Andrew Churchill is out to ‘break the mould’ of gas-turbine blade manufacture by using his high-speed five-axis machining centres to machine blades complete from solid billet in a single set-up, rather than machine large batches of forgings to size.
The managing director of the Midlands precision engineering company JJ Churchill says that its process route offers a number of advantages over traditional blade production. “For a start, machining from billet negates the need for relatively large batch sizes; one-offs to 90-off are feasible compared to a minimum batch of, say, 300 when forgings are used.
The resultant time savings can be enormous: lead times for forgings are usually extensive, sometimes taking a year from ordering the die to the delivery of forgings, whereas production from billet has a lead time of just a few weeks.
“Furthermore, the argument that blade integrity from billet is weaker than a forging is being dispelled by exhaustive fatigue and stress testing; and, most importantly, a blade that is milled from solid can be held to far tighter tolerances than a forged blade. Ultimately, maintaining better tolerances means that the engine runs more efficiently and cleanly — and therefore far more economically.
“We are already proving the cost-effectiveness of the process at both the blade design/development stage and in the ‘legacy’ manufacture of spares/replacement blades in typical batch sizes of 80-90; and it’s only a matter of time before the viability of machining from solid or over-size forgings challenges precision forgings in volume production on a cost per part basis.”
Key investment
The route to achieving such a highly flexible method of blade production was mapped out by JJ Churchill around six years ago, when it started its investment in Starrag high-speed five-axis blade production machining centres.
That said, JJ Churchill has been involved in compressor blade machining since 1947, when it began supplying parts to Rolls-Royce (turbine blade production being added more recently). Company founder Walter Churchill (Andrew Churchill’s grandfather) worked with Air Commodore Sir Frank Whittle, who is credited with the invention of the turbo-jet engine.
Today, a company speciality is the prototype development and spares supply for a variety of aircraft programmes; these include developmental blades for the Airbus A350 Trent engine and F35 Joint Strike Fighter through to ‘kitted’ production volumes for the Rolls-Royce RB211 and ‘legacy’ demand for the Tornado RB199.
JJ Churchill continues to develop its expertise in the principal markets of aerospace, defence and power generation; it is also a first-tier supplier to OEMs such as Rolls-Royce, BAE Systems, Cummins, Perkins, Siemens and Alstom. Today, the company has 120 employees and a turnover of £20 million, although Mr Churchill says his plan is to achieve a turnover of £50 million by 2019 — mainly relying on his Swiss-manufactured Starrag machining centres, which were supplied by Birmingham-based Starrag UK Ltd
(www.starrag.com). Blade work undertaken on these machines currently accounts for 25% of JJ Churchill’s business, but Mr Churchill says by making use of the machines’ impressive capabilities, he intends to “prove without doubt the viability of the milled-aerofoil approach to higher-volume production.
“While we continue to successfully undertake both development and legacy work for ‘blue chip’ clients, I could see that if we stayed the same, we wouldn’t grow; it was clear that the market was changing, with fewer suppliers attracting a greater amount of work. A main benefit of being a family-owned SME is the ability for quick decision-making. The larger companies eventually ‘get there’, but small firms are ‘nimble’ and can be quicker off the mark.”
Route to growth
In 2008 — a recessionary year that saw JJ Churchill’s turnover halved — Mr Churchill doubled the company’s capital investment and installed its first Starrag machining centre — a model SX 051B, which is the predecessor to the current LX 051. “The adage of ‘if you stand still, you will disappear’ rings true, but to invest in this way during recession, we had to ensure that we had a robust strategy; we needed to be certain that our targets were realistic.
“We decided to investigate machines and machining methods that would transform our approach to blade production. We needed to be better — right first time — faster and to achieve lower costs than anyone else — including the OEMs themselves — through shorter cycle times. We are well on our way to achieving this with our Starrags. These are very complex machines, but everything about them is designed for the purpose of machining gas-turbine blades. I’m interested in the cost of the blade, not the cost of the machine.”
Power generation
JJ Churchill’s first blade order comprised gas turbine blades for power generation — machined from nimonic 105 — and came from Siemens.
“Siemens saw that we had a Starrag and knew we were serious. Our work in this field has since expanded to include industrial gas-turbine stators and rotors, as well as variable vanes. Once we had proven the technology, we didn’t hesitate to continue to invest in Starrag blade centres.” The company added four more machines over the years, including the larger-capacity LX151 and three LX 051 models; between them they offer machining capacities up to 700mm long x 400mm diameter and spindle speeds to 18,000rev/min.
A key to the success of these machines at JJ Churchill is the use of RCS CAM software, which has been developed by Starrag specifically for five-axis high-speed blade machining. With its extensive selection of machining strategies, RCS provides highly efficient and effective programming, thanks to its parametric input structure; moreover, cycle times are minimised via the software’s optimal selection of milling strategies.
RCS is used by JJ Churchill in conjunction with Unigraphics CAD; all machining programs are transmitted to the machines via DNC link. In addition to creating difficult features such as variable fillet radii (now a feature of the latest RCS software), JJ Churchill also developed an in-process ‘polishing’ routine for the Starrags.
Blades are rough-milled to within 2-3mm of final form before being finish-machined; the Starrags’ ‘super finish mode’ sees blades finished to typically 0.7-0.8Ra, and every blade is 100% inspected on Mitutoyo co-ordinate measuring machines; there are four such CMMs in the cell, operating with the same software used by Rolls-Royce to generate a variety of data, including SPC.
In conclusion, Mr Churchill says: “Starrag’s machining technology has created a significant shift in what’s possible in gas turbine blade manufacture. With the appropriate technology, investment and software, coupled with suitable staff training that includes apprenticeships, we know we can meet every expectation.”
He adds that the company’s use of Starrag blade-machining technology has earned it several supplier awards in recent years. These include Rolls-Royce Global Aerospace Supplier of the Year and the Cummins Supplier Award for Europe, Middle East and Africa Regions.