by Michael Paloian, President, Integrated Design Systems
Mike Paloian is an acomplished designer, inventor, lecturer and educator. Integrated Design Systems Inc. (IDS), is an award-winning industrial design firm with practical expertise in medical, analytical and testing, and plastic display and plastic product design. Mr. Paloian serves as Chairman, Product Design & Development for the Society of Plastics Engineers. He is a faculty member, Plastics Engineering, University of Massachusetts Lowell, and a Contributing Design Editor, RotoWorld Magazine.
Better Plastic Design Challenge:
Rethink the Commercial Dishwasher
How to Design a Non-traditional Solution for a Better Conventional Product
New markets for rotational molding—and plastic design in particular—are being uncovered every day. The versatility of the process continues to benefit manufacturers in ever more challenging applications. Forward-thinking designers and molders who are always pushing the boundaries of the process typically develop exciting new opportunities in plastic design.
Solar Plastics, headed by Chuck Carlsen, is a forward-thinking molding company. This firm has successfully introduced the benefits of rotational molding to numerous companies in a wide range of new markets. This dynamic business philosophy is the reason Solar Plastics remains a leader in the industry.
Peers recognize Mr. Carlsen as a progressive, market-savvy individual. He develops new opportunities through design, processing expertise and cost competitiveness in compelling presentations tailored to prospective customers. He frequently partners with outside design firms to introduce fresh ideas to companies who have been entrenched in the same production methods for decades.
The synergy derived from innovative plastic design concepts, combined with proprietary technological capabilities, enables Solar Plastics to penetrate lucrative and untapped markets that are typically beyond the mainstream of conventional plastic design rotational molders.
This case study provides an excellent example of how this marketing philosophy was applied to a revolutionary new design for a surprisingly conventional product: a commercial dishwasher.
A few years ago Mr. Carlsen invited me to participate in the development of a rotationally molded commercial dishwasher. Most commercial dishwashers are constructed from stainless steel. They are designed to withstand harsh environments, constant use, serious abuse, and deliver reliability with quick cycles of less than two minutes per run. Unlike consumer dishwashers, function overrides appearance. Efficient use of detergents, ease of cleaning and low water consumption are additional requirements.
These are some of the reasons that stainless steel has traditionally been the choice of material for commercial dishwashers. However, despite their rugged design and construction, commercial dishwashers experience chronic problems that require costly field maintenance repairs. The many parts and high labor content inherent in each unit, as shown in Figure 2, cause most premature failures.
Although the primary objective of the project was to design a washer to reduce overall manufactured cost, improvements in appearance, added functionality and improved reliability were also major project goals.
Our first priority was to define product requirements. These criteria were to be prioritized based on cost, risk, and level of importance. This project was only developed to a conceptual level, which provided enough information to verify the feasibility of the design and associated costs. The remainder of this article will describe the design evolution during each phase of development.
Phase 1 – Information Gathering, Technical Feasibility Study and Product Specifications
The project was initiated with a research phase dedicated to accumulating and organizing information critical to the design of the product.
CAD files, documents and drawings of all purchased parts: An assembly of all major components was modeled in a 3D CAD file which established a foundation for all subsequent design and development throughout the remainder of the project as shown in Figure 3.
Exact height and specifications for work surfaces: Standard height ranges for the dish rack tables were also documented to set the optimum height and dimensions for the new washer as shown in Figure 4.
Codes and industry standards including NSF: Codes and international standards specifically affecting the washer were also documented.
Installation procedure: The installation procedure was meticulously documented with videos, photographs and comments from installers. This information enabled us to design the optimum product configuration to minimize installation time.
Shipping and handling: Shipping and handling of the dishwasher were documented to identify opportunities for improving packing, storage, inventory control, transportation and delivery.
Environments of use: Photographs and floor plans of commercial kitchens were gathered to ensure that the new dishwasher design would be compliant with typical plumbing and special settings as shown in Figure 5.
Product use/Human Factors: Videos recording the current dishwasher during the loading of various size plates, glasses, and utensils were documented. Operation of doors, insertion, and removal of dish racks as well as abuse was also recorded to optimize human factors in design considerations.
Refurbishing: Our design team also documented the frequency and replacement cost associated with washer components. This information was used to determine the break-even point for possibly higher costing components with improved reliability.
In addition to identifying overall product requirements, we also documented important engineering parameters affected by material and process selection. The differences between the traditionally used stainless steel and polyethylene required us to carefully examine many physical properties associated with the latter.
Temperature: Since the heat distortion temperature of polyethylene ranges from 135 F to 155 F, thermal tests were conducted to verify its performance in this application. The normal operating range for commercial washers ranged from 140F to 170F within a 90 sec. wash cycle. Solar Plastics agreed to conduct preliminary tests with rotationally molded door panels using a prototype mold. The test panels were used in place of the current stainless steel panels to verify performance as shown in Figure 6.
Creep: Long term creep (permanent deformation under load) was also another critical physical property to examine. Since time, temperature and stress level affect creep rate, long time periods for testing were planned to attain accurate results. Areas of the washer subjected to constant stress included the motor, door counterbalance, washbasin and drain pan as shown in Figure 7.
Environmental stress cracking: Environmental stress cracking or ESC is also a time-dependent phenomenon affected by chemical concentration, temperature and stress. Susceptibility to ESC was determined with published data as well as testing of specific chemicals on samples of polyethylene.
Ultraviolet light stability: Since dishwashers are typically exposed to extensive amounts of UV light emitted from fluorescent lights as well as light passing through windows, UV stability was included as a material specification.
Flammability rating: Flame-retardants were also specified in the material properties to minimize fire risks.
Rigidity: One of our foremost concerns was rigidity since the modulus of polyethylene is about .5% that of stainless steel. To offset this vast difference, we compensated with structural design features that optimized the design for polyethylene.
Impact strength: Generous radii, avoidance of sharp notches and inclusion of contours were applied where ever possible to maximize impact strength.
Tolerances:Careful considerations for tolerances were conducted with Solar Plastics to assure that parts could reliably be molded within specifications. Critical parameters included flatness, part-to-part dimensions and twist.
Thermal expansion: Differential thermal expansion was also investigated due to polyethylene’s relatively high coefficient of thermal expansion. Thermal expansion would have contributed toward warpage and interference between close tolerance parts causing binding.
During this first phase, our design team also investigated the preliminary economic feasibility of a rotationally molded commercial dishwasher based on a true overall product life cost accounting for the average NPV costs of the following:
- Basic costs including materials and labor to assemble
- Amortization of initial investment including development, testing and tooling. This cost will be a function of units manufactured in a given period of time-based on NPV
- Installation and removal costs
- Shipping costs for initial installation and removal
- Service and maintenance costs including parts and labor
- Refurbishing costs
This information was compiled in a product specification report that was referenced for the remainder of the design project.
Phase 2 – Concept Development
The second phase was dedicated to developing viable concepts for the washer based on the specifications defined in Phase 1. This phase included the following tasks.
- Assembly of all major components of the dishwasher in a 3D CAD file used as the basis for the overall structural design
- Alternative design possibilities and variations based on alternative manufacturing methods were explored
- We evaluated each concept based on the overall design, product specifications, investments, costs and risks
- Develop a viable design and prototype to verify the concept
Our design team developed numerous options based on a wide range of ideas and a combination of materials and processing methods. In addition, to satisfy the practical product requirements, we were also searching for a design that could provide our client with a new image. This would be an image to reinforce their well-established brand identity. Product branding is conveyed with a readily identifiable overall appearance as well as details pertaining to surface contours, handles, graphics and colors.
Following are examples of the many concepts developed for the rotationally molded washer and a brief description of each.
- The concept illustrated in Figure 8depicts an evolutionary design based on the original sheet metal washer. It consisted of four extruded aluminum corner posts which were bolted to three rotationally molded sections; a lower support platform, a middle washbasin and a top roof. The four walls surrounding the wash chamber would be fabricated in either stainless steel or plastic sheet. Internal plumbing was to be integrated within the rotationally molded walls whenever possible.
- An alternative design shown in Figure 9 illustrates a concept based on a different principle of operation for the three-sided sliding doors. Instead of moving three separate panels in precisely aligned tracks like the current stainless steel washer, this design proposed a single folded three-sided stainless steel chamber. The one-piece chamber would be capped with an injection molded top cover and would include a set of rollers at the rear. The rollers would run in a pair of tracks within the rear stainless steel sheet metal wall. A rotationally molded washbasin and lower support platform consolidated numerous parts for the two most complicated assemblies of the washer. Tubular legs and miscellaneous hardware completed the remainder of the assembly.
- Figure 10 represented a design based on greater consolidation of parts. It included a one-piece rotationally molded lower platform with integral legs, an upper wash basin/rear wall component and a one-piece, three-walled sliding chamber door that would track along the rear wall. This concept was a major departure from the current sheet metal design with a minimum number of parts. Although the design was a bit too ambitious for rotational molding, it did provide many good ideas for the next iteration.
- Figure 11 represented a concept based on the culmination of all the work and evolutionary improvements that preceded it. This design maintained a balance of minimizing the number of parts with technological limitations of rotational molding. The rear wall was designed as a one-piece rotationally molded structure that would include a track for the sliding one-piece door assembly as well as providing rear legs. A one-piece multifunctional wash basin/lower platform included features for supporting the motor as well as many other components, including the front legs. The sliding one-piece door was designed for rotational molding.
This summary of concepts was selected from the countless design iterations to convey the thought process and development that took place in this project. A final design was ultimately derived and detailed in the next phase.
Phase 3- Design Refinement Preliminary Prototype and Cost Analysis
The last concept developed in the previous phase was further refined in the third phase. Tasks in this design phase paid closer attention to product details in appearance, shipping, graphics, color, handle design and function. A partial functional prototype was also constructed to validate the design for a counterbalanced door mechanism based on a one-piece rotationally molded door. Refined cost estimates for tooling and parts were summarized based on CAD files of the completed assembly. A comparative cost of the newly proposed design and the current washer was finally consolidated in a detailed spreadsheet.
Review of the Final Design Concept
The final design proposal is shown in Figure 12 was derived from a combination of ideas developed in the previous concepts. Major sections of the washer were designed for rotational molding with the exception of a tubular metal handle wrapping around the sliding chamber door. Colors and graphics were specified to comply with corporate standards for enhanced product branding. Clean lines, smooth surfaces and minimal crevices yielded a washer that could easily be sanitized. Rotational molding eliminated all of the sharp edges, brackets, hardware, and springs in the previous stainless washer.
Access to the inner chamber was easily attained with the one-piece rotationally molded door which could conveniently be lifted as illustrated in Figure 13. Standard stainless steel work surfaces could easily be assembled in right angle or straight configurations in relation to the washer providing maximum versatility for any commercial kitchen as shown in Figure 14.
Troughs for routing tie-wrapped bundles of wires and tubing were integrated into the molded parts. These arteries provided a convenient means of distributing, protecting and isolating delicate electrical cables. The vertical trough in the rear wall provided a channel for electrical wires and tubing to be guided down the rear of the unit to the underside of the tub.
Parts were consolidated with molded-in features. This provided support for the motor, solenoids, containers and control box components. Fewer parts equated to faster assembly, lower production costs and higher reliability.
The blue handle wrapping around the sliding one-piece door also provided additional rigidity and dimensional stability by limiting flexing. The counterweight sliding within the rear wall was attached to the handle as shown in Figure 15.
Lap joints were molded into the door panels and washbasin to contain water as shown in Figure 16. Additional parts consolidation was achieved by integrating a roller assembly into each side of the chamber door/hood. Specification of roller bearings on either side of the door assembly minimized friction while accommodating a wide tolerance range as shown in Figure 16.
Since this design was a significant departure from the original sheet metal washer, a prototype was fabricated to verify its viability.
A special prototype design was developed specifically to test the roller system. Figure 20 illustrates CAD files for the simple low-cost design evaluation prototype. This prototype was constructed to determine maximum tolerance allowances for the roller system as well as its overall performance. Prototype costs and complexity were minimized limiting the design to a welded frame and fabricated designed rear wall that simulated the rotationally plastic design molded part. The actual prototype is shown in Figure 18 was tested and verified to function as expected, thus establishing the necessary confidence in the proposed concept.
Final Cost Analysis and Part Count
At the conclusion of this project, our client was presented with a comprehensive presentation. This included an analysis of the final concept based on the following information:
- Review Tooling Budget.Part Cost, Lead Times. An analysis of projected sales versus tooling budget, amortization and number of parts was completed for final product design as illustrated in the exploded view in Figure 19.
- Review Servicing Requirements. Design details pertaining to each subassembly were reviewed based on ease of access during field service. This information influenced how parts are designed, manufactured, and assembled.
- Review Manufacturing and Assembly issues. Parameters pertaining to assembly steps, preferences, testing procedures, and overall production methods were reviewed for specific subassemblies. A summary of the assembly is illustrated in the sequence of pictures shown in Figure 20.
Conclusion and Final Decision
After reviewing the comparative costs and trade-offs between the existing sheet metal versus the proposed rotationally molded design, our client decided to remain with the former. This decision was based on a number of reasons. One major factor was China. Management compared the costs of manufacturing the rotationally molded unit domestically versus manufacturing the sheet metal unit in China.
Another factor that influenced the final decision was the costing methods used to evaluate the comparative costs. Unfortunately, the cost analysis was based on a bill of materials cost, burdened with arbitrary labor and overhead cost. These factors imposed a significant disadvantage to the rotationally molded washer. In addition to cost, marketing had reservations about the perception of a plastic washer into a market that was so heavily accustomed to stainless steel. Unlike the consumer market, commercial institutions are traditional and slow to accept change.
It is the author’s opinion that the final design satisfied all of the original design objectives, especially lowering cost. Unfortunately, the cost analysis did not account for many of the typically overlooked costs such as reliability, labor, shipping, assembly and service.
In addition, the question of customer acceptance for a plastic commercial dishwasher was not adequately addressed. Stainless steel details could have been added to the proposed design to lower the barrier of potential customer resistance to new materials. Since this design project demonstrated so many positive benefits of rotational molding for a very demanding application, it may provide an inspiration for others to find new markets for this versatile process.
With 30-plus years of professional experience, Mike Paloian is a designer, inventor, lecturer and educator. His firm, Integrated Design Systems Inc. (IDS), is an award-winning industrial design firm with practical expertise in medical, analytical and testing, and plastic product design. The company is known for designs optimized for the end user and human factors—with award-winning aesthetics, superior functionality and minimal cost. Integrated Design Systems has been recognized by the IDSA, ID Magazine, SPI, and SPE for design excellence.
Michael Paloian serves as Chairman, SPE PD3 (Product Design & Development) for the Society of Plastics Engineers; he is a faculty member, Plastics Engineering, University of Massachusetts Lowell, and a Contributing Design Editor, RotoWorld Magazine. He holds an undergraduate degree in Plastics Engineering and a Master of Industrial Design degree.