Automating Centerless Grinding
New technology for complex grinding configurations in exotic materials
December 1, 2009
In machining operations, once the viability of NC was proven, the logical next step was combining multiple processes in a single machine.
With more and better capabilities and automatic tool changing, the milling machine became a machining center and the lathe a turning center. As refinements continued, machines were linked by various methods ranging from robots to carts to pallet change systems.
Certain process systems, however, including centerless grinding, remained virtually static except for the introduction of improved cutting materials. A major reason for this was that, in some manufacturing applications, centerless grinding had for years been partially automated through the use of purely mechanical load/unload systems.
More recently, as parts requiring centerless finishing have become more complex and profiling has become used more frequently, demand has increased for fully automated systems capable of handling small to medium batch lots of nontraditional parts and exotic materials. Today these needs are being met thanks to the development of high-performance centerless grinding machines with fully automated production capabilities.
Able to step-grind and profile parts with exacting tolerances, these systems offer a number of features developed in response to extensive customer research.
“Increasingly, our customers are experiencing demand for more complex configurations in nontraditional materials. We understood that any automated system had to be extremely flexible and that ease of setup was key,” said Tom Lebel, application manager for grinding system supplier Tru Tech.
Developing an Automated Grinder
According to Lebel, after reviewing the company’s product line, Tru Tech engineers selected the TT-8500 centerless profile grinder to automate and create a novel grinding system.
The unit, which accommodates parts up to 7.5 in. long and 3 in. in diameter, incorporates an 8-in. standard wheel powered by a 2-HP drive. The input increment for the system is 0.000010 in. with accuracies up to ± 0.00010 in. and repeatability of ± 0.000050 in.
“By laying the part on a precision-ground regulating roller, we can eliminate any and all deflection,” said Lebel.
The loading system uses a SCARA robot which moves between a specially designed pallet and the grinding area. A unique gripper system, designed by Tru Tech, consists of a fixed finger and moving finger that loads in one direction.
Thanks to an auto-offset system, the gripper never comes in contact with the regulating roll. The pallet size for standard applications is 8 in. by 10 in. and it accommodates 0.125-in. to 1-in. diameters. Custom pallets also can be provided for specialty applications. For more extensive automation, multiple pallet storage systems featuring recognition and load/unload capability are available.
The complexity of the parts involved – coupled with the fact that at the finishing stage parts typically have acquired a high intrinsic value – has resulted in the development of pallets that offer protection and ensure part integrity.
A specially engineered plastic minimizes scratching, chipping, or other problems resulting from poor alignment during loading and unloading. Additional protection comes from a dual-pallet system in which finished parts are unloaded onto a second pallet.
In terms of user-friendliness and ease of setup, programming also was a primary consideration.
“In developing a system for shorter runs of multiple parts, flexibility is critical, so we developed a control that uses an interactive voice tutorial,” said Lebel. “The instructions are simple and precise and are delivered in sequential formats that take the operator through the programming process. As a result, training is simplified and, if the instructions are correctly followed, virtually error-free.”
The software was redesigned to permit the entry of basic values instead of G-codes. Once the operator enters the values, part views are displayed on the screen.
“We’ve also designed other desirable features, including trig help and radius help,” said Lebel. “Using trig help, the operator has to enter only two values of the basic 3, 4, 5 triangle. The control calculates the rest. Radius help defines the angle necessary to successfully blend radii from the height and depth of the part.”
Realizing that automated systems involve a combination of multiple machines or machines and associated equipment, Tru Tech was an original participant in the development of MTConnect.
MTConnectSM is a system that is designed to enable individual components of a manufacturing process to interconnect and communicate better.
As a result, the automated centerless controls readily recognize G-codes and can be networked with other MTConnect-compliant controls and software. Controls likewise interface with MRP software and can be accessed for remote reporting.
“Along with special control modifications required for automated operation, we’ve included many features to facilitate extended runs. These include a filtration system that eliminates swarf above 1 micron and maintains a constant temperature to prevent thermal expansion,” said Lebel.
In addition, the automatic lubrication system delivers real-time lubrication and will stop the machine if there is a pump failure or lubricant shortage. On-site diagnostic capability also provides instant reference regarding any machine problems.
To maintain continual accuracy, the company included real-time, in-process gauging, as well as in-process wheel dressing with automatic compensation at the control.
According to Lebel, in the relatively short time since its introduction, automated centerless grinding has received enthusiastic acceptance for multiple applications worldwide. He also sees automated grinding moving into new areas.
“The economic situation and intense competition have sparked a re-evaluation of many production processes,” said Lebel. “Historically, grinding has been thought of as a finishing process, but increases in profiling capability now enable manufacturers to create and finish the desired shape in a single operation. This not only saves time, money, and materials, but frequently eliminates the need for multiple machine operations – resulting in improved quality and greater accuracy. Now that automation is a reality, I believe that we will see an exponential increase in abrasive machining applications.”
For more information, visit www.trutechsystems.com.
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