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issue: February 2003 APPLIANCE Magazine

Engineering: Laundry Appliances
Co-Design Key in Plastic Tub Production

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Merloni Elettrodomestici and Meccanica Generale used the co-design approach to create a plastic washing machine tub that allows for faster production, streamlined assembly, and a lighter-weight washing machine.

Pictured is a computer rendering of the plastic tub for Merloni's TOP 2001 washing machine. Merloni and Meccanica Generale co-designed this tub, which allowed Merloni to use less expensive materials and simplify the assembly process, while maintaining a high level of quality.

In the European appliance market, approximately two-thirds of washing machines produced use plastic for the washing machine tub, and the number is expected to grow. A variety of factors influence this trend, including greater freedom of design, which in turn allows greater flexibility in designing and integrating other parts; the noise and energy reductions since plastic is lighter weight and flexible; and the ease of recycling plastic parts. Additionally, the competitive washing machine market demands that producers offer quality performance while maintaining prices, and plastic helps meet that goal.

Co-Design Offers Solutions

When appliance company Merloni Elettrodomestici (Fabriano, Italy) began development of the TOP 2001 top-loading washing machine with the goals of reducing the weight and improving the productivity of its previous top-loading washer, the company knew plastic would be part of the picture. Also, because the competitive marketplace means that producers cannot afford to have a lengthy development time to avoid costly setbacks, Merloni knew it would turn to a plastics specialist for help in designing the TOP 2001.

Meccanica Generale, a plastic parts specialist and injection mold manufacturer also located in Ancona, Italy, proved to be the ideal partner for the development of the new washing machine. The two companies, which have worked together on various projects since 1993, chose to use the co-design approach. Explains Mr. Montevecchio, Sales and Marketing director at Meccanica Generale, "The co-design approach makes the most of the synergy coming from complementary experiences and skills. Furthermore, the possibility [of cooperating] with a partner able to work out the milestones of the product development phase usually results in shorter lead time, reduced project management cost, and reduced risk of unexpected modifications."

Mr. Dino Bongini, Research and Development manager at Merloni's Brembate plant in Bergamo, Italy, confirms, "[The co-design process] reduces time to market and, because maximum know-how is involved from the beginning, [it] minimizes modifications." Together, Merloni, led by Mr. Bongini, and Meccanica Generale defined technical specifications and market needs and created a preliminary model of the tub. Meccanica Generale then created 3D finite element models and testing began.

Testing, 1-2-3

The partners worked in close cooperation throughout the structural and rheological computer simulations, which aimed to verify the balancing of the tubs and positioning of the counterweights; locate the most stressed areas; define the optimal geometry in terms of weight/performance ratios; check the dynamic behavior of the washing unit and its interaction with the base; and analyze the geometry of critical areas such as the damper and spring fixation. A mold flow study was performed as well to help analyze and improve the injection process with the goal of achieving maximum productivity.

The weight/performance ratio was particularly important, as both companies wanted to use the plastic material PP+40%CaCo3, which costs half as much as PP+30% glass fiber, the standard material used in plastic tubs.

Of course, Merloni was not willing to sacrifice performance in order to use the cheaper material; the tub still had to perform optimally at speeds up to 1,200 rpm. Meticulous simulations and the depth of experience available due to the co-design process were said to have contributed to meeting this goal. The tub does indeed utilize the PP+40%CaCo3, offering a significant competitive advantage, according to Mr. Bongini. He explains, "[With PP+40%CaCo3], the process and the costs are better. Specialized design helps the final product to be as high quality or better [than with PP+30% glass fiber]."

The finished product includes a washing tub and related base made of plastic. The two parts are linked by dampers. Due to this design, the cabinet in the TOP 2001 is said to have limited structural function, allowing a lighter cabinet and easier assembly. These modifications helped achieve the major goal of this project: to achieve the highest performance possible while reducing expenses by using the least amount of material and streamlining assembly.

Meeting this goal was important because every cost savings counts in the very competitive washing machine market. Explains Mr. Montevecchio, "[There is] very strong competition to reduce the cost of the washing unit, [while keeping] high performance. This means the development stage must be very accurate, in order to calculate the best geometry to reach the specifications with the lowest weight." An additional competitive advantage was gained because the entire process took only 18 months - critical timing, according to Mr. Bongini, who says that a shorter time to market was one of the main reasons for embarking on the co-design with Meccanica Generale in the first place.

Positive Results

In this partnership, the co-design approach seemed to produce results. At Merloni, production of the molds is far higher than production of the previous project. This is currently the highest production in the market for this type of mold, according to Mr. Montevecchio.

At Meccanica Generale, the process opened the door for a new focus on providing solutions for its customers. Says Stefano Mancini, Meccanica's Technical Director, "Looking to the future, we have decided to further improve our co-design approach by presenting to our customers innovative solutions and ideas. For this reason, one of the main areas of activity of our Domestic Appliances Technical Team is the Research and Design and Laboratory Test Center."


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