Self propelled lawnmower
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|Shoulder Bolt || || 4 || Attaches the wheel to the Pivoting arms with are then attached to the deck of the mower, allows the wheel to spin freely about the smooth section of the of the bolt. || Stte || Forged and rolled || | |Shoulder Bolt || || 4 || Attaches the wheel to the Pivoting arms with are then attached to the deck of the mower, allows the wheel to spin freely about the smooth section of the of the bolt. || Stte || Forged and rolled || | ||
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Revision as of 14:15, 20 September 2008
Contents |
Major Stakeholders and Needs
The self-propelled lawn mower has drastically improved the efficiency and quality of lawn mowing since the era of the push mower. The stakeholders involved include the customer, the manufacturer, the supplier of raw materials, and lawn owners. The customer can be anyone from a lawn owner to a commercial lawn mowing business. The customer must be ensured efficiency, quality, safety, and convenience. Therefore, it is essential that the self-propelled lawn mower is not too cumbersome, heavy, and well enough secured so that a customer of any size or strength can safely and effectively cut any lawn. This is also important when considering the lawn owner because the owner desires an attractive lawn, but wants to achieve this as quickly as possible so as to utilize the lawn. The manufacturer is responsible for producing a vast quantity of operative and safe lawn mowers, which can only be attained through the efficient and reliable shipment of raw materials from the raw material supplier.
PART LIST
| Part # | Name | Weight | Quantity | Function | Material | Manufacturing Process | Image | |||
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Front Wheel | 2 | Attaches to the front of the mower and allows the mower to roll horizontally | Plastic | Plastic Mold Injection | 
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| 2 | Rear Wheel | .5kg | 2 | Drives the Lawnmower, translates drive shaft motion into horizontal movement | Plastic | Plastic Mold Injection |
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| 3 | Rear Wheel Drive Gear | 2 | Translates the rotational motion of the drive shaft gear into rotational motion of the the wheel. Also the particular gearing provides more torque to the wheels. | Steel | Cast, Turning, milling |
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| 4 | Drive Gear Shield | 2 | Keeps grass adn other particle sfrom getting tion the drive gear mesh, also keeps the greas from leavintg the gears. | Black ABS Plastic | Plastic Mold Injection | |||||
| 5 | Shoulder Bolt | 4 | Attaches the wheel to the Pivoting arms with are then attached to the deck of the mower, allows the wheel to spin freely about the smooth section of the of the bolt. | Stte | Forged and rolled | 6 | Deck |
DESIGN FOR MANUFACTURE
FMEA
FMEA (Failure mode and effects analysis) is used to determine the potential problems with designs. It takes each component in a mechanical system and analyzes its failure modes and effects using three main criteria. These criteria are severity of the failure (S), probability of occurrence of the failure (O), and ease of detection of the failure (D). Each of these is ranked on a scale of 1 to 10. For severity, 1 is least severe and 10 is dangerous or catastrophic failure. For probability of occurrence, 1 is very unlikely and 10 is almost certain. For ease of detection, 1 is easiest to detect and 10 is impossible to detect. Once each component is assigned one number for each of the three criteria, the numbers are multiplied together to determine the RPN (risk priority number). This number can range from 1 to 1000. The higher the RPN for a specific component the greater the chance that this component needs to be looked at and improved. Along with assigning a numerical value to the risk of certain components, FMEA also attempts to determine the origin of the problem and possible solutions to improve components. It is important to note that design controls and recommended actions are intended to help the manufacturer improve the problem. The following table provides an FMEA analysis for the key components of the lawnmower.
| Item | 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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wheels | Translate power from drive shaft to horizontal motion | Plastic dries out and cracks | Mower can get stuck and won't move | 8 | Use of mower in dry weather too often | 5 | Use plastic that is less likely to dry out | 2 | 80 | Fatigue testing | Wheel manufacturer | 8 | 5 | 2 | 80 | |
| Wheels | Translate power from drive shaft to horizontal motion | Plastic dries out and cracks | Mower can get stuck and won't move | 8 | Use of mower in dry weather too often | 5 | Use plastic that is less likely to dry out | 2 | 80 | Fatigue testing | Wheel manufacturer | 8 | 5 | 2 | 80 | |
| Blade | Cut grass | Dulls | Grass cutting in ineffective | 8 | Natural wear with time | 7 | Use harder material that is less likely to dull | 2 | 112 | Fatigue testing | Design engineers | 8 | 7 | 2 | 112 | |
| Blade | Cut grass | Rusts | Grass cutting is uneven | 8 | Natural wear with time | 7 | Use material that does not rust | 3 | 168 | Waterproof coating | Design engineers | 8 | 7 | 3 | 168 | |
| Belt | Transfer power from engine to transmission | Rubber dries out and breaks | Rear wheel drive won't work | 6 | Use of mower in dry weather too often | 5 | Provide extra belts with mower | 5 | 150 | Analyze tension in belt | Design engineers | 6 | 5 | 5 | 150 | |
| Tires | Provide traction on wheels | Tread wears with time | Mower will lose traction and ability to climb hills | 4 | Natural wear with time | 7 | Consider different tread pattern that takes longer to wear | 1 | 28 | None, unlikely occurrence | 4 | 7 | 1 | 28 | ||
| Rear Wheel Gears | Gears down power from engine to rear wheels for increased torque | Teeth break | Rear wheels will not turn evenly or consistently | 1 | Too much strain on rear wheels | 2 | Consider different material for gears | 9 | 18 | None, unlikely occurrence | 1 | 2 | 9 | 18 | ||
| Cables | Attach to mounting bracket to engage transmission | Stretch | It will be difficult for the user to engage drive mechanism | 4 | Overuse of drive system | 5 | Improve connection points | 7 | 140 | Failure tests of connection points | Design engineers | 4 | 5 | 7 | 140 | |
| Cables | Attach to mounting bracket to engage transmission | Break | User cannot engage drive mechanism | 1 | Overuse of drive system | 2 | Lower required tension in cable by adding a system that provides mechanical advantage | 1 | 2 | None, unlikely occurrence | Design engineers | 1 | 2 | 1 | 2 | |
| Gas Tank | Holds fuel for engine | Leak | Engine will not be able to operate | 6 | Puncture from debris | 4 | Locate critical puncture points and reinforce them | 6 | 144 | Puncture testing | Design engineers | 6 | 4 | 6 | 144 | |
| Wheel Brackets | Allows user to change ride height and attaches wheels to chassis | Knobs for changing height break | Height cannot be changed | 8 | Constant Pressure on weld seam | 7 | Replace with removable piece so that it can be easily replaced if it does break | 1 | 56 | Knob redesign | Design engineers | 8 | 7 | 1 | 56 | |
| Wheel Brackets | Allows user to change ride height and attaches wheels to chassis | Constant bending can cause plastic deformation | Bracket is at risk of breaking | 7 | User bends bracket too much when changing height | 4 | Use material with a higher elastic modulus | 1 | 28 | None, unlikely occurrence | 7 | 4 | 1 | 28 | ||
| Driveshafts | Transfer power from transmission to rear wheels | Shear | Rear wheel drive won't work | 1 | Engaging rear drive while rear wheels are stuck | 1 | Reanalyze the key points where the driveshaft is attached | 2 | 2 | None, unlikely occurrence | 1 | 1 | 2 | 2
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