Group 6 - Black and Decker Power Drill - Gate 4

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Contents

Purpose

The purpose of this portion of the project is to reassemble the Black & Decker DR202 Power Drill. The reassembly process is documented in a step-by-step procedure along with pictures and videos for easy reconstruction. Further analysis of the drill is completed and improvements at the system level were considered. The change propagation that came with these alterations also was investigated.

Product Management: Critical Project Review

Cause for Corrective Action

In terms of group functioning, our group has been working effectively as a team. We have been able to successfully overcome challenges that have improved our quality of work. Previously, we were concerned about the brevity of our gates. While we thought we were answering questions completely, we realized that we were not going into enough depth. We resolved this issue and saw better results on our third gate. We completed our gate earlier which allowed us to speak with the instructor and ask questions that clarified parts of the assignment. We also printed out a hard copy of our gate and proof-read what we had written. This allowed us to catch several grammatical errors. In addition, we went into a lot more depth than we had in the first two gates. We made sure we were specific in answering every parameter of the question and added captions to all of the pictures which we had neglected to do in prior gates. We have also revised our meeting schedule which was a previous concern. Our group has increased its meetings to two times a week, on Tuesdays and Thursdays after our MAE 204 class. While one meeting a week was only necessary in the earlier weeks of our project, we now see that two meetings will be required during these final weeks to assure that the work is completed.
At this stage of the project we have been working very well together. However, this has also become an issue because of the new friendships that have been created. As we have become more comfortable with one another we seem to have become less focused on completing the task. We are enjoying working together to the point that we sometimes get distracted during our group meetings. While it is beneficial to meet other engineers we realize that we need to create a better balance of work and social interactions. We need to remind ourselves that we are meeting to work for a graded project and not just to spend time with each other. We plan to resolve this issue by remembering what roles we were initially assigned. Our leaders, Laura and Sarah, will take responsibility and encourage the other group members to focus on the task at hand. Since this issue was also brought to light, we will also be more conscience of the situation. This will help us to reduce the amount of distraction. This will also help our group significantly because we will be able to complete the gate more efficiently.

Product Archaeology: Product Explanation

Product Reassembly

The difficulty scale for the individual steps of the reassembly process is based on how taxing and intuitive each step was to complete:

  • 1 Requiring minimal effort - A step requiring minimal effort would only require the use of the hands. The reassembly of the individual parts would be obvious, and the parts could only be oriented in one way.
  • 2 Requiring moderate effort - A step requiring moderate effort would require the use of hands or a screw driver. Some knowledge of the internal component orientation or some notable physical energy input is necessary.
  • 3 Requiring maximum effort - A step requiring maximum effort would require the most technical knowledge. It would be necessary to fully understand how the components interact with one another to assure that they are connected properly. Still, only the use of the hands or a screwdriver would be required.

During the assembly process, our group found that it was harder to reassemble the drill than it was to take it apart, but only by a small amount. We developed this scale based upon the amount of time that each step took to complete as well as the tools and labor that were required for that process.

Table 9 Step-By-Step Reassembly
Step Instructions Tools Required for Step Estimated Time for Step (minute:seconds) Difficulty (Scale of 1 to 3) Picture and Link to Video of Step
1 Starting with the disassembled armature, first slide the red washer onto the shaft of the armature. Next, slide the heat sink on top of the red washer making sure the flat side of the heat sink is facing away from the actual armature. If this is done incorrectly, there will not be enough space for the plain washer and the armature will not fit into the drill housing properly. After this heat sink is in place, slide the plain washer onto the armature shaft. Lastly, use a flat-headed screwdriver, to replace the retaining ring to hold the other three pieces in place. To do this apply pressure with your thumb behind the head of the screwdriver to force it onto the armature shaft. Applying pressure with your thumb will also allow for more control over the motion of the screwdriver head. Hands
Flathead Screwdriver
0:45 2 - Due to notable physical energy input
Armature
Click Here to View Armature Assembly Video
2 First, screw the stationary reversal ring onto the field using a flathead screwdriver. To do this, line up the square protrusions on the stationary reversal ring with the indents on the field and screw in the two long screws. Next, the movable reversal ring is placed on top of the stationary reversal ring and turned clockwise to secure it in place. (NOTE: The movable reversal ring for our drill is broken into 3 parts and is, therefore, not included in the reassembly process). Finally, slide the field with the reversal ring facing away from the fan on the armature. Hands
Flathead Screwdriver
0:45 2 - Due to notable physical energy input
Armature Assembly
Click Here to View Field Assembly Video
3 Take the keyless chuck with the attached gear and place the axle of the gear and pinion into the hole on the front bearing plate. Make sure that the smaller gear on the gear and pinion is aligned with the gear on the keyless chuck. Next, place the rear bearing plate onto the two previous axles so that the radii of the holes of the rear bearing plate correspond to the radii of the two axles. Then take the armature and field assembly constructed in step 2 and slide the geared end of the armature shaft into the large center hole on the rear bearing plate. Hands 0:15 2 - Due to knowledge of orientation
Gear Assembly
Click Here to View Gear Assembly Video
4 In this step, take the cord with the cord protector and insert it into its proper location in the handle of the drill housing. Then, screw the cord clamp using a flathead screwdriver into its respective location to secure the wires of the power cord. Hands
Flathead Screwdriver
0:40 2 - Due to notable physical energy
Inside of Drill With Cord Clamp and Cord
Click Here to View Cord Fitting Video
5 The entire internal assembly of the drill is now placed into the left side drill housing. This step requires significant knowledge of the orientation of the bearing plates, field, and heat sink within the housing. The following descriptions reference an aerial view of the inside of the drill. Viewing the drill in this way, the larger hole of the front bearing plate is oriented toward the top of the drill. The rear bearing plate is oriented in a way in that the curved edge is closest to the you. The two flat sides of the field face the top and bottom of the drill to make sure the field fits securely into the drill housing. The heat sink is arranged so that the square protrusions also face the top and bottom of the drill casing. Hands 0:20 3 - Need to understand how the internal components fit together and fit into the drill housing.
Internal Assembly and Cord Inside of Drill
Click Here to View Internal Assembly Insertion Video
6 Place the bit holder in its correct location at the top of the drill housing. The circular end faces away from the keyless chuck and the indented portion of the bit holder faces outward. Next, the VS switch is placed in its respective location. The triangular protrusion faces downward and fits into the hole in the left side drill housing. The wires wrap up and to the left and attach to the field (NOTE: The wires in our drill are disconnected so they simply lay in the extra space in the drill casing.) The level holder then fits into the upper left section of the drill with the level facing the backside of the drill. Finally, the reverse lever fits into the drill housing right above the VS switch. The trapezoidal end of the reverse lever remains outside the drill housing. The hollowed face of this end face is oriented upward, toward the gear assembly. Hands 0:30 1 - The parts can only be oriented in one way
All Inner Components Inside of Drill
Click Here to View External Component Insertions Video
7 The right side housing is then replaced over the left side housing. They should line up perfectly. The nine screws are then placed in the nine screw holes. A flathead screwdriver is then used to fasten the nine screws in place. This secures the housing around the components which keeps these parts from moving around within the drill. Hands
Flathead Screwdriver
1:00 2 - Due to notable physical energy
DR202 Drill Without Screws
Click Here to View Attachment of Housing Video


Challenges During Reassembly

Several challenges arose during the reassembly of the drill. We disassembled and reassembled the drill multiple times in order to reference parts and transport the drill. With each disassembly and reassembly the screws used to secure the drill housing became less resilient to the force of the screwdriver. As a result, some screws were stripped during the first and final steps of the disassembly and reassembly processes respectively. Fortunately, we noticed this problem early enough before too much damage was done. Our solution to this issue was to decrease the number of times we opened the drill to prevent further damage to the screws. During our initial reassembly, we also struggled during step 5 of the reassembly process which involved the proper orientation of the armature and gear assembly within the drill. This was a major issue because if the internal assembly is not properly aligned, the right drill housing will not fit properly over the left housing and the drill cannot be closed. We solved this process by referencing pictures we had previously taken during the disassembly process. This allowed us to orient each of the components so that the internal assembly fit correctly into the casing.

Original Assembly

When the Black and Decker DR202 drill was initially assembled all individual components were first manufactured through injection molding, drawing, hobbing, and other machining processes. Then all of the internal components were put together and placed inside the drill casing by assembly line workers. This includes the bit holder, level housing, chuck, gear assembly, electric motor, trigger, power cord, and other smaller components. This had to have been done manually due to the way the components connect to each other and their specific orientations within the drill housing. Then the casings were joined by the nine screws that hold them together by automated machines. Evidence of this can be seen by the torx head screws that are used to hold the casing halves together because these types of screws can easily be picked up and moved horizontally by machines. The whole assembly process is automated on an assembly line. The drills are then packaged individually by automated machines and shipped to retailers worldwide. The original assembly process is very similar to the way in which we reassembled the drill. We had to manually put the components together to assure that they were properly aligned. We then placed these components within the drill housing. The only difference in our reassembly was in the insertion of the nine screws. We had to manually screw in the nine screws, whereas these screws were inserted by automated machines during the original assembly.

Comparison Between Reassembly and Disassembly

The assembly process was essentially the same as the disassembly process in reverse. The tools required for the two processes were identical. Only hands and a flathead screwdriver were required to disassemble and reassemble the drill. Human energy was also the only type of energy input required in these two processes. The two processes were different, however, in that more knowledge was required for the reconstruction of the drill. For example, during disassembly the entire armature and gear assembly was simply lifted out of the drill housing. For the reassembly process, it was necessary to understand how the different components of the armature and gear assembly were oriented. If a single component was not arranged properly, the entire assembly could fit not precisely into the left drill casing. In addition, during the disassembly process the gears could simply slide apart, whereas in the reassembly, it was necessary to determine how the gears were arranged. More attention was also needed to fasten the screws than remove them. The screws had to be properly aligned in order for the threads to catch. The opposite was true for the retaining ring. Much more effort and energy was required to remove the retaining ring from the armature shaft. A significant force must be applied to pry off the ring, and its tendency to project makes it necessary to remove it with caution. During the reassembly process, only a small force applied behind the head of the screwdriver was required to replace the retaining ring. In terms of the time required to disassemble and reassemble the drill, these two processes were nearly identical.

Design Revisions

Rechargeable Battery:

12 Volt Rechargeable Lithium-Ion Battery
One design revision on the systems level that we considered deals with the wiring system. We propose to replace the power cord with a rechargeable battery, such as the one depicted to the right. This battery would either be a Lithium-ion battery or a standard 12V battery. A Lithium-ion battery would be ideal, but it costs around $30 more than than the standard battery. This would increase the cost of this drill from $40 to around $70. This major increase in cost would bring the Black & Decker DR202 out of the targeted range for its class of drills. Other drills at this price would have additional features that would justify the higher cost. This drill is targeted toward consumers who do not use a drill on a regular basis, but need a power drill for simple home repairs. Replacing the power cord with a 12V battery would be a feasible design revision because it would only increase the cost of the drill about $5, meaning that this drill would still be price competitive for its class of drill. This would make the drill easier to move around because there would be no cord restricting the movement. The battery would make the drill slightly heavier than its current design, but when considering the weight of other drills, the additional weight would not exclude the drill from its market. This added weight will also not be significant when considering the physical capabilities of the average consumer. Globally, this drill would become more practical in terms of safety because there would be no cords to potentially trip over. A societal impact this revision would have is that it would increase the mobility of the drill. As a result, the drill would become more convenient which would improve its ease of use and flexibility. An economic concern is that the price of drill will increase because the battery will be more expensive than the corded drill option. The addition of this battery will also slightly increase the cost of manufacturing the drill. However, the additional cost of this design tradeoff will be offset by the added benefits of this feature. The consumer will find the design revision beneficial because they will not be restricted by a cord that is only 7 feet long, which is not conducive for many household projects. Having a cordless drill will stop the consumer from having worry about buying and dealing with extension cords. This change to the drill will also propagate throughout the rest of the drill. The addition of a battery will require that the drill housing be changed. It will need to be enlarged and reshaped at the base of the handle to accommodate the battery. This will cause a change in the shape of mold used in the injection molding process. Likewise, the components will most likely have to be reconfigured as a result of the change in the drill casing. Both of these alterations to the drill’s design will cause notable changes the manufacturing process.

Reversal System:

Our Broken Reversal Ring
Proposed Location for New Reversal Lever
We also considered a major design revision to the reversal system of the drill. This would involve improving the design of individual components of the system. These revisions would ultimately alter the function of the entire system. We would start with revisions to the reversal ring. This revision is on the component level, but altering this single component would result in an improvement to the entire reversal system. We propose adding a steel ring to strengthen the reversal ring so it does not break into separate pieces so easily. As seen in the top picture to the right, our reversal ring was made out of thin plastic and the weakness of this part caused it to break into three pieces. The plastic would be injected molded around the steel ring so the plastic would act as a covering for the new ring. The reversal ring could, therefore, still maintain its original shape and design. However, the addition of the steel ring would change the manufacturing process by adding a forging process. A societal impact from the design revision would be that this component of the drill would not break so easily. Since the reversal ring completes the circuit within the drill, the drill itself would not become dysfunctional as easily. The ring would have a higher durability and a longer life expectancy. An economic concern would be the increase in cost due to the addition of a manufacturing step and a second material. However, since the design revision would create a more durable product, the economic concern would become a cost versus strength issue. Although the revision will cost more initially, it will save the consumer money in the long run due to an increase in the lifespan of the product. It can be argued, therefore, that this additional cost would be offset by an increase in quality of the product. Black & Decker could absorb the added cost of this revision so that the consumer would see no rise in price and receive a higher end product. Changing the design of the reversal ring will not propagate in other regions of the drill. The original shape and size of the reversal ring would remain the same and, therefore, internal orientation of the components could be maintained. Another design revision to the reversal system would be to replace the reverse lever with a straight rod that goes through the drill housing. With the current design of the reverse switch, it can be accidentally hit by a finger during the drilling process. This poses a major safety concern because if someone is not expecting the change in motion, they could be caught off guard and possibly injury themselves or others. Currently the reverse lever is pivoted so that when it is pushed to the left by the user the reversal ring is moved by the opposite end of the lever to the right. This causes the drill to spin clockwise when the trigger is pulled and vice versa. The new reverse switch would be a bar that passes entirely through the drill housing in the location as specified by picture on the right. In this reversal system, when this bar is pushed completely to the left the reversal ring is also moved to the left causing a counterclockwise rotation of the drill bit and vice versa. This would also incorporate a locking feature when the bar is situation in the center. This would prevent the trigger from being pulled which is an appealing safety feature. Changing the lever will reduce the chance of accidentally hitting and switching the motion. Its societal impact is that it will add simple convenience because it is not making the changing aspect any more complex, just more practical. Economically, the same amount of material will be used in the new design which will cause no change in cost in this respect. There will, however, be a slight rise in cost associated with the changes this will cause to the drill housing. A new mold would need to be made to incorporate the new switch. This mold will come at a high initial cost but no additional cost over time. The added convenience will be greater than the heightened manufacturing cost. The change in the reverse lever will not affect the overall design in any major way. There is a hollow space within the drill housing where the reverse lever is now, which is where we propose placing the new switch. No components would have to be rearranged. The only change to the manufacturing process would be in the housing production and the creation of the new switch. A new mold would have to be created that would incorporate the new holes in the correct location for the reverse bar as already mentioned.

Level:

Level
We as a group have deemed the level an unnecessary component on the Black and Decker DR202 drill. This is because the level is not practical on the drill; it is very narrow so that when the bubble is lined up properly it is still almost touching the walls of the level, making it very difficult to get it centered accurately. Using the level also requires you to keep your eyes in two spots simultaneously because you have to be watching the bit to make sure you are hitting your target location as well as keeping focus on the level to keep it straight. Another reason for the level’s removal is because once you pull the trigger to start drilling/screwing the entire drill moves slightly making the time spent lining up the level wasted. Due to these factors we have determined the drill level unneeded. Removing the level actually benefits the manufacturing of the drill as well; the housing of the level is made up of three pieces, which can be simplified by its removal. With the level, Black and Decker had to purchase/manufacture the level and the level housing and mold the drill casing to fit them. With our proposed change the level and level housing will be left out and the casing mold will be changed so that it takes up the space in which these parts are currently situated. Removing the level from the DR202 will benefit the environment because when the drill is disposed of the chemicals inside the level will not sit in the landfill and be released into the environment. This will be economically smart revision as well because the manufacturer will save money by not having to produce the level and its housing and instead just redesign the casing to fill in their spots keeping it to just one material.

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