Aerospace subcontractor continues investment in one-hit mill-turning

Citation

(2003), "Aerospace subcontractor continues investment in one-hit mill-turning", Aircraft Engineering and Aerospace Technology, Vol. 75 No. 1. https://doi.org/10.1108/aeat.2003.12775aab.002

Aerospace subcontractor continues investment in one-hit mill-turning

Aerospace subcontractor continues investment in one-hit mill-turning

Keywords: Aerospace, Manufacturing

It is impossible to manufacture aerospace components economically these days without minimising the number of separate machining operations, one-hit production being the goal. Mindful of this, last year subcontractor, Doughty Precision Engineering (DPE), based in Nottingham, UK, doubled its number of Nakamura Tome 7-axis CNC mill-turning centres to four (Plates 3 and 4).

Supplied by Mills Manufacturing Technology, the machines are devoted to the production of electrical connector parts for the aerospace industry from stainless steel bar up to 65 mm diameter. Called receptacles, the components are milled and drilled on the Nakamura Tome lathes for about 50 per cent of the cycle time. The only subsequent operations needed are keyway machining on a CNC slotter and deburring using a boring bar on an older CNC lathe that no longer performs mainstream production duties.

Plate 3 One of the Nakamura Tome WT-250 7-axis mill-turning centres in use at subcontractor, Doughty Precision Engineering, Nottingham

Plate 4 A selection of connector components mill-turned by Doughty Precision Engineering on its Nakamura Tome 7-axis mill-turning centres

Simultaneous front- and reverse-end machining minimises the cycle time, which is set by the sequences needed to complete the front end. Then after part-off and synchronous pick-up by the right hand spindle, as much milling as possible is completed from the back as the turning operations are fairly limited. The benefit the Nakamura WT machines is said to offer is that both turrets pan work on either right or left spindle to ensure 11 minimum total cycle times with maximum throughput.

During the mid 1990s, DPE was finding that repeated “cost-down” requirements from aerospace customers were eroding margins to the point where jobs were becoming financially unviable. So in 1997 it started down the twin-opposed-spindle mill-turning route with the purchase of two Nakamura Tome WT-20s. It is the latest generation of this lathe, the WT-250, that was installed last year (2001). Mills part exchanged one of the existing WT-20s under the flexible finance package it offers, so DPE now operates three WT-250s and one of the original lathes. Under normal trading conditions the machines run 24 h a day, but since September 11th this has been cut to 100 h per 5-day week. DPE is sure that the volumes will return as the aerospace industry picks up and confidence levels improve.

Founded in 1925 by Alan Doughty, grandfather of the current owner, Peter, DPE originally specialised in manufacturing diesel fuel injector parts for locomotive engines, an area that still forms part of the business today, as does work for the motorsport industry. However aerospace contracts, principally for the Amphenol group of companies, now accounts for the majority of the subcontractor’s business. Around half of turnover is generated in the UK with the remainder accounted for by a recent export contract awarded by Amphenol headquarters in the USA.

Winning the latter business prompted investment in the extra Nakamura Tome machines, as the US contract increased throughput at the Nottingham subcontract facility by 100 per cent to 20,000 parts per month. A problem for DPE, however, is the large variety of receptacle permutations; there are 10 sizes and five keyway varieties per family of connector and a total of 800 part numbers overall.

Said Peter Doughty, “We are locked into a price irrespective of how many connectors we produce. As the parts are relatively low cost and the material accounts for around 20 per cent of the finished component price, an ideal batch size for us is 1,000-off. Smaller quantities are less economic, and we do not gain much on larger runs. So we have adopted the policy of producing for stock receptacle blanks that are nine tenths complete, then finish-machining them according to the permutation and quantity ordered by the customer.”

He continued, “For the size of component we are producing the WT-250s are big machines, but we find we need this physical size as it translates into high rigidity and hence component quality. Furthermore, it enables us to use the correct feeds and speeds for the material mainly 303, 304 and 316 stainless steel – without compromising accuracy, so throughput rate is high.”

DPE also operates five Daewoo lathes from Mills, the latest being a Puma 230MC large bore CNC turning centre with live tooling purchased last year. All are equipped with Multifeed short bar magazines, as are the Nakamura Tome lathes. The 3-axis Daewoo machines perform a variety of less complex, single operation turning jobs including production of plug shells that fit on top of the receptacles to complete the connectors. Other materials regularly machined by the subcontractor include mild steel, titanium, nickel and aluminium alloys up to 75 mm diameter for bar, 350 mm diameter when chucking.

Details available from: Mills Manufacturing Technology Limited. Tel: +44 (0) 1 926 736736; Fax: +44 (0) 1 926 736737;E-mail: qcurran@millacnc.co.uk; Web site: www.millscnc.co.uk