Gate 3 - Product Analysis.
Cause for Corrective Action - Gate 3:
After completion of the first two gates, our group is satisfied with our performance. As stated in the group review from gate 2, one of our goals was to improve quality of work by giving more time for the other group members to review submissions, and this was definitely successful. Instead of turning a piece in directly to the group leader to be submitted, it was first reviewed by at least one other group member, and the group leader. The grade we received on gate 2 was much better than gate one because we paid more attention to the details, and exactly what was being asked.
One aspect of our group that has been good in many cases, but does leave room for improvement is communication. Communication with each other is very important because it keeps everybody on the same page and it lets one member know what another member expects. It has been beneficial when certain members have reviewed others work, and made suggestions for improvement. Sometimes, the communication process fails in our group when individuals become busy and forget to check in. To solve this, we are working hard to remain connected with all group members even if somebody is not available to meet in person on a regular basis. We have agreed that when a member is not available for a meeting, it is their responsibility to contact the group leader and catch themselves up. This is not ideal, but as a group we understand that everybody is busy and it is not always possible to be present for meetings and class.
We have also found that it is tough to have group meetings where everybody can be present for an extended period of time because of the fact that everybody is so busy with tests, projects, and homework from other classes. To deal with this, we have been jumping on the work early and dividing it up so the work can be done individually and then combined at the end. In an ideal world, we would prefer to work together on more of the tasks, but finding the time is very difficult. This system has been successful so far, and we plan to continue to do this as the end of the semester approaches.
Overall, we are still working well together as a group. The members are getting along with each other and seem to be responding positively to constructive criticism. This is crucial to remaining successful. In the future we will continue to follow the same procedures we have been implementing, while trying to improve them whenever possible.
When choosing which components to analyze, we considered the pieces that were designed specifically to be part of a leaf blower. The tube, handle, and fan were all designed for the sole purpose of making a leaf blower, while other components were only used to help put the leaf blower together. Pieces such as the screws, spark plug, magneto, and engine are used in a variety of products and were not necessarily designed with a leaf blower in mind.
For Component Complexity, the complexity scale used will be based on a scale from one to four. One indicates the simplest parts, such as a screw or nut. Four indicates the most complex parts, such as the combustion chamber or the fan. The interaction scale will also be from one to four. One indicates the most basic interactions, such as the connection of the handle to the body. Four indicates the most complex interactions, such as the engine to the fan.
Leaf Blower Tube:
Figure A The leaf blower's tube
Component Function: The tube's main function is to direct the air flow from the fan, as well as slightly increase the air velocity with its decreasing diameter. In addition, it also allows for the air to cover the maximum amount of area due to the design of the end of the tube. Instead of one round opening, it splits into three openings, the two outside ones having a flatter shape. This provides a thin, flat air flow which is more precise than one large, round air flow. The main flow that is associated with the tube is air and mass flow. The tube is meant to function in many environments, from hot, dry climates to cold climates. The tube’s plastic material blocks surrounding forces that would affect the direction of air flow. Plastic can break, however it is unlikely that the cause would be from the environment.
Component Form: The general shape of the leaf blower's tube is a long cylindrical object made of plastic that condenses down (in cross sectional surface area) to three separate air flow exits. The center exit of the air flow is in the shape of a circle while the two ends on either side of the circle are oval-shaped, which are specifically engineered to provide control over the air flow after it exists the tube. The beginning of the tube (where it is connected to the body of the leaf blower) has a cross sectional area that is approximately twice that of the end of the tube, which allows for the air flow to increase in velocity as it exits the tube. This part is primarily three dimensional and has two symmetric halves in order to keep the air flow uniform from side to side. The tube is approximately 22 inches long, 2.5 inches in diameter (at the beginning of the tube), and the three different air flow exits are approximately 0.75 inches in diameter.
Several factors were considered when determining the length. One reason the length is around 2 feet is to allow the user some space and distance from the leaves and/or debris. It also must be long enough to give the air flow a precise direction by the time it exits the tube. Conversely, the tube must be at a reasonable length for storing purposes. The tube weighs roughly one pound. Weight is an important consideration when designing it due to societal concerns, namely, in this case, each component should be as light as possible since the user will be holding it while operating. For this reason, plastic was chosen as the material for the tube.
Choosing plastic for this component was a smart decision because the tube is not subject to any severe stress or strain. In addition, economic factors influenced the chosen material because it is a cheap material that is light weight. As mentioned before, societal factors influenced the decision to use plastic because it is light weight and therefore easier to hold, control, and move than a heavier material such as metal.
The tube does not need to satisfy aesthetic purposes as much as its function. However, there were some aesthetic considerations while designing the tube. It has a fairly smooth finish that looks professional, appeals to consumers, and feels good on the hands of the user. The inside of the tube is even smoother than the outside as to allow consistent, smooth air flow. The color is black, which was chosen because black is a neutral color that will match with any other color of the leaf blower.
Manufacturing Methods: The tube for the leaf blower was most likely blow molded in two separate halves and then combined at high heat, so the two halves would fuse together. There are several clues that lead to this assumption. There is a clear line down the entire side of the tube, providing evidence that it was made in two separate halves. Also, the end of the tube where the air comes out appears to be cut, which is where the excess material or flash would have been removed. In addition, there are riser marks from where the pieces of the tube were supported when they were removed from the mold that formed them. The choice of material definitely impacted this decision. Plastic is very easily molded using pressure. Blow molding would be the cheapest and easiest method in this case. If the tube were made of some sort of metal, this method would not work. The round shape of the tube also impacted the decision to use blow molding. This method is most effective with rounded edges because there are no sharp corners that could develop weak spots. Economic factors were most likely the most influential when designers were determining how the tube would be manufactured. This method would be quicker, and use less energy than waiting for the material to form to a mold under gravity alone. By saving time and energy, the company is able to save significant amounts of money, considering the volume of tubes that are being produced.
Component Complexity: Based on the complexity scale described above, the tube would be considered a two. The tube in itself is one of the more basic components of the leaf blower. However, there is a considerable amount of thought and design analysis that influences its shape. The three categories that were described above have a great big impact when determining the complexity of this component. The tube was only given a two on the complexity scale because of its simple geometric shape, its cheap and abundant material, and its simple, cheap manufacturing methods.
The interactions of this component could be considered fairly complex. The idea that the air entering the tube can be accelerated simply using the geometry of the tube is subject to a great deal of analysis by the designing engineers. Based on the interaction scale described above, the tube’s interaction with other components would be a two. It has a simple connection to the leaf blower using a clamp. Other than that, it is the shape of the leaf blower’s body that actually directs the air into the tube.
Leaf Blower Handle:
Figure B The leaf blower's handle
Component Function: The handle of the leaf blower allows the user to hold the leaf blower using one hand and direct the tube toward leaves and other debris. The component helps to perform multiple functions, as it not only allows the user to hold the leaf blower, but also allows the user to point the tube in a desired direction. The only flow that is associated with this component is the transfer of human energy into the leaf blower in order to move the leaf blower in any direction. The handle of the leaf blower will function in many environments because it can withstand both cold and warm temperatures.
Component Form: The handle is in the shape of a half octagon with the two ends, both top and bottom, extruding only a small distance. The component is primarily three dimensional, due to the fact that the user must grab the handle in order to hold the leaf blower. The handle is axis-symmetric because if you were to cut the piece down the middle and flip it either up or down you would find that the two halves would align. The component is an inch and a half in diameter, approximately 8 inches in length from top to bottom, and 3 inches wide from left to right.
The handle’s shape is crucial in order for the component to be easily picked up and easily maneuvered. If the component were bent in a weird direction or extruded as a helical path then that would make it much more difficult for the user to control the leaf blower. The component weighs roughly one half a pound which is crucial because the handle should provide sufficient support without adding sufficient weight.
The handle of the leaf blower is made of plastic which was specifically chosen to reduce the overall weight. Another reason plastic was chosen is because it would be easy to make a large quantity of handles using injection molding for this product. Economic factors also influenced this decision due to plastic’s inexpensive cost and abundance. Societal factors were also considered when designing the handle because it allows for the consumer to easily pick up the leaf blower and hold it for long periods of time if needed.
Aesthetics do not seem to play any part of the handle’s design besides its color. The handle is black because it is visually appealing, it is a neutral color that matches the color of other components, and the handles of most yard tools seem to be black. Otherwise, the handle was designed for functional reasons. The finish is somewhat rough where the user’s palm makes contact to increase friction and give the user a better grip. Everywhere else is a smooth finish to allow for a more pleasant touch.
Manufacturing Methods: Like the tube, injection molding was used to manufacture the handle in two separate halves. The two halves were then combined at high heat causing the two pieces to fuse together. This is evident in the riser marks that are present on either side of the handle, and the fact that there is a line down the middle of the handle. Both sides are symmetrical, so the same mold could be used for both halves. The choice of plastic made it easy for designers to settle on this method. Injection molding is a very common method to form plastic parts with complicated geometries such as the fan. The awkward shape of the handle would make it hard to blow or form using some other method. This method is the cheapest and most economical for the producers considering the high volume of parts required. Also, this method would reduce waste, because excess plastic can be reheated and used again. By using a method that reduces plastic waste, the environment is not harmed as much as it would be otherwise.
Component Complexity: Using the scale defined above, this component could also be categorized as a two. It is not as simple as a screw, yet there was thought that went into the three dimensional shape in order to have a handle which would be comfortable for the user to hold for long periods of time while providing enough support to hold the entire leaf blower. The only interactions with this component have to deal with the user. The user is the one who will grab the handle in order to pick up the leaf blower and turn it whichever way they would like; therefore, we believe that the interactions of this component are rather simple, and would be a one on the interaction scale.
Leaf Blower Fan:
Figure C The leaf blower's fan
Component Function: The fan is one of the most crucial components that aids in the leaf blower’s main function. This component rotates inside the casing of the leaf blower to generate the air flow needed to travel through the tube. The fan not only circulates to accumulate air velocity inside of the casing, but it also pushes the air that is generated from its rotation into the tube of the leaf blower. The flows that are associated with the fan would be the air flow through the leaf blower. The fan will be able to function in many environments. Like the handle and the tube, it is made of plastic, which is very unlikely to break due to environmental reasons. Also, since the fan is positioned inside the body of the leaf blower, the casing acts as a shield to protect it, even in the most severe environments.
Component Form: The fan is a circular component that extrudes up with 7 different blades which are curved at certain angles in order to capture the maximum amount of air flow and distribute it into the tube of the leaf blower. This component is primarily three dimensional which is important because it needs to be able to catch the maximum amount of air possible to push into the tube. The diameter of the fan is 7.25 inches and the heights of the blades are 1.9 inches. The shape of this component is extremely important when it comes to the function that it must perform.
In order for the tube to receive the maximum amount of air, it is essential that the fan is shaped in a way to capture the most amount of air while rotating. It is symmetrical so that the air produced is uniform, and to keep it stable while rotating at a high speed. The fan weighs roughly one half a pound. This weight should be as light as possible for several reasons. First, every component should be as light as possible because the user will be holding the entire leaf blower during operation. Second, having a heavy fan will require more power to rotate it at sufficient speed to create the desired air velocity. The lighter the fan, the less power is needed to rotate it at a necessary speed.
The fan is made of plastic which allows for the material to be as light as possible, as described above. It is also rigid which is important because if it deforms from the air flow, it will not produce the required air velocity. When choosing the material, manufacturing decisions did not have as big of an impact as the sheer need for a very light weight material. Economic factors were considered when making this part because plastic is an abundant and inexpensive material.
Since the fan is completely hidden by the leaf blower’s casing, aesthetic properties had no influence on its design. It has a smooth surface finish for several reasons. First, the fan is designed to rotate at high speeds, so friction must be at a minimum. Second, like the tube, a smooth surface finish allows for consistent, smooth air flow.
Manufacturing Methods: The fan was created using injection molding. It has clear riser marks from where it was removed from the mold. Although this is the only physical clue that indicated it was injection molded, this process makes the most sense because it works well with plastic, and it is good for high volumes of parts that require high dimensional accuracy. The decision to create the fan using injection molding was influenced by the fact that it is made of plastic. This process works well with plastic, and results in a reliable final product. This method addresses societal and economic concerns for the company. Injection molding could be considered safe for the workers in the factory because they are not required to use dangerous machinery to form the product. In addition to this, it is cheaper than other methods, because after the mold is made, many units can be made with little adjustment to the process. Injection molding is very conducive to the repetitive production of items such as the fan.
Component Complexity: The complexity of the fan would be considered a four on the complexity scale. This is because there are many curvatures that were taken into consideration when creating this part in order to generate the maximum amount of air flow into the tube. The intricate geometry increases the fan's complexity. In terms of interactions, the fan receives rotational energy from the piston rod and transfers that to pneumatic energy. It is physically connected to the piston rod through a bolt. This bolt is pressed into the center of the fan and has a circular opening with one flat side that allows the piston rod to lock into the bolt. These complex interactions give the fan a four on the interaction scale.
Note: The manufacturing of all of these products would have been affected by the global concern of available resources. For this reason, the company would have placed the manufacturing facility in an area where raw materials could be easily obtained by water, well developed roads, or railways. In addition, they would make sure that there is a reliable and affordable source of power for the plant to use.
CAD Assembly Drawings
**Note: Here is the link to the CAD files: Media:AutoCADfiles.zip
Bill of Materials
The CAD package that was chosen to draw these models is AutoCAD 2011 Student Version. Using it in a previous class, we are familiar with the basic functions of this package. Certain group members still have the tutorial textbook and DVD to refer to as well.
The components that were chosen to draw using the CAD package were the handle, fan and tube. These components are each a very crucial part of the leaf blower.
The handle must be designed in a way to be able to support the weight of the leaf blower without sufficiently adding to the weight. It must feel comfortable in the hands of the user and provide good control over the leaf blower. The handle on this leaf blower is bent 30 degrees in the middle. This allows the user to hold the leaf blower at different angles without putting strain on the user’s wrist to hold it at a desired angle.
The fan is designed to convert the maximum amount of rotational energy from the piston rod to pneumatic energy. The main function of the leaf blower is to transport leaves and other debris from one area to another using high-velocity air flow. Since the fan is what generates that air flow, many factors had to be considered in the design, such as the shape of the fan and the size and number of blades.
Many factors were considered when designing the tube as well. Its decreasing diameter produces an increase in the air velocity, and its length gives direction to the air flowing through it. This direction continues even after the air exits the tube by the way the opening of the tube is designed. Instead of one round opening, it splits into three openings. The center is round, but the outsides are an egg shape, as shown in Figure 1. The very outsides of the tube’s opening have the smallest diameter, putting out air at the highest velocity. This helps control the direction of the air coming from the center of the opening, as shown in Figure 2.
Engineering Analysis of the Fan:
We choose to take a closer look at the fan, because we feel that it requires significant design and testing.The fan in a leaf blower is specifically designed to move the largest amount of air as efficiently as possible. It translates the engine's rotational energy output into a fast moving volume of air which exits through the tube for a wide variety of uses. Fans come in an infinite number of shapes. There is no specific formula that dictates a fans shape. When designers need a fan, they rarely come up with a radically or really new innovative shape; they generally just tweak a few things about an existing shape. The fan is important, because it directly affects the flow of air produced, and the performance of the engine. If the fan is too small, not enough air would be displaced, but if it were too large, the engine would not be able to rotate as needed. Designers are faces with the difficult task of maximizing air flow while considering efficiency.
Fans are designed and tested empirically by using lab tests and complex computer programs. For example, when the designers of the leaf blower created the fan they most likely chose the final product from a group of prototypes. The one that performed the best in lab tests became the final product. While there are no specific formulas that take advantage of certain geometry aspects, through empirical testing, using dimensional analysis and similitude one can choose a fan that best fits their needs.
Because empirical testing is the main aspect of the fans design, assumptions would take the form of lab conditions. It would be important for no external forces to be acting on the fan being tested. Also, each design tested would required identical treatment. For example, every fan would have to be tested in uniform air density with a uniform source of power.
Six main variables dictate how a fan will operate. The equations below use relationships to evaluate fan performance for these various parameters. The variables and equations are as follows:
Q = Airflow Rate: generally measured in m3/s or CFM (ft3/min)
P = Pressure Rise: generally measured in Pa or psi (lbf/in2)
H = Power: generally measured in W or hp
N = Rotational Fan Speed: generally measured in m/s or mph (mi/hr)
D = Fan Diameter: generally measured in m or in
ρ = Air Density: generally measured in kg/m3 or slug/ft3
Note: The subscript 'r' represents the known, or reference, operating conditions that the new conditions are based off of.
The equations are in the form of ratios in order to illustrate how a change of one variable will affect the other. For example, if the fan speed is doubled and the diameter is kept constant, the flow rate will also double. Although the equations are very accurate based on multiple lab tests, certain conditions must be met in order for them to calculate a relevant answer. As mentioned above, fans can come in a variety of shapes such as having a different amount of blades, among other things. In order for the equation to relate properly, fans of different diameters must have a similar and proportional geometric shape. Other things to consider are changes in air density, as a fan running at one elevation will not push the same amount of air at a different elevation.
Figure D Front and top view of the fan with dimensions
Design Revisions (Component Level)
The current handle on the leaf blower has straight edges and has a rougher surface on the top half where the user’s palm makes contact. To increase control and comfort, the handle could be designed to have a rough surface on all sides. This will increase friction between the user’s hand and the handle, minimizing any slipping, and therefore increasing the strength of the user’s grip. The grip can be further enhanced by changing the shape of the handle on the side where the user’s fingers make contact, as shown in Figure 1. By designing a wave-like shape on the bottom side of the handle, the user has a place to put their fingers, providing better comfort and control. These design revisions will affect societal factors as they will appeal to the consumer. It will slightly increase manufacturing costs, however it will become an additional marketing tool.
Currently, to start the leaf blower, the user must pull the cord with enough force to turn the engine over. This can be very difficult for many people, especially after sitting in the cold for months during winter. To solve this problem, the way the pull-cord/spring mechanism works can be reversed. Instead of having to pull with a large force, the system can be redesigned so that the user can pull the cord all the way out at a comfortable speed and let go. The spring would then recoil fast enough to turn the engine over itself. Engineers will have to look into the spring mechanism to implement this design revision. The spring must be anchored, positioned, and have the right spring constant to pull the string back fast enough to turn the motor over after being fully extended. Additional cost to implement this will be minimal, as the revision only calls for a basic reversal of the spring mechanism. Like the handle revision, this societal factor can be used as marketing tool to consumers.
Additional Throttle Settings:
Another recommendation would be to add more throttle settings to the blower’s carburetor, as well as place it in a more convenient location for the user. The throttle currently has only two settings: half and full. For jobs such as blowing grass after it has been cut, very little power is required. Using a throttle setting lower than half for such jobs would not only help control light-weight debis such as grass, but also improve fuel efficiency. Environmentally, using less fuel would reduce the product’s emissions. In terms of societal factors, changing the location of the throttle to make it easier and more convenient for the user to access will appeal to the user. The new location would be near the user's thumb while holding the leaf blower by the handle, as shown in Figure 2. This will allow the user to change the velocity of the air flow while focusing on the debris and the area in which the user is aiming to blow the debris. The current location, as seen in Figure 3, requires the user to disrupt his/her attention on the debris and find the throttle switch to change the air flow velocity. Implementing this revision would be fairly simple. The actual throttle itself may remain in place, saving time and money from possible engine redesigns. The throttle control (i.e. the red switch in Figure 3) would be placed as shown in Figure 2 with simple mechanical connections. This would not require a significant amount of money to implement.
Figure 2 Possible addition of throttle settings and new placement
Figure 3 Current placement of throttle settings