Upside-down design and automation resolve age-old precision grinding challenges
Inside Machines: One Echo Hill Tactic 8 machine does the work of four centerless grinding machines, while improving gauging technology and keeping equipment cleaner, with advanced automation and an inverted machine design.
As automation technology enables machinery to advance into ever-greater precision in ever-smaller product runs, automated manufacturing of "lot size one" is increasingly in demand. "Centerless grinding" technology, a special technique for precision grinding of cylindrical machine parts, is one example where these manufacturers' demands can be at their greatest. Based in Beamsville, Ontario, Canada, Echo Hill Automation has more than 20 years of experience in grinding technologies, rapidly moving past the time when machining of precision parts required tremendous manual skills to manufacture components to very demanding specifications.
Today, many precision parts are first worked on in primary machining processes, such as with a lathe; then they are finished to a precise size with a grinder. Centerless grinding machines, such as those from Echo Hill, use high-performance grinding wheels to finish components at the highest levels of tolerance required to the micron level. Centerless grinding applications run the gamut from automotive component manufacturing to the machining of aerospace parts, with the highest tolerance demands imaginable.
Automated grinding challenges
Most grinders on the market can only grind one part at a time with acceptable quality and efficiency. Because of variations in fixturing (holding of parts), there must also be updates to the grinding profiles for all parts to be precisely machined. Until recently, most of these updates were manually entered, with a computer aided manufacturing (CAM) profile or a computer numerical control (CNC) dresser. Machine operators had to type in micron-level increments just to grind parts to the correct size and precision.
Another notable shortfall in centerless grinding industry-wide has been in the gauging of parts. To address this and create a competitive advantage, Echo Hill has spent considerable research and development (R&D) effort to improve the gauging technology on the company's machinery. "Complicating matters, customers often have a wide range of different parts so they demand short production runs and frequent product changeovers," said Harry Schellenberg, president, Echo Hill Automation. These demands required Echo Hill to make its centerless grinding systems even more flexible to accommodate innumerable part sizes and dimensions.
Grinding machine performs a spectacular 180
Over the years, tolerances have become much tighter for machined parts to increase reliability during end use. Also, manufacturers today typically demand "zero defect" production, which puts more demand on machine builders to eliminate production defects and waste. Today, highly specialized machinists are fewer and farther between, which puts more responsibility on machine builders and the automation system to craft high-precision parts without defects.
Grinding heads for these types of machines weigh upwards of 1000 lb, so with repeated movement, intense wear points could develop in the sliding mechanisms and ball screw that drive machine components back and forth. In addition to mechanical wear and tear, grinding applications are notoriously dirty as grime and fluids from machining processes are difficult to manage. In many machines, coolant is sprayed continuously on ball screw housings and sliding mechanisms. Over time, these factors make it increasingly difficult to meet tight tolerances even with highly precise grinders.
In 2009, after years of intensive R&D efforts in all areas of machine and controls design, Echo Hill arrived at its innovative solution to these challenges in its new Tactic 8 machine with an 8-in.-wide grinding wheel. The Tactic 8 design flips the moving equipment "upside down" by using highly precise linear motors mounted at the top of the machine. Instead of having the spindle carriage underneath the grinding wheels, Echo Hill instead mounts them above the grinding wheels. Echo Hill has coined this patented new way of thinking, "Powered From Above."
Minimizing wear and tear, the linear motors' magnetic attraction counteracts the weight of the slides, essentially neutralizing the weight on the recirculating roller slide mechanisms, which dramatically increases their life. The equipment and mechanisms also are kept clean because they are suspended above the process. Gravity prevents contact from most grime and coolant used in grinding.
Streamlined control architecture
In addition to mechanical advancements, the new Tactic 8 from Echo Hill also successfully reduced the number of different control platforms used to increase overall efficiency.
Echo Hill initially looked at new automation in 2008 for "control of robots used to load parts into the grinding machines," Harry Schellenberg said. "Up to that point, we had separate controllers for the machine, robots, and another to control gauge data-this required complex communication among all controllers. Echo Hill found a competitive advantage by designing a platform that could handle the robotics, gauging, and machine automation in one controller, one software platform, and one network, representing a turnkey package for us."
To achieve this, Echo Hill uses an industrial PC (IPC) equipped with a 2nd Generation Intel Core i3 processor (2.2 GHz, 2 cores) that runs a unified software platform for full machine control, including robotic and measurement systems. The IPC is completely solid-state with no rotating parts by using CFast [a CompactFlash variant for serial ATA bus] cards for the boot and storage media. In addition, an external heat sink on the IPC safely dissipates heat out of the side of the control cabinet, eliminating the need for a fan. Connected to the IPC on the other side of the pole-mounted control cabinet is an economy control panel for machine visualization.
For human machine interface (HMI) software, Echo Hill uses a different vendor.
"Running the HMI software on the same ... IPC that runs our automation software is a significant improvement as well," said Dan Schellenberg, vice president and controls expert at Echo Hill Automation (and Harry Schellenberg's brother and business partner). "Prior to standardizing on PC-based control, we used a hardware PLC and a separate 'white box' PC that ran the HMI. Communication between these two systems added complexity and reduced the overall performance of the control system. However, these problems are in the past."
There were numerous benefits of using the IPC as the robot controller, including reductions in cost, panel space, and system complexity. Echo Hill controls the grinding cell, each with three robots per cell, with IPC running the unified control software.
"Implementing all robot coordination ... while handling 3 axes of interpolated motion for our grinding wheels with one controller and one software represents a game-changing system with fewer obstacles to implement leading-edge performance," Dan Schellenberg said. "Also, by running G code in a PC-based control platform to perform complex motion, I can more easily rewrite the programs when the parameters change. We have the flexibility to use multiple programming languages, from standard to highly specialized ones, depending on which is best suited for a particular task in one standard, unified programming environment. Simpler motion control elements are frequently handled using ... function block libraries, which saves programming time."