Group 15 - Black and Decker Drill

Revision as of 19:50, 19 November 2006

Executive Summary

Our group was chosen to dissect, examine, and reassemble a Black and Decker Power Drill.

Before assembly, our group discussed the possible mechanical and/or electrical components in the drill and their functions.

The disassembling process was both educational and exciting for our group. We took each component out of the drill and examined it to try to figure out its purpose and function. A detailed list of these components is listed in the Pre Disassembly section.

Further examination of each of these components, and some research led to the conclusion of each of their function. Pictures and CAD Drawings of each part and its function is located in the After Disassembly section.

During the assembling of the drill, it was extremely challenging for everything to fit correctly. The steps that we took to assemble the drill are located in the Assembly Procedure section.

After we disassembled, examined, and assembled the drill, we all now have a complete understanding of how any power drill operates. A full conclusion of our project is located in the After Assembly section.

Introduction

Our product for this project is a Black & Decker DR202B 3/8” Variable Speed Reversible Drill and Driver. The objective of this project is for our group to get a better understanding of the thought process that went into the manufacturing of this product. Moreover, on the basis of our analysis we aim to be able to make suggestions which would further better this product.

Our group consists of five members and all tasks for our report were distributed as follows:

1. Douglas Byrne (Group Leader): Pre Disassembly, Parts List and CAD Drawings.
2. Lauryn Brown: Disassembly Procedure and Parts List.
3. Holly Czechowski: Reassembly Procedure and Post Assembly Discussion.
4. Jonathan Barsa and Rohan Thadani: Introduction and Executive Summary.

For the Disassembly of the product we worked together and input from all the group members were considered and discussed for the Analysis and Suggestions part of our report.

Before Disassembly Section

Basic Description

The Black & Decker DR202B 3/8” Variable Speed Reversible Drill and Driver is designed to accept various bit sizes in order to drill holes and drive screws through a number of different materials. Attachments can be bought to use the drill as a mixer for cement and other compounds. It takes electrical energy supplied by an electrical outlet, and converts it to rotational energy using the motor. The rotational energy is then transferred through a set of gears to provide greater torque to the bit.

Product Operation

The drill has a two pronged polarized plug and operates on standard 120 VAC and draws 5 A. It uses a keyless chuck to hold the bit in place. There is a direction reversal switch and a trigger that can be depressed at different levels to operate at different speeds. The trigger can be locked in the fully depressed position. The product was in working condition before disassembly and performed with great ease. The bit experiences rotational motion and the motor makes a slightly higher pitched humming noise.

Part List

1. Cord
2. Strain Relief
3. Plug
4. Housing (2 pieces)
5. Level
6. Trigger
7. Trigger lock
8. Direction Switch
9. Motor
10. Shaft
11. Fan
12. Gears
13. Chuck
14. Bit
15. Screws (9+)

Materials

1. Plastic (Various Types)
2. Rubber
3. Metal
   1. Copper wire
   2. Shaft
4. Permanent Magnet
5. Liquid in Level

Disassembly Procedure

Step No.	Step Description	Relative Difficulty (Easy) 1 ↔ 10 (Difficult)	Tool(s) Required	Image
1	Remove Chuck The shorter end of an Allen Key is inserted into the chuck, and the hammer is used to turn the chuck in a counterclockwise direction (With respect to the front of the drill). Once loosened, the chuck can be removed by hand.	5 Requires a great deal of force to be applied, although this is by design.	≥¼ Inch Allen Key Hammer
2	Remove 9 Screws Screws are easily removed with a Phillips Head screw driver.	2 No real difficulty in removing the screws but doing so was rather tedious. Would be nearly impossible to do without proper tools.	#15 Torx Screwdriver
3	Remove Top Shell Once the 9 screws are out the top shell can be easily lifted off with your hands.	1	none
4	Bubble Level and Drill Bit attachment Both attachments are located on the top of the drill and fit in between the two sides of the casing.	1	none
5	2 screws holding the cable clamp in place Easily removed with screwdriver.	1	#15 Torx Screwdriver
6	Cable Clamp Lifts off after screws are removed.	2	none	After Removal
7	Trigger Lifts right out after the cable clamp is removed.	1	none
8	Directional Switch Found under the motor. Slightly difficult to remove due to its position in the casing.	3 Fits tightly into place, needed to be pried out.	none
9	Gearbox When directional switch is removed this component lifts out of the casing without the aid of any tools. However, some pressure is needed to condense the part in order for it to be lifted out. Sort of like a spring.	3 Some difficulty removing this component, due to the tight fit.	none
10	Motor and Fan Motor and fan slide away from the rest of the assembly and are removed last.	1	none
11	Separate Stator and Armature The springs holding the brushes in place are removed and the brushes slid out of the way. The two pieces then can be separated.	5 The springs are small and are under a relatively large force. Care must also be taken to prevent damage to the carbon brushes.	Pliers or a Small Screwdriver to remove the springs.	Here the Armature has been removed and both springs removed.

After Disassembly

Part Table

Part No.	Part Name and Function	# Of This Type	Material and Reason for Choice of Material	Reason for Part's Shape	Manufacturing Process	Image
1	Screw Hold material in place.	11	Metal Strength and Durability	Torx heads make manufacturing more efficient. They are easily aligned like Phillips head screws, but unlike Phillips heads, the screwdriver does not turn out.	Machined
2	Top Shell Protect Inside Pieces (Motor and Gear Assembly)	1	Plastic Lightweight, Non-Conductive, Strong	Designed to accommodate parts inside and for ease of use.	Injection Molding
3	Bottom Shell Protect Inside Pieces (Motor and Gear Assembly)	1	Plastic Lightweight, Non-Conductive, Strong	Designed to accommodate parts inside and for ease of use.	Injection Molding
4	Rubberized Grips Place to hold drill.	2 pcs	Rubber Ergonomic Comfort and Easy Grip	Fits around plastic shell.	Injection Molding
5	Rear Plate Ventilation and holds Bubble Level	1	Plastic Lightweight & Non-Conductive		Injection Molding
6	Bubble Level Make sure drilling/driving occurs perpendicularly to the surface.	1	Plastic & Mineral Oil The Plastic is Transparent & Mineral Oil will not break down or react with the plastic	Has two gauges, so one level can be used for both vertical and horizontal leveling.	Injection Molding
7	Accessory Bit Holder Easy access to extra bit.	1	Rubber Soft enough to allow the bit to be removed and inserted easily, yet hard enough to retain the bit		Injection Molding
8	Accessory (Screw driving) Bit Object that drills/drives.	1	Metal Strength and Durability		Machined
9	Power Cord Transports power to drill.	1	Plastic Flexible & Non Conductive Copper Good Resistance/Cost ratio		Extruded
10	Main Plug Supplies power.	1	Plastic & Copper	The plastic shell does not need to be grounded, allowing a two prong plug to be used. A two prong plug can fit in more outlets than a three prong plug.	Injection Moldeding & Sheet Metal Forming
11	Strain Relief Provides flexibility of cord without strain on wires.	1	Rubber Flexibility		Injection Molding
12	Wire/Cable Clamp Keeps wires in place to prevent strain on them.	1	Metal Strength		Die Cast
13	Anti-Theft Strip Reduce theft of the product.	1	Plastic & Metal Readily detected by store security system.	An industry standard part. There are multiple types available, this being one of the smaller ones.	Injection Molding & Sheet Metal Forming
14	Trigger Determines speed of drill.	1	Plastic & Metal The plastic serves to insulate the user from the current inside		Injection Molding
15	Internal Wiring	1	Copper & Plastic Insulation		Extruded
16	Direction Switch Allows for easy change in rotational motion.	1	Plastic Lightweight, Non-Conductive, Strong		Injection Molding
17	Motor Shaft See also: Motor Parts Table Gearbox Parts Table	1	Metal Good Torsional Strength		Machined
18	Motor See Motor Parts Table	1	Various	A universal motor can run on either AC or DC current. Therefore, one motor can be used in both the corded and cordless lines. A universal motor, unlike other AC motor types, can run faster than the cycle rate of the power supplied.	Various
19	Shaft Alignment Alignment of Components	1	Metal		Die Cast
20	Fan Cool down system, reduce heat loss, increase lifespan of parts.	1	Plastic Lightweight, reducing wasted power		Injection Molding
21	Gearbox See Gearbox Parts Table	1	Various	The gearbox converts the rotation supplied by the motor from High Speed/Low Torque to Lower Speed/ High Torque. Torque is more important than speed in this application, especially when drilling into hard materials.	Various
22	Chuck Provides spot to hold bit.	1	Plastic & Metal The plastic is Lightweight & Non-Conductive, protecting the user. The plastic is not strong enough to hold the bit under high stress, therefore metal is used for the core.		Injection Molding & Die Cast & Machined

Motor Parts

A basic motor parts diagram

Part No.	Part Name	# Of This Type	Material	Manufacturing Process	Image
17	Motor Shaft	1	Metal	Machined
18A	Commutator	1	Metal (Copper)	Machined & Sheet Metal Forming
18B	Armature	1	Copper Wire & Metal Core	Wire is wound around the Die Cast Core
18C	Brushes	2	Carbon	Machined
18D	Brush Holders	1	Metal	Sheet Metal Forming
18E	Stator Coils	1	Copper Wire	Copper Wire is wound around the Core
18F	Stator Core	1	Metal	Die Cast

Gearbox Parts

CAD Model zipped packages include .bmp and .png images, Autodesk Inventor .ipt files, .igs, .stl and .stp files. The package for the overall assembly includes .bmp and .png images, Autodesk Inventor .ipa and .ipn files, .igs, .sat and .stp files. The .ipa and .ipn files are dependent on the .ipt files. All the .ipt, .ipa and .ipn files can be found in a single separate package.

Overall Assembly: Group15 Gearbox Assembly.zip
Package of all .ipt, .ipa and .ipn files: Group15 Inventor Files.zip
Explosion Animation: Group15 Gearbox Explosion.wmv

Part No.	Part Name	Material	Manufacturing Process	Image	CAD Model
17	Motor Shaft	Metal	Machined		Cad Model
21A	Plate A	Metal	Die Cast		Cad Model
21B	Motor Shaft Bearing	Metal	Die Cast		Cad Model
21C	Shaft 1	Metal	Extruded		Cad Model
21D	Metal Spacer	Metal	Machined		Cad Model
21E	Gear A	Metal	Machined		Cad Model
21F	Gear B	Metal	Machined		Cad Model
21G	Shaft 2	Metal	Machined		Cad Model
21H	Gear C	Metal	Machined		Cad Model
21I	Rubber Spacer	Rubber	Injection Molding		Cad Model
21J	Plate B	Metal	Die Cast		Cad Model
21K	Fabric Spacer	Fabric	?		Cad Model

Design Changes on a Component Level

The rear plate could easily be incorporated into either of the shell halves. In the current design, the level would be located at the joint between the two halves of the shell. However, this issue could be designed around with relative ease. The level also needs a different method of retention. It currently fits loosely into a slot and can be rotated along its horizontal axis, rendering it rather inaccurate. Some sort of adhesive or mechanical fastener could be used.

Assembly Procedure

After Assembly

How It Works

The drill works mostly by converting electrical energy to mechanical energy. More specifically, voltage from the electrical outlet travels through the cord and goes into the stator. The trigger switch varies the amount of voltage supplied to the motor, hence the variable speed aspect. A magnetic field exists between the stator and the armature. The armature carries current across the field and produces an electromotive force from the voltage that acts opposite to the current. There is a commutator attached to the armature that controls the direction of the current in the armature, allowing the motor to run on DC instead of AC current. The electrical energy is turned into a torque which turns the rotor/armature in a particular direction. There is a switch that is attached to the motor that allows it to alter the direction in which the torque is created. The torque created in the armature then transfers its energy to a set of gears which in effect drives the drill bit. There is also a fan between the motor and gears to cool down the system and provides a default load, preventing the motor from spinning too fast and damaging itself. This is needed for efficiency purposes.

Disassembly/Reassembly Discussion

The disassembly and reassembly procedures were actually done twice. The first time the drill was taken apart, the actual motor was not disassembled into its separate parts. The reassembly for this was still a little bit difficult. It was a challenge to get the motor and gears back in the right spot, most likely due to a lack of experience in working with the components and the fact that the pieces were in there fairly tightly. However, once they were back together, the drill was plugged in and it worked fine. The second time the drill was disassembled, the motor was taken apart further to show its component parts, i.e. the commutator, stator, brushes, and armature. When reassembling the drill this time, the parts went together with more ease, but when plugged in it had a very bad burning smell. The burning smell probably came from some small shavings of the carbon brushes, left over in the drill casing from the reassembly process. The same sets of tools were used for the disassembly and reassembly procedures. The processes were almost reverses of each other except for the time factor. It took considerably longer to reassemble the product than to take it apart, i.e. one minute for disassembly and ten minutes for reassembly. In all, the product was completely reassembled, but it is suggested that it be used with extra caution.

Types of Analysis

A strength of materials test is suggested for the plastic casing. It would test to see if the casing could withstand a drop from a certain height without breaking/cracking. An actual drill could be used to serve as the model in this test. Another type of analysis would be an efficiency/size/shape analysis on the motor. People want the most power for their money, so increasing the efficiency would be ideal. The fan is crucial in terms of efficiency because it removes the excess heat from the system. For example, when you have a 100HP motor that is 90% efficient it means that 90HP is actually doing the work and 10HP is being lost to heat. The fan could reduce the amount being lost to heat, therefore increasing the efficiency. Perhaps the fan in the drill could be a different size/shape in order for it to remove the heat more effectively. In this case a precise model probably should be used. The fan is also important because cooling down the components could also extend the life of the product. Moreover ergonomic analysis also plays a crucial role in the manufacturing of this product. The drill is insured to be light weight and has a fairly good grip to give the consumer proper handle on the tool.

Recommended Design Changes

One recommended change would be to have a longer cord to the drill. A longer cord could get rid of the need for extension cords, however it could also start to get in the way for smaller jobs if the cord is too long. The cost of a longer cord also comes in to play here. In this case, a customer survey with a promotional coupon might result in the preferred cord length. A customer survey could also be used to see whether or not they use the level on the end and its' efficiency. In an evaluation of the drill, the level was found to be somewhat useless and a waste of money. Also, a keyless chuck could be convenient to the user, but a lot of times the bit can be adjusted tighter when you have a key. In this case a force analysis could be done to see how tight one really needs the bit to be to drill/drive into certain materials or perform certain tasks. That would determine whether a keyless chuck would be sufficient for most uses of the drill. It might be the case that a keyless chuck is fine for drilling through certain thicknesses or materials, but once a certain thickness is surpassed or a different material is used, a chuck with a key might be necessary. Also during our analysis we found that it would be advantages to the consumer if the trigger could be locked into intermediate speeds and not only on its maximum speed. This decision may increase the cost of production but would improve overall customer satisfaction with the product. Yet another suggestion is to vary the color of the product. Black and Decker equipment is primarily orange and black. However, from a marketing stand point, these colors may represent to the customer a standard duty tool. A heavy duty drill could be created in a different color combination, say silver and black or all black. This would indicate to the consumer the variation in Black and Decker products. It will also provide an easier visual separation between standard duty and heavy duty equipment. This could increase sales for Black and Decker because it would signify a wider variation in their product line. Diversifying your product can lead to a broader consumer audience thus improving sales.

References

Commutator (electric). (2006, September 18). In Wikipedia, The Free Encyclopedia. Retrieved 22:01, November 14, 2006, from http://en.wikipedia.org/w/index.php?title=Commutator_%28electric%29&oldid=76368620

Armature (electrical engineering). (2006, October 13). In Wikipedia, The Free Encyclopedia. Retrieved 22:02, November 14, 2006, from http://en.wikipedia.org/w/index.php?title=Armature_%28electrical_engineering%29&oldid=81309367

Black & Decker. (2003). Instruction Manual for Models DR201, DR202, DR211, DR220, DR403, DR501 and DR601. Towson, MD: Author.