Doughnut maker

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Revision as of 15:50, 20 September 2009

1 Executive Summary
2 Bill of Materials
3 Major Stakeholders and Needs
4 Usage and Usability
5 Mechanical Function
6 Design for Manufacturing and Assembly (DFMA)
- 6.1 Design for Manufacturing (DFM)
- 6.2 Design for Assembly (DFA)
7 Failure Modes and Effects Analysis (FMEA)
8 Design for Environment (DFE)
9 Mechanical Analysis
10 Team Members & Roles
11 References

Executive Summary

Bill of Materials

Main Components

Dough Dispenser Cup Assembly
Part Number	Name	QTY	Weight (g)	Function	Material	Manufacturing Process	Image
001	Dispenser spring	1	1	Keeps dispenser closed when not in use	Steel	bending
002	Dispenser support	1	19	Guides the plunger for straight release	Plastic	Injection molding
003	Dispenser plunger	1	9	Pushes the dough from the cup into the machine	Plastic	Injection molding
004	Dispenser funnel	1	27	Guides the dough to the hole in the cup	Plastic	Injection molding
005	Dispenser stop	1	4	Stops the dough from leaving dispenser and gives the doughnut its "hole"	Plastic	Injection molding
006	Dispenser cup	1	122	Holds the dough for dispensing	Plastic	Injection molding
Dispenser Motor and Conveyer Motor Assembly
Part Number	Name	QTY	Weight (g)	Function	Material	Manufacturing Process	Image
007	Doughnut Dispenser Motor Casing	1	23	Covers and protects the two switches connected to the housing	Plastic	Injection molding
008	Dispenser motor	1	204	Drives the dispenser assembly	N/A	Purchased part
009	Motor rotational output	1	4	Connects to the motor and rotates with it	Plastic	Injection molding
010	Dispenser motor guide	1	11	Moved by motor to push the dispenser spring down	Plastic	Injection molding
011	Dispenser motor housing	1	113	Houses and protects the dispenser motor assembly	Plastic	Injection molding
012	Dispenser motor switch 1	1	5	Alerts for dough release	N/A	Purchased part
013	Dispenser motor switch 2	1	5	Halts the dispensing process	N/A	Purchased part
014	Dispenser switch housing	1	4	Positions switch to alert for dough release	Plastic	Injection molding
015	Capacitor	2	5	Stores electrical charge	N/A	Purchased part
016	Doughnut dispenser motor cover	1	52	Gives access to and protects the motor	Plastic	Injection molding
017	Dispenser motor latch	1	4	Secures and aligns the motor dispenser assembly	Plastic	Injection molding
018	Conveyor belt motor	1	219	Drives the conveyor belt assembly	N/A	Purchased part
019	Drive gear 2	1	4	Moved by the motor and translates motion to conveyor gear	Plastic	Injection molding
020	Conveyor motor switch 1	2	23	Connects and controls dials	N/A	Purchased part
021	Motor switch holder	1	10	Holds the switch and cradles the motor	Plastic	Injection molding
022	Adjustment Knob	2	6	Used to open and close the oil drain.	Plastic	Injection molding
023	Wire guide	1	0.5	Secures wires to housing	Steel	Stamping
024	Power jack	1	15	Connects to power cord	N/A	Purchased part
025	Power jack housing	1	5	Covers and protects the power jack	Plastic	Injection molding
Conveyor Belt Assembly
Part Number	Name	QTY	Weight (g)	Function	Material	Manufacturing Process	Image
026	Belt motor gear	1	14	Translates motion from motor to conveyor belt	Plastic	Injection molding
027	Conveyor belt link assembly (60 links with 60 rivets)	1	123	Driven by the motor to move doughnuts through system.	Plastic	Injection molding
027	Release link	4	1	Alerts the motor to release the dough	Plastic	Injection molding
028	Doughnut carriage	4	22	Used to carry doughnuts through the system during operation	Aluminum alloy	Punching then Stamping then Welding
028	Doughnut carriage arm	4	5	Connects carriage to conveyor belt	Plastic	Injection molding
029	Conveyer belt holder	2	0.5	Guides and supports the conveyor system in its cycle	Plastic	Injection molding
030	Conveyor belt gear (doughnut side)	1	85	Rotates and moves conveyor belt system	Plastic	Injection molding
031	Conveyor belt gear (dough side)	1	109	Rotates and moves conveyor belt system	Plastic	Injection molding
032	Belt gear washers, thick	2	5	Holds belt gears in place	Steel	Punching
033	Belt gear washers, thin	2	2	Separates the belt gear from back housing	Steel	Punching
034	Belt guides	2	14	Guides the belt on lower portion of the cycle	Plastic	Injection molding
035	Yellow Washer, belt guide	3	0.25	Separates the belt guide from housing	Plastic	Injection molding
Oil System Assembly
Part Number	Name	QTY	Weight (g)	Function	Material	Manufacturing Process	Image
036	Doughnut flipper	1	10	Flips donuts to opposite side	Steel	Cut then drawn
	Oil bath tub	1	313	Fills with oil and becomes very hot.	Aluminum Alloy	Drawing then cutting
	Oil bath heating unit	1	313	Causes the oil bath tub to become hot.	N/A	Purchased part
037	Oil bath supports	4	6	Holds the oil bath in place	Plastic	Injection molding
038	Temperature controller bracket	1	13	Connects heating element to the oil bath	Steel	Stamping
039	Temperature controller	1	20	Regulates the heating element	N/A	Purchased part
040	Knob housing	1	32	Protects oil drain components and user	Plastic	Injection molding
041	Drain switch cover	1	12	Protects from accidentally enabling the drain switch	Plastic	Injection molding
042	Adjustment Knob	1	6	Used to open and close the oil drain.	Plastic	Injection molding
043	Dial connector	1	3	Translates knob movement through the housing	Plastic	Injection molding
044	Drain lever	1	6	Used for securing switch in both positions	Plastic	Injection molding
045	Oil drain valve mount	1	4	Mounts the drain in appropriate location	Plastic	Injection molding
046	Oil drain valve	1	33	Controls the flow of the oil	Brass	Purchased part
047	Oil drain tube	1	2	Channels the flow of the oil	Rubber	Purchased part
048	Oil drain tube clamp	2	.5	Secures the tube onto the valve and drain	Steel	Purchased part
049	Oil collection tray	1	237	Collects the oil that drains after use	Plastic	Injection molding
050	Oil collection tray guide	1	7	Guides the oil collection tray into place.	Plastic	Injection molding
Exterior Panel Assembly
Part Number	Name	QTY	Weight (g)	Function	Material	Manufacturing Process	Image
051	Front panel	1	1160	Protects the inside machinery from the outside	Plastic	Injection molding
052	Back panel	1	1160	Protects the inside machinery from the outside	Plastic	Injection molding
053	Top window 1	1	55	Allows heat to escape when opened during production	Plastic	Injection molding
054	Top window 2	1	123	Cannot be opened. Allows user to view doughnut production	Plastic	Injection molding
Miscellaneous Components
Part Number	Name	QTY	Weight (g)	Function	Material	Manufacturing Process	Image
055	Power cord	1	107	Connects to the outlet and supplies power to the machine	N/A	Purchased part
056	Measuring cup	1	27	Used to measure out correct amount of ingredients	Plastic	Injection molding
057	Doughnut slide	1	36	Removes doughnut from machine and into the doughnut bin	Plastic	Injection molding
058	Doughnut bin with oil drain	1	100	Collects doughnuts after production and drains oil off doughnuts after production	Plastic	Injection molding
059	Doughnut cover feet	4	3	Contacts surface	Plastic	Injection molding

Additional Parts

Screws

Nuts and Washers

Assembly Diagrams

Dough Dispenser Cup Assembly

Dispenser Motor and Conveyor Motor Assembly
NOTE: P/N 016 and P/N 017 Not Shown
NOTE: P/N 021, P/N 022, P/N 023 and P/N 024 Not Shown
Dispenser Motor and Conveyor Motor Assembly Schematic

Conveyor Belt Assembly
NOTE: P/N 033 Not Shown
Cooking Oil Assembly
NOTE: P/N 041, P/N 042, P/N 043 and P/N 050 Not Shown
Exterior Panel Assembly

Major Stakeholders and Needs

Consumer

Ease of use - The product must be easy to assemble after purchase and must be easy to operate.
Ease of cleaning/maintenance - It must be easy to clean the product after use and to maintain or repair the product if something is to malfunction.
Effectiveness - The quality of the doughnuts produced should be satisfactory.
Efficiency of operation - The product must work quickly and efficiently.
Safety - There should be no safety hazards associated with the operation of the product, including potential risks to children that may be using or near the product.
Cost - The doughnut maker should be affordable and be priced reasonably for its function and quality.
Reliability/Consistancy of function - The product must work correctly and consistantly.
Portability - The product should be relatively small and light weight such that it is easy to move and carry.
Ease of storage - The product must be compact and easy to store when not in use.
Aesthetics - The doughnut maker should be pleasing to look at.

Retailer

Ease of shipping/storage - Small size, light weight, and standardization are important. The product should be easily stacked and easily moved.
Customer satisfaction - The reliability and quality of the product are essential to there being few returns of the product.
Cost/profit margin - The sale of the product should be profitable for the retailer.
Customer appeal - The customers should want to purchase the product, so it should have appealing features and good reviews on functionality and reliability.

Manufacturer

Material cost - The materials should be low in cost but of sufficient quality to keep the price reasonable.
Manufacturing cost - There should be fairly low manufacturing costs, so the manufacturing methods used should be appropriate for the desired shape and quality of each part.
Complexity - There should be few parts and few different materials to reduce the cost of manufacturing by reducing the number of different manufacturing methods required. This will also make assembly easier and faster.
Standardization - Repeated parts, such as screws, should be standardized whenever possible to reduce complexity.
Ease of assembly - There should be few different tools necessary, and assembly should be simple.
Speed of production/assembly - There should be few enough parts and enough simplicity to allow for quick and efficient assembly.
Ease of packing - The product should be easy to pack for safe shipping and storage.

Shipping/delivery companies

Weight - The product should be light in weight to make moving the product easier and shipping less costly.
Size - The size should be such that the product is easily carried and easily stored, prefferably in such a way that many can be stored in a small area.
Durability - The product should be durable enough that the shipping process will not damage it.

Usage and Usability

A user study was performed in which the doughnut maker was used and analyzed in terms of how easy it was to use and how well it worked. The different steps of using the product are discussed one by one.

Making the dough

The doughnut maker instructions come with three recipes that the directions claim will work with the doughnut maker. These recipes are designed to produce dough with the correct viscocity and other physical properties to allow the dough to flow properly from the dough dispenser (P/N 001-006) and cook correctly at the set temperature and in the amount of time that the machine leaves them in the hot oil.
It was found that even after following the directions exaclty in making the dough, it would not properly flow from the dough dispenser. The doughnuts would not be the correct shape, but would be small and irregular. Also, the doughnuts would occationally not be cooked well enough for the doughnut flipper (P/N 036), and would be squished by it instead of being flipped.

Preparing the machine for use

The instructions call for several parts of the machine to be cleaned before use, namely the parts that can be easily removed from the machine. These parts include the dough dispenser, doughnut slide (P/N 057), doughnut bin (P/N 058), and oil collection tray (P/N 049). The user must also make sure that the oil drain is closed (P/N 046), the oil collection tray is in place, the doughnut slide is open, and the doughnut bin is in place. The machine is then plugged in, the oil bath (P/N 036) is filled, and the machine is set to pre-heat the oil.
It was found that a few of the parts were somewhat difficult to remove and clean. The doughnut slide was hard to detatch from the machine, and the dough dispenser had to be further disassembled after its removal from the doughnut maker. The method of disassembly for the dough dispenser was not obvious, and it could easily be reassembled incorrectly.

Filling the dough dispenser

The dough dispenser must be filled by rotating the dispenser motor subassembly to the side, filling the dispenser cup (P/N 006), cleaning off any dough that may have gotten on the rim of the dispenser cup or the top of the dispenser plunger (P/N 003), and then rotating the motor subassembly back into place.
Filling the dough dispenser without spilling dough was found to be very difficult. There was no good place to pour the dough such that it would simply go to the bottom of the cup, but rather the dough often spilled onto the top of the plunger or the sides of the machine.

Letting the machine run

The doughnut maker is supposed to run by itself, creating one doughnut per minute and eventually producing 18-20 dozen mini doughnuts for each batch of dough, according to the given recipes.
There were several problems encountered with letting the machine run on its own, such as the fact that the doughnuts absorb the cooking oil, so the oil level must be monitored and periodically refilled. However, while the initial amount of oil was specified, the markings on the oil bath showing the level that should be maintained are very hard to see. Also, at a speed of one doughnut per minute, the machine takes several hours to complete operation. Overall, it was found that because of all of the periodic problems, the user had to almost constantly attend to the machine over its several hour operation. Other problems are detailed in the specific sections of operation below.

Dough leaving the dough dispenser

When the dough dispenser dispenses a doughnut, the dispenser motor turns on for a few seconds and pushes down the dispenser plunger to allow the dough to run out of the bottom of the dispenser and around the cone-shaped dispenser stop (P/N 005) by gravity to create the doughnut shape.
It was found that, as previously stated, the dough did not flow properly from the dispenser and often created small and irregular doughnuts. Also, the dispenser cup had to be refilled occationally, so the user must attend to this during the operation. After these observations were made, it was necessary to move the dispensor motor subassembly to the side and press down the dispenser plunger by hand in order to observe the effects of the rest of the machine on a properly sized doughnut. Also, the dough at the bottom of the dispenser would often get slightly cooked due to the heat of the oil below and clog the dispenser.

Doughnut carriage and flipping mechanism

The doughnut is pushed toward the doughnut flipper mechanism by the front end of the doughnut carriage (P/N 028). The flipper then grabs the doughnut and holds it while the carriage moves such that the doughnut is flipped over a small edge near the front of the carriage and lands in the large back end of the carriage.
The doughnut flipper worked very inconsistantly. It would occationally squish the doughnut rather than flipping it if it was a particularly large doughnut and got to this point relatively undercooked. On the other hand, it would simply scrape the uncooked top of the doughnut if it was small. Even when the doughnut flipper mechanism did manage to flip the doughnut, the undercooked side would often get stuck to the flipping edge on the carriage such that the doughnut would not sit low enough in the oil to cook properly. It was often necessary to reach into the machine through the top window (P/N 053) to correct the problem with a fork.

Doughnut slide

At the end of the cycle, the carriage lifts the doughnut out of the oil and rotates as it moves forward such that the doughnut falls from the carriage and onto the slide and finally out into the doughnut bin.
While this part often worked properly, there were several problems. First of all, if the doughnut was too small, such as the irregular doughnuts created by independant operation of the dough dispenser, they would often fall short of the doughnut slide and end up in the oil collection tray at the bottom of the machine. Also, if the doughnut happened to fall more to one side, the slide was too narrow and the doughnut would miss. When this happened, the doughnut would either land in the oil collection tray or to the side of it in the bottom of the machine, as there is a large gap for the doughnuts to fall through.

Stopping operation and cleaning

To end operation, the user must turn the dispenser and conveyor adjustment knob and the heater adjustment knob (P/N 042) to off and unplug the machine. The instructions call for the machine to be allowed an hour to cool before opening the oil drain and cleaning the machine. To clean the doughnut maker, the user must remove the oil collection tray, the top windows (P/N 053-054), the dough dispenser, doughnut slide, and doughnut bin and clean them in warm soapy water. The oil bath can be wiped with a dry paper towel, and the exterior should be wiped clean. The whole doughnut maker can be tilted over a garbage can at this point to remove any dough that may have fallen into the bottom of the machine. Finally, the doughnut maker should be reassembled and stored for later use.
The doughnut maker was very hard to clean. Only the aforementioned removable parts could be fully cleaned. The slide, and especially the top windows, were very difficult to remove from the machine. The oil bath could not be easily accessed and could not be removed and would remain quite greasy after the recommended cleaning. The doughnut carriages were also very hard to access for cleaning. Much of the interior could not be accessed at all, including several of the areas that small dough particles tended to fall when they did not reach the slide.

Safety concerns

There were quite a few safety concerns observed in the user study. First of all, when the oil was heated, the exterior of the machine became quite hot. Also, the user is instructed to leave one of the top windows open to maintain proper operating temperature. These problems both create a great risk to anyone, and especially children, who might touch or reach into the machine during operation. Also, the bottom of the dough dispenser becomes quite hot during operation as well, so if it needs to be removed in the middle of operation to be unclogged, the user must be very careful to avoid burns.

Doughnut quality

The doughnut recipe that was tested created properly shaped doughnuts only when the dough was dispensed manually. When the doughnuts were warm, they were fairly good, but after several hours they became hard and dry.

Other observations

The instructions for the doughnut maker where poorly written and often not detailed enough, forcing the users to figure out the machine themselves.

Mechanical Function

The purpose of this doughnut maker is to provide users with a simple and automatic method of cooking fresh mini doughnuts in the comfort of their own homes. All the user is required to do is to mix up the dough to put into the dough dispenser, turn the appropriate knobs at the right times and fresh mini doughnuts would appear at the rate of 20 per hour.

Powering up

Plug in the doughnut maker into a standard wall outlet via the power cord [P/N 055]. The interface of the power cord with the power jack [P/N 024] of the doughnut maker is a magnetic clasp. In the case of a person tripping over the power cord, the magnetic clasp prevents the doughnut maker from flying off the table. This would be highly dangerous as the doughnut maker contains a hot oil bath with could splash on nearby people. The power cord also has a protrusion at the interface so that it is only possible to connect it to the power jack in by matching it to the notch in the power jack housing [P/N 025].

Heating up the oil

First, the bottom adjustment knob [P/N 022] is turned to the right to 'Heat Oil'. This knob is connected to the switch [P/N 020] which is screwed on to the back of the front panel [P/N 050]. This switch turns on both the LED indicator light and the heating unit [P/N 036]. This then heats up the oil in the oil bath tub. Once the temperature goes past a certain point, the temperature controller [P/N 039] kicks in and turns off the heating element. This also turns off the LED indicator light and lets you know that the oil in the oil bath is now at the right temperature for cooking doughnuts. Once the temperature goes below the optimal temperature, the temperature controller turns the heating element back on again until the optimal temperature is reached. This forms a simplistic feedback loop.

Moving the conveyor belt

Once the LED indicator light goes off, the user knows that the oil is hot enough now and proceeds to turn the bottom adjustment knob to the left to 'Turn on Conveyor' and the top adjustment knob [P/N 022] for the dough dispenser to 'On'. The bottom adjustment knob is connected to the conveyor belt motor [P/N 018]. The shaft of the conveyor belt motor is attached to a small drive gear [P/N 019], which is then connected to the belt motor gear [P/N 026] and finally to the conveyor belt gear (doughnut side) [P/N 030]. On the other side of the conveyor belt gear (doughnut side), there are teeth that mesh to the conveyor belt link assembly [P/N 027]. The conveyor belt link assembly has release links [P/N 027] and doughnut carriage subassemblies [P/N 028] attached to it. It is guided along by the conveyor belt holders [P/N 029] and belt guides [P/N 034] and meshes with the conveyor belt gear (dough side) [P/N 031] on the other side. The conveyor belt gears are held in place by belt gear washers [P/Ns 032 and 033]. The conveyor belt guide is held in place by yellow washers [P/N 035].

As the conveyor belt motor drives the conveyor belt, it moves past the dispenser motor switch 1 [P/N 012] which is held in place by the dispenser switch housing [P/N 014]. The release links on the conveyor belt hit the dispenser motor switch 1 at regular intervals. This tells the dispenser assembly to start dispensing dough.

Dispensing the dough

The top adjustment knob is connected to the motor switch [P/N 020] which is screwed on to the back of the front panel [P/N 050]. This switch connects to both the dispenser motor [P/N 008] and two motor switches [P/Ns 012 and 013]. When the dispenser motor switch 1 is activated, it turns the dispenser motor on. This rotates the motor rotational output [P/N 009] that engages the dispenser motor guide [P/N 010] and affects a vertical linear motion of the guide. The extrusion from the dispenser motor guide then pushes out past a hole in the dispenser motor housing [P/N 011] and engages the dispenser plunger [P/N 003]. The dispenser plunger goes through the dispenser support [P/N 002] and pushes down on the dispenser stop [P/N 005]. This then creates a ring-shaped gap between the dispenser stop and the dispenser funnel [P/N 004]. The dough is then free to flow from the dispenser cup [P/N 006] through that ring shaped hole and drop into the hot oil bath as a fully formed ring of dough. As the dispenser motor continues to rotate, it moves the dispenser motor guide upwards and there is a notch at the top of the guide that presses the dispenser motor switch 2 [P/N 013] housed in the switch cover [P/N 007]. This halts the dispenser motor and the dispensing process until the dispenser motor switch 1 is activated again by the release link on the conveyor belt. The dispenser plunger is then restored in its up position by the dispenser spring [P/N 001].

Cooking the doughnut

Once the ring of dough has been dispensed into the oil bath, it floats there until the conveyor belt moves the doughnut carriage [P/N 028] into place. The doughnut carriage scoops the doughnut up in its front section and carries it along in the oil bath until it encounters the doughnut flipper [P/N 036]. The doughnut flipper is notched and angled at the end so that it is able to passively flip the doughnut around. This ensures that the doughnut is cooked evenly on both sides. Users can watch the cooking process via the transparent top windows [P/Ns 053 and 054].

Finished doughnuts

The doughnut carriage carries the cooked doughnut up and out of the hot oil bath and deposits the doughnut onto the doughnut slide [P/N 057]. The doughnut then slides down into the doughnut bin with oil drain [P/N 058] and once it cools down, it's ready to eat!

Cleaning up

The dough dispenser assembly, oil collection tray [P/N 049], doughnut slide and doughnut bin with oil drain are the only parts that can be removed for washing and cleaning. If the user wishes to drain the oil from the oil bath tub, he would turn the adjustment knob in the knob housing [P/N 040] to 'Drain oil'. This then engages the dial connector [P/N 043] and drain lever [P/N 044], which then opens the oil drain valve [P/N 046]. Oil from the oil bath tub then flows into the oil collection tray through the oil drain tube [P/N 047].

Design for Manufacturing and Assembly (DFMA)

Design for Manufacturing (DFM)

Manufacturing Processes

Injection molding is used for bulk manufacturing of identical plastic products. The cost of the tool itself is very high, but with the speed of production and the quality, with bulk manufacturing it will save money over other processes. The unit cost is incredibly low, making injection molding the ideal process for manufacturing the plastic pieces of the doughnut maker. Given the use of ribs on the front and back panel, injection molding is the likely process, which allows for both added strength and avenues for molten plastic. Large plastic components, such as the exterior panels, and large gear wheels are probably manufacturing in their own mold. However, multiple smaller pieces can be made in one mold to decrease manufacturing time per part.

Metal stamping is used to form shallow sheets and bends from a piece of sheet metal. Similarly to injection molding, the cost of creating the custom tool for each component is expensive, however the per unit cost is relatively low and is ideal for rapid, high volume production with a high quality finish. Stamping is not as aesthetically pleasing as drawing. Drawing is a similar process that uses a punch to force a piece of sheet metal into a die to form a particular shape. Drawing also has a high cost, but unlike stamping, the unit cost is also high. Drawing is more applicable to deeper profiles, while stamping is used for shallow ones. In the doughnut maker, stamping is more likely for the shallow stamps because it is cheaper and when only functional bends are needed stamping is more cost effective. Stamping is also ideal because it allows for high recyclability of the scrap metal and reduces waste. Pieces such as the temperature controller (P/N 038), are manufactured uses stamping for this reason. The oil bath (P/N 036) on the other hand appears to be drawn. A rounded, even shape with smooth corners can be achieved with drawing. Despite drawing being more expensive, with more important pieces a more expensive process is acceptable.

A large number of purchased parts are used throughout the assembly for the electrical components. All motors, screws, nuts and other standard parts were most likely purchased and then included in the assembly. Especially for mass produced consumer goods such as this doughnut maker, it is more efficient and cheaper to purchase these parts instead of manufacturing and assembling them individually.

Materials

The majority of components are made of plastic. Plastics are manufactured by heating them up to a given temperature at which they become a fluid, and forming them into shape. Particularly for consumer electronics plastics are ideal because they are often cheap, lightweight and can be easily formed and colored to be more ascetically pleasing. In most cases, plastic is strong enough to service the purpose for a consumer product. In addition, use of the doughnut maker involves significant heat to cook the doughnuts and the thermal conductivity of the plastic means that it doesn't get dangerously hot nearly as fast as other materials. Overall, any component that could be made out of plastic was made out of plastic to reduce cost and increase efficiency in manufacturing.

Metals are more expensive than plastics are, however, in some cases the extra expense is justified. In the doughnut maker studied, a portion of the oil bath is heated to heat the oil to a hot enough temperature to cook the dough. Because of the high temperature of the oil bath, the bath itself and other temperature controlling components must be made from metal for safety. Plastic would likely melt and cause injury. Metal is a more effective conductive surface so it can heat the oil more efficiently as well. When necessary, metal was used at an extra cost.

Design for Assembly (DFA)

Given the huge number of components, this is not a quick and easy process to assembly by hand, but given the complexity and the size of many of the parts hand assembly is likely. While it is intended to be a mass produced item, clearly machining costs to automate this process would be unnecessarily expensive.

There are 59 components of the doughnut maker studied, not including sub-assemblies. Almost every component is distinct and must be manufactured separately, this vastly increases the number of parts to be manufactured and then assembled and increases the complexity of the overall assembly. By reducing the number of parts and simplifying the assembly design, the assembly process can be simplified and more cost efficient. In addition, with a complicated assembly design, such as the doughnut maker, the error in assembly is drastically increased. A more "idiot-proof" design would result in fewer errors in the assembly process.

Standardization of parts is key to good assembly design. At least nine different kinds of screws were used throughout the assembly. A single screw driver is capable of removing all kinds of screws, but there are a variety of lengths and diameters used in all components of the assembly. The same dial is used on all three of the front dials (P/N 022 and P/N 042), so the same mold can be used to make all three dials. However, very few other components of the overall are identical and usable in other areas of the assembly. The design of the assembly requires two different motors and multiple distinct gears. Common parts will reduce the parts to be manufactured and decrease the overall inventory to decrease cost and increase overall quality of the product.

There are five major sub-assemblies that can be assembled separately and then brought together. Particularly, the conveyor belt assembly and the motor assemblies, so each can be assembled independently and then brought together. Many of the components of the conveyor assembly are gears which can only fit in one way on a moon-shaped shaft allowing for little error when putting the gears on the assembly. Any gear that doesn't require exact alignment, or needs to be able to rotate freely, can be assembled in any orientation and function correctly and allow for easy assembly as well.

Failure Modes and Effects Analysis (FMEA)

This product has several glaring failures which must be addressed while performing a necessary redesign. Although most of the analysis is on the component level, the major failures occur as a result of several components interacting and thus they are considered on the assembly level. Although there are many failures exhibited by this system, only the most severe will be discussed in detail.<ref name="CAA_Definition">Template:Cite web</ref>

A dramatic improvement on this product can be made to the dispenser system. The dispenser motor and the rotational output (P/N 11) both attribute to the failure of the dispenser to emit the correct amount of dough producing small burnt blobs. In a redesign, the motor speed should be reduced or the rotational output should be enlarged to allow for more dough to be released from the dispenser. This will dramatically improve the production of doughnuts and make the product more enjoyable.

In addition, the oil tub has several failures with high RPN's (270). Because the user is unable to clean the oil tub, the machine remains dirty and greasy and therefore has a safety issue involved. In addition, the doughnut flipper is unable to turn the doughnut which results in a poorly cooked product. In order to improve the system, a panel should be introduced to the plastic housing to allow the user access to clean the oil tub. Also, the doughnut flipper should be completely redesigned in order to perform its desired function.

There is also a serious safety failure present in this product, as can be seen in the table below. The top window (P/N 53) must be opened during use in order to prevent overheating, but this allows oil to escape and possibly burn the user. In addition, the housing heats up during use and can burn the user if touched. Since this product is used by children, these concerns must be addressed in a redesign of the system. By designing the product to allow heat to escape efficiently, both of these failures can be avoided.

The following table outlines the basic Failure Modes and Effects Analysis (FMEA) for the doughnut maker. The severe failures are in bold. The scale used can be found in the Engineering Design textbook by Dieter and Schmidt.

Part #	Item and Function	Failure Mode	Effects of Failure	S	Causes of Failure	O	Design Controls	D	RPN	Recommended Actions	Responsibility and Deadline	Actions Taken	S	O	D	RPN
001	"Dispenser spring" Keeps dispenser closed until needed	Deformed spring (too long/short)	Unable to fully open/close causing incorrect dough dispensing	7	Improper manufacturing	2	Inspecting dispenser spring	2	28	Introduce quality control measures to ascertain accurate spring dimension	Manufacturing and Quality Control	None	7	2	2	28
002	"Dispenser support" Guides plunger for straight release	Warped	Dispenser plunger moving at angle disrupting dough shaping	6	Improper manufacturing	2	Inspecting dispenser support or dispenser plunger	2	24	Introduce quality control measures to ascertain dispenser quality	Manufacturing and Quality Control	None	6	2	2	24
003	"Dispenser plunger" Pushes the dough from cup into oil tub	Cracked	Dough unable to be pushed into system	8	Improper manufacturing	1	Inspecting dispenser assembly	1	8	Introduce quality control to ascertain dispenser quality	Manufacturing	None	8	1	1	8
005	"Dispenser stop" Stops dough from seeping from cup Produces the "hole"	Leaking or cracked	Dough seeps from dispenser cup to machine	6	Improper manufacturing	3	Inspect dispenser assembly for leaks	3	54	Introduce quality control measures to ascertain dispenser quality	Manufacturing and Quality Control	None	6	3	3	54
006	"Dispenser cup" Holds dough for dispensing	Cracked	Dough seeps from dispenser cup to machine	6	Improper manufacturing	3	Inspect dispenser assembly for leaks	2	36	Introduce quality control measures to ascertain dispenser quality	Manufacturing and Quality Control	None	6	3	2	36
007	"Switch cover" Protects user from internal components Positions internal components correctly	Warped	Misalignment of components	8	Improper manufacturing	1	Specify process, Material selection	1	8	None	Manufacturing	None	8	1	1	8
007		Fractured	Exposure / Misalignment of components	8	Improper handling	2	Material Selection, Packaging	2	32	Drop test with and without packaging	Reliability	None	8	1	1	8
008-010	"Dispenser motor assembly" Pushes on dispenser plunger releasing dough Timed to release sufficient dough	Motor operates too fast	Insufficient dough released from dispenser	6	Poor design, motor rotates too quickly	9	Lab test with various motor rotational outputs	5	270	Redesign is necessary. Alternative motor speed or alternate motor	Research and development	None	6	9	5	270
008-010		Rotational output (part 11) too small	Insufficient dough released from dispenser	6	Poor design, part too small to release sufficient dough	9	Lab test with various sized parts	5	270	Redesign is necessary. Larger sized rotational output (part 011)	Research and development	None	6	9	5	270
011	"Dispenser motor housing" Protects and positions the dispenser motor	Fractured	Motor is moved off position, disrupting dispensing process	7	Improper manufacturing	1	Material selection, placement	3	21	Introduce quality control actions to check dispenser motor assembly	Reliability	None	7	1	3	21
012	"Dispenser switch 1" Alerts motor to open plunger	Sticking	Plunger stays open, dough pours into oil tub	8	Improper manufacturing or assembling	1	Inspect control systems	5	40	Take quality control actions or may redesign for extra clearance	Manufacturing	None	8	1	5	40
013	"Dispenser switch 2" Halts the dispensing process	Sticking	Plunger does not open, no dough released	8	Improper manufacturing or assembling	1	Inspect control system	5	40	Take quality control actions or may redesign for extra clearance	Manufacturing	None	8	1	5	40
014	"Dispenser switch housing" Positions switch	Fractured	Plunger stays open/closed	8	Improper manufacturing	1	Inspect dispenser motor assembly	2	16	Introduce quality control measures on dispenser motor assembly	Manufacturing	None	8	1	2	16
018	"Conveyor belt motor" Drives the conveyor belt assembly	Conveyor belt assembly moves too slow	Doughnuts take a very long time to move through system	4	Motor rotates too slowly	8	Lab test with different motor speeds	5	160	Purchase more powerful motor, redesign for smaller drive gears	Research and development	None	4	8	5	160
019	"Drive gear 2" Translates motion to conveyor assembly	Fracture	Conveyor belt system unable to move	8	Improper manufacturing	1	Inspect conveyor belt assembly	1	8	Introduce quality control measures on conveyor assembly	Manufacturing	None	8	1	1	8
023	"Wire guide" Secures wire to housing	Dislocating from position	Wires come into contact with oil bath	9	Improper handling	1	Material selection, packaging	1	9	Drop test with and without packaging	Reliability	None	9	1	1	9
024	"Power jack" Connects to power cord	Short circuit	Unable to function	8	Internal problem	1	Choose reliable supplier	4	32	Test completed units before distribution	Assembly	None	8	1	4	32
026	"Belt motor gear" Translates motion from motor to conveyor belt	Fractured	Conveyor belt unable to move	8	Improper handling	2	Material selection, packaging	2	32	Drop test with and without packaging	Reliability	None	8	2	2	32
027	"Conveyor belt link assembly" moves doughnut through the system	Fracture	Doughnut unable to move through system, machine unable to perform function	8	Improper manufacturing	1	Inspect conveyor belt assembly	4	32	Introduce quality control measures on conveyor assembly	Manufacturing	None	8	1	4	32
028	"Doughnut carriage assembly" Used to carry doughnuts through oil bath	Bends too easily	Contributes to doughnut being unable to flip	5	Poor design, part too flexible	9	Lab test different materials with various flexibilities	4	180	Redesign using a less flexible material	Research and development	None	5	9	4	180
030-031	"Conveyor belt gear" Rotates and moves conveyor belt system	Fracture	Conveyor belt system unable to move	8	Improper manufacturing	1	Inspect conveyor belt assembly	1	8	Introduce quality control measures on conveyor assembly	Manufacturing	None	8	1	1	8
034	"Belt guides" Guides belt on lower track of conveyor belt	Fracture	Conveyor belt system unable to move	8	Improper manufacturing	1	Inspect conveyor belt assembly	1	8	Introduce quality control measures on conveyor assembly	Manufacturing	None	8	1	1	8
036 & 039	"Oil bath assembly" Cooks doughnut on both sides	Flipper does not turn doughnuts	Doughnut unevenly cooked	6	Poor design, doughnut pushes flipper	9	Inspect oil bath assembly	4	216	Redesign the oil flipper by making a more rigid connection	Research and development	None	6	9	4	216
		Oil bath temperature fluctuates too greatly	Doughnut burnt (usually) or undercooked	5	Oil bath diminishes too fast, temperature controller too poor	7	Inspect oil bath assembly	4	140	Purchase a better temperature controller	Research and development	None	5	7	4	140
		Fractured/Leaking	Release of hot oil into system, possibly onto user	9	Improper handling	1	Material Selection, Packaging	3	27	Drop test with and without packaging	Reliability	None	9	1	3	27
		Oil tub hard to clean	Oil stays in system and machine gets very dirty/greasy	6	Poor design, no access to oil tub	9	Inspect oil bath assembly	5	270	Redesign needed. Make removable panel to access oil tub	Research and development	None	6	9	5	270
043-045	"Oil drain knob assembly" Used to open and close oil drain	Fracture	Oil drain system unable to function	7	Improper manufacturing	1	Inspect oil drain assembly	1	7	Introduce quality control measures on oil drain assembly	Assembly	None	7	1	1	7
046-048	"Oil drain tube, clamps, and valve" Channels the flow of hot oil	Leaking	Hot oil released into machine and possibly onto user	7	Improper manufacturing	2	Inspect oil drain assembly	4	56	Introduce quality control measures on oil drain assembly	Assembly	None	7	2	4	56
049	"Oil collection tray" Collects the oil that is drained after use	Warped/Deformed	Misalignment of components, improper fit	7	Improper manufacturing	1	Specify process, Material selection	1	7	None	Manufacturing	None	7	1	1	7
049		Fractured/Leaking	Hot oil released from machine, possibly onto user	9	Improper handling or manufacturing	3	Material Selection, Packaging, Quality control measures	4	108	Drop test with and without packaging	Reliability	None	6	3	4	108
051 - 052	"Front and Back Panels" Protects user from internal components and heat Positions internal components correctly Encloses and protects internal components	Reaches excessive temperature during use	Burns user if contacted accidentally	9	Poor design, material selection, heat transfer	6	Material selection, Safety analysis	4	216	Redesign necessary, choose less conductive material, insulate the housing	Research and Development	None	9	6	4	216
051 - 052		Fractured	Exposure/Misalignment of components and heat release	6	Improper handling	4	Material Selection, Packaging	4	96	Drop test with and without packaging	Reliability	None	6	4	4	96
053	"Top Window 1" Opened during use to allow heat to escape	Oil splatters from machine	Hot oil able to get on user	9	Poor design, alternative ways to release heat	6	Inspect alternative designs for heat transfer	4	216	Design alternative ways to safely release heat	Research and Development	None	9	6	4	216
055	"Power cord" Provides electricity for toaster unit	Short circuit	Unit unable to function	8	Cord Pinching	2	Set assembly process	4	80	Test completed units before distribution	Assembly	None	8	2	4	64
055	"Power cord" Provides electricity for toaster unit	Short circuit	Unit unable to function	8	Internal cord problem	1	Choose reliable supplier	4	32	Test completed units before distribution	Assembly	None	8	1	4	32

Design for Environment (DFE)

Surface Level Environmental Impact

In considering environmental implications of this appliance, it is important to consider both the direct effects (material flow) and the indirect effects (gaseous emissions) during the complete life cycle. Whereas market research demonstrated the material flow associated with consumer use, the product dissection showed the complex array of individual components and sub-assemblies required for proper function, implying that much of the material and energy consumption will occur during the manufacturing phase. An inexpensive kitchen appliance is designed to have a finite lifespan, where it becomes cheaper to replace the product than to repair it. This conclusion is justified by the excessive difficulty with which the components are removed and replaced, indicating that disposal will be a significant aspect to consider.

The direct, or visible, effects were observed during the market research. From a consumer’s perspective, this includes:

Large amount of detergent/water/paper towels to clean, as oil gets on nearly every component of appliance

Waste oil must be disposed of after each use

Plastic casing gets extremely hot, leading to waste heat energy

Only one doughnut is pulled through at a time, implying that the conveyor/heater must remain active for a much longer period of time to produce one batch, drawing much more energy

This consumes an obscenely large amount of electricity per doughnut

Excess dough is wasted due to the dispensing unit

Complexity of product ensures that it can never be reasonably recycled by consumer, as it cannot be separated into plastic/metal components

The indirect effects come from further research, and will be highlighted in the following subsection of EIO-LCA.

Material Considerations

The product dissection allows us to further understand the material flow put into the product during manufacturing and assembly.

Plastic
- Nearly the entire assembly is built of injection-molded plastic and is designed to be disposable. Non-recycled plastic will not degrade in a landfill. These parts cannot be easily disassembled for replacement. Energy is consumed (and consequently pollutants emitted) during the processing of such plastics.
Metal
- Several crucial parts are built of metal, but they are designed to be removed and will not be recycled by the consumer. Energy is consumed in the extraction and processing of metals.

EIO-LCA Model

The Economic Input-Output Life Cycle Assessment (EIO-LCA) model allows us to explore the tangential sectors that will contribute to the product’s net environmental implications. An automated doughnut maker can best be described as a novelty kitchen appliance designed for a niche market; it is not expected to be found in every home. However, from an engineering and environmental impact perspective this product follows a similar life cycle to that of a toaster, coffee pot, or waffle iron. It combines injection-molded plastic pieces with a simple heating element and basic mechanical components. Therefore, while it does not explicitly fall under a category, we can make a reasonable assumption that the life cycle of our product is comparable to those found in #335211 Electric Housewares and Household Fan Manufacturing.

Economic Activity

This table shows the relevant economic activity associated with the full life cycle of 10,000 units. This is dominated by energy consumption, primarily in the form of electricity. This product is very energy intense given the duration of operation for each batch.

Conventional Air Pollutants

This shows the creation of air pollution over the entire lifespan of the product from manufacturing through disposal. These emissions come from power generation, which is the direct result of the large electricity consumption. The manufacturing process itself is the second largest contributor to conventional air pollution. This includes chemicals that form smog, acid rain, respiratory disease (from particulate matter), and other direct atmospheric and health effects.

Greenhouse Gases

This models the life cycle releases of greenhouse gases such as carbon dioxide and ozone-depleting chlorofluorocarbons (CFCs). These have become increasingly relevant to today's engineering market demands.

Energy

This shows the distribution of energy sources as demanded by 10,000 products over the course of the life. This accounts for fuel type used to generate the energy. As this product consumes primarily electricity (during usage), we see a similar pattern of coal/natural gas, which is the main source of fuel for electrical generation in the United States.

Toxic Release

The toxic releases are categorized by point/non-point source and environmental area in which it is released.

Conclusions

This model simulates environmental response values for $1,000,000 of economic input activity. We see that the majority of emissions come from power generation, which constitutes approximately 31% of all CO2 emissions. This doughnut maker, at $100 per unit, can be produced at 10,000 units per $1,000,000 input. Therefore, if 10,000 units produce 693 metric tons of CO2, this equates to 69.3 kg-CO2 per doughnut maker.

Beyond the effects of electricity generation, other major sources of CO2 emissions come from the production of metals (8%), transportation (8%), and the product’s manufacturing process itself (7%).

Electricity generation associated with this product accounts for more than half of all sulphur dioxide (SO2) emissions, one of the chief chemicals contributing to acid rain. Truck transportation is responsible for the large quantity of Carbon Monoxide (CO) that is released into the atmosphere, a chemical that is characteristic of incomplete combustion.

Given the knowledge that electricity consumption has far more critical implications than the materials involved in creating the product, it seems unreasonable to attempt to change these. There are no particularly elaborate materials used and there are areas of consumer usage that would be ideal for environmental analysis and redesign.

The most significant improvement would come by reducing the electrical consumption per doughnut. This could be achieved by carrying multiple doughnuts through the oil simultaneously (instead of letting each doughnut cycle fully (~1 min) before the next doughnut is dispensed). This has the potential to reduce the time from 2+ hours to a matter of minutes without significantly affecting the production. Maintaining oil temperature and powering the conveyor belt for this duration is extremely energy intense. This time should be kept to a minimum.

Mechanical Analysis

Team Members & Roles

Michael Barako - DFE, Mechanical Analysis

Meng Yee Chuah - Mechanical Function

Katie McManus - Assembly Photos, DFMA

Sam Powers - Bill of Materials, FMEA

Sara Whitby - Executive Summary, Major Stakeholders, Usage and Usability

References

Carnegie Mellon University Green Design Institute. (2009) Economic Input-Output Life Cycle Assessment (EIO-LCA) US 1997 (491) model [Internet], Available from: <http://www.eiolca.net/> [Accessed 18 Sep, 2009]

Thompson, Rob. Manufacturing Processes for Design Professionals. New York, NY:Thames & Hudson, Inc., 2009.

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