Heavy-duty quality

Appliance manufacturing makes a total commitment

by Donald B. Dobbins, Senior Technical Editor

Maintaining the highest possible quality level within the appliance manufacturing industry requires a total commitment. It begins with a corporate philosophy and requires dedicated process control procedures throughout the material acquisition, manufacturing, and assembly phases of production.

The global marketplace

Today more than ever, the appliance industry is worldwide in scope. According to Whirlpool Corp., Benton Harbor, MI, it competes in an environment made up of more than 235 million major home appliances, worth approximately $70 billion. This means the global market is four times the size of the North American market and is growing twice as fast.

Throughout 1999 and into 2000, Whirlpool solidified its leadership position in the global appliance industry. According to published reports, the company holds the leading market position in North America and Latin America, third place in Europe, and the top spot among Western companies doing business in Asia.

In the "Chairman's Letter" that appears in the most recent Whirlpool Annual Report, David R. Whitwam, chairman and CEO elaborates on global aspects of the appliance industry and how they are shaping Whirlpool's corporate structure. "We spent the decade of the '90s transforming from a company largely focused on the United States to an enterprise today that is 40 percent larger in global market share than our closest competitor," Whitwam says.

"Because of this global business platform, our focus and opportunities are not limited to the $24 billion US appliance business, where we have the number one market position," he continues. "We are equally dedicated to building our share of the $70 billion worldwide consumer appliance market--that within the decade, will swell to $120 billion."

Whitwam goes on to explain that trend lines show that consumer appliance markets outside of the United States will expand at twice the pace of the North American market by 2010. He also says that Whirlpool has demonstrated its capability to translate growth into significant earnings improvement through an intense focus on operational excellence and to leverage that capability throughout its global operations.

"We define operational excellence as our ability to drive total cost productivity, quality improvements, working capital and asset management, and global leverage to assure that revenue growth translates into consistent and sizable improvement in earnings," Whitwam says. "Each year we take operational excellence to a higher level through the use and refinement of global tools and practices, such as Six Sigma quality, procurement practices, supply chain and working capital management processes, product development and design, and the application of information technology."

Process control

Michael O'Brien, president, Signature Technologies Inc., Dallas, TX, reports that while metalforming operations tied to the appliance manufacturing industry have invested in conventional press control systems to provide die protection, light-curtain guarding, and tonnage monitoring, he hasn't seen any great interest in the application of process control instrumentation to monitor part quality.

This heavy duty automated storage and retrieval system (ASRS) was developed for a major appliance company to store massive dies used in its stamping operations. Here, the retrieval unit is shown undergoing testing at Orchid Automation's manufacturing facility in Cambridge, Ont., Canada.

"When it comes to the metalforming side of manufacturing," O'Brien observes, "I definitely can say that appliance builders are in the same mechanical business as the car manufacturers. By this, I mean a lot of the parts they make are large panels and there are a lot of drawing applications.

"Of course, for many years, the automotive industry has been working to reduce vehicle weight. Many times they did this by using more plastics and composites. However, when it came to the body, steel still was the material of choice--to keep the cost down. To cut weight, they went to thinner materials."

The initial venture into thinner materials resulted in doors that dented easily, O'Brien says. Anybody who owned a car in the late '80s will remember how easy it was to dent the door. Yet today, you still may see a lot of door dings, but they are more likely to be scratched paint than dented metal. This is because the industry is using special alloys that work harden during the stamping process, and employing stretch drawing technology as the process of choice.

"When performing a stretch draw," O'Brien explains, "the material is clamped firmly in place and is stretched during the drawing operation, unlike a conventional draw where the material is allowed to flow. As the material thins, it hardens and becomes more like a tempered panel.

"In the automotive industry, by going to the stretch draw, designers have given themselves the ability to have a lighter product, and it resists dents," says O'Brien. "However, the cost to them is the fact that now, they really need to monitor the process because if something goes wrong, they're going to get a tear, or they're going to get wrinkles. The propensity for something bad to happen is a lot higher when you're doing a stretch draw versus a regular draw."

Engineers at Signature Technologies have developed a program that runs in their process control system where it monitors the forces being applied by the tool, as a function of tool position, during the drawing operation. By looking at the force signature, a stamper can monitor the accuracy of the process and consequently, the quality of the part produced by the process. "A phase shift in the leading edge of a signature is indicative of a change in material thickness," O'Brien explains. "If thickness changes, the force generated at a particular position is going to be more or less than it would have been if thickness didn't change because the tool is contacting the material at a different point in the stroke.

"On the other hand," O'Brien points out, "if a material gets harder, there will be a slope change in the signature curve because, although the tool is still contacting the material at the same point, if the material is harder, it will require a higher force to form. Conversely, if the material is softer, a lower force will be registered in the signature."

When looking at these two things independently, if the software monitor sees a phase shift, and hardness is constant, all the user has to do is measure the phase shift, correlate it to crank position, and he or she knows what the thickness change is. Likewise, if the material is a constant thickness, and hardness changes, all that is necessary to detect the change is to monitor an amplitude change for each point on the signature curve.

"Unfortunately," O'Brien says, "we never have hardness changes without thickness changes. If we look at one particular point on the signature, and we're doing a stretch draw, we're making the steel thinner and harder at the same time. This means we'll have changes in position in both directions, and the question is, how do we know which one is which?

Figure 2: This drum expander takes a cylindrical part and forms it into a washer tub or basket, or a dryer drum. Both mechanically and hydraulically actuated models are available depending upon cycle speed required. The expander is manufactured by Newcor-Bay City, Bay City, MI.

"Using the algorithm we use in our monitoring equipment, what we actually do is to look at multiple points along the signature. If we're looking at a thickness change, all of those points are going to move by a certain amount that will be the same. If it's a hardness change, the points are going to move in amplitude by a certain amount. The end result is that we end up with the ability to differentiate between how much of the change is thickness and how much of the change is hardness.

"Now, that's not the end of the story," O'Brien says. "When an engineer is designing a panel, there are equations used to determine material hardness. There is another module in our software that actually uses that equation, and it solves for hardness, in real time, based upon the other measurements. What the user actually gets as the measured parameters in the processor is the work-hardening coefficient and that's what determines whether or not they've made a good body panel."

Watching for slugs

Probably the biggest issue relating to metalforming in the appliance industry, and the area in which Signature Technologies has been most successful, is in slug detection. During panel fabrication, the same die that forms the panel is used to punch out holes to receive the fasteners used in assembly. If one of the punched slugs ends up in the press, it will cause a defect in the finished material because it will generate a "crescent" somewhere in the panel surface. Also, that defect is going to be extremely difficult to eliminate in the finishing process.

Even worse, if the manufacturer is using prefinished material, and ends up with a slug in the die area, when that part comes out, the finish will be gone where the slug was and the part becomes scrap.

According to O'Brien, slug detection is extremely easy to do. "We do it by putting strain gages on the edges of the stripper," he says. "We're able to detect very small slugs. In the lead-frame industry, for example, we're talking about detecting a slug that's the size of a grain of sugar in a die space that's about 12´´ or 18´´ by 36´´, operating at 600 strokes per minute. The system is not detecting the amount of force. It's detecting the presence of that force in a part of the stroke where it doesn't belong by measuring an imbalance across the stripper plate.

"There are companies that make sensors to put on a stripper plate and look for slugs," O'Brien points out, "but the problem with those is that their sensitivity may not be adequate for this type of application.

"When we're talking about something like an appliance where the finish of the product is already there, even a minor slug--like a shaving--that ends up in the die space will leave a mark that makes that part a piece of scrap. They'd never pick that up with basic slug detection products that are available, but you would pick it up with our system," he concludes.

Handling is critical

Keith Cornacchia is director of sales for Orchid Automation, Cambridge, Ont., Canada. He talks about some of the effects that die handling outside the press and material handling both inside and outside the press can have on part quality.

"When it comes to die handling," Cornacchia says, "it's very difficult for people to understand how that relates to quality. As an example, one of our customers had a real problem with dies that were all over the floor. These were fairly heavy dies, many weighing up to 60,000 pounds. They also were stored very close to the machine.

"One problem was that any time they needed to get to that machine to do any type of maintenance, or any die maintenance while a die was running, they were removing dies, shuffling them around, and causing a lot of damage. What made the situation even worse was that they wouldn't find out a die was damaged until it was put into the press to make parts."

When they found out that part quality was not good, Cornacchia explains, they would end up with a lot of down time on the machine. "In a couple of instances," he reports, "we learned that poor part quality actually escaped detection in the pressroom and bad parts made it to the next level of production, which is assembly. We solved the problem by installing one of our storage and retrieval systems."

The initial intent was to get inactive dies away from the press--which wasn't so much a quality issue as it was to open up floor space and boost productivity. However, the most important reason for moving them away from the press was to keep them from being handled repeatedly as they were being moved out of the way.

In this particular installation, dies were being handled by overhead cranes using slings. During the handling operation, dies were subject to damage by being bumped around. In addition, they were being stacked one on top of the other, which can cause problems if the dies are not handled properly. Often material handling personnel do not understand that stamping dies, even though they are large and heavy, can be delicate and must be handled properly.

With the storage and retrieval system, dies are placed on a table from which they can be lifted directly onto the bolster of the press on which they will be running. This eliminates repeatedly putting them down and picking them up, which happened with floor storage.

"When we look at the before and after situation in that particular facility, the amount that handling was reduced is very significant," Cornacchia says. "Most, if not all, of the presses in this facility have dual rolling bolsters.

"Many of the parts being produced on these presses are outer panels which must pass muster in terms of both accuracy and appearance. The die storage solution worked so well that plans are underway to expand this system to accommodate additional tooling that is coming into the plant."

Another manufacturer uses Orchid Automation equipment on its dishwasher line. This is an in-press transfer system that has reduced human intervention--the handling of parts from station to station within a press. "Not only has this led to a high production rate," says Cornacchia, "but it is much safer for employees working on this line, because it eliminates people reaching into a transfer press and doing a hand transfer through the stations. In addition, it ensures that handling of these parts has a higher degree of repeatability because it does not rely on the human touch. Everybody's touch is different."

Destackers are another item that can have a positive impact on quality, Cornacchia says. "Many times it's how you handle the material at the front end of the press, as well as the die, that can affect quality. If material is damaged coming in, there will be problems with non-conforming parts. On one of the projects I'm working on right now," Cornacchia says, "we're trying to take steps to protect the blanks--even though they are blanking within the plant. There can be a lot of material damage to blanks during transport, even within the same plant. Of course, many appliance lines are coil fed and have their own set of issues to prevent damage."

Drum expanders boost quality

The machine shown in Figure 2 takes a cylindrical part and sizes it or shapes it depending on what the end product will be. This type of machine can be mechanically or hydraulically actuated and is used to produce washer baskets and dryer drums used in laundry appliances.

Using a timed air pulse instead of guesswork to control the size of each grease deposit, operators at Mountain View Fabricating are able to apply a consistent amount of lubricant to every subassembly.

Starting with a preformed cylinder, the machine forms the part by forcing segments against the shell and expanding it to a size larger than print because an allowance must be made for material springback. "In other words," explains Ron Derdowski of Newcor-Bay City, Bay City, MI, manufacturer of this equipment, "we form the shell by expanding it beyond its elastic limits to its shape. When we collapse the expander, the formed metal part shrinks, forming a part to print size."

The amount of expansion needed to overcome springback and form the final part size can sometimes be a matter of trial and error to set the parameters of the machine, according to Derdowski. "If we're doing a straight cylindrical part that has very little or no form to it and we're just sizing it to make it round, it's something we can calculate," he says. "On the other hand, if there is a lot of shape to the part, especially if one end has just a slight curvature to it in form and the other end has a convoluted track in it that might be ¹/₂´´ deep, we'll get different springback on one end of the part than on the other. In that case, we make the first part with an expander that's machined but not hardened. Once we make a set of parts that are just what we want, we tear the expander down, polish it, and send it out to be heat treated.

"Sometimes if the parts aren't quite right, we have to remachine (re-turn) the expander to give us the exact shape we want. Once we have it, then we're all set and the consistency is always there."

These machines can be used in a single cell, manually fed operation. Or, they can be built into an automatic line with a cycle as quick as 10.5 sec. In the latter instance, a part is brought into the cell and automatically loaded into the expander. After being expanded, it is automatically unloaded into a transfer system.

Parts produced on this type of equipment typically are made out of draw-quality, cold-rolled steel, enameling iron, or stainless steel. The draw quality and enameling iron are just as they come off of a coil and are welded, formed, and typically powder coated or porcelainized, according to Derdowski. Stainless steels generally are prefinished with very little or no polishing afterwards.

"The users buy this type of equipment because they get a part with greater consistency compared to forming a part by deep drawing. In addition, there's a lot of scrap associated with the deep drawing production technique. It's also a slower process, which means that the user can increase their production and get a better quality part, with less waste in terms of material scrap."

A critical assembly process

When its parent company decided to relocate a product assembly line from a sister plant to their facility, Mountain View Fabricating, Mountain View, MO, took advantage of the opportunity to increase the accuracy and efficiency of a critical grease dispensing operation.

Mountain View Fabricating is a division of Coin Acceptors, Inc., St. Louis, MO, the world's leading manufacturer of coin acceptors and bill validators. The company's products are used in vending machines throughout the world, in locations that range from international airports to local post offices.

In a key assembly process, six gears inside the subassembly responsible for returning change to the customer are lubricated with a clear, medium-viscosity grease to ensure smooth and reliable operation under demanding field conditions.

Controlled grease application is critical as any excess lubricant can ooze out of the gears and onto nearby electrical components.

With the original process, operators would transfer grease from five-gallon buckets into smaller tubs, then dip small paintbrushes into the open containers and apply the grease to the gears--a messy and inefficient operation.

The challenge of finding a more consistent alternative to the old lubrication method was given to engineer Russ Jackson. During his evaluation of different methods and equipment, Jackson contacted EFD, East Providence, RI, to determine whether their timed-pulse dispensing equipment could help Mountain View improve its lubrication process.

After discussing the company's initial process and overall objectives with Jackson, EFD product specialist Steve Hardcastle recommended the Model 900 dispenser and explained how it could eliminate variations in deposit size by using a timed air pulse to control the amount of grease applied.

With timed-pulse dispensing, Hardcastle explained, there is no guesswork or subjective operator judgment involved--volume of the deposit is determined by a combination of time, air pressure, and size of the dispensing tip.

Lubricant is loaded into a disposable barrel that is fitted with a precision tip and connected to the dispenser by lightweight, flexible tubing. The compact dispenser console is connected to a compressed air source, which supplies pressure needed to move material through the barrel and tip and onto the part. The timer is used to control the duration of the dispensing cycle.

The advantage of this approach over manual application is control--once time and pressure have been set, the operator positions the tip on the part and makes a consistent deposit by pressing an electric foot pedal.

EFD's timed-pulse technology sounded like a good fit for Mountain View's application, and by the next day Jackson had a unit on the shop floor for evaluation.

After experimenting with different tips, times and pressures, Mountain View came up with a combination that provided just the right amount of lubrication. Satisfied that they had found the ideal deposit size and the means to accurately and consistently repeat it, Jackson recorded the time and pressure settings, and ordered six more Model 900s.

The right amount of grease

The transition from manual to automatic dispensing was fast and easy. Since deposit size was controlled automatically, very little operator training was required. "The great thing about dispensers is that no guesswork is involved," says Jackson. "By using the same tip and duplicating the time and pressure settings we used with the first unit, we were able to get the same results at every workstation. That really took the variability out of the lubrication process."

In addition to standardizing the size of grease deposits, the EFD dispensers have helped Mountain View streamline its lubrication process and lower the risk of repetitive stress injuries.

To increase efficiency and save production time, an entire shift's worth of 55cc barrels is loaded with grease in advance. During the filling process, the barrel is connected directly to the pail pump with an EFD fitting for fast, clean filling without mess or waste.

The large-capacity barrels also protect the lubricant from contamination and allow operators to apply grease without repetitive hand and arm motions. When a barrel is empty, the operator simply rotates it 90 degrees to remove it from the adapter, installs another prefilled barrel and resumes dispensing within seconds, without waste, mess or downtime.

"Controlling deposit size is critical to our operation," Jackson concludes. "Changing from manual to automatic dispensing has given us neat, consistent dots and made it much easier to visually confirm that grease has been applied in the right location."

SOURCES:

• Whirlpool Corp., Benton Harbor, MI. Circle 214 or go to www.1rs.com/011qm-214
• Signature Technologies, Dallas, TX. Circle 215 or go to www.1rs.com/011qm-215
• Orchid Automation, Cambridge, Ont., Canada. Circle 216 or go to www.1rs.com/011qm-216
• Newcor - Bay City, Bay City, MI. Circle 217 or go to www.1rs.com/011qm-217
• Mountain View Fabricating, Mountain View, MO. Circle 218 or go to www.1rs.com/011qm-218
• EFD, East Providence, RI. Circle 219 or go to www.1rs.com/011qm-219

Please Note:
Some pictures or diagrams are only
available through the printed media.

This article was originally published in the November/December 2000 issue of Quality in Manufacturing.

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