell will potentially have to measure a wide range of items, from a fully assembled car to a single component.

The purpose will be to investigate build issues, verify supplier measurements and make data available to the engineering and design departments for finessing and continuous product improvement.

A further duty will be to support the development of future Aston Martin car models through their prototype stages.

In addition to inspecting the DB9 body during its development, the LK LY90S cell was used routinely to measure a wide variety of parts from simple brackets to a complete transmission, as well as to check fixtures used on the framing machine in which the car body is bonded.

To achieve this breadth of measuring capability, the flush-floor steel bedplate has been drilled at 200mm centres to accept flexible fixturing, allowing components of any size to be clamped accurately for inspection.

To ease the workload on the cell when measuring smaller components, an additional LK bridge CMM, a G90-C with a measuring envelope of 800 x 700 x 600mm, has been installed in the same temperature-controlled room.

Programs are interchangeable between the two machines.

According to Simon Skinner, Projects Engineer for the Manufacturing Engineering Department at Gaydon: "The LK LY90S cell supported the DB9's prototype phase right from the start, helping to reduce the lead time to develop the car.

This was possible because LK's Camio interface software, uniquely at the time, was immediately able to read the I-Deas CAD files from our design department, enabling inspection programs to be written in advance of prototypes becoming available".

So successful was this process that Senior Dimensional Technician Richard Winspear had prepared all the programs for inspecting the DB9 "body complete" before the LK CMMs had even been installed in January this year.

It was then a simple matter to prove out each program on the machine and make minor adjustments.

Said Winspear: "I programmed each element of the car body separately using an offline LK Camio terminal, so we ended up with a suite of modules that can be run in any sequence using LK's graphics-based Launchpad software.

The automatic cycle can be overridden as required to enable manual inspection of additional features".

"This approach is helpful during the development phase while we need to check individual elements.

When inspection starts in support of production, the modules can be stitched together into one seamless, fully automatic sequence for measuring 700 points over the entire body".

When production starts, Aston Martin will take advantage of LK's statistical process control software to analyse manufacturing trends and will be able to embed SPC charts in graphical reports generated automatically by a further software module.

The reporting system has been adapted from that used by sister Ford Premier Automotive Group companies, Land Rover and Jaguar, which use LK CMMs to support their metrology requirements.

Skinner concluded: "Our investment in the new metrology facility at Gaydon sprang from a projected doubling of annual production next year.

Moreover, an additional model to be introduced in 2005 will double production output again".

"Our previous inspection techniques using portable measurement arms, verniers and gap gauges would be too slow to support these larger volumes, which is why we have moved over to automated inspection using LK CMMs".

"In any case, the immediate availability of measured results in electronic form and the ability to tie them back to the CAD model allows us much wider scope in integrating the quality function with other departments and brings us in line with best practice within the volume car manufacturing sector".

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