Think total grinding package
Weighing all the options is key to choosing a truly productive grinder.
Since every aspect of a grinder affects its overall performance, shops looking to purchase one must consider not only how the machine is built, but also how it dresses wheels, programs, sets up, changes over, and handles part loading/unloading. By optimizing these aspects, shops acquire a total grinding package that meets and even exceeds productivity goals.
Machine designs According to David Drechsler, vice president of sales & marketing at Huffman Corp. in Clover, S.C., grinding-machine customers should look for a machine design that best fits their application. A modular design, for instance, lets a builder draw from a pool of proven, reliable modules to configure a grinder thats for either a specific, dedicated, high-production application or a flexible one for a variety of jobs. Both machine types can include anywhere from 3 to 6 simultaneouscontouring axes, and their modularity means the builder didnt waste time developing and debugging a completely new design. Whenever possible, shoppers should seek machine designs that combine operations for lean manufacturing. Several builders offer machines with multiple grinding wheels and multiple part fixtures, and some even combine grinding with milling. The results are higher-quality parts, less work-in-progress and inventory, and lower costs. Combining multiple operations in a single machine, says Russ Kaiser, vice president of engineering at Landis Grinding Systems, responds to a shops need to minimize its number of machines and reduce capital expenditures. For physical machine qualities, Drechsler of Huffman believes total system stiffness is critical. Often, the workpiece or the fixture is the weak link in the system-stiffness chain, he says. Along with being stiff, a grinding system must be accurate. Randy Ragnini, regional manager at Toyoda Machinery USA in Arlington Heights,
Ill., says that most CNC grinders accommodate such things as inprocess gaging, special width and outer-diameter-combination gages, and lateral locators also known as flagging for enhancing machine accuracy. Grinding-machine shoppers looking for even more machine accuracy may want to add other features such as dynamic wheel balancing, acoustical-vibration detection and compensation, coolant chillers, and special wheelhead or workheadbearing components. John Drake, president of Drake Manufacturing in Warren, Ohio, concurs and encourages shoppers to look for grinders with interlocking accuracy systems that include linear scales, rotary encoders, millioncount servo feedback, and acoustic sensing. A properly specified coolant system is also important, adds Ragnini of Toyoda. Aside from delivering adequate coolant to the grinding wheel, coolant systems with bed wash and filtration enhance grinding accuracy and reduce setup time. When contemplating grinding-machine capacity, Gerry Sandstrom, sales engineer at Service Network Inc. in Worcester, Mass., advises that buyers focus not only on part size, but also weight. A combination of heavy grinding chuck and hefty workpiece may cause an improperly engineered or light-duty workhead to sag, resulting in accuracy and machinemaintenance problems. The shifting of heavy weights on long-stroke slides, likewise, affects part accuracy. Sandstrom also offers advice on machine horsepower. With modern drives and spindles, many shops, especially those doing I.D. grinding, tend to select one spindle and drive to handle all machine operations. This is a risky approach related to the drive motors horsepower curve. A linear-shaped horsepower curve may compromise speed or horsepower depending on the range of operation. This, in turn, negatively affects grinder productivity.
Dedicated or universal For small-to-medium batchproduction work in a jobshop environment, universal-type grinders Several grinding machine builders offer machines with multiple grinding wheels and multiple part fixtures, and some even combine grinding with milling.
Hardinge in Elmira, N.Y. These machines quickly and accurately do I.D., O.D., and surface grinding, but for high-volume production work, a shop might want to consider a dedicated grinding system, he advises. Dedicated systems, according to Winstanley, have only the components necessary for a particular application, which makes for extremely fast cycle times. However, choosing a universal grinder is not a compromise in accuracy. The machines are just as accurate and reconfigure in less time if the part changes. offer the best flexibility, says Robert Winstanley, North American sales manager, grinding, at cause their heads accommodate multiple grinding wheels. Jobs that often take up to 5 setups are usually completed in one or two. Universal heads come in various configurations. For instance, shoppers can equip heads with four O.D. wheels, three O.D.s and one I.D., or one O.D. and two I.D. While these heads are dedicated in a sense, the machine itself is still extremely flexible, says Winstanley of Hardinge. Wheel dressing on a universal is versatile. Shops can locate dressing units at the tailstock, behind the wheelhead, on the workhead, sliding up and down the worktable length, or anywhere convenient for a particular job, says Winstanley. Where and how a shop dresses its wheels greatly influences part cycle times, he adds. Taking dewater out of grinding swarf
Handling grindingswarf sludge is an often-troublesome and costly aspect of highvolume operations. If not dewatered, sludge is hazardous waste under both federal and state regulations and must go to designated waste sites. Without proper disposal, the wet-waste generator faces fines and penalties. By producing dry swarf, shops avoid such liability. A high-density extruder (HDE) such as the National-Sebright HDE from National Conveyors, East Granby, Conn., provides an efficient and versatile method for dewatering grinding swarf. The unit uses a hydraulically powered ram box that moves forward and back. In the forward position, the ram-box top is the bottom surface for the feed hopper that accepts loads of wet swarf. During forward motion, the ram presses the newly deposited wet swarf with progressively increasing force, partially compressing and dewatering it. The discharge gate then closes partially. A separate hydraulic accumulator remains charged until remaining swarf solids are compressed, dewatered, and ready for discharge. The unit then ejects a dry swarf cake.
Wheel-dressing systems for CNC grinders include singlepoint, two-point, three-point, and rotary diamond. Singlepoint diamonds straight-dress grinding wheel
O.D.s, while two and three-point ones interpolate forms in wheel
O.D.s. Rotary dressers also interpolate forms, but do so more accurately, while lasting longer than single-point diamonds, explains Michael Willard of Parker Majestic, a division of Penn United Technology, Butler, Pa. Machines with rotary dressing, over-the-wheel plunge dressers, or other special dressing capabilities, such as software that automatically tracks multiple dressers, all reduce dressing time and maximize machine output, comments Ragnini of Toyoda. Shops looking for both
I.D. capability in one machine should consider a universaltypegrinder.
Universal grinders let shops program angled, straight, and internal grinding on one machine. They are often the most advantageous option for reducing setups and increasing accuracies fewer setups means less chance for stacked inaccuracies, says Toyodas Ragnini. Universal grinders O.D., I.D., and face grind parts in single setups be-
A grinding machines control hardware should last for at least 10 years.
Shops also have a choice between manual or automatic dressing. Auto dressing is well suited for maintaining a specific wheel form or part finish during unattended machine operation. Manual dressing is seldom used in a CNC environment, but it is available as an on-command function for situations when operators have to dress wheels. To reduce dressing cycle times, explains Sandstrom, liftup wheel-dressing units quickly drop into position for dressing and lift clear during grinding, so machine slides dont have to traverse to and from remotely positioned dressing stations. These systems also let shops use shorter grinding-wheel quills/ arbors for a more-rigid and productive grinding system.
Controls and programming Having the right grinding machine CNC reduces setup and cycle times, improves part quality, and lets one operator handle more machines, says Ken Larson from the sales & marketing dept. at International Tool Machines of Florida Inc. in Palm Coast, Fla. Grinding-machine shoppers should ask if the machines control uses industrystandard interfaces between CNC and drives, CNC and I/O systems, and standard software interfaces for inclusion of third-party software, recommends Tim Hykes, manager of controls engineering at Landis Grinding Systems. Most grinders include ethernet, RS-232, and floppy-drive ports for importing programs and managing files, adds Willard of Penn United Technology. In addition, they may offer extensive selections of canned conversational programs. A grinding machines control hardware should last at least 10 years. However, advises Landiss Hykes, many standard CNCs dont use common interfaces between components, so if one of the pieces becomes obsolete, the user is left holding the bag. He suggests opting for an open-architecture control that integrates several new generations of computers, drives, and I/Os. Such flexible and adaptable systems permit easy upgrading. To further protect machines from obsolescence, some builders make each new generation of grinder appear as familiar as possible-to operators by carrying forward the original, simple, and intuitive control features, while simultaneously improving system performance and reliability. Such improvements include digital servo drives and Sercos standard interfaces that reduce wiring up to 60% and absolute encoder feedback that eliminates datum switches. Willard of Penn United Technology suggests buyers ask suppliers if the machine can import programs from CAM systems as well as whether its control includes
Lift-up wheel-dressing units quickly drop into position for dressing and lift clear during grinding, so machine slides dont have to traverse to and from remotely positioned dressing stations.
canned cycles. Some controls house extensive libraries of easytouse conversational programs that walk operators through most common grinding and wheeldressing programs. Ragnini of Toyoda recommends simple conversational-programming features like pictogram sequencing, automatic grinding-conditions determination, position memory teach-in capabilities, copy and edit functions, and access to machine and programming-maintenance functions. Other desirable capabilities are contour dressing and simple program back up. According to Drake of Drake Manufacturing, shoppers may want to consider machine builders that incorporate a customers part programming into menu-driven control software. For complex parts, this software reduces setup and changeover times from hours to minutes. And since all process parameters are built-in, the machine is easy to operate.
Setups and changeovers What buyers often neglect to investigate are grinding machine setup and changeover times, points out Merk Roland of Agathon in Bethel, Conn. Pertinent questions include: how long does it take to set up the machine from scratch, and how long does it take to change the machine over to a new job? Machine accessibility influences setup time. Shops should choose a grinder that provides operator comfort. Machine doors should swing open and provide plenty of room at the wheel and work envelope, says Winstanley of Hardinge. Also, automated touch-off mechanisms that locate wheels to workpieces speed setup. By Patricia L. Smith, executive editor Behind the grinding wheel
Time to pick a grinding wheel? Dont judge products on price tags alone. Instead, focus on grinding efficiency. The best way to match appropriate wheels to applications is to evaluate machine tool, work material, abrasive, and operational factors separately and in relation to one another. Using such a systems approach helps curb costs, improve workpiece quality, and extend wheel life. End users should begin the wheel-selection process by evaluating priorities, cost drivers, and constraints, says Bob Smith, Saint-Gobains technical director, application engineering.
Thats because low, medium, and high-volume producers have different needs. For instance, productivity may be the most important consideration for one company, while another may focus on versatility or precision. And different companies have varied capacities and costs in terms of material, abrasive, and manpower. Prioritizing these factors and recognizing their constraints is an essential step in the wheel-selection process.
Grinding grits and grades Grinding wheels come in two general grit categories: conventional abrasives, which include aluminum oxide and silicon carbide, and superabrasives such as diamond and cubic boron nitride (CBN). In general, what grit size and grade to use depends on the workpiece material. Soft, ductile
By matching grinding wheel to application, end users can boost grinding efficiency, quality, and wheel life.
Part considerations Saint-Gobains Smith recommends shops review the following with their grinding-wheel manufacturers: Application details: Part type and dimensions
Surfaces to be ground
Required tolerances for surface finish and geometry (size, roundness, and form)
Average production run
Spindle rpm at the wheelhead
Coolant type/volume/ concentration
Shops should determine if wheel life or speed of grind is more important. A new vitreous (glass) bond system combined with new CBN grains tackles high-volume, ultra-precision grinding and holds profiles up to 3 longer than standard CBN-vitrified technologies.
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Some grinding machine builders embed acoustic sensors in grinding spindles to locate wheels to workpiece, comments Drake of Drake Manufacturing. These sensors reduce setup time by automatically locating the dresser, and the wheel acts as a probe to detect misloaded parts. Huffmans Drechsler tells customers to consider machines with quick-change wheels, fixtures, and coolant-nozzle assemblies, along with software and programming techniques that simplify setup and changeover. Shops have to stop thinking in terms of single-digit changeovers less than 10 mi. and start s h o o t i n g f o r p a r t changeovers that take seconds, he says. According to Willard of Penn United, one feature that speeds setup/changeover times is special libraries for keeping track of shapes and forms for several wheels. Another is custom macros that reduce setup time for families of parts. Also, machine features such as repositioning footstocks, hydraulic actuation of the footstock center, automatic compensating work drivers, pressure work drivers, work supports, and/or steadyrests (manual or automatic) all shorten setup time.
Automation Like a grinding machines purchase price and its efficiency, automation is also a function of operating cost, says Sinkora of Walter Grinders. Thus, a shop should de-
High-quality surface finishes are a priority for an upcoming job at AM Mfg. Co., so the shop is evaluating several grinding systems. While the somewhat-high-volume job is a good candidate for dedicated grinding, the shop is uncertain how long the job will last, so universal grinding with its flexibility to handle different parts and operations is a strong consideration. No matter what grinder it chooses, AM Mfg. wants a complete grinding package, including in-process gaging, automatic wheel dressing, and automated part loading/unloading. The shop will run the job, for the most part, unattended, so it requires a machine that is easy to set up, program, and changeover for other hot jobs that may arise.
termine how much of its grinding process loading/unloading, wheel opening, dressing, and measuring it can automate at an efficient price. Automating a grinding operation usually involves part loading/ unloading and gaging, points out Hardinges Winstanley. For loading, shops can choose a simple pick-and-place robot, gantry loader, or for small parts, a vibratory-bin loader. Some builders, says Drake at Drake Manufacturing, offer automation packages with robot loading integrally controlled by a machines CNC. So during setup when part parameters change, the robots movements automatically adjust. When thinking automation, shoppers should address such machine issues as swivel versus fixed tables and stacked axes versus independent wheel and table motion, advises Ragnini of Toyoda. They should also investigate programmable swivel tables, programmable C-axis workheads, programmable B-axis wheelhead rotation with automatic wheel selection, and special wheelhead infeed capabilities (for crankpin or camlobe grinding). Ragnini of Toyoda. They should also investigate programmable swivel tables, programmable C-axis workheads, programmable B-axis wheelhead rotation with automatic wheel selection, and special wheelhead infeed capabilities (for crankpin or camlobe grinding).
AMERICAN MACHINIST would like to thank the following for their contributions to this article: Agathon, Bethel, Conn. Citco Diamond and CBN Products Operations/Landis Grinding Systems, Chardon, Ohio Drake Manufacturing, Warren, Ohio Erwin Junker Machinery Inc., Dayton, Ohio Hardinge Inc., Elmira, N.Y. Huffman Corp., Clover, S.C. International Tool Machines of Florida Inc., Palm Coast, Fla. Landis Grinding Systems, Waynesboro, Pa. Mitsui Seiki USA Inc., Franklin Lakes, N.J. National Conveyors Co. Inc., East Granby, Conn. Parker Majestic, a division of Penn United Technology Inc., Butler Pa. Saint-Gobain Abrasives, Worcester, Mass. Service Network Inc., Worcester, Mass. Stahli USA Inc., Wauconda, Ill. Toyoda Machinery USA, Arlington Heights, Ill. Tru Tech Systems, Mount Clemens, Mich. United Grinding Technologies, Miamisburg, Ohio Universal Superabrasives Inc., Romulus, Mich. Walter Grinders Inc., Fredericksburg, Va.