Borin

i love jumperhand

Toasters are commonly used kitchen appliances, and are typically not too expensive to purchase. They can be found at most department stores from anywhere between 6$ to 50$. They are small and compact, and are used to toast or heat slices of bread, and other bread-like foods. There are 3 kinds of toasters; pop-up, toaster oven, and toaster conveyer. For this design project, we will focus on the pop-up toaster. The following study involves analysis of a $10.00 Chefmate toaster which was purchased from Target. In the course of this semester, we may analyze a more expensive toaster to compare what extra features are included for the price. Our hope is to find an innovative way to change current toaster designs, to address some common problems which users complain about most frequently. Our analysis involves studying how the toaster is usually operated and how it works, combined with evaluating the toaster through Design for Manufacture and Assembly (DFMA), Failure Mode Evaluation and Analysis (FMEA), Design for the Environment (DFE), and a quantitative mechanical analysis. Our first steps were to disassemble the toaster, to figure out what parts and components were involved in its operation. We were also able to understand the basics about how each of the parts of the toaster functioned. We categorized all the parts and assemblies, which can be seen in the assembly parts list.

After disassembly, we concluded that there were far too many parts in a toaster. We believe that this makes assembly extremely tedious, and increases the complexity of the product.

The purpose of a toaster is to assist in the making of food. Specifically, if the user wants toasted bread or bagels, warmed up waffles, etc. The toaster provides these functions.

To pictorially explain how a toaster is used, pictures from our usability study were taken to show customer product interaction. Following from that, we will delve into how a toaster actually works. From the outside, one might not think a toaster is a complex piece of equipment, but its internals are actually quite intricate. The inputs to the toaster are:

• 800 Watts of power
• food into the slot
• a toast setting
• a force to activate the latching and heating mechanisms.

With these inputs provided, the activating handle is depressed, which completes two separate circuits:

• First, a circuit is completed which provides power to an electromagnet and the timing circuit, holding the toastee inside the toaster where it can be heated.
• The second circuit that is completed is the heating circuit. A current is run through high resistance Nichrome wire, creating heat.

The timing system works as such:

• The variable resistor (regulator knob) controls current to a capacitor, regulating its charge rate. As soon as the capacitor reaches its maximum voltage, it discharges and breaks the power to the electromagnet.
• A spring then pulls the bread holder and toastee back up to where it can be safely removed from the toaster.
• As the spring pulls up the bread tray, the mechanism breaks the heating circuit.

Thus, the outputs of the toaster are heat and warmed food.

The toaster is manufactured using several different processes. The main two process used are injection molding and stamping. Extrusion, deep draw methods, and an hydraulic press were also used.

Exterior of Toaster -
The case, bottom, and user interface of the toaster were all injection molded. Although injection molding is an expensive process due to its high price equipment and molds, with the toaster it is probably a good option. With the number of toasters being made and the consistency of the toaster design, the mold for a toaster is more than paid for. There are probably three different injection molds for this product: one mold for the case, one for the bottom, and one for the various buttons and knobs on the user interface. This combination of multiple parts in one mold is allowable due to the small size of the various parts and the lack of detail needed for each part. The shape of each of these parts were designed to be most efficient for injection molding. The bottom, which consists of many slots or vents, is the most complex of the shapes and is made up for this by having four locations that the plastic is injected.

Exterior Metal Slots-
The slots of the toaster was made through a deep draw process. This is a special type of stamping that gives radial stress to the flanges of the metal, and allows it to be stretched radially as well linearly. This gives the metal a rounder finish, making it look more complete and attractive. This process was used only for the exterior metal on the slots for the toaster. Its purpose was to make the toaster attractive. Although this process is more expensive than just stamping and bending metal, in mass quantities the cost is not unreasonable. This process in the toaster manufacturing could definitely be taken out, but it would also hinder the quality and attractiveness of the product.

Interior Metal Plates and strips-
The metal in the interior of the toaster was all stamped and bent. This is an easy process which uses sheet metal and then stamps out the shape of the metal needed. All unused sections of sheet metal can then be re-melted and used again. This is a very cost-effective method of manufacturing. You start of with the sheet metal, cut it in to shape by stamping it and then bend it to give it more strength and durability. This process is easy, low time, and easy to automate.

Metal Rods and Wires-
All of the metal rods and wires in the toaster were made through metal extrusion. Where metal is heated and then pushed through a die to its desired shape. This process is easy to do, and it is cost-efficient as while extruding the pieces can be easily cut to their desired length. This creates very little waste in material and makes the whole process extremely quick.

Mica Sheets-
Mica is a great insulator and hard to burn. Thus is a great choice to contact the heating wires and insulate the various circuits and wires. In order to produce mica sheets, mica is ground fine and mixed with a colloid agent and water. A single sheet of uniform thickness is formed by pouring the mixture onto a mesh screen. Vacuum means and a hydraulic press are used to complete the formation of a sheet. Mica is not inexpensive, but its special properties make it a extremely valuable material, its used in a wide variance of products from dry wall to cosmetics for this reason. In this product's case, due to the restraints of needing an insulation, structure, and resistance to heat, mica was a perfect choice.

If you look at the toaster as a whole, you realize that the toaster was manufactured the way it was to try to optimize time, efficiency, and cost. They made some sacrifices in the manufacture for aesthetic appeal, by deep drawing the metal plate on top of the toaster. One problem with the design for manufacture is the number of parts needed to make a toaster. Since there are so many parts, many different processes are needed to be used to make them all. You have extrusion of metal and plastic (electrical wiring), stamping, press, injection molding, and all the electrical components. This gets expensive in the amount of machinery and tools needed, and how much time it takes. Even though there were so many parts, looking at all the different individual choices it is obvious that each part was made in the optimal way, looking at time and cost. Thus even though there are many parts, each was made as well as it possibly could.

The toaster is designed to be assembled by hand. It is made in China, where labor is cheap, and its parts were designed to allow easy and quick assembly.

Each of the metal plates in the entire were connected together with a series of tabs. The plates connected together when the tabs fit into small slots and were then folded over by hand. This allowed the plates to be easily and quickly adhered together. The one problem is that is it requires a lot of tedious work for the laborer. It was easy to see that different people worked on the tabs on our toaster, as different tabs were folded dramatically different for each plate.

There were also holes punched into the metal plates to allow for easy assembly of having either rods, wires, or metal pieces fit easily through a space into their correct location. This once again was optimized for hands-on assembly. As you can see from the picture below, this design was even incorporated for somewhat complex shapes and assembly to quicken the process and keep it accurate. This step, though most likely still quite challenging, has been helped a lot by this step. It allows the bread shelf to be assembled later on in the process (allowing other components to be placed first) while being able to reach its position easier than before.

The injection molded bottom had some built in slots that the circuit boards easily slipped into, making the circuit board addition a last minute process. All that needed to be done was to slide them in, connect the two boards together, and solder the wires to the leads. The stamped metal insides were also able to be slid into place, to secure the toasting cavity to the toaster base.

The hardest part of the assembly is probably trying to put in the mica sheets and wires into the stamped metal area. This requires sliding the mica sheets down while threading the wires at the same time. The toaster did a good job of organizing the assembly process so that there was little obstruction and everything was reachable.

Looking at the whole assembly process, the toaster has a lot of parts to put together. Automating more of this process would be beneficial for time and getting rid of labor. This would also increase costs due to machinery and maintenance. Although the toaster is made entirely by hand, the parts were designed to limit the laborer to easy tasks, improving time and reliability of the assembly.

Putting a slice of bread in the toaster, one does not often think about the environmental implications this act may have: “What steps were taken to enable this toaster to arrive on my countertop, how much power is it using while toasting, and what will happen to it after it I throw it away?” Delving into the life cycle of a toaster, we see that there is much room for improvement.

While nearly all the materials in the toaster are recyclable, due to the complex nature of a toaster, it is costly to fully recycle one. Thus, toasters generally end up in landfills at the end of their lives.

However, the key element in the life cycle of this appliance is energy. In both the production and use phases of a toaster, power generation and supply is the overwhelming contributor of greenhouse gas emissions. This seems fairly straightforward for the use end – in use, toasters produce little more than heat, from electrical power, and (hopefully) golden brown toast – but this may come as a surprise for the manufacturing end. Indeed, power generation and supply produces nearly four times as much CO2-equivalent than the nearest sectors, truck transportation and steel mills, during the manufacturing of such appliances.

Using the EIO-LCA software from Carnegie Mellon University’s Green Design Institute (results pictured below), we see that every $1,000,000 of production in the ‘Electric housewares and household fans’ sector produces 693 MTCO2E. Given our $10 toaster, this shows us that approximately 0.007 MTCO2E caused by the manufacturing of one toaster. To compare that to the use end, a simple calculation is done:

From the EIO-LCA, we see that for every $1,000,000 of production in the ‘Power generation and supply’ sector, 10500 MTCO2E are emitted. Assuming: $0.10/kWh electricity cost, power consumption is 800W, usage is 3 min (0.05hr) per day, used 300 days out of the year, over the course of a 4 year use-life.

We see that it would cost approximately $4.80 to run this toaster over the course of its life. Given this information, it is seen that the use phase of a toaster’s life emits approximately 0.050 MTCO2E. This is an entire order of magnitude higher than the emissions production phase. Clearly, one of our assumptions, above, needs to be modified. The only option which may not impact the functionality and longevity of the toaster is the power consumption. Furthermore, looking at other toasters, we see that this 800W usage is on the low end of the spectrum. All residential toasters use the same heating method – running current through a filament, which generates heat.

The results for conventional air pollutants, such as SO2, NOx, and CO, show the same result: power generation, both for the creation and use of a toaster, is the largest contributor to harmful emissions.

The numerical results of GHG emissions, above, come with a good level of confidence. Though there are many sub-sectors of the ‘Electric housewares and household fans’ segment, the ‘Small electric household cooking appliances’ sub-sector represents nearly 1/3 of the overall sector.

From our analysis, it appears the best way to approach the DFE is to reduce the power consumption of a toaster. Perhaps an alternative heating method should be considered. A more realistic and attainable possibility is to better insulate the toasting area, as to reduce the amount of heat lost during the toasting process. Also, reducing the complexity of a toaster would increase its potential to be recycled, further reducing its environmental footprint.