Big flexibility for Mini

In the current economic climate, flexibility in manufacture is a high priority. Many firms have struggled to lower production volumes without seriously eroding margins. So it has been the job of the design engineer to come up with a solution. Managing director of Excel Automation, Gary Sweeney, outlines the problem. He says: "We are seeing a trend in particular areas, for example in the food and beverage sector, where we are getting a lot of enquires as companies look for slicker ways to operate. "But, I think with society the way it is now, consumers demand more choice, so we are seeing a high demand on flexibility. For example, the days of simply making one car on one line are long gone." The company has designed and built production lines for Harley Davison Motorcycles in the US as well as automated systems for the nuclear industry. Excel itself faces a paradoxical challenge, as it would like to standardise its systems to lower its own costs. But customer demand for flexibility means that is impossible. "It is very difficult to describe a typical automation system because we have never done two systems the same," says Roy Eastwood, a senior engineer at Excel. "If we talk about a conveyor system, all the ingredients are there. You calculate what size roller you need, the style of conveyor, there are different designs of drive. But when you go away from conveyors, there is a awful lot of separate design work to be done." The company has recently installed a handling and storage system into Magna's Intier Automotive facility in Redditch. Magna supply fully assembled dashboards, or 'cockpits', to BMW's Mini manufacturing plant in Oxford. "Our contract with BMW is for Just in Time deliveries," says Intier production manager Bob Clifford. "We need to ensure that every one of the 255,000 unique cockpits leaving Redditch every year is united line-side with its unique Mini, 40miles away on the assembly line in Oxford. "We also wanted to maintain a buffer stock in Redditch so the decision was taken to create an automated storage area adjacent to the main cockpit assembly line. "The number of cockpits we were able to hold in the storage area would therefore depend on the resourcefulness of the design put forward." The build process starts each Monday when an electronic file is sent from BMW in Oxford detailing the build schedule for cockpits required the following week. From this point the whole operation, including assembly line, conveyors, cranes and despatch, is run by an Intier designed build system called Magic that instructs the assembly line via a Siemens PLC. The production line uses a monorail system, where individual carriers follow each other. Each dashboard is built, loaded and delivered in sequence. But problems began to occur as individual dashboards couldn't go out of sequence. If an alteration or repair was needed then it meant the sequence was wrong. Magna needed a much more flexible build system if it was to keep up with the demand for fast flexibility. "We supplied Inductive Powered Transferred (IPT) powered trolleys," says Eastwood. "These use cables in the floor and a pick up on the trolley to get power. The trolleys are on wheels and can be easily disconnected from the line and taken out of sequence, put it in to a rework area, and put back in the line." This worked well, but they had a problem with sequencing the completed dashboards. So Excel has put in a random access and staking system with a stacker crane. The assembly and storage systems are capable of delivering 60 cockpits an hour, with the Excel cranes automatically sequencing them to ensure that the right cockpits are put into a false lorry. A false lorry is a series of conveyors that holds 30 cockpits on an upper and lower level. These are placed in sequence so they can be automatically loaded straight into the actual lorry for delivery to Mini's Oxford production line where they will correspond to the correct car. Clifford says: "Increases in efficiency and productivity come from the combination of automated storage and intelligent crane management. Where previously cockpits had to be stored in order, they can now be stored randomly and the crane sorts it out. This has proved to be a major benefit when re-working is required." The cranes use a laser guidance system that positions them to within 2mm, the extreme accuracy being necessary due to the space limitations in the area. An on-board PLC allows manual, semi-automatic and fully automatic control of the cranes. "So they build it, transfer it to the automated store, the automated stacker crane puts them away and picks up a batch when needed," says Eastwood. "And at the same time as it is loading the false lorry, it is putting in cockpits that have just been built. "This system is much more flexible. Before we put this system in, it was so inflexible; there was a major panic every time there was a problem." There are 20 or so build stations which used to operate on a station fast setup. This is where the dashboard will move down the line and stop, a bit of the assembly is done, and then everything moves down one station. "The problem with that is, you end up with the operator deciding what speed the line is going to go," says Eastwood. "So we modified it to be a constantly moving system, very slow, so instead of the operator pressing a button to say move on, he has to press a button to say stop, I have a problem. So the system then is driving the operator, not the other way round. "This identifies operators that are perhaps not working quite quickly enough, or potential bottlenecks if the system is moving to fast." Pointers *Flexibility in automated processes is becoming an increasingly high priority as mass customisation and lower production volumes are demanded * Magna's Intier Automotive facility in Redditch needs to ensure every one of the 255,000 unique cockpits leaving Redditch every year is united line-side with its unique Mini, 40miles away in Mini's assembly line in Oxford *The assembly and storage systems is capable of delivering 60 cockpits an hour designed and built by Excel Automation based in Worcester