Group 6 - Black and Decker Power Drill - Gate 3

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Contents

Purpose

After completing a dissection of the Black & Decker DR202 Power Drill, we were able to analyze the individual components. By examining the parts, we were able to gain further insight into the materials that made up the drill, as well as the manufacturing processes behind its construction. This further increased our knowledge of the design of the drill and why the drill was made in this fashion.

Product Management

Cause for Corrective Action

We have faced no major conflicts in completing our tasks and we have no unresolved issues involving group cohesiveness. However, as a group we feel as though we need to change the way in which we are completing our assignments. Although we think we answer every question for a given gate, we have realized that we are continuously too brief in our explanations. As a group we have come up with a few solutions to ensure that our responses are specific and thorough. We plan to make a greater effort to finish our gate a few days before the due date. This will allow us to check our gate with our instructor for completeness. This way we will have some suggestions as to what we can improve, and what we are lacking. We also plan to do a better job proof-reading our gates. We will be sure to read over sections completed by other group members to see if all questions were answered completely. As a result we will have a fresh pair of eyes looking at the responses. This will guarantee that all of the parameters of the question are answered.
We have been working well as a group and each member has been contributing their share. Our one issue has been in scheduling our meetings. We have planned to leave the time on Tuesdays and Thursdays available, but we decide on these days if a meeting as a group is necessary. So far, this plan seems to have been working better than having two meetings per week. We use our time in these meetings more effectively and are more focused in completing the task. We have been getting work done in a more timely fashion as a result. Communication outside of our weekly meetings has also been strong. Our group checks our progress after each MAE 277 and MAE 204 class, so we know what has been done and what we need to complete. Each group member has been responsible and trustworthy in meeting their assigned objectives. We plan to continue following the same procedures for scheduling meetings for the remainder of the project, but are willing to make adjustments as we see fit if problems do arise.

Product Archaeology

Component Summary

Table 7 lists the parts that comprise the DR202 drill. This table also tells the function of the component, how the component was manufactured, and the materials used in the production of the drill.
Table 7 Component Summary
Component Number (Referenced to Figure 2) Part Number Component Name Number Required Component Function Material Manufacturing Process Image
1 614362-00 Drill Housing 2 (Right Side and Left Side) The drill housing encases and protects the inner components of the drill. It provides stability and comfort while drilling by giving the consumer a strong base to hold onto. The housing also adds aesthetic appeal to the drill. Plastic (Polystyrene: a plastic also used to make fast food trays and disposable silverware) and Rubber (Handle) Injection molding (Two separate molds), The rubber is also injection molded and attached over the plastic shell using a strong adhesive.
Drill Housing Right side
Drill Housing Left side
2 387870-01 Spindle 1 The spindle keeps the gear and the keyless chuck on the same axis so that they rotate together. It also serves to transpose the mechanical energy of the gears to rotational energy of the chuck. Stainless steel for high durability and low cost Machined (lathed/hobbing)
Arrow Points to Spindle
3 391710-00 Gear 1 The gear transforms the mechanical energy of the motor into the rotational energy of the chuck. The gear ratio serves to increase torque and decrease velocity of the chuck. Stainless steel for high durability and low cost Machined (Hobbing)
Gear
4 330016-09 Washer 1 The washer prevents the front bearing plate from rubbing up against the gear. Stainless steel for low cost Machined (Punched out of a steel sheet)
Arrow Points to Washer
5 385681-00 Front Bearing Plate 1 It serves as a spacer and holds the keyless chuck in place by preventing it from moving back and forth inside the drill. Stainless steel for durability Metal Casting
Front Bearing Plate
6 330075-49 Keyless Chuck 1 The keyless chuck holds the bit and is responsible for its rotation. Hard Plastic Exterior (Polystyrene), Stainless Steel Interior Metal Casting and Injection Molding
Keyless Chuck
7 620285-00 Rear Bearing Plate 1 The gear and pinion are held in place by the rear bearing plate. Stainless steel for durability Metal Casting
Rear Bearing Plate
8 385988-00 Gear and Pinion 1 The gear and pinion serve as a gear reduction from the armature to the keyless chuck. It increases torque and decreases the velocity of the chuck. Stainless steal for durability Machined (Hobbing and Lathe)
Gear and Pinion
9 385537-02 Armature 1 The armature turns magnetic energy from the field into electrical and rotational energy. The current in the wires of the field creates a magnetic field near the armature and causes a force. Plastic, Copper Wires, Stainless Steel Copper wires are drawn, Plastic is injection molded, Steel is machined and hobbed
Armature Assembly
10 607888-00 Retaining Ring 1 The retaining ring is used to keep the heat sink, the red washer, and the plain washer on the armature assembly. Stainless Steal Punched out of a metal sheet/machined
Retaining Ring
11 148902-00 Plain Washer 1 The plain washer is used to keep the heat sink from rubbing up against the retaining ring. Stainless Steal Punched out of a metal sheet
Plain Washer
12 158478-00 Heat Sink 1 The heat sink is used to absorb any excess heat that is given off by the rotation of the armature. Iron Metal Casting
Heat Sink
13 37381-00 Red Washer 1 The red washer is located between the heat sink and the coils of the armature. It is used to keep the heat sink in one place and keep it from touching the armature. Fibers The fibers are made into dense sheets then stamped into the appropriate shape
Red Washer
14 385849-00 Field/Stator 1 The field is used to convert the electrical energy imported from the power cord and turn it into magnetic energy to be used by the armature. Plastic, Copper Wires, Steel The plastic was injection molded and the wires were drawn.
Field
15 385995-01 Reverse Ring 2 The reversal ring is used to change the direction of the rotation. It is a transmission used in the drill. Plastic, Bronze (cheep conducting metal) The plastic was injection molded and the bronze was machined.
Stationary Reverse Ring
16 611278-00 Reverse Lever 1 The reverse lever is used to move the reverse ring. This in turn makes the drill change directions. Plastic Injection Molding
Reverse Lever
17 611719-01 VS Switch 1 The trigger is used to close the switch inside the drill to let the electrical energy flow to the field. Plastic, Copper Wires Injection Molding, Drawn (wires)
Trigger
18 330073-98 8 Foot Electric Cord 1 The cord is used to move the electric current from the wall to the drill. Copper Wires, Flexible Rubber (harder than rubber to retain some shape) Wires were drawn
Power Cord and Cord Protector
20 380414-00 Cord Clamp 1 The cord clamp is used to keep the wires from the cord from moving around inside the drill. Stainless Steel Punched out of a metal sheet then formed with pressure
Cord Clamp
21 330019-03 3/4" Screw 11 This small screw is used to hold the cord clamp in place and keep the two halves of the housing together. Stainless Steel Machined (lathed)
Small Screw
22 330019-08 1 7/8" Screw 2 The long screw is used to keep the stationary reversal ring on the field. Stainless Steel Machined (lathed)
Large Screw
19 611721-00 Cord Protector 1 The cord protector is used to keep the cord from bending or pulling too much at the base of the drill. This keeps the copper wires on the inside of the drill from breaking or sliding out of the drill. Plastic Injection Molded
Cord and Cord Protector
28 389818-00 Felt Washer 1 The felt washer is used to keep a space between the front bearing plate and the keyless chuck. Felt The washers are punched out of woven felt sheets using sharp razor blades
Felt Washer
29 612596-00 Level Holder 1 The level holder is used to keep the leveling device in a secure location outside the drill for easy reference. Plastic (polystyrene) Injection Molded
Level and Level Holder
30 611723-00 Level 1 The level is used to keep a reference as to if the drill is on a horizontal plane or not. Plastic (covering) and viscous chemical liquid Injection Molding
Level
31 612861-00 Bit Holder 1 The bit holder keeps the bit from being lost by holding it on the outside of the drill. Plastic (polystyrene) Injection Molded
Bit Holder


Figure 2 shows the exploded view of the DR202 Type 2 Drill. This shows the relationship between the inner components of the power drill.

Figure 2: Exploded Component View
Exploded parts.GIF
This is the source of the picture.

Product Analysis

The following component complexity scale is used as a basis for comparison in the analysis of the drill components.

Low- A component with a low complexity profile would be constructed using one manufacturing process. A low complexity component would also be comprised of a single material. The production of these components would require minor knowledge because these parts are easy to design and fabricate.
Medium- A component with a medium complexity profile would be constructed using two to three manufacturing processes. They may also consist of up to two different materials. The production of these components would require general knowledge of manufacturing processes, but these skills could be acquired through experience.
High- A component with a high complexity profile is constructed using four or more manufacturing processes. These components are made using one or more different materials. The production of these components would require and in depth understanding of multiple manufacturing processes.

The following interaction complexity scale characterizes the relationships between components within the drill.

Low- Low complexity interactions are classified by usually one type of flow between the components. This is usually characterized by a physical or structural connection between the components.
Medium- For a medium complexity interaction two components within the drill are joined physically by more a more complicated interaction. This type of interaction could include a bearing joining or more than one flow of energy.
High- The most complex interactions within the drill are defined by those interactions that occur through a non-physical bond. For the drill, this could include interactions through adjacent magnetic fields.


Drill Housing:

Component Function

The main function of the drill housing is to encase and protect the inner components of the drill by acting as a solid outer shell for the drill. The inner components of the drill are all contained within the upper portion of the housing. The housing also includes the handle at the base of the drill. This handle provides stability and comfort for the user. The handle is ergonomically designed so the user can easily grip the drill, which reduces stress while drilling. Human energy is inputted into this component. This form of energy is responsible for keeping the drill in an optimal position that allows the most force to be delivered to the screw. The drill housing operates in a standard atmosphere, up to a certain temperature to prevent deformation. The range of environments in which the drill can operate is anywhere from households to small construction sites.

Component Form

Right Side of Housing - Inside
The drill housing is essentially L-shaped in nature, but includes a number of contours. The right and left housings are similar in shape, but are not quite mirror images of one another. This is due to the internal arrangement of the components. The drill housing is three dimensional in nature. It must be three dimensional for the three dimensional inner components to fit inside the housing. Since the drill housing is the outer shell for the drill, it is the largest component. It is approximately 8 inches from the back to the keyless chuck, and 9 inches from the base to the top. It is also approximately 3 inches in width. The shape of the drill housing is determined by the assembly of the components. The housing is formed around the components in such a way that minimizes the volume of the drill. The handle is tilted to a slight angle for maximum comfort and stability. The grip includes grooves to guide finger placement on the drill handle. While the drill housing is the largest component of the drill, it is comparatively light compared to its size. It is roughly a pound. This is due to the materials with which it is made. The housing is made out of plastic called polystyrene which is a harder plastic also used in fast food trays and disposable silverware. The choice to use injection molding as the manufacturing process stems from its inexpensive nature. The material often used in injection molding is plastic. In order to adequately protect the inner components, the material used for the drill casing must be rigid. If the drill is subjected to large forces, the housing must be able to withstand those forces and maintain its shape. It must also have a high melting point to prevent deformation in higher temperatures. The plastic material is cheap, so as to not increase the cost of the drill. It is also safe because it does not contain any harmful chemicals such as mercury or lead. The plastic is also recyclable because it can be melted down and used again. This way, it will not take up more space in the landfills. Globally, any country that would have a need for a power drill would also have the capability of producing the plastic required for the housing. Therefore, there are no geographical limitations for this component. The handle also has a rubber overlay that was produced using injection molding. Aesthetically, the drill housing is appealing to the eye because of its curvature and coloring. The signature color of Black & Decker is red. The drill housing is made with a red pigment for quick association with the company. The color red also signifies power, which would appeal to the male consumer. The drill casing has a dull and slightly rough finish. This finish has a functional purpose in that it serves to prevent the slipping of the hand.

Manufacturing Methods

Injection Molding Overview
Injection molding was used to manufacture the drill casing. For this particular manufacturing process, a mold is used. As the two halves are attached a series of parting lines often appear. Since the two drill halves are joined by screws at this line, parting lines do not appear. A number of riser marks appear on the inside of the drill casing, however. This leads us to believe that injection molding was used. Plastic is the material of choice for injection molding. Other materials could not be used with this process. The shape of the drill casing is also important for injection molding. The drill casing has no protrusions or cavities that would prevent its removal from a mold. Injection molding is a relatively cost efficient process once the mold is created which is an economic benefit. It is a safe process which would meet the safety regulations of most countries. It has minimal waste residue since the mold is consistently reused and the excess plastic can also be re-melted and reused. Since injection molding is a relatively easy process, any developed country can make use of this manufacturing technique.

Component Complexity

According to the above complexity scale, the drill housing can be classified as a medium complexity component. Two injection molds are used in the production - one for each the black and red portions. Two different materials, plastic and rubber, are also used in its production as stated before. The number of manufacturing processes used is the major factor in determining the complexity, followed by the number of materials used. Generally, the more manufacturing processes a component requires, the more knowledge is required on behalf of the manufacturer.
  • The drill housing holds all the inner components of the drill in place by fitting them into the slots defined by the molding of the casing. Complexity: Low
  • In the drill housing, the left side is attached to the right side of the housing of the drill by screws. Complexity: Medium

Armature:

Component Function

The main function of the armature is to convert magnetic energy from the stator to mechanical rotational energy. The armature creates a magnetic field opposite to that of the stator which results in its rotation. While the component itself performs this single function, the armature serves as a major component in the continuation of the flow of energy to the bit through its rotation. Magnetic energy flows and rotational mechanical flows are associated with the armature. This conversion of energy is necessary for the drill to perform its task. The armature operates in a high heat environment due to energy dissipation in the copper wires of the armature and stator. This component also operates in a high precision environment. The armature must remain on its axis because any lateral movement would cause it to touch the inner walls of the stator. The uniform magnetic field inside the stator, however, prevents the armature from touching its inner walls. This is also a high velocity environment, as the armature rotates at a speed of 1,350 rotations per minute.

Component Form

Armature
The armature is primarily a small cylinder adjacent to a larger cylinder with two hemispheres at each end. It is axially symmetrical about its length. That is if you take a cut along the diameter of the armature it is symmetrical on both sides. The coiling of the copper wires is also a distinguishing feature of this part. The copper wires lie on top of each other and make a pattern around the central axis which creates the dome shape. The armature is three dimensional because it is essentially a solid cylinder with a substantial length. It is 2 ¾ inches long, with a ¾ inch radius for the larger cylinder, and ½ inch diameter for the smaller cylinder. This part is cylindrical because it is rotating within the stator. If it were to have perpendicular edges, it would not be able to spin freely in the cavity. Since it is constantly spinning, it must also be symmetrical about its length to ensure that it is uniform. The cylindrical shape of the armature also causes it to have properties similar to that of a solenoid. This means that magnetic field around the armature would be uniform, allowing it to rotate smoothly. The armature is roughly the same weight as the stator at about 1 pound. The fact that the materials within the armature are compacted, would justify this weight. The armature is made from a series of different materials. The wires are copper and the shield around the armature is steel. The armature requires a metal that can be drawn into wires and have electricity flow easily through it. Copper is a suitable choice to carry out this function because it is a good conductor of electricity and is cost efficient. The shield must be durable to protect and encase the copper wires. Steel is a rigid metal that is also fairly inexpensive. Aside from the lower cost of these materials, other factors also influenced the material choice. Copper is readily available in mines and can also be recycled which is an environmental benefit. Mining the copper, however, would be a societal concern since this process can be dangerous to those employed. Noise pollution would also affect surrounding towns. The other benefits to using copper would outweigh these negative effects. Steel is used due to the availability of iron ore. Similar to copper, mining may be dangerous and disruptive to neighboring communities. Environmentally, steel can be melted down and reused for other products causing less harm to the atmosphere. The armature has no aesthetic purpose rather the armature is designed for functionality. The coloring of the armature is simply the natural colors of the materials from which it is made. The copper wires are not finished and neither is the steel. They are left in their natural state to prevent any extra unnecessary costs.

Manufacturing Methods

Process for Wire Drawing
The copper wires in the armature are drawn which is the traditional method for manufacturing wires. The copper is an appropriate material for this process because it is ductile. The wires must be thin to create a large enough electric current to oppose the magnetic field of the stator. This is achieved through drawing the wires. The cross sectional area of the wires must also be uniform to ensure a consistent flow of electrons so the magnetic field is undisrupted. The steel strips comprising the shield of the armature were produced through a machining process in which they were punched out. A forming process was then used to shape the strips into their desired profile. Machining and forming processes are used to shape metals. Plastic is not as flexible and cannot be easily shaped except through molding. Since a metal is needed to withstand heat generated by the armature and the stator, a machining and forming process must be used. The shape of the shield influences what manufacturing process is used. It would be quite difficult to die cast metal pieces that small. Machining processes can easily create small metal pieces of any shape. The processes used to manufacture this component are cost efficient for the pieces that are being produced. The methods pose no major safety factors to those running the operations. These processes are generally simple and can be performed by any developed country with available resources. Drawing does not produce a lot of waste material and while punching does produce excess material, it can be reused for other components.

Component Complexity

The armature is a highly complex component in the drill based on the aforementioned criteria. It is made up of two materials – copper and steel and three manufacturing processes are employed to create it. Since multiple processes and materials are required, a greater understanding of the manufacturing methods is required.
  • The armature is connected to the rear bearing plate through a hole with cylindrical roller bearings. Complexity: Medium
  • The armature is set into the drill housing on the left side into plastic sleeves. Complexity: Low
  • The armature is connected to the stator through a magnetic connection. Complexity: High

Reverse Lever:

Component Function

The main function of the reverse lever is to toggle the reversal ring. While the component itself only has only one function, the activation of the reverse lever coincides with many flows within the drill. Human energy is transmitted through the reverse lever, to the reversal ring. The reversal ring, when switched, changes the direction of the electrical current flowing inside the stator. This ultimately changes the direction of rotation of the drill bit. This allows the user to remove screws from the given material. The component acts both inside and outside of the drill casing. The reverse lever operates in a high friction environment because of the nature of the function of the part.

Component Form

Reverse Lever
The reverse lever is irregularly shaped, but is generally planar when viewed from the side profile. From the top, the reverse lever has a diamond shaped base with a trapezoidal head where the switch is activated by the user. Despite its irregular shape, it is axially symmetrical lengthwise. The tail of the lever is also ball shaped where it comes into contact with the reversal ring. While some of the component is flat, it is primarily three dimensional in nature. The lever is approximately 3 ½ inches long. Its head is 1 1/8 inches wide and the body ¾ inches wide. The head is 3/8 inches thick, while the body is 3/16 inches thick. This is not including the protrusions that keep the lever in place while it is moving. The shape of the reverse lever is coupled with the function it performs. Since it has to activate the reversal ring in the back of the drill, it must be longer that it is wide. The head of the lever must also be of adequate size to allow for easy human interaction. There is also a slight curve to the lever to accommodate the slight difference in height between the lever head and where the reversal ring is located inside the drill. This component is quite light, weighing less than 1 ounce. It is made out of plastic that is slightly flexible and of lesser quality than the plastic of the drill housing. Since this is a small component of the drill, and the demand for durability is not as high as the drill housing, a cheap material was chosen. This would allow for injection molding to be used which is at first expensive, but cheaper as more parts are mass produced. The materials must be rigid enough to switch the reversal ring and some friction must be present at the head to ensure that the finger will not slip across the switch. Economically, the material used to produce the lever is relatively cheap. Excess plastic can be melted down and reused, making it recyclable. Little energy is required for the production of this part, and any advanced country would have the resources required to manufacture the lever using this material. Socially, this material poses no safety concerns since the material is used in a number of other common items such as plastic soda bottle tops. The reverse lever does not have a major aesthetic purpose. It is mainly designed for functionality. The black coloring and round edges, however, coincide with the coloring and curvature of the drill housing. This allows for some consistency in the design of the drill. The component is not finished and was taken right out of the mold. This rough surface serves a functional purpose by maximizing the friction between the human finger and the switch.

Manufacturing Methods

The reverse lever was manufactured by injection molding. The head of the lever was produced using a different mold than the body. This is evidenced by seams in the head and riser marks in both the head and the body. The presence of draft angles also supports the case that injection molding was used. The use of plastic for the reverse lever impacts the manufacturing process. Injection molding is the cheapest procedure that utilizes plastic which is a major economic benefit. The shape also impacts the method. The lever can be broken down into a few simple shapes that can be easily molded. Environmentally, excess plastic from the lever can be melted down and reused. There are no geographical, language, or other cultural barriers that prevent a country from using injection molding. Most countries would have the resources and the knowledge required to produce parts using this procedure.

Component Complexity

The reverse lever would be considered a low complexity component. It requires only one type of manufacturing process - injection molding, to produce it. It also is comprised of only one material. The number of manufacturing processes used is the major factor in determining the complexity, followed by the number of materials used. Generally, the more manufacturing processes a component requires, the more knowledge the manufacturer is required to know. Since only one manufacturing process and one material are used, only a very basic knowledge of the procedure would be required.
  • The reversal lever is held in place by a slot in the casing, which allows it to swivel back and forth. Complexity: Low
  • The reversal lever interacts with the reversal ring by pushing it one way or the other by the ball on the end of the lever fitting into the loop on the ring. Complexity: Low

Power Cord:

Component Function

The main function of the power cord is to bring electrical energy into the drill. All the components need the power cord to work. Without them, the electrical energy cannot be changed into rotational energy, which in turn allows the drill to perform its main function. Human energy is used to plug in the electrical cord to provide electrical energy to the drill. The power cord can operate in any environment where there is an electrical power supply. The power cord operates in a standard atmosphere, ranging from household projects to construction sites. It is tested up to 60 degrees Celsius. A small amount of the electrical cord is also incorporated inside the drill housing. This is where the wires are connected to the trigger, which is the first step in transforming the electrical energy to rotational energy.

Component Form

Power Cord
The power cord is a flexible rubber cord that can be molded into numerous shapes. It contains copper wires and a threaded cotton insulator. The power cord contains product numbers, which allow for easy replacement of parts. The cord has a 2-pole plug on the end and a cylindrical shape parallel to the center of the length of the cord. The power cord is three-dimensional. The end of the cord, which is the plug, has a pyramidal shape. The prongs of the plug are approximately 2/3 inches long. The length from the base of the plug to where it meets the cord is 1 3/4 inches. The rectangular base of the plug measures 3/4 inch by 1 inch. The length of the cord is 6 feet 9 inches. The diameter of the power cord is approximately 1/5 inches. The circular power cord holds circular wires. The flexibility of the cord allows for the power drill to be used around any obstacle. It has solid metal pins that transfer electricity into energy. The power cord weighs between 7 and 8 ounces, making it relatively light. The power cord’s outer layer is made out of a long tube of rubber. The rubber can withstand a temperature of 60 degrees Celsius, which adds to the safety factor. It waterproofs the wires, removing the risk of shock. The wires are drawn through draw plates. The plug portion of the cord is made through injection molding, which is inexpensive and efficient. The common material used in injection molding in plastic, which is exactly what the plug is made out of. Using this cheap plastic material does not increase the cost of the drill. Plastic also has a positive environmental impact because it can be melted down and reused again. Aesthetically, the power cord is made to be as thin as possible to make it pleasing to the eye. The cord is black to blend into the surroundings and not be very noticeable. The cord’s outer finish is smooth due to the rubberized finish. This allows for consumers to run their hands along the cord without injury. It also aesthetically makes the cord more pleasing to the eye.

Manufacturing Methods

Injection molding was used to manufacture the plug end. This is apparent from the seams down the sides. The plastic material is commonly used in injection molding, and it is also a very durable material. Therefore, it was chosen for this application. The shape is symmetrical, which is ideal for injection molding. A mold of the plug is made, and then the two halves are put together and the seams are cleaned up. Economically, injection molding is cheaper because the mold, once it is created, can be reused over and over again. It a safe process so it is socially accepted in a multitude of countries. The rubber jacket is made out of rubber because it is easy to work with and can be molded into different shapes. This also makes the cord flexible, which is a major benefit. Copper is used in the wires inside the cords because it is an excellent conductor of electricity.

Component Complexity

The electrical cord would be considered a medium complexity component. It is made up of copper, rubber, plastic, and also cloth. Injection molding and drawing are both used in the manufacturing of the cord. It only performs one task for the drill but that task is the most important. Without electricity being inputted into the drill, there would be no rotational energy being made thus making the task of the electrical cord vital to the drill operating correctly.
  • The power cord is held down onto the casing by a clamp and two screws. Complexity: Medium
  • The power cord interacts with the trigger by transmitting a power from the outlet to the trigger housing. Complexity: Medium

Stator:

Component Function

The stator imports electricity from the power cord to the copper wires which produces a magnetic field. This magnetic field causes the armature to spin which is ultimately transformed into the rotational mechanical energy of the bit. This component helps to indirectly perform multiple functions such as the rotation of the gears. The stator itself, however, has only one function which is to convert electrical energy into magnetic energy. The stator must be able to withstand high temperature environments. As electrical energy flows through the wires resistance causes a significant amount of energy dissipation in the form of heat.

Component Form

Stator
The stator is essentially a hollow cylinder. It is axially symmetric through its x and y axes when looking through the center. The stator is also flat on two sides where it sits inside the drill so it remains stationary. It is a three dimensional component because the armature must rotate within the stator. This component is one of the large components of the drill. It is 2 ½ inches in length with an outside radius of 1 1/8 inches and inner radius of ¾ inches. The shape the component is coupled with the component’s function. The stator must be hollow in order for the armature to rotate within. It also must have curved surfaces to allow it to freely rotate. Its cylindrical shape is important for creating a uniform magnetic field within the stator. The stator is one of the heavier components of the drill at around 1 pound, assuming we are on Earth. The weight of the stator is due to the materials of which it is comprised. The stator consists of tightly wound copper wires, a plastic shell, and a steel shield. There is also a strong adhesive that holds the copper wires together. The materials used in the stator were chosen for the function they perform. The manufacturing processes were not a major factor in the material selection. For example, the shell is plastic because of its insulating properties. If the shell were steel or another metal, a charge could be conducted through which could affect the magnetic field generated by the stator. This could alter the rotation of the armature. The stator also needs copper wires to conduct electricity. The durability of steel is also an essential property for the shield which serves to reinforce the stator. Economically, the steel and the plastic for the stator are quite cheap and are readily available. The copper wires are more expensive, but are necessary for proper conduction. These wires have the ability to be recycled along with the other materials once they are separated. Since copper is mined, the location of copper veins influences where the copper can be produced. The action of mining can disturb communities due to noise, and also has negative effects on the environment. Safety is also a major factor in the acquisition of this ore. In addition, another societal concern that should be taken into account is the effect of electrical and magnetic fields on implanted defibrillators, pacemakers, and similar implanted medical devices. The intensity of the electric field required to interfere with these devices varies with frequency and waveform. There are no aesthetic properties of the stator due to its location inside the drill housing. The design of the stator is strictly functional in nature. The component is copper and silver due to the natural properties of the materials from which it is made. The black plastic shell serves no aesthetic purpose. The black coloring is most likely for neutrality and cohesiveness. The stator does not have a refined surface finish although the steel shield is relatively smooth. The inside of the stator is smoother than the outside for functional reasons. A smooth surface ensures that the field created within the stator is uniform, which allows the armature to rotate freely within.

Manufacturing Methods

The copper wires in the stator are drawn which is the method used for all wires. The copper is a typical material used for this process. The long, uniform shape of the wire is necessary for its function. This shape is most efficiently achieved by drawing the wire. The plastic shell is injection molded as evidenced by the riser marks adjacent to the screws. Plastic is the material used in this particular manufacturing process. The shell does not have any major protrusions or cavities that would hinder its removal from a mold. Therefore, injection molding would be a practical method. The steel shield is punched from steel sheets then layered and fitted together using a strong adhesive. Metals are often used in machining process, which would explain the chosen manufacturing technique. Since the steel rings are all the same shape, punching them would be a quick way to mass produce them. Injection molding, punching and drawing are relatively cheap and quick processes. There are no major safety issues with using these methods. They are not complex processes, which would allow most developed countries to utilize these techniques. While machining involves the removal of material, this excess material can be melted down and used for other processes within the drill. These processes also involve small energy input compared to more advanced methods.

Component Complexity

The stator can be classified as a highly complex component according to the defined complexity scale. Three individual materials make up this component and three separate manufacturing processes are used. Both the number of materials and the number of manufacturing methods are important in determining the complexity of the product. With the addition of materials and processes, more knowledge is required on behalf of the manufacturer.
  • The stator is connected to the drill housing through molded plastic sleeves that it sits inside of. Complexity: Low
  • The stator is connected to the armature through a magnetic field. Complexity: High
  • The stator is connected to the power cord through wires and electricity. Complexity: Low

Rear Bearing Plate:

Component Function

The main function of the rear bearing plate is to hold the gear and pinion in place. The component alone has only one function – holding other components in place – but it contributes to many other functions of the drill. The plate makes it possible for mechanical rotational energy to transmit throughout the gears by holding all these components in place. The plate also holds the end of the armature shaft. The rear bearing plate must be able to withstand a variety of environments. The hole holding the pinion would experience a lot of friction from the rotational motion of the component, resulting in the creation of heat.

Component Form

Rear Bearing Plate
The plate is essentially a rectangular shape from the front view and L-shaped from the side view. The bottom of the L-shape is round to fit into the mold of the drill housing and has a round hole in the middle to hold part of the gear system. This part of the L-shape also has three rounded ridges to help hold the rear bearing plate in place firmly within the drill housing. The rest of the plate contains two round holes for the pinion and the armature shaft. The hole holding the pinion is smooth on the inside, while the hole holding the shaft has teeth to fit the shaft, allowing it to remain firmly in place. This hole has a diameter of ½ inch. Inside this hole a piece that contains ball-bearings, which decrease the factor of friction between the metal on metal, can be popped in. The hole in which the pinion is held is ¼ inch in diameter. The rear bearing plate is three-dimensional. The plate measures 1 7/8 inches by 2 ¼ inches, and is 3/16 inches thick. The L-shape, which is 5/8 inches long, gives the gears more support while at the same time leaving ample room for the gear and pinion to fit into the drill housing. The inner diameter on this portion is ¼ inch, and the outer diameter is ½ inch. The different notches and bump-outs on the plate were specifically manufactured that way to fit perfectly into the drill housing. This way, the whole system of components is held firmly in place without the use of extra components such as screws. The rear bearing plate is made out of stainless steel, weighing about 0.2 lb. Stainless steel is a very durable yet strong material, which is essential for withstanding the motion that is occurring through the component. The decision to use metal comes from the fact that it is strong, durable and relatively cheap. The manufacturing process then would have to be die casting. Stainless steel is one of the most common metals used in products, and it is also relatively light, which is socially acceptable by consumers because it does not add a lot of weight to the drill. Economically, steel is relatively cheap so it does not add a large amount of cost to the drill. Globally, almost every country has the ability to mine this ore. There are no geographical limitations for this component. The rear bearing plate is not designed for aesthetic purposes. It is also hidden inside the drill so most consumers would not even see the component. The plate is designed purely for functional purposes, as seen by all the different grooves and cut-outs. It is in the common stainless steel finish because the color cannot be changed unless a coating was to be used. For this product, there is no need to cover the original color of the stainless steel. The finish on the stainless steel is a smooth finish, ideally for a clean fit of all the components into the drill housing. The inside of the holes were smoothed down to allow for the adjacent components to rotate efficiently.

Manufacturing Methods

Die casting was used to manufacture the rear bearing plate. The material used is stainless steel, which specifies the casting process to metal casting. This is supported by the seams and the rounded edges. The common material for die casting is metal; therefore this material choice completely impacted the manufacturing process. The shape of the plate is quite simple geometry; therefore, casting is an appropriate process to use. The plate does not contain many design features that would cause the removal of the component to become a hassle. Die casting becomes a societal concern because it has some safety risks associated with it due to the molten metal being dealt with. The mold can be reused, so even though it is a higher initial cost, overall it is an economical manufacturing process.

Component Complexity

The rear bearing plate would be considered a low complexity component. It is manufactured out of one material, stainless steel, through one manufacturing process. The purpose of the plate is to hold the pinion, armature, and the gear in place so that the rotational energy can be transferred from one component to another. It allows the gear reduction to occur so that the user can properly and efficiently use the drill.
  • The rear bearing plate is held in place by the drill casing. It is manufactured to slide into a slot molded into the casing. Complexity: Low
  • The rear bearing plate is connected to the armature shaft through a hole with a cylindrical roller bearing. Complexity: Medium
  • The rear bearing plate interacts with the gear and pinion by the pinion held in place by a hole in the plate which allows it to spin. Complexity: Low
  • The rear bearing plate holds the keyless chuck shaft in place by the fitting on the plate. Complexity: Medium

Gear and Pinion:

Component Function

The main function of the gear and pinion is to act as a gear reduction and from the armature to the keyless chuck. It changes the rotational energy by decreasing the velocity and increasing the torque at the chuck. This component connects the armature to the gear in order to make the chuck rotate. It is held in place by the front bearing plate and the rear bearing plate. The gear and pinion operates in a high friction and high velocity environment inside the casing because of the gear reduction process that is occurring. It is also a high precision environment due to the tight fitting between the gears.

Component Form

Gear and Pinion
The gear and pinion is circular and contains several different diameters due to the gears. It is axis-symmetrical along its length. It is three-dimensional along the entire portion of the component. The gears are shaped to interact with the other gears. All the gears meet up with corresponding gears on the armature and chuck. The gear and pinion consists of a middle shaft, a large gear in the middle, a longer gear with larger teeth, and a disk to stop the component from moving back and forth. The middle shaft has a diameter of 3/16 inch, the larger gear has a diameter of 1 ¼ inches, the long gear has a diameter of ½ inch, and the disk has a diameter of 6/16 inch. The length of the entire component is 2 1/8 inches. All the gears including the pinion portion are made from steel. Steel has a good strength to price ratio; it is strong and relatively cheap. This component is 0.1 lb. The gears are machined using the lathe and a special type of milling machine called a hobbing machine. Steel can be mined in any country that has the resources, specifically the necessary tools and machines, and these gears can be produced globally. Environmentally, steel becomes a concern because it takes a long time to decompose in the environment. With its durability and strength, however, these gears can withstand years of use. The gear and pinion has no aesthetic value. It is the color of steel because this color cannot be changed unless with a coating and there is no reason to have a coating on the gears. In fact, having a coating would detract from the gear’s function. The surface on the middle shaft is polished smooth for functional purposes. By having a smooth finish, the gear and pinion can rotate smoothly and freely. The teeth on all the gears are smooth in order to allow for smooth rotations. If the surface finish was bumpy, then the rotational motion would become interrupted and no longer smooth, which would disrupt the continuous flow of energy throughout the drill.

Manufacturing Methods

Hobbing Picture
The gear and pinion was manufactured using two different manufacturing processes. The pinion was made on a lathe, which produced the long symmetrical shape. A lathe is a machine tool which spins the piece while holding the ends and cuts the shape. The component is axis-symmetrical, which implies that a lathe was used. Two more characteristics which are evident of the lathing process are the smooth finish and the high precision. The lathe was also used to manufacture the rough shape of the gears. The hobbing machine was then used to create the teeth on the gears using the cutting tool that is called a hob. This is economical and environmental because it is all cut of out one piece of steel. Globally, iron ore is readily available. This means that steel can be found in countries all over the world because steel is made mainly of iron. Economically, hobbying is a relatively inexpensive process yet still moderately accurate.

Component Complexity

The gear and pinion is considered to be a medium complexity component. It is made of only one material but it is made with two different manufacturing processes. The lathe is used to get the general shape and the hobbying machine is used to create the teeth on the gears. Although there is only one material used, the manufacturing process must be very precise to form the complex function that the gear and pinion performs. Without this component, the bit would spin too fast for the user to operate.
  • The gear and pinion is held in place by the front and rear bearing plates where it fits into the holes in both plates that allow it to rotate. Complexity: Low
  • The gear and pinion interacts with the armature shaft by the larger gear on the pinion joining the gear at the end of the armature shaft, which is what causes the rotation. Complexity: Medium
  • The gear and pinion spins the gear of the keyless chuck shaft by the smaller end of the pinion joining the gear of the chuck, which spins the chuck shaft. Complexity: Medium

Solid Modeled Assembly

CAD Programs Used:

  • AutoCAD 2011
  • AutoCAD 2007
  • Solidworks 2010-2011


The sub-system of the Black and Decker Drill we decided to solid model was the gear system. We choose the gear assembly because it is a critical part of how the drill works. The electric motor of the drill produces a high RPM but at a very low torque so the gear reduction system lowers the RPM and increases the torque making it ideal for driving screws and drilling holes. As well as being a vital part of the drill, the gear assembly was also chosen due to its relative ease to construct as compared to other drill components (i.e. the field and armature of the motor). This was important in the decision making process because no group member had ever used a solid modeling program before. Because of this we decided it would be best to first draw 2D multi-view drawings of the individual components of the gear system in AutoCAD, a program we were already familiar with. From these drafts we used Solidworks to create the 3D models, through a process of extrusion and cutting. This allowed us to just create 3D models from our previously drawn 2D diagrams rather then have to learn to draw in Solidworks. Solidworks was also chosen as our solid modeling program because it is available to us for use here at University at Buffalo’s campus (1019 Furnas). The components we solid modeled include the armature shaft, the rear bearing plate, the gear and pinion, and the gear and front bearing plate, as these are the individual parts of the gear assembly. The 2D and 3D models of the chosen components of the gear system can be seen in Table 8.


Table 8 Modeled Components
Armature Gear Rear Bearing Plate Gear and Pinion Gear and Front Bearing Plate
2D Drawing of Component
Armature Shaft - 2D Drawing
Rear Bearing Plate - 2D Drawing
Gear and Pinion Assembly - 2D Drawing
Gear and Front Bearing Plate - 2D Drawing
Solid Modeled Component
Gear on Armature Shaft
Rear Bearing Plate
Gear and Pinion
Gear and Front Bearing Plate on Keyless Chuck


We then used Solidworks to combine these individual parts in assembly in sequence through a process of mating and shifting; these assemblies are shown in Table 9.
Table 9 Gear Assembly Process - Solid Modeled
Armature Shaft Merged With Rear Bearing Plate
Armature Shaft and Rear Bearing Plate Merged With the Gear and Pinion
Armature Shaft, Rear Bearing Plate, and Gear and Pinion Merged With Gear and Front Bearing Plate

Engineering Analysis

The gear system is responsible for transforming the electrical energy imported from the motor into the mechanical rotational energy of the bit. The series of gear reductions serve to decrease the velocity while increasing the torque. If the rotations per minute of the bit is not high enough, the power drill would not be a suitable or economic solution to a screw driver. On the contrary, if the velocity of the bit is too high, then the user would not be able to properly control the device and not enough torque would be generated. The drill works optimally when there is a particular balance between the rotational velocity of the bit and the amount of torque generated. Using a mathematical model, engineers can easily use equations relating rotations per minute and gear ratios to determine the most favorable balance between these design trade-offs. In the gear system we have modeled below, variables such as the gear ratios can be altered to determine the effect on the speed of the bit. Engineers can then perform small tests on the gear system to determine the optimal speed of the drill for different gear sizes or drilling materials.


Problem Statement:

Using the rotations per minute of the armature, determine the rotations per minute of the bit at the output, given that gear 2 and gear 3 have the same rpm. The rotations per minute of the armature is 1,350. The gear ratio between gears 1 and 2 is 9:41 and the gear ratio between gears 3 and 4 is 12:49.

Diagram:

Diagram for Engineering Analysis.PNG

Assumptions:

  • Friction is neglected
  • The armature rotates at a constant velocity
  • There is a perfect fit between the gears
  • The armature rpm is 1,350
  • Gear 1 rotates at the same speed as the armature
  • The gear ratio between gear 1 and 2 is 9:41 (This is a variable change that can be made in the design process)
  • The gear ratio between gear 3 and 4 is 12:49 (This is a variable change that can be made in the design process)
  • Gear 2 and gear 3 have the same rotations per minute
  • The bit and gear 4 have the same rotations per minute
  • An average user can rotate a screwdriver 30 times per minute
  • The drill bit does not slow down while drilling
  • The drill bit does not slip


Governing Equations:

(Teeth Driven)/(Teeth Driver) = Gear Ratio
RpmDriver/(Gear Ratio) = RpmDriven

Calculations:
For the transfer of speed between gears 1 and 2:

(Teeth Driven)/(Teeth Driver) = Gear Ratio
(41 teeth)/(9 teeth) = Gear Ratio (Gear 2:Gear 1)
4.556 = Gear Ratio
RpmDriver/(Gear Ratio) = RpmDriven
1,350 rpm/4.556 = 296.31 rpm

For the transfer of speed between gears 3 and 4:

(Teeth Driven)/(Teeth Driver) = Gear Ratio
(49 teeth)/(12 teeth) = Gear Ratio (Gear 4:Gear 3)
4.0833 = Gear Ratio
RpmDriver/(Gear Ratio) = RpmDriven
296.31 rpm/4.0833 = 72.57 rpm

Solution Check:

Our units of rotations per minute are appropriate for the output. There are no mathematical errors in our calculations. An output of 72.57 rotations per minute is a realistic output. This means that the bit would spin just over one time per second which is feasible.

Discussion:

The rotations per minute determined by the calculations is more than double the rotations per minute achieved using a screwdriver. This result makes sense because a power drill should turn faster than a human powered screwdriver. If the drill is used to screw a screw into a harder word wood such as maple, the force needed for penetration would be much greater. This would result in pushing the drill to its limits. It would then either slow down or stop completely causing our proposed analysis to break down. For drilling, friction is also a factor for almost any material. Therefore, for a more analysis, friction should not be neglected unless using softer materials such as balsa wood or drywall.

Design Revisions

While we were analyzing the components of the drill, we came across design revisions that could increase the efficiency and convenience of the drill and its components.

Similar Cordless Drill
Cordless Drill:
There are several aspects of the Black and Decker drill that can be modified to make it less expensive or more convenient for a homeowner. One component whose design can be modified is the cord on the drill. This can be replaced with a lithium ion battery which would make the drill cordless and therefore more convenient for the homeowner. The drill would look much like the power drill seen in the image to the right. A major global concern that influences the design of a product is the safety factor. A cordless drill would eliminate the risk of tripping over wires which greatly improves the safety of the drill. However, there are some problems with a cordless drill. An economic concern for a cordless drill is it becomes roughly 30 to 40 dollars more expensive, while still outputting the same amount of power as the corded drill. The societal feature that a cordless drill would give a homeowner outweighs the cost of the product. Some societal factors that come into play are that it can be used anywhere which makes it more convenient for the targeted consumers. Normally cordless drills output less power but for the intended use of this drill, this power loss would not be a concern.


Current Bit Holder
Magnetic Bit Holder:
Another design revision of the drill could be to replace the rubber bit holder shown in the image to the right with a magnetic bit holder. Economically, the cost of the magnets and the manufacturing would increase, but ultimately the cost of the replacement bits would still be greater than the cost of the revisions to the drill. With a magnetic bit holder, fewer drill bits will be lost. Also, time management would increase because the consumer would not need to locate commonly used drill bits. The bits needed would be right at the consumer's disposal. One downside of the magnetic bit holder would be that when disposing of the drill, it would have a negative impact on the environment. The magnets lose their magnetic field over time which would mean you would have to dispose of them, resulting in a piece of metal that would not decompose in the environment.


Broken Reverse Ring
Strengthen Reverse Ring:
We also propose changes to the design of the reversal ring that would increase its durability. We would add a steel ring to strengthen the reversal ring so it does not break into separate pieces as was the case in our particular drill. The current reversal ring is composed of a thin plastic which caused it to break into three pieces as evidenced in the picture to the right. The plastic would be still be manufactured by injection molding, but in this case it would be molded around the steel ring. As a result, the actual shape of the reversal ring would not have to be modified from its current form. A forging process would have to be added, however, to produce the steel ring reinforcement. By increasing the strength of the reverse ring, the DR202 would have a longer life expectancy. This would make the drill more appealing to the consumers. An economic concern would be the increase in cost due to the addition of a manufacturing step and a second material. The increased durability of the drill, however, would offset the minor increase in the cost by saving the consumer from the need to buy replacement parts. Black & Decker could even absorb the added cost of this revision. The consumer would see no rise in price of the drill and receive a higher end product.

References

“Black and Decker DR202 Type 2 Drill Parts.” eReplacementParts.com. 14 November 2010 <http://www.ereplacementparts.com/black-and-decker-dr202-type-drill-parts-c-4167_4168_4186.html>.

"Cutting." Learning Space. 18 December 2010 <http://openlearn.open.ac.uk/mod/resource/view.php?id=198390>.

“How Electric Motors Work.” How Stuff Works? A Discovery Company. 16 November 2010 <http://electronics.howstuffworks.com/motor4.htm>.

“How It's Made - Electrical Wire.” You-Tube. 15 November 2010 <http://www.youtube.com/watch?v=svgW0YYSSOA>.

"Injection Molding." Custompart. 18 December 2010 <http://www.custompartnet.com/wu/InjectionMolding>.

“Polystyrene.” Polystyrene. 13 November 2010 <http://pslc.ws/mactest/styrene.htm>.

“What is Gear Hobbing?” Wise Geek. 14 November 2010 <http://www.wisegeek.com/what-is-gear-hobbing.htm>.

"Wire Drawing Machine" BC. 18 December 2010 <http://www.blogcatalog.com/blogs/wire-drawing-machine>.

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