Less Lube, Less Cleaning, Better Paint Job
The pressroom at Truth Hardware, Owatonna, MN, produces hundreds of various stamped window-hardware parts, in volumes measured in the millions. One family of stamped parts in particular recently caught the attention of manufacturing engineer Joe Miller and his cohorts: casement-window operator track. Track sections are stamped from 15.5-in.-wide steel strip 0.035 in. thick, in 13 1.5-in. progressions. To say the sections have a lot of formed crevices would be an understatement (see the photo), and any excess stamping lubricant can’t help but become trapped in those crevices.
“It’s a big runner for us,” says Miller, emphasizing the importance of the job to the company. “The dies making those parts run every day, turning out parts at 40 strokes/min., with annual volumes of more than 2 million.”
The numerous formed crevices on these casement-window operator-track stampings can’t help but trap lubricant, and residual lubricant buildup caused paint defects that cost Truth Hardware more than $20,000 in scrap in 2011.
As the track parts do not need further secondary finishing before heading to the firm’s paint department, residual lubricant buildup often became a thorn in the company’s side. Excess lube unable to reliably be removed during cleaning, caused paint defects that cost the firm more than $20,000 in scrap in 2011.
To tackle the problem head-on, the firm upgraded its stamping-lubricant delivery systems to a more readily controlled and programmable fluid-delivery setup. As a result, it has completely eliminated paint defects on the track sections, and easily justified the investment to outfit all 11 of its progressive-die presses with the programmable lube system, according to Miller.
Lube Consumption Slashed
Truth Hardware maintains an inventory of some 500 dies. Presses are 75- to 300-ton Minster models, the latest a 200-ton press purchased in 2000. The firm takes in coils of mild and high-strength-low-alloy (HSLA) steel, as well as stainless steels in the 200-, 300- and 400-series alloys. Strip measures 1/2 to 17 5⁄8-in. wide.
Stainless steel represents 15 percent of the firm’s stamped-parts volume, and continues to become more and more popular with customers. As such, Miller notes a handful of key adjustments made in the toolroom to accommodate stainless vs. carbon steels. These include opening up die clearances from 10 percent for carbon steels to 12 to 14 percent for stainless; the use of powdered-metal tools steels for stamping of stainless steels; and fine-polishing of form tools used in stainless-steel applications.
In addition to focusing on improving the quality of its stainless-steel stampings, as noted above Miller and his peers have long-sought a better solution to managing consumption of die lubricant.
“In 2000,” recalls Miller, originally hired as a toolmaker at the company in the 1980s, “we installed our first automatic roller-style lubrication units on one of our presses. This four-roll unit (a UniRoller Type C, from Unist) was our first attempt at applying lubricant to the top and bottom of the strip.”
Compared to using felt wiper pads to drip oil onto the strip, the roller-style system represented a big step in the right direction. Lubricant pumps evenly through a dispenser tube inside the rollers and transfers to the stock through polyurethane-foam or polyester-felt roller covers.
A drawback to the system, notes Milller: Adjusting the unit to alter lubricant flow from job to job requires an operator to turn a knob to adjust a plunger on a cam that controls the mount of fluid that goes into the rollers. “And for some reason, we struggled to consistently build that adjustment procedure into our job-changeover routines at the presses,” Miller says. “As a result, we knew that on most of our jobs we were using more lubricant than was needed. And, we also had that lingering and costly issue of poor-quality paint jobs on our track stampings.”
Options: Spray, or Adjust the Cleaning Solution
Miller also tried using a spray-application process, but found the lubricant the company uses simply would not spray well. “We’ve standardized throughout the plant on a fairly viscous lubricant—Sulf-O-Cut 1200 (supplied by Lube-Tech, St. Paul, MN),” says Miller. “We use the same lube on stainless steels and on mild and HSLA steels, and we just could not get it to spray evenly.”
Sulf-O-Cut 1200, according to Lube-Tech literature, is a “medium-viscosity heavy-duty neat oil blended from severe hydro-treated base stocks containing varying combinations of synthesized sulfur and fat additives.” The fluid carries a kinematic viscosity rating of 46 cSt at 40 C.
A Scientific Approach
Thinning out its lubricant film ultimately required a renewed commitment to tighter process control, and a scientific approach to deciding just how much lubricant to apply. This next step in Truth Hardware’s stamping-lube evolution began in 2006 when Miller (with the help of Peter Danzer from Press Line Industries, Inc., Farmington, MN) decided to convert one of the UniRoller Type C systems over to a Unist UniRoller Type S system, equipped with Unist’s SPR-2000 programmable controller. The Type S unit replaces the standard plunger/cam-style lubricant pump used in the Type C units with a fitting that enables fluid lines to connect directly to the controller.
Having evaluated the setup for a couple of years, the firm converted a second press in 2008 and a third press in the fall of 2011. During the first half of 2012, the remainder of the firm’s 11 prog-die presses were converted. Ever since, not a single track stamping has been scrapped due to paint defects. And, lubricant consumption is expected to drop by at least 30 percent.
“Every time we set a new die, the operator only has to call up the appropriate lubrication program at the SPR-2000 control console,” says Miller. “There’s no need for him to go to the press and turn any knobs or make any adjustments. The lubrication programs we’ve developed manage the key variables—lubricant pulse duration (how long the lubricant flows into the system’s rolls) and cycle count (how often the valves open to allow the lube to flow).”
Miller created 60 different lubrication programs using various combinations of cycle rate and pulse duration. He did so having settled on a standard lubricant flow rate of 4.3 cc/sec., a line pressure of 40 psi, and a film thickness of 3.6 microns. Minimum pulse duration is 0.05 sec.
“We decided to develop a new program for every 2-sq.-in. variation in coupon size,” Miller says. Coupon size is calculated as strip width x progression x 2 (to accommodate application of lubricant to both sides of the strip. He created a spreadsheet for calculating surface area and to keep track of all of its tools and their accompanying lubrication programs.A scientific yet simple and very effective approach to not only improving quality but also to reducing lubricant consumption—a worthy goal for any metalformer. MF
See also: Unist, Inc.
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