Gate 3 (group 8)

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Contents

COMPONENT SUMMARY

Part Name Description Manufacturing Reason for Shape Reason for Using Materials Forces Applied Functional/Cosmetic Quantity Complexity Picture of Part
Armature Assembly The motor and its components consisting of the Armature and a copper coil around the armature shaft the armature was made by milling and turning due to the precision need for the

armature shaft to fit in the field casing and rotate freely without any friction.

The copper coil is made by shaping and wound around the armature shaft.

The armature is cylindrical so that it can rotate freely and be place with ease into the field casing. Steel was used because it is a tough and strong alloy and can withstand the torque

provided by the field assembly. Copper is used for the wiring because of the low resistance and to maximize the cost effectiveness.

armature assembly is subject to torque provided by the field assembly. This part is purely functional as it is very important to move the blade. 1 4
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Field Assembly Components providing power for the motor to rotate and consists of a stationary coil housing and stationary coil The housing is machined for maximizing cost and time efficiency and the coil is shaped to fit inside the housing. The housing is fairly cubical in shape which has a cylindrical hole in its center to properly house the armature and deliver a magnetic field. Steel is used to steadily hold the coil in place and copper is used because of its efficiency in conducting electricity. none This part is purely functional as it houses the armature as well and provides power to the blade. 1 4
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Switch Assembly Switch for controlling the power in the circuit The switch housing is made by plastic injection molding and the copper wire is shaped drawn into a thin wire. the switch assembly is cubical to snugly fit into the casing to hold it steady and not move around. the switch assembly is cubical to snugly fit into the casing to hold it steady and not move around. none This part is functional as it completes or breaks the circuit to operate the jigsaw 1 2
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Clamshell set Used as a housing for the components of the jigsaw The Housing is made using plastic injection molding. The plastic is molded in such a way that the user feels comfortable handling and operating the jigsaw. Plastic is used because its easy to mold and also easy to create spots to fit components in The user applies force on the handle to keep the jigsaw in place and to guide it. This part is functional and cosmetic as it bears the name plate and company logo and houses most of the components. 2 1
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Brush and spring Used to transmit power to motor The Brush was made using molding and the spring was made by drawing copper into the shape of a spring The brushes are semi circular rings to effectively allow the armature to move between them. carbon is used because it can conduct electricity in its most famous allotrope, graphite which is a very efficient conductor of electricity. The springs apply force to hold the brushes in place. This part is purely functional as it powers the armature as well

Materials: Carbon(graphite) and copper

2 3
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Brush box Used to hold the Brush and spring together Plastic injection molding is used none Plastic is used to provide a cheap and efficient way to hold the brush and spring. the spring applies forces on both the brush and the brush box. Purely functional as it holds the brush and spring. 2 1
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Thrust plate Used as a washer between the counter weight and the armature assembly Metal casting is used to make the plate and the holes were made by drilling. The plate is rectangular to mirror the front piece of the armature assembly which holds the counter weight. Steel is used because it would make the plate sturdy. various forces from the parts onto the plate. functional as it acts as a washer. 1 2
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counterweight Used to hold the armature assembly in place Metal casting is used to make the plate and the holes were made by drilling. The plate is rectangular to easily hold the components and hold them in place Steel is used because it would make the plate sturdy to hold up all the parts various forces from the parts onto the plate functional as it holds the main parts in place 1 2
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Gear Assembly Used to deliver power from the motor to the blade. Milling is used to manufacture the gears. The standard gear shape is used. steel is used to efficiently deliver power to the blade. torque is applied on the gear which further applies torque to the blade. Functional as it delivers power to the blade. 1 3
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Actuator Locking gear. injection molding is used. be easily rotated by the user as a locking mechanism plastic is used as an inexpensive way to control the mechanism of the jigsaw since steel is not really required. torque applied to operate locking mechanism Cosmetic as it provides the user with more control over the jigsaw 2 3
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Shoe Assembly A plate for the user to push down on to keep the tool in place Metal casting is used and drilling to make holes on the plate for screws The plate is rectangular to evenly spread the force on the cutting surface Steel is used for it can withstand a huge amount of force from the user Downward force applied by the user. Functional as it balances the saw and keep it in place 1 2
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Blade support A support for the blade. Metal casting was used The shape is that of a small beam to accommodate the thin dimensions of the blade Steel was used as it provides a sturdy support for the blade The support provides a force to holds the blade to keep it steady cosmetic as it helps other components to keep the saw blade in place. 1 2
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Locking screw used to hold the shoe plate in place Thread rolling is used to manufacture this component none Steel is the most common material to use for screws and is a good sturdy metal. Force used to hold the plate in place and is usually opposite to gravity functional as holds the shoe plate in place 1 2
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Guard A safety feature for the blade Plastic injection molding was used to make this component The Guard is made in a semicircular shape to surround the blade so that it wont cut any of the user’s digits. Plastic is used because it serves as a good guard none component is cosmetic due to the importance of safety in its function 1 1
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Button lock The button to lock the desired speed of the blade Plastic injection molding was used none was used because it is a common material for switches the user pushes the button This part is purely cosmetic as it is a handy feature for the user to extend his control 1 2
Blade clamp Used for clamping the blade in place plastic injection molding None plastic is used The clamp locks the blade in place This part is purely functional 1 2
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Screw Used for the fastener shaft assembly Thread rolling is used none Steel is a good material for product integrity none This part is purely functional as it holds the shaft assembly together 1 2
Bearing, sleeve A cylindrical support and also allows vertical movement of the blade. metal casting was used and machining for the hole cylindrical shape so that the shaft assembly fits snugly into the bearing steel is a good metal for structural integrity none This part is functional because it supports the shaft assembly 1 3
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Cord protector The cord protector acts as insulation Flexible plastic molding is used The shape is slightly conical to fit snugly onto the tool The PVC used is flexible to allow free movement of the wire and the tool None this part is functional 1 1
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Power cord power cord delivers power to the tool from the power outlet The insulation is manufactured by flexible plastic molding and the copper wires are drawn. The cord is long and flexible to allow free movement of the tool PVC in insulation is used because it’s the most common various forces will be applied if the tool is close the wire will contract and if the tool is far the tension will stretch the cord this part is functional 1 1
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Lead assembly, lead wire assembly and lead wires used to transport power around the internal circuit Flexible plastic molding is used for the PVC and the copper is drawn into thin wires The wires are flexible to allow the wires to blend in with the internal circuit and not require extra space PVC is used for insulation and copper is used because of the efficiency in conducting electricity none the wires are functional because they transfer power within the circuit 4 1
screws Used to hold various components together which include the casing and the switch component. Thread rolling is used standard shape is used steel provides good structural integrity none Functional as they hold the tool casing together 7 2
Group8gate2p19.JPG


DESIGN REVISIONS

The Black and Decker Jig Saw is a well designed product for small to medium duty usage. But we felt that certain changes could improve its productivity and ergonomics.

• Instead of a handle that has gel padding for grip we can eliminate the pads and use a rubber surface coating that will provide a better and more comfortable grip, resulting in more accuracy in use of the tool.

• The plastic guard in the front that covers the blade can be removed and the base plate could be curved upward. This would help in covering the blade as well as clearing the accumulating dust. It is ergonomically better as well as cutting down production cost.

• Adding a laser light would help the user designate his or her cutting path would greatly help in cutting accuracy

• It would also be ergonomically sound to use lighter materials for the body and parts.


o To improve the performance of the jig saw we could use a slightly larger armature for a little more torque.

o Also a longer shaft and longer blade with narrower teeth would be suggested.

o The jig saw is neat for small jobs but if we improve the motor we could get more power out of it and cut tougher surfaces.

o The reduction of weight could help in making the device more accurate and this could be done by reducing motor weight.

o The trigger could be made to be locked at various different levels to provide different power to the blade.

o Another addition to the device would be an emergency kill-switch that goes off when the device slips from hand.


• The power cord of the device can be attached to a reel so that it can be folded and stored easily and maybe have a little more length added to the wire.

• Excess use of lubrication and grease for the internal part is not necessary and cutting down on these can help in manufacturing and maintenance.

• Different size screws with similar threads could be standardized to a single size screw and this would help in reducing cost of production.

• There were a lot of internal wirings that were unnecessary long. These wires could be shortened so that the assembly of the product is faster. Also, this could cut down production cost.

• The outer body could be attached at some point, instead of two separate pieces, with a hinge mechanism that would help in faster reassembly of components and better fit.

• The internal parts have many holes and drillings that have no apparent purpose. Reducing these would significantly help in lowering manufacturing costs.

SOLID MODELED ASSEMBLY

We chose to 3-D model it in Pro Engineer because we felt that it would be the most convenient way to model the components as everyone in the group was familiar with the program. Modeling this assembly was quite complex as we selected the most important and complex components which included the armature assembly along with the copper wiring, the thrust plate, the counterweight and the gear assembly.

The Armature assembly, the gear and the thrust plate were the parts chosen to model in 3d. The armature was chosen because it is one of the most important parts of the motor. The armature shaft is inserted into the stator and connected to carbon brushes to provide maximum power for the blade. The best possible dimensions were obtained and a few assumptions were made to simulate the actual components itself in the 3-D model. The dimensions of the component were slightly difficult to obtain at some areas of the component for example the armature assembly. Therefore a few assumptions were made to compliment the obtainable dimensions. While trying to maintain as much accuracy and precision as possible modeling the components, we still encountered problems while assembling the parts. We further made assumptions to obtain symmetry and correct the errors in the main assembly where all the components are put together. 3-D Modeling these parts would have been a lot easier if we had the dimensions of the armature assembly. The rest of the dimensions were easily obtainable.


Group8gate2cad1.jpg

3D Model 1- The Armature assembly


The Armature is a fairly complex part as it has three manufacturing processes involved in making it namely; milling, turning and drawing.


Group8gate2cad2.jpg

3D Model 2- The thrust plate

The thrust plate provides an alternative for a washer between the counterweight and the armature assembly. It has a rectangular shape to

keep the counterweight edges from interfering with the edges of the front piece of the armature.


Group8gate2cad3.jpg

3D Model 3- The counterweight

The counterweight is the component that helps the thrust plate to hold the armature assembly in place and connects it to the gear assembly.

The part does not have any functional role but it is indispensible as it keeps the motor from moving around in the casing.


Group8gate2cad4.jpg

3D Model 4- The gear assembly


The gear assembly modeled is attached to the armature to transfer the power form the armature assembly to the blade.

The gear is made using the standard milling process and also serves as an important bridge of power between the armature and the blade.

Group8gate2cad5.jpg


3D Model 5- Exploded view

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3D Model 6- Assembly view 1


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3D Model 7- Assembly view 2

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3D Model 8- Complete assembly view

ENGINEERING ANALYSIS

Introduction

Group number 8 was given the task of analyzing a Black and Decker Jigsaw. One important function of the Jigsaw is for small projects where precision is needed. For example: if a person is making furniture and needs a tool to carve shapes and designs into that piece, then the Jigsaw would be a very good tool for such a project. Problems can arise from improper use of the Jigsaw, where a person trying to use the Jigsaw to shape pieces of wood that are too big or the blade of the Jigsaw coming into contact with an object such as a nail. In the case of the blade coming in contact with a nail, buckling can occur which would then cause the blade to break resulting in a broken Jigsaw or worse injury. In the initial stages of the design process of a Jigsaw, the manufacturer should do extensive testing of the blade to insure such problems never arise when customers use their product. Group number 8 will focus on a buckling problem in which the Jigsaw blade will come into contact with a nail which might cause the blade to break.

Problem Statement

To calculate the stress on the Jigsaw blade that will cause it to break in the event of the blade coming into contact with a nail.

Figure of System

Group8gate2en1.jpg

Engineering analysis 1- the diagram on the left shows a beam without any force acting on it.

The diagram on the right shows the system acted upon by a force

causing it to buckle. This beam will represent the Jigsaw blade under buckling.

Assumptions

1. The force exerted from the nail onto the Jigsaw blade is axial, that is, it acts on the axis of the blade.

2. Both ends of the blade would be fixed, that is, there is no movement of the blade or the nail.

3. The blade used is stainless steel.

4. Assume length of blade to be 10.16cm and width to be 1.5cm

5. Yield strength of steel to be 200MPa

Governing Equations

Group8gate2eq1.jpgEquation 1

Group8gate2eq2.jpgEquation 2

Group8gate2eq3.jpgEquation 3

Calculations

E=1.9^5 MPa

K=0.5

L= 10.16cm

I=(0.01s*(0.1)^2)/12= 1.25 * 10^-6m^4

F= ((3.142)^2*(1.9)^11*(1.25)^-6)/(.5*.1)^2


stress= F/A = (9.4*10^8/ (.1*.015)) = 6.25^11 Pa

Yield Strength =200Mpa= 2.0*10^8 Pa

Solution Check

Dimension analysis was conducted on all three of the equations and the units cancelled as required. The force required to cause the calculated stress is very large,

so large that it would be impossible for the average person to exert. This value is not reasonable solely because the value of the moment inertia (I) is too large, or the value of the area of the blade (A), is too small.

Discussion of Results

The forces exerted on the Jigsaw are axial, that is, the force acts along the axis of the Jigsaw. If other forces were acting at different points along the blade then the problem would not just be a buckling problem. Torsion would then have to be considered making the problem very complicated. The blade support helps to keep the blade from bending in such a way to produce torsion so it is okay to say that the only force that acts on the Jigsaw is an axial force.

Stainless steel was the material used for the blade of the Jigsaw because it is very strong and hard. An aluminum blade might be considered too soft and would have smaller yield strength. The greater the yield strength, the less likely a material will break so a company should aim for materials with higher yield strength.

Comparing the stress calculated to the yield strength of the blade, it is clear that the calculated stress exerted on the blade will cause it to break because it has gone past the yield value. This value calculated is quite large and an average person would not be able to apply such a large force. Even though the blade might not break, persons should still use appliances with caution to prevent injury.