Group 26 - Craftsman 1/2 in Impact Wrench - Gate 4

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Contents

Purpose

This gate is all about the reassembly of the wrench back to its original state from craftsmen. We will be talking about the order in which each component is put back together and how the components are reassembled inside the wrenches plastic body. Also we will be talking about a specific mechanism that has a key role in the job of our impact wrench. Lastly we will come up with three different design revisions that could potentially improve our device through at least one of the four GSEE factors.

Project Management: Critical Project Review

Workload

Nearing the end of the semester and finals week just two weeks away, the workload is getting larger and larger for almost all of the group members, so this is has caused a need to be as efficient as possible when working on this gate. This means getting all of our group members together and splitting up the workload so no two or three group members are putting in a much larger workload than the rest of the group. For our last gate we ran into a serious issue with people not putting forth the work needed to split up the sections evenly. So for this gate we have ben forced to come up with a meeting minute that will be emailed out to all of the group members and an instructor to show what everyone is assigned and make it so there are no excuses for not getting the work done that is assigned to each member. We hope by doing this the group members that were not putting forth the necessary work in the beginning will be held accountable for their lack of work and/or lack of quality of work. So now by emailing everyone their assignment for the gate instead of just verbally going over what is expected from each member, as a group we can easily keep track of what is being asked and expected of each other.

Group Meetings and Group Management

With gate four we are met with a new obstacle in thanksgiving break. We had group members going home at all different times for break which made it hard to get a group meeting before everyone left for break. So because of this we agreed as a group we would just meet up as soon as possible once we were back on campus, and stay in contact over email during our break. Although it would make for our first group face to face meeting just five days before the gate was due it was the only option we had. As far as anything that has changed from the previous gate for group meeting and management; not much has changed in that we are holding two group meetings each week. Our problem is just getting our whole group to show up to these meetings to get our plan across and make sure we are all on the same page to complete the gate early so we can go over it at an office hour.



Reassembly Process

Product Archaeology and Reassembly

During the reassembly of our Craftsman ½” impact wrench our group used the same process as in gate 2 except in reverse. In the reassembly process, there were minimal challenges that existed as we started to piece the impact wrench back together. When the wrench was disassembled in gate 2, all internal parts such as screws, mechanisms, springs and gaskets were neatly categorized. Every part within a subsystem component was placed in label plastic zip lock bags. Although the impact wrench does not have an extensive parts list their were man screws that were identical in thread pitch but different in overall length. Having each subsystem component categorized helped the ease of assembly for our group. The reassembly process took place with all group members present. Each member had a specific tasks they were in charge of. This included photo documentation of all steps, providing assembly description/ complexity level, and uploading all graphs onto the wiki page. All group members were able to receive a hands on experience with assembling the impact wrench and see how each subsystem is connected together. This process gave everyone a greater knowledge of the mechanical component interactions involved within the tool.

Procedure

All subsystem component bags were categorized depending on which one was dissected out of the impact wrench first. It was agreed upon by all group members that the reassembly process started with the major system components with the most mechanical parts. The subsystems will be assembled in the following order:

  1. Rotational Assembly
  2. Impact Assembly
  3. Regulator System
  4. Trigger System

All of the tools needed to perform this task were gathered and organized. In order to start assembling the impact wrench the tools needed are listed below.

  1. Metric Allen key set
  2. 8T Torx head bit
  3. Screwdriver w/ 1/4” drive attachment
  4. 3/8” Socket drive wrench
  5. 1/2” Socket w/ 3/8” drive attachment
  6. Philips head screw driver
  7. Flathead screwdriver

The impact wrench also came with and exploded assembly diagram which was included with the purchase. This exploded diagram included and isometric view of how the impact wrench was assembled and a numerical list of all internal parts and part numbers. This list will be referenced to ensure the tool gets assembled properly and precisely.


Description of Difficulty for Assembly Processes
Level of Difficulty Requirements
1 The process requires minimal effort or force to complete and involves relatively simple components. No tools or devices other than bare hands were required in this step of the assembly. This process can be completed with in a matter of moments.
2 This part of the assembly process may require slightly more thought to complete and involve the interaction with complex moving parts. While no tools may be required for this step, how the process is executed is critical to the product's performance. This step can be completed in under half a minute.
3 This step of the assembly requires a at least one tool to complete and involves a slightly more thought. The components being assembled are complex and crucial to the products overall function. This phase takes greater than thirty seconds to complete.
Table of Assembly Procedures
Step # Process Description Tools Required Difficulty Level Visual Representation
1 Place the rotary wheel and the rear rotor end plate inside of the cylinder. A small dowel located on top of the cylinder slid into a small slot located on the rear plate. This ensures proper alignment of top dead center between both parts. Hand 1
Step1.2012.JPG
2 Once this is completed the rotor wheel, cylinder and backing plate should be stood upwards vertically on a flat surface. From a top view, the rotor slots have a larger clearance between the bottom cylinder walls than top. Each of the six rotor blades could be placed into the rotor wheel via this large clearance area. The rotary wheel was then spun to fit the remaining blades in. Hand 2
Step2.2012.JPG
3 After assembling all the rotor plates in each slot, place the rear back plate on top of the rotary cylinder. There is a dowel pin located on top of the cylinder where the plate is aligned. This ensures the plate is oriented top dead center between the rotor cylinder. Hand 1
Step3.2012.JPG
4 Set the rotor assembly inside of the impact wrench body orienting the assembly so that section with the dowel pin is on the upper side of the wrench body. Hand 2
Step4.2012.JPG
5 Place the hammer dog inside the widest of the three holes of the hammer cage. The tapered side should fit the hole perfectly and the cam slot should face out towards the opening. Hand 1
Step5.2012.JPG
6 Align the hammer cam so that the hole running through it aligns with the smallest hole on the hammer cage. the smaller end should fit into the cam slot went positioned this way. Hand 1
Step6.2012.JPG
7 Slide the hammer pin into the hole of the hammer cage and hammer cam. Hand 1
Step7.2012.JPG
8 Place the impact system on the rotary wheel splines. The splines should fit snuggly inside the hammer dog. Hand 1
Step8.2012.JPG
9 Insert the notched end of the anvil into the hammer cage making sure the bottom rest on the hammer dog. Hand 1
Step9.2012.JPG
10 Place the hammer casing with gasket over the hammer assembly making sure to line up the four holes in the casing with the four holes on the hammer body. Hand 1
Step10.2012.JPG
11 Set the regulator inside of the diversion cylinder located on the rear of the gun. Hand 2
Step11.2012.JPG
12 Place the rear end plate with gasket on the side off the wrench opposite of the hammer case. Hand 1
Step12.2012.JPG
13 Screw in the four bolts that run through the back plate, wrench body, and hammer casing. Torx Head Screwdriver 3
Step13.2012.JPG
14 Place the directional air switch on the shaft of the regulator. Align the switch so that it is in between the forward and reverse directions then screw a bolt in from the bottom to hold the switch on the regulator. Allen Wrench 3
Step14.2012.JPG
15 Place the trigger spring on the trigger assembly. Hand 1
Step15.2012.JPG
16 Place the trigger assembly in the wrench body in the slot right below the hammer casing. Hand 1
Step16.2012.JPG
17 Place the trigger pin in the hole adjacent to the trigger slot. Hand 2
Step17.2012.JPG
18 Place the throttle valve and spring in the bottom of the wrench handle in the slot thats towards the back of the drill. Hand 2
Step18.2012.JPG
19 Put the sound deflector balls in the slot at the bottom of the wrench handle that is towards the hammer casing. Hand 1
Step19.2012.JPG
20 Place the exhaust deflector at the base of the handle. Hand 1
Step20.2012.JPG
21 Screw the quick connect air fitting into the bottom of the handle. Ratchet 2
Step21.2012.JPG

Difficulty During the Assembly Process

During the reconstruction of our 1/2” impact wrench our group did not face any serious problems. Each step taken for the reassembly of each mechanical subsystem had minimal complexity. This is mainly because it only required a few tools to be taken apart and put back together. Most of the internal components were set into their desired locations by hand and lined up for proper orientation. The steps that required some finesse were assembling the rotator and impact assembly in the impact case. The rotary assembly had no hard ware required with installation. Each component sat in place was until it was installed. Our first difficulty was trying to figure out a way to install the six rotor blades into their required slots in the wheel. We first tried placing all the blades in the wheel assembly and then installing the cylinder over top to hold the unit in place. This did not work at first because the blades kept on falling out of their slot. Our next option was to set the rotary wheel into the rear backing plate so it can be supported vertical upwards on the work table. The rotary cylinder was then placed over top of the wheel making sure the dowel pin located on the top aligned with a slot on the rear plate matting surface. Now that the assembly was standing upwards the six rotor blades can be installed. From a top view, the rotor slots have a larger clearance between the bottom cylinder walls than top. Each of the six rotor blades can were placed into the rotor wheel via this large clearance area. The rotary wheel was should be spun to fit the remaining blades in any way. The front plate could now be place over top making sure the top dowel pin and slot aligned with the cylinder. The next hardship we face was installing this complete assembled unit into the impact wrench upper case. This was difficult because the assembly was not supported or held together by any hardware. Two hands where used to hold the rotary components together while another group member slid the impact case over top.

Assembly vs. Disassembly

The assembly and disassembly process were very much alike in gate 2 and 4. During the deconstruction of our product each subsystem was taken out from top to bottom, For example, the rotary assembly was disassembled first, following the impact regulator and trigger assembly, Each internal component associated with their subsystem was categorized in plastic bags to ensure all parts were kept together and not mismatched. Each step was documented with detail so we know every part was oriented together. The order of operation for assembly was the same from disassembly. An instruction booklet of the impact wrench was also used during re construction. This booklet included exploded parts views along with numerically categorized parts list. This was used as a reference to ensure the impact wrench was assembled properly and no parts were misplaced.

Mechanisms

The Craftsman ½” impact wrench contains a impact assembly system that generates and strong mechanical impact force to loosen and tighten hardware. This system is composed of a hammer cage, dog, cam, pin, anvil and case to perform its entitled function. It is to be noted that this system only uses mechanical rotational force to operate instead of pressurized gas. Therefore it converts potential rotational energy to a quick impulse force. As pressurized gas spins the rotary wheel connected to an anvil. When there is a load force on the gun, a hammer dog hits the anvil causing a very quick impulse force. This force translates through the anvil to the desired part to be loosened or tightened. this system only engages when there is a resulting force on the impact gun. If the gun is held in the air freely with no load, it will spin at a very high RPM. The impact system only works when a bolt needs to torqued down or taken off. This quick succession of force is prominent in removing stubborn hardware without breakage or failure. All parts contained within the impact system are simultaneously spinning from the spline connection between the rotator wheel. These parts are spinning at a very high RPM creating rotational energy due a moment of inertia from angular acceleration.

               Erotational=12Iω2
               Erotational:Energy due to Rotation
               I:The moment of inertia around axis of rotation
               w:Is the angular velocity

The moment inertia of the impact assembly describes where the mass is distributed depending on its axis of rotation. Moment of inertia is a measure of an objects resistance to changes in rotation direction. Moment of Inertia has the same relationship to angular acceleration as mass to linear acceleration. For a point mass the moment of inertia about a sphere is:

             I=12mr2
             m=mass ob obect (lb)
             r=radius of oject (in) 

The angular velocity of the rotator wheel is defined as the rate of change between angular displacement. This is a vector quantity which specifies the angular speed about an objects axis of rotation. The shaft direction of angular velocity is perpendicular to the plane rotation. it is represented in the following formula below:

              ω=θt=ω0+αt
              ω=angular velocity (rad/s)
              ωo=intial angular velocity at t=0 (rad/s)
              θ=angular displacment (in)
              α=angular acceleration (rad/s2)
              t=time (s)


Impulses are created when anvil meets resistance from a resulting load. This causes grooves on the anvil to line up the hammer dog, which is attached to the hammer cage via a pin. These grooves are rounded and the hammer dog is pinned connected and free to rotate slightly. As a result the grooves will unlock once the anvil is met with enough resistance allowing the hammer cage to spin freely again. Impulse is defined as the integral of force with respect to time. When a force is applied to a rigid body it subsequently changes its momentum. This can be described in the below equation.

Impulse=F∆t=m∆v=∆p
J=t1t2Fdt    since F=dpdtdt
J=t1t2dpdtdt=p1p2dp=∆p 
∆p=change in momentum from a specific time interval 



The Craftsman ½” impact wrench utilizes a rotational shaft with blades to convert pneumatic energy to rotational force. The force of compressed air has to be greater than the sum of forces required to move the shaft. Although the shaft rest on ball bearing contained in the cylinder, there are small frictional forces acting against the net-work output. The impact wrench is designed to operate at a specific air pressure and volume flow rate. These values for our ½ drive wrench are 90psi at 5.2CFM. The rotational or angular kinetic energy is the amount of energy due to rotation of an object. its quantity is a part of total kinetic energy . Kinetic energy of a rotating mass is proportional to the angular velocity and moment inertia this can be described in the following equation.

               Erotational=12Iω2
               Erotational:Energy due to Rotation
               I:The moment of inertia around axis of rotation
               w:Is the angular velocity

The moment inertia of the cylindrical rotator wheel describes how the mass is distributed about the object. Moment of inertia is a measure of an objects resistance to changes in rotation direction. Moment of Inertia has the same relationship to angular acceleration as mass to linear acceleration. For a point mass the moment of inertia about a sphere is:

       I=12mr2
       m=mass ob obect (lb)
       r=radius of oject (in) 

The angular velocity of the rotator wheel is defined as the rate of change between angular displacement. This is a vector quantity which specifies the angular speed about an objects axis of rotation. The shaft direction of angular velocity is perpendicular to the plane rotation. it is represented in the following formula below:

              ω=θt=ω0+αt	
              ω=angular velocity (rad/s)
              ωo=intial angular velocity at t=0 (rad/s)
              θ=angular displacment (in)
              α=angular acceleration (rad/s2)
              t=time (s)

In order for compressed air to spin rotator shaft it must overcome the forces resisting relative motion of solid surfaces and material elements sliding against them . The shaft is pressed into two ball bearing on either side to minimize the negative potential effect. Tool lubrication oil is also used to create a viscous fluid layer between relative moving parts. Lubrication is a technique employed to reduce wear on component surfaces When these surfaces contact each other during operation it converts the rotational energy into heat which robs product efficiency. This relationship is described below:

             ff≤μfn
             ff=frictional force
             μ=coefficient of friction 
             fn=m*g=normal force 


The dynamic air flow contained in the rotational assembly is described by Bernoulli’s equation. It states that an increase ion speed of the fluid occurs simultaneously with a decrease in pressure or potential energy. This equation is derived from the conservation of energy theorem which states in a steady flow process, sum of all forms of mechanical energy in the steam line is the same. Therefore the energy entering the system is equal to the energy exiting the system. Bernoulli’s equation below describes the flow air at any stream line point in the cylinder:

            v22+gz+pρ=constant
            v=fluid flow speed at any point
            g=acceleration due to gravity
            z=elevation at poin above reference plane
            p=pressure at that choosen point
            ρ= density of the  air at all points.

Design Revisions

Design revision 1-Two way trigger (butterfly trigger)

One system level feature that our group decided to modify is the impact wrench trigger system. The Craftsman 1/2” impact wrench operates off a one way directional trigger that controls the pressurized air flow source. In order to start operation of the tool, the user must firmly press and hold the trigger down. Once the trigger is released, tool operation is terminated. The current trigger system is composed of a trigger, valve, and throttle spring. The trigger sits in the impact case front mid-section resting on a small spring. When the trigger is engaged a vertical pin collides into the throttle valve. This impact forces the valve down allowing pressurized air to pass into the regulator chamber. Our group has decided to alter the current switch design to increase productivity and efficiency. The main goal of this redesign is to combine two system components together which will increase the controllability of the impact wrench during tool operation. Currently in order to change tool rotation direction, one hand must be free to twist the regulator direction switch clockwise or counter clockwise. We thought it would be an effective idea to control tool output direction via the trigger switch. This would be done using a two way directional switch similar to one on a hair dryer. This two way switch would toggle up or down allowing for a clockwise or counter clockwise tool rotation. The output magnitude force will be dependent on how hard the trigger pull is. Now the user can control tool engagement, rotation and direction using only his or her pointer and forefinger. There are a few internal components that would need alterations allowing for this simplistic function. The switch is to be mounted on a pin connection allowing it to oscillate up or down freely. The overall trigger length should be long enough so two fingers can fit comfortably on the mechanism. The switch will engage two directional valve solenoids placed behind the system. These solenoids would direct the air flow direction entering the rotational cylinder depending on trigger orientation. Some governing equations that would be considered during this design alteration are:

Pv=mRT (ideal gas law)
12*kx^2=kinetic spring energy
F=ma (equation of motion)
m=lim∆t→0 ∆m∆t= dmdt (mass flow rate)

The user can now control tool direction motion with two fingers while keeping both hands firmly on the impact wrench. This a social engineering factor since it simplifies the control complexity by combining two systems together. Another added benefit to this feature is an increased efficiency while working on a specific task. This trigger system allows a quick change of tool direction by cutting down on necessary time needed for repair jobs. This is considered an economical factor since it shortens the overall time of a repair job. For example if a mechanic using this new trigger systems had a decrease in repair time at an automotive shop due to this new system implantation then we have increased workforce efficiency. One disadvantage to this product is that it also requires a more complex system of solenoids and valves. Added expenses of parts along with engineering cost may drive the retail price up slightly. This economical factor would have to correlated between tool efficiency, desirability, and added manufacturing costs.

Design Revision 2-Power Control Regulator

The third system design revision to our ½” pneumatic impact wrench is to add a regulator control switch on the bottom handle. This dial would change the amount of airflow into the device when engaging the trigger. Currently there is no way to control the amount of air flow entering the tool. It is necessary to implement a regulator dial to control the impact wrench output force. Therefore the user can optimize the operating conditions and efficiency of the tool. The dial works by having a scale 1 to 4 with 1 being the lowest amount of airflow and 4 being the greatest amount of flow. At the scale of 1, only 25% of the air can flow into the impact wrench. At the scale of 2, the dialer allows 50% of the air flow into the impact wrench. Then, at the scale of 3, it allows 75% of the air flow into the impact wrench. Finally, the scale of 4 allows 100% of the air to flow in to the impact wrench. A small plastic circular plate can be installed at the handle of the impact wrench. The number of the scale will be carved on the plastic plate to show the amount of air flow the user intends to allow in. The small circular plate acts like a dialer. At scale 1, 75% of the plate will cover the input at the bottom of the impact wrench. At scale of 2, 50% of the plate will cover the input hole. At scale of 3, 25% of the plate will cover the input hole. At scale of 4, the plate can turn to the other side of the handle without blocking the input hole of the impact wrench. The user can now control the output force of the tool by regulating the incoming pressurized airflow. This new feature allows the gun to be used in a variety of situations where the maximum tensile strength of the working hardware cannot exceed a certain value. By limiting the output force reduces possible risks of failure when tightening or loosening hardware. This is a social factor in that it would broaden the lifestyle of the wrench because it could now be used for smaller jobs. The impact wrench is also marketed towards homeowners and automobile enthusiasts. This new feature allows the average consumer to use the impact wrench in a variety of different situations. The dial with the basic 1-4 scale is an example of a global factor because numbers are used throughout the whole world and anyone who would be buying one of these wrenches would easily understand the scale. As for the economical factor, this adjustment allows the user to save the cost of utility bill as this impact wrench able to adjust the usage of the air flow which mostly powered by a motor that uses electricity.

𝑃𝑣=𝑚𝑅𝑇 𝑖𝑑𝑒𝑎𝑙 𝑔𝑎𝑠 𝑙𝑎𝑤
𝑚=lim∆𝑡→0∆𝑚∆𝑡=𝑑𝑚𝑑𝑡 (𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒)
𝜏=𝑟×𝐹 (𝑡𝑜𝑟𝑞𝑢𝑒)

Design Revision 3-Carry-on tank for portable use of the pneumatic impact wrench

We realized that the need for an air compressor becomes a nuisance. First of all, air compressors are heavy whether they are portable air compressors or not. To increase the convenience of the customer, we thought of a solution to increase the portability of the impact wrench. The solution was to add a CO2 tank to the design. We decided that there will be a swivel quick-connect air fitting to connect the CO2 tank to the coiled air hose, then to the impact wrench through the tapered female threads on the bottom of the wrench. The CO2 tank will come with a quick-connect coiled air hose to fit into the quick-connect swivel. The coiled air hose allows the user to be able to maneuver through tight spaces and there will be no limit to where the user can use his or her impact wrench as a result of the portable CO2 tank. CO2 is a more efficient gas than air and nitrogen when compressed. This is because CO2 is a much denser gas under massive pressure. By changing the supply source, the impact wrench can be used away from any actual power source and at the same time be more efficient by using CO2 instead. The CO2 tank will increase the cost of the wrench by around 80 to 150 dollars depending on the size of the tank, but compared to an air compressor, it’s significantly cheaper. The impact wrench requires a source to flow 5.2 CFM of pressurized gas at a maximum of 90 PSI so the tank size must be compatible with those requirements. Filling up a CO2 tank is also cheap and available usually at fire extinguisher places, sporting stores, industrial gas companies, etc. This design results in societal, economic and environmental impacts. A societal impact is the increase in convenience for the user due to the impact wrench’s increase in portability but at the same time, the user will have to carry with him the CO2 tank. Economically, the impact wrench will be cheaper as a result of buying a CO2 tank instead of an air compressor. An environmental concern is that CO2 is harmful to the environment unlike compressed air.