Electrode machining package erodes machining times
Electrode machining package erodes machining times
Keywords: Electrodes, Machining
"It is the best electrode machining solution on the market," is how Mike Malby, Managing Director of the MH Group Plc., summed up the Fanuc T14iB Robodrill vertical-machining centre with its 600 Centre developed electrode machining package. Installed in the West Sussex factory of group company MH Mould Tools some 15 months ago, this high speed vertical machining centre and application specific engineered package has had a major impact on the speed and efficiency with which complex 3-D copper and graphite electrodes can be machined for forms and cavities in plastics injection mould tools.
As Mike outlines, the new Robodrill has cut his machining times by some 20 percent, improved quality and provides a reliable, unmanned capability at night for round- the-clock working. "When you are producing up to 100 different electrodes each week, fast, accurate and efficient machining is a prime requirement," he insists.
He follows on to describe how the 600 Centre of Shepshed near Loughborough supplied package of high speed spindle, 14-station tool turret and advanced control and software allows highly intricate 3-D electrode forms to be produced which just could not have been tackled before. He said: "The 700 mm long table means that we can multi-fixture up to six electrodes at a time and run them through the night with no-one around."
Unusually, both graphite and copper are machined wet using a dielectric as the cutting fluid on the Robodrill. MH has found that this causes far less problems in terms of dust build-up and prevents the production system becoming clogged. The practice of wet machining with dielectric also prevents any abrasive particles causing damage to the machine's bearings,ballscrews and moving elements. And, as well as being easier to manage, wet machining is said to be far more environmentally friendly by eliminating any problems caused by airborne dust. In addition, this technique claims the added advantage for MH as it impregnates the electrode with dielectric during the cutting process.
This enables a finer level of surface finish to be achieved during the actual erosion process, about which Mike comments: "The electrode tends to cut sweeter." Multi-flush type nozzles have also been installed on the machine to flush away all the graphite dust and this goes directly into a special cyclone separator to centrifuge the solid matter.
MH Mould Tools has been using the wet machining technique for several years on its larger electrodes or multi-electrode type tools. However, as the purity and quality of copper alloy has progressively improved,the trend has been to change over to this material for any smaller electrodes.
Based in Bognor Regis, MH is a leading designer and manufacturer of plastics injection mould tools for the electronics, automotive,white goods and aerospace sectors. The company has World Class, toolmaking status achieved in 1998 as part of the GTMA initiative to benchmark UK toolmaking companies and regularly invests in the latest production equipment. It also has multiple stations for designing and draughting while programming terminals for 2 and 3-D surfaces are linked by a DNC network to all the CNC machines in the machine shop.
Key production equipment at MH includes: the Fanuc Robodrill T14iB, for high speed electrode manufacture and various high speed vertical machining centres, for roughing out 3-D profiles/cavities which sometimes involves hard metal cycles. System 3R pallet-type tooling is used throughout from electrode machining through to the actual erosion of cavities,so that ultra-precise location is assured from machine to machine without the need to establish separate datums and set-up locations for each new job. Full 3-D measuring and inspection equipment ensures that tools are ready to run,before in-house trials.
Virtually all 2-D electrode forms tend to be wire eroded as this is thoght to be quicker and more cost-effective than milling and less material is wasted. All the complex 3-D electrodes are now machined on the Robodrill which is programmed off-line using NURBS-based software and a 3-D modelling package. These electrodes are then used to produce plastics injection mould tools for a wide range of components including: hand sets for aircraft in-flight entertainment, fascias and consoles for cars, various refrigerator parts and retail display lighting elements.
When the decision was made to replace an original 8 year old Robodrill for electrode machining Mike's team looked very closely at several different machines, before finally deciding the Fanuc Robodrill T14iB best met the all-round needs. As Mike maintains: "In terms of performance, accuracy,capacity and cost, the Robodrill was by far the most suitable machine on the market. We also were very conscious that we had 8 years of trouble-free operation with our previous machine and so we knew from experience that Fanuc machines were extremely reliable. And when we compare the latest version, they are a good six times faster than most of our other vertical machining centres."
The company produces a wide variety of single copper and graphite electrodes,in sizes ranging from 1 mm2 up to around 500 mm by 400 mm, that the cycle times enable the machine to run out of normal hours unmanned. So, to take full advantage of the situation, the T14iB was specified with a sub-table in order that multiple fixtures, and therefore electrodes, could be set up. Typically, this means that up to six components can be loaded and with average machining times of around 1h, this provides sufficient material capacity for extended.
As a matter of course, electrodes requiring longer cycle times tend to be machined at night to ensure maximum productivity and almost continuous production with the spindle running at its maximum speed and with feed rates between 700 and 1,000 mm/min. Depths of cuts tend to range between 0.5 mm for roughing to 0.1 mm for finishing.
One job which highlighted the performance of the latest Robodrill was an ultra-thin electrode for a large mould tool to produce drop-down lighting consoles on a new model of car. Machined from a 152 mm by 101 mm by 55 mm deep solid block of copper, the aerofoil styled form finished up just 0.7 mm thick by 45 mm deep and within a tolerance of 10 microns.
Mike confirms how the Robodrill accurately produced this form. "It particularly maintained a very high level of surface finish on the face of the thin section", he said. While on a graphite electrode required for an in-car CD player facia, small upstandings, which were less than 1 mm apart,were also machined successfully.
Mike recounts: "Both these jobs would have been extremely difficult and very time consuming to produce on any other machine in the factory. And in the case of the mould tool for the CD fascia, we would have had to produce separate electrodes for the upstandings. However, being able to machine them all together on a single-piece electrode is typical of the advantages we have gained from the 600 Centre machine."
For further details contact: 600 Centre. Tel: +44 (0)1509 600600; Fax: +44 (0) 1509 600159; E-mail: cnctool@600centre.co.uk, sales@lkuk.co.uk; Web site: www.600centre.co.uk; www.ik-cmm.com
