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issue: July 2004 APPLIANCE Magazine

Engineering
Cutting Development Time


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Fast prototype turnaround allows Electrolux Home Products to conduct trials, improve, retest, and reapprove component design without the delays or expense of production tools.

For Electrolux Home Products (EHP) Group of Orangeburg, SC, U.S., it seems the grass is always greener when, in fact, the grass is growing fast.

Electrolux Home Products’ new three-blade, 54-in mulching mower deck was developed and approved for production in a shorter time frame, thanks to a fast turnaround of steel-stamped prototype parts.

The good news for EHP, the parent company of Poulan-and Husqvarna-branded outdoor equipment and a supplier to the Sears Craftsman line of lawn and garden equipment, is that suburban sprawl in the U.S. continues to multiply the number of lawns to care for, and rural areas are starting to build larger yards. While this may mean an increase in lawn and garden appliance sales, it also means that EHP has to continually develop and incorporate new elements, design features, and performance improvements into its products, while still providing time-proven quality and reliability.

During the last few years, the appliance maker has implemented several time-saving elements into its lawn and garden products, including the mulching mower, which cuts and recuts grass clippings several times, creating smaller pieces that helped speed up decomposition. The mulching option reportedly eliminates the need for bagging or raking, in addition to reducing the amount of yard waste.

A second timesaving results when mower decks are made larger, cutting a wider path and a larger area of lawn with each traverse of the yard. Combine the two—mulching and larger mowers—and the traditional time to mow the grass is said to be significantly reduced.

Bringing the two elements together in a new mower, however, can be a design engineering challenge, according to Chad Boerst, senior project engineer at EHP. “Every deck design and size requires unique design features that allow it to give the maximum performance in several cutting modes,” Mr. Boerst explains. “For those with both mulching and bagging options, this is extremely important…to generate the lift to throw the clippings back into the blades for recutting, or to send them up the bagging chutes.” The deck design also has to take into consideration its use in several parts of the U.S. with different grass types and varying conditions. In other words, the design of a 22-in wide deck with single cutting blade action will not work for a 38-in wide, two-blade unit.”

Mr. Boerst adds that every time the company makes a change in shape to enhance performance or to make a larger mower available, several prototypes are needed to conduct the proper testing, including field testing, durability cycle testing, and performance testing. “A steel-stamped prototype housing, approximating actual production processes and components, gives us the real-world results and the flexibility to do those tests,” he says. “In the past, unfortunately, getting large stamped mower deck prototypes has been an expensive and time-exhaustive process waiting for tooling, and even longer if secondary modifications were required. Recently, though, we found a prototype facility that delivered parts in a time frame we thought impossible between 3 to 4 weeks for the first set and just 2 weeks after we (Electrolux) made minor design changes for the second set of prototypes.”

That prototype facility is 3-Dimensional Services of Rochester Hills, MI, U.S., a rapid prototype firm that specializes in design, engineering, and analysis, in-house tool construction, and complete build of first-off parts and low- to medium-volume production runs. The supplier says that its use of advanced process methods and manufacturing technologies means that prototype parts are typically provided up to 70-percent faster than conventional prototype shops can offer.

The EHP prototypes for this application were new 54-in wide, three-blade mower decks for garden tractors in the Husqvarna, Poulan Pro, and Sears Craftsman lines. The prototype decks were made from 10-gauge, low-carbon steel. In addition to the 56 1/2-in actual width, the pieces measured 27 1/2-in front to back and approximately 6-in high.

Scott Duffie, the senior sales engineer at 3-Dimensional Services who coordinated the mower project, says that the EHP project was straightforward and began with EHP submitting CAD-generated files to the prototyper’s workstations, where they were reviewed and analyzed for manufacturing intent. In this case, data was good, and both companies agreed that no modifications were required in terms of the mower deck’s manufacturability.

The actual tooling began with the pouring of Kirtsite to make the die sections. Because Kirtsite is said to offer easy maneuverability, high machining speeds, and feeds that can shorten the die-making process with a comparatively moderate durability, it allows for accurate stampings for a limited quantity of parts. CAM programs used and translated the CAD data, generating machining programs and tool-cutting paths that were then downloaded to 3-Dimensional’s CNC machining department for completion of the dies.

Once the dies were ready, the mower decks were formed on an 800-ton press. To facilitate faster tool making, punches for the mower blade mounting holes were not included in the die, so a 5-axis laser was used to trim and cut holes for the three blades as well as to cut the discharge opening and create the mulching latch cover.

Once the trim work was complete in the laser department, the mower decks were returned to the stamping operations, where forming tools were passed through the holes to create flanges around the openings in order to facilitate blade mounting.

“For us, the biggest challenge was the deep draws that were needed to make sure our prototypes were done correctly and to ensure that production tooling, when started, would give Electrolux engineers the same results,” Mr. Duffie says. “It worked out fine…we delivered 20 initial parts in the 3- to 4-week period (after receipt of the CAD file). Electrolux then field tested the original parts and requested minor alterations be made, and a second set of modified parts were made. These parts—15 were in the second run—were completed within 2 weeks of their request.”

Mr. Duffie adds that his company can provide fast prototype turnaround because for almost every job it does, most if not all of the work is done in-house, including all tooling construction, machining, stamping, assembly, and molding.

“The build up of these prototypes and their close approximation to actual production components helped verify fit and function of the decks before the final production tools had ever been released, saving time and costs,” Mr. Boerst of EHP adds. “The benefit in their speed of execution, providing us with sample steel parts within 4 weeks was significant in reducing the overall product development time.”

 

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