Single-hit machining means big savings

Single-hit production of aero engine parts results in big savings and reduced lead-time – all thanks to the purchase of an Okuma MU5000V 5-axis vertical machining centre from NCMT.

A few years ago, T&R Precision Engineering in Foulridge, East Lancashire, started manufacturing parts from Inconel 625 castings for the hot air side of the GE-Safran LEAP-1A turbofan that powers the Airbus A320neo family of single-aisle jets. The problem was that the work involved a labour-intensive sequence of three or four operations on separate machines. Not only was there a significant risk of introducing human error, but it also necessitated the production of a batch of eight components to start each day - but each batch would take one week to complete.

A more efficient process route for the drilling, milling, chamfering and turning operations was therefore sought by the aerospace components supplier, which employs more than 70 people. The ideal solution identified by engineering manager, Graham Gilbert involved the purchase from NCMT of a Japanese-built Okuma MU5000V 5-axis vertical machining centre (VMC) equipped with a Dutch-made Cellro 30-station pallet storage and retrieval system served by a 6-axis industrial robot.

“The improvement in production performance has been enormous across the four different LEAP-1A castings that we machine,” explains managing director Tim Maddison. “All parts are now produced in one hit in a one-hour cycle, which means that eight components are now ready the same day rather than after a week.

“The substantial saving in lead-time is accompanied by vastly less workpiece handling and work-in-progress on the shopfloor, while at the same time fewer free-issue Inconel castings need to be supplied by our US customer at any given time, saving them money as well.”

Savings all round

A further benefit is a 50% reduction in total processing time compared with when the parts were produced in three or four separate operations. An additional saving that Maddison describes as ‘massive’ comes from inspecting every completed part in the VMC in a 10-minute routine at the end of the cutting cycle. So instead of 100% inspection on a coordinate measuring machine, only one part per day now needs to be checked off-line.

The production cell was installed in November 2019, shortly before the start of the pandemic. The aircraft build rate promptly collapsed from 63 per month to zero, but Maddison advised that by the start of 2022 it had recovered to 50 per month, will return to pre-Covid levels by the end of the year and is predicted to rise by a further 20% during the course of 2023.

The contract machinist could not have coped with these increased volumes without investment in the Okuma/Cellro plant, but is now in a position to take full advantage. The layout of the equipment is such that, if future volumes dictate, there is space for a second Okuma MU5000V to be installed adjacent to the first and to be served with pallets of pre-fixtured components from the same Cellro robotic store. It was this potential that steered the manufacturer away from sourcing a machining centre with its own integrated pallet storage and retrieval system.

A number of notable technical advances have been incorporated into the latest production cell. One is the provision of Okuma's turn-cut software in the proprietary OSP machine control that allows, without the need for special fixturing, turned features to be produced that are not on the centreline of a component. Three of the castings require this technology to be used.

Features are machined by rotating a turning tool in the VMC spindle, circular interpolating the X and Y axes at the same rotational speed and feeding the spindle forward in Z. Had interpolation turning not been available, it would not been possible to produce all the parts in one hit. There is no production efficiency penalty through the use of relatively slow turn-cutting, as it is not feasible to turn Inconel at high speed anyway due to the material becoming difficult to machine when hot.

All shapes and sizes

To compensate for there being a lot of variability in the shape of the castings, another process improvement is the use of a combination of Renishaw's Inspection Plus and Productivity Plus probing software packages running in the control coupled with spindle probing of the workpiece. The various elements of a casting can be measured and manipulated by the measurement cycles so that the workpiece can be placed in a position where it can be machined successfully; and if it cannot, the part will be rejected.

Alternatively, if any given feature is predicted to be out of tolerance, the customer can be informed so a decision can be made as to the feature's relevance and whether machining should go ahead anyway. The importance of harnessing all these technologies can be gauged by the fact that the raw castings are so expensive that machining adds only 20% to the cost of a finished component. For the same reason, scrap is assiduously avoided, accounting for only 0.015% of cell throughput.

Another feature of Okuma machines that T&R Precision appreciates is the Thermo-Friendly Concept design, involving both the machine structure and the spindle. It allows the aero engine parts to be machined to within ±25µm, despite a significant variation of temperature on the shopfloor in Foulridge.

Space for 30 machine pallets in the Cellro store allows up to 30 hours’ production without operator attendance, so there is no need for a manned night shift and full advantage can be taken of lights-out operation at the weekend. With an overall equipment effectiveness in excess of 80%, it adds up to a highly productive facility in its present form, while the flexibility to add a second VMC has the potential to double output and extend unattended running further.

The final word goes to engineering manager, Graham Gilbert who says: “The support provided by NCMT throughout the project was fantastic. It was useful to be able to visit Okuma's European headquarters in Germany with them to prove out various parts of the process.

“The engineer the agent deployed in our factory for several weeks after installation was knowledgeable and very patient with us during the training period. This was important as, although we operate a couple of dozen multi-axis CNC machining platforms on a daily basis here in Foulridge, the MU5000V was the first machine we had bought from this source so we were on a steep learning curve at the outset.”

www.ncmt.co.uk