Full Metal Jacket

Article From: 6/1/2002 Automotive Design & Production, , Contributing Editor

Lord Corp. says its newest steel coating technology is environmentally friendly, corrosion resistant, durable, and easy to apply. However, like the Model T, it's available in only one color.

Let’s start with some basic facts: Toyota Motor Manufacturing Kentucky’s (TMMK’s) Plant Two paint department is the only one in North America that paints both cars and minivans on the same line. It processes approximately 500 Camrys and Siennas per shift on two shifts. It uses solvent for primer and clearcoat, but basecoat is water-borne. From the electrodeposition process to the application of cavity wax, there are 13 distinct steps that a body-in-white goes through to become a painted body ready for the assembly line, and it all takes about 10 hours.


Cars and Minivans…Together

The simple statement that cars and minivans are processed on the same line encompasses a lot. In doing this, Toyota has chosen a path that diverges from its competitors. Most automakers find that though the flexibility to produce different body styles on the same line may be theoretically desirable, in reality the modifications that must be made to accommodate vehicles that vary significantly in size inevitably argues for a dedicated facility. However, unlike other car companies that have dedicated minivan platforms, Toyota designed the Sienna on the Camry platform with an eye toward making both models on the same line. This has entailed some adjustments in the paint shop, but arguably far fewer than you would expect.

The main accommodation is that the Sienna can only use two of the three basecoat/clearcoat lines. This is chiefly because it only takes two lines to handle Siena production volumes and some modifications in paint flow rate are necessary, but also because Toyota wants to maintain one line for exclusive production of the Camry. The basecoat painting process on a Camry takes 118 seconds. But because of the greater surface area for the Sienna, a process time of 150 seconds is required. So, Toyota sets aside one line that can crank through its bread-and-butter product at the fastest pace allowable, instead of reducing the line speed of all three.

This all gets sorted out by computer in a large staging area. After bodies are primed and masked they roll on their dollies into the staging area. As they cross the threshold, a magnetic plate on the bottom of each dolly is read which tells the sorting computer what color the body is to be painted. Based on this information the computer moves the dollies onto one of four tracks that lead to each basecoat booth.


The Vagaries of Water-borne

Plant Two paints only two bodies on its water-borne basecoat lines before flushing the lines and bells with alcohol and de-ionized water. This is a lot of purging, but Dale Beatty, assistant manager of the department, says that otherwise the paint would dry on the bell and shaping air plate, leading to uneven paint application or “spitting.” He points out that the water-borne material is uniquely problematic on this count since the solvent-based clearcoat is applied to 14 cars before the lines are flushed.

Having a paint lot size of only two theoretically enables Toyota to be more flexible in synchronizing supply and demand and giving dealers only the car colors that they want. In reality, given that both the Camry and Sienna are only available in 10 colors apiece, any advantage may be non-existent. However, the fact that Toyota can effectively paint and build in such small increments could weigh in their favor as the industry moves toward a quick-build, quick delivery pull system. For example, Toyota’s arch nemesis Honda builds in comparatively gargantuan lots of 30.

The chief advantage to using water-borne paint is clearly the environmental benefit of the reduction in toxic solvents, but that benefit comes at a price. In addition to the increased purge rate, water-borne material is much more sensitive to humidity changes. Beatty says that optimum humidity for the paint booth is 72% with a window of acceptable variance set a mere +/- 3%. If a malfunction in the automatic humidity control equipment causes an unacceptable spike, an alarm sounds that brings immediate attention lest the body in the booth need re-painting. If the humidity is too low, the basecoat dries too quickly and loses luster. If it is too high, the water is incompletely flashed off of the body and later boils up through the clearcoat, marring the finish with a phenomenon called “popping.”


Incremental Improvements

As is typical of Toyota’s continuous improvement culture, refinements tend to come in small increments in the paint department. One example is a recent switch to an air-assisted nozzle for applying sealer to weld seams. Toyota uses a lot of sealer on its bodies-in-white, and in the past it was all applied in a continuous bead that often had to be spread by hand. By making the simple change of adding the air-assisted nozzle, which lays down a flat spray of sealer that does not need to be spread, the company was able to eliminate one process and reduce almost a pound of sealer per car for a cost savings of sixty-one cents a unit.

More surprisingly, the paint department has increased the quality of the paint finish by shutting down part of the line. When plant two became operational in 1994, one feature of the paint line was an automatic wet sanding machine. Primed bodies would first pass through a manual wet sanding area and then move into the sanding machine that would give the body the once over and send it on to a shower of de-ionized water. Toyota’s engineers thought that the combination of the sanding machine and the shower would result in a body largely free from the dirt and impurities that are the bane of a uniform finish. However, just the opposite happened. The machine created significantly more sludge than the manual sanding alone and the shower could not clean it off with sufficient thoroughness. So the machine, which had started out as a technological point of pride, was shut down. And after re-focusing emphasis on better manual wipe down techniques, dirt-related problems dropped.


Back to Basics

TMMK is currently putting a big emphasis on training in an effort to eliminate paint flaws. It has started a program called “Target Zero Seeds” that aims to remove every particle of dirt and dust, known as “seeds,” from the bodies before they are painted. To do this, the company went back to basics and re-trained workers in the basic problem solving skills of the Toyota Production System (TPS). It then launched a program called “Practicals of Paint,” or POP. Through POP, team leaders from different parts of the paint shop spent time learning the fundamentals of areas outside of theirown—including such hands-on exercises as mixing the chemicals used for electrodeposition. Cheryl Jones, general manager of Paint at TMMK, says that the key purpose of this cross-training is to give workers a broader perspective that she hopes will lead to higher quality. On a little less esoteric level, POP also teaches skills like the proper way to wipe down a body so as not to leave any of those inimical little seeds.


What’s Next

TMMK will soon be able to put the lessons they have learned while wrestling with the temperamental water-borne process in Plant Two to good use in Plant One. That paint department, which deals exclusively in solvent-based paint, is scheduled to undergo a major overhaul within three years that will give it the capability of painting with both solvent- and water-borne materials. The move is part of a Toyota initiative to convert to water-borne paint systems in its plants worldwide. It will mean reconfiguring the line to add ovens that can flash water from the basecoat, but will also include replacing equipment and robots. This project is sorely needed since, according to Jones, the Plant One equipment is “so old you can’t even buy replacement parts on the market anymore.” The combination of new, more efficient equipment and the institutional knowledge gained from years of dealing with the water-borne process should further increase the capabilities of the quality leader. And that should make Toyota’s competitors a little nervous.

Workers in TMMK’s Plant Two paint shop wipe down primed Camry bodies before they journey into the basecoat booth. Toyota has instituted a program designed to eradicate all dirt and dust particles that can ruin paint finishes.

The Electromatic XVI (right) is more compact than its predecessor, which has been proven in action for more than 30 years.

That’s film not paint, on the B-pillar

Toyota recently started using an air-assisted nozzle to apply sealer on its bodies. The nozzle flattens the sealer so that it doesn’t have to be spread by hand, saving material and process time. The left part of the sealer line shown was applied using the air-assisted nozzle. The right part is a standard bead.

Want your Volvo S80 in white pearl? You must be an American.

This applicator is designed for the electrostatic application of water-borne material. The cylindrical portion is actually a reservoir where charged paint is contained.


Coat It

Looking for a means by which metals can be coated with anti-corrosion fluids or lubrication oils, one that is not only precise and uniform but comparatively waste free? The people from United Air Specialists (Cincinnati) maintain that the TotalStat system does the trick. It is an electrostatic system, one that uses what is termed “soft spray” technology, as opposed to the harder spray of air pressure-based systems. The system is said to be so mist- and over-spray-free that no fume hoods or exhaust systems are necessary. The system’s pump works in conjunction with the speed of the line for the material being coated (thereby assuring coating thickness consistency). To learn more, write in 112 on the Reader Service Card.
An electrostatic shower of coating for consistency and waste minimization in application.

Treating metal parts with zinc phosphate coatings can be an environmental nightmare. The tanks must be regularly purged of sludge – a substance classified by the EPA as hazardous waste – and disposed of accordingly, an expensive process. In addition, the chemistry of the phosphate dip tank has to be monitored closely, especially as the humidity changes. Plus, bonding rubber to a zinc phosphated piece requires the separate application of a primer and adhesive topcoat before the part is molded. Granted, this rubber-to-metal process provides an excellent bond, but the exposed areas lack adequate corrosion protection unless the part is post-painted, which also adds significant cost. And in an industry where price is the driving force and quality is imperative, that expenditure is getting harder to justify.

Lord Corp. (Huntington, IN) created MetalJacket to answer these concerns, and created Lord Coating Technologies (LCT) to be the exclusive customer coater and development source for the process. "MetalJacket is applied using a simple dip process," says Brett Retrick, a senior engineering specialist at LCT. "It eliminates the need for zinc phosphating, adhesive primers, or post-painting ferrous parts, yet provides corrosion protection similar to E-coating." Plus, the application process is fairly straightforward.

Clean, non-pretreated steel parts receive an alkaline clean and rinse, and an acid pickle and rinse before being dipped in the MetalJacket treatment tank. Once coated, the parts are dried and cooled before being dipped in the corrosion-resistant coating tank, after which they are dried, baked, cooled, and unloaded. The entire process takes just a few minutes.

"In some rubber-to-metal applications," says Retrick, "the initial metal treatment step is enough." Which begs the question whether it's possible to apply the MetalJacket coating without the treatment process. "No," says Retrick. "The coating polymers react with the metal, which changes the viscosity of the coating that is in contact with the part. This slows down the deposition reaction as film thickness builds so each part receives a consistent film thickness." Something that wouldn't be possible without the treatment step.

The coating itself has two functions: It acts as a primer for rubber-to-metal bonding, and coats the exposed areas of the part. In addition, when compared to zinc phosphate – which can be brittle – MetalJacket adheres under extreme circumstances. "We've tested the coating under various conditions," says Retrick, "including swaging bushings. The maximum swage the zinc phosphating could achieve before failure was 7%, while MetalJacket reached 16%." To emphasize the point Retrick takes a small, coated piece of metal, bends it 180º in a die, then bends it again. There is no creep in the damage areas. The coating is intact. "This performance means a supplier might want to alter where and how he crimps a part, and opens up the possibility of using different grades of steel," says Retrick.

Unlike zinc phosphate, the MetalJacket chemistry is temperature and humidity tolerant, making control of these variables less critical. Other advantages are the coating's VOC-compliance, as well as a lack of odor and fumes. "About all you have to do is top up the tank at the end of the day," claims Retrick, and a far cry from the sludge removal and disposal inherent in the zinc phosphating process.

Though Lord Coating Technologies is currently the only source for this process, Retrick says the company can help suppliers install their own coating lines. "We've developed the process knowledge in-house, which makes it easier to move it into the customer's plant and adapt it to prevailing conditions," he says. Or the customer can avoid purchasing new equipment entirely by leaving the coating process to LCT. The company will even arrange for the adhesive application on rubber-to-metal assemblies. About the only thing they can't do at the moment is coat steel in a color other than black.

"We're working on that," laughs Retrick. "The Army was the first to request another color because they want us to develop an olive drab coating for tank treads." So far, automotive suppliers appear to be satisfied with the satin black finish.

MetalJacket is used on the engine mounts of some Saturn vehicles, as well as various automotive threaded fasteners and bushings used throughout the industry. "The coating lends itself to parts that can be hung or clipped, and that drain well after being dipped, no matter how complex their geometries," says Retrick. Small, light parts currently require bulk processing, but LCT is working on a version that can be tumble sprayed. Since MetalJacket meets or exceeds DaimlerChrysler, Ford, and GM corrosion specifications, and reportedly outperforms E-coating, an obvious question arises. "No. We haven't been approached to coat a body-in-white," says Retrick. "At least, not yet."