Harder Materials Are a Constant Challenge
New coatings open new markets
By Robert B. Aronson
Stuart Salmon, Advanced Manufacturing Science & Technology (Rossford, OH), sees these trends for the grinding industry:
- The increasing sales of abrasives and machines/equipment are clear evidence that grinding and abrasive processes are growing. The message is out that grinding is not just precision finishing—it is abrasive machining with the accuracy of grinding and is competing well with milling, broaching, and turning.
- Growth in superabrasives, and in particular plated superabrasives, is continuing. Plated superabrasive wheels are increasing in popularity as there is no need for a dressing system or the time for a dressing cycle. It is plated superabrasive wheels that will take the industry into the ultra-high-speed era too.
- Grinding is still a materials-driven process, but not just for hard steel. It's also used for superalloys, ceramics, cermets, glass, rubber, polymers, and whisker-reinforced plastics. Though hard turning is competing with cylindrical grinding, and both grinding and abrasive machining are competing with large-chip machining processes, when it comes to the nonmetals and the ever-expanding world of next-generation materials, there is no alternative but to grind them.
- Despite all the information on dry and near-dry machining, grinding will be staying wet for a long time to come. Research into the next generation of grinding fluids is heating up. Though straight oils are favored for CBN, there are water-based fluids that are now performing well. Though the proper application of the fluid is well-known, the chemistry is being reinvented. Lubrication and cooling may not be the key factors for a good grinding fluid.
- Machining centers are being built to incorporate both large-chip (milling, drilling and turning) processes as well as abrasive grinding processes.
- Grinding wheel speeds are continuing to increase. Where safety was once an issue, in the presence of an operator, the proper guarding in an automated cell—where the potential for human exposure is greatly decreased—is opening doors for higher-wheel-speed machines.
"The grinding industry is finding more opportunities in working with harder materials, such as tungsten, cobalt, and ceramics, where conventional machining has difficulty. One special challenge is the move to coatings using the high-velocity oxy-fueled (HVOF) system of coating.
The use of HVOF is becoming more popular, particularly in the aerospace industry, where it is replacing chromium in many applications," says Hans Ueltschi of the UGT (Miamisburg, OH) cylindrical products division. It's a type of flame spray that uses confined combustion and an extended nozzle to heat and accelerate a powder at hyper velocities onto the coating material. The result is a dense, strongly adhered coating. But this coating is sometimes rough and irregular. That has created a good opportunity for grinding as a finishing operation.
"Although flexible, multifunction machines are needed for their versatility, we are seeing a lot of action among more simple machines more closely tailored to the needs of a specific product, or family of products," says Ueltschi. These are more simple CNC machines, usually single wheel, or double wheel in the case of ID/OD operations.
The company is also developing systems that combine hard turning with grinding. The hard turning prepares the surface and the grinding provides a quality finish.
More manufacturers are emphasizing loading and unloading as a critical time element in a grinding operation. UGT is developing more versatile equipment to fill this need. For example, they recently offered a very simple high-speed loader for some machine models.
Customer demand is driving new developments in grinding. "At Drake Manufacturing Services Co. [Warren, OH], the green movement, need for more oil, and popularity of hand-held electric devices have all led to new markets," explains company president James L. Vosmik.
On the green issue, many auto manufacturers are dropping hydraulic control of the power steering function and going to electronic control. Electronic steering is less demanding on the engine.
This energy-saving move has created a need for precision mechanical parts, such as ballscrews and ballnuts, amd wormgears and wormwheels. "A rack may be as small as 25 mm," says Vosmik. "Precision is necessary because of noise and vibration issues, plus the turning action must feel smooth to the driver."
The oil industry's link to precision grinding is less direct. The significant increase in oil exploration and recovery requires more oil pipe. These pipes are screwed together. A pipe-connection failure can mean the loss of millions of dollars in equipment and drilling time, therefore the pipe threads have to be very precise. That's where Drake comes in. They manufacture machines that make the thread gages. "Our customers are the gage makers. For this market we have an ID grinder with a 500-mm swing," explains Vosmik.
Finally, the boom in hand-held electronics, such as cell phones and Ipods, has created a parallel boom for screws as small as 0.1-mm diam to hold things together. Drake has developed equipment specifically to make form taps which, in turn, make the holes for the screws. One such machine is the GS:TEM, which has linear motors. "The advantage of form taps is that they create no chips. They function much like wood screws in that they displace metal, they don't cut it," explains Vosmik.
"Customers are buying a lot more accessories and peripheral devices," says Nelson Beaulieu Grinding Product Manager for Hardinge (Elmira, NY). "For a while many customers wanted stripped-down machines, now they want them loaded.
"Part of this trend is a way of not losing more customers overseas. Some manufacturers are now willing to buy the best equipment to provide the highest quality to their customers."
Another trend is more requests for machines that can make bigger parts. "Normally we sell mostly units with 28–40" [711–1016-mm] wheels. Now we are selling a higher percentage of machines with grinding lengths up to 60" [1524 mm]. The chief market for these units is aerospace and defense," says Beaulieu.
He also notes a surprising market in the wind-turbine business. These units need a lot of high-quality elements, such as precision bearings. "This could be another growth market if the current interest in energy conservation persists."
The company is now filling a need for a lower-cost grinding machine aimed at customers who specialize in mid-range production. Capable of higher performance, it's called Kel-Vita. The machine is a much-advanced version of the Kel-Vista, Hardinge's entry-level CNC unit.
The goal was to design a lower-cost unit with many of the features found on larger machines. Included in the new machine are bigger grinding wheel capacities, a Fanuc 310i control, and higher horsepower. It has automatic indexing, can do OD and ID grinding, and can make threads and elliptical profiles.
In general, the demand for more automation has resulted in the design of grinding systems that can run untended. That requires longer-lived abrasives, automated dressing, and more efficient feeding and part-removal equipment.
Rollomatic Inc. (Mundelein, IL) has been keeping up with industry trends. According to company President Eric Schwarzenbach, the company has been achieving successes in these areas:
- Developing grinding systems that work well with the newer, tougher materials.
- Developing a line of less sophisticated, lower-cost machines that can be more closely tied to specific production needs.
- More automation, chiefly for the load/unload portion of the cycle.
Schwarzenbach notes that it is not always necessary to have complex equipment for all processes, such as burr-grinding. Rollomatic has, for example, designed a simple, fast, low cost mechanical system.
"But, before taking advantage of any new developments," Schwarzenbach cautions, "remember that machines, abrasives, part materials, and processes are constantly changing. It's not practical to generalize on what will work in a given situation. Therefore it's very important that the customer and supplier have a detailed review of any process changes, and that especially includes testing."
The grinding industry is finding more opportunities in working with harder materials containing tungsten, cobalt, and ceramics, where conventional machining has difficulty. "One special challenge is the move from chrome plating to HVOF," explains Bruce Northrup, general manager, Meister Abrasives USA (North Kingstown, RI). This material provides a tough, inexact, and rough coating surface on many aerospace parts. This surface must be ground, which has been a good market for us."
As in many automotive-related industries, fuel injectors continue to be a benchmark for precision. "The pressure for improvement has become quite strong since the dramatic rise in gasoline and diesel-fuel prices. The demand is for very small, high-precision parts, many of which must be ground. And these needs are moving outside the auto industry with interest from the medical, semiconductor, and aerospace industries as well," says Northrup.
Cost cutting and higher speed production are resulting in more automation. To fill this need manufacturers want grinding systems that can run untended. That means longer-lived abrasives, automated dressing, and more efficient feeding and part removal equipment.
"We meet these needs for our customers chiefly with high-precision CBN and diamond wheels," he says. "Under development we have a new system for flute grinding of precision medical tools. They were formerly made of high-strength steel and the move is to ceramic."
The drive for precision is also influencing the type of abrasive bondings used. "We are replacing a lot of lower-tech resin and metal-bonded wheels with our vitrified and hybrid bonded wheels," says Northrup.
"But buyers should be aware that the type of abrasive and bonding used must be matched carefully with the product specifications and the condition of the grinding machine. On newer high-precision CNC machines, the benefits offered by the latest vitrified and hybrid bonded CBN/diamond wheels are clear and easily measured. On older or less-sophisticated machines, it may be more challenging to measure the improvements offered by these new wheel technologies," Northrup concludes.
More machines are being designed with both a grinding wheel and the related cooling nozzle mounted in the toolchanger. "The nozzle need not be configured separately, it's designed to work with a specific grinding-wheel application," explains John A. Webster, Cool-Grind Technologies (Storrs, CT). "This minimizes a lot of shop-floor inventory and gives you multiprocessing in the same fixture." — Robert B. Aronson
This article was first published in the August 2008 edition of Manufacturing Engineering magazine.