AUTOMATION AND ATTENTION TO DETAIL IS KEY TO SUCCESS FOR STUART TURNER

Everyone with an engineering bent would be spellbound upon walking into the entrance hall of Stuart Turner. On display in the company’s museum are more than 100 working models, all in impeccable condition, of engines, pumps, generators, boats and even a Stuart Turner motorcycle - glowing testimony to the glorious early 1900s heritage of this Henley-on-Thames business.

Today, still privately owned, Stuart Turner is a re-focused business, having sold its models division to a Guernsey-based company to allow it to concentrate on three key areas of pump design, development and manufacture for customers in the building services, commercial products and leisure markets.

The 105-person company produces more than 120,000 pumps a year and generates sales in excess of £17 million. It is clear that the same attention to detail as was applied to its modelling ancestry is now being maintained today in its modern production and assembly areas. Indeed, the company is certainly enjoying the benefits of keenly applied automation to stave off the competition – especially from overseas.

According to machine shop supervisor, Craig Geeson: “We are mindful of making the maximum use of automation to maintain competitiveness and develop the business, and our Citizen M32–III CNC sliding head mill/turn centre fits exactly into what we are trying to achieve.” This he qualifies in the production of more than 620,000 parts – one every 47 secs, which also includes all non-productive time - that have been produced on the machine in the 23 months following installation.

In keeping with the automation mindset of the production team, Craig Geeson maintains very detailed comparisons of the 17 different parts produced in quantities that vary between just 12 and 170,000 per year, where the CNC sliding head mill/turn centre has decimated previous floor-to-floor times.

For instance, a drive spindle is now produced in 120 secs complete in a single operation against 406 secs previously, a saving of 238 per cent! The time to completely machine a plug has been slashed from 71.2 secs to 22.5 secs - a 216 per cent saving - and a hose end coupling is now produced 74.8 per cent faster. This record of the machined coupling reflects a massive return on investment against the previous automated fixed-head lathe method saving 18.7 secs on each component – especially when 170,000 couplings were produced in the last 12 months.

“ Overall,” he maintains, “the Citizen has shown a cycle time saving of 117.69 per cent.” Such is the rate of production, for which 16 hours/day are under ‘lights-out’ conditions, that the machine will normally deposit 900 kg of brass into the swarf cart every 24 hours.

The machine and its supplier, NC Engineering of Watford, were introduced to Stuart Turner by his local Sandvik Coromant technical sales engineer, Gary Wilson. Subsequently, Stuart Turner has a very close relationship with NC Engineering and Sandvik which has led to the development of advantageous methods, introducing new tooling and the reduction of cycle times.

The previous fixed-head, six-axis gantry loaded mill/turn machine with twin-turrets and subspindle was not slow. It had been progressively improved with Sandvik’s help but it was suggested that the type of parts produced would be better served by sliding head technology. To this Craig Geeson is quick to add: “We had a learning curve because we had to evolve a different approach to programming the parts, but it has certainly paid off!”

The Citizen M32 has a 7.5 kW main spindle delivering up to 8,000 revs/min and a 3.7 kW subspindle having a top speed of 7,000 revs/min. The vertical gang tool post has four driven tools and five turning tool positions and an independent back tool post has three driven positions. Combined with the turret, these three toolholding areas enable three tools to cut simultaneously. The 10-station turret can accommodate multiple tool holders and driven tools that bring the total tool carrying capability to 72 tools which are put to good use by Stuart Turner’s setters. As a matter of course, they leave a common set of tooling permanently on the turret and by using effective pre-setting, can change the tool post tooling in a matter of minutes. Quite often, two changeovers are made in a day.

The machine was specified from NC Engineering with an Iemca TS560P barfeed system that comprises multiple bar racks with a total capacity of 56 bars of 32 mm diameter material up to four metres long or 224 bars of 8 mm diameter. Adds Phil Horsley, general factory manager: “This helps us to extend our unmanned running and minimises bar end wastage. The company tends to run 32 mm, 25 mm, 15/16”, 13/16” and 8 mm bar sizes of which 98 per cent is CZ121 brass, the balance being stainless steel.

As part of the automation package that enables a direct ‘bar to wash’ scenario to be maintained, Stuart Turner utilises the NC Engineering unload gantry on the Citizen to transport the parts from the subspindle of the machine for placement onto a slatted conveyor for feeding to a longer conveyor that runs the length of the barfeed. From this conveyor the parts are deposited into plastic boxes ready for washing and the plastic boxes are fed to the unload point on a separate conveyor that also runs beside the barfeed. Due to the amount of unmanned running and the volume of swarf produced, a higher output LNS Microfine II swarf conveyor was retrofitted.

Stuart Turner is very complimentary over the stability of the Citizen machine: “Our general tolerances are 0.1 mm but we have some requirements of 20 microns,” says Craig Geeson. “Once set, it is rare to change an offset at the control and we are confident to leave the machine running over the weekend without fear of problems. We have people willing to come in and re-bar and check parts through this period. Even if we turn the machine off for a day it will immediately go back to the sizes set, whereas our other machines in the shop tend to need a while to stabilise after a long break in production.”

Typical of the type of component produced is a shuttle valve from 32 mm C2121 brass that is machined to 30 mm diameter by 130 mm long. This part previously took 122.8 secs which was cut to 75 secs on the Citizen M32 III. Altogether 25,500 of these components are produced a year.

The process involves step diameter turning to 25 mm diameter, deep hole drilling, cross drilling and tapping, the milling of flats, internal and external grooving, the cross drilling of three holes followed by the tapping of two with 1/8 BSP and 3/8 BSP threads and the chasing of a 3/8 BSP on the end spigot. Says Craig Geeson: “We try to balance main and subspindle operations and have found that by overlapping parts of the cycle we have been able to virtually eliminate any dead time.”

Meanwhile, with the focus on production, the Citizen has also proven its worth on prototype components and for machining items of tooling and fixturing where some cycles involve very intricate milling and profiling. “These parts would probably have been made outside – but our policy is to machine and assemble everything in-house under our control. This means the Citizen has proven to be a very flexible and essential piece of equipment to us,” summed up Phil Horsley.