Substantial cost and technology benefits have been introduced into BAE Systems Samlesbury to support Typhoon assembly manufacturing. The project team of MSP and BAE Systems, for the fixture, and Delcam, for the systems integration, has now achieved maximum benefits. Analysing production data of over 700 foreplanes, machining time has been reduced in excess of 60%, and part quality and production scheduling has been improved.

This small front wing for the Typhoon is an essential component of the strategic and tactical performance of the aircraft. It is designed with inherently unstable flight and only remains airborne due to flying attitude corrections being applied to the component 100s of times a second. Consequently, it is a critical flying component, which makes its manufacture of crucial importance to BAE Systems.

This complex, high-value part is diffusion bonded out of a number of titanium sheets then

super-plastic formed. The process involves extremely high temperatures and, after completion, only a loose relationship exists between the part's new state and any previously defined datums. Due to the nature of the SPF process, these deviations can be as much as 4mm.

After forming, excess material required for the SPF process has to be milled away so that the machined surface blends closely with the adjoining formed aerofoil surfaces. The shallow, tapered shape adds to the problems of recovering from the datum shift to proceed with the milling operations.

Old Process

The original process started with the foreplane being located manually on a fixture to machine one side of the part. It was then turned over and re-located by the operators prior to running another part program. This was repeated two further times, each time requiring a different fixture. The quality of the finished part was totally reliant on the ability of the operator to manually adjust the foreplane position and machining supports relative to the fixture datums.

Although this four-stage setup compensated for the SPF-created datum shifts, it inevitably took many hours. Furthermore, it suffered from a high degree of process variability due to the large amount of manual setting. This not only created quality issues that required manual reworking to achieve specification, but also had substantial adverse effects on job scheduling.

BAE Systems recognised that something needed to be done to improve the process to reduce variable part quality and stabilise the erratic production times.

New Process

After a detailed study of the process, BAE Systems' engineers and machine tool and metrology experts Metrology Software Products Ltd. (MSP) designed an innovative new process to solve the problems. Drawing on the experience of the team, the original fixtures have been replaced by a single vacuum fixture, which allows the part to overhang. This removes the need to turn the part over and all key areas can be machined in one operation. To complete the solution, manual alignment has been entirely replaced by a computerised fixturing process.

The heart of the new system is NC-PartLocator adaptive machining software developed jointly by MSP and Delcam. The foreplane now only needs roughly locating and the workspace alignment is automatically calculated, removing most of the manual set up and adjustments necessary in the old scheme. Even the alignment upload from the host PC to the machine-tool controller is automated using a high-speed data link.

The details of the process are as follows:-

1. The part is located roughly (to within 4mm), then secured on the vacuum fixture.

2. The operator enters part details (serial no. etc.) into NC-PartLocator. These are used later to archive all the data and results to ensure the process is fully traceable.

3. A five-axis probing program measures a set of carefully selected points on the part surface.

4. NC-PartLocator uses the results to calculate a new workspace alignment adjustment. Axis constraints are used due to the gentle curvature of the part surfaces. They were defined by BAE Systems and MSP after a detailed set of trials. There are checks to allow the operator to verify that the movement of the datums does not exceed pre-defined tolerances.

5. NC-PartLocator automatically uploads the new machine workspace alignment to the controller before the machining programs are run to cut the part.

6. The part programs are run and machine another perfect foreplane.

Benefits Summary

Over 700 production Foreplanes have now been produced and the benefits of the new process are appearing:-

1. Manufacturing time has been reduced by in excess of 60%; each foreplane used to require 20-30 hours.

2. Improvement in quality and reduction in process variability has virtually eliminated the need for manual rework, in contrast to the previous process where almost every item needed rework.

3. Manual set-up has been dramatically reduced; the part now fixtures in one hit.

4. Consistent set-up times have been achieved due to the single fixture, rough initial location and automated alignment, significantly reducing scheduling disruption. Coupled with the reduction in machining hours, this has allowed BAE Systems to bring sub-contract work back in-house.

5. Redundant fixtures have released storage floor space, handling equipment and, if the process had been active from day one, would have saved the cost of their manufacture.

6. Operator variability has been further reduced with in-process tolerance checks.

7. The project has been recognised internally and won a coveted BAE Systems Chairman's award for the improvements made.