Smiths Aerospace takes on lean manufacturing policy

Citation

(2002), "Smiths Aerospace takes on lean manufacturing policy", Aircraft Engineering and Aerospace Technology, Vol. 74 No. 4. https://doi.org/10.1108/aeat.2002.12774dab.001

Smiths Aerospace takes on lean manufacturing policy

Keywords: Smiths Aerospace, Lean manufacturing, Productivity

It is reported that by replacing three existing CNC machines with its first Hitachi Seiki HT30G mill/turn centre, Smiths Aerospace's Actuation Systems – Wolverhampton factory was able to immediately cut sot up times by 40 per cent and machining cycle times by 35 per cent. In addition, the as machined, surface finish from the new lathe was said to be good enough to eliminate intermediate grinding operations, which allows components to go directly from turning to chromium plating (Plate 1).

Plate 1 Hitachi Seiki Super HiCELL 250 helping to increase productivity at Smiths Aerospace Actuation Systems

So impressed have Smiths Aerospace Actuation Systems been with the huge improvement in productivity of the HT30G that three other Hitachi Seiki machines have since been purchased from Hitachi Seiki UK of Egham in Surrey and now form key elements in the company's move to adopt lean manufacturing practices. The additional Hitachi Seiki Super HICELL 250, HT25G and HT23R have, like the HT30G, are reported to have recorded a significant reduction in the number of operational set ups for components as well as overall set up times and registered high levels of increased productivity.

Smiths Aerospace Actuation Systems operates seven factories in the UK and the United States and specialises in the design, development and manufacture of primary and secondary flight control systems for civil and military aircraft which include electronically controlled hydraulic actuators used to trim control surfaces such as rudders, ailerons, elevators and thrust reversers.

The company also produces mechanically operated high lift systems that are used to actuate flaps and leading and trailing edge slats found on major civil aircraft programmes for Airbus and Boeing, as well as military aircraft projects including both Eurofighter and Joint Strike Fighter. Smiths Aerospace Actuation Systems also manufactures specialist actuators used on the Bell Augusta 609 tilt rotor aircraft.

John Payne, manufacturing manager for the Wolverhampton factory outlines the activities of the company: "We have capability for design, manufacture, assembly and test of the complete product, and we have straight to line certification from major customers. In practice we use external subcontract suppliers for some parts but retain core components and high value added items in-house."

To that end, the factory supports a full range of manufacturing processes including heat treatment and plating as well as machining, for which it can call upon 65 CNC as well as a number of manual machines. Components are produced from billet, investment castings and forgings with final tolerances often as close as two microns.

Until recently manufacturing has been organised on group technology principles with around 1,000 live part numbers spread across prismatic components, cylinders, ram bodies, valves, spools, sleeves and gears. However, this is currently being refined through the adoption of lean manufacturing techniques.

"We're aiming to concentrate our resources on the more highly engineered components and outsource the more simple parts," John Payne explains. "So rather than the group technology approach we're moving into cells and family of parts production techniques, referred to as flow clusters', which support a flowline based manufacturing process. In total we are planning to have 10 flow lines, each supported by an average of three flow clusters."

A key requirement of the flow cluster concept is versatility to allow a variety of complex components to be machined with reduced batch sizes without any penalty addition due to set-up time. Quantities are typically 30 to 40 for gears and 10 to 15 for ram and rod components. But to achieve the level of demand, the machines have to demonstrate high levels of reliability.

While the technical requirements of its machine tools are largely defined by the intended application, the company attaches equal importance to the commitment and technical competence of the vendor. "Although there was no turnkey element to any of the new machines we wanted to be sure that the people we were buying from had an understanding of our manufacturing needs. We also needed the confidence that if machines broke down, we would get an efficient response and it was that side of the equation that identified Hitachi Seiki as the machine supplier," he maintains.

The investment in machines was paralleled by a large investment in tooling. The target is to achieve rapid re-setting in circumstances where successive batches demand re-tooling. The use of pre-set KN short taper tools further reduces set-up times. However, the downside is that a high proportion of tools tend to be stored in their pre-set condition but tool availability never becomes a problem.

The 22kW HT30G which has a maximum turning diameter of 500mm was the first of the Hitachi Seiki machines to be installed as John Payne recounts: "It generally reflects the major advantages of the investment programme as it replaced older equipment and was capable of much higher productivity with heavier cuts, faster rapid traverses and the capability to support use of more advanced tooling."

Paul Starzak, the machine's setter/operator reports set-up times are now taking up to half the previous times and machining cycle times have been reduced by up to 30 per cent. He commented: "One thing that really helps our set-up is that the machining area of the HT30G has the space to leave the steady permanently in position."

It's a similar story with the company's new Super HICELL 250, which superseded an existing mill turning machine. Its key advantage is said to be the 7.5kW, 6,000revs/min three-axis single tool head which is serviced from a separate 40-tool magazine. Not only does this claim greater power for rotary tool applications but the single tool configuration eliminates any potential collision problems that could arise from a turret full of tools. In addition, the machine is equipped with a quick-jaw change chuck. As a result a job can reportedly be completely changed over in less than one hour roughly half the time needed before.

Most of the components machined on the HICELL, are out of S80 case hardening steel and stainless steel such as 15-SPH in typical batches of 40. The more robust Hitachi machine design has paid dividends on operations such as all-over machining of gears following heat treatment, where it is thought to be around 33 per cent quicker than the older machine. The HICELL also uses CBN and ceramic tooling while the polar milling capability of the single tool head is regarded as being very positive, effective and accurate.

One of the future developments on the machine will be to gun drill 12mm holes up to 225mm deep. To achieve the penetration rate and tool life, high pressure through-tool coolant was specified on the machine. The drilling process will involve a pilot hole to act as a guide bush for the manually exchanged gun drill tool.

"We've been impressed with the HiCELL's capabilities," says John Payne, "to the extent that we're considering purchasing a second, similar machine for our shaped gear cell."

The third machine, a heavy-duty HT25G is utilised mainly for chuck and fixtured work. With a 620mm swing and 18.5kW spindle it is thought to be ideal for parts which are required in small volumes but demand complicated deep or stepped bores to be machined. The nature of these tasks means that the ease of set-up afforded by availability of G54/G10 codes for fixture set-up, and the repeatability provided by dedicated tooling set-ups on the 12 station turret is highly valued.

"We now have complete confidence in the repeatability of the machining process," John Payne confirms. "We use a lot of special tools on this machine but whereas we used to go through a laborious tool alignment process every time a tool was changed, the alignment of pre-set tools is immediately guaranteed by the drive dogs of the KN system. We also achieve more rapid machining cycles; on one manifold component for example, the cycle has shrunk from almost three hours to just one."

The high torque 358Nm spindle Hitachi Seiki HT23R, is the only one of the four machines to be supplied with a 65mm bar magazine. Because the machine has a 3.7kW AC, 12mm diameter capacity for powered tooling on the turret, it has reportedly proved ideal for machining spool type components with cross holes and other features which can be produced in-cycle. This makes the geometric alignment accuracy of component featured integral with the machining process whereas it previously depended on the accuracy of a second set-up on a separate milling machine. In addition, the machine was specified with a chuck, making it suitable for a wide variety of other work.

"The HT23R is very quick with 30m/min rapid traverse so we've seen worthwhile reductions in cycle times as well as improved lead times," says John Payne. He also maintains that from their overall experience with Hitachi Seiki it confirms their original decision to purchase with the objective of building an ongoing relationship.

"The technology has certainly lived up to expectations in respect of machining performance and although the machines were not turnkey purchases, we have received considerable support with applications development and general after-sales service. Our immediate next step is to upgrade our DNC program management facilities in a move towards paper-less manufacturing and we will certainly be using Seiki Systems FlexLink software to achieve our goals."

Details available from: Hitachi Seiki UK Ltd. Tel: +44 (0) 1748 433711; Fax: +44 (0) 1784 437691; E-mail: info@hitachiseki.co.uk