Design Evaluation of a Hand Mixer
(Note: this document was originally written as part of a midterm exam in ESC101. Some ambiguous passages were revised, but most of the text was preserved)
Often in Engineering Design, compromises need to be made to different aspects of the product in order to meet a set of constraints. The M31 hand mixer, manufactured by Proctor-Silex and sold at Canadian Tire under the Traditions brand, is a good example, as its design is constrained by cost and safety considerations.
The design of the mixer emphasizes design for manufacture. The design of the mixer was constrained by its retail price of $10 CDN, so DfM became critically important for reducing costs. The mixer follows many of the DfM guidelines set out by Dieter in his book Engineering Design: a Materials and Processing Approach on page 399. The mixer is only available in white, to take advantage of economies of scale. Its case is made of only 3 injection moulded pieces, as per Dieter's guideline to "minimize total number of parts". Finally, the injection moulded pieces are only shiny on their exterior, and polishing of the inside of the case is not done as it would not contribute aesthetically to the product.
Another aspect of the design that cannot be compromised is safety. Again, according to Dieter, safety can be accomplished by creating a user-friendly product. In the product, the motor speed control and the whisk ejection control is set with one knob: the whisks can only be ejected when the knob is moved away from the "On" positions and past the "Off" position. This prevents the whisks from being ejected when the motor is on, reducing the possibilities of human error. Indeed, the knob is one distinguishing aspect of the design, as signified by the statements advertising it on the packaging.
The presence of the unified knob, however, leads to obvious compromises. In addition to the previously mentioned safety aspect, the knob also plays a role in usability: the knob is placed in the area where the operator's thumb would usually rest, so motor speed and whisk ejection can be performed easily. However, this feature is not suited to design for manufacturability. The ejecting feature operates via springs, which were difficult to place in their correct positions on the base of the device, as our group discovered when attempting to reassemble our mixer. The decision to use one knob for eject and power further complicates this, as stiff wiring had to be attached to the switch, making it even harder to align with the opening on the top halve of the case. Finally, the custom assembly prevents the company from using a standard power switch, and the company had to manufacture a custom knob. This goes against Dieter's rule on DfM that standard components should be used when possible to lower design and manufacturing costs. The knob can be seen as a concession to safety and usability while de-emphasizing manufacturability: significant as the product is designed mainly for low cost, and therefore manufacturability in mind.
One area which is neglected to meet the price constraint is reliability. On the Canadian Tire website, there are reviews which suggest the whisks on the product often corrode after heavy usage. When we examined the whisks, we agreed that they were not designed for durability, as the seams on the metal were exposed, which would allow liquids to enter and cause corrosion to the assembly. The usage of plastic gears also shows a lack of design for durability, as plastic gears are softer than metal gears, and are more likely to be damaged when gears slip. However, it may be noted that the framing of the original designers was for a mixer for infrequent use - and, indeed, many positive reviewers on the website noted that they only used the mixer once a month, which would not require design for durability.
One area of the device that can be improved is its packaging. The packaging is made of thin cardboard and Styrofoam blocks. From a Design for Recyclability standpoint, Styrofoam is not a very good choice, as it is not usually recyclable, even in major cities. Egg carton material is an alternate biodegradable packaging material, so it would be a more suitable choice to meet recycleability. Since egg carton material is often used in the packaging of higher-end devices, manufacturability would not be significantly reduced. While the cost of egg carton material may be greater than Styrofoam, the extra cost may be offset by the marketing power that a claim of eco-friendlyness may bring. While the switch may not agree with the primary goal of manufacturabiity and meeting price constraints, I believe this compromise can help differentiate this mixer from others on the market.
From the design of our Traditions hand mixer, it can be seen that the main goals of the design were manufacurability and safety, but also that some features, such as the knob, were given importance even though they go against economy in manufacturing. I believe that the introduction of biodegradable packaging would be another important improvement that would, like the knob, be worth more in marketing the mixer than the production cost it incurs.