Machining techniques and different configurations can assist in eliminating waste and improving efficiency in production
The Nissan Decherd powertrain assembly plant, some 128 kilometres south of Nashville, Tennessee, has the capacity to build 950,000 engines and 300,000 transaxles annually. It produces all the engines for the complete line of Nissan and Infiniti vehicles manufactured in the United States, including a 2.5 litre 4-cylinder, 3.5 litre 6-cylinder, 4.0 litre 6-cylinder, and a 5.6 litre 8-cylinder. Its 3.5-litre V6 VQ has made it onto the Ward’s Communications ‘Ten Best Engines’ list for the past 10 consecutive years.
The person entrusted with keeping the machine shop functioning smoothly and efficiently is Brent Gill, Director of Manufacturing at Decherd. His challenges will be familiar to all managers of machine shops – increasing overall efficiency, controlling scrap and ensuring the facility is flexible enough to meet a fluctuating product mix.
The first item that Gill mentions is scrap, something that is important to Nissan and high on its benchmarking priorities. “Our biggest challenge now is to keep our scrap low,” he confirms. “This is something that everybody is faced with. We look across the industry, especially internally at Nissan and then compare against other plants and try to keep waste as low as possible, but we see that we have got some opportunity there.”
Keeping scrap low involves working closely with external suppliers to ensure the high quality and suitability of incoming parts. A key aspect of that input until now has been forgings, but with a new forging line due to start operating soon at Decherd, that will be within the plant’s own control. This will ensure that forgings are of a high quality, require as little machining as possible to maximise tool life as well as crucially being able to adapt to engineering changes.
“One good aspect of doing our in line forging straight into our machine line is that we are able to modify some of our forging dies to reduce some of the material going to them,” Gill explains.
“Since the process has moved in-house, similar dies are being examined to see if we can modify them to remove some of the excess material in forging. This will reduce the number of machines that are actually required in some cases,” he continues.
A more traditional measurement of productivity is overall equipment efficiency (OEE) and this is where Decherd has made huge strides. When the plant opened in May 1997, the benchmark was 70 OEE – a figure that was the norm at the time for Nissan globally. Productivity expectations have grown, and so too a higher expectation of OEE. Today the benchmark figure is 90. “Most of that is because of the growth in machining, we were able to get up to the eighties so quickly, to set the benchmark a bit higher in the nineties. I haven’t looked at it lately, but I think that most of the lines are running close to ninety now.”
The Decherd plant recently celebrated its tenth anniversary of engine making but there has been no significant investment in new equipment for the past four years. It’s had to concentrate on process improvement for efficiency and scrap gains. “We changed over the crank lines about four years ago and a few small machines were added,” Gill explains.
Block castings are currently brought into the plant, although some of these will be done in-house in the future.
“Our scrap rate really depends on our suppliers. When we start talking about block castings in terms of the porosity, the pinholes and those types of things, during our machine shop process it makes us remove that part from the process itself; all of that counts against our scrap. It also counts against the supplier scrap, but it is a part that we lost,” he continues.
Gill says the Decherd plant has improved its V8 blocks and 3.5 litre V6 block a great deal. “We still struggle with the 4.0 a bit because of the process involved. I think our impregnation has decreased substantially on the 3.5.” The plant has a fairly steady product mix, thus flexibility is not a major concern. What is a challenge is keeping production at the agreed level, even if a particular machine fails.
Gill reveals that although the company builds four different engines at Decherd, the product mix has not changed much.
“We do have volume swings between the products, but as long as we are not over capacity, we are still in fairly good shape, so we can move between lines and thus have that type of flexibility,” he says. “We haven’t gone to new models yet, other than the changes mentioned earlier. The crank lines were changed a bit to a super-micro finish, to get a better roughness. We haven’t faced the dilemma of being outside our capacity yet.”
Gill tells AMS that flexibility will allow the plant to shut down some of the lines this year to carry out certain changes for the new K3 model. It is also possible because of the plant’s flexible transfer lines (FTL). “As regards head and crank machining, we have multiple FTLs. We have the flexibility to shut down one line and modify it while maintaining production on the other lines. So we have flexibility from that point of view,” Gills explains.
A key factor for increasing the efficiency of the plant is to decrease cycle times, which involves working with the engineering department to analyse where bottlenecks are occurring in the operation. Gill explains that the teams examine the reasons for any bottlenecks – “Is it because there is a wait for parts? Can we speed up the robot? Can things be moved closer to the lines? Getting improvements in cycle time by eliminating a bottleneck will give you a higher OEE over the entire line,” he says.
“The other factor is that you might have eight drilling operations doing the same thing on the same line. One can be down and you can still have a reasonable OEE. But if you have a piece of equipment and it only performs one function, and there isn’t another piece of similar equipment, whether it is a pin milling or a line bore on a block, you have got to maintain the equipment by total productive maintenance (TPM),” he adds.
“You have to maintain that equipment because its up time is crucial. If it goes down, it directly impacts on the OEE.
So we would do extra things with the TPM. The maintenance department is aware that a particular piece of equipment has to continue running, so they will examine it during down hours to make sure it is ready to go. By implementing these types of activities and improving our cycle times with the help of the engineering department, the OEE has gone up,” Gill tells AMS.
Something that Nissan has been implementing globally in its machining operations is minimum quantity lubrication (MQL) and recycling cutting fluid. Engineers at Decherd visited Nissan’s plant in Britain to see these systems in action. When Nissan Motor Manufacturing United Kingdom (NMUK) installed its fluid recycling system in March 2004, the initial target was to reclaim between 60 and 80 per cent of its production cutting waste fluids. Within months, the plant was reclaiming levels of 90 to 95 per cent.
The results continue to surprise with reclaim efficiency levels of 100 per cent being recorded in recent months. This has helped NMUK’s control of on-site waste and ISO 14000 environmental objective, in particular its on-site waste management volumes.
Demand on the system has grown in line with NMUK’s increased production of cylinder heads at its Sunderland plant. This resulted in its swarf-centrifuging system extracting upwards of 1,000 litres of machining fluids per day. This water miscible system is specifically configured to remove tramp oil and particulate matter from coolant, and wash fluids down to eight microns or less. The unit is equipped for use on high temperature and high pH fluids and, being mobile, it is able to process fluids in different locations within NMUK’s engine parts manufacturing facility.
Gill confirms that the Decherd facility has had success with MQL. “We have it on our number two crank line and have not had any problems,” he says. “That type of technology is going to help reduce costs, and help the environment too, because very little coolant has to flow through it. It uses exactly what you need, so there is no waste. I’m not sure whether that would help us on the line, but it would help us on tool life and reducing costs.”
He explains that where it has helped, is with the tooling. “We have been able to do trials on new types of tooling, because if you increase tool life, you increase OEE as you are able to run that tool longer. You are able to get more cuts out of that tool; instead of getting 1,000 cycles you get 1,500 cycles, thus you are not down for tool changes. That also increases your OEE.”
Ford’s Bridgend engine plant has enjoyed much success recently, prompting a decision to increase camshaft production by 40 per cent to 1.4 million units a year. The carmaker wanted to achieve this without investing in extra machinery, so its engineers undertook a detailed analysis and identified cam lobe grinding as one process where improvements could be made.
Because of the complexity of the process, Ford called in Tyrolit, its grinding wheel supplier, to suggest ways to increase throughput and, at the same time, improve the quality and accuracy of the cam surfaces. Tyrolit formed a working party with Ford engineers to define the project targets and collect data on the existing process for analysis.
The supplier then submitted a detailed cost reduction plan in which savings were broken down into making cuts in consumables, set-up and machining costs. Floor-to-floor time was reduced from 124 to 112 seconds and the increase in grinding machine capacity was more than 12 per cent, allowing production of 1.4 million camshafts in a year without building a new facility.
Central to achieving the optimisation targets was the adoption of a newly developed Tyrolit CBN grinding wheel, which draws less spindle power, as it is 60 per cent lighter than conventional products. Also, the new tool absorbed vibration better, allowing a harder bond to be used. Together with improved dressing, this resulted in longer wheel life, and a significant reduction in cost per part. Overall, the saving in cam lobe grinding was calculated at over £300,000 ($599,000) per year over the lifetime of the project.
“The structured approach to this project was key to its success,” Mike Jones, Ford’s Senior Manufacturing Engineer, says. “It is a good example of our philosophy of working closely with partners and suppliers. The successful outcome proves how extraordinary results can be achieved when innovative minds and production tools are at work.”