Optimizing spray nozzle performance for lubrication:
The importance of selection, maintenance, and automation
Although mandrel bending is the method most likely to produce a high-quality bend, it is by no means an exact science. Material, size, bend dimensions, and machine variables make it necessary to consider each application individually—and some of these considerations require experience and judgment. So it is not surprising that when lubrication is necessary for mandrel bending, it may be difficult to define a standard process that works for a variety of materials, sizes, and bends. One Wisconsin company that makes a few hundred thousand bends per year needed to do a better job at lubrication, so it created a process that helped it increase quality and productivity, while reducing maintenance and mess.
R & B Wagner Inc., Milwaukee, does a lot of tube bending. It specializes in architectural railings and creates custom and stock designs for everything from bridges to bike racks for customers both inside and outside the U.S. Since it was founded in 1955, it has developed a line of 11,000 railing components. Most of its work is in traditional metals, such as carbon steel, aluminum, stainless steel, brass, and bronze, but sometimes it ventures into more exotic materials, such as cable and glass.
The company runs quite a few blanks—about 40,000 a year on three CNC bending machines. Part sizes are 1 inch to 2 in. OD with bending radii from 1 in. to 12 in. Production Manager Justin Wesser, who has worked in the stock bending area for 31⁄2 years, said the company hasn't experienced any major production problems during his tenure, but he and others in the department continuously evaluate the processes to identify opportunities for improvement.
Lubricant on the Finished Parts
A particular issue, one related to part quality, eventually led to a more careful look at lubrication. Some of the finished elbows contained unacceptable amounts of lubricant following the mandrel bending process. Even after washing, many of these parts required hand cleaning to remove the lubricant completely. This level of detailed cleaning was not always necessary, so it was not always performed. But when the few customers who needed completely clean parts brought it to the company's attention, Wesser and his team went to work on the problem.
The lubrication process used at that time was simple—and typical—for mandrel bends. Equipment operators used brushes to apply lubricant by hand. They applied a thick lubricant, one almost as viscous as grease, to the inside of the tubing or onto the mandrel before inserting the mandrel. This lubrication method appeared to be working fine—no crisis here—facilitating quality bends at reasonable production speeds. However, as discussions moved forward addressing the cleaning issue, other problems surfaced, such as part galling caused by uneven lubricant distribution and a persistent mess caused by too much lubricant, some of which ended up on the machines and on the floor.
Wesser and others in the department, including veteran operator Roosevelt Kimble, decided if they could direct the lubricant to the location where the mandrel makes the bend, they would go a long way in solving these problems. Wesser had seen setups in which the lubricant was applied through the mandrel, but did not have a clear idea of the best way to supply the lubricant to the mandrel and distribute it evenly throughout the bend. After experimenting with a few scenarios, Wesser and Kimble shared their ideas with Steve Taylor of Ritter Technology.
Ritter Technology LLC is an industrial equipment provider. Taylor, one of Ritter's field engineers, discovered that Wesser's mandrel lubrication ideas were similar to his own. He knew the lube had to be controlled as it went into the mandrel and delivered evenly once it was there.
"We had a pretty good idea what we wanted," said Wesser. "Steve got us the rest of the way."
Lubricant Under Control
To control the lubricant, Taylor set up a system using components from UNIST Inc. The company specializes in minimum-quantity lubrication (MQL), which it refers to as Micro-Fluidization™. The idea is to control fluid and lubricant application by delivering the exact amount of lube where it is needed at the interface between the tool and the workpiece—in this case, the mandrel, bend die assembly, and the tube.
The system, designed by Taylor, is fairly simple, but Wesser recalled it still took four to six months to fine-tune it. During this time they added a couple of features. The setup delivers lubricant using a UNIST 3 drop injector pump. Each time the pump cycles, it can deliver up to three drops, or about 0.09 cubic centimeters. The pump is capable of cycling over 100 times per minute.
The project began by testing a smaller pump, one that delivers a single drop. In the end, the system was built with a pair of three-drop pumps ganged together and connected to one outlet line. This allows the system to deliver greater amounts of fluid necessary for some bends without losing the ability to control the precise amount.
The pumps are actuated by a machine signal, so fluid flows only when the machine is making a bend, and continues to flow throughout the entire bend. The outlet line is coaxial, so compressed air and fluid both flow through the line, but do not mix until they arrive at the outlet inside the mandrel. Air and fluid volumes are controlled by separate knobs located on the pumps, so selected amounts are introduced into the tubing.
A hole drilled through the push rod allows the tubing to be brought down through the mandrel (see Figure 1 and Figure 2).
"The bender's mandrel rod is not typically used to apply lube," said Wesser, "but in this case, it works especially well." The tubing is then threaded into the end of the mandrel.
"The key to this system is the pumps bringing lube through the mandrel rod," Taylor said.
Even though the pump controls the fluid volumes, the even distribution actually is accomplished by some custom work on the mandrel. The R & B Wagner team machines orifices in the mandrels used for these applications, so the fluid exits the mandrel evenly and can be applied to the tube throughout the entire bend length.
After establishing control of the lubricant, Wesser and Kimble looked for a lube that would work well for the process and the materials. After many tests, they decided on a couple of specialty products manufactured by Tower Oil. Because R & B Wagner bends several materials, it needs two lubricant types and keeps a supply of both ready at each bending station. Separate reservoirs on the system allow the operators to toggle between lubricants (see Figure 1).
Tower's Klenedraw W-4801 has become R & B's choice for bending steels. For stainless and aluminum, Tower created a customized product, Towerdraw TC-94. Wesser said that the combination of the Towerdraw TC-94 and the even distribution the delivery system provides are responsible for eliminating galling. The combination of air and fluid exiting the coaxial line creates a unique paste, a benefit the project crew had not anticipated.
"The air somewhat emulsifies the oil," Wesser said. "The small amount of air helps the fluid adhere better."
The fluid is still rather viscous before it is applied, but it takes on some characteristics of the previously used grease while still achieving the distribution benefits of a water-soluble fluid.
"Because of the control which can be accomplished with this system, there is no problem in getting the right amount of fluid where it is needed, and applying it consistently," Taylor said.
The new lube method resolved R & B Wagner's main concern, the excess lube on the finished part. Since the changeover, very little lubricant remains on finished parts. The aluminum and stainless parts go through a washing process that renders them completely clean. The steel components have such a small amount of lube that it is inconsequential.
The biggest benefit to R & B Wagner is lubricant cost reduction. The new system has reduced this production line's lubricant consumption by 70 percent. This means that only 30 percent of the amount previously applied is now used in this process. According to Ritter, these results are fairly typical, but R & B Wagner considers them to be outstanding, and is pleased with the impact on the bottom line and the environment.
The Tower products are more costly than the previous lubricant. However, even with the increase in purchase price, R & B Wagner's overall lubricant cost in this department is 30 percent less in 2007 than in 2005. Wesser said he is confident that the company has benefited from additional, undocumented cost reductions associated with shipping, handling, and storing fluids now that usage quantity is much smaller. For example, the need for cleanup and absorbent materials around the machine nearly has been eliminated, except for occasional wiping with a rag. Some previously required mandrel maintenance, the application of a ball dressing, also is no longer required.
Of all the factors affected by the process change, production speed changed the least. Although the lube process is completely automated, the increase in speed was only about 10 percent, or less than six minutes an hour. The extra 15 minutes in each shift is both a benefit to the company and evidence that it was performing the manual process as efficiently as possible. The reduction in cleaning and other housekeeping activities also contributes to a more efficient operation.
STAMPING Journal is the only industrial publication dedicated solely to serving the needs of the metal stamping market. In 1987 the American Metal Stamping Association broadened its horizons and renamed itself and its publication, known then as Metal Stamping.