Titanium machining times halved at aerospace subcontractor

Citation

(2008), "Titanium machining times halved at aerospace subcontractor", Aircraft Engineering and Aerospace Technology, Vol. 80 No. 6. https://doi.org/10.1108/aeat.2008.12780fab.001

Titanium machining times halved at aerospace subcontractor

Article Type: Aerospace world From: Aircraft Engineering and Aerospace Technology: An International Journal, Volume 80, Issue 6

Four-fifths of production at contract machinist, Gardner Aerospace, Wales, involves prismatic machining of Ti64 (6 per cent aluminium/4 per cent vanadium) titanium alloy; the remainder is aluminium. Yet three years ago the reverse was true – 80 per cent of throughput was aluminium.

Winning a major contract in 2005 for the supply of titanium nacelle frames for the Bombardier Dash 8-400 turboprop was the catalyst for change. However, machining the tough material in larger volumes combined with greater component complexity meant that Gardner’s existing machining centres, and the cutting tools, were struggling to achieve the required accuracy and production volumes.

So Gardner, whose plant in Wales specialises in machining medium-size structural parts for aircraft, decided to install a turnkey system to produce the mid and forward nacelle frames, which are horseshoe-shaped and measure approximately 900 × 750 mm and from 50 to 115 mm thick. The chosen supplier was Mazak, which delivered one of its FH8800 four-axis, twin-pallet, horizontal-spindle machining centres complete with programs and tooling.

For the latter, Mazak selected Iscar tooling, predominantly solid carbide cutters and a variety of indexable insert mills and drills. Paul Hughes, Mazak’s Regional Manager, commented, “In a highly demanding production environment like Gardner, we rely heavily on the tooling supplier to ensure the customer gets the best from our machines.” “Iscar has excellent engineers including ex Mazak employees that are conversant with our product range. We always receive a high level of technical support from them, which is why we have entered into a partnership arrangement with them on a number of projects over the years.”

David Walters (Figure 1), General Manager of the factory in Wales, confirmed that he receives good service from Iscar, adding that the performance of the cutters is markedly superior to that of the solid carbide and high-speed steel end mills Gardner was using at the outset to produce the nacelles on older machining centres. Then, cycle times were at least twice as long and it was difficult to maintain the required level of accuracy, leading to an unacceptably large number of components being scrapped.

Figure 1 David Walters (right), General Manager, Gardener Aerospace, Maestag, wiht Iscas Area Sales Manager, Darren Taylor, in fornt of one of the Mazak FH8800 horizontal machining centres used for producing titanium aerospace parts

Productivity has been doubled using Iscar tools by being able to take larger depths of cut at higher feed rates, which the modern Mazak machines support owing to their greater rigidity and high-torque spindles.

David Walters says that tool breakage is rare these days, which combined with the ability to hold tolerance easily, has resulted in a four-fold reduction in scrap rate to below 1 per cent of the 200 frames produced annually. This is important to maintain profitability, as components can cost as much as £10,000 each.

Moreover, whereas 4-5 h of hand fettling was previously needed to finish each nacelle to the required standard, finishing time has been reduced to around 45 min per component.

So successful was the first new Mazak machining centre installation that Gardner won enough new business to justify buying a second, identical FH8800 at the end of 2006 to cope with the increased workload.

Such is the current level of titanium machining at Gardner Wales that the two newest machining centres cannot complete all of it. So older horizontal machining centres on site continue to be used to machine titanium, as do a number of vertical machining centres (VMC). To increase their capability for machining the tough material and to raise productivity, they have been retooled by Iscar following its appointment as preferred cutting tool supplier to Gardner Aerospace with effect from May 2008.

For instance, improvements have been made to Boeing 777 titanium wing rib production by utilising Iscar Mill2000 cutters, which have reduced cycles by 40 per cent compared with the previous solid carbide and HSS tooling (Figure 2). The latter in particular suffered from cutter push-off, which has been eliminated using the new tools.

Figure 2 A Twin-spindle machining centre at Gardner Aerospace, equipped with Iscar Mill2000 milling cutters that have reduced cycles by 40 per cent compared with the previous solid carbide and HSS tooling

Part of the productivity benefit has come from Iscar re-engineering the jobs and part from the rigidity of the new, indexable-insert milling cutter, which has strong, dovetail-shaped, AXKT-style inserts that clamp securely in the seats on the cutter body. Mr Walters said larger depths of cut at higher feed rates can be taken with these tools and in addition, accuracy and surface finish have been improved.

To realise these benefits, Iscar engineers advised careful control over the coolant. As through-spindle delivery is not available on the older machinery, sufficient external flow rate and accurate direction are essential. So too is coolant cleanliness and regular skimming to remove tramp oil was instigated, resulting in a marked increase in the life of the inserts.

As regards the tooling on a Mazak AJV50/120 VMC on the shop floor, Iscar suggested using Helido Upfeed six-edge milling cutters with the latest SumoMill coated carbide grades (Figure 3). These have a low stress, CVD (chemical vapour deposition) coating on top of the PVD (physical vapour deposition) layer to minimise thermal cracking and ensure smooth chip flow. With very similar tooling types, titanium machining rates have been increased by up to 30 per cent on this machine. Iscar has also targetted aluminium cutting at Gardner Wales in another facet of what has become an ongoing project to upgrade the tooling throughout the shop floor. Two Makino horizontal machining centres have been equipped with HeliMill 90° pocketing cutters using SumoMill S845 inserts with helical cutting edges and positive rake angles. Significant productivity benefits have been recorded when roughing.

Figure 3 Machining area of one of the Mazak FH8800 HMCs

Other machines on site to benefit from an Iscar tooling makeover for the machining of aluminium wing components are a Mazak VTC300C-II VMC and two Cincinnati five-axis machines.

The latter have been equipped with the unusual Iscar FiniShred solid carbide end mills. They have two serrated flutes and two continuous flutes to enable simultaneous roughing and semi-finishing of components, drastically reducing cycle times as well as freeing up a pot in the tool magazine. This particular tool is also effective at machining titanium, stainless steels and high-temperature alloys.

Details available from: Iscar Tools Ltd. Tel: +44 (0)121 422 8585, Fax: +44 (0)121 423 2789.