Driving force

Car makers are increasingly using banks of smaller CNC machines to provide a flexible way to meet fluctuating demand within the constraints of just-in-time and lean manufacturing. Mark Venables reports


For the first time in years, the machine tool industry is looking forward to a healthy future, according to a recent report.

The results of the Manufacturing Technologies Association Trends survey for the first quarter of 2006 show that orders accelerated in the early part of the year and that respondents predict further growth, albeit at a more modest pace, for the second quarter.

‘It is encouraging to see that the demand for manufacturing technology in the UK is growing – a trend confirmed by recent data on investment by the engineering sector which also showed that strong growth and the short-term outlook for the sector is positive,’ said MTA director-general Andrew Manly.

One sector that is always an important customer to machine tool companies is automotive. And despite the demise of Rover and Peugeot’s decision to close its Coventry plant and move production to eastern Europe, the sector is thriving in the UK, producing more cars than ever.

The fact that a drive towards greater flexibility in machining processes is the order of the day for automotive OEMs and Tier One suppliers will come as no surprise to those close to the industry. flexibility, or agility as some prefer to call it, has been the watchword of car manufacturing for some time now.

Where once transfer lines reigned supreme, banks of smaller CNC machines are beginning to appear, each allowing greater agility and the ability to meet fluctuating demand within the constraints of just-in-time and lean manufacturing, and collectively matching the productivity and efficiencies of their grandiose forbears.

Other factors driving productivity and quality improvements in the modern machining line are quick changeover – allowing smaller quantities to be manufactured efficiently – better tool management and a better trained workforce with more responsibility.

With a capacity of 1,000 engines a day, Honda’s Swindon engine plant can best be described as medium volume. The current portfolio is three basic engine types along with their various derivatives, and to enable the output flow to be balanced from the factory the company has been gradually moving away from traditional transfer line set-ups towards a more flexible approach with smaller, CNC machines.

‘Certainly the trend for us is going away from the traditional transfer lines, although we still have a mixture here,’ said Grant Mcpherson, Honda’s director of production for engine, weld and paint. ‘We are looking at flexibility and multiple model – our machining line is currently producing three different models, as well as the different sizes within those models – so we have to be able to model change reasonably quickly.’

Flexibility inevitably means that car manufacturers are looking for smaller machines. On Chrysler’s next engine project, already under development in the US, Brian Harlow, general manager of transmission/casting/machining manufacturing, predicted that each operation will be carried out by banks of between 10 and 12 small CNC machines.

He confirmed that the Chrysler Group is as dedicated to moving away from the restrictive transfer line concept as Honda. ‘We find smaller, CNC machines to be a relatively short-term inexpensive approach,’ he said. ‘So for any change in model or product it’s just a matter of programming changes and minor tool adjustments rather than a transfer line with dedicated heads where, for example, if you change the location of a hole you have to completely change the head.’

Machine tool supplier Cross Huller UK accepted that the world has changed as regards high-volume machining. ‘Production requirements are down and cycle times are up, so the tendency is to make more use of time through more flexible, multi-axis machining modules,’ said technical director Harry Miller.

‘Flexible or agile systems based on machining centres cater for production volumes up to 250,000-300,000 parts per year, with variations according to whether parts are cast iron or aluminium. Many lines we supply are mixed transfer lines and machining centres, or transfer lines with automatic multi-spindle head-changing modules.’

Honda has the big advantage of a sister company in Japan that can manufacture its machine tools but without that luxury Chrysler has to scour the market. The reality, as Harlow explained, is that when it comes to price and overall value it tends to look no further than Japanese suppliers. ‘Two big users that we have on our engine side are NTC, for prismatic parts and MHI (Mitsubishi Heavy Industry),’ he said. ‘When it comes to turning machines Fuji has been an excellent supplier, and for grinders Toyota is big for us.

‘But at the same time I don’t want to exclude German suppliers, because we have a significant number of German-based OEM supplied machines – especially in our transmission business – because of our affiliation with Mercedes. We have undertaken some joint activities using their expertise, and Ex-Cell-O, GroB and Emag make very good turning machines. The sad part is that I am not naming any US suppliers.’

when it comes to specifying and selecting machine tools, Grant’s maxim is ‘keep it simple’. He reckons that the more advanced a machine gets, the more it breaks down. ‘I try to find machines with very few bells and whistles, because when you are in mass production, 24 hours a day, you don’t want a machine breaking down because it’s got some fantastic sensor on there that breaks,’ he said.

‘I also find that many machines don’t cope well with the environments where there is a lot of swarf and coolant – some of the areas I have yet to see major advances on are swarf and coolant management.’

Speed is normally king in high-volume production but it comes at a price, which is why at Swindon Honda shies away from superfast machines. ‘When you are mass producing – we are making one engine every 57 seconds – obviously the faster you go the more efficient you can get, said Grant.’

‘But we have never found superfast machines particularly reliable or robust. if you do have a mislocation or a crash they damage themselves significantly. We have found that machines of this type that accelerate above 1g or 1.5g don’t really offer any advantage to us,’ he said.

Alongside the Honda-built gang-head driven machines at Swindon, the company operates standalone machines – six have recently arrived from Heller UK to form integrated cells on the line that will give it greater flexibility. ‘Because we are making petrol and diesel engines on the same machining line, to avoid having very long lines we have put in a few NC machines to add some special processes,’ said Grant.