Founded in 1994 by Mark Bevan, MJB Precision Engineering relocated 10 years later to its current premises at Sturminster Newton. The move allowed the sub-contractor to offer a modern manufacturing facility for prototyping and small-batch work through to the mass production of mill-turned parts.
In October 2011, the 15-employee company took its business to the next level by investing in a 22mm-capacity Index CNC multi-spindle automatic from Gosport-based Geo Kingsbury Machine Tools Ltd (Tel: 023 9258 0371 – www.gkholdings.com). Until the German-built MS22C six-spindle auto was installed, the sub-contractor relied on sliding-head lathes to produce components of 20mm diameter and below, while single-spindle fixed-head lathes were used for diameters up to 300mm.
The company focusses on providing support to manufacturers in the UK and beyond, co-operating closely on R&D with customers in the bearing, aerospace, medical and defence industries in particular. Components are routinely machined from plastics, carbon steels, stainless steels, tool steels, aluminium, copper-based alloys, titanium and exotic alloys.
It was winning a large automotive contract that prompted Mr Bevan to analyse the best way of producing four different tool-steel parts in weekly batches of 3,000 each, to be assembled into a new product for luxury passenger cars. He also had to take account of the fact that quantities are set to rise steeply this year.
At the outset, Mr Bevan began machining the components on three sliding-head lathes for 20hr a day (including ‘lights-out’ running), six days a week. Five more sliders would have been needed to cope with the predicted demand, but there was insufficient space in the factory to house that number of extra machines together with their full-length bar magazines, so reloc-ation to larger premises would have been necessary.
Furthermore, the extra staff needed to operate another five lathes would have raised overheads and consequently increased unit production costs, which are notoriously sensitive in the automotive industry.
Problem solved
The space and labour cost issues were resolved at a stroke by the decision to install an Index CNC multi, which can mill-turn in one 24sec cycle a component that takes a sliding-head lathe 120sec to complete — a five-fold increase in productivity. The capital investment in the multi was equivalent to buying five sliders, but being a single machine, the multi fits neatly into the available space in MJB’s factory.
The family of four automotive parts is in the process of being transferred to the MS22C, which has a Scara back-working unit with a synchronous pick-up spindle for presenting each parted-off component to dedicated back-working tools. PPAP (production part approval process) has already been carried out on the first component, with the other three approvals to be completed imminently.
Mr Bevan says: “The Index multi not only keeps down overheads and occupies a small footprint, it also offers other advantages. We find that the machine is more rigidly built than our single-spindle lathes, so vibration is minimised, leading to much better tool life. We typically machine 400 components on one of our sliders before a tip needs changing, whereas the figure for the Index is 1,000. Higher feeds and speeds can also be used — and there is no need to compromise the parameters at any of the spindles, as they are all individually adjustable, unlike on old cam-type multis. This means that productivity and quality are maintained, and the process is more predictable, allowing us easily to hold the required 1.67 Cpk on the parts and fulfil our customer’s Kanban delivery requirements next year. Moreover, the output of the single Index multi is high enough for it to cope with producing the required volumes of all four automotive components for the foreseeable future.”
Further economies
Mr Bevan adds that a further benefit of using the MS22C derives from it being a fixed-head lathe, albeit with six C-axis spindles: bar remnants are now around five-times shorter than the 300mm of tool steel left after machining the last part on a sliding-head machine, which equates to material worth about £10 being saved on each bar.
Furthermore, the flexibility of having CNC on a multi has dramatically reduced the economic batch size (compared to a cam-type multi) to between 5,000 and10,000 parts, giving the machine much more scope than before for taking work from single-spindle machines. Change-over is faster than on a cam multi; it can be as short as 1hr, if the same collets and most of the same tooling are used for producing the next part; and naturally, the expense of machining or purchasing cams is avoided.
Further versatility is provided by having two tool slides serving each spindle. Both slides are capable of performing internal or external turning, or boring, or driven-tool work, so the user is not restricted to designating one type of tool in any position — a factor that helps to further optimise flexibility and reduce machining times. Standard equipment on MS-series machines includes high-pressure through-tool coolant and a filtration system that extracts all particles of metal larger than 20µm (which improves tool life). In addition, coolant temperature is constantly controlled, ensuring continuous, high-accuracy machining.