Bike lock
From DDL Wiki
(→U-Lock) |
Current revision (15:12, 3 February 2014) (view source) (→FMEA) |
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+ | [[Image:BikeLockStudy1.jpg|thumb|upright=2|Left: Serfas Puck Lock Right: OnGuard U-Lock]] | ||
+ | |||
= Executive Summary = | = Executive Summary = | ||
- | = Product | + | The goal of this project was to break down a product in order to take a look at the design decisions made in manufacturing, assembly, failure modes, and environmental impact. In each area, we assessed the weaknesses and strengths of the product and suggested possible improvements that could be made. The products we analyzed were two types of bike locks: a U-Lock and a Puck Lock. The first step was to understand how each was used and how each worked. That involved using the two products and dissecting the two products. After breaking down the bike locks into their individual parts, we were able to get a better understanding of how they worked, how the were manufactured, and how the were assembled. This allowed us to assess what were good design decisions and what design decisions could be improved with regards to manufacturing, assembly, failure modes, and environmental impact. |
+ | |||
+ | In terms of manufacturing and assembly, the products sacrifice some efficiency in the manufacturing and assembly fronts to achieve goals related to the better functioning of the product. With that being said, the manufacturability and ease of assembly of these products was not forgotten. A number of steps are taken to help improve the ease of manufacturing and assembly of these products, but it is evident where design trade offs were made. Especially in the housings of each lock, the need to have a strong casing that is resistant to the elements won out over the ease of assembly and manufacture of the lock. | ||
+ | |||
+ | In terms of failure modes, the product is relatively safe. Because the product uses no electricity and is used when the user is not riding his/her bike, the risk of injury to the user is greatly reduced. Most failure modes simply affect the operation of the lock from making it difficult to use to making it unusable. There is one failure mode, however, that stands out from the rest, and it occurs when the lock is actually not in use but in storage. Both bike locks come with bike frame attachments that allow the lock to be mounted to the bike when the user is riding his/her bike and not using the lock. Unfortunately, these attachments are not reliable, and the screws that clamp the attachments tend to come loose. This could result in the lock falling off the bike frame and getting in the way of the bike while the user is riding leading to possible damage to the user, bike, and/or lock. An action that we recommended to prevent this problem was to use screws with self-locking nuts that are more resistant to loosening under vibrations. | ||
+ | |||
+ | In terms of environmental impact, using the product itself has very little impact because it is completely mechanical and requires no electrical energy. As such, all of the environmental impact associated with this product comes from the manufacturing processes needed to produce the materials for the product and to produce the product itself. Therefore, in order to reduce the environmental impact, different materials with cheaper manufacturing processes could be considered for the production of the product as well as lower energy manufacturing processes overall. | ||
+ | |||
+ | = Product Stakeholders = | ||
+ | |||
+ | The following table lists the major stakeholders and their major product needs. | ||
+ | |||
+ | |||
+ | {|border="1" | ||
+ | |- | ||
+ | ! Stakeholders | ||
+ | ! Needs | ||
+ | |- | ||
+ | | Consumers<br />(Students, Enthusiasts, Families, etc.) | ||
+ | | align="left"| | ||
+ | *Cost Effective | ||
+ | *Strong Material | ||
+ | *Secure/Reliable (Difficult to Defeat Lock) | ||
+ | *Durable/Weatherproof | ||
+ | *Portable | ||
+ | *Lightweight | ||
+ | *Easy to Use | ||
+ | |- | ||
+ | | Distributors<br />(Retail Stores, Specialty Bike Shops) | ||
+ | | align="left"| | ||
+ | *Easy to Stack | ||
+ | *Easy to Display | ||
+ | *Aesthetically Pleasing Packaging | ||
+ | *Brand Name | ||
+ | *Low Cost but High Retail Price | ||
+ | |- | ||
+ | | Shipping/Transport | ||
+ | | align="left"| | ||
+ | *Easy to Store/Stack | ||
+ | *Durable | ||
+ | *Lightweight | ||
+ | |} | ||
+ | |||
= Product Usage Study = | = Product Usage Study = | ||
Line 41: | Line 85: | ||
= Product Function Study = | = Product Function Study = | ||
+ | |||
=== U Lock === | === U Lock === | ||
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[[Image:Puck4.jpg|thumb|center|upright=3]] | [[Image:Puck4.jpg|thumb|center|upright=3]] | ||
+ | |||
= Bill of Materials = | = Bill of Materials = | ||
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| align="center"|Spring sits under clasp and provides force on clasp to keep Lock attached to frame attachment. | | align="center"|Spring sits under clasp and provides force on clasp to keep Lock attached to frame attachment. | ||
| align="center"|Steel | | align="center"|Steel | ||
- | | align="center"|Off the | + | | align="center"|Off the Shelf |
| align="center"|[[Image:ThisIsASpring.jpg|100px|center]] | | align="center"|[[Image:ThisIsASpring.jpg|100px|center]] | ||
|- | |- | ||
Line 314: | Line 360: | ||
| align="center"|Key is specially made to line up with each of the pins in a specific lock. The track pulls the pins into the correct position, which allows the lock to rotate. | | align="center"|Key is specially made to line up with each of the pins in a specific lock. The track pulls the pins into the correct position, which allows the lock to rotate. | ||
| align="center"|Steel and Plastic | | align="center"|Steel and Plastic | ||
- | | align="center"| | + | | align="center"|Machining |
| align="center"|[[Image:ULockKey.jpg|100px|center]] | | align="center"|[[Image:ULockKey.jpg|100px|center]] | ||
|} | |} | ||
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=== Puck Lock === | === Puck Lock === | ||
[[Image:PuckLockAssem.jpg|thumb|center|upright=3|Exploded View of Puck Lock]] | [[Image:PuckLockAssem.jpg|thumb|center|upright=3|Exploded View of Puck Lock]] | ||
- | [[Image: | + | [[Image:NumberedThing.JPG|thumb|center|upright=2|Frame Clamp]] |
- | The following table contains information about each part labled in the above | + | The following table contains information about each part labled in the above images. |
{| border="1" align="center" | | {| border="1" align="center" | | ||
Line 468: | Line 514: | ||
| align="center"| 14 | | align="center"| 14 | ||
| align="center"|Worm Gear | | align="center"|Worm Gear | ||
+ | | align="center"|2 | ||
+ | | align="center"|Bike Frame Attachment | ||
| align="center"|1 | | align="center"|1 | ||
- | | align="center"| | + | | align="center"|Gears move the ridged straps tighten around the bike frame. Locks the straps in place. |
- | + | ||
- | + | ||
| align="center"|Plastic | | align="center"|Plastic | ||
| align="center"|Injection Molded | | align="center"|Injection Molded | ||
- | | align="center"| | + | | align="center"|[[Image:Wormgear.JPG|100px|center]] |
|- | |- | ||
| align="center"| 15 | | align="center"| 15 | ||
Line 480: | Line 526: | ||
| align="center"|1 | | align="center"|1 | ||
| align="center"|Bike Frame Attachment | | align="center"|Bike Frame Attachment | ||
- | | align="center"| | + | | align="center"|42 |
| align="center"|Wraps around the bike and lets you store the lock on the bike | | align="center"|Wraps around the bike and lets you store the lock on the bike | ||
| align="center"|Plastic | | align="center"|Plastic | ||
Line 488: | Line 534: | ||
= DFMA = | = DFMA = | ||
+ | |||
+ | ===Manufacturing=== | ||
+ | |||
+ | Our analysis of the manufacturability of the puck and u locks showed a number of design features and choices that greatly aided the overall manufacturability of both locks. One common feature of both is there avoidance of fasteners. Both designs made heavy use of highly specialized parts, press fits, and snap fits to reduce the need for fasteners. These choices allow for fewer surfaces and operations to hold and align fasteners while maintaining the high standard of weather resistance and robustness of the final design. Additionally, both locks maintain a very low number of unique components in each design. Either by keeping the locking mechanism simple, or using the same parts multiple times, the number of different types of parts is minimized to help simplify final assembly and necessary machinery for production. Lastly, both locks make heavy use of injection molded plastic components, which allows for cheaper and faster high volume production of complex plastic parts. Also, the puck lock combines stamped metal parts with injection molded coatings to produce multifunctional parts that had properties that better matched their proposed usage. While both locks possessed many good features that aided in manufacturability, there were also some design decisions that may have made the locks much more difficult to manufacture. | ||
+ | |||
+ | One major design choice that hurt manufacturability of these locks was a heavy reliance on secondary and finishing operations on a number of components. While often necessary for corrosion resistance or better operation within the given design, both locks make use of various coatings on metals, including injection molded plastic, power coating, and a possible titanium nitride finishing coating. Additionally, the puck lock’s housing consists of a complex set of two castings that given the nature of casting and the casting suggestions found in Rob Thompson’s ''Manufacturing Processes for Design Professionals'', we believe must have some kind of secondary operation to achieve the multiple cavities required in the design. In addition to the heavy reliance on secondary and finishing operations, both locks make heavy use of press fit components to reduce the number of fasteners and simplify manufacturing and assembly. While this is a positive for many design goals, this requires a much higher degree of accuracy when producing parts that may add to the cost and maintenance requirements of difficult to maintain production machines. Also, the additional features needed to help align press fit and snap fit components add to the overall complexity of the manufacturing. While many of these short comings for manufacturing are necessary trade-offs to achieve many of the design goals of these locks, we believe that it is possible to adjust the designs to reduce the difficulty of manufacturing caused by a number of these design choices. | ||
+ | |||
+ | ===Assembly=== | ||
+ | |||
+ | Both the u lock and the puck lock take similar steps to improve ease of assembly, but they also make a few missteps in the design stage that added complexity for the final stages of assembly. One positive factor is the heavy use of parts and sub-assembly with multiple functions. This is especially visible in the puck lock where plastic end caps serve as both chain retention mechanisms and interfaces for attaching to a user’s bike, as well as the housing which acts as the reel for the chain as well as the surface the lock latch engages with to lock the chain in place. In addition to multifunctional parts, both locks can be assembled in a “base up” fashion that allows for minimal rotation or adjustment of partial assembled locks throughout the full assembly process. Thanks to a heavy use of sub-assemblies that allow for greater access to difficult to assemble portions before they are tucked away within the lock body, both locks do a good job of taking advantage of assembling various portions of the lock before final assembly. Lastly, both locks make use of a minimal number of fasteners in their final assembly. Much of the u lock is press fit into place with a few pins and rubber pads to secure the lock and the entire housing of the puck lock is held together by two blind roll pins, two snap fit plastic guards, and a chain that is securely pinned to the housing. When coupled with adequate tapers and radii to aid in final alignment, these minimal fastener assembly methods greatly reduce the overall complexity of assembling both locks. | ||
+ | |||
+ | But, in order to maintain strength and corrosion resistance, two of the major design goals of lock design, both locks say an increase in assembly complexity that may be corrected in future iterations. One major problem is that some surfaces lack added features to help align press fit and tightly fit parts. While a number of areas do have these features, the u lock’s internal lock sub assembly is a cylinder that is carefully placed within its cylindrical housing with very tight tolerances and minimal guiding features to prevent slight misalignments in both insertion and proper alignment of the lock with the holes in the housing. As for the puck lock, the main roll pins used to hold the frame together would be difficult to align with the rounded face of the lock housing, making for a fairly difficult high pressure insertion of the roll pin. Another shortfall of both locks is their reliance on complex means of interfacing sub assemblies. For the puck lock, the custom chain requires repeated swaged pins to hold each member together as well as to hold together three separate components that all need to be aligned. As for the u lock, after placing the central lock assembly into its housing, the subsequent steps require careful alignment of compliant end caps and plugs to fit into the ends of the cylinder, requiring both special considerations to assemble once, and to perform again on the opposite side. With careful considerations during the design phase, a few of these inefficiencies can be alleviated, but some are the results of the need to build a robust, environmentally harden lock that will protect a consumer’s investment. | ||
+ | |||
+ | |||
=== U-Lock === | === U-Lock === | ||
{| border="1" align="center" | {| border="1" align="center" | ||
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Weaknesses: | Weaknesses: | ||
* If tolerances are too tight, the U-bar/locking assemblies do not fit together rendering the lock useless | * If tolerances are too tight, the U-bar/locking assemblies do not fit together rendering the lock useless | ||
+ | * Snap and slip fit components require tighter tolerances | ||
|- | |- | ||
| align="center"|'''Minimize Secondary and Finishing Operations''' | | align="center"|'''Minimize Secondary and Finishing Operations''' | ||
Line 562: | Line 623: | ||
| align="center"|'''Minimize Assembly Surfaces''' | | align="center"|'''Minimize Assembly Surfaces''' | ||
| Strengths: | | Strengths: | ||
- | * Main lock and latch sub assemblies | + | * Main lock and latch sub assemblies are assembled from one direction, main assembly can be easily assembled with minimal reorientation of the assembled parts |
|- | |- | ||
| align="center"|'''Use Sub Assemblies''' | | align="center"|'''Use Sub Assemblies''' | ||
Line 593: | Line 654: | ||
* Most of the lock can be assembled from either end and sequentially, requiring no repositioning to the finished assembly | * Most of the lock can be assembled from either end and sequentially, requiring no repositioning to the finished assembly | ||
Weaknesses: | Weaknesses: | ||
- | * Insertion of the | + | * Insertion of the U-bar into the lock for packaging and shipping may require additional manufacturing considerations of orientation of the lock during assembly and positioning of various assembly equipment |
|- | |- | ||
| align="center"|'''Provide Unobstructed Access''' | | align="center"|'''Provide Unobstructed Access''' | ||
Line 633: | Line 694: | ||
| align="center"|'''Commonize Product Line''' | | align="center"|'''Commonize Product Line''' | ||
| Strengths: | | Strengths: | ||
- | * | + | * Individual components have features that prevents them from being assembled incorrectly which eliminates any specialized training |
Weaknesses: | Weaknesses: | ||
* The complex shape of the housing may require additional complex steps to produce essential features | * The complex shape of the housing may require additional complex steps to produce essential features | ||
Line 737: | Line 798: | ||
= FMEA = | = FMEA = | ||
- | + | Through the Failure Modes and Effects Analysis, it was determined that bike locks as products overall are fairly safe to use. They are completely mechanical products that do not consume any electrical power, and their primary function is served not when the user is actually using a bike, but when he/she needs to securely store his/her bike. Because of this, during its primary use, a bike lock is highly unlikely to cause injuries to the user even if it fails. Failures with a bike lock will primarily result in an unusable product and/or compromised security for the user's bike. The only other instance when failure of the product would be of concern is when it is not in use and is being stored while the user is riding his/her bike. In fact, the FMEA indicates that if a bike frame attachment component is used to hold the lock while the user is riding, then that is when the user is at the most risk. Looking at the components of the bike lock, the bike frame attachment component received the highest Risk Priority Number by far because a failure with this component could cause the bike lock to come loose and get in the way of the bike as the user is riding resulting in potential damage to the lock, bike, and user. Additionally, after speaking with the employees of Biketek, a bike shop in Pittsburgh, it was discovered that the bike frame attachment components are not very reliable and that that is a main concern for users. Many users are looking for a better way to store their bike locks on their bikes. One factor that was seen to contribute to the unreliability of the bike frame attachment components was the screws used to connect the attachment component to the bike. These could easily come loose, and it would be difficult for the user to detect this. As such, the recommended action is to use screws with self-locking nuts to decrease the possibility of the screws coming loose. While this is a simple, inexpensive, and immediate solution, other options should be researched and assessed. | |
+ | There are two other failure modes that jump out from the rest, and these affect the usability of the bike lock. The first deals with dirt, grime, and water getting into the lock mechanism and housing. This could cause corrosion of the lock mechanism and housing, which would affect the moving components of the lock mechanism making the lock more difficult to use. While the dissected locks were fairly well sealed against the outside environment, the keyholes are always exposed. A cheap and simple solution to this would be to attach some form of rubber or plastic cover to the housing that could be press fit over the keyhole when it is not needed. The second failure deals with the bike lock getting cold enough that it can be easily cracked or damaged through impact. In a Popular Science article, it was demonstrated that if cooled to a low enough temperature, a bike lock would be brittle enough to be easily smashed with a hammer. While not highly likely to occur, it is possible depending on the user's location and the season. Plus, this failure is severe because it renders the bike lock unusable, and it compromises the security of the user's bike. A proposed solution is to incorporate some sort of insulating material around the lock housing. | ||
+ | |||
+ | The complete FMEA tables can be found below along with the criteria used to assess severity, probability of occurrence, and detectability of failure. These criteria were taken from Dieter and Schmidt's Engineering Design (5th Edition). | ||
+ | |||
+ | {| border="1" align="center" | ||
+ | |+ '''Rating for Severity of Failure''' | ||
+ | |- | ||
+ | ! Rating | ||
+ | ! Severity Description | ||
+ | |- | ||
+ | | align="center"| 1 | ||
+ | | align="center"| The effect is not noticed by the customer. | ||
+ | |- | ||
+ | | align="center"| 2 | ||
+ | | align="center"| Very slight effect noticed by customer; does not annoy or inconvenience customer. | ||
+ | |- | ||
+ | | align="center"| 3 | ||
+ | | align="center"| Slight effect that causes customers annoyance, but they do not seek service. | ||
+ | |- | ||
+ | | align="center"| 4 | ||
+ | | align="center"| Slight effect, customer may return product for service. | ||
+ | |- | ||
+ | | align="center"| 5 | ||
+ | | align="center"| Moderate effect, customer requires immediate service. | ||
+ | |- | ||
+ | | align="center"| 6 | ||
+ | | align="center"| Significant effect, causes customer dissatisfaction; may violate a regulation or design code. | ||
+ | |- | ||
+ | | align="center"| 7 | ||
+ | | align="center"| Major effect, system may not be operable; elicits customer complaint; may cause injury. | ||
+ | |- | ||
+ | | align="center"| 8 | ||
+ | | align="center"| Extreme effect, system is inoperable and a safety problem. May cause severe injury. | ||
+ | |- | ||
+ | | align="center"| 9 | ||
+ | | align="center"| Critical effect, complete system shutdown; safety risk. | ||
+ | |- | ||
+ | | align="center"| 10 | ||
+ | | align="center"| Hazardous; failure occurs without warning; life-threatening. | ||
+ | |} | ||
+ | <div class="center" style="width: auto; margin-left: auto; margin-right: auto;"><small>Source: Dieter and Schmidt, Engineering Design</small></div> | ||
+ | |||
+ | |||
+ | {| border="1" align="center" | ||
+ | |+ '''Rating for Occurrence of Failure''' | ||
+ | |- | ||
+ | ! Rating | ||
+ | ! Approximate Probability of Failure | ||
+ | ! Description of Occurrence | ||
+ | |- | ||
+ | | align="center"| 1 | ||
+ | | align="center"| <0.000001 | ||
+ | | align="center"| Extremely remote. | ||
+ | |- | ||
+ | | align="center"| 2 | ||
+ | | align="center"| 0.00001 | ||
+ | | align="center"| Remote, very unlikely. | ||
+ | |- | ||
+ | | align="center"| 3 | ||
+ | | align="center"| 0.00001 | ||
+ | | align="center"| Very slight chance of occurrence. | ||
+ | |- | ||
+ | | align="center"| 4 | ||
+ | | align="center"| 0.0004 | ||
+ | | align="center"| Slight chance of occurrence. | ||
+ | |- | ||
+ | | align="center"| 5 | ||
+ | | align="center"| 0.002 | ||
+ | | align="center"| Occasional occurrence. | ||
+ | |- | ||
+ | | align="center"| 6 | ||
+ | | align="center"| 0.01 | ||
+ | | align="center"| Moderate occurrence. | ||
+ | |- | ||
+ | | align="center"| 7 | ||
+ | | align="center"| 0.04 | ||
+ | | align="center"| Frequent occurrence. | ||
+ | |- | ||
+ | | align="center"| 8 | ||
+ | | align="center"| 0.2 | ||
+ | | align="center"| High occurrence. | ||
+ | |- | ||
+ | | align="center"| 9 | ||
+ | | align="center"| 0.33 | ||
+ | | align="center"| Very high occurrence. | ||
+ | |- | ||
+ | | align="center"| 10 | ||
+ | | align="center"| >0.5 | ||
+ | | align="center"| Extremely high occurrence. | ||
+ | |} | ||
+ | <div class="center" style="width: auto; margin-left: auto; margin-right: auto;"><small>Source: Dieter and Schmidt, Engineering Design</small></div> | ||
+ | |||
+ | |||
+ | {| border="1" align="center" | ||
+ | |+ '''Rating for Detection of Failure''' | ||
+ | |- | ||
+ | ! Rating | ||
+ | ! Description of Detection | ||
+ | |- | ||
+ | | align="center"| 1 | ||
+ | | align="center"| Almost certain to detect. | ||
+ | |- | ||
+ | | align="center"| 2 | ||
+ | | align="center"| Very high chance of detection. | ||
+ | |- | ||
+ | | align="center"| 3 | ||
+ | | align="center"| High chance of detection. | ||
+ | |- | ||
+ | | align="center"| 4 | ||
+ | | align="center"| Moderately high chance of detection. | ||
+ | |- | ||
+ | | align="center"| 5 | ||
+ | | align="center"| Medium chance of detection. | ||
+ | |- | ||
+ | | align="center"| 6 | ||
+ | | align="center"| Low chance of detection. | ||
+ | |- | ||
+ | | align="center"| 7 | ||
+ | | align="center"| Slight chance of detection. | ||
+ | |- | ||
+ | | align="center"| 8 | ||
+ | | align="center"| Remote chance of detection. | ||
+ | |- | ||
+ | | align="center"| 9 | ||
+ | | align="center"| Very remote chance of detection. | ||
+ | |- | ||
+ | | align="center"| 10 | ||
+ | | align="center"| No chance of detection; no inspection. | ||
+ | |} | ||
+ | <div class="center" style="width: auto; margin-left: auto; margin-right: auto;"><small>Source: Dieter and Schmidt, Engineering Design</small></div> | ||
+ | |||
+ | |||
+ | === U-Lock === | ||
{| border="1" align="center" | {| border="1" align="center" | ||
Line 756: | Line 950: | ||
|- | |- | ||
| align="center"| Key | | align="center"| Key | ||
- | | align="center"| *unlocking and locking U-Lock | + | | align="center"| |
- | | align="center"| *deformation and/or breaking due to bending stress and/or torsional shear stress | + | *unlocking and locking U-Lock |
- | | align="center"| *can no longer unlock or lock bike *need to replace key | + | | align="center"| |
+ | *deformation and/or breaking due to bending stress and/or torsional shear stress | ||
+ | | align="center"| | ||
+ | *can no longer unlock or lock bike | ||
+ | *need to replace key | ||
+ | | align="center"| 6 | ||
| align="center"| | | align="center"| | ||
+ | *improper use | ||
+ | | align="center"| 2 | ||
| align="center"| | | align="center"| | ||
+ | *multiple keys provided | ||
+ | | align="center"| 1 | ||
+ | | align="center"| 12 | ||
+ | | align="center"| None | ||
+ | |- | ||
+ | | align="center"| Lock Mechanism | ||
+ | | align="center"| | ||
+ | *takes input from key and engages or disengages the lock | ||
+ | | align="center"| | ||
+ | *lock mechanism gets jammed or becomes difficult to turn | ||
+ | | align="center"| | ||
+ | *unlocking and locking bike is more difficult | ||
+ | | align="center"| 5 | ||
| align="center"| | | align="center"| | ||
+ | *dirt and grim get into the lock mechanism via keyhole or connection to U-Bar | ||
+ | *water gets into mechanism and causes corrosion | ||
+ | | align="center"| 4 | ||
| align="center"| | | align="center"| | ||
+ | *system is well sealed against environment with exception of keyhole | ||
+ | *aside from housing, lock system is composed of brass, plastic, and titanium nitride coated steel, which all resist rust | ||
+ | | align="center"| 3 | ||
+ | | align="center"| 60 | ||
+ | | align="center"| | ||
+ | *incorporate a plastic/rubber cover for keyhole | ||
+ | |- | ||
+ | | align="center"| U-Bar | ||
+ | | align="center"| | ||
+ | *connects bike to locking structure | ||
+ | | align="center"| | ||
+ | *bending | ||
+ | | align="center"| | ||
+ | *can no longer use lock | ||
+ | | align="center"| 7 | ||
+ | | align="center"| | ||
+ | *impact/improper use | ||
+ | | align="center"| 2 | ||
+ | | align="center"| None | ||
+ | | align="center"| 1 | ||
+ | | align="center"| 14 | ||
| align="center"| | | align="center"| | ||
+ | *use a stronger material | ||
+ | |- | ||
+ | | align="center" rowspan="2"| Lock Housing | ||
+ | | align="center" rowspan="2"| | ||
+ | *contains all the elements for the lock mechanism and creates a closed loop with the U-Bar | ||
+ | | align="center"| | ||
+ | *metal pipe housing corrodes | ||
+ | | align="center"| | ||
+ | *difficulty using lock since moving components could be affected by corrosion | ||
+ | | align="center"| 3 | ||
+ | | align="center"| | ||
+ | *excess water getting into lock housing due to rain or other reasons | ||
+ | | align="center"| 4 | ||
+ | | align="center"| | ||
+ | *coating on outer surface helps prevent corrosion | ||
+ | *system is well sealed with exception of keyhole | ||
+ | | align="center"| 5 | ||
+ | | align="center"| 60 | ||
| align="center"| | | align="center"| | ||
+ | *incorporate a plastic/rubber cover for keyhole | ||
+ | |- | ||
+ | | align="center"| | ||
+ | *metal pipe housing cracks | ||
+ | | align="center"| | ||
+ | *security of lock compromised | ||
+ | *can no longer use lock | ||
+ | | align="center"| 8 | ||
+ | | align="center"| | ||
+ | *cold temperatures during winter months cause the metal to become more brittle and impacts could cause cracking | ||
+ | | align="center"| 1 | ||
+ | | align="center"| None | ||
+ | | align="center"| 8 | ||
+ | | align="center"| 64 | ||
| align="center"| | | align="center"| | ||
+ | *incorporate an insulated covering for lock housing | ||
+ | |- | ||
+ | | align="center" rowspan="2"| Bike Frame Clamp | ||
+ | | align="center" rowspan="2"| | ||
+ | *carries lock on bike when lock not in use | ||
+ | | align="center"| | ||
+ | *plastic components crack | ||
+ | | align="center"| | ||
+ | *attachment clip can no longer be used | ||
+ | *bike lock could come loose during riding and cause injury to the rider and/or bike | ||
+ | | align="center"| 7 | ||
+ | | align="center"| | ||
+ | *impact/improper use | ||
+ | | align="center"| 3 | ||
+ | | align="center"| None | ||
+ | | align="center"| 8 | ||
+ | | align="center"| 168 | ||
| align="center"| | | align="center"| | ||
- | |- | + | *look at other attachment options that use softer plastics |
- | | | + | |- |
- | | | + | | align="center"| |
- | | | + | *screws come loose |
+ | | align="center"| | ||
+ | *attachment clip can no longer be used | ||
+ | *bike lock could come loose during riding and cause injury to the rider and/or bike | ||
+ | | align="center"| 7 | ||
+ | | align="center"| | ||
+ | *wear over time causing threads to get stripped | ||
+ | | align="center"| 4 | ||
+ | | align="center"| | ||
+ | *initial check to make sure all screws and corresponding components work | ||
+ | | align="center"| 5 | ||
+ | | align="center"| 140 | ||
+ | | align="center"| | ||
+ | *use self-locking nuts to secure the screws | ||
|} | |} | ||
+ | |||
=== Puck Lock === | === Puck Lock === | ||
+ | |||
+ | {| border="1" align="center" | ||
+ | |+ '''Failure Mode and Effects Analysis''' | ||
+ | |- | ||
+ | ! Item | ||
+ | ! Function | ||
+ | ! Failure Mode | ||
+ | ! Effects of Failure | ||
+ | ! S | ||
+ | ! Causes of Failure | ||
+ | ! O | ||
+ | ! Design Controls | ||
+ | ! D | ||
+ | ! RPN | ||
+ | ! Recommended Actions | ||
+ | |- | ||
+ | | align="center"| Key | ||
+ | | align="center"| | ||
+ | *unlocking and locking U-Lock | ||
+ | | align="center"| | ||
+ | *deformation and/or breaking due to bending stress and/or torsional shear stress | ||
+ | | align="center"| | ||
+ | *can no longer unlock or lock bike | ||
+ | *need to replace key | ||
+ | | align="center"| 6 | ||
+ | | align="center"| | ||
+ | *improper use | ||
+ | | align="center"| 2 | ||
+ | | align="center"| | ||
+ | *multiple keys provided | ||
+ | *key is for a tubular lock, so the shape is more resistant to bending and torsion | ||
+ | | align="center"| 1 | ||
+ | | align="center"| 12 | ||
+ | | align="center"| None | ||
+ | |- | ||
+ | | align="center"| Lock Mechanism | ||
+ | | align="center"| | ||
+ | *takes input from key and engages or disengages the lock | ||
+ | | align="center"| | ||
+ | *lock mechanism gets jammed or becomes difficult to turn | ||
+ | | align="center"| | ||
+ | *unlocking and locking bike is more difficult | ||
+ | | align="center"| 5 | ||
+ | | align="center"| | ||
+ | *dirt and grim get into the lock mechanism via keyhole | ||
+ | *water gets into mechanism and causes corrosion | ||
+ | | align="center"| 4 | ||
+ | | align="center"| | ||
+ | *lock mechanism is made of stainless steel and resists corrosion | ||
+ | | align="center"| 3 | ||
+ | | align="center"| 60 | ||
+ | | align="center"| | ||
+ | *incorporate a plastic/rubber cover for keyhole | ||
+ | |- | ||
+ | | align="center"| Chain | ||
+ | | align="center"| | ||
+ | *wraps around locking structure and bike to secure the bike | ||
+ | | align="center"| | ||
+ | *bending | ||
+ | | align="center"| | ||
+ | *chain can no longer be wrapped up for storage | ||
+ | | align="center"| 4 | ||
+ | | align="center"| | ||
+ | *improper use | ||
+ | | align="center"| 2 | ||
+ | | align="center"| None | ||
+ | | align="center"| 1 | ||
+ | | align="center"| 8 | ||
+ | | align="center"| | ||
+ | *use a stronger material | ||
+ | |- | ||
+ | | align="center" rowspan="2"| Lower Outer Plastic Cover | ||
+ | | align="center" rowspan="2"| | ||
+ | *for aesthetics | ||
+ | *has a "retaining" bump that holds the chain in place when it is wrapped around the lock housing for storage | ||
+ | | align="center"| | ||
+ | *entire component or part of component snaps off | ||
+ | | align="center"| | ||
+ | *not as aesthetically pleasing | ||
+ | *chain can no longer be wrapped up for storage | ||
+ | | align="center"| 4 | ||
+ | | align="center"| | ||
+ | *impact/improper use | ||
+ | | align="center"| 4 | ||
+ | | align="center"| None | ||
+ | | align="center"| 1 | ||
+ | | align="center"| 16 | ||
+ | | align="center"| | ||
+ | *lock should come with replacement parts | ||
+ | |- | ||
+ | | align="center"| | ||
+ | *"retaining" bump wears down | ||
+ | | align="center"| | ||
+ | *not as aesthetically pleasing | ||
+ | *chain can no longer be wrapped up for storage | ||
+ | | align="center"| 4 | ||
+ | | align="center"| | ||
+ | *wear/fatigue over time | ||
+ | | align="center"| 4 | ||
+ | | align="center"| None | ||
+ | | align="center"| 3 | ||
+ | | align="center"| 48 | ||
+ | | align="center"| | ||
+ | *lock should come with replacement parts | ||
+ | *locking mechanism should also be used to lock the chain in place when it is stored instead of using a "retaining" bump | ||
+ | |- | ||
+ | | align="center"| Outer Plastic Cover | ||
+ | | align="center"| | ||
+ | *for aesthetics | ||
+ | | align="center"| | ||
+ | *entire component or part of component snaps off | ||
+ | | align="center"| | ||
+ | *not as aesthetically pleasing | ||
+ | | align="center"| 3 | ||
+ | | align="center"| | ||
+ | *impact/improper use | ||
+ | | align="center"| 4 | ||
+ | | align="center"| None | ||
+ | | align="center"| 1 | ||
+ | | align="center"| 12 | ||
+ | | align="center"| | ||
+ | *lock should come with replacement parts | ||
+ | |- | ||
+ | | align="center" rowspan="2"| Lock Housing | ||
+ | | align="center" rowspan="2"| | ||
+ | *contains all the elements for the lock mechanism and creates a closed loop with the free end of the Chain | ||
+ | | align="center"| | ||
+ | *corrosion | ||
+ | | align="center"| | ||
+ | *difficulty using lock since moving components could be affected by corrosion | ||
+ | | align="center"| 3 | ||
+ | | align="center"| | ||
+ | *excess water getting into lock housing due to rain or other reasons | ||
+ | | align="center"| 2 | ||
+ | | align="center"| | ||
+ | *coating on outer surface helps prevent corrosion | ||
+ | *material is stainless steel, which resists corrosion | ||
+ | | align="center"| 5 | ||
+ | | align="center"| 30 | ||
+ | | align="center"| | ||
+ | *incorporate a plastic/rubber cover for keyhole | ||
+ | |- | ||
+ | | align="center"| | ||
+ | *cracks/fractures | ||
+ | | align="center"| | ||
+ | *security of lock compromised | ||
+ | *can no longer use lock | ||
+ | | align="center"| 8 | ||
+ | | align="center"| | ||
+ | *cold temperatures during winter months cause the metal to become more brittle and impacts could cause cracking | ||
+ | | align="center"| 1 | ||
+ | | align="center"| None | ||
+ | | align="center"| 8 | ||
+ | | align="center"| 64 | ||
+ | | align="center"| | ||
+ | *incorporate an insulated covering for lock housing | ||
+ | |- | ||
+ | | align="center"| Bike Frame Attachment | ||
+ | | align="center"| | ||
+ | *carries lock on bike when lock not in use | ||
+ | | align="center"| | ||
+ | *worm gears securing attachment to bike come loose | ||
+ | | align="center"| | ||
+ | *bike lock could come loose during riding and fall off causing injury to the rider and/or bike | ||
+ | | align="center"| 7 | ||
+ | | align="center"| | ||
+ | *plastic worm gears and grooves experience wear since system is relying upon tension to hold everything in place | ||
+ | | align="center"| 4 | ||
+ | | align="center"| None | ||
+ | | align="center"| 5 | ||
+ | | align="center"| 140 | ||
+ | | align="center"| | ||
+ | *employ screws and self-locking nuts to secure the Bike Frame Attachment to the bike | ||
+ | |} | ||
= DFE = | = DFE = | ||
Line 817: | Line 1,292: | ||
[[Image:mtCO2eGraph.png]] | [[Image:mtCO2eGraph.png]] | ||
- | = Group = | + | |
+ | = Group Task Allocations = | ||
+ | |||
+ | For our group, we split into teams to perform the dissections because we had multiple bike locks to dissect. Afterward, we assigned the following roles, but we tried to work together as much as possible in case anybody had questions or needed to discuss issues concerning their part. Communication outside of group work was established via email and group text messages. | ||
+ | |||
Team Leader and FMEA Lead - Jeremy Jiang | Team Leader and FMEA Lead - Jeremy Jiang | ||
- | Bill of | + | Bill of Materials - Ryan Chang |
- | DFMA Leads - Rachel Chow and Alex | + | DFMA Leads - Rachel Chow and Alex Muñoz |
DFE Lead - Melissa Mann | DFE Lead - Melissa Mann | ||
- | = | + | = References = |
+ | |||
+ | Thompson, Rob. "Manufacturing Processes for Design Professionals." New York: Thames & Hudson, 2012. Print. | ||
+ | |||
+ | |||
+ | Gray, Theodore. "Science Of Theft: Freeze A Bike Lock With Canned Air, Then Smash It With A Hammer." Popular Science. N.p., 24 Sept. 2012. Web. 02 Feb. 2014. | ||
+ | |||
+ | |||
+ | Dieter, George Ellwood., and Linda C . Schmidt. Engineering Design. 5th ed. New York: McGraw-Hill, 2013. Print. | ||
Current revision
Contents |
Executive Summary
The goal of this project was to break down a product in order to take a look at the design decisions made in manufacturing, assembly, failure modes, and environmental impact. In each area, we assessed the weaknesses and strengths of the product and suggested possible improvements that could be made. The products we analyzed were two types of bike locks: a U-Lock and a Puck Lock. The first step was to understand how each was used and how each worked. That involved using the two products and dissecting the two products. After breaking down the bike locks into their individual parts, we were able to get a better understanding of how they worked, how the were manufactured, and how the were assembled. This allowed us to assess what were good design decisions and what design decisions could be improved with regards to manufacturing, assembly, failure modes, and environmental impact.
In terms of manufacturing and assembly, the products sacrifice some efficiency in the manufacturing and assembly fronts to achieve goals related to the better functioning of the product. With that being said, the manufacturability and ease of assembly of these products was not forgotten. A number of steps are taken to help improve the ease of manufacturing and assembly of these products, but it is evident where design trade offs were made. Especially in the housings of each lock, the need to have a strong casing that is resistant to the elements won out over the ease of assembly and manufacture of the lock.
In terms of failure modes, the product is relatively safe. Because the product uses no electricity and is used when the user is not riding his/her bike, the risk of injury to the user is greatly reduced. Most failure modes simply affect the operation of the lock from making it difficult to use to making it unusable. There is one failure mode, however, that stands out from the rest, and it occurs when the lock is actually not in use but in storage. Both bike locks come with bike frame attachments that allow the lock to be mounted to the bike when the user is riding his/her bike and not using the lock. Unfortunately, these attachments are not reliable, and the screws that clamp the attachments tend to come loose. This could result in the lock falling off the bike frame and getting in the way of the bike while the user is riding leading to possible damage to the user, bike, and/or lock. An action that we recommended to prevent this problem was to use screws with self-locking nuts that are more resistant to loosening under vibrations.
In terms of environmental impact, using the product itself has very little impact because it is completely mechanical and requires no electrical energy. As such, all of the environmental impact associated with this product comes from the manufacturing processes needed to produce the materials for the product and to produce the product itself. Therefore, in order to reduce the environmental impact, different materials with cheaper manufacturing processes could be considered for the production of the product as well as lower energy manufacturing processes overall.
Product Stakeholders
The following table lists the major stakeholders and their major product needs.
Stakeholders | Needs |
---|---|
Consumers (Students, Enthusiasts, Families, etc.) |
|
Distributors (Retail Stores, Specialty Bike Shops) |
|
Shipping/Transport |
|
Product Usage Study
U-Lock
First, the user will place their bike next to a locking structure. The user will unlock the U-Lock, place the U around the locking structure and the bike frame, then they will return the base to the U-Bar and remove the key. The bike frame is now secured to the locking structure.
Possible User Issues
Lock can only secure one part of the bike, most commonly the frame. The wheels are still unprotected with this. This constraint is due to the geometry of the U-Bar. It must be small enough to not be a burden to carry around, but must also be large enough to easily fit around most structures and the bike frame. Some users do not use the included clamp, as it may not fit around every bike. They must find some other method of securing the lock to the bike. It sometimes can be difficult to get the notches in the U-Bar to line up properly with the locking bars. If they are misaligned, the key will not turn back, causing frustration.
Puck Lock
First, the user will place their bike next to a locking structure. The user will then unravel the chain around the puck lock. User will wrap the chain around the locking structure and as many parts of the bike as possible. (eg. frame and wheel) The user will then resecure the chain to the central lock cylinder and lock the lock.
Possible User Issues
Small chain makes it hard to connect multiple bike components. May leave some parts unsecured. The links can rotate around each other in the wrong way, which makes it difficult to wrap the lock. The long chain, when fully extended, can act as a lever arm and bend the links.
Product Function Study
U Lock
Two bars are moved into place while the key is in the locked position, as indicated by the arrows in the image below. These bars are attached to small nubs on top of the lock assembly. When the key is turned, these nubs turn, which translates to the bars sliding. Only the correct key will match up with the pins in the correct location in order to move the bolts. This locking assembly runs through the center of the base. These bars fit into the notches indicated out in the below figure. Two bars adds a layer of redundancy and makes the lock less prone to being broken compared to single bolt U-Locks.
Puck Lock
This lock consists of a central housing with tubular tumbler locking mechanism and a series of plastic covered metal linkages. The linkage chain stays coiled around the center cylinder of the lock via a plastic retainer at the bottom of the lock, keeping the chain securely and neatly stowed when not in use. This plastic retainer on the bottom of the housing has a circular bump that fits into the free end of the last link holding it tightly in place until the clip is depressed. This releases the chain end allowing it to be unraveled from the center cylinder. Once fully unraveled, the main lock pin can be disengaged via the tubular tumbler lock mechanism located in the center of the housing. The key is used to open the tumbler lock and disengage a pin that runs through the center of the lock housing allowing the free end of the chain to be inserted into a slot at the bottom of the housing. The pin can then be depressed fitting into the open joint on the free end of the last link thereby locking the whole system. The pinned together metal plates act as the chain while the housing functions both as the storage device and lock for the system. To unlock the mechanism, the key is once again used to unlock the central pin freeing the chain to be unraveled from the bike and rewound around the central cylinder where it can be neatly stored until its next use.
Bill of Materials
U-Lock
The following table contains information about each part labled in the above image.
Part # | Name | Quantity | Subassembly | Mass [g] | Function | Material | Manufacturing Process | Image |
---|---|---|---|---|---|---|---|---|
1 | Rubber Shielding | 1 | N/A | 68 | Provides weatherproofing for the U-Bar. It keeps dirt and grime out and prevents scratches. In comparison to the U-Bar it is plush and nice to the touch. | Rubber | Extrusion | |
2 | U-Bar | 1 | N/A | 330 | Can be placed around the chosen locking surface and the bike frame. This is then inserted into the base of the U-Lock and secures the bike to the locking surface. | Steel | Extruded, Bent, Cut | |
3 | U-Bar Clamp Attachment | 1 | Bike Frame Clamp | 15 | Provides nice mating surface for U-Bar and bike frame bracket. | Plastic | Injection Molding | |
4 | Frame Attachment Screws and Nuts | 4 | Bike Frame Clamp | 1 | Screws and nuts used to press clamp edges together around the U-Bar. | Steel | Off the Shelf | |
5 | U-Bar Frame Attachment Clasp | 1 | Bike Frame Clamp | 13 | Nicely holds onto the U-Bar and connects to a base piece that can be attached to a bike frame. | Plastic | Injection Molding | |
6 | U-Bar Frame Attachment Locking Tab | 1 | Bike Frame Clamp | 4 | Tab presses over edge of Clamp attachment on the U-Bar to secure it to the bike frame. | Plastic | Injection Molding | |
7 | U-Bar Frame Attachment Spring | 1 | Bike Frame Clamp | <1 | Spring sits under clasp and provides force on clasp to keep Lock attached to frame attachment. | Steel | Off the Shelf | |
8 | Frame Attachment Joining Screw | 1 | Bike Frame Clamp | <1 | Fastens the two major parts of the frame bracket together | Steel | Off the Shelf | |
9 | Frame Bracket Base | 1 | Bike Frame Clamp | 17 | Holds clasp. Has specific points of rotation so one can change the orientation of the clasp as it connects to the bike. Represents half of the frame bracket clamp. | Plastic | Injection Molding | |
10 | Mating Pad | 2 | Bike Frame Clamp | 2 | Snap in part is smooth and offers a nice mating surface between the clamp and the bike frame (Not Pictured), and the U-Lock and clamp. | Plastic | Injection Molding | |
11 | Bike Frame Bracket Clamp | 1 | Bike Frame Clamp | 18 | Part is placed around bike frame and fastened to the rest of the bracket via screws. Second half of frame bracket clamp. | Plastic | Injection Molding | |
12 | Locking Bars | 2 | Locking Mechanism | 26 | Bars fit into notches cut into the U-Bar. When they are in place they secure the U-Bar in place and prevent its removal. The hooks on either edge sit on nubs that rotate when the key is turned, sliding the locking bars back and forth. Typically coating is used on parts that slide around. | Steel | Forged and Coated with Titanium Nitrate | |
13 | Lock Component Housing Cylinder | 1 | Lock Mechanism | 28 | Neatly holds all the parts necessary to actually lock the lock. It has slots cut such that one cannot insert the lock upside down, tracks for the lock bars to slide on, and is designed such that all force imparted to the lock in an attempt to shock it open are directed around the lock bars. | Plastic | Injection Molding | |
14 | Lock Housing | 1 | Lock Mechanism | 15 | Housing is made to nicely keep the lock in place inside of the component housing cylinder. It has a tab to prevent incorrect insertion of lock. | Brass | Off the Shelf | |
15 | Rubber Grommet | 2 | N/A | <1 | Acts as both a seal to prevent dirt or water from entering the lock component housing cylinder, as well as a cushion to protect the cylinder from rubbing directly against the U-Bar | Rubber | Stamping | |
16 | Lock Stopper Pin | 2 | Lock Mechanism | <1 | Grooves in the lock housing fit around these spring loaded pins. When the key is concerned, These pins are compressed and allow the lock to turn. | Brass | Stamping | |
17 | Pin Housing | 1 | Lock Mechanism | 8 | Housing has space for spring and pins as well as the stopper pins and springs. Has a slot for a key to be inserted. Pin Housing will rotate around inside the lock housing. | Brass | Off the Shelf | |
18 | Pin Springs | 12 | Lock Mechanism | <1 | Pins sit on top of these springs. When the key is inserted and turned, these springs will compress or extend to get all the pins to the same height so the pin housing can rotate. They will return to their natural length after the key is removed. | Steel | Off the Shelf | |
19 | Pins | 8 | Lock Mechanism | <1 | These pins are each individually made with notches at a different height. The height of the notch corresponds to the pattern on the key. The correct key will line up with the notches, allowing the pins to be moved out of the way, allowing the pin housing. | Brass | Off the Shelf | |
20 | Plastic Endcap | 2 | N\A | 13 | Acts as a weatherproofing seal for the outer casing of the lock base. It also seals off the ends of the lock base via a tight fit, discouraging the user from tampering with the internals of the lock. Adds a stylistic element to the lock. | Soft Plastic | Molding | |
21 | Rubber Shock Absorber | 2 | N\A | 4 | Part acts as a weatherproofing seal as well as a shock absorber. Cushions any force that is applied to the ends of the lock. This prevents the lock from being bumped open. | Rubber | Stamping | |
22 | Lock Bar Actuator | 1 | Lock Mechanism | 3 | Slides into grove on back of pin housing. When pin housing rotates, this part rotates as well. The Lock Bars are attached to the nubs on top and turning the pin housing causes the lock bars to slide from unlocked to locked. | Brass | Off the Shelf | |
23 | Outer Housing | 1 | Lock Housing | 127 | A powder coated outer case that neatly houses the entire lock assembly. Has holes in it to accomodate the U-Bar ans well as a small hole in it, presumably for assembly alignment purposes. Coating adds plesant feel in comparison to unfinished steel. | Steel | Stamping and Welding | |
24 | Key | 5 | N\A | 6 | Key is specially made to line up with each of the pins in a specific lock. The track pulls the pins into the correct position, which allows the lock to rotate. | Steel and Plastic | Machining |
Puck Lock
The following table contains information about each part labled in the above images.
Part # | Name | Quantity | Subassembly | Mass | Function | Material | Manufacturing Process | Image |
---|---|---|---|---|---|---|---|---|
1 | Chain Link | 14 | Chain | 20 | Multiple links connected by pins allow for folding and extending of chain. Chain can be put around a locking structure and the bike frame in order to secure the bike to that structure. | Steel | Stamping | |
2 | Protective Plastic Cover | 14 | Chain | <1 | Provides weatherproofing for the links to reduce the likelihood of rust for each chain link. | Plastic | Injection Molding in 2 halves | |
3 | Pins and Washers | 13 | Chain | 3 | Connects chain links. Allows for smooth rotation of the links about the axis of the pin. | Steel | Off the Shelf | |
4 | Outer Plastic Cover | 2 | N\A | 5 | Covers outside of lock. Provides weatherproofing for the inner lock components. Provides a nice surface to the touch in comparison to the metal underneath. | Plastic | Two halves injection molded | |
5 | Upper Lock Housing | 1 | Lock Housing | 68 | Provides a place for the chain to lock to the lock body in a compact manner. This part is powder coated to prevent rust and wear. It protects the inner lock mechanisms from the elements. | Steel | Injection Molding | |
6 | Lock Actuator | 1 | Lock Housing | 8 | Spans the lock cylinder and holds everything together. This part is moved when the key is turned. | Steel | Off the Shelf | |
7 | Lock Housing | 1 | Lock Housing | 11 | Holds the two parts of the lock in a nice case. Its hard to break into, to prevent tampering. | Steel | Off the Self | |
8 | Pins | 8 | Lock Housing | <1 | Pins slide into the second pin housing. When they intersect the second pin housing, its impossible to rotate the pin housings. This is how the lock locks. | Brass | Off the Shelf | |
9 | Upper Pin Housing | 1 | Lock Housing | 4 | Second part of pin housing. Does not rotate. When the pins are extended into this piece, the housing cannot rotate. | Steel | Injection Molding | |
10 | Roll Pin | 2 | Lock Housing | <1 | Pins hold the two sides of the Metal lock housing together. These are very difficult to remove without advanced tools to prevent tampering. | Steel | Off the Shelf | |
11 | Lower Pin Housing | 1 | Lock Housing | 11 | Houses the pins and contains keyhole for the locking mechanism. When the pins are extended, they intersect the second part of the housing and prevent the housing from rotating. | Steel | Off the Shelf | |
12 | Lower Lock Housing | 1 | Lock Housing | 64 | Secures the lock parts and prevents tampering. | Steel | Injection Molding | |
13 | Lower Outer Plastic Cover | 1 | N\A | 7 | Provides weatherproofing and a nice surface to the touch for the lock | Plastic | Injection Molded | |
14 | Worm Gear | 2 | Bike Frame Attachment | 1 | Gears move the ridged straps tighten around the bike frame. Locks the straps in place. | Plastic | Injection Molded | |
15 | Bike Attachment Strap | 1 | Bike Frame Attachment | 42 | Wraps around the bike and lets you store the lock on the bike | Plastic | Injection Molded |
DFMA
Manufacturing
Our analysis of the manufacturability of the puck and u locks showed a number of design features and choices that greatly aided the overall manufacturability of both locks. One common feature of both is there avoidance of fasteners. Both designs made heavy use of highly specialized parts, press fits, and snap fits to reduce the need for fasteners. These choices allow for fewer surfaces and operations to hold and align fasteners while maintaining the high standard of weather resistance and robustness of the final design. Additionally, both locks maintain a very low number of unique components in each design. Either by keeping the locking mechanism simple, or using the same parts multiple times, the number of different types of parts is minimized to help simplify final assembly and necessary machinery for production. Lastly, both locks make heavy use of injection molded plastic components, which allows for cheaper and faster high volume production of complex plastic parts. Also, the puck lock combines stamped metal parts with injection molded coatings to produce multifunctional parts that had properties that better matched their proposed usage. While both locks possessed many good features that aided in manufacturability, there were also some design decisions that may have made the locks much more difficult to manufacture.
One major design choice that hurt manufacturability of these locks was a heavy reliance on secondary and finishing operations on a number of components. While often necessary for corrosion resistance or better operation within the given design, both locks make use of various coatings on metals, including injection molded plastic, power coating, and a possible titanium nitride finishing coating. Additionally, the puck lock’s housing consists of a complex set of two castings that given the nature of casting and the casting suggestions found in Rob Thompson’s Manufacturing Processes for Design Professionals, we believe must have some kind of secondary operation to achieve the multiple cavities required in the design. In addition to the heavy reliance on secondary and finishing operations, both locks make heavy use of press fit components to reduce the number of fasteners and simplify manufacturing and assembly. While this is a positive for many design goals, this requires a much higher degree of accuracy when producing parts that may add to the cost and maintenance requirements of difficult to maintain production machines. Also, the additional features needed to help align press fit and snap fit components add to the overall complexity of the manufacturing. While many of these short comings for manufacturing are necessary trade-offs to achieve many of the design goals of these locks, we believe that it is possible to adjust the designs to reduce the difficulty of manufacturing caused by a number of these design choices.
Assembly
Both the u lock and the puck lock take similar steps to improve ease of assembly, but they also make a few missteps in the design stage that added complexity for the final stages of assembly. One positive factor is the heavy use of parts and sub-assembly with multiple functions. This is especially visible in the puck lock where plastic end caps serve as both chain retention mechanisms and interfaces for attaching to a user’s bike, as well as the housing which acts as the reel for the chain as well as the surface the lock latch engages with to lock the chain in place. In addition to multifunctional parts, both locks can be assembled in a “base up” fashion that allows for minimal rotation or adjustment of partial assembled locks throughout the full assembly process. Thanks to a heavy use of sub-assemblies that allow for greater access to difficult to assemble portions before they are tucked away within the lock body, both locks do a good job of taking advantage of assembling various portions of the lock before final assembly. Lastly, both locks make use of a minimal number of fasteners in their final assembly. Much of the u lock is press fit into place with a few pins and rubber pads to secure the lock and the entire housing of the puck lock is held together by two blind roll pins, two snap fit plastic guards, and a chain that is securely pinned to the housing. When coupled with adequate tapers and radii to aid in final alignment, these minimal fastener assembly methods greatly reduce the overall complexity of assembling both locks.
But, in order to maintain strength and corrosion resistance, two of the major design goals of lock design, both locks say an increase in assembly complexity that may be corrected in future iterations. One major problem is that some surfaces lack added features to help align press fit and tightly fit parts. While a number of areas do have these features, the u lock’s internal lock sub assembly is a cylinder that is carefully placed within its cylindrical housing with very tight tolerances and minimal guiding features to prevent slight misalignments in both insertion and proper alignment of the lock with the holes in the housing. As for the puck lock, the main roll pins used to hold the frame together would be difficult to align with the rounded face of the lock housing, making for a fairly difficult high pressure insertion of the roll pin. Another shortfall of both locks is their reliance on complex means of interfacing sub assemblies. For the puck lock, the custom chain requires repeated swaged pins to hold each member together as well as to hold together three separate components that all need to be aligned. As for the u lock, after placing the central lock assembly into its housing, the subsequent steps require careful alignment of compliant end caps and plugs to fit into the ends of the cylinder, requiring both special considerations to assemble once, and to perform again on the opposite side. With careful considerations during the design phase, a few of these inefficiencies can be alleviated, but some are the results of the need to build a robust, environmentally harden lock that will protect a consumer’s investment.
U-Lock
Design for Manufacture Guidelines | ||
---|---|---|
Design Objective | Comments | |
Minimize Part Count | Strengths:
Weaknesses:
| |
Standardize Components | Weaknesses:
| |
Commonize Product Line | Strengths:
| |
Standardize Design Features | Weaknesses:
| |
Keep Designs Simple | Strengths:
Weaknesses:
| |
Multifunctional Parts | Strengths:
| |
Ease of Fabrication | Strengths:
| |
Avoid Tight Tolerances | Strengths:
Weaknesses:
| |
Minimize Secondary and Finishing Operations | Strengths:
Weaknesses:
| |
Take Advantage of Special Process Properties | Strengths:
|
Design for Assembly Guidelines | ||
---|---|---|
Design Objective | Comments | |
Minimize Part Count | Strengths:
Weaknesses:
| |
Minimize Assembly Surfaces | Strengths:
| |
Use Sub Assemblies | Strengths:
Weaknesses:
| |
Mistake-Proof | Strengths:
Weaknesses:
| |
Minimize Fasteners | Strengths:
Weaknesses:
| |
Minimize Handling | Strengths:
Weaknesses:
| |
Minimize Assembly Direction | Strengths:
Weaknesses:
| |
Provide Unobstructed Access | Strengths:
Weaknesses:
| |
Maximize Assembly Compliance | Strengths:
Weaknesses:
|
Puck Lock
Design for Manufacture Guidelines | ||
---|---|---|
Design Objective | Comments | |
Minimize Part Count | Strengths:
Weaknesses:
| |
Standardize Components | Strengths:
Weaknesses:
| |
Commonize Product Line | Strengths:
Weaknesses:
| |
Standardize Design Features | Strengths:
| |
Keep Designs Simple | Strengths:
Weaknesses:
| |
Multifunctional Parts | Strengths:
| |
Ease of Fabrication | Strengths:
Weaknesses:
| |
Avoid Tight Tolerances | Strengths:
Weaknesses:
| |
Minimize Secondary and Finishing Operations | Weaknesses:
| |
Take Advantage of Special Process Properties | Strengths:
|
Design for Assembly Guidelines | ||
---|---|---|
Design Objective | Comments | |
Minimize Part Count | Strengths:
Weaknesses:
| |
Minimize Assembly Surfaces | Strengths:
Weaknesses:
| |
Use Sub Assemblies | Strengths:
| |
Mistake-Proof | Strengths:
Weaknesses;
| |
Minimize Fasteners | Strengths:
| |
Minimize Handling | Strengths:
Weaknesses:
| |
Minimize Assembly Direction | Strengths:
Weaknesses:
| |
Provide Unobstructed Access | Strengths:
Weaknesses:
| |
Maximize Assembly Compliance | Strengths:
|
FMEA
Through the Failure Modes and Effects Analysis, it was determined that bike locks as products overall are fairly safe to use. They are completely mechanical products that do not consume any electrical power, and their primary function is served not when the user is actually using a bike, but when he/she needs to securely store his/her bike. Because of this, during its primary use, a bike lock is highly unlikely to cause injuries to the user even if it fails. Failures with a bike lock will primarily result in an unusable product and/or compromised security for the user's bike. The only other instance when failure of the product would be of concern is when it is not in use and is being stored while the user is riding his/her bike. In fact, the FMEA indicates that if a bike frame attachment component is used to hold the lock while the user is riding, then that is when the user is at the most risk. Looking at the components of the bike lock, the bike frame attachment component received the highest Risk Priority Number by far because a failure with this component could cause the bike lock to come loose and get in the way of the bike as the user is riding resulting in potential damage to the lock, bike, and user. Additionally, after speaking with the employees of Biketek, a bike shop in Pittsburgh, it was discovered that the bike frame attachment components are not very reliable and that that is a main concern for users. Many users are looking for a better way to store their bike locks on their bikes. One factor that was seen to contribute to the unreliability of the bike frame attachment components was the screws used to connect the attachment component to the bike. These could easily come loose, and it would be difficult for the user to detect this. As such, the recommended action is to use screws with self-locking nuts to decrease the possibility of the screws coming loose. While this is a simple, inexpensive, and immediate solution, other options should be researched and assessed.
There are two other failure modes that jump out from the rest, and these affect the usability of the bike lock. The first deals with dirt, grime, and water getting into the lock mechanism and housing. This could cause corrosion of the lock mechanism and housing, which would affect the moving components of the lock mechanism making the lock more difficult to use. While the dissected locks were fairly well sealed against the outside environment, the keyholes are always exposed. A cheap and simple solution to this would be to attach some form of rubber or plastic cover to the housing that could be press fit over the keyhole when it is not needed. The second failure deals with the bike lock getting cold enough that it can be easily cracked or damaged through impact. In a Popular Science article, it was demonstrated that if cooled to a low enough temperature, a bike lock would be brittle enough to be easily smashed with a hammer. While not highly likely to occur, it is possible depending on the user's location and the season. Plus, this failure is severe because it renders the bike lock unusable, and it compromises the security of the user's bike. A proposed solution is to incorporate some sort of insulating material around the lock housing.
The complete FMEA tables can be found below along with the criteria used to assess severity, probability of occurrence, and detectability of failure. These criteria were taken from Dieter and Schmidt's Engineering Design (5th Edition).
Rating | Severity Description |
---|---|
1 | The effect is not noticed by the customer. |
2 | Very slight effect noticed by customer; does not annoy or inconvenience customer. |
3 | Slight effect that causes customers annoyance, but they do not seek service. |
4 | Slight effect, customer may return product for service. |
5 | Moderate effect, customer requires immediate service. |
6 | Significant effect, causes customer dissatisfaction; may violate a regulation or design code. |
7 | Major effect, system may not be operable; elicits customer complaint; may cause injury. |
8 | Extreme effect, system is inoperable and a safety problem. May cause severe injury. |
9 | Critical effect, complete system shutdown; safety risk. |
10 | Hazardous; failure occurs without warning; life-threatening. |
Rating | Approximate Probability of Failure | Description of Occurrence |
---|---|---|
1 | <0.000001 | Extremely remote. |
2 | 0.00001 | Remote, very unlikely. |
3 | 0.00001 | Very slight chance of occurrence. |
4 | 0.0004 | Slight chance of occurrence. |
5 | 0.002 | Occasional occurrence. |
6 | 0.01 | Moderate occurrence. |
7 | 0.04 | Frequent occurrence. |
8 | 0.2 | High occurrence. |
9 | 0.33 | Very high occurrence. |
10 | >0.5 | Extremely high occurrence. |
Rating | Description of Detection |
---|---|
1 | Almost certain to detect. |
2 | Very high chance of detection. |
3 | High chance of detection. |
4 | Moderately high chance of detection. |
5 | Medium chance of detection. |
6 | Low chance of detection. |
7 | Slight chance of detection. |
8 | Remote chance of detection. |
9 | Very remote chance of detection. |
10 | No chance of detection; no inspection. |
U-Lock
Item | Function | Failure Mode | Effects of Failure | S | Causes of Failure | O | Design Controls | D | RPN | Recommended Actions |
---|---|---|---|---|---|---|---|---|---|---|
Key |
|
|
| 6 |
| 2 |
| 1 | 12 | None |
Lock Mechanism |
|
|
| 5 |
| 4 |
| 3 | 60 |
|
U-Bar |
|
|
| 7 |
| 2 | None | 1 | 14 |
|
Lock Housing |
|
|
| 3 |
| 4 |
| 5 | 60 |
|
|
| 8 |
| 1 | None | 8 | 64 |
| ||
Bike Frame Clamp |
|
|
| 7 |
| 3 | None | 8 | 168 |
|
|
| 7 |
| 4 |
| 5 | 140 |
|
Puck Lock
Item | Function | Failure Mode | Effects of Failure | S | Causes of Failure | O | Design Controls | D | RPN | Recommended Actions |
---|---|---|---|---|---|---|---|---|---|---|
Key |
|
|
| 6 |
| 2 |
| 1 | 12 | None |
Lock Mechanism |
|
|
| 5 |
| 4 |
| 3 | 60 |
|
Chain |
|
|
| 4 |
| 2 | None | 1 | 8 |
|
Lower Outer Plastic Cover |
|
|
| 4 |
| 4 | None | 1 | 16 |
|
|
| 4 |
| 4 | None | 3 | 48 |
| ||
Outer Plastic Cover |
|
|
| 3 |
| 4 | None | 1 | 12 |
|
Lock Housing |
|
|
| 3 |
| 2 |
| 5 | 30 |
|
|
| 8 |
| 1 | None | 8 | 64 |
| ||
Bike Frame Attachment |
|
|
| 7 |
| 4 | None | 5 | 140 |
|
DFE
This product has very minimal GHC emissions already due to the lack of energy or material consumption during product use. The primary contributer during the manufacturing to this is the production of steel followed closely by the energy consumption during manufacturing. While these are hard to reduce, considering lower energy machining processes or considering replacing some or all of the steel within the product with recycled aluminum could likely further lower the GHC emissions associated with product production.
A $30 CO2 tax would only effect product price by approximately 58 cents, a fairly insignificant cost change and would therefore be unlikely to effect product sales.
The one downside to these estimates is that they are not the most accurate representation of a bike lock manufacturing. While bike locks are similar in composition to the primary industries represented by Hardware Manufacturing, they are not one of the main representations within the category, dominated by furniture, builders' and motor vehicle hardware. Locks are represented in the second and third of those categories, but not specifically bike locks.
Bike Lock Production | |
---|---|
Best Match economic sector number | 332500: Hardware Manufacturing |
Reference Unit | 1 unit |
Units consumed per product life | 1 unit |
Cost per unit (2002 $) | $30.89 |
Lifetime Cost | $30.89 |
Economy-Wide mtCO2e Released per $1M of Output | 640 |
Implied mtCO2 per Product Life | $0.0197696 |
CO2 tax @ $30/mtCO2e | $0.593088 |
Group Task Allocations
For our group, we split into teams to perform the dissections because we had multiple bike locks to dissect. Afterward, we assigned the following roles, but we tried to work together as much as possible in case anybody had questions or needed to discuss issues concerning their part. Communication outside of group work was established via email and group text messages.
Team Leader and FMEA Lead - Jeremy Jiang
Bill of Materials - Ryan Chang
DFMA Leads - Rachel Chow and Alex Muñoz
DFE Lead - Melissa Mann
References
Thompson, Rob. "Manufacturing Processes for Design Professionals." New York: Thames & Hudson, 2012. Print.
Gray, Theodore. "Science Of Theft: Freeze A Bike Lock With Canned Air, Then Smash It With A Hammer." Popular Science. N.p., 24 Sept. 2012. Web. 02 Feb. 2014.
Dieter, George Ellwood., and Linda C . Schmidt. Engineering Design. 5th ed. New York: McGraw-Hill, 2013. Print.
Carnegie Mellon University Green Design Institute. (2014) Economic Input-Output Life Cycle Assessment (EIO-LCA) US 2002 (428 sectors) Producer model [Internet], Available from: <http://www.eiolca.net/> [Accessed 2 Feb, 2014]
Bureau of Labor Statistics. Inflation Calculator [Internet], Available from:<http://http://www.bls.gov/data/inflation_calculator.htm> Accessed 2 February, 2014.