Precision Stonecutting

The "hardest" challenge facing the stonecutting industry isn't cutting through solid marble or granite. It's designing automated machines that do the work with maximum productivity, precision and efficient use of valuable materials.

Stonecutting tool builder Advanced Industrial Machinery Inc. (AIM) recently redesigned one of its top products, the MasterJetSaw 3200 cutting saw/waterjet system, to reduce design/build costs and improve stonecutting throughput and productivity.

To achieve these goals, AIM incorporated a new drive and control system from Bosch Rexroth into the MasterJetSaw 3200, including a CNC machine control platform, Profibus remote I/O and integrated motors and drives.

The MasterJetSaw 3200 is AIM's top-of-the-line tool, combining a rigid, high-accuracy 20-hp rotary cutting head, high-speed diamond-tipped blade and a 50-hp abrasive waterjet cutter into a single unit. The saw lets fabricators cut accurately and repeatedly in stone up to 4-inches thick, and the waterjet is used for radiuses, sink cutouts and other circular or curved cuts.

"Reducing the footprint, component cost and machine build time were all important goals for us. We cut the machine electrical build time in half," says AIM President Bob Pharr.

Until recently, the machines used conventional servo drives and motors. But switching to 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 24 x 24-inch cabinets mounted on the machine.

A single combination cable containing both power and SERCOS communications saved on cabling costs. Units are connected in a "daisy-chain" sequence with one cable running to each unit, eliminating the need to run separate power and communication cables.

The system also improved operational efficiency. Previously, the machine utilized an incremental encoder feedback system for position feedback, requiring 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.

The MasterJetSaw 3200 has four axes of motion. The cutting heads are mounted on a gantry for X and Y motion; the Z axis moves the cutting heads and the C axis controls the rotary saw blade. In stonecutting, circular cuts are the most challenging, and rounded cuts require true closed-loop control and multi-axis interpolated motion.

A critical method for getting the most material from each slab is called "nesting," where the goal is cutting as many countertops, facings and other finished products as possible out of one 6 x 10-ft or 7 x 12-ft slab.

In the past, tool operators had to leave 3 inches of space between each piece to be cut to avoid cutting into another countertop. The MTX precisely controls the movement of the circular saw and waterjet to make sure each piece is cut with minimal waste and much greater accuracy to get 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," says Pharr. "Because the original cut is more accurate, it speeds up the finishing process."

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