Group 10 - Line Trimmer/Coordination Review

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Contents

Coordination Review

Delivery Date: 11/30/2009

Causes for Corrective Action

Overall, the progress of the reverse engineering of the line trimmer has gone smoothly. The component summary, design revisions and solid modeling were all roughly completed in the desired time frame mentioned in the work proposal. The engineering analysis was be to be adapted from question three in assignment four. The issue of meeting time was resolved from the previous gate. The group decided not to meet collectively as often, but rather to contact each other via text message to meet and exchange information individually. The project manager, Justin Storms, still monitors the overall progress of the project and establishes a common meet time if necessary.

Family Emergency

  • There was one obstacle that was encountered during the Coordination Review. One group member had to travel home due to a family emergency for a couple weeks. He was still able to communicate with the rest of the group through email and completed his portion of the design revisions.

Solid Modeling

  • One group member who assigned to be the leader of the solid modeling was struggling with figuring out how to make the components, so another group member took over the responsibility of creating the solid models for the line trimmer.

Presentation

  • A meeting to discuss and create a presentation will be organized by the project manager. The slide show will be made during this meeting and the speaking roles will be divided up. The meeting will take place on Tuesday, December 1, 2009 at 4:15pm in 101 Bell.


Component Summary

Below is a summary of the components and the parts that make up those components in a line trimmer. The function of each component is described briefly. Information is given about the material these parts are primarily made of and the manufacturing process involved in making them. Each component is rated on a scale of complexity described below. Further discussion of the components is included after Table 2.

In order to compare the components, a scale of complexity will be established. The scale will range from 1 to 5, with 1 being the least complex component of the line trimmer and 5 being the most complex component of the line trimmer. A complexity rating of 1 corresponds with a simple component like a foot guard that can be made quickly and easily in manufacturing. It is a component that is easy to understand how it functions. A rating of 5 corresponds to a component like the carburetor on the line trimmer. This component is made up of many small parts. It is not easy for the average user to understand how it works just from looking at it. It has several gaskets and small screws.

Note - Table 2 is best viewed in 1920 x 1200 resolution. Lower resolutions may distort table formatting.


Table 2 - Component Summary

Item # Component Complexity Parts Included (Quantity) Materials Function Manufacturing Process Picture
1 Foot Guard 1 Foot guard (1)

Foot guard clamp (1)


1/4" Slotted tapping screws with a hex washer head (2)

Plastic

Steel


Steel

The foot guard serves to protect the user from the spinning trimming attachment. Injection molding

Metal Stamping


Die casting and machining

Click to View
2 Trimming Head 1 Trimming Head (1)

Hex Nut (1)

Plastic

Steel

The trimming head spins to cut weeds and brush. Injection molding

Die casting and machining

Click to View
3 Lower Handle 1 Handle (1)

Shape 1 wing nut (1)


Clamp (1)

Plastic

Steel


Steel

The lower handle serves for a place to hold and support the line trimmer to allow for better control. Injection molding

Die casting and machining


Metal stamping

Click to View
4 Throttle Handle 2 Throttle housing (2)

Throttle lever (1)


Throttle cable (1)


#2 Phillips tapping screws (4)

Plastic

Plastic


Woven Steel


Steel

The throttle handle serves as a grip for the user to support the device and control the speed of the spinning trimming attachment. Injection molding

Injection molding


Cable weaving


Die casting and machining

Click to View
5 Drive Shaft 1 Drive shaft (1)

Drive shaft housing (1)

Steel

Steel

The drive shaft transfers the power from the crankshaft spun by the motor down to the trimmer attachment. The housing protects the user from the fast spinning drive shaft. Die casting and machining

Die casting and machining

Click to View
6 Engine Housing / Fuel Tank 2 Upper engine housing (1)

Fuel tank (1)


Fuel line (1)


Lower engine housing (1)


Button head 5/32" hex socket cap screws (10)


Hex nuts (2)

Plastic

Plastic


Plastic


Plastic


Steel


Steel

The engine housing encloses most of the components of the line trimmer. It protects the user from the moving parts inside. The fuel tank and line hold and deliver the fuel to the carburetor. Injection molding

Injection molding


Injection molding


Injection molding


Die casting and machining


Die casting and machining

Click to View
7 Pull Start 2 Pull cord (1)

Pull cord disk (1)


Starter spring (1)


#2 Phillips button head machine screw (2)


Button head 5/32" hex socket cap screw (2)

Nylon string

Plastic


Steel


Steel


Steel

The pull start is used to start up the line trimmer by spinning the flywheel. The cord retracts back into the engine housing due to tension in the starter spring. Weaving

Injection molding


Metal stamping


Die casting and machining


Die casting and machining

Click to View
8 Crankcase Assembly 4 Crankshaft (1)

Drive coupling (1)


Flywheel (1)


Ball bearing (1)


Washer (1)


Gasket (2)

Steel

Steel


Aluminum alloy


Aluminum alloy


Steel


Rubber

The crankcase assembly transfers the power from the piston moving up and down to the drive shaft. The ball bearing allows this to spin very fast and smooth without generating too much heat. Die casting and machining

Die casting and machining


Die casting and machining


Die casting and machining


Die casting and machining


Injection molding

Click to View
9 Piston Assembly 3 Piston (1)

Piston ring (1)


Piston pin (1)


Piston pin retainer (1)


Connecting rod (1)

Aluminum alloy

Aluminum alloy


Aluminum alloy


Aluminum alloy


Aluminum alloy

The piston assembly is the device that moves up and down in the combustion cylinder as explosions occur. The connecting rod transfers this power to the crankshaft. Die casting and machining

Die casting and machining


Die casting and machining


Die casting and machining


Forging

Click to View
10 Combustion Cylinder 4 Combustion cylinder (1)

Standard head 3/16" hex socket cap screw (2)

Aluminum alloy

Steel

The combustion cylinder is where the fuel is injected and ignited by the spark plug. The combustion process that occurs here is the source of power. Sand casting and machining

Die casting and machining

Click to View
11 Air Filter 2 Air filter (1)

Air filter plate (1)


Air filter housing (1))

Foam

Steel


Plastic

The air filter is responsible for trapping dust that may enter with the air coming into the carburetor. Baked chemical mixture

Metal stamping


Injection molding

Click to View
12 Carburetor 2 Carburetor (1)

Choke shutter (1)


Carburetor spacer (1)


Gaskets (2)


Standard head 5/32" hex socket cap screw (2)


Button head 5/32" hex socket cap screw (2)


Phillips #2 button head machine screws (2)

Steel / Plastic

Steel


Plastic


Rubber


Steel


Steel


Steel

The carburetor mixes air with fuel for the combustion process. Air comes in through the air filter and fuel from the fuel, then depending on how much the throttle is engaged this air and fuel mixture is drawn into the combustion cylinder. The gaskets help to give a tight seal with the carburetor to the different parts so now fuel is lost. The choke shutter controls the amount of air in the fuel mixture. Metal casting, machining, injection molding

Metal stamping


Injection molding


Die casting and machining


Die casting and machining


Die casting and machining

Click to View
13 Muffler 3 Muffler cover (2)

Muffler baffle (2)


Tension springs (2)

Steel

Steel


Steel

The muffler system functions to quiet the combustion process for the user as well as slow down the combusted gas exiting. Metal stamping

Metal stamping


Wire drawing and winding

Click to View
14 Ignition Module 5 Ignition module (1)

Ignition module spacer (1)


Wire leads (3)


Spark plug (1)


On/off switch (1)


Standard head 5/32" hex socket cap screw (2)

Plastic

Steel


Rubber, copper


Plastic


Steel


Steel

The ignition module works to produce the spark that ignites the fuel mixture. There is a magnet on the flywheel and when this passes by the ignition module it induces a current with is fed to the spark plug inside the combustion cylinder. This occurs once every revolution when the piston reaches the top of the combustion chamber. Injection molding

Die casting


Wire drawing


Die casting and machining


Die casting


Die casting

Click to View

Component Details

Due to the great number of components in the product, only ten will be chosen to be looked at more closely. Components that are thought to be particularly interesting or used a lot in the line trimmer will be focused on. Many of the insights for these components may also be true for the components not focused on.


Foot guard

Part number- 530-069299
Choice of material- Plastic was chosen because it is relatively light weight compared to steel. High density plastics can offer relatively good strength to absorb impact from rocks kicked up by the trimming attachment. Aluminum could have offered the same light weight advantages and strength at plastic but would have been more costly.
Forces applied- around 20-30 lb from rocks kicked up
Shape- The foot guard has a triangular shape with a lip on it to provide a barrier between the user and the trimming attachment. The shape was chosen to minimize size and weight while still protecting the user from the spinning trimming attachment.
Choice of manufacturing process- Injection molding was chosen because it very effective for plastics. These guards are probably produced on a large scale for many other line trimmers, so this was a cost effective method.
Functional/cosmetic- The part is functional because it serves as a safety device to protect the user from the spinning trimming attachment and debris that is kicked up.


Trimming head

Part number- Unknown (aftermarket)
Choice of material- A high density plastic was chosen for this part because it is relatively strong for its purpose of trimming small brush and grass. A metal trimming attachment would be more dangerous to the user considering the speed that it is spinning at. A metal trimming attachment would be for professional use, where as the plastic trimming material is more for home use. Most individual do not need to trim extremely thick brush.
Forces applied- around 30 lb
Shape- The trimming head is circular with little plastic strings sticking out. This is because circular objects usually spin best due to their inertia. The extended strings allow for a greater for a greater tip velocity because they have a farther distance to travel at a given angular velocity.
Choice of manufacturing process- Injection molding was chosen because it very effective for plastics. This trimming attachment is probably produced on a large scale for many other line trimmers, so this was a cost effective method.
Functional/cosmetic- The trimming head is functional because it is the actual device that cuts the grass and brush. The choice of colors of the plastic is cosmetic because it is not as essential to the function.


Shape 1 Wing Nut

Part number- 530-091373
Choice of material- Steel was chosen to make the wing nut. This is because steel is a very strong, rigid material and will not deform very easily after being spun off and on a screw. The wing nut is so small that the decrease in weight by choosing aluminum would not be cost effective due to the greater expense.
Forces applied- around 12 lb
Shape- A wing nut was chosen because it is easy to loosen by hand. This is advantageous for the lower handle because it allows the user to easily adjust the position of the handle to the most comfortable spot.
Choice of manufacturing process- Die casting and machining were chosen. These are common processes for most fasteners. The shape of the wing nut was most likely achieved purely through die casting. Some machining was probably necessary to get the threads done.
Functional/cosmetic- The wing nut is functional because it holds the lower handle in place and allows for the user to easily adjust the position of it.


Button Head 5/32” Hex Socket Cap Screw

Part number- 530-015934
Choice of material- Steel was chosen to make all of the fasteners on this particular line trimmer. This is probably because steel is relatively inexpensive compared to aluminum and does not add a lot of weight considering fasteners are relatively small compared to the line trimmer. Plastic fasteners would break more easily and deform, where as steel fasteners are more durable and will last longer if they are removed for maintenance procedures.
Forces applied- varies- most are not subjected to more than a couple lb
Shape- The choice of a hex socket is probably because they are less prone to stripping than a Phillips or slot head screw. At the same time, most people who have somewhat of a toolbox will have a set of hex keys. A button head was most likely chosen because it allows for a lower profile considering most of these fasteners are on the case of the line trimmer.
Choice of manufacturing process- Die casting was chosen because these are produced on a very large scale. This fastener is used in many other things besides this particular line trimmer. Machining was probably made minimal for the threads to cut down costs and time of production.
Functional/cosmetic- These fasteners are functional because they serve to hold together many of the parts and components of the line trimmer. The choice of making them black is cosmetic rather than having them be grayish like steel.


Drive shaft cable

Part number- 530-094671
Choice of material- Steel was chosen for the drive shaft cable because it was the most practical option. A plastic drive shaft would wear down very fast and could deform due to heat from friction. An aluminum drive shaft would be more costly and unless a good alloy was used, the aluminum drive shaft could deform. Steel is able to hold its form very well, but at the same time be flexible as it was designed to be for this part.
Forces applied- moments of around 70 lb*ft
Shape- The drive shaft cable was made to be flexible so that it could follow a variety of shapes from the engine to the trimming attachment. This allows for a variety of designs of the line trimmer that will cater to the comfort of the user. The cable is also square at the ends and circular in the middle section. The square ends allow for a good connection between it and the drive coupling and trimming attachment. This will prevent slippage of the drive cable in each of these pieces. The cable is circular in the middle section because this will allow it to spin more smoothly inside the drive shaft.
Choice of manufacturing process- The cable was most likely die cast and machined. The small notches along the entire cable appear to be too sharp to be done in the casting process. Some sort of machine most likely cut in all of the small grooves along the cable.
Functional/cosmetic- The drive shaft cable is purely functional. The user cannot see the drive shaft cable while the line trimmer is in operation because it is inside its housing.


Starter Spring

Part number- 530-029395
Choice of material- Steel was chosen for the starter spring. Steel is chosen for nearly all springs. Steel is resistant to deforming from its current shape, so it tends to coil back to its shape when it is pulled on (if it is deformed a lot or bent it will not return to its shape).
Forces applied- around 10 lb
Shape- The spring was chosen to be wound in a spiral so that when the pull start was pulled it compressed the spring. The spring then pushed back on the pull cord disk which spun it in a direction so that it retracted the pull string. This shape is a relatively compact way to retract the pull cord.
Choice of manufacturing process- The spring was most likely stamped out of a large thin sheet of steel. The strip of thin steel that was stamped out was then wound into a spiral and the coil was placed into a disk.
Functional/cosmetic- The starter spring is functional. It serves to retract the pull cord after the line trimmer has been started (or attempted to be started).


Flywheel

Part number- 530-039149
Choice of material- Aluminum alloy was chosen to make the flywheel. This is most likely because the flywheel is a more crucial part of the device. A lighter weight flywheel is easier to spin and power. A steel flywheel would be heavier. Steel could also cause a problem with the ignition module. There is a magnet on the flywheel which triggers the spark plug on each revolution. A steel flywheel could become magnetized and induce an electric field on the ignition module at the wrong time and cause combustion at the wrong moment.
Forces applied- moments of around 70 lb*ft
Shape- The flywheel has fins around the edge rather than being a solid disk to save weight and material. There is a notch in the center of the flywheel so that it only fits onto the crankshaft one way. This is to ensure that the magnet on the flywheel will induce a magnetic field on the ignition module only at the desired moment when the piston is near the top of the combustion chamber.
Choice of manufacturing process- The flywheel was die cast to get the rough shape of it. Most of the surfaces are not finished, so the only machining was probably done to make sure that it fit well around the bearings and crankshaft.
Functional/cosmetic- The flywheel is purely functional. It is not seen by the user during operation. It serves to regulate the timing of the combustion process.


Combustion Cylinder

Part number- 530-012309
Choice of material- The combustion cylinder is made of aluminum alloy. Aluminum alloy offers a good strength to weight ratio. A steel combustion cylinder would have added a considerable amount of weight to the line trimmer. Aluminum is also better at dissipating excess heat from the combustion process to the surroundings.
Forces applied- around 80 lb
Shape- The combustion cylinder was designed with fins all around it. This was done intentionally to give added strength by having a thicker outer support as well as provide a larger surface area to dissipate excess heat from the combustion process. It can be see that the fins taper as the go out from the combustion cylinder. This is a sign that the cylinder was most likely die casted.
Choice of manufacturing process- The cylinder was die cast because it was most likely produced on a larger scale for other small gasoline engines. It is evident from the mold lines that can be seen up the side of the cylinder that this was a permanent mold cast. Machining was required to achieve a very smooth finish inside the combustion cylinder so that the piston could slide smoothly up and down in the cylinder while reducing losses to friction.
Functional/cosmetic- The combustion cylinder is function. It serves to house the combustion process. It is not painted to designed to be aesthetically pleasing because it is hardly visible to the user while the line trimmer is assembled.


Muffler

Part number- 530-069389
Choice of material- The muffler is made from a relatively thin sheet of steel. The muffler does not need to be very strong because there are not many forces of great magnitude applied to it. It does need to be able to handle warm gas coming from the combustion cylinder, which makes steel a more favorable choice than plastic. Aluminum would have been rather expensive and unnecessary because the weight saved is not significant.
Forces applied- around 15 lb (tension springs that hold it to the cylinder)
Shape- The muffler has a box shape with rounded corners. Inside there are baffles with staggered holes. The purpose of this shape is to slow down the exhaust coming out, giving it some extra time to cool down as well as decrease the amount of noise that is produced by the combustion inside the cylinder. This shape makes a less direct route for the exhaust gas to exit.
Choice of manufacturing process- The muffler was most likely shaped by metal stamping. Sheet steel is relatively cheap and easy to stamp out compared to casting. The muffler is not an extremely sensitive part, nor does it need to be exceptionally strong in a line trimmer, making stamping sufficient.
Functional/cosmetic- The muffler is a functional component. It serves to quiet the noise produced by combustions, as well as slow down and cool exhaust gases.


Carburetor

Part number- 530-035308
Choice of material- The carburetor contains plastic, rubber and steel. Steel was chosen as the main frame of the carburetor due to cheaper price. Rubber was chosen to make gaskets and other connections because of its ability to make good seals. Good seals are necessary because the carburetor mixes fuel with air. Plastic was used to cover some of the internal workings of the carburetor. Perhaps plastic was chosen to make one less set of parts that could rust together.
Forces applied- none
Shape- The carburetor has both a fuel and air inlet and a single outlet for the mixture of these two. It is relatively small because the line trimmer does not require a lot of fuel since it is a small engine with only one cylinder.
Choice of manufacturing process- Injection molding was chosen for the plastic and rubber parts because it is very common for these materials. It is cost effective on the larger scale that these would be produced at. Die casting and machining were chosen for the steel frame of the carburetor. Machining was necessary to get a smooth finish on the inlets and exits of the fuel and air, so these substances could flow smoothly through and be delivered to the engine.
Functional/cosmetic- The carburetor is purely functional. It serves to mix air with fuel before flowing into the cylinder. It has many small parts and seals, thus is not meant to be tampered with a lot. It is concealed by the air filter and engine housing.


Materials Chosen

The components of the line trimmer are made of common materials that are relatively inexpensive. One of the most common materials of the components was steel. Steel is relatively strong and is cheap in price. One of the sacrifices with steel is weight. Steel has a higher density than many other metals such as aluminum and magnesium alloys. Many of the steel components are relatively small, such as hardware, springs, and sheet metal, so a significant amount of weight would not be saved by making some of these components out of aluminum alloys, which are more expensive. The larger components like the combustion cylinder, piston, and flywheel are made of a lighter weight aluminum alloy. Choosing an aluminum alloy for these components most likely saved a couple pounds, which makes the line trimmer more appealing to the user justifying the extra cost. Plastic was used for the entire engine casing, trimming attachment and handles because it is relatively lightweight and strong. Plastic is cheap and can be molded into many shapes, colors and give a smooth finish. Rubber was used for many of the gaskets and lines because it can seal off connections well making them close to air tight. The foam air filter is a simple device than can keep large dust particles out of the internal workings of the engine and prevent it from getting even dirtier inside. The foam air filters were most likely cut out of a very large block of foam that was cooked.


Manufacturing Process Chosen

The choice of material has a significant effect on the manufacturing process. The components made of plastic needed to be injection molded. The components made of steel and aluminum alloys were mostly die casted. Die casting leaves a relatively smooth finish, but some surfaces that needed more precision were then machined. Machining can but costly for metal parts because it is time consuming, so the amount of it is usually minimized. Some components that were cast and have a rougher finish were most likely sand cast. Other steel components that are relatively thin were most likely stamped out. This is a relatively fast and inexpensive way to make parts that are made of sheet metal. Foam is a chemical mixture that has to be baked in the size of a large block. It can then be cut up into nearly any shape or size for use. Many of the wires and cables were drawn through a wire die where they were forced to a smaller diameter. For the electrical wires, they were then put inside rubber tubing.

Permanent mold casting was chosen for many of the metal components because it is one of the best options for components that are going to be made on a moderately large scale. Many of the components are common in small gas engines so they are probably used in engines other than that of a line trimmer. Machining was required for many of the screws and fittings between components because permanent casting alone is difficult to attain a high level of precision. It is more realistic to machine threads onto a screw that has been cast. Plastic components were chosen because they are light weight and plastic can be molded into nearly any shape. Injection molding is relatively cheap considering its flexibility.


Shape

Shape has a significant effect on the manufacturing process. Components that need square edges or intricate details can be difficult to manufacture in some processes. For plastics, these details can usually be achieved with injection molding. For metals, permanent castings typically cannot attain high levels of small detail and machining is necessary. Investment casting is capable of having higher levels of detail, but it is more expensive. The fluidity of metal is often a limiting factor when casting. On the combustion cylinder it is easy to see that the fins around the outside taper and the corners are round, which is typical of permanent mold casting. Components that can be made of thin sheet metal are most easily stamped out. This is a relatively fast and cheap process and is desirable when it is appropriate.

Many of the components have a particular shape. The components are shaped in a way that they can be assembled together in a way such that they do not interfere with each other’s function. The combustion cylinder has fins on around the cylinder that taper. This allows for better heat transfer from the combustion cylinder with the surrounding air so it does not overheat. The shape of the drive shaft housing is curved in a way that it makes the line trimmer more comfortable for the user to hold and trim with. The handles are designed in a way that the user can support the line trimmer easily.


Functional vs. Cosmetic

Nearly all of the components in the line trimmer are functional. One of the cosmetic components is the plastic engine housing. The line trimmer would run without the engine housing, but it would not look very user friendly because there would be lots of moving parts exposed. The engine casing is functional in a sense also that it protects the user from the moving parts of the small gas engine as well as some of the components that might be hot or dangerous for the user to touch.


Note- Part numbers are taken from the LT 7000 Part List, which can be found on the Weed Eater website.

Adobe Acrobat or Reader software is required to view PDF files, and can be downloaded from the Adobe Website.

Design Revisions

Our revisions to the line trimmer mainly focus on ease of use and transportability. The three components we chose to focus on were the starter, adding a sling, and the material of the drive shaft. The reason we chose to focus on these parts because we felt as users of this product at one time or another would be the best place to enhance the product to make it more marketable.

Electric Starter: This would replace the pull cord with an electric button of which would start the engine. This would greatly improve ease of use for the consumer because the pull start can be very difficult to use correctly and often malfunctions. The target group for this product is for families who often times have teenagers mow the lawn and a pull cord start can sometimes be challenging and harmful. To prevent shoulder injury and labor a electric start will ease the effort you have to put into the machine in order to use it. As a downside to this improvement, it would cause an increase in price. Also with the electronic components the machine is more susceptible to water damage and shocks. As with any additional components added to a machine it will also add maintenance.

In order to set up an electric start system, a few changes would have to be made. The pull cord and starter spring could be removed from inside the engine housing. A starter motor would then need to be installed in place. Instead of adding in an alternator, it would be easier add a rechargeable battery pack that the user could detach and recharge inside their home via a wall outlet between uses. An electric start system of this nature would not add much weight, if any.

Sling: This would add a sling just above the engine. The sling could attach on the engine casing and near the top of the drive shaft housing. This would increase the comfort level for the consumer because after extended use the line trimmer can be very uncomfortable. This sling will more evenly distribute weight across the body allowing you to use more major muscles to help support the bulky device. This will also reduce back injury as the stress on the back will be dramatically minimized. Often times an individual that has to support or carry a device of this nature will put the majority of the load on their back muscles and this is the most common source of back injury with such devices. The sling will prevent any hunching over and overall just increase comfort to the user. This improvement would only cause a slight increase in price. Also, some people prefer to mow their lawn and use a line trimmer shirtless and this strap could cause irritation to the skin. To overcome this, the strap would be removable.

Drive Shaft Housing: It would be beneficial to make the drive shaft housing out of an aluminum alloy rather than steel. Steel is heavier than an aluminum alloy would be, so this would assist in decreasing the overall weight of the line trimmer. This would be an advantage to the user because it would increase comfort during operation. A disadvantage to doing this is that aluminum alloys are more expensive than steel, so the cost of the line trimmer would most likely increase slightly. More extensive calculations would have to be made to see if the increased cost would outweigh the decrease in weight. An aluminum alloy drive shaft housing could be manufactured in a similar manner to the steel housing. The only increase in cost should be a result of the greater price of aluminum alloys.

Conclusion: All of these revisions coupled together will increase ease of use and comfort to the customer while not significantly increasing the price. This will make the product much more marketable to a wider range of potential buyers.

Solid Model Assembly

Choice of Components:

  • Combustion Cylinder - The component is essential to the functionality of the Line Trimmer. There are several associated components which interact with the Combustion Cylinder, making it a logical choice. Combustion Cylinder Model
  • Muffler - While not being an essential component for basic functionality, the muffler represents Engineering problem solving. The muffler both makes the engine run quietly as well as slows down the combusted gas that exits the Combustion Cylinder. Muffler Model
  • Spark Plug - This is responsible for transferring the induced current to the Combustion Cylinder. It shows how the simple chemical process of combustion is initiated with real components. Spark Plug Model


Assembly

  • Muffler Attached - The Muffler connects by fitting inside an orifice on the Combustion Cylinder and is additionally held on by compression springs (not shown). Muffler Attached View
  • Spark Plug Attached - The Spark Plug connects by inserting the threaded end into a threaded orifice on the Combustion Cylinder. Spark Plug Attached View


Choice of CAD Package:

Autodesk Inventor 2010 was used for all solid modeling. Inventor is free to college students, thus making it useful for group collaboration. Computers in the Bell Computing Lab additionally have Inventor installed, providing a useful backup solution in case of individual computer failure. Inventor also features easy-to-use manipulation tools such as simple threading which was important for the chosen components.

Engineering Analysis

Due to formatting constraints in wiki code, this section is linked below as a PDF file. Adobe Acrobat or Reader software is required to view PDF files, and can be downloaded from the Adobe Website.

Engineering Analysis

Engineering analysis can be used in the design and test stages to reduce the negative effects of possible problems, as well as reduce the possibility of problems occurring. Failure modes and effect analysis (FMEA) is a process often used in industry to predict possible failures in a product and classify each one by severity and determine the possible effects on the system. This process could be used in the design and test of line trimmers. Problems and failures that have a higher probability of occurring need extra attention. Possible points of failure that could cause injury should receive special attention to ensure that they do not occur. Solving engineering analysis problems, such as the one previously demonstrated, can give insight to the effect of a possible problem. Further testing could be done on the engineering analysis performed to see what kind of force would need to be applied to the fuel line to cause a leak of the size assumed. It could then be decided if this is a point of failure that could realistically occur and if action should be taken.


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