Ski rack
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Contents |
Executive Summary
Stakeholders
During the product usage study, the following stakeholders were identified with their respective needs.
- Skier
- Ease of ski loading/unloading
- Number of skis/snowboards that can fit in the rack
- Interaction between road salt and skis
- Pinch points (when closing rack)
- Ski loss and security(ski theft)
- Rack Freezing Shut
- Car owner/driver
- Car damage (skis scratching paint)
- Skis blocking doors/tailgate/sunroof
- Loss of efficiency (lower gas mileage)
- Visibility (impairment by skis)
- Rack theft
- Noise from wind on rack
- Removability
- Shipping Company
- Weight
- Size
- Possible packaging damage from sharp parts
- Manufacturer
- Materials
- Complexity
- Tolerances
- Cost
- Retailer
- Size (storage or display)
- Cost
- Marketability
- Aesthetics
- Installer
- Require Tools
- Complexity
- Time to install
- Other Drivers
- Ski security (ski loss that could cause hazardous conditions for them)
- Garage owner
- Ski rack crushing into the garage.
Usage
User interaction with the ski rack is in three ways. The first way a user interacts with the rack is during installation of the ski rack onto a car roof rack. The second way a user interacts with the rack is made up of loading/unloading the rack with skis. The third interaction is driving a car with the rack on it.
Installation
Installing the rack is probably the hardest part of using the ski rack. In order to install the rack, the user must be able to access the roof of their vehicle. On the car we tested this on, it was rather simple as the car is quit low to the ground. However, on larger vehicles such as vans and SUVs, this can be an issue, and will make installing the rack much more difficult.
The first step in installation is to put the mounting brackets onto the ski rack. This is a fairly simple step as the rack is not yet on the car, and the rack can easily be manipulated. There is a bolt that has to go down through the bottom rubber compression pad and then screw into a nut that is captive in a sliding slot. Lining up the bolt and the nut is quite difficult and is rather frustrating. The process can be made much easier by removing the rubber pad that keeps the nut captive in the upper bail/slider assembly. This was not mentioned in the instructions and was not noticed until the product was dissected. This bolt should not be tightened the entire way at this point, as the mounting bracket slider assembly needs to be loose so it can slide during the mounting process.
Once the mounting brackets are attached to the rack, the bail screws need to be undone and the rack mounted on the car. This takes two people because you cannot hold the rack in place and tighten the bail screws at the same time. You have to tilt the rack all the way to one side to access one of the bail screws, and then all the way to the other side to access the other. Reaching half of the bail screws is very difficult because they are positioned towards the center of the car. They are impossible to reach without climbing on the car.
At this point, the bolt that connects the rack to the mounting bracket needs to be tightened. This is a very difficult as the rack is now on the roof of the car and the screws are blind. The user ends up fumbling around trying to fit a hexkey into a bolt that is recessed in a rubber pad. It took a few minutes to tighten these bolts a few turns each. Most of the time was spent simply trying to find the bolt with the hexkey.
Loading/Unloading Skis
Driving
Bill of Materials
Mechanical Analysis
The Yakima Powderhound ski rack is designed to mount onto myriad crossbars. The mounting device is oval shaped, with a set of long and a set of short bolts to allow for mounting on a wide variety of shapes and sizes of crossbars. There is a rubber pad to hold the mounting bracket in place on the crossbars. The bottom crossbars are rigidly attached onto the mounts, while the top crossbars are hinged onto the bottom crossbars. The latch is designed to hold the crossbars securely in place, and release the crossbars to provide access to the skis at the push of the release.
Design for Manufacture and Assembly
Failure Mode and Effects Analysis
In analyzing the Yakima PowderHound Ski Rack, we looked at failures with a high RPN as well as failures with a severity of 9 or higher, indicating that severe human injury could occur from the failure. The only identified way of severe human injury was from an undesired release of the ski rack while in transit. This could cause the skis to release at highway speeds possibly causing a fatal car crash. The failures identified to cause this failure were from the crossbars and the latch.
However, the severe failures of the crossbars are easily identifiable and preventable, thus yielding a low RPN value. However, all of the latch failures presented a mid to high RPN value, amplifying the concerns of the failure. The two failure methods that presented a high RPN and the possibility for severe human injury are the rack opening on its own and the user forgetting to close the rack. The unexpected opening can be addressed by changing the ratching device in the latch. Forgetting the close the rack could be addressed by making it more apparent from the drivers seat that the rack is still open, either by a visual aide or possibly an electronic alert.
The only failure method that did not present a risk for severe human injury was the latch failing to open on demand, caused either by a frozen lock or plastic deformation. The frozen lock is a common issue with all ski racks since the racks are used in the cold weather, and the moisture can freeze the metal in the lock, preventing it from unlocking. To prevent the plastic from deforming, the proper material and thickness should be used.
Assembly | Function | Potential Mode of Failure | Potential Effect of Failure | Sev | Potential Cause of Failure | Occurance | Detection Controls | Detection | RPN |
---|---|---|---|---|---|---|---|---|---|
Bracket | Hold the rack onto the crossbars | Plastic Cracks | Rack Unstable | 5 | Cold | 2 | Material Choice | 1 | 10 |
Bracket | Hold the rack onto the crossbars | Plastic Cracks | Rack Unstable | 5 | Poor Manufacturing | 4 | N/A | 6 | 120 |
Bracket | Hold the rack onto the crossbars | Plastic Cracks | Rack Unstable | 5 | Vehicle Crash | 4 | N/A | 10 | 200 |
Bracket | Hold the rack onto the crossbars | Plastic Cracks | Rack Unstable | 5 | Overtorque | 4 | Allen Key Size | 7 | 140 |
Bracket | Hold the rack onto the crossbars | Bolt Shears | Rack Unstable | 5 | Vehicle Crash | 4 | N/A | 10 | 200 |
Bracket | Hold the rack onto the crossbars | Bolt Shears | Rack Unstable | 5 | Rust | 7 | Use Stainless Steel | 5 | 175 |
Bracket | Hold the rack onto the crossbars | Bolt Shears | Rack Unstable | 5 | User Bolt - Not Factory | 3 | Specific Shape and Thread | 10 | 150 |
Bracket | Hold the rack onto the crossbars | Bolt Shears | Rack Unstable | 5 | Overtorque | 4 | Allen Key Size | 7 | 140 |
Bracket | Hold the rack onto the crossbars | Bolt Shears | Rack Unstable | 5 | Undertorque | 3 | Allen Key Size | 7 | 105 |
Bracket | Hold the rack onto the crossbars | Mounting Grooves Wear | Rack Unstable | 5 | Vibrations | 3 | Material Choice | 5 | 75 |
Latch | Open and Close the Ski Rack on Request | Will Not Open | Cannot go skiing | 7 | Frozen | 5 | Material Choice | 8 | 280 |
Latch | Open and Close the Ski Rack on Request | Will Not Open | Cannot go skiing | 7 | Deformation | 6 | Material Choice | 8 | 280 |
Latch | Open and Close the Ski Rack on Request | Will Not Open | Cannot go skiing | 7 | Lost / Broken Key | 4 | Extra Key | 1 | 28 |
Latch | Open and Close the Ski Rack on Request | Will Not Open | Cannot go skiing | 7 | Broken Rivet | 2 | Material Thickness | 6 | 84 |
Latch | Open and Close the Ski Rack on Request | Will Not Close | Cannot go skiing | 7 | Broken Latch | 5 | Material Choice | 2 | 70 |
Latch | Open and Close the Ski Rack on Request | Will Not Close | Cannot go skiing | 7 | Deformation | 6 | Material Choice | 4 | 168 |
Latch | Open and Close the Ski Rack on Request | Will Not Close | Cannot go skiing | 7 | Lock Frozen Locked | 4 | Seal Lock to prevent moisture from entering | 4 | 112 |
Latch | Open and Close the Ski Rack on Request | Will Not Close | Cannot go skiing | 7 | Broken / Worn Spring | 3 | Spring Choice | 5 | 105 |
Latch | Open and Close the Ski Rack on Request | Will Not Close | Cannot go skiing | 7 | Broken Rivet | 2 | Material Choice | 6 | 84 |
Latch | Open and Close the Ski Rack on Request | Opens on its own | Loss of Skis, Potentially Fatal Accidents | 9 | Deformation | 6 | Material Choice | 4 | 216 |
Latch | Open and Close the Ski Rack on Request | Opens on its own | Loss of Skis, Potentially Fatal Accidents | 9 | Weakened Plastic | 7 | Material Choice | 6 | 378 |
Latch | Open and Close the Ski Rack on Request | Opens on its own | Loss of Skis, Potentially Fatal Accidents | 9 | Driving Forces Break Latch | 3 | Minimize Forces, Material Choice | 10 | 270 |
Latch | Open and Close the Ski Rack on Request | Opens on its own | Loss of Skis, Potentially Fatal Accidents | 9 | Ratchet Tooth Failure | 4 | Avoid Use of Ratchet Teeth | 8 | 288 |
Latch | Open and Close the Ski Rack on Request | Opens on its own | Loss of Skis, Potentially Fatal Accidents | 9 | Broken / Worn Spring | 3 | Spring Choice | 5 | 135 |
Latch | Open and Close the Ski Rack on Request | Opens on its own | Loss of Skis, Potentially Fatal Accidents | 9 | Broken Rivet | 2 | Material Thickness | 6 | 108 |
Latch | Open and Close the Ski Rack on Request | Not Fully Closed | Chance of Opening leading to loss of skis, potentially fatal accidents | 9 | Ratchet Tooth Barely Engaged | 6 | Color Notification | 2 | 108 |
Latch | Open and Close the Ski Rack on Request | Not Fully Closed | Chance of Opening leading to loss of skis, potentially fatal accidents | 9 | Debris in the Way | 8 | Color Notification | 2 | 144 |
Latch | Open and Close the Ski Rack on Request | Not Fully Closed | Chance of Opening leading to loss of skis, potentially fatal accidents | 9 | Too much in the rack | 6 | Color Notification | 2 | 144 |
Latch | Open and Close the Ski Rack on Request | User Forgets to Close | Loss of skis, potentially fatal accidents | 9 | Distracted User | 4 | Warning System | 6 | 216 |
Latch | Open and Close the Ski Rack on Request | User Forgets to Close | Loss of skis, potentially fatal accidents | 9 | Cannot See Open Rack | 2 | Visual Aide | 7 | 126 |
Crossbars | Holds the Skis Securely in Place | Does not hold the skis with sufficient force | Loss of skis, potentially fatal accidents | 9 | Different height of skis | 5 | Individually sliced rubber | 1 | 45 |
Crossbars | Holds the Skis Securely in Place | Does not hold the skis with sufficient force | Loss of skis, potentially fatal accidents | 9 | Bent Crossbars | 2 | Material Choice | 1 | 18 |
Crossbars | Holds the Skis Securely in Place | Does not hold the skis with sufficient force | Loss of skis, potentially fatal accidents | 9 | Unevenly worn rubber | 3 | Individually sliced rubber | 1 | 27 |
Crossbars | Holds the Skis Securely in Place | Holds the skis too tightly | Damage to skis | 6 | Too thick of a ski | 4 | More space between crossbars, taller rubber | 1 | 24 |
Crossbars | Holds the Skis Securely in Place | Holds the skis too tightly | Damage to skis | 6 | Bent Crossbars | 2 | Material Choice | 1 | 12 |
Crossbars | Holds the Skis Securely in Place | Holds the skis too tightly | Damage to skis | 6 | Rubber too hard | 3 | Material Choice | 3 | 54 |
Crossbars | Holds the Skis Securely in Place | Does not apply uniform pressure | Loss of skis, potentially fatal accidents | 9 | Different height of skis | 5 | Individually sliced rubber | 1 | 45 |
Crossbars | Holds the Skis Securely in Place | Does not apply uniform pressure | Loss of skis, potentially fatal accidents | 9 | Bent crossbars | 2 | Material | 1 | 18 |
Crossbars | Holds the Skis Securely in Place | Does not apply uniform pressure | Loss of skis, potentially fatal accidents | 9 | Unevenly worn rubber | 3 | Individually sliced rubber | 1 | 27 |
Crossbars | Holds the Skis Securely in Place | Does not keep skis from sliding | Loss of skis, potentially fatal accidents | 9 | Not enough friction | 1 | Material choice | 1 | 9 |
Crossbars | Holds the Skis Securely in Place | Does not keep skis from sliding | Loss of skis, potentially fatal accidents | 9 | Rubber too soft | 1 | Material choice | 3 | 27 |
Crossbars | Holds the Skis Securely in Place | Improperly loaded | Loss of skis, potentially fatal accidents, Damage to rack | 9 | Attempt to load over the binding | 4 | Less space between crossbars | 2 | 72 |
Crossbars | Holds the Skis Securely in Place | Improperly loaded | Loss of skis, potentially fatal accidents, Damage to rack | 9 | Attempt to load non-skis | 5 | Less space between crossbars | 4 | 180 |
Inside hinge | Align the crossbars as it closes | Does not align properly | Rack will not close | 7 | Crossbars bent | 2 | Material choice | 1 | 14 |
Inside hinge | Align the crossbars as it closes | Does not align properly | Rack will not close | 7 | Plastic | 6 | Material choice | 4 | 168 |
Inside hinge | Align the crossbars as it closes | Does not align properly | Rack will not close | 7 | Rivet broken | 2 | Material thickness | 6 | 84 |
Inside hinge | Align the crossbars as it closes | Does not fully open | Crossbars will not stay open | 3 | Customer cannot open it far enough | 4 | Create an easier way to open the rack | 2 | 24 |
Inside hinge | Align the crossbars as it closes | Does not fully open | Crossbars will not stay open | 3 | Plastic deformed | 6 | Material choice | 4 | 72 |
Inside hinge | Align the crossbars as it closes | Does not fully close | Cannot go skiing | 7 | Spring worn or broken | 3 | Spring choice | 5 | 105 |
Inside hinge | Align the crossbars as it closes | Does not fully close | Cannot go skiing | 7 | Plastic | 6 | Material | 4 | 168 |
Inside hinge | Align the crossbars as it closes | Does not hold the top and bottom crossbars together | Cannot go skiing | 7 | Rivet broken | 2 | Material thickness | 6 | 84 |
Inside hinge | Align the crossbars as it closes | Does not hold the top and bottom crossbars together | Cannot go skiing | 7 | Broken plastic | 4 | Material choice | 1 | 28 |
Riser | Increase clearance | Binding still does not clear roof | Vehicle gets scratched and dented | 3 | Not enough of a lift in design | 1 | Better design | 1 | 3 |
Riser | Increase clearance | Mount does not attach properly | Cannot go skiing | 7 | Rivet breaks | 2 | Material thickness | 6 | 84 |
Riser | Increase clearance | Mount does not attach properly | Cannot go skiing | 7 | Plastic breaks | 4 | Material choice | 1 | 28 |
Design for Environment
Team Member Roles
Jeff Bizzak - FMEA
Chris Bondoc - DFMA
Wil Hamilton - BoM
Ben Streeter - DFE