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issue: April 2005 APPLIANCE Magazine

Designing with Plastics
Breaking the Mold

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by Erin Biesen, Assistant Editor

After talking to retailers such as The Home Depot and Lowe’s, Chicago, IL, U.S.-based Wobble Light realized that it would need to produce tens of thousands of its lighting appliance per month to fill order demands.

Using injection molding, Wobble Light was able to mass-produce its unique lighting appliance with greater speed and more ease than rotomolding would allow.

Rotational molding (rotomolding), Wobble Light’s previous form of production, was simply inefficient for that amount; it was only producing 700 to 1,000 units per month. Therefore, the manufacturer decided on injection molding as its new form of production for its “self righting” light that bounces back up if it is tipped over in garage or industrial settings. “Rotational molding produces a very nice part, but it is a very slow process,” Ron Reda, president of Wobble Light, says. “Using injection molding, I get a part every 50 sec. With rotational molding, I was getting four parts an hour.”

In order to produce parts at a faster rate, injection molding uses high pressure to mold the product. After raw pellets are transformed into a liquid state, high pressure forces the material into a mold that shapes the plastic. The plastic then quickly sets, and the finished part is ejected out.

After interviewing several companies, Wobble Light decided on Phillips Plastic Corporation™ (Hudson, WI, U.S.) not only for its plastic needs, but to be its one-stop shop for everything from front-end engineering all the way to packing and shipping.

Molding the Design

Phillips began redesigning for an economical manner to mass-produce the plastic light. Wayne Phillips, design team leader at Phillips, said his team used 3D CAD modeling to create
theoretical plans for the product, keeping in mind all of the important needs for design, manufacturability, assembly, and disassembly. “We took all the different components that needed to go in and started analyzing features that we could use to attach these different components in such a manner that we could mold the part,” explains Mr. Phillips. “It was basically trying to solve a puzzle.”

It took roughly 3 months to solve this puzzle. Phillips began working with the appliance’s body, the shock disk, the dome, the vent cap, and all the internal components. After the team created a new design on the computer, it went through several prototypes to make sure that the product could be easily assembled.

Feeling the Heat

The original lighting appliance used only one type of bulb, but after Wobble Light did research with its customers, it discovered that some wanted more light, while others wanted less. “We ended up developing a family of lights that went from 8,000 lumens all the way up to 40,000 lumens,” explains Mr. Reda. The product now uses five lights, from a 120-W fluorescent bulb to a 500-W halide light, which produces a lot of light, along with a lot of heat.

Wobble Light began experiencing issues with the heat and size of the new bulbs, so Phillips reworked the design of the dome and vent cap. “The concept of its vent cap and its dome already existed, but we basically redesigned it so the new body fixed some heat and lighting issues from the type of lights they were going to use,” explains Mr. Phillips. “We actually had to increase the diameter of the dome and the body to accommodate the issues that they were seeing.”

The variety of lights Wobble Light uses created another challenge. Phillips focused on these five different light packages, all with different types of internal electrical components. Designers also had to consider the weight in the base of the light, which allows the unit to bounce back up if it tips over. “We had to accommodate all these different versions of lights and different versions of weights with a common design,” notes Mr. Phillips. “There are features that are in this body where you might use one feature for a particular lighting scenario, and on another lighting scenario, you might not use it at all.” The end product was one design that includes all the different electrical and weight component possibilities.

In order to keep costs low, Phillips decided on a clamshell design so that Wobble Light would only need one tool. It then created a body half that could be molded twice so the two halves could be joined to form the final body structure. Mr. Phillips explains, “We had to integrate so that those were uniform and would fit together nicely.”

Wobble Light was pleased with the outcome of its new project. “When you have a one-piece part, it is generally more durable than two pieces since you have to fasten the two parts together,” notes Mr. Reda. “Now we have two pieces that are fastened together, but I think we’ve achieved a pretty tough, durable product.”

After designing the product, it was time to find a material that would handle the stress the product would experience. Phillips looked to the material that Wobble Light previously used with rotomolding. “We identified polypropylene as one of our first candidates because it was cost-effective,” notes Mr. Phillips. “As we sampled the tools, we found that the polypropylene had a great deal of problems with warping. We started putting parts together, and edges weren’t coming together.”

After extensive testing of materials, Phillips and Wobble Light decided on using an ABS material to solve the warp issues. “We would have stayed with the polypropylene, but when you change from rotomolding to injection molding, certain materials don’t work as well,” Mr. Reda says. “ABS is a much easier material to work with in injection molding versus the polypropylene.”

Wobbling with Ease

Production speed and ease of assembly are two of the benefits that Wobble Light experienced after switching from rotomolding to injection molding. “Basically we have two halves that we put together, and we are able to stuff all the components into the cavity of the light,” explains Mr. Reda. “When we put the other half on, it captures the components so we don’t have to screw all of the components together. They’re captured in the two halves of the body, and it decreases our assembly time significantly.”

Injection molding also allows for designing a much cleaner part with corners and different radii. “With injection molding, you are forcing a thousand tons of pressure on the plastic into this mold, forcing it into very small radii, [which results in] much crisper design lines,” comments Mr. Reda. Because rotomolding does not utilize pressure to force the plastic into the crevices and creases, there needs to be rounded areas with larger radii to create the product. “You have no pressure on the plastic wall whatsoever; it’s strictly a lining, and the plastic just kind of bounces around in there and lines the inside,” notes Mr. Reda.

Additional designs can also be worked into the product when using injection molding. “With rotomolding, if you want a hole or a vent, you have to cut that in, resulting in a secondary operation,” explains Mr. Phillips. “But with injection molding, we can mold it in that shape, and when it comes out of the mold, we are ready to assemble.”

Phillips not only solved the design puzzle for five different types of bulbs, but also accelerated the production process for Wobble Light to meet customer demands. Mr. Reda says, “The benefits are the assembly time is much quicker, the cycle time is quicker, and the overall cost is cheaper.”

Suppliers mentioned in this article:
Phillips Plastics Corp.

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