CNC machine gets integrated drive system
Cutting large stone slabs into high-end kitchen countertops, reception desktops, and other interior and exterior fixtures takes tough machinery and a lot of power and control. However, cutting through solid marble or granite isn’t the hardest challenge facing the stonecutting industry isn’t cutting; it’s doing so with maximum productivity, precision, and efficient use of raw materials.
Stonecutting tool builder Advanced Industrial Machinery (AIM) in Hickory, NC redesigned one of its top products — the MasterJetSaw combination cutting saw/waterjet system — to reduce design/build costs and significantly improve stonecutting throughput and productivity.
To achieve these goals, AIM incorporated a new drive and control system into the MasterJetSaw: the IndraMotion MTX CNC machine control platform, Profibus remote I/O, and IndraDrive Mi integrated motor and drive system, all from the Bosch Rexroth Corporation’s Electric Drives and Controls technology group.
The MasterJetSaw is AIM’s top of the line tool, designed for high-throughput stonecutting for major commercial and residential stone surface applications. Combining a rigid, high-accuracy 20-horspower (hp) rotary cutting head, high-speed diamond-tipped blade, and a 50 hp abrasive waterjet cutter into a single unit, the tool lets fabricators cut accurately and repeatedly in stone up to 4 inches thick. Most cuts are straight, using the 20 hp rotary saw. The waterjet is used for radiuses, sink cutouts, holes for pipes and fixtures, and other circular or curved cuts.
Until recently, AIM built waterjet and saw machines using conventional servo drives and motors. They were looking for new technology that would:
Reduce machine footprint;
Lower machine component costs;
Reduce the time to build machines and deliver to market;
Improve stonecutting productivity and materials utilization.
Compact drives saves space, money
AIM worked with Livingston & Haven (Charlotte, NC), a supplier of manufacturing productivity technology solutions and a major distributor of Bosch Rexroth products, to identify the best solution to satisfy their requirements for the MasterJetSaw. Together, engineers chose to upgrade the machine with the Rexroth IndraMotion MTX CNC platform and the IndraDrive Mi integrated servomotor and drive system, for a complete drive and control solution.
“A lot of companies claim they can do controls, but all they can really do is point-to-point process control. Process control and interpolated motion of multiple axes are two totally different things.” said AIM president Bob Pharr. “Rexroth proved they could cut a radius at high speed, with a high degree of accuracy, and then match that cut with a different tool or a different size, with the highest levels of throughput.”
Rexroth’s IndraDrive Mi combines a servomotor and drive into a single, ultracompact unit that’s about 50% smaller than conventional servomotor and drive systems. By mounting the drive electronics on the motor instead of in a separate control cabinet, it’s possible to dramatically reduce machine footprint and component costs.
Using IndraDrive Mi integrated motors and drives allowed AIM to replace a large freestanding enclosure that previously housed all the servo amplifiers, power supplies, contactors and other components with two smaller, 24-in. by 24-in. cabinets mounted on the machine. This reduced the overall machine footprint considerably, and saved costs on the enclosure.
Significant cabling savings
The IndraDrive Mi’s cabling design — a single combination cable containing both power and SERCOS communication — also provided significant savings. The IndraDrive Mi units are connected in a daisy-chain sequence with one cable running to each unit. This eliminates the need to run separate power and communication cables from each servomotor back to the control cabinet. For AIM, which uses four IndraDrive Mi units on the MasterJetSaw, this reduced cabling requirements significantly compared to the previous servo setup.
“Reducing the MasterJetSaw’s footprint, component cost and machine build time were all important goals for us,” said Pharr. “The Rexroth IndraDrive Mi was key to meeting all three. [Using it,] we cut the machine electrical build time in half,” he said.
The integrated drive system also improved the MasterJetSaw’s operational efficiency. Previously, the machine used an incremental encoder feedback system for position feedback, which required over-travel and home-limit switches on each axis. Any time stonecutting was interrupted, each axis had to reset back to “zero” to resume cutting. In addition, holes for the limit switches had to be machined into the steel frame and wired back to the control cabinet, increasing labor and material costs.
IndraDrive Mi offers drive-based absolute encoder feedback, eliminating the need to reset the servomotors anytime cutting is stopped — saving time for busy fabricators needing to fill orders for countertops. In addition, using the absolute encoder feedback allowed AIM to eliminate 12 proximity sensors previously used for over-travel and home-limit switches.
Controller boosts efficiency
The MasterJetSaw has four axis of motion. The cutting heads are mounted on a gantry for X and Y horizontal motion. The Z axis moves the cutting heads vertically in minute increments, and the C axis controls the rotary saw blade.
In stonecutting, the most challenging cuts are circular: rounded edges, oval and circular holes for sinks and fixtures, curving details on stone surfaces, etc. According to AIM’s Pharr, rounded cuts requires true closed-loop control of multi-axis interpolated motion, which is why AIM chose Rexroth’s IndraMotion MTX CNC system for its machine control.
IndraMotion MTX is a high-productivity machine tool CNC that contains all the components — drives, controller, operator software and a powerful engineering framework — optimized for machine tool automation. It can support up to 64 axes of motion and 12 independent CNC channels, providing the shortest CNC cycle times and minimum PLC program processing times. This helps tool builders achieve high-speed machining and reduce non-productive setup and changeover times.
The MasterJetSaw uses the MTX platform running on a Rexroth 15-in. IndraControl VSP model industrial PC. The controller communicates via SERCOS to a Rexroth 70-amp IndraDrive drive unit and Rexroth KCU unit, from which a single cable system runs carrying DC bus, power, control power and communication to the integrated motor and drive servo axes.
Being able to deliver true CNC control — and having the engineering expertise to make the MTX platform work for the MasterJetSaw — was absolutely essential, and the reason AIM decided to choose Bosch Rexroth solutions, said Pharr.
For example, a critical method for getting the most material from each slab is called “nesting,” which is cutting as many different countertops, facings, and other finished products as possible out of one rectangular 6- by 10-foot or 7- by 12-foot slab. It’s akin to cutting out the pieces of a jigsaw puzzle.
In the past, tool operators had to leave three inches of space between each piece to be cut, to make sure cuts for one piece didn’t end up cutting into another countertop. The MTX precisely controls the movement of the circular saw and waterjet to make sure each piece is cut properly with minimal waste and much greater accuracy. As a result, operators can space parts with much tighter tolerances, cutting more pieces from each slab.
“The parts are accurate to within four to five thousandths of an inch — far more accurate than what’s been done in the past,” said Pharr. “Because the original cut is more accurate, it speeds up the finishing process.”
Innovation, partnership, labor savings
With a desire to continually improve and innovate rather than imitate, Pharr says he values the proven expertise and beneficial partnership AIM has with Rexroth and Livingston and Haven. “When we make a change on a system, I want the technology to be good, but also the people behind the technology have to be good,” he says.
Pharr says he was particularly impressed with Rexroth’s technical expertise, especially in the area of CNC controllers and complex, multi-axis interpolated motion. “I had a lot of detailed questions about crucial issues such as masses, accelerations, damping and inertia ratios. Everyone I dealt with there knows what it takes to make a true CNC platform work– and that made all the difference,” he said.
One of the first companies to use the updated MasterJetSaw was Elite Installation and Designs, Inc. of Hendersonville, TN. Before using the MasterJetSaw, president Chris Brown said their order book was so full they were running at maximum capacity with high amounts of overtime, and sometimes cutting until 9 pm.
Within the first week of using the MasterJetSaw, said Brown, Elite was able to eliminate overtime entirely. Operators were cutting so fast, they moved five days ahead of their production schedule, he added.
“The nesting alone is incredible—we virtually have crumbs for waste,” said Brown. “We’re cutting at 166 inches-per-minute. In the first six hours of using the tool, we cut 10 slabs and pushed them through our CNC polisher. Our fabricators were looking at us like we were crazy,” he exclaimed.
According to Bob Pharr at AIM, other companies that have begun using the MasterJetSaw calculate their return on investment to pay off within less than a year, and in some cases, half that.
|Earl Scruggs is senior sales engineer for Bosch Rexroth Corporation.|