G W Martin – CNC Machining Process Case Study
|Machine Type:||CNC Lathes|
|Materials:||Steel, brass, aluminium and plastics|
|Sector:||Aerospace & Energy|
Subcontractor invests in plant and people to target aerospace and energy sectors
Family-owned subcontract machining and assembly specialist, GW Martin, has invested over £1 million in new machine tools since 2012, including three Index CNC lathes from Kingsbury, installed in April this year. It is part of an ongoing upgrading of the company’s manufacturing facility, which occupies 25,000 sq ft on a 13-acre freehold site in Eastleigh, Hampshire.
The last three years has also seen an increase in staff from 35 to 50, mainly shop floor personnel, including four new apprentices to bring the total to six. Half are studying at Eastleigh College while the others are with Southampton Engineering Training Association. The subcontractor is a keen advocate of growing its own talent and has been running its apprentice scheme virtually since George William Martin founded the company in 1959.
An established supplier to the defence and automotive industries, the company has seen particularly good trading conditions in these sectors over the past couple of years and is now keen to start approaching aerospace primes. It already holds ISO 9001:2008 quality and ISO 14001:2004 environmental accreditations and is working towards AS9100 approval for aerospace quality management. Another target is green energy, especially nuclear and offshore wind.
Managing director Stuart Yalden, grandson of the founder, believes that the company is ideally placed to produce components for these new markets due to its expertise in machining difficult materials to tight tolerances for the defence industry. Various grades of stainless steel account for a large part of throughput. Alloyed and heat treated steels are also routinely processed at the factory, along with other materials such as brass, aluminium and plastics.
The core business is round-the-clock CNC machining of high quality, medium to high volumes of components in batches from 100- to 1,000,000-off. National and international clients span a wide manufacturing spectrum which includes the electrical, filtration and medical sectors. Company policy is to continually invest in the latest machine tool technology to deliver high quality components at competitive prices.
Triple-turret lathe cuts cycle time by more than one-third
An example of this policy is the recently installed Index C200 lathe, which is the first triple-turret CNC turn-milling centre on site. GW Martin has used twin-opposed-spindle twin-turret lathes (G200s and ABCs) from the same German manufacturer for over 15 years and is familiar with their strengths, but one particular long-running job prompted the purchase of the C200 with its extra turret.
It involves machining a connector that requires a modest amount of driven tool work but a lot of turning from brass bar. The problem on a twin-turret lathe was that the design of the part made it impossible to anywhere near balance the machining times at the main and counter spindles.
The overall cycle time was 4 minutes 24 seconds, dictated by work performed at the main spindle, while simultaneous cutting at the counter spindle had to be restricted to a little over a minute. By employing the third turret, the two operations are now much more closely balanced and the cycle has been reduced to 2 minutes 47 seconds. The 37 per cent time saving significantly lowered unit production cost and justified the purchase of the new lathe.
Fanuc control option on Index ABCs
At the request of GW Martin, the two latest Index twin-turret ABC turn-mill bar automatics at Eastleigh are fitted with the Fanuc 31iB CNC option, rather than a Siemens control. Apart from Index lathes, all other machine tools on the shop floor have the Japanese manufacturer’s ISO control.
It is a simple matter to transfer pre-existing cycles from Index machines to the new control, according to the subcontractor’s production manager, Paul Skelton. He added that commonality of programs across the shop floor and the ability to swap them between Fanuc-controlled machines is beneficial and allows optimal use of plant. Most programs are prepared off-line at the factory, although manual data input of some simpler cycles maintains skill levels on the shop floor.
The slant-bed machines produce components up to 60 mm in diameter from bar and are ideal for relatively simple jobs required in quantities of, say, 20,000 per week. Nevertheless, the two turrets have live tooling for more complex work.
The main spindle is opposed by a synchronous spindle mounted in a permanent position in the upper turret. Including the backworking tool station, up to 19 cutters may be deployed. Three tools can be in cut simultaneously on two workpieces in the main and counter spindles and idle times are particularly short owing to the lathe’s compact design and short traverse distances.
In conclusion, Mr Yalden said, “We are keen to speak with companies, particularly in aerospace and energy but also across the board, that are looking for additional capacity.
“Apart from highly productive prismatic machining centres and the lathes already mentioned, we also operate a six-spindle Index CNC multi and a sliding-head lathe on which we currently have spare capacity.
“The other area where we are growing strongly is assembly of machined parts and we have set up a new area on the shop floor dedicated to this work.”