Cutting it closer
- May 16, 2013
by Andrew Brooks
Machining automotive parts is a game of inches and speeds, with no time or room for error
Lighter. Smaller. Stronger. Harder. Faster. It might sound like a mixed-up version of the Olympic Games motto, but it’s actually just a (partial) list of the terms and conditions big car makers impose on the massive automotive supply chain that provides them with parts. Lighter, smaller parts that don’t compromise on strength, new metals and composites that are harder to machine, all produced to tighter deadlines and within faster cycle times.
“There’s never enough time to do everything you need to do in automotive in terms of product development and prototyping–and even in production,” says Mike Whatling, plant manager for Niagara Precision Ltd. “It’s very fast-paced and a lot of times you only get one shot at it, which puts a lot of pressure on job shops as well as the production facilities.”
One of the primary challenges Whatling identifies in machining automotive parts is the increasing use of advanced high-strength steels (AHSS) in the automotive manufacturing industry. These advanced steels are becoming increasingly important as auto manufacturers seek to produce cars that weigh less, employing parts
and components that are smaller and lighter, but that continue to meet the same–or even tougher–strength requirements.
In addition to favouring the use of AHSS, the automotive industry's demands have also driven research and development into advanced composite materials, and as these make their appearance on the shop floor they have proven to pose problems from the point of view of machining. Job shops are often on their own when learning how to adapt their processes to cope with new material characteristics.
“A lot of composites that are coming out now are difficult to machine, period,” Whatling says. “There’s not enough information out there, or the tooling doesn’t exist for machining these components. So everybody develops their own procedures for machining exotics.”
At least there are some ways for industry innovators to recoup some of the costs of developing those procedures–notably the Scientific Research and Experimental Development (SR&ED) federal tax incentives and credits. And educational institutions with automotive and engineering faculties are available to support research and development. But ultimately, Whatling says, it comes down to a matter of trialing new procedures in the plant.
“The more exotic metals create new issues for machining techs that are evolving as the components are being designed and produced,” Whatling says. “From the prototyping standpoint–which is a lot of what we do at Niagara Precision–we’re faced with some pretty serious challenges as far as being able to machine these exotic materials and composites.” Hardness is one challenge, material composition is another, and the continual reduction in part size while strength characteristics are maintained means it’s always getting tougher to machine components without encountering distortions and tolerance problems.
“Many of the composites we’re seeing are all different,” says Randy McEachern, product and application specialist, holemaking and tooling systems for Sandvik Coromant Canada, Mississauga, ON. “Nowadays many materials are manufactured for the specific component. I seldom see any two materials that are the same, which means for optimum performance, the tools you use need to be specifically designed for that material.”
Sandvik does have some general purpose tooling, McEachern says, but he estimates that when it comes to machining composites, most tools have to be engineered for the specific material they’ll be working on. The composites now offer the strength to (light) weight ratio so sought after by the auto makers, a big improvement over the early days when composite materials arrived. “They’re becoming more reliable,” McEachern says, “but users still have to know their stuff.”
For Steve Geisel, senior product manager at Iscar Tools, Oakville, ON, shaving cycle times is a paramount challenge in automotive work, thanks in large part to the sheer numbers. “These are very high volume runs,” he says, “and they’re dealing with near-net-shape parts–a lot of forgings, castings, parts that don’t have a lot of material on them to rough out. But it’s worth saving whatever time you can. When it costs $60 to $180 an hour to run one of these machines (that's $1-$3/min), this can quickly add up to a lot of money.”
Reducing cycle times means faster cutting, says Mark Hatch, product director of taps and thread mills for Emuge Corp., West Boylston, MA, which offers “full-speed” taps that are two to five times faster than conventional tools.
“The speed is achieved through unique design characteristics of the taps in areas such as relief, back-taper, length of thread and flute geometry.”
Hatch estimates if tapping is reduced by ten minutes per hour at a machine rate of $150, a manufacturer can achieve annual savings of $125,000 and increase capacity by 833 machine hours.
Looking specifically at turning processes, Geisel notes that many automotive parts aren’t cylindrical in profile so it’s not always possible to attain efficiencies by increasing spindle speed. “You look for other savings. You run multiple tools at a time, or you get a higher depth of cut, or maybe higher feed rates. These can all affect the overall time of a work piece, rather than increasing the spindle speed.”
Geisel says Iscar focuses on optimizing machining processes by making tools last as long as possible and balancing the speed, feed and depth of cut. “It’s not always just that one insert just lasts 50 pieces and another lasts 60 and that’s all you can do,” he says. “Sometimes the advantage of lasting 10 more pieces can be offset by shaving one or two seconds off the cycle time. These are processes involving thousands, hundreds of thousands and even millions of parts, so you can get significant savings from small improvements.”
One factor that can sneak up on parts suppliers and job shops is variation in material quality, particularly when a shop switches suppliers in an effort to cut material costs. But a lower up-front cost can create pitfalls further down the road. “We’ve had issues where we’ve had offshore material come in that machines nothing like the material we procure domestically,” says Whatling. To ensure consistent material characteristics, Niagara Precision buys domestically only, and insists on aviation-quality steel. “I tell customers that if they understand the potential problems with offshore material and want to use it anyway, I’ll do it. But I make sure they’re aware of the potential problems.”
Invariably, Whatling says, the cheaper metals prove to have inclusions or cold shuts that lead to failure during post-machining tests. “So the parts have to be made with something else, which in most cases is a domestically produced steel. The purchase price may be lower [for less expensive metals], but in the long run the higher quality material really is cheaper.”
Of course variation in material quality also impacts tools. “Sometimes you get different material batches coming in and it has a huge impact on cutting tool performance,” says Iscar’s Steve Geisel. “Where the material is made will have a huge impact on how easy it is to machine, which impacts tool life.” Geisel often gets calls from customers who’ve seen tool life drop 10 to 30 per cent. “When we go and have a look we often find it’s a new material batch.” Geisel says that Iscar–and he says this goes for competitors too–builds so many checks and balances into its own manufacturing that tool quality is very high.
With machining centres being asked to take heavier cuts at higher speeds, the programmability of machines plays a huge role. “You’re dealing with rapid feeds of over 1500 ipm now, where ten to 15 years ago you were lucky if you had a machine that would do 5 ipm,” Mike Whatling says. “The technology plays a huge role in being able to make these parts.” SMT
Andrew Brooks is a freelance writer based in Toronto.