December 2012 / Volume 64 / Issue 12|
Inside and out
By Alan Richter, Editor
| When IDs and ODs must be concentric, a combination ID/OD grinding machine might be just the ticket.
Similar to a multitask machine, a machine tool that combines ID and OD grinding enables producing a part in one chucking. This is beneficial when the part requires a high level of concentricity because part refixturing can increase total indicator runout through tolerance stack up.
“If your TIR needs to be in the low tenths, say 0.0002 " and under, you’d better consider doing all the grinding in one chucking,” said Denny L. Rowe, director of sales and marketing for Weldon Solutions, York, Pa. The grinding machine builder targets production applications and offers the Model 1632 Gold ID/OD CNC grinder (see photos on page 39).
Courtesy of United Grinding
In one application, Weldon Solutions reported that Aero Gear Inc., Windsor, Conn., uses the Model 1632 Gold with a 16 "-dia. faceplate for workholding to rework aerospace components with various IDs, ODs, tapers and radii while minimizing setup. The parts manufacturer performs ID grinding with a 30,000-rpm high-frequency spindle. OD grinding, for parts up to 16 " in diameter and 26 " long, is done between centers, and a live-spindle workhead accommodates a variety of chucks and other workholders.
Rowe emphasized that job shops, on the other hand, tend to use so-called B-axis ID/OD grinding machines that have multiple spindles on a turret—a universal grinder. “We don’t go after that market at all,” he said. “We strictly go after high-production work.”
Grinding machine builder Usach Technologies Inc., Elgin, Ill., also targets production applications, but doesn’t avoid the job shop market, noted Martin Nobs, the company’s technical director. For example, Usach is building two OD/ID grinders, a 200 OD-L with 80 " between centers and a 300-OD-L with 135 " between centers, for a shop that repairs helicopter parts. “They need to be able to regrind anything,” he said. “That is typical of a repair facility.”
Both machine models hold parts between centers for OD grinding and have ID grinding capabilities, Nobs explained. He added that Usach also offers machines more tuned to ID grinding with OD capabilities. On those models, the part is chucked like on a lathe without the need for a tailstock. Most Usach machines have spindle turrets that hold multiple grinding spindles for added flexibility and to allow parts to be completed in one setup.
Courtesy of Usach
Using a center-drive, hollow-workhead design, Usach is also building an ID/OD grinder model that enables grinding features on one side of a part with one X-axis and one Z-axis cross-slide and simultaneously grinding features on the other side through the hollow workhead with a second X-axis and Z-axis cross-slide.
A Universal Approach
United Grinding Technologies Inc., Miamisburg, Ohio, specializes in CNC universal grinding machines for ID and OD grinding. One such offering is the Studer S41, which has 10nm scale resolution, a hydrodynamic and hydrostatic way system, axis drives with linear motors and extremely fast direct drive of the B-axis, according to the company. “The hybrid StuderGuide way system allows you to be extremely precise when positioning the slide and grinding to size,” said Hans Ueltschi, vice president, sales, cylindrical division of United Grinding. “That, in conjunction with the linear motors, gives better repeatability and faster movement.”
Ueltschi pointed out that United Grinding originally saw universal grinders as mainly for job shops because of their flexibility and versatility to handle whatever comes through the door, but is witnessing increasing interest from tier suppliers and OEMs, such as in the aerospace and automotive industries. “It’s a trend because of the accuracy requirements for multiple industries,” he said. “It all comes down to getting a part done as complete as possible in one clamping.”
In the job shop realm, Joe Tenebria, owner of Myers Precision Grinding Co. Inc., Warrensville Heights, Ohio, and International Grinding, Richfield, Ohio, noted an ID/OD grinder is advantageous for achieving tight concentricity tolerances on parts such as rings, bushings and spindle shafts. For dimensions and surface finishes, Myers Precision holds tolerances as tight as 0.000050 " and imparts finishes as fine as 8 µin. Ra. Tenebria pointed out that 40 percent of Myers Precision’s work is thread grinding, 30 percent is OD and ID grinding and 30 percent is machining. “Our main field is thread grinding and everything revolves around it.”
Courtesy of United Grinding
ID/OD grinding can also beneficial when cycle time is long. “You have a much longer setup but the payoff is, with CNC, the machine is doing most of the work, so the operator can run multiple machines,” Tenebria said, noting he has a Studer S40 ID/OD grinder with three grinding wheels. For ID grinding, Myers Precision uses Okamoto semimanual machines in which the user sets parameters such as feed and stroke with the machine’s computer but table motion, for example, is not computer-controlled, Tenebria added. By not being CNC, the machines grind faster because there is no lag time—however short—required for a machine to read the code.
Talk It Up
According to Victor Truelsen, technical sales engineer for Okamoto Corp., Vernon Hills, Ill., the most successful job shops he deals with offer ID grinding. They have a large number of customers with ID work but those customers don’t have enough individually to justify purchasing an ID grinder, which isn’t as common as an OD machine. “They might have 300 customers and each of those customers is sending them 100 to 200 parts a week,” he said.
Truelsen noted Okamoto builds an ID/OD grinder that’s not fully automated. An end user needs to weigh the advantage of grinding a part in one chucking on an ID/OD grinder vs. grinding it on a dedicated ID and dedicated OD grinder and having a quicker cycle time by running two parts simultaneously. “If you have good chucks, you shouldn’t lose concentricity,” he said about grinding on dedicated machines.
Regardless of the type of grinder, Truelsen emphasized that conversational programming is the predominant programming method, especially at job shops, as it suits most workers’ limited experience with G- and M-code programming. That can present limitations when automating a machine because the large number of variables to be input often requires G and M code, but 90 percent of ID and OD grinding can be performed with conversational programming, he added.
Courtesy of Weldon Solutions
Because doing everything in code enables more automation, only a small percentage of universal grinders are automated, according to Weldon Solutions’ Rowe. In contrast, he noted the company regularly automates its production grinders and offers two basic styles: a FANUC robot, the recommended route, and a gantry hard tool.
“We have customers who still prefer the old-style gantry, even though they’re paying a little higher price for it, because their service techs and maintenance guys can work on it,” Rowe said. “There are still people who are intimidated, believe it or not, about having a robot in front of a machine tool.”
Pictorial programming also avoids the need to know code. Bruce Hammond, vice president of sales and engineering for Campbell Grinder Co., Spring Lake, Mich., noted the grinding machine builder developed a user-friendly, pictorial front-end interface in which operators select shapes and routines from a series of menus for IDs, ODs, tapers, faces, wheel configurations and more. “It’s custom-written behind the scenes,” he said. “Operators don’t have to know how to write G code.”
For experienced operators and setup specialists who prefer G code, Pick-N-Place “talking” software from Tru Tech Systems Inc., Mt. Clemens, Mich., offers an expert mode they can select, noted Toby Roll, vice president of sales for the grinding machine builder. Otherwise, the software enables operators to select icons and enter values for the pictured part feature, such as a radius, while the software tells them what to do next. “Some almost hate the conversational side because they’re so picky about being able to control the machine through code,” Roll said.
He emphasized, however, that both modes provide the same options and functionality. A conversational screen “is not a dumb-downed screen,” Roll said. “It’s just a different way to show it. The software is catering to left-brain people or right-brain people.”
But the software enables those without any grinding experience to set up and run a machine with only a few days of training, Roll said. “Ask any grinding shop owner what the biggest challenge is and he’ll tell you it’s finding good people.”
Most ID/OD grinding machines have a horizontal axis, but a vertical design is available, which is the case on ones from Campbell Grinder. A vertical axis is advantageous when mounting a heavy part on the worktable because gravity provides assistance. “It’s easier to get the part on center because you lay the part on the table, unlike a part that’s hanging horizontally,” Hammond said, adding that a vertical grinder has a smaller footprint.
Part quality is also a critical factor, according to Hammond. “Without the additional requirements of chucking the part between centers or using a steady rest or tailstock, in most cases, [vertical grinders] produce a part that’s much more accurate.”
A vertical ID/OD grinder is somewhat limited by part length, but Campbell Grinder has built ones for grinding an OD up to 18 ', Hammond noted.
Courtesy of Okamoto
Although Usach Technologies builds horizontal ID/OD grinders, it has experience with vertical configurations through a previous collaboration with a European builder, Nobs pointed out. He concurred a vertical configuration can be a better solution, but only when workpieces measure above approximately 40 " in diameter and are quite heavy.
According to Nobs, one of the disadvantages of a vertical grinder is the operator has to walk into the machine and stand on the rotary table to avoid an ergonomically unacceptable reach into the center of the table. A horizontal grinder, on the other hand, can have a 40 " part swing while still allowing the operator to conveniently access the part. “That’s an advantage of the horizontal vs. the vertical grinder,” he said.
Turbine Control Inc. is one shop that successfully implemented a vertical ID/OD grinder into its operation of overhauling and repairing aircraft components, including engine parts, according to Richard Nicewarner, production manager of machining and blending for the Bloomfield, Conn., company. Prior to purchasing a Campbell Model 750 CNC ID/OD grinder, TCI’s grinders were all manual. He stressed the productivity gains with CNC, reducing 6-hour cycle times to 2 to 3 hours, as well as the time savings from eliminating multiple, unnecessary setups on an ID/OD grinder.
“I like the Campbell grinder for hubs, discs and similar components,” Nicewarner said. “The vertical configuration definitely helps, especially when loading a 300-plus-lb. part.”
Sometimes, part capacity can be increased beyond what the machine builder might have intended. “The table on the machine is 36 ",” he said, “and I’ve ‘squeezed’ it and put a 42 " part into the machine.”
Deburring is also possible on the machine by applying high-pressure coolant. For example, coolant allows TCI to deburr honeycomb material while grinding, Nicewarner noted.
Having high-pressure coolant also enables TCI to perform wheel scrubbing and remove particle loading between abrasive grits so a wheel doesn’t have to be dressed as frequently, which extends wheel life.
Users generally only scrub superabrasive wheels because of their high cost. “Wheel scrubbing is an additional coolant circuit operating at 1,000 psi or higher,” said United Grinding’s Ueltschi.
Courtesy of Campbell Grinder
Okamoto’s Truelsen concurred that wheel scrubbing is limited to superabrasive wheels, but indicated high-pressure coolant is applied more when surface grinding whereas a different method is used to scrub an ID or OD grinding wheel. “Sometimes, the diamond dresses the wheel but the steel substrate in which the diamond is set in clogs the wheel,” he said. “So after you dress/true the wheel, you might have to scrub it with a white stick to pull the steel out and have a nice, sharp wheel.”
Another problem-solving measure focuses on setup. Although setup can be longer on an ID/OD grinder compared to a dedicated machine, probing systems are available to reduce setup time. They enable users to register the workpiece with a single probe rather than registering each wheel to the workpiece when doing changeovers, according to Ueltschi. “That’s up to a 90 percent savings on a three-wheel machine vs. a conventional setup and touching off each wheel,” he said.
Touch probes are also being used to measure a ground part without moving it and do offsets based on the measurements. This approach requires less operator attention, Ueltschi noted. “It’s always difficult once you release a part and measure it to then clamp it back in the same position,” Ueltschi said. “That’s why people want to do a measurement before the part is let go from the chuck, and it’s all possible because of the high accuracy and repeatability of a B-axis.”
Regardless of the type of ID/OD grinder, combining the operations in one machine is an area of growth, according to those interviewed. “The demand is incredible,” said Weldon Solutions’ Rowe. “Never have I seen the business at this level and I’ve been doing this since 1976. That runs the gamut of every customer we’re dealing with right now.” CTE
About the Author: Alan Richter is editor of CTE. He joined the publication in 2000. Contact him at (847) 714-0175 or firstname.lastname@example.org.
Taking a hard turn on an ID/OD grinder
Courtesy of Tim Wheeler/Tru Tech Systems
The centerless revolt
Some ID/OD grinding machines require the user to perform separate setups for OD and ID grinding with different spindles and indicate the part before the ID grinding setup to ensure concentricity between the OD and ID. One way to avoid indicating is to use the Revolution Perimetric grinding system, which automatically ensures concentricity within 0.000030 ", according to its builder, Tru Tech Systems Inc.
The Perimetric workholder, which is similar to a centerless grinding fixture, enables a user to quickly load and position a part on the machine’s regulating roller against the work blade, explained Toby Roll of Tru Tech. “That regulating roller has been ground perfectly true to the machine within 0.000030 ",” he said.
In addition to the approximate 30 seconds it takes to indicate a part, eliminating that step also eliminates the time to pull the part out of the machine, check it, load it back in, as well as seek supernatural assistance, according to Roll. “You pray your operator is good enough to indicate that part properly to get it concentric.”
Similar to centerless, Perimetric workholding employs a regulating roller to drive the workpiece and work blade, but the Perimetric method precisely locates and qualifies the blade and regulating roller to the grinding wheel by introducing a precision tension roller, the company stated. The tension roller ensures solid contact is maintained between the workpiece, blade and regulating roller, whereas centerless relies upon gravity, allowing the workpiece to float in position. Most importantly, the part is located along its perimeter, or shank, instead of an imaginary centerline that is difficult to locate or inspect. For that reason, it is virtually impossible to introduce shank runout when using a dressed Perimetric workholder, according to the company.
Roll noted making drawing dies is the main ID/OD grinding application for the Revolution, which toolmakers frequently use for OD work. Tru Tech also offers the Revolution Auto for automated grinding.
CUTTING TOOL ENGINEERING Magazine is protected under U.S. and international copyright laws. Before reproducing anything from this Web site, call the Copyright Clearance Center Inc. |
at (978) 750-8400.