A new standard in forming bathtubs

American Standard's manufacturing facility in Salem, Ohio, invested more than $1 million to fully automate its bathtub forming line, which consists of a lubricator, two hydraulic presses for deep drawing, two mechanical presses for secondary forming activities, a flange bender, an automated piercing unit, and a robotic bathtub-stacking cell.

Slipping into a bathtub can lead to some relaxing moments. A slip-up in automating an existing press forming line during a holiday shutdown can result in some not-so-relaxing moments.

American Standard wanted to avoid as much stress as possible as the company recently looked to modernize its bathtub line at its Salem, Ohio, facility. But the stakes were large. Without the new line, the company would risk losing its competitive edge in the marketplace.

American Standard knows a thing or two about producing bathtubs and sinks. The Salem facility, 450,000 square feet of manufacturing space spread over three floors, produces thousands of steel bathtubs and steel sinks per week. All of the bathtubs and sinks receive a porcelain enamel coating, and all but a small percentage of the bathtubs then receive a proprietary polyurethane backing called Americast®.

That volume of bathtub production made the press forming line a logical place to start as the company began to look for ways to eliminate waste from the production operation in 2006.

"We were looking at our processes as far as where we have labor involved, what the value added [contributed during that process] is, and what the opportunities are," said Jim Wilgus, manager of engineering. "The press line showed up early as an opportunity."

Salem plant management convinced its corporate bosses to invest more than $1 million for automation upgrades on the bathtub line. The goal was to reduce cost, free up shop floor employees for other work, and eliminate the risk of injury associated with manually handling the 80-pound bathtub forms.

American Standard elected to work with press automation company Wayne Trail Technologies Inc., Fort Loramie, Ohio, on the retrofit and field installation. The parties targeted the facility's year-end shutdown to get the job done.

The risk was huge: If the line didn't run when the company's 400 workers returned from the Christmas break at the close of 2006, production and jobs would be in jeopardy. The challenge was huge as well: The automation enhancements had to work with legacy equipment, such as a dope roller lubrication applicator, two 1,200-ton hydraulic presses, two 500-ton mechanical presses, a flange bender, and an automated piercing station—'all preceding a semiautomatic tub-stacking system.

"The main key to this whole effort was integrating the old equipment with the new within the established time frame," said American Standard Plant Manager Paul Lee.

Challenge No. 1: Same Presses, Same Footprint

In 1996 American Standard moved its bathtub-forming line from the south side of the facility to the northwest side. During that time the company installed two new hydraulic presses and two refurbished mechanical presses. Management had no intention of moving those presses again.

An automatic blank destacker, with double-blank detection capability, moves the blanks into position to be fed through a lubricant applicator. The mild steel blanks can range from 63 to 68 inches wide and 72 to 74 in. long and are typically 0.056 in. thick.

"Most of the time, when you are working with newer equipment and good documentation, CAD drawings, detailed dimensions, and available electrical information are used to ensure that everything will go together as planned," said Bob Lewinski, Wayne Trail's vice president of sales and marketing.

In this case, however, rough floor plans existed, but drawings that provided mechanical and electrical details did not. Field measurements and pictures helped to fill in the information gaps. During site visits, Wayne Trail engineers also made note of other line details, such as die change components and electrical connections.

These early field trips to Salem, Ohio, also gave the engineers the chance to hammer out communication issues among the PC-based controller, drives, servomotors, and the legacy equipment's own controllers and programs.

In the end—'besides the servo-operated press loaders/unloaders that were required—'a total of four separately driven belt conveyors, starting at the exit side of the second hydraulic press, were used as a "flexible linkage" to move the formed bathtubs between the mechanical presses, flange bender, and to end-of-line operations.

Challenge No. 2: Setting up Head-of-line Operations

An automated destacker consistently delivers blanks to the lubricator. A motor-driven overhead gantry drives to a position over the stack of blanks and a pneumatic lift lowers a vacuum effector to the stack, where it picks up the blank. The gantry then moves the blank above the drop-off point and deposits the blank on the conveyor feeding the roller lubricator.

Lubricant type and location are critical when deep drawing parts such as bathtubs. It cools the die and workpiece during forming, acts as a boundary between the two, prevents metal-to-metal adhesion, and cushions the die during the operation. Although American Standard has conducted some preliminary exploration into synthetic alternatives, an animal-based product is still the specified lubricant. The metered amount applied to the blank is closely monitored by one of the line operators.

When a stack of blanks is emptied after feeding them into the lubricator, the gantry drives to a second stack of blanks on the opposite side of the line. Material handlers can replace the empty stack with a new stack of blanks, ensuring a constant inventory of blanks for the press forming line.

Challenge No. 3: Feeding the Presses

What's the most cost-effective way to feed this type of operation? Wayne Trail thought it was adapting its servomotor-driven, front-and-back transfer module for the task. American Standard agreed.

Wayne Trail generally employs a variety of techniques to create "transfer" systems for presses. Servomotors are used to power transfer bars to move blanks or parts from one station to the next in between press strokes.

In this case, the servo transfer module was to become a "servo loader" on all of American Standard's presses. The loader unit, attached to the press's entry side on a mounting bracket to simplify mounting in retrofit applications such as this, relies on two servomotors. One motor drives the lift, and the other drives the pitch. The pitch was customized with a compound sled to extend the reach of the loader into the bed area of the first press.

A servo-driven press loader equipped with vacuum-type tooling loads formed parts into a mechanical press where trimming takes place.

At the bottom of the pitch frame is a vacuum effector that picks up the blank at the centering station—a necessity because the first deep draw relies on precise location of the blank. The servo loader then drives the blank into the press and loads it into the die.

This same type of customized module is installed on the front of the two mechanical presses farther down the line. Only these servo-driven blank handlers are equipped with end effectors that are designed to pick up the formed part—which can be as large as 34 by 60 in., have a draw depth of approximately 13 in. or more, and weigh about 80 lbs.

Challenge No. 4: Unloading the Formed Parts

After a deep draw, formed parts don't want to leave the tooling. That's why press operators previously needed to pull and twist the parts to get them out of the press.

To automate the process, engineers had to develop a method to pull the tub out of the die. They decided that a similar unloader unit based on the servo transfer technology of Wayne Trail would do the trick.

The unloader on the first hydraulic press is mounted to the exit side of the press. The unloader comprises a servo-driven pitch bracket and a spring-actuated "puller finger." When the forming process is complete, the puller finger is driven into the press and across the bathtub. The finger "flips" across the top of the bathtub flange as it enters and drops back behind the edge of the formed tub. With the finger in place, the puller pitch bracket drags the part out of the press and onto a conveyor that feeds the second hydraulic press where further drawing of the bathtub takes place.

The line designers were able to use the existing conveyor between the two hydraulic presses because the formed bathtub easily can slide into the die cavity for the second forming operation.

"In many cases, the very hardest task is to get a part to position properly on a die," Lewinski said. "In this case, you have a part that nests almost perfectly into the second draw die all on its own."

The unloader on the second hydraulic press is similar to the unloader on press No. 1.

The untold story of the unloading operations is the steps taken to ensure the part removal took place quickly between press strokes. A few extra seconds during a forming cycle can add up to minutes during a shift.

"Every piece of equipment needed to know where the other piece of equipment was," said Kirk Kennedy, an Amerian Standard maintenance supervisor. "There was a lot of communication going back and forth between each press and the automation.

A between-press conveyor takes the formed tub to an automated piercing unit that knocks out the hole for the drain.

"For example, you didn't want to have the arm come in while the tub was coming up or the press was coming down. You need to know where everything is," he added. "Every little step you take in the communication process takes a little bit more time. So you try to refine that."

Challenge No. 5: Working With the Flange Bender

Everyone on the project knew it. Automating the material handling to the existing dedicated flange bending machine located between the two mechanical presses was going to be difficult.

"When you had a person there, he brought the tub over, shoved it in, shook it, and got it where it needed to be," Kennedy said. "It was a repetitive thing that the guys were doing. Their know-how made it work successfully in a manual operation.

"Now you have the automation where it has to be picked up correctly and spun around so that it sits down in the right place."

The team went with a pneumatic lift equipped with a vacuum effector to secure the part from the conveyor. The lift then raises the bathtub, and a pneumatic rotary actuator rotates the part 180 degrees for presentation to the flange bender. After the rotation, a pneumatic cylinder loads the part into the equipment in a slightly tilted manner, and the flange is made. The vacuum handler grasps the bathtub with its new "apron" and deposits it on the conveyor destined for the second mechanical press.

"A robot also could have been used in an application such as this, but with the line speed requirement being fairly high and the motion required being more or less identical for all parts, the fixed automation approach was a lower-cost solution," Lewinski said.

Challenge No. 6: Automating the End of the Line

Originally a robotic tub-stacking system at the end of the forming line wasn't part of the automation upgrade plan. However, once everyone dove into the project, they realized such an investment made sense to truly extract as much efficiency as possible from the line.

"It quickly became apparent for the variety of tubs they wanted to run and the need to place spacers between the tubs," Lewinski said.

Now, inside a Wayne Trail-designed workcell, a Motoman robot with a special end effector does the heavy lifting and stacking of the tubs. The dual-purpose robotic tooling picks up four PVC spacers (from a bowl feeder magazine) before each lift and moves into position above the four corners of the bathtub's undercarriage, which has been flipped into place after leaving the automated piercing unit. The vacuum effector secures the bathtub, and the robotic arm moves the formed piece from the conveyor to a stacking location.

After a stack—usually 15 tubs—is complete, a roller conveyor moves the full stack to the exit conveyor, and the integrated pallet loader automatically loads a fresh, empty pallet.

Before removing a formed bathtub from the conveyor, a robotic arm retrieves four PVC tubes, which act as spacers between the formed parts, and then picks up the bathtubs for stacking. After 15 bathtubs are stacked on a pallet, the full stack is moved out, and an empty pallet is moved automatically into position.

Wayne Trail engineers were able to design common robotic tooling that could accommodate the 15 different bathtub models formed on this line. That eliminated the need for changeover and for other, additional tooling.

"One tool for all—sometimes you can achieve it and sometimes you can't," Lewinski said. "Our engineers did a lot of overlays to find the 'sweet spot' for this design goal."

Even with all the automation, American Standard didn't assume good quality would just happen. The company required that the tub-stacking system accommodate an exit chute for bathtubs to bypass the stacking robot for quality inspection.

"One of the working lessons out of this is that even though we set up the machine to run fully automatic &hellip' and, by and large, it's the same thing every time, you still need periodic inspections because things in the process can drift," Wilgus said.

Every 15 minutes a quality inspection takes place on the bathtub model that is being formed at that moment.

Enjoying the Rewards

In early 2007 when workers returned to work, the line was, for the most part, ready to run. The old came together with the new, and American Standard was emboldened with a new outlook on life.

The company made a big commitment to change and accomplished it in a very tight time frame with the help of Wayne Trail. Also in 2006, American Standard tackled two large conveyor upgrades and a redesign of the bathtub assembly area.

"We lived through 2006, so I think we can live through anything," Lee said.

Continuous improvement activities at the Salem facility never end, but plant personnel don't have to worry about the bathtub forming line. Because the line is now able to run with two people instead of nine, plant management believes the company will achieve a return on its investment by the end of the year.