Boiler rules change results in FMS ousting TL

Change in UK domestic boiler legislation led to a boiler manufacturer to replace a dedicated transfer line with a 'FMS', which is served by a highly flexible pallet handling system.

As a result of the Kyoto agreement, UK Government legislation due to come into force in April 2005 stipulates that most new boilers must operate at 95 per cent efficiency or better, rather than the current norm of 85 per cent.  The only way to achieve this is to use the condensing principle, which in turn means that a secondary heat exchanger is needed to extract more energy from the hot exhaust combustion gases used to heat the water in the boiler.  The impact of the impending new law has been profound on Baxi Potterton, whose condensing heat exchanger production volumes at its Bamber Bridge factory are set to rise four-fold from the 2003 level of 45,000 units to a projected 188,000 per year by 2006.

  Part of the companys strategy to address such a sharp upturn in throughput, against a background of increasing product variety, has been to oust its dedicated, inflexible, in-line transfer machine.  In its place, two new twin-pallet, horizontal machining centres from Toyoda Mitsui have been installed and linked with a similar, pre-existing Mazak machine to create a flexible manufacturing system (FMS).

  Fastems, Dartford, supplied the enabling technology in the form of an automated, three-level storage and retrieval system for fifteen 630 x 630mm fixture plates utilising the Wixroyd Zero Point system and 34 raw material bins.  The Zero Point quick change fixturing system was chosen to enable the different machine tools within the FMS to accommodate the same workpieces without restriction.  Handling is carried out by a 4.7m high, linear-robotic stacker crane travelling at up to 3.5m/sec on rails running the 26m length of the compact, space-efficient store.  Pallet scheduling and crane control are provided by PC-based software developed by Fastems specifically for its FMS installations.  Its capabilities for production planning, system monitoring and reporting are high-end and extensive, and are best reviewed on the web site: www.fastems.com   In addition to increasing production capacity, another effect of moving away from discrete machining centres has been to reduce the unit production cost of each heat exchanger, partly by limiting the number of operators and using their time more efficiently.  The problem before was a mismatch between the cycle time to machine four castings on a cube fixture compared with the time it took to unload the components and clamp fresh castings.  The latter took just over half of the machining cycle, so there was a lot of non-productive time, but not enough for one person to look after two machines.

  The beauty of the Fastems system is that pallets fixtured with raw castings are held within the store ready for transfer to a machining centre immediately one becomes free.  Thus spindle running times are maximised and fewer machine tools are needed for a given production output.  In the same crane cycle, a pallet of finished parts is transferred from the machine to one of two manned load/unload stations.  The result is a better balance between handling and machining times, resulting in two fully utilised rather than three under-utilised operators attending the machines.

   According to Baxi Pottertons engineering manager, Jon Williams, reducing labour cost content is enabling the company to compete more effectively with low-wage economies, particularly those in the Far East and Eastern Europe.  The threat that they pose to the business is clear, as Baxis seven other factories are mainly in affluent economies - UK, France, Germany, Italy, Denmark, Sweden - only the plant in Turkey has relatively low wage rates.

  Logistics in the vicinity of the machines at Bamber Bridge has been dramatically improved by moving away from batch-based production at individual machines and avoiding the considerable work-in-progress that was entailed.  As machined parts are taken from their fixtures in a localised area, it has been possible to position the heat exchanger assembly area back-to-back with the load/unload stations for efficient component transfer.

  Furthermore, raw castings from Baxis on-site foundry delivered twice a day are taken by the FMS crane from a high level conveyor and stored within the three-tier Fastems racking alongside the fixture plates, freeing space on the shop floor.  Lift trucks are therefore no longer needed to deliver castings to the machines and transfer them afterwards to assembly.  On average, 1.5 drivers per shift were employed for this work and more would have been needed had the machine shop been expanded conventionally.  In any case, there would not have been enough space on the shop floor to allow the installation of sufficient extra stand-alone machines to meet the new production targets.

  Between 15 and 24 heat exchangers per hour for six main product lines are machined in the FMS.  This large volume manufacture is supplemented by production, assembly and testing of low volume products and spares in another machine shop on the site.  Bamber Bridge is devoted to component manufacture, boilers being assembled in nearby Padiham and fires in Baxi Pottertons Birmingham plant.

  That 300,000 of the two million boilers of all makes sold annually in the UK are shipped from Padiham gives an indication of the quantities involved, which are equivalent to car sales and places boiler manufacture in the mass production sector.  Each Baxi Potterton high efficiency - hybrid boiler based on existing designs requires two heat exchangers - one of traditional cast iron and a second made from aluminium to withstand corrosive condensate - so production volumes are even greater than they at first appear.  It is true that newer boiler models need only one aluminium heat exchanger, but the machining content is higher.

  Choice of the two Toyoda Mitsui FH630S 2APC 4-axis machining centres with rotary tables, which replaced outdated models from another supplier, was based on careful analysis by a Baxi project team, led by Jon Williams, of the cutting cycles involved in heat exchanger manufacture, which comprise mainly drilling and tapping of near-net-shape castings and very little milling.  The proportion of non-value-added machine movements is therefore high compared to in-cut times, so a machine with fast axis traverse rates was essential to ensure economical manufacture.

  The 40-taper Toyoda Mitsui machines with their roller bearing linear slideways in all axes offered the best specification at 1G acceleration to 60m/min in all linear axes around the 1,000 x 800 x 850mm working envelope.  Additionally, rapid indexing of the 40-pocket tool magazine combined with fast tool change give a chip-to-chip time of 2.7 seconds ? half that taken by some large horizontal machining centres.  Similarly fast is the 180 degree table indexing speed of 2.4 seconds.  This high-speed performance, together with the use of combination drill/tap tools, has maximised the metalcutting to air-cutting ratio.  Other factors on Williams points-weighted selection criteria chart that led to the choice of these Japanese-built machines were customer support, reliability and price.

  The FMS as described above is the first phase of Baxi Pottertons reorganisation of its machined component manufacture and was implemented in a short time frame from the decision to purchase, made during the Milan EMO at the end of October 2003, through ordering in February 2004 to installation/commissioning in July/August 2004.

  Phase 2, planned for 2005, will involve adding new machines as required, extending the FMS system and perhaps adding another load/unload station, according to production demand.  The feasibility of this approach highlights a benefit of Fastems modular FMS in that capital expenditure is made only when the level of business dictates, and not speculatively up-front.  Phase 3, being considered for 2006, may involve installation of robotic loading stations combined with deburring, also from Fastems, to reduce the labour content further.

  Concluded Williams, "The project has progressed so smoothly that plans are in place to start manufacturing heat exchanger components in the FMS in 2005 for our other European assembly operations.

  "The FMS has proved a worthy successor to our previous transfer-line approach to high volume manufacture, translating its economies to short batch runs of a much bigger variety of product lines.

   "We found it impossible to achieve this result using stand-alone, labour-intensive machine tools.  In my view, had we not gone down the FMS route, it would have threatened the future of heat exchanger machining within Baxi Potterton in the long term".

Back to top