Subcontractor chooses robust sliding-head lathe for aerospace applications
Article Type: Aerospace technology From: Aircraft Engineering and Aerospace Technology: An International Journal, Volume 81, Issue 5
Most of the components produced by APPH Nottingham are destined for the aerospace sector, particularly the landing gear that its parent group designs and manufactures. Many components are mill-turned from stainless steel and titanium bar, so in June 2007, when the company was looking for its first sliding-headstock CNC turning centre, particular attention was paid to the robustness of the machines on offer.
The decision was taken to buy a Star sliding-head lathe (Figures 2-5) owing to its rigidity and significantly heavier construction than other makes on the market. The high-power drive to the live cross-working and end-working tools was another factor in the purchasing decision.
Figure 3 Dave Fell (right), Manufacturing Engineer at APPH Nottingham, with Star SV-32 operator, Dave Broadfoot
Figure 3 Dave Fell (right), Manufacturing Engineer at APPH Nottingham, with Star SV-32 operator, Dave Broadfoot
Figure 5 A selection of mill-turned components produced for the aerospace industry by APPH Nottingham on its Star SV-32
Figure 5 A selection of mill-turned components produced for the aerospace industry by APPH Nottingham on its Star SV-32
The model chosen was a nine-axis Star SV-32, which has an installed weight of 3.8 tonnes. Bar up to 3.2 m long is fed into the working area by an FMBTurbo 3-36 magazine. The machine has turret-mounted tooling as well as a gang toolpost and has been equipped with high-pressure coolant delivery for improved chip control and tool life when producing safety-critical components from exotic aerospace metals.
The investment in the Star was part of a major plant upgrade that also saw the installation of a Mazak Integrex turning centre and, prior to that, three CNC mill-turns from WFL.
The SV-32 is used for highly efficient, one-hit mill-turning of parts up to 32 mm diameter, mainly stainless steel and high-carbon steel plungers. Each is subsequently match-ground to fit the bore in the body of a hydraulic actuator.
Another regular contract fulfilled by the SV-32 is the production of titanium alloy vortex tubes in batches of 2,000-off, 27 of which fit into a titanium ring that forms part of the fuel distribution system in an aircraft.
The remainder of the sliding-head lathe's time is spent on mill-turning intricate sleeves, connectors and other components to tight tolerances. Formerly, such parts had to visit two, three or even four machines. These were typically a fixed-head lathe, a CNC milling machine for adding prismatic features, and perhaps a manual machine for hole drilling at compound angles and a wire-cut or die-sinking EDM machine for adding serrations.
In addition, a part number is engraved on some components, which is also performed in-cycle on the Star lathe, saving a further separate operation.
The benefits that result from consolidating repeated set-ups on several different machines into a single operation are well documented. They include faster turnaround, better component accuracy by eliminating tolerance build-up,and lower costs through reduced operator involvement and less work-in-progress.
By April 2009, 25 components at the APPH Nottingham factory in Kirkby-in-Ashfield had benefitted from being re-engineered to run on the Star SV-32. Accuracy of parts is verified on Hommel optical inspection equipment by checking the profiles against DXF files derived from the original CAD data.
Commented APPH Nottingham's manufacturing engineer, Dave Fell, “We opted for a sliding-head mill-turning centre rather than a fixed-head CNC lathe with counter-spindle and live tooling because of the large variety of shaft-type components we produce, up to 14 times longer than their diameter.”
“Having said that, some of our parts are relatively short, say twice their diameter, and these are produced just as efficiently on the SV-32.”
“The other benefit of the sliding-head configuration is that three tools are often in cut simultaneously, so productivity tends to be higher than on fixed-head lathes, few of which can deploy more than two tools cutting at the same time.”
“Irrespective of shape, complexity and material, provided that it is of 32 mm diameter or less, a component can usually be machined more efficiently on the Star sliding-headstock lathe.”
Machine operator Dave Broadfoot added that there had been no problems with either the SV-32 or the FMB bar magazine in nearly two years of operation. He added that, even though APPH Nottingham was new to sliding-head turning at the outset, on-site training for one week was sufficient to ensure proficiency in machine programming and operation, despite the nine controlled axes.
Details available from: Star Micronics GB Limited, Tel.: +44 (0)1332 864455;Fax: +44 (0)1332 864005.
