Herman Miller Adds Powder Coating

With squared off edges, 90-degree angles and a "boxy" look, cubicle used to be an appropriate term for the portable furniture seen in many offices. However, at office furniture giant Herman Miller, Inc. (Zeeland, MI) the term cubicle no longer applies. With the rise of collaborative work and the expansion of complex technology, the company saw an opportunity to re-examine the work environment and resolve critical issues regarding its office furniture.

The result is the Resolve line of workstations. The workstations have 120-degree angles, which frame an open and inviting area that allows people to work together easily. The design allows a greater diversity of layouts as well as a more efficient use of space compared to previous office furniture systems.

While Herman Miller often used high-pressure laminates to finish the medium-density fiberboard (MDF) used to construct its office furniture, the company was unable to use high-pressure laminates with the Resolve line. Why was this the case? High-pressure laminates only bend in one plane, but the Resolve line's multiple curves and waterfall profile (as opposed to a straight edge) meant the laminates would have to be bent in multiple planes.

So, the company developed a process called Formcoat™, a trade name for the thermal cure powder coating process used to coat the MDF. The powder process allows the designers more freedom in the shapes and curves they can use. "There is not an easy way to do complex shapes with high-pressure laminates," said Rich Saddler, a finishing engineer at Herman Miller. "So, powder coating fit with this product. Since then, we've started to expand into other product lines."

Developing a Powder System

As powder coating has become the preferred method for finishing MDF furniture with multiple curves and waterfall profiles, Herman Miller needed to find a supplier to build a system for the company. The company turned to ITW Gema to build a state-of-the-art system.

The foundation of the powder coating system is the ColorMagic cylinder and Chameleon Color Management System, a new color change technology that provides users with quick and clean powder changes. By automating parts of the cleaning process, the color management system reduces the time required to convert from one color to another. A programmable logic controller (PLC) system is used to automate cleaning by managing the internal purging and cleaning of the suction tubes, powder pumps, powder hose and gun. It does this by pulsing compressed air over the gun exterior and powder path. This process works so effectively to free the guns of powder that color contamination is virtually eliminated.

Mr. Saddler admits that powder coating on MDF is an evolving process. "We're still in the infancy stages of powder coating on wood," he stated. "We're probably now where powder coating of steel was 30 years ago. We learn something new every day about the wood, the process and the materials. But, every day we're learning means that next week we have more of a knowledge base to deal with production issues." The company has learned a great deal about different woods, density profiles, sanding and other process variables. And, Herman Miller has learned that it definitely needs a higher quality of MDF to withstand the heat generated by the UV curing process.

As an example of this learning process, Saddler recalls troubles with an 8 x 15-inch board that was coming out of the powder application process lighter than necessary. "We thought that the pre-heat oven was drying the board out, and we were losing our conductivity," Mr. Saddler explained. "We started to reduce the pre-heat temperatures lower and lower trying to get the powder to attract better. Then, one of my technicians suggested that we try to raise the pre-heat oven's temperature, and it worked. It turned out that it wasn't a moisture issue of the board becoming too hot and drying out. It was a temperature issue of not being hot enough when we applied the powder. It was too cool, and the powder wouldn't stick to it."

The powder process also helps Herman Miller employ a variety of just-in-time manufacturing techniques. Herman Miller uses 100% Sierra Pine MDF manufactured in Medford, OR. It is shipped via railroad car to nearby Grand Rapids, MI, and then delivered on a daily basis to the powder coating facility in Holland, MI. It sits in inventory for perhaps a day before it starts the process that includes routing, sanding, powder coating, assembling and packing. Raw board can come into the production area at 8 a.m. and be shipped out by 4 p.m. on that same day.

To powder coat the MDF, the board is hung on a rack and heated in a pre-heat oven before it is ready to enter the powder coating booth. There are 15 PG2-AX guns in the booth, which are turned on and off automatically by the PLC. This is accomplished via a part recognition system on the entrance to the booth as parts pass through a profile, which is identified and recorded in the PLC.

Quick Color Changes

Time is of the essence when performing a color change. "She has to be efficient and quick because there are parts coming," said Mr. Saddler. "You can't dilly-dally at this point in time." The first step is to pump air through the hoses in order to clean out any of the old powder in the hoses. The operator can spray the powder directly from the powder manufacturer's original shipping container. This improves color change time by eliminating the process of using hoppers as well as other equipment usually required to reclaim powder.

"I've been very happy with it," proclaimed Mr. Saddler. "We're able to do quick color changes both in the reclaim and the non-reclaim mode." The ColorMagic enables Herman Miller to do a color change in 12 min in a reclaim environment and 6 min in a non-reclaim environment. Herman Miller estimates that in the reclaim application, it gets 50% first-pass transfer efficiency and greater than 95% reclaim efficiency, which means that there is very little waste.

The company saves valuable time with the color management system because of the easy cleaning process. Mr. Saddler says that the operators don't even have to use a vacuum. The booth is simply blown down with compressed air. "That is not the case with a traditional stainless steel powder coating booth," he stated. "You would have to vacuum that." Vacuuming isn't necessary because the clear booth material is non-conductive. Consequently, the powder does not attract to the booth walls when the booth is electrostatically charged.

In nearly a year of operation, Herman Miller has not had any significant down time with the powder coating system. But it's the functionality of the process and the end result that please him most. "We are spraying horizontal work surfaces - things that people use five days a week," said Mr. Saddler. "So we need to have that scratch-resistance, stain-resistance and color stability in order to meet what the customers' expectations are of a high-pressure laminate surface."