Gateshead-based Impress Group has a diversified portfolio of customers that are serviced by a similarly diverse range of manufacturing technologies from the group‘s five businesses units. These provide metal pressings, fabrication, laser profiling, high volume turned parts, coded welding and general sub-contract machining. The materials it processes are equally varied, but with a growth in the aerospace sector it is seeing more and more light alloy parts on its range of XYZ VMCs. It is here that it called on the expertise of WNT to improve productivity on one particular, high volume, component.
Maximising the efficiency of both machine tool and operator is vital to all businesses and, for one such as Impress where it is making inroads into manufacturing sectors such as aerospace, being competitive becomes more important. Having won a long-term contract for the machining of some light alloy brackets in relatively high volumes, Impress Director, Steven Young wanted to set about improving the process. “Our desire to break into the aerospace sector saw us quote a very keen price for this job and, having won the contract we knew we would have to work extremely hard, or clever, in order to both make it profitable and also ensure that we retained the work in future.” Having already built a good relationship with tooling supplier WNT (UK) Steven called on local Technical Sales Engineer Rob Buxton to asses the job and come up with a solution.
The opportunity to take advantage of the high speed (12,000 revs/min) spindle on the XYZ 1060 HS high speed VMC made WNT’s Centro P toolholding system an obvious choice. The Centro P range of precision collet chucks are ideal for maximising the performance of solid carbide milling cutters. Due to their precision and power is the main benefit of Centro P is their ability to run at high spindle speeds with runout accuracy of 3 micron, while reducing vibration due to their design and clamping forces. The Centro P collets were paired with WNT’s W-HPC Alu Ripper cutters for the roughing operations, with the objective being to remove as much material as possible in the shortest space of time. Additionally, the original HSS drills were replaced with WNT’s solid carbide tools, which delivered further cycle time gains.
“Throughout the process Rob stood with the operators on the duckboards to ensure that everything went according to plan and ensure that everything was running to its optimum performance. Not only that, in these initial stages the trials of the tooling and workholding were at zero risk to Impress as WNT was willing to make the investment in our processes on an ‘if it works you buy it’ basis,” says Steven Young. Having proved the actual machining strategy the next step was to further rationalise the manufacturing process. This was achieved by the introduction of new workholding in the form of WNT’s ZSG mini concentric vices. The decision was made to load multiple of these low profile vices on to the machine table. This has a number of positive benefits the first being that by having several components available to be machined at the same time reduces takt time by virtue of reducing the number of tool changes and workpiece loadings.
With these vices in place and with them fully loaded the machine is able to run without any operator intervention for an extended period. The machine is now monitored by any one of Impress‘ operators who can reload components once the cycle is complete. Furthermore, each individual tool is presented to multiple components before the next tool change is required, which has a significant impact on the overall cycle to complete the load of components. For example, if we take a simplified machining cycle of drilling, countersinking and tapping a hole in a component, using a single clamping vice this would require three tool changes to complete the operation 1) drilling the hole, 2) countersinking the hole, 3) tapping the hole and while the actual machining time is only 15 seconds, the cycle takes 45 seconds to complete, taking a typical 10 second tool change time into consideration. Now, if you multiply the number of vices and clamp ten workpieces in a single setup, the savings are realised immediately with cycle time reduced to 18.5 seconds to give a saving of near 60 per cent as the sequence is now to drill ten parts, countersink ten parts then tap ten parts eliminating multiple tool changes. The new cycle time would now be 10 pieces drilled = 69.5 sec; 10 pieces countersunk = 29.5 sec; 10 pieces tapped = 84.5 sec, giving a total of 183.5 seconds to complete ten parts or 18.35 seconds per part saving 26.65 seconds or 59.22% compared to the single clamping. The ability to use multiple clamping setups generate major savings due to faster throughput, freeing up valuable machine and operator time. The results at Impress saw the cycle time to machine one individual component reduce from 58 minutes to just 14 minutes.
“The work that Rob and WNT did on this project has been invaluable. By looking at the project with a fresh pair of eyes they have come up with a very viable solution enabling us to maximise the machine and operator capacity that we have and ensure that we remain competitive as we move forward into new market sectors,” says Steven Young.
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