Americanmachinist 2567 Remanuf0100png00000002873
Americanmachinist 2567 Remanuf0100png00000002873
Americanmachinist 2567 Remanuf0100png00000002873
Americanmachinist 2567 Remanuf0100png00000002873
Americanmachinist 2567 Remanuf0100png00000002873

Remanufacturing a path to automation

Sept. 1, 1998
Besides having stand-alone machines remanufactured, today's companies also want them tied into existing plant automation.

Besides having stand-alone machines remanufactured, today's companies also want them tied into existing plant automation.

Goldcrown remanufacturing jobs can include linking restored grinders, such as this, to a plant's existing automation.

Perhaps known best as a builder of new centerless grinders, the Goldcrown operation of Landis Gardner, a Unova Company, also remanufactures existing centerless, center-type, chucker-type, and shoe-type grinding machines. While most of the firm's projects are simple upgrades or complete remanufactures, they often include adding peripheral equipment such as process control gages, load/unload devices, and links for system automation. Some projects can also involve multiple machine packages with a mix of new and remanufactured machines.

Gary Roeder, Goldcrown vice president of operations, makes it clear, however, that the Cincinnati company's role in adding automation to remanufactured machines is not that of a systems integrator. "Our responsibility is to automate individual grinders with systems that can connect them to the plant's own automation," he says.

For example, Goldcrown links multiple machines (two or three throughfeed-type centerless grinders) using an automated conveyor system for progressive grinding of cylindrical parts, such as piston pins or shock absorber rods. In these operations, parts move through a primary machine for rough grinding, then through one or two additional grinders for finishing. "In many cases, we remanufacture machines in an existing line and add the necessary automation," Roeder notes.

In a special project, Goldcrown had remanufactured and integrated four infeed-type centerless grinders used to machine three different surfaces of air-conditioning compressor shafts. The machines, which were arranged in a racetrack configuration, were connected to existing part-transfer automation via load/unload devices made by Goldcrown. "Typically in these installations, plant automation first conveys the part from a prior process—say a turning operation on a lathe in front of the grinder," Roeder explains. "It will then place the part next to a machine-loading device, which positions it for grinding. When the grinding cycle is completed, the same device retrieves the part and places it in position for the plant automation to take it away for additional processing—say heat treat or polishing." Along with successfully moving parts from one machining operation to the next, Goldcrown or the customer may suggest some type of process gaging.

In-process gaging is not always used with centerless grinding machines, due to insufficient space inside the grinding envelope. However, post-process gaging is frequently applied, especially in progressive grinding systems using multiple throughfeed-type machines. But, contamination of gage systems is an issue.

"In some cases, we can automate a progressive grinding system for in-line, post-process gaging with feedback for automatic size control," Roeder says. "The system conveyor is simply extended to transport each part from the finishing machine to an in-line bench gage. This is not done, however, if there's risk of gage contamination from grinding swarf in the area."

Where there is a risk, shops monitor size by manually transporting sample parts from the finish grinding machine to a controlled environment outside the

grinding area for gaging by a qualified QC operator. The same operator then manually adjusts the line, if required, based on the gaging data.

Retrofitable centers battle harmful grinding forces

Enforcer is a retrofitable, process-control tool with active centers that measure and dynamically control harmful grinding forces.

According to EDO Electro-Ceramic Products, Salt Lake City, the U.S. industrial base includes hundreds of thousands of aging cylindrical grinders used for metal finishing operations. As these platforms age, increased vibration levels develop because of component wear, causing harmful dynamic forces at the grinding wheel/workpiece interface, which are known to cause surface errors in finished parts. To improve part quality and increase component throughput, EDO has developed a retrofitable center tool that eliminates dynamic grinding forces without effecting the basic functions of O.D. cylindrical grinders.

The system, states its manufacturer, is capable of increasing part throughput by 10% to 20% by reducing conservative spark-out times and employing an auto-retraction feature that is ten times faster than conventional methods. It installs on most medium-sized, O.D. cylindrical grinder platforms via dead center placement in less than 2 hr and typically requires no machine modifications.

Called Enforcer, the process-control tool measures and dynamically controls harmful grinding forces throughout the metal finishing process on medium-sized, between-center, O.D. cylindrical grinding machines.

Active centers replace common dead centers and use embedded piezoelectric ceramic sensors (to measure real-time contact and cutting forces) and piezoelectric ceramic actuators (to compensate for unwanted dynamic forces). A conventional DSP (digital signal processor)-based controller automatically monitors grinding force conditions, requiring no operator involvement.

The low-profile piezoelectric, shear-force sensors can detect hundreds of pounds of force with a dynamic resolution of 0.05 lb over a 1.0 kHz frequency band. The process takes place between the center points supporting the workpiece as it rotates against the grinding wheel.

Co-located with the shear-force sensors are EDO's EC-98 PMN piezoelectric actuators. A conventional high-speed DSP, using machine-specific control algorithms, measures system dynamics via the grinding force sensors and optimizes forces by sending control signals to actuators, which position center points to correct for unwanted force deviations. The process takes place hundreds of times per second to improve the metal finishing operation.

Remanufacturing calls for linear scales and DROs

Heidenhain's ND series 900 displays and LS linear encoders work well for grinding-machine retrofits.

Rick Glos, a vice president at Heidenhain, believes that the reman-ufacturing stage is the ideal time to consider linear scales and digital readout. This is especially true in grinding, which, he says, requires a level of precision several orders above what is expected from other machine-tool configurations.

Normally, position on manual grinders is provided by a finely calibrated screw/dial combination. Heidenhain of Schaumburg, Ill., however, offers two products, LS series linear encoders and ND 900 series displays, that increase both machine accuracy and productivity.

LS linear encoders are sealed within an aluminum housing with flexible sealing lips at the bottom, protecting them from chips, swarf, dirt, and splashwater. The scanning unit travels on a low-friction guide with the scale housing and is connected to the external mounting block through a coupling that compensates axial misalignment.

Mounting blocks attach to the stationary machine element relative to the measured axis. Electrical wiring runs through the connecting web to the mounting block, then through a shielded cable to the display.

Program memories of the ND 900 series displays hold up to 99 positioning steps for small-batch production on conventional machines. All models have a distance-to-go display feature that lets users quickly approach positions by traversing to a zero display value. For datum setting, it is possible to freeze tool-position values. Then after touching the workpiece, operators can retract the tool to facilitate workpiece measurement.

Multiple machine remanufacturing
According to Roeder, Gold-crown's multiple machine remanufacturing projects involve a mix of technologies and skills. Depending on particular machine features and the availability of existing machines—either from the customer or on the open market—multiple machine projects often include a mix of remanufactured and new machines. "Both of which stand side by side and must be indistinguishable in terms of operation and performance," says Roeder.

"All new electronic packages must accommodate the same type of dresser, the same type of infeed system, and same regulating-wheel drive. Machine-control panels should all be the same to provide uniform operating procedures, making it easier to train operators to run multiple machines," Roeder says.

Goldcrown recently delivered eight throughfeed-type centerless grinders of various sizes and types for deployment in two different plants of a leading manufacturer of precision ground components. Of the eight machines, four were new, three were in-plant upgrades (restoring essential machine components), and one was a complete remanufacture.

Automation connects three of the machines to form a progressive grinding line, and others are equipped with parts-handling devices for adaptation to overhead plant automation.

Goldcrown also remanufactures multiple machines over an extended period. One automotive customer, for example, has 10 lines of two throughfeed grinders each for progressive rough and finish grinding. Four of the lines have already been remanufactured, and the extended plan calls for an additional line each year.

Machine components getting special attention
Goldcrown believes that certain centerless grinding machine components have significant affects on part accuracy, three of which are regulating wheels, regulating-wheel spindles, and in-feed assemblies.

During remanufacture, the company focuses on the regulating wheel because it plays an essential role in workholding and serves as a kind of brake that controls part spin. "A grinding wheel might be running at 6,500 to 7,500 surface feet and the 'reg' wheel at only 30 rpm. If part rotation is not regulated, it will shoot off the work-support blade," warns Thomas Klotz, a Gold-crown manager.

Technicians replace AC or DC motors with a stepper or servomotor. These, he says, provide constant torque and infinitely variable speeds ranging from 10 to 300 rpm.

In addition, a single moving shaft running through the housing on an eccentric replaces the multiple transmission gears and levers of the regulating wheel. This design, developed by Goldcrown and called Quiet Torque, not only eliminates the gear box, but also noise, backlash, contamination, and wear. Wheel drive is smooth and consistent, giving better part rotation control, which, according to Klotz, reduces the chance of rotational errors that can lead to part inaccuracies.

For the regulating-wheel spindle, the company replaces all worn parts, precision hand scrapes and fits bearing shoes, and coats with titanium dioxide and grinds bearing journals to minimize friction.

To further control part size and reduce maintenance, Gold-crown uses stepper or servomotor in-feeds with ballscrews to replace a machine's existing hydraulic in-feed assembly. Ballscrews are 2 1 /2 in. in diameter, which puts substantial mass through the in-feed assembly and controls high grinding pressures, notes Klotz.

"The grinding and regulating wheels can push apart, and the bed actually bends like a cat arching its back. To accurately compensate for grinding wheel wear in these conditions, the adjustments must be made in minute increments, and we can supply a compensation system capable of adjustments as fine as ten-millionths of an inch," Klotz says. "The trouble is, you may not actually get compensation that fine using plain slides because of possible slip-and-stick." For this reason, Goldcrown installs a special non-stick slide system that combines a recirculating roller and squeeze-film dampeners. The system is especially indicated for use on finish grinding machines.

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