Pioneers in Machining Technology
Scrap rates reduced by 40 per cent
Installation of an automated tool presetter from Speroni, Italy, supplied through UK agent, NCMT, has reduced the variability of machining processes at the Denham factory of Martin-Baker, the world's leading manufacturer of ejector seats.
According to production engineer, Andrew Jay, the greater precision with which cutters are preset has reduced scrap rates by 40 per cent from a Makino a55 FMS (flexible manufacturing system). Supplied by NCMT some 17 years ago, the system comprises four horizontal machining centres each with 208 tools, fed by a 75-pallet automated storage system and run in shifts by 16 operators, 24/7.
The complexity of the installation, coupled with a need to produce a product portfolio of 500 different parts to high accuracy in small batches, led to variability in the quality of the machined components. Some were out of tolerance and had to be scrapped. Although it was only a small proportion of production, many ejector seat parts are complex and of high added value, so the monetary cost was significant.
A project to reduce component variability from the FMS was instigated in early 2010 by Mr Jay, who identified the main problem as being the accuracy of tool geometry offsets entered into the CNC systems controlling the four Makino a55s.
Mr Jay commented, "Using one of our manual pre-setters, 16 operators obtained differing results when measuring maximum cutter diameter in X and the length in Z from the tool tip to the gauge line of the BBT40-taper BIG Daishowa toolholders.
"The spread of results was marked, bearing in mind that general drawing tolerance is ± 0.005 inch and is often as tight as ± 0.001 inch. Any measurement system has to be up to 10 times more precise than the tolerance it is trying to achieve.
"The programmable Speroni presetter has underpinned measuring to this level of accuracy and considerably reduced the variability in geometry offsets."
Tests with the tool presetter were originally carried out at NCMT's Coventry technical centre, followed by expanded trials at the factory in
Italy and further tests during commissioning at Denham. Programs were written to measure automatically in X and Z four 3-flute solid carbide end mills of 20, 16, 10 and 6 mm diameter. Four machine operators were then asked to use the Speroni equipment and the results were logged.
The spread (variability) of tool length and diameter measurements taken by the four operators were all within three-tenths of a thou (one thousandths of an inch), or 7.6 microns, significantly better than when the tools were put on a manual presetter. The spread in length for two of the tool types, measured in tenths of a thou, was actually zero.
The Speroni Esperia presetter is fully operational and programs have been written for the range of tools used in the FMS. This has had a positive impact, with scrap levels down 40 per cent on the corresponding period in 2010. This level of saving will amortise the cost of the presetter in nine months.
The Speroni Esperia normally takes around 30 seconds to complete its automatic measuring routine, or a little longer if it is a complex form tool. The highly accurate readings are transferred directly to the appropriate machine CNC via the FMS control screen, avoiding the risk of operator error in transcribing the values from the Speroni screen and entering them by hand on the shop floor.
In conclusion, Mr Jay said, "The accuracy and repeatability of Speroni Esperia automated tool measuring has exceeded our expectations, allowing us to enter more precise offsets into the machines than was previously possible.
"Apart from the productivity and cost advantages, a further benefit is that we are now in a position to introduce statistical process control based on six-sigma methodology and raise the quality of components from the FMS to the next level."
About the Speroni Esperia
The Speroni Esperia tool presetter has a thermo-balanced structure made of artificially aged, pearlitic cast iron to ensure the equipment is fully isostatic and will not deform or distort over time or as the temperature changes.
Unlike most presetter designs, the homogeneous structure avoids the drawbacks of systems that use light alloys and/or granite, which have different and unstable reactions to changes in temperature and the environment. There is consequently no need for frequent recalibrations.
Both hardware and software are developed and produced in-house by Speroni, whilst peripheral equipment is sourced from the very best suppliers – Schneeberger linear guideways, Heidenhain encoders, Sony camera, etc.