Applying lean manufacturing techniques to powder coating operations

impact on a powder coatingoperation.

To understand the poten-tial impact, it’s necessary tounderstand what each of thethree principles represents.Pull systems use signals toinstruct upstream processesto replenish parts that areconsumed downstream. Takttime is the available timedivided by the number of fin-ished units required in thattime period. Takt time mightalso be referred to as the“drumbeat” of the plant.One-piece flow involvesprocessing one part at a time,rather than in batches.

What does this mean forthe production floor? Itmeans that if three opera-tions are required to make apart, lean thinking dictatesthat all three operations becompleted for the first partbefore an operation is startedon the second part.

The Relation toPowder Coating

For the benefits of pullsystems and takt time to berealized, color changes mustbe fast, and first-time appli-cation of powder coatingmust be of consistently highquality.

Fabricators who powdercoat can expect the numberof color changes to increasedramatically when theyimplement pull systems.With pull systems, demanddictates what color is appliednext. If color change time isnot minimized, significantloss of capacity results.

Ideally, all plant operationswould produce consistently atthe designated takt time.However, on a powder line,product flow is interruptedwhenever color changes areneeded or when parts arerejected because of finish flaws.Because most powder coat

Powder coating booths can be specially designed to fit into a lean manufacturing environ-ment. In many cases, because fabricators are attempting to make the most of their floorspace, the lines are smaller in size than traditional powder coating systems.

By Dan Beachum

n an effort to improve the flow, management, and efficiency of theirmanufacturing systems, many fabricators have adopted lean manufac-turing principles, modeled after the Toyota Production System. Inthis type of production environment, customer demand drives daily

production schedules, and inventory is minimized.Companies that have implemented lean practices have realized substantial improvements

in the productivity of both workers and equipment. They have also achieved higher productquality and more on-time deliveries, reduced lead-times, and increased profitability.

Fabricators who powder coat or who are considering a powder coating line should realizethat powder coating is compatible with these same lean principles. In fact, the three principlesof lean manufacturing—pull systems, takt time, and one-piece flow—can have enormous

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lines do not change colors instantly or pro-duce 100 percent perfect parts on the firstrun, parts are stockpiled between the finish-ing department and the operation that fol-lows to avert part shortages downstream.

Supporting the goal of one-piece flowrequires a different approach to fixturing.Many companies have discovered thatthe common practice of batch loading bypart groups or families is incompatiblewith lean ideology. Instead, it’s advanta-geous to load all the parts required toassemble one unit on a single rack. Asthe rack comes off the line, all parts areavailable for assembly.

Finally, minimizing the overall size ofthe powder coating system is criticalwithin a lean environment. Traditionally,companies have increased their capaci-ties to meet sales growth with plantexpansions and added equipment. Lean,on the other hand, uses continuousimprovement concepts to increase capac-ities, while simultaneously seeking toreduce the footprint of production.

A Lean PowderLine Design

Here are some of the most importantfactors to consider when designing apowder line for lean manufacturing.

Color Change. The more frequentthe color change, the less practical arestandard roll-on/roll-off booths.Preparing an offline booth for the nextbooth in “reclaim” mode can take anhour or two. Rolling the first boothoffline and moving the other booth intothe painting position takes five minutesor more, depending on the length of thebooth and line speed.

One option for faster color changes ismultiple application booths, coupledwith an overhead power and free(OP&F) conveyor. In this arrangement,a common conveyor leads to an applica-tion room housing two or more powderbooths. Just inside the room, the convey-or branches into multiple spurs, eachrouted to a single booth. With an OP&Fconveyor, the upper rail hosts the drivechain and the bottom chain contains theload carrier, which can be engaged or dis-engaged from the drive chain. Colorchanges are made by specifying the loadcarrier number and desired booth usingthe operator interface.

Programmable logic controllers typi-cally manage and track part location,verify the color to be applied, and directthe carrier load to the appropriate booth.So, while one booth is operating, anotheris color changing and being prepared forthe next job.

Disadvantages of this option includeinherent system complexity, more elab-orate controls, and higher capital costsfor conveyors and related systems. Thisstrategy also creates a bigger equipmentfootprint.

An alternative for achieving quickcolor changes is a multiple-booth, 100percent spray-to-waste system. Ratherthan several spray booths and reclaim,two separate booths—one automaticand one manual—are used. With thisarrangement, the emphasis is on hightransfer efficiency rather than reclaim-ing. Using two separate booths insteadof a single, larger one enables thesequencing of color changes and greaterefficiency in evacuating suspended pow-der particles, both of which are important.This application technique is more consis-tent because 100 percent virgin powder isused. Powder that has not undergonethe mechanical stresses imparted byreclaim equipment will inevitably pro-duce a higher-quality finish.

In a basic spray-to-waste colorchange, four tasks take place: empty thebooth of work, purge the previous colorfrom hoses and guns, connect the nexthopper, and burp the guns a second time.The advantage of multiple booths, espe-cially small ones, is that it’s possible toperform each task in each booth quickly.

For larger powder coating operations,powder feeding centers are available. Theadvantage of coupling automatic guns toa powder feeding center is that all gunscan be purged simultaneously.

If short color runs are common, amanual booth makes sense. Colorchanges can be achieved in about 30 sec-

onds in this configuration. Floor Space Minimization. To

streamline a powder coating system, lookto the “big boxes,” the cleaning and pre-treatment stages and ovens.

In a traditional clean and pretreat-ment operation, a three-stage (clean,rinse, and dry in place) or a five-stage(alkaline, clean, rinse, phosphate, andrinse) setup is used. However, a dry-in-place, polymer-based chemistry technolo-gy is emerging that replaces traditionalphosphates and could signal a change incleaning strategy.

For many applications, especially sim-ple parts, this dry-in-place technique pro-duces excellent adhesion and corrosionprotection. It also occupies a smaller foot-print compared to traditional cleaningoperations. Typically, the dry-in-placepretreatment application requires only acouple of risers with misting nozzles. Post-rinsing isn’t required, and parts movedirectly into the dryer.

With conventional iron phosphatepretreatment systems, a dwell time of 60seconds is needed in the iron phosphatetank. With dry-in-place systems, about10 seconds is needed.

A common space-saving technique isto mount ovens on the roof or on a mez-zanine. Many companies elevate sec-tions of process lines to allow parts toenter the oven from below, so heatescape is minimized.

For this to work, there must be asignificant change in elevation (a declineout of the washer, then incline into theoven, for instance). This adds time to thefinishing cycle time and introduces aspace consideration of a different kind:

Pretreatment systems are becoming smaller in size with the emergence of dry-in-place pretreatment chemicals. With this technology, parts don’t require a post-rinse before they move to the dryer.

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Parts must have sufficient space betweenthem to prevent contact with each otherwhen the racks are climbing or descend-ing. The size and complexity of the partsto be coated ultimately determine justhow much space must be allotted per partper rack.

Curing. A typical powder coating sys-tem requires a 20-minute dwell timeinside the oven, a specification that curesa variety of parts and geometries effec-tively and together. This dwell time iswhat most powder chemistries require toachieve proper color and gloss.

The disadvantage is that at normalconveyor speeds, 20 minutes of dwelltime means a big oven is needed.

An alternative is a combination oventhat exposes parts to two or three min-utes of intense infrared heat and then 10to 12 minutes of conventional convec-tion heat. Because the oven uses bothinfrared and convection technologies, itis not limited to flat parts, which is usual-ly the case with ovens that rely solely oninfrared curing.

But the combination oven does havetrouble with highly complex shapes,which confound the infrared curing tech-nology because the entire surface has tobe exposed clearly to the infrared beams.

Unless the oven is engineered specificallyfor that complex shape and the beamscan be angled appropriately, the partwill not cure properly.

Near-infrared is a newer technologythat uses infrared emitters with a high-energy light source and focused reflec-

tors. It produces instantaneous heating, ahigher cure temperature, direct activa-tion of an accelerated curing mechanismwithin the powder coating chemistry,and a lower substrate temperature.

With this combination, the melt-to-gel-to-cure progression is reduced to sec-onds. This makes it suitable for finishingheavy-gauge parts or for use in high-speed tube and pipe production.

The main limitation associated withnear-infrared curing is the requirementfor a specially formulated powder. Thepowder formula must provide the rightpenetration characteristics and reactionto the near-infrared energy.

Another oven option is high-velocityconvection, which circulates high vol-umes of air through small orifices. Air isimpinged onto the part, quickly raisingthe substrate temperature. The powder’sblocking agents, which help protectagainst premature curing, come off thepowder, and a faster cure occurs.

Unfortunately, high-velocity systemsare not as forgiving as conventional sys-tems. Color and gloss, for example, canbecome distorted if a line stops.

Cooling Tunnels. In a typical linelayout, eight to 10 minutes of conveyorspace (the time it takes a conveyor tomove a part from Point A to Point B) isprovided after the dryoff and curingoven for parts cooling.

An alternative to the traditional cool-ing tunnel is a tunnel that pulls outside airinto the chamber at one end and expelshot air at the opposite end. Such forced-cooling tunnels cut cooling times in half.

The Lean MantraThe central tenets of lean thinking

are to shorten the order-to-deliverycycle time, invest in simpler systems,

and reduce work-in-process inventories,all without compromising quality.Fabricators who follow these principlesand invest the resources needed to becomelean realize significant savings that arequickly reflected on the bottom line.

This goes for fabricators who powdercoat as well. Thanks to technologicaladvancements and creative equipmentlayout, the benefits of lean manufactur-ing are now open to all.Dan Beachum is the manager of WalgrenCompany’s Organic Finishing Group, 3677Sysco Court S.E., Grand Rapids, MI 49512,616-942-8910 or 800-831-5555, danb@wal-gren.com, www.walgren.com.

For many applications, especially simpleparts, this dry-in-place technique produces

excellent adhesion and corrosion protection.

Reprinted with permission from THE FABRICATOR, August 2003. © The Croydon Group, Ltd.All Rights Reserved. Visit our website at www.thefabricator.com FosteReprints: 866-879-9144

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Walgren Company offers a unique set ofskills and experience, and proven solutions to thespecialized needs of production powder. For morethan 30 years, we have focused our energy andresources on challenging projects for automotive,off-highway and aerospace applications. Walgrenis your best source for new, turnkey powder coating systems, and upgrades and retrofits toenhance productivity and reduce costs.

WALGREN COMPANY3677 Sysco Court SE • Grand Rapids, MI 49512 • Phone: 616-942-8910 • 800-831-5555 • Fax: 616-942-8915 • www.walgren.com

Industry’s #1 Choice for • Chromic, sulfuric, phosphoric or hardcoat anodizing equipment • Zinc, copper, nickel, chrome, tin and electroless nickel plating systems • Cleaning, etching, zinc and iron phosphate pretreatment systems • Wastewater treatment and air emission control • Chemical recovery • Automation controls and reporting• Comprehensive, safe and ergonomically designed material handling • Specialty powder coating systems for long sections and aluminum extrusions

QS-9000 TE Certified

Walgren has set the standard for parts handling efficiency in powdercoating operations. We have solid credentials, with major OEMs and contract shops, in all major parts handling methods: split rail, hoist, powerand free, and monorail, and combination (“hybrid”) systems.

Walgren provides comprehensive waste treatment for multiple finishing processes, and will handle all cleaner/rinse chemistries: acid, alkali,zinc-based, chromate and phosphate. Many systems include filter pressing;all are engineered to minimize sludge volumes and disposal.

Walgren can design your powder coating system in SolidWorks to create highly detailed 3D models, rather than flat 2D drawings.

Walgren provides controls design, implementation, and training.

Controls include simple relay devices to the most sophisticated PC/PLC-based systems. We specialize in data collection and traceability at the part,batch or load-bar level, and frequently interface controls with ERP (shopfloor/material planning) systems.

Independent Self-Diagnostics for major powder coating modules areprovided on Walgren lines.

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