16-axis welding cell for maximum productivity.

16-axis welding cell for maximum productivity

How do you plow new ground and stay a few furrows ahead of the competition when you're a small independent maker of farm equipment? For M&W Gear, Gibson City, IL, the answer has been judicious use of high technology in its manufacturing processes. The firm converted to CNC over 15 years ago, and was among the earliest users of MRP, reports Richard Ertel, director of manufacturing. Now, M & W is breaking new ground with the installation of a key robot welding cell, state-of-the-art in both size of parts it can handle and number of axes under cell control.

The results have been gratifying, says Ertel, "The automated cell cuts welding time up to 70 percent for large plate-steel fabrications, ranging in size to 10 ft x 16 ft. This allows faster turnaround for our just-in-time production, while reducing in-process inventory and labor costs."

Sweet sixteen

Equipment in the cell provide a total of 16 axes under control: 1. A six-axis Cincinnati Milacron T'646 long-arm robot with Mila-Trac through-arc seam tracking and Lincoln DC-600 GMAW arc-welding equipment. 2. A single-axis Milacron servo transporter for the robot to move it along a 16-ft track for increased range and versatility. 3. Two two-axis Aronson RAB-60 tilt-and-rotate positioning tables of 6000-lb capacity each. 4. A five-axis RIDE-5 indexing table with tilt/rotate capabilities at each end of the cell for welding smaller parts.

The robot and its transporter track are located in the center of the cell with a large RAB-60 positioning table on each side. Workpieces can be loaded/unloaded from one table while a part is being welded on the other. All table and robot motions are coordinated by the closed-loop, 12-axis AcraMatic control. This synchronous activity on complex routines reduces cycle times on large parts. Parts are presented to the weld torch at optimal orientation, maximizing weld penetration and deposition, and maintaining the weld puddle in an ideal flat position. Integration of part handling into cell control also reduces handling time, costs, and need for dedicated jigs and fixtures.

The smaller RIDE-5 double-end positioning table is located at one end of the transporter track. Used primarily for second-shift welding of smaller parts, it provides the same loading/unloading efficiencies as the two larger tables. This table is controlled by the robot through an open-loop system because the simpler, shorter welding routines for smaller parts don't usually require simultaneous, coordinated movement between robot and positioner.

Who needs a robot?

M & W Gear decided on the robot welding cell for large parts after five years of experience with a smaller Milacron T'726 six-axis robot supported by a 180-deg indexing positioning table. "That first one was the hard sell," recalls Ertel. "Some people thought I was nuts to want to try a robot."

That system proved the versatility and efficiencies a robot could bring to a small manufacturer producing a wide range of products in relatively small quantities and batches. After using the small cell for automatic welding of over 100 different parts, they were ready to apply robotics to the plant's big jobs. Despite the substantial capital cost of such a system for a small company, Ertel states, "nobody doubted the big cell would work out."

Beyond their automation efficiencies, the welding robots give M&W application flexibility to respond to changes in the unpredictable agricultural market. To assure a business base through bad times as well as good, the 225-employee firm makes a wide range of farm products in two general categories: diesel-engine rebuild equipment (sleeve and piston sets) and farm implements (balers, wagons, plows, and mowers).

Just in time

Equipment and parts are produced in small batches as orders come in, Ertel explains. These JIT factors demand high manufacturing flexibility and throughput for two key product lines: mower decks and a special deep plow.

The rigid rotary-mower decks provide a core production base for three quarters of the year. Up to 10 ft x 16 ft in size, the deck mounts behind a farm tractor and is driven by its power take-off. They are in high demand for mowing non-producing acreage, shredding corn stalks, and mowing highway berms and divider strips.

The largest took 3 hr to weld manually, says Ertel. The new robot cell cuts this to about 50 min and adds a quality improvement. They were skip welded before and now have a continuous weld. Fabricated of 10- and 11-gage plate, they require heavy-deposition welds and precision weaves.

A combination disc/chisel plow (sold under the Earthmaster brand name) is produced over the summer for fall delivery. Described by Ertel as a "huge V-ripper", it busts up soil 10" to 16" deep and is used in the fall so that winter freeze/thaw cycles further break up the turned soil. Made of 4" x 4" and 4" x 8" rectangular tubing (1/4" and 3/8" wall thickness), the 8 ft x 10 ft frames are loaded flat on the Aronson table for welding. The table rotates to any angle including full vertical to allow the robot access to all sides of the frame, including reaches that would exceed the work envelope of the robot if it were statically mounted. The long-arm robot has a maximum reach of 102", but the transporter adds 16 ft of lateral movement, and a three-roll wrist provides additional dexterity for reaching complex parts. As a result, the robot can perform continuous-weld routines without time loss to back out and reorient the torch.

Key software capabilities - 3D align, all-position weave, and relocatable sequence - allow welding programs to be easily relocated to reduce programming time.

Special challenges

Developed for M&E Gear by Cincinnati Milacron's Industrial Robot Div, the cell started up in Sept '88, shortly after Milacron introduced their AcraMatic Version 5 control that provides six auxiliary servo axes along with six robot axes. This allows multiple devices and functions to be controlled by the robot and expands the range of applications and complexity of routines that can be performed by the cell.

The Milatrac seam-finding and tracking software enables the robot to make precise, single-pass welds at high speeds. With it, the robot adjusts automatically to production variations in part fit-up and positioning, much as human welders do. This is critical with the 8- and 9-ft mower-deck welds. Even minute deviations at the start of the weld could cause significant run-out by the end without sensing and compensation.

During seam finding, the tip of the weld wire acts as the touch sensor. The operator needs only to locate the tip at the start or end of the weld, usually a corner, to orient the software. The tip then uses voltage feedback to sense the sidewalls of the joint in locating the seam and executing the correct weld routine. With this center-line tracking, the weld torch adjusts left or right, up or down, to part fit-up deviations.

The weld program can be interrupted for rotation of the larger decks, and a relocation sequence shifts the program to the new part orientation. An offset register feature further factors in compensation for part fit or positioning that was processed and applied in welding the first side. These features enable automatic resumption of the weld sequence without downtime or operator intervention for reprogramming.

System sensors monitor gas levels, electric voltage, and water cooling to the GMAW torch. The robot control automatically shuts down operation if any of these critical services drop below pre-set levels.

Menu-format software permits shop-floor personnel to handle everything from minor path adjustments to the creation of new programs. The software provides instructions and messages in familiar welding terms and gives step-by-step directions for creating or revising a program. Macro commands allow single-keystroke execution of a sequence of steps such as weld start, weld stop, weld size, and weave. A special operator panel provides process statistics on wire and gas consumption, status displays on positioners and welding equipment, and diagnostic information for problem resolution.

The technology edge

Ertel recognizes that some might be surprised to find a small manufacturer in farm country so advanced in robotics. However, he feels that robotics can have greater benefits and impact for small firms than large ones.

The key, he feels, is not being afraid of technology. "We're firm believers in technology. It's the one area where we can stay ahead."

PHOTO : Weld cell tackles an 8 ft x 10 ft frame of a new agricultural plow, automatically rotating it for the best orientation of torch to weld joint.

PHOTO : With direct command of four auxiliary positioners, robotic cell cuts welding time for large plate-steel mower decks from 3 hr to 50 min.