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Founded in 1994 by Mark Bevan, MJB Precision Engineering has recently expanded its machining capacity by investing in a 22mm capacity Index CNC multi-spindle automatic from Geo Kingsbury Machine Tools.
Until the German-built MS22C six spindle auto arrived, the subcontractor relied on sliding headstock lathes to produce components of 20mm diameter and below while single spindle fixed head lathes were deployed for diameters up to 300mm.
It was winning a large automotive contract that prompted Mr Bevan to analyse the best way of producing four different tool steel parts in batches of 3,000 per week each which are assembled into a new product for luxury passenger cars. He had to take into account that quantities are set to rise steeply in 2012.
At the outset, Mr Bevan began machining the components on three sliding head lathes, 20 hours a day plus lights out running, six days a week. However, five more sliders would have been needed to cope with predicted demand. There was insufficient space in the factory to house that number of extra machines together with their full length bar magazines so relocation 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.
The space and labour cost issues were resolved at a stroke by deciding to install an Index CNC multi, which can mill/turn in a 24 second cycle a component that takes a sliding head lathe 120 seconds to complete, representing a fivefold productivity increase. Capital investment in the multi was equivalent to buying five sliders and being a single machine, the multi fits neatly into the available space in MJB's factory.
The family of four automotive parts are in the process of being transferred to the MS22C, which has a scara backworking unit with synchronous pick-up spindle for presenting each parted-off component to dedicated backworking tools. PPAP (Production Part Approval Process) has already been carried out on the first component with the other three approvals to be completed in early 2012.
Mr Bevan comments: “Apart from keeping down overheads and occupying a small footprint, the Index multi has delivered other advantages as well. 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 number rises to 1,000-off on the Index.”
He continues: “Higher feeds and speeds can be used and there is no need to compromise the parameters at any of the spindles as all are individually adjustable, unlike on old cam-type multis.
“Generally, 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. Also, 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."
He adds that a further benefit of using the MS22C derives from it being a fixed head lathe, albeit with six C-axis spindles. It means that bar remnants are around five times shorter than the 300mm of tool steel left after machining the last part on a sliding head machine, which equates to around £10 in material saved on each bar.
The flexibility of having CNC on a multi has dramatically reduced the economic batch size to between 5,000- and 10,000-off, giving the machine much more scope than before for taking work from single spindle machines. Changeover is faster than on a cam multi and can be as short as one hour if the same collets and most of the same tooling are used for producing the next part. Naturally, the expense of machining or purchasing cams is avoided.
Further versatility is afforded 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, helping to optimise flexibility and reduce machining times.
Standard equipment on MS-series machines includes high pressure, through tool coolant and filtration to extract all particles of metal larger than 20µm which improves tool life. Coolant temperature is constantly controlled, ensuring continuous, high accuracy machining.