— Reprinted with permission from Modern Application News, July 2003.
Mike Strange is Director of Engineering at List Industries in Deerfield, FL.
With serious problems from excess metal build up on its dies, List Industries Inc. had to find a way to extend die life and fast. What they eventually found was a way to boost die life to levels never imagined.
List Industries, Inc. (Deerfield Beach, FL) was founded in 1936 and manufactures athletic, school, and storage lockers and portable gates. Moving from Chicago to Florida in 1979, the family-owned business started out with 45 people and grew to over 250 with two full-time shifts. In Memphis, TN, the company also has a 50,000 sq. ft. facility for storage, sales, assembly, and light manufacturing.
“We were experiencing problems with our cutoff die on a frame line for our main shelving models,” said Tool Room Manager, John Bolton. “Once or twice a week we were down because of a huge buildup of steel on the cutter's face.”
Upright posts or frames for List's shelving products are manufactured on a roll-form line with a flying cutoff cutting the part to length. Bolton said, “The flying cutoff was giving us a lot of problems with excessive buildup of metal on the sides of the blade. A vendor said they had experience with some surface treatment hardening from the TD Center (Columbus, IN). The company's process called the TD Coating puts a super-hard surface treatment on the tool giving a high polish that wouldn't allow scuffing or excess metal and burrs to accumulate on the cutter's sides. We decided to try the process on this flying cutoff blade, because it was giving us too much downtime. After about a year since our first TD Coating, the die has been out only once for sharpening. And when this happens, it doesn't remove the surface treatment. It now has about half a million hits on it. I've never come across such a process that gave us such a good return for our investment.”
“Peace of mind is also important and the TD Coating gave me this when we finally found something that would allow our cutters to go beyond 500 pieces,” added Bolton. “My Tool Room Foreman is constantly under pressure, because this line must run. We would typically produce between 300 and 500 parts and then pull the cutter to polish out the buildup. We were always under pressure to get a few more pieces. That line has not been down since we put the treated blade back into operation, because the buildup problem was virtually eliminated.”
Coating Wiper Dies
Another problem that the TD Center Vanadium Carbide Coating solved was for wiper dies. The wiper dies are part of a three-stage progressive die with the first operation being a pierce, the second forming, and the third a flying cutoff. Bolton said that the progressive die is an extended die that can handle several different part lengths up to 24" long.
On this second forming operation where the wiping occurs, they where experiencing problems. “We're running commercial-quality cold-rolled steel and it usually has an oily film on it so it doesn't require any lubrication. But in Florida, there's a lot of salt and sand in the air, and I think that contributed to some of our downtime,” remarked Bolton.
“We were getting a huge buildup on the wiping sections of our wiper dies. So we polished out the wiping sections and sent them out for the TD Coating,” he added. “They further polished them to a high gloss and did the hardening treatment. We've been running for over a month and half now and haven't experienced any downtime. Previously, we were down quite regularly to remove the metal buildup on the wipers, and it was costly, because a toolmaker had to do it.”
Build-up and die wear prior to the application of the thermal diffusion coating presented quality problems and machine downtime for List Industries.
“We also found that we didn't need any lubricant,” remarked Bolton. We had tried lubricant before on the wiping sections to see if it was a factor in the buildup on the wipers, which it wasn't. It was the softness of the wipers, and we were hardening our wiping sections, made from A2 steel, to a 58/60 Rockwell C hardness, but still we experienced buildup.” These wiper dies were run on a two to three-week basis producing about 6,000 parts. Before List did the TD Coating, their downtime was up to 30%. “We have not experienced any downtime in a month and a half. I'd say that's a winner,” added Bolton.
But for List, dollars saved on the die is only part of the story. The other part is the manpower needed to service the tooling, having workers idle while a tool is being repaired, and the costs associated with downtime for critical products that are often on a just-in-time delivery schedule. Also, because the components are linked with each other to produce a completed shelf, the holdup of one component can stop the assembly of the entire finished product.
“Normally what happens is that we run parts simultaneously and assemble them at the same time,” said Bolton. Parts are moved to a storage facility before going to paint or directly to paint without storage. “We have designed our operation to take raw materials, process them, and then have a finished part at the end of the line. Because of limited storage capacity, we need to manufacture this way. Also, the cost of storing and retrieving parts is expensive. We run on a just-in-time basis inside the plant. We rely on the computer to tell us when materials are needed and where they should be at a certain time in our 1-1/2-week processing schedule. With two million pounds of steel a month processed, one glitch can hold up the part the die was used for along with the operation of two or three dependent items. Keeping our machines running is very critical.”
TD Center Coating
TD is short for Thermal Diffusion, an advanced method of hardening steel surfaces. It's a thermal-reactive process resulting in a hard vanadium-carbide layer diffused into and onto the surface of steel and cemented-carbide substrates.
It's used to improve and extend the tooling life for many industries by greatly reducing galling, seizure, corrosion, and wear on tools, dies, and other high wear industrial components. Tool life is extended up to 10 times or more, resulting in increased uptime, better machine use, and greatly reduced die maintenance costs. Dramatic decreases in die lubricant usage often result.
For piercing and shearing operations, shear and stab blades and pierce punches are subject to extremely high abrasive wear while under pressure. Almost all of the wear on a blade and punch occurs on the sides as it enters and exits the work material.
To protect the tool, the TD Coating is harder than the work material and adheres well. At over 90HrC in hardness, the vanadium carbide isn't dependent on an ‘envelope’ for adhesion; tools can be re-sharpened many times. The process can be used for roll forming; tube bending; drawing, forming and swaging dies/blocks; piercing and shearing dies, core pins for aluminum; expanding dies; extruding and bending dies and many others.
Coating thickness is about 0.0002–0.0003", similar to other thin-film coating methods. Using a solution of molten salt, the coating is grown at the austenitizing temperature of steel, 1800° F. Only when steel is in an austenite stage is carbon available for the vanadium carbide to form. It works with steel with at least 0.3% carbon including A2, D2, M2, M4, all CPM and VAN steels, H-13, DC-53, and sintered carbide. A part that fits within a cylinder 18" in diameter and 22" deep can use for the TD Coating.
Bolton said they are building a die to form a plate that covers the reverse side of a locker's recessed handle. They are looking at the TD Coating for the forming section of the die.
Cutters are another area that Bolton said they would try using the coating. “We have 12 roll-forming lines that all use some form of cutting device at the end. With approximately two million pounds of steel a month going through here with 60% roll-formed, these cutters are good candidates for the TD Coating.”
Another area Bolton said they'd try the coating is for roll-form tooling. “Any downtime in the roll-forming area is expensive,” he said. “Because these parts affect the production of many other components, you can't calculate how much you've lost in costs when a roll-forming operation experiences downtime. You have to look at the bigger operation, and what's being affected in the sub-assembly areas when the roll-formed parts aren't ready.”