Cordless drill

From DDL Wiki

(Difference between revisions)
Jump to: navigation, search
(Failure Mode and Effects Analysis)
(Failure Mode and Effects Analysis)
Line 195: Line 195:
|- align="left" valign="top"  
|- align="left" valign="top"  
|Chuck<br />*Secures bit<br />*translates torque
|Chuck<br />*Secures bit<br />*translates torque
-
| Jams || Chuck can no <br />longer secure <br />a drill bit || 8 || Chuck does not have proper stop.<br />Chuck is able to tighten until stuck.<br />(Opened or closed.) || 7 || Test each drill for proper stop || 6 || 336 || Increase lab testing.<br /> Improve mechanical<br />stop and lubricaiton. || N/A || N/A || 8 || 4 || 4 || 128 ||
+
| Jams || Chuck can no <br />longer secure <br />a drill bit || 8 || Chuck does not have proper stop.<br />Chuck is able to tighten until stuck.<br />(Opened or closed.) || 7 || Test each drill for proper stop || 6 || 336 || Increase lab testing.<br /> Improve mechanical<br />stop and lubricaiton. || N/A || N/A || 8 || 4 || 4 || 128
|-  
|-  
|- align="left" valign="top"  
|- align="left" valign="top"  

Revision as of 15:21, 11 February 2007

Group II
Ming Huo
Scott Miller
Vishesh Nandedkar
Mark Rockwell

Contents

Cordless Drill Product Analysis Report

Executive Summary

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 last 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 X-X summarizes the top five areas of concern for customer need and product requirements.

Table X-X: 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. We are not sure if it may be used under water, but assume it is not ever meant to be. 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 is squeezed, a potentiometer measures the depth the trigger has been depressed and allows a proportional amount of voltage to the motor. The motor spins at very high speeds, so to translate this speed to power, the shaft of the motor is connected to a planetary gear train which spins the chuck assembly. 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. When turning, there will normally be some material, whether a screw or board, etc. that resists the drill’s rotation. To counter this, a torque must be input by the operator’s hand and wrist to keep the drill steady. Most cordless drill operations also require an axial force pushing the bit forward into the material it is perpendicular to.

Operation

To operate the drill, one must first charge the drill’s battery. 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 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 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 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.

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. 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. [Insert more extensive introduction to product dissection here]

The cordless drill, pre-dissection is pictured above.


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 4 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 1 Secures bit and translates torque from motor to bit (Complex Process)
Assembly Line
Machining
Injection Molding
Cast

Manufacturing Discussion

DFMA:

Manufacture:

  • The majority of non-electrical components in the drill are hard plastic.
  • Because of the complexity of most of the hard-plastic parts, they appear to have been produced from injection-molding.
  • Most plastic parts come from molds that would have been simple to produce- no complex geometries or angles/cutoffs.

Assembly:

  • Made with as few parts as possible while still allowing easy assembly.
  • Slots made in side pieces to allow other components to slide into place.
  • Pieces manufactured so top pieces can be held together without additional screws.
  • 4 different types of screws used of varying lengths and thread types- can be confused because of their small size.

Disassembly:

  • Manufactured so main components of drill can be taken apart quite easily.
  • Electronic components packaged into simple groups for easy identification.
  • Chuck/torque control assembly proved extremely difficult to disassemble- reason possibly being that forces applied to the component necessitates such structural integrity and rigidity that the chuck assembly was press-fit together.
  • No special tools necessary for special assembly.
  • Drill was very sturdy before disassembly, but came apart very easily.
  • Ball bearings spilled out of casing during disassembly, and proved to be extremely difficult to find and re-position- a problem that may arise in assembly of product.


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.

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 Redesign brake
for longer life
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
Personal tools