Cordless drill

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Group II
Ming Huo
Scott Miller
Vishesh Nandedkar
Mark Rockwell

Contents

Cordless Drill Product Analysis Report

Executive Summary

Scope The use of the cordless drill is varied and depends much upon the “bit” placed in the chuck. Though these bits are important, our focus will remain on the operation of the drill itself.

Needs and Requirements There are certain customer needs that the drill should address: battery life, portability, comfort, durability and the ability to perform in unusual places. In addition to that however, there are certain requirements that should be expected of the cordless drill. Like in the customer needs, the drill should have a long lasting battery and be portable. It also should be safe, have reliable parts and in general be more convenient than a conventional corded drill.

System Function The drill is activated by depressing the trigger on the front of the handle. The result is the chuck spinning at a speed proportional to the degree to which the trigger is depressed. To effectively use the drill, it is necessary for the user to have decent hand strength and finger control to insert the bit as well as keep the drill from spinning out of their hand. In addition, proper use must be defined by the environment the drill is used in factoring in good lighting, reasonably low ambient noise and a lack of excessive moisture (like rain) getting into the casing.

Manufacturing The drill seems very cost effective, with a low number of parts, most if not all of which are mass produced with techniques like injection molding. From an assembly perspective, the drill seems well designed. The frame for example snaps together and is then secured with screws. One area for improvement could be in the number of types of screws used. We found five distinct screw types and feel four of these sizes could have been consolidated.

Failure Modes and Effect Analysis Potential problems in the drills operation may stem from the clutch, chuck, battery and case. For the clutch, the action is very stiff and doesn’t change direction very easily. This could lead to fracture from the user using too much force. For the chuck, break failure is possible and for the case, ergonomics might be lacking making for an uncomfortable grip. The problem we see as most important though is in the battery. The power seems very low and our recommendation is to find a higher quality battery to replace the 9.6V.

Major Customer Needs and Product Requirements

Upon brief observation it becomes obvious the major purpose of a drill is to spin a “bit” with high enough speeds and torque to perform a task. Many different “bits” exist to perform many different tasks, the most common being drill bits, and screw-driver type bits. These type “bits” are used mostly in functions that ultimately involve fastening two or more objects together in some capacity. Other uses include egg-beaters, water pumps, dremeling, etc. Although many of these “bits” exists, our focus is on the cordless drill itself, therefore, our discussion will not directly involve the use of these “bits” but the role the drill plays in spinning them and what is required from the drill.

In terms of average customer use we found that users have very basic needs from cordless drills. Users want their cordless drill to have a battery that lasts a long time or has a very quick recharge time because it becomes major inconvenience to have to stop a project just to recharge battery. For continuous use over the maximum amount of time the battery allows the drill design should be ergonomic, light-weight, and yield low vibration/noise as to not cause the user any discomfort, such as blistering, joint swelling, or arm soreness. Other average customer needs are maximum power, easy and relatively intuitive use, and the ability to use the drill in tight spaces, awkward corners, or obstructed areas. Ultimately, a cordless drill should be functional enough to allow a user to get a small project completed in a more efficient manner than using hand-tools.

The design of a cordless drill requires its use to have a clear advantage over its hand tool equivalent along with being able to perform in ways its corded counterpart could not. Cordless drills must have power to generate necessary amounts of torque for what are deemed average use functions in a quicker and significantly easier manner than a hand tool. Durable and reliable enough to with stand prolonged repeated use without failure or harm to the user. Markings and labels on the tool must be adequate enough to allow an inexperienced average person to understand and use. Battery life and recharge time should optimize to be as long and short (respectively) as possible with 2 hour for each being a reasonable standard. Cordless drills must provide sufficient power while being portable and lightweight in order to perform functions that mandate use in areas where corded or pneumatic drills are an inconvenience.

This information was gathered through research involving talking to individuals familiar with using cordless drills, observing those unfamiliar with drills try to operate them, and our own personal expertise. Later we will discuss special use scenarios, but in general we determined the largest groups of users use small cordless drills for personal non-commercial small projects, including home-improvement, hobbies, etc. Our user needs and product requirements reflect this user group and how cordless drill design needs to be focused around reliability and user convenience. Table 1-1 summarizes the top five areas of concern for customer need and product requirements.

Table 1-1: Summary of top 5 Customer Needs and Product Requirements

Rank Customer Needs Product Requirements
1 Battery Life/Recharge Portability
2 Portability Overall Convenience
3 Ergonomics/Comfort Safety
4 Use in awkward spaces Reliability
5 Durability Battery Life/Recharge



How the System Functions

Function/Purpose:

The purpose of the cordless drill is to spin “bits”. “Bits” are the tools that go in the end of the drill and they come in many different shapes, to accommodate driving, drilling, mixing or cutting. Things that can be driven include screws with Philips heads, flat Heads or hex shaped heads. For drilling, drill bits come in many sizes, from small fractions of an inch up to about an inch in diameter. The material of the drill bits varies as well, depending on the surface being drilled in to. There are also attachments for mixing, such as egg beaters or whisks. For cutting, one could even insert small cutting wheels, though in general, the main intended use for cordless drills, are drilling and driving. The cordless drill is meant to be portable and small enough to get in tight places, making it suited for the home or automobile. It has no harmful exhaust so it may be used indoors or outdoors but kept from getting water inside the casing. Aside from making holes, it is also used to bind materials together with screws, or can be used to drill weaker objects such as stripped screws or broken locks. It is often used for installation of hardware, or removal of covers or anything really which is secured in place with screws. It can even be used to unscrew completely stripped screws, by tightening the chuck around the screw head and putting the drill in reverse.

Inputs/Outputs:

The physical input to the drill is an axial force to the trigger which is normally delivered by the index finger, with the shaft of the drill in the palm of ones hand. When the trigger (022) is squeezed, a potentiometer (part of clutch/switch controller, part 024) measures the depth the trigger has been depressed and allows a proportional amount of voltage to the motor (016). The motor spins at very high speeds with low torque, because power = torque*speed (assuming no losses) and the drill's performace relies on high torque rather than high speed there is a planetary gear train (028) that lowers the speed and increases the drill's torque. The planetary gear train (028) in turn spins the chuck assembly (027). If the clutch is set to forward, the chuck spins clockwise, if the clutch is in the middle, the trigger would not have been able to depress, and if the clutch is set to reverse, the chuck would spin counter clockwise.

Image:FBD-Drill-1.JPG


The above is a free body diagram of the drill. The user's hands are placed at (A) and (C), their index finger placed at (B) and the bit is placed in the chuck at (E). To operate the drill when either drilling or screwing, a force is required from the user at (A) and (C) to push the drill into the material. The reaction force is felt at (E) through the bit into the chuck. When the drill is operational, there will be a force on the trigger at (B) from the user's index finger as well as a torque about the X Axis through the chuck at (D) from the material opposing the drilling or screwing action. This torque is counteracted by the user's hands at both (A) and (C). The user's hand at (A) is capable of providing a moment in any direction, while the hand at (C) is mostly used to counter moments about the X Axis with forces in the Z direction.

Operation

To operate the drill, one must first charge the drill’s battery (001). This involves sliding the battery off the drill and onto the 12V charging device that plugs into the wall. After about 2 hours, the battery will be fully charged and may be slid onto the base of the drill. Once the battery is in place, the chuck’s (027) teeth must be opened to allow a bit to slide in. To open the chuck’s teeth, hold the top of the drill steady, and turn the collar (026) on the end of the drill counter-clockwise. The teeth will begin to open up. When they are open wide enough for the bit you desire to use, place the bit into the chuck and turn the collar clockwise to tighten the teeth. When the bit is secure select the cutoff torque you desire to use by spinning the collar with drill bit pictures to the desired setting. Push the clutch into forward or reverse depending on the application, and place the bit on the desired surface. While bracing it firmly, gently squeeze the trigger (022) while pushing forward. Continue squeezing until the drill is moving at the desired speed. Once the task is completed, push the clutch back into the center position and set the drill down.

Cordless Drill User Trials

Internally, the squeezing of the trigger (022) applies a voltage to the motor (016) with the clutch/switch (024) controller. This rotational speed and torque is translated to the planetary geartrain (028) which significantly reduces the speed and increases the torque. This rotation is then translated to the chuck assembly (027), which securely holds the bit and spins it, allowing the drill to cut. Once the trigger is released, a chuck brake stops the bit quickly so as to not be a safety hazard. We were unable to take apart the chuck assembly (as you can see in the photos below), and we are not exactly sure how the chuck brake works. Online research indicates that the chuck brake may be electrically operated, although we are skeptical about this (we saw no wires leading to the clutch assembly).

Different Users / Use Scenarios

Some foreseeable problems with the design of the drill arise from unintended use and abnormal users. For the most part, the drill is meant to be used for drilling and driving. Using it for other purposes is just not consistent with the initial intent. Users may use the drill to widen holes or engrave objects or etc. but these are beyond the original scope of the item. However, there is a concern with use in wet areas. While a common cordless drill will most likely never be used underwater, we feel that limited use in wet spaces may be a useful need for the consumers, especially if emergency repair work needs to be done in inclement weather. This could be a major safety concern because of risk of electrocution and slipping in the water. Such a modification would have to include electrical insulation as well as extra grip to prevent the user from dropping or slipping on the drill and causing harm either to the user or the user’s project.

Even with the auxiliary handle we found use of the cordless drill requires decent hand strength. The handle allows a user better control in maintaining alignment during use. However, this handle is offset from the point of primary force contact (at the bit), which can cause a moment for which the user must compensate for this with their primary hand (on the trigger). Unfortunately, this makes it necessary for the user to have “decent hand strength.” We found this auxiliary handle does allow a “weaker” user to use a heavier drill because the weight of the drill is not supported in one hand, even if the trigger hand has to compensate for the moment caused by the auxiliary arm.

Other problems come from special consumers. These problems could arise from users with a weak grip or shaky hands. Poor eyesight could make usage difficult as well as poor lighting or being unable to push the drill forward with reasonable power. Putting the bit in the chuck can prove a challenge for even normally capable individuals and stripping screws is a common occurrence. Deaf individuals may not be able to even hear when the bit is skipping on the screw and applying too much torque can also happen, if the material is too soft and the drill isn’t set to the right torque setting (which is quite confusing on the drill). Even having the wrong bits is a concern, as well as really tight areas not allowing the drill to be perpendicular to the object.

Product Dissection

Before doing anything else, we dissected our drill to take a look at each part up close and understand how the drill works from a technical standpoint.



The cordless drill, pre-dissection is pictured above. The numbers label the easy-to-see external components. The numbers correspond to the part numbers in the table below.



Above is an exploded view of a similar drill, showing some of the internal components.

Parts List

Part Description Qty Function Manufacturing Process Photo
001 Battery 1 Provide electricity Injection Molding
Purchase
Assembly Line
002 Support Handle 1 Provide support for non-dominant hand Injection Molding
003 Supp. Handle Screw 1 Secure Support Handle Purchase
004 Nut 1 Secure Support Handle Screw Purchase
005 Screw 5 Secure Case Purchase
006 Screw 1 Secure Case Purchase
007 Screw 7 Secure Case Purchase
008 Casing Part 1 Hold in parts Injection Molding
009 Casing Part 1 Hold in parts Injection Molding
010 Strap 1 Helps to provide a secure grip Purchase
Folding
011 Plastic Plate 1 Provide drill information Injection molding
012 Large Case R 1 Hold in parts Injection Molding
013 Large Case L 1 Hold in parts Injection Molding
014 Clutch Trigger 1 Move clutch Injection Molding
015 Screw 3 Hold motor to chuck Purchase
016 Motor 1 Provide torque Purchase
017 Spacer 1 Provides support for motor and gear housing Injection Molding
018 Ball Bearings 14 Minimize friction of moving parts Purchase
019 Screw 2 Secure Spacer to Motor Purchase
020 Heat Sink 1 Dissipate Heat into the air Cast
021 Battery Terminal 1 Connect Battery to Motor Injection Molding
Solder
Stamp
022 Trigger 1 switches motor on and off Injection Molding
023 Secondary Clutch Trigger 1 Translates movement from Clutch Trigger to Clutch Injection Molding
024 Clutch/Switch 1 Allowes Motor to be engaged, selects direction of rotation Injection Molding
Solder
Assembly Line
025 Clutch Selector 1 Selects stopping torque Injection Molding
026 Collar 1 Covers Chuck Injection Molding
027 Chuck Assembly
(including chuck brake,
clamp, etc)
1 Secures bit and translates torque from motor to bit (Complex Process)
Assembly Line
Machining
Injection Molding
Cast
028 Planetary Geartrain
Assembly
1 adjusts speed and torque of motor Injection Molding

Manufacturing For Design and Assembly

We were very impressed with the compact nature of the drill, inparticular how nicely the great number of components fit into the drill. We feel that outside commonization of screws and design for dissasembly there are were no obvious improvements that would make a major impact on the drill’s cost or performance. Obviously, if we were to conduct a more extensive study concentrating solely on DFMA of the drill and its manufacturing facilities we may be able to find more areas for improvement. However, DFMA is one of the strong points of your drill we suggest an optimization in a different area would have a be a overall improvement for the cordless drill.

Manufacture:
In the initial inspection of the assembled cordless drill, several things were things were noted. The majority of the drill’s non-electrical components are made from hard plastic. These plastic pieces were manufactured in such a way as to snap together and hold their position with minimal use of screws. The complex shape, as well as many support ridges suggest that these parts were manufactured by means of injection molding.

Assembly:
The disassembly of the drill was quite simple; the screws holding the outer pieces together were identified very quickly, and removed with a regular Philips head screwdriver. After removing the outer shell of the drill, the internal components (chuck/torque setting assembly and electrical circuits) were also easily identified. Disassembly of the inner pieces of the drill revealed some more complex assemblies, particularly the component that transfers the torque from the electric motor to the drill bit. During the disassembly of this part, we spilled some ball bearings that were very difficult to find and reposition into the casing that held them. We were unable to completely take apart the chuck assembly, as the pieces seemed to be press-fitted onto each other.

Disassembly:
After disassembling the entire drill, we were able to make the following observations about the way the drill was assembled. The number of plastic parts in the drill seemed to have been kept to a minimum; no unnecessary or redundant components were found during the disassembly. In addition, the top of the drill was made in a way so it could be held together without the use of additional screws. However, it was noted that 5 different types of screws were used in the assembly of the drill, 4 of which were similar in length and thread. Because of the the similarity of these screws, they may be difficult to identify and distinguish from one another.

Opportunities for improvement:
Because the drill was so inexpensive, we can deduce that the manufacturing process from which it was made was extremely cost-effective. This drill is a result of mass-production; therefore the total number of parts would have been kept to a minimum on the part of its designers. Because of this fact, we believe there is little that can be done in DFMA of this cordless drill to improve it.

Failure Mode and Effects Analysis

Because of the intense resources required to create an accurate and thorough FMEA, only the top 5 failure modes will be presented here.

Since our product is piece of relatively safe and lightweight machinery, the serious risk to the user is low. In general, the failures of our product are more likely to be related to ergonomic issues and/or deterioration over time, rather than a catastrophic failure. In our analysis, we are considering the screw/drill bits and screws to be separate products from the drill. Thus, our FMEA does not consider failures like stripping a screw head, breaking off a screw head, or breaking a drill bit.

According to our FMEA, the most serious failure issues are related to the chuck jamming, the battery dying, the chuck brake failing, the casing bothering the user's hand, and the clutch trigger sticking. The safety issues associated with these failures are not serious, though they do exist. If the chuck jams, for example, the user could wrench very hard with his hands (or a clamp), with potential injury to the hand if he/she slips. The cluch brake failing could cause the user to attempt to stop the chuck with his/her hand, which would be unsafe.

In some cases, failure causes the product to be entirely unusable (chuck jamming or battery dying). However, in other cases the failures only cause a minor inconvenience to the user, such as dealing with an uncomfortable grip or a sticky clutch trigger. The failures that cause the drill to be unusable should be addressed first in order to reduce the cases of complete inoperability.

We recommend that all of the top 5 failure modes be further researched and improved upon if economically feasible. Clearly, safety is a top priority, and it may be okay to increase the cost of the drill in order to fix a safety issue.

Item and Function Failure
Mode
Effects of Failure S Cause of Failure O Design Controls D RPN Recommended
Actions
Responsibility
& Deadline
Actions Taken S O D RPN
Chuck
*Secures bit
*translates torque
Jams Chuck can no
longer secure
a drill bit
8 Chuck does not have proper stop.
Chuck is able to tighten until stuck.
(Opened or closed.)
7 Test each drill for proper stop 6 336 Increase lab testing.
Improve mechanical
stop and lubricaiton.
N/A N/A 8 4 4 128
Clutch Trigger
*Selects forward, reverse, or neutral
Sticks Forward/Reverse
gear is hard
to select
5 Poorly designed part 10 Quality control test
by pushing button
3 150 Redesign for more
clearance and less friction
N/A N/A 3 5 3 45
Chuck Brake
*Stops chuck after power is cut
Fails to brake Brake can no longer stop chuck
Chuck spins until friction slows it down
7 Brake wears from use 6 Failure observed by user 7 294 Conduct more research to find causes for failure and recommended solutions N/A N/A 7 4 4 112
Casing
*Secures mechanical parts
*Aesthetics
*Provide grip
Non-ergonomic handle Uncomfortable grip causes blisters or discomfort on user's hand 5 Poorly designed casing 8 Failure observed by user
Quality control testing in lab
7 280 Redesign case for ergonomic support N/A N/A 5 5 4 100
Battery
*Provides voltage
Does not hold charge well Drill is no longer operable (or at a lower level) due to a short battery life 7 Rechargable battery loses charging ability 8 Failure observed by user
Extended life testing
5 280 Explore alternative power methods
Purchase more expensive, better battery
N/A N/A 7 6 4 168

Design For Environment

With our preliminary research we were able to identify the five following items seem most obvious as major areas of concern in terms of the cordless drill and Design for Environment: design for disassembly, number of parts, variety/diversity of parts, battery usage, and modularity/upgradeability design. Details concerning each of these are laid out here:

  • Design for disassembly – The drill is not designed to be easily taken apart and then put back together. This creates two major DFE problems particularly when considering end-of-life factors. This factor makes it difficult to salvage any materials/parts for use in either new drills or refurbishing slightly used versions. Moreover, the inability to disassemble makes it difficult to repair the drill in the event something breaks or goes wrong, shortening the lifespan and potentially creating waste that could have been avoided.
  • Number of parts – The cordless drill used many different parts of many different materials. We feel that the amount of energy necessary to create this vast number of parts could be decreased simply by optimizing the number of parts used.
  • Variety & diversity of parts – There are 5 different types of screws used in putting this drill together. Our observation leads us to believe this number can be lowered to two, potentially eliminating the energy of three machines needed to make these screws.
  • Battery usage – we would recommend a study to verify how efficient the battery is and how much energy it saves over its lifespan in contrast to corded drills and equivilant disposable batteries. We identified this as the primary DFE concern and discuss it in more depth after this list.
  • Modularity of design – The cordless drill will only work in its out-of-the-box configuration. There is no way to expand its functionality which leads to upgradeability and “change in market” issues. The easiest change we predict could be the ability for a cordless drill to be able to accept batteries of different voltages.

The most important feature of a cordless drill is its battery life because the user's time for to complete a task is constrained by the life of the battery. If a user is in the middle of a project and the battery goes dead there is no way to make more progress until the battery recharges. Moreover, it takes significantly longer to charge the battery then to discharge it through use of the cordless drill. Therefore, we find users leave their batteries plugged into their chargers much longer than is necssary for charging, just to be sure the battery is always charged. This creates a serious DFE problem because of an excessive amount of wasted energy. Our suggestions are to find a way to either extend battery charge time or modify the charger to disconnect from its power source if the battery is fully charged.

In addition to these recommendations we found the drill was successful in other DFE considerations the most important being: use of rechargeable battery, optimized use of plastics for the drill casing, diverse availability of “bits” allows drill to multi-task easily, an its packaging (with battery removed and charger) wastes little space. A more comprehensive and exhaustive study would be necessary to give a more in depth analysis concerning the cordless drill’s design for the environment. But, we feel these items give a good estimate of the direction those studies would take and the where most obvious areas of improvement are.


Link To Design Report II http://www.andrew.cmu.edu/user/vsn/Cordless%20Drill%20Design%20Report4.doc

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