The level of after-sales service provided by coordinate measuring machine (CMM) suppliers is sometimes limited to a few days training and the supply of spare parts if the machine breaks down. At the opposite end of the scale is the service provided by Nikon Metrology, which as a CMM manufacturer and software developer is well placed to support a customer’s metrology function in its entirety.
A good example is the relationship with commercial aircraft component manufacturer, Hurel Hispano UK, Burnley. LK, now Nikon Metrology has not only supplied two CMMs, but has also written part programs, supplied fixtures to clamp components for inspection, and regularly supported the customer by providing an on-going service contract, telephone helpline and machine calibration.
In a recent project, Nikon Metrology produced a suite of 24 programs to inspect key parts, made predominantly from 1 mm gauge aluminium sheet, that go to make up the thrust reverser blocker door used to slow a regional jet on landing. Hurel Hispano UK had seen a dramatic increase in production volumes from two dozen blocker doors in total to 36 per month as sales of the regional jet grew rapidly. At the original volumes, it was easy to carry out minor reworking on the production line to make the parts fit together, but as orders continued to roll in it was clear that this approach was not sustainable, as it would have delayed deliveries. So the company embarked on a production capability study to ensure that all parts assemble first time.
This initiative injected a sudden urgency into an ongoing project started mid 2001 by Julian Rishton and Mike Mitchell, the engineers in charge of Manufacturing and Development at Hurel Hispano UK, to analyse thrust reverser production with a view to reducing manufacturing costs. The idea was to review the real tolerances of the manufactured components in relation to the design tolerances in the light of their accumulation as the product is assembled, a technique known as error budgeting. As the company’s CNC programming section is responsible for writing programs for machine tools on the shop floor as well as for the CMMs, the sudden increase in metrology workload to support capability studies as well as product development meant that additional programming resources were needed.
So CAD models with datums and inspection points for each of the 24 key parts for the regional jet blocker door were sent to Nikon Metrology, which wrote the inspection programs for running on the G-90C CMM on the Burnley site. A set of flexible fixtures was also provided by Nikon Metrology to enable a majority of the parts to be clamped on the machine table; only four special fixtures had to be made.
Checks were then carried out by Hurel Hispano UK on batches of 16 thrust reverser components to verify the capability of the manufacturing process, which involves stretch wrap forming and fluid cell pressing. Inspection cycles, entailing measuring of between 30 and 150 discrete points, took up to 20 minutes. Considering that the parts are of sheet metal that has been heat treated and quenched, tolerances on surface profile, edge of part and machined features are very tight at ± 0.50 mm, opening slightly to ± 0.75 mm for the larger components.
Included in the Nikon Metrology package, in addition to inspection programs, was a pictorial front-end called Launchpad that allows the operator simply to click on a photograph of the component to be measured in order to select the correct inspection routine. Another bespoke feature was automatic generation of hard copy graphical reports to suit Hurel Hispano’s requirements and those of its customer. As well as containing the raw results, without any manual intervention the reports link them to easily understood illustrations based on the CAD model and include ‘traffic light’ colour-coded results for each dimension measured.
The process capability studies included CMM inspection of each component at various stages in its production, and investigation and improvement of the tools used in the forming and pressing operations and in subsequent blocker door assembly. As a result, manufacture is now considerably faster and there is less rework. Overall component quality has been improved and there is a significantly higher level of repeatability, as confirmed by the hard gauging used for 100 per cent inspection of the fully assembled thrust reverser at the end of the production line.
The Nikon Metrology G-90C on which the measurements were made was installed at Burnley in 2000, but Hurel Hispano UK, formerly Lucas Aerospace, had been associated with the CMM supplier since the mid 1980s when a Nikon Metrology Metre Four was installed with a very large measuring envelope. In 2001, it was upgraded with new drives, controller and the latest CAMIO Windows-based, DMIS programming software that works directly from the 3D CAD model of the part to be inspected.
When the G-90C was purchased, Nikon Metrology’s customer support department was asked to supply fixtures and programs for carrying out pre-production interchangeability (ICY) checks on two types of blocker doors for a large passenger jet, so Hurel Hispano UK had early experience of the supplier’s capabilities in this area. It was followed shortly afterwards by Nikon Metrology providing four programs and fixtures for final inspection ICY checks using the Metre Four CMM. In this case, the whole profile was inspected of the upper and lower left- and right-hand blocker doors for another twin-jet aircraft, as well as key interface features such as edges, bushes and latch positions.
Programs may be swapped between the CMMs, both of which have been provided with a written driver to enable use of third-party geometric dimensioning and tolerancing software, a cornerstone of error budgeting when dealing with 3D assemblies.
Hurel Hispano UK proposes to upgrade another CMM on site with new drives, controller and CAMIO software to increase measuring capacity and flexibility. The machine will also be equipped with a loading system to assist handling of large, pivoting blocker doors on and off the granite.