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Cbn Grinding a Tempting Technology

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Cbn Grinding a Tempting Technology Reprinted from MANUFACTURING ENGINEERING, February 1994 Issue Don’t let initial cost and perceived risk scare you CBN GRINDING A TEMPTING TECHNOLOGY or years, CBN grinding This material also offers was on the fringes of the potential for improved F machining technolo- production through better gy. Manufacturing engi- finish, greater part consis- neers used it only when tency, and tighter toler- they had to, usually because ances. CBN can offer a sig- a metal was too difficult to nificant time saving in high cut or finish any other way. speed production because The picture is changing wheel dressing is less fre- today with about 25% of all quent. CBN grinding is not industrial grinding in Japan limited to traditional fin- done with CBN, 15% in ishing operations. Its Europe, and 10% in the US. potential for fast material Although CBN use in the US removal means it can is statistically low, interest is sometimes eliminate quite high. Predictions are machining steps. In some that its use will expand dra- cases, grinding can do in matically for three reasons: one setup what would oth- conversion from other erwise require milling, abrasives, chiefly alum- grinding, heat treating, and inum oxide; introduction of polishing. Grinding drill CBN compatible grinders; bits from bar stock is one and new applications as such application. harder, more complex work ‘Today, high-speed materials are introduced. Landis CBN machines, shown doing pin journal grinding, are grinding (16,000-40,000 According to data from gaining acceptance in the US automotive industry. sfm, 80-200 m/s) accounts GE Superabrasives (Worthington OH), total use. Aerospace and gear manufac- for about 3% of all CBN grinding. Some global sales of CBN wheels was $145 turing follow with 9% and 8%, respec- experimental systems claim 100,000 million in 1988, reaching $300 million tively. As to grinding techniques, CBN rpm. But “high speed” is not well last year. The company estimates use has made its greatest inroads with ID defined. According to Mike Brooks, a can grow another 4.5 times to reach grinding because wheels are smaller Borozon CBN engineer with GE Super- $1.6 billion. and, therefore, less costly. abrasives, most work with CBN is done In the US, CBN wheel sales for 1992 at speeds between 8000 and 12,000 sfm were an estimated $63 million, only a Why It’s Better (40 and 60 m/s), although cam grind- 13% penetration of the potential $480 CBN has many advantages over con- ing, a major CBN application, is done million market. Currently, the automo- ventional abrasives. It is twice as hard at 16,000 sfm (80 mps). These speeds tive industry is the largest user of CBN as aluminum oxide, so a CBN wheel are also typical of most aluminum wheels with 30% of the market, says lasts longer, often 100 times or more. oxide grinding. “But,” says Brooks, GE. Tool production (both production ■ “because CBN grinding is cooler, there and resharpening) is the second largest is less tendency to burn. The bottom market with about 20% of sales. Robert B. Aronson line is higher speeds mean lower wheel Bearing manufacturing is a growing Senior Editor cost because of longer life and application now representing 12% of improved quality. “ Society of Manufacturing Engineers Another unique feature of CBN, resid- and it can’t be treated like a $10 wheel. (Wixom, MI) has specialized in automo- ual compressive stress, leads to higher The first step in exploring CBN is to tive applications such as camshaft quality parts. Evidence indicates metal know your costs and production needs grinding and made major sales to Ford. surfaces contract during CBN grinding, intimately. In trying to sell CBN grinding Conventional cylindrical grinders eliminating the microscopic surface wheels and machines, suppliers com- operate at 6500-12,000 sfm (32-60 m/s). cracks that typically exist in steel. This plain that manufacturing engineers The most recently introduced Toyoda makes the metal stronger in machine, the GZ32P operates at many applications. On the other 40,000 sfm (200 m/s) using a thin hand, when grinding burns vitrified CBN wheel for slot metal, the heat generated grinding. European based expands the surface and opens grinder manufacturers, such as the microcracks and encourages Junker (West Springfield, MA), early failure. Guehring (Sussex, WI), and Some CBN users say residual Maegerle (Schaumburg, IL) are compressive stress allows reduc- known for specialized app- ing component size because the lications such as high-speed individual elements can take cylindrical, surface, and greater loads. One example is an creep-feed grinding. automotive transmission where In the US, some grinder man- smaller, but stronger, ufacturers are just turning their CBN-ground gears allowed a attention to grinders designed size reduction. for CBN. According to Pat Harrington, vice president, engi- Cost Problems neering, Bryant Grinder Corp. The major negative is initial (Springfield, VT), his company cost. First, there is the cost of the has designed machines around wheel. A 10” (254 mm) alu- the CBN process for six years, minum oxide wheel might cost but the company only recently $150; whereas a comparable designed one from the ground CBN wheel might sell for $1500. up for CBN, their UL2. Bryant This “sticker shock” keeps many specializes in ID grinding with first-time buyers away. CBN most wheels in the 1. 5” Remanufactured machines, such as this thread grinding wheel prices have dropped 50% (38-mm) diam. range. “We over the last 10 years, according machine from Drake Manufacturing, is one way around the high cost of new CBN grinders took on this design because to data from GE Superabrasives, the effectiveness of CBN was and continue to fall as sales volume usually don’t have a clear understanding becoming obvious,” he says. Bryant increases. This trend encourages users of their own grinding costs. They usually to look at CBN as a viable production have data available on the cost of the is also working with the University technology, but total cost, performance, work material and expendable supplies of Connecticut to develop a super and part quality are still the deciding such as wheel and coolant costs, but lit- high-speed OD CBN grinder. factors. tle beyond that. You need a more com- Huffman (Clover, SC), another Another major cost consideration is plete analysis, both up and downstream. old-timer in the US grinding industry, the grinding machine. It isn’t always This includes an in-depth analysis of the recently offered a six-axis grinder with practical to just bolt a high cost CBN less obvious items that increase operat- CBN capability. The company has had wheel onto a conventional grinder. ing costs such as scrap, coolant mainte- Absence of a truing and dressing system significant success in tool manufac- nance, waste disposal (both swarf and ture and maintenance with CBN. or lack of machine rigidity won’t give the coolant), production downtime due to user the full benefits of using CBN. Top wheel changes and other maintenance, One of the newer entries with a of the line machines sell for around diamond truer cost, and wheel break- machine specifically designed for $100,000 to $500,000. If those costs are age. Then it’s important to get numbers CBN is Edgetek, (Middlefield, CT), a too great, a user might upgrade or for the benefits of increased production company that offers a plated-wheel rebuild an older machine to use CBN cycle, lower scrap rates, and higher part system selling for about $225,000. wheels. quality. With those figures in hand, They refer to the type of grinding A difficult-to-predict cost is loss from CBN’s benefits may become more obvi- their machine does as high-efficien- operator error. One crash of a large CBN ous. cy deep grinding (HEDG), a form of wheel can instantly wipe out any eco- nomic advantages, so operator training What Machine? high-speed creep-feed grinding. is essential. CBN wheel makers say that Many of the grinders using CBN in HEDG is said to have the advantages working with CBN is not difficult, it’s just the US are imported. The Japanese have of material removal rates as high as different. Operators must understand broad experience and have done well in those of conventional machining the CBN wheel takes careful handling grinding production parts. Toyoda and ability to cut hardened parts with no damage due to heat. any major redesign of our machines speed was unnecessary. Nelson Campbell Grinding Co. (Muskegon because we have always had a rigid Beaulieu, an engineer for Blohm MI), a company with an aerospace design. We did have to add the precise Grinding Systems, says their company industry niche, makes rotary vertical dressing and positioning systems CBN feels they can do most CBN grinding grinders using all types of CBN wheels. requires, however.” tasks adequately at speeds around The company’s major market is in the The company now offers surface 9000 sfm (45 m/s). jet-engine part manufacture, chiefly grinders with both plated and vitreous shafts and vanes. But it is What’s Required? expanding into other aero- For a grinder to use CBN suc- space and automotive applica- cessfully, it must have the nec- tions. Campbell recently intro- essary stability, conditioning duced a model with a turret devices, positioning, gauging, changer and automatic part spindle speed, and cooling sys- inspection. This design allows tem. using both CBN and conven- Stability. The machine must tional abrasive wheels on the be strong and stiff to resist the same part, but needs a wide dynamic loads and minimize speed range to accommodate vibration.
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