Group 26 - Craftsman 1/2 in Impact Wrench - Gate 3
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*Front/rear cylinder end plates
*Front/rear cylinder end plates
Revision as of 00:12, 16 November 2012
Project Management Review
As a dissect engineering group, we have been having very serious problems with group members not contributing to their given work load. This forces resulting group members to take on a tremendous work load with analyzing the product and formatting the wiki-page. This is a problem our group is trying to find a solution for. Multiple discussions have been made with the professors to resolve our situation at hand to make our group work as dynamic and efficient as possible.
Cause for corrective action
As a group our biggest problem is trying to fix and resolve issues pertaining to work load contribution. A couple of members in the group are refusing to do work and don’t seem to be interested or willing put in the allotted time to complete each gate section. In order to try and change this we have been gradually warning that we will not tolerate their lack of effort. Since they have not responded to our warnings and continue to put forth almost zero effort into this project, a minute proposal will be created at each meeting. This minute meeting plan will include the group members present, issues talked about, and responsibilities of each member until the next meeting. We will then turn this list into the professors so it is very clear as to what work is expected from them and how it is not being done. As far as the work that is and has been done for the gates we ran into some trouble not getting all of the details that we needed to be getting out of the assignment. At first we took each assignment straightforward outline for what is expected for each gate. We have now realized that we need to break down each part more in depth and include more details that may not be on the assignment sheet. This is going to be extremely important in the forthcoming gate in order for our group to receive quality grades.
Group Meetings and Management
With the continuing problem of a couple of members not willing to put in work on these gates, we have had to make some changes in the way we communicate and schedule group meetings. We have had to start sending out emails in order to create official documents that we can show the professors to get members present and projects meetings. This has put added stress on the group members that are willing to put forth hard work pertaining to each gate. Ultimately increasing the amount of time that each person needs to put into every section. For the members that are constantly communicating and willing to put forth the effort, no problems with meeting up and figuring out the work to be completed within a specific timeline. Another change that we are making in order to improve our performance on the gates is to completed the gate a week prior to the turn in date. This allows us to meet with a TA of Professor to review and problems that are evident in the gate.
In gate 3, a component summary is created below of each part contained within the Craftsman ½” Impact wrench. This table includes the part function, material used, manufacturing processes implemented, model number and dimensions. This analysis process made our group closely examine the subsystem level complexity of each part. The impact wrench is a pneumatic power tool that converts pressurized gas to a rotational impulse force. To do this function each part mechanically interacts with one another to create a resulting action. It is essential also to remember the conservation of energy principle though the analysis process.
𝐸𝑖𝑛𝑝𝑢𝑡 𝑒𝑛𝑒𝑟𝑔𝑦−𝐸𝑜𝑢𝑡𝑝𝑢𝑡 𝑒𝑛𝑒𝑟𝑔𝑦=∆𝐸𝑠𝑦𝑠𝑡𝑒𝑚.
This equations states how the energy consumed by a an object is equal to the energy or work expelled. Therefore energy can’t be created or destroyed, only transformed. In our impact wrench the conservation of energy equation is modeled.
𝐹𝑜𝑟𝑐𝑒 𝑎𝑖𝑟 𝑝𝑠𝑖+ 𝑊𝑜𝑟𝑘 𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑜𝑟−𝑇𝑜𝑟𝑞𝑢𝑒𝑜𝑢𝑡𝑝𝑢𝑡−𝐼𝑚𝑝𝑢𝑙𝑠𝑒𝑜𝑢𝑡𝑝𝑢𝑡−𝑄ℎ𝑒𝑎𝑡 𝑒𝑥𝑝𝑒𝑙𝑙𝑒𝑑=∆𝐸𝑠𝑦𝑠𝑡𝑒𝑚
To define a practical measure of complexity for a part, the component's shape, function, and material composition must be taken into account. Multiple indentations as well as asymmetrical structure are typically strong indicators the original stock material had to be greatly modified to achieve the desired shape of the component. How a part connects and functions with the other components in a system is also a factor of complexity because more functions and connections involved with a certain component usually call more accuracy with the dimensions of the part thus making the manufacturing process more elaborate.
- Function is limited to fastening, securing, or housing other components
- Simple manufacturing process; i.e. few indentations or cuts, simple finished
- Non-complex figure which can be described by a few geometric forms
- Function may involve housing moving parts or regulating energy flow
- Semi-complex manufacturing that requires few incisions or steps; i.e. castings, lathe
- Form is a simple form with some gaps, indentations, or other modifications
- Has two or more functions involved with the transfer or regulation of force
- Was made using multiple manufacturing processes and has a finished surface
- Has many complex and elaborate indentations and grooves that would call for a significant amount of dimensional accuracy
Table of Components
|Component Function||Material Composition||Manufacturing Processes Implemented||Dimensions (inches)||Complexity Rank||Part #||Visual Representation|
|External case- holds together all of the internal components of the impact wrench. Must be strong enough to endure the physical interactions and internal forces of parts reacting with each other during operation.||Light weight Composite plastic||The impact wrench case was made through a plastic injection molding process. There is an evident seam line along the outside rim from where the two molds met. Extrusion marks were also found on the bottom and top edges. The inside was milled after production to ensure perfect fitment of internal components.||7.0X2.5X2.6||2||F19982-01N|
|Hammer case-contains the impact system of the wrench which include the hammer cage, dog, pin and anvil. These parts interact with a high amount of kinetic energy and force. The encasement is very thick to ensure these parts do not fail. The matting surface was horizontally milled so a rubber gasket could be placed in between. This acts as a barrier to keep tool oil in and dirt out.||Stainless steel||The hammer cage was assumed to be produced by a metal forging process. The outside was then polished for aesthetic purposes. The inside was milled to ensure close tolerance where achieved. The screw holes were drilled and threaded.||2.8X2.6X2.4||2||FS2147R-47|
|Rear case end plate- encloses the rotational assembled of the impact gun by four long screws . This plate also contains the regulator switch and direction valve. A rubber gasket is used between the matting surface to keep tool oil in and dirt/water out during use.||Lightweight composite plastic||The rear case end-plate was made by an injection molding process. This was concluded from mold seam lines along the matting surface. The composite plastic part was then drilled so four screw could be placed to hold the entire unit together.||3.6X2.5X0.7||3||FS2147R-22|
|Hammer cage- is a part of the impact system which contains the hammer dog, cam, pin and anvil. When this system Is loaded, it converts rotational energy to a quick succession of impact force. This cage has to be strong enough to endure such energy and force during operation.||High strength carbon steel||The hammer cage is thick in nature and has a textured finish. It was made from a metal forging process. The part was then drilled and reamed to fit the hammer pin and anvil through the center body.||2.0X2.0||2||312-248-19B|
|Hammer Cam-converts rotational energy to an impulse force when external loaded during operation. The cam is held in the hammer cage through a pin and rests on the anvil. This part is strong enough to endure a rapid succession of impulses between itself and the rotating anvil.||High strength carbon steel||The hammer cam is assumed to produce from a milling process due to its evident smooth and sharp surface finishes and edges. The part was then drilled out to fit a hammer pin holding it inside the hammer cage while rotating.||2.1X1.0X0.8||2||9287163|
|Hammer dog- is contained within the hammer cage. This part is held in place by the anvil. The hammer dog causes the anvil and cam to lock and release 1 impulse per revolution. The grooved slot on the outside allows this action to happen against the anvil while rotating.||High strength carbon steel||The hammer dog was produced by horizontal lathe that turned the part on one axis while removing excess metal to achieve proper dimensions. The impact slot was presumed to be milled out since a lathe cannot achieve this multi-axial cut. This part may also receive thermal heat treatment to ensure optimum micro structure.||1.3X0.6||2||9287162|
|Hammer pin- is a vital component that holds the hammer in the external cage. This part experiences very strong internal forces between the cam, dog and anvil. This is a vital component that keeps all parts in place while operating.||High strength carbon steel||The hammer pin is made from a common metal rolling process. The steel ingots are heated to a malleable state passed between grooved rolls to reduce in size. The metals dowels are then cut to a specified length. This part may also receive thermal heat treatment to ensure necessary strength and optimum hardness.||2.0X0.1||2||312-248-20B|
|Anvil-is a key component of the impact wrench. This part excerpts both rotational energy and impulse force to tighten and loosen hardware. The anvil is where impact desired size sockets and torque extensions are connected to.||High strength carbon steel||In order to achieve this unique shape the anvil was milled on a horizontal lathe. The cam edge and square socket attachment points were then CNC milled.||3.8X0.8||3||9287159|
|Rear rotatory end plate- holds the rotatory wheels and blades in place during operation. This plate contains a pressed in ball bearing where the rotational wheel seats and spins freely. Creates an air tight seal in the rotating cylinder.||Aluminum||The rear rotatory plate was spun on a vertical lathe. The part was then cut to size. There are groves on the inside surface edge that were vertically milled to allow airflow between rotatory blades.||2.1X0.2||3||9287172|
|Rotational wheel- is a key component that converts pressurized air to rotational energy. The wheels has six slots that hold the rotatory blades. A sprocket end connects the wheel to impact cage. This transmits rotational energy from the wheel to impact cage system||Steel||The rotatory wheel was manufactured from a horizontal lathe. This method turns and cuts the object on a single axis. The six blade slots and connection spline where CNC milled after to achieve a multi-axial dimension cut.||2.3X1.5||3||9287168|
|Rotor blades- are housed in the rotatory wheel slots. These blades move in and out because the wheel is of centered in rotatory cylinder. This movement achieves a constant seal between blade ends and cylinder walls. Air passes between blades to convert pressurized gas to kinetic energy.||Composite polycarbonate plastic||These six rotatory blades area CNC milled from a composite polycarbonate plastic||0.1X1.3X0.5||2||9287169|
|Rotatory cylinder- contains the rotatory wheel and blades. This is chamber is pressurized with air that spins the blades and wheel. Air enters from an intake port and exits through an exhaust port located on the bottom cylinder wall.||Aluminum||The rotatory cylinder is made from a casting process. This was assumed from evident seam marks on the outside edges and textured finish. The internal cylinder walls were finish cut from a lathe to produce a very smooth surface. The intake/exhaust ports were vertically drilled out.||2.1X1.3||2||9287176|
|Front rotatory end plate- holds the rotator wheels and blades in place during operation. This plate contains a pressed in ball bearing where the rotational wheel seats and spins freely. Creates an air tight seal in the rotating cylinder.||Aluminum||The rear rotatory plate was spun on a vertical lathe. The part was then cut to size. There are groves on the inside surface edge that were vertically milled to allow airflow between rotatory blades.||2.1X0.5||3||9287166|
|Trigger/spring/pin- the trigger allows user to engage/disengage tool. When a force is applied to the trigger the throttle valve is opened allowing air charge the regulator system. The spring returns trigger to original position when finger is removed. Trigger pin keeps trigger in place.||Trigger-plastic
|Directional valve- controls the direction of air flow into the rotator cylinder. This enables the wheel to spin clockwise or counter clockwise depending on user input.||Aluminum||This part was produced from a horizontal lathe which achieved in circular figure. There are slotted flat groves that were milled into the part after being turned.||2.0X0.5||3||9106136|
|Regulator switch- enables user to turn the directional valve left or right to tighten/loosen hardware. The switch slides over a grooved slot on the valve and is held in place by a small set screw.||Plastic||The regulator switch was manufactured from an injection molding process. This was determined from evident seam marks and extrusion points on backside.||1.5X0.8X0.5||1||9106133|
|Throttle valve- controls the air flow into the regulator system. When the trigger switch is engaged the throttle valve is pushed down allowing pressurized air to charge the impact gun and start operation.||Brushed Steel||This small part was die cast manufactured||0.1X0.3X0.5||2||9287185|
|Throttle spring-exerts a kinetic force on the throttle spring to ensure it is closed when trigger is released. This also keeps the valve closed when impact gun is connected to an air source but not in use.||Spring Steel||The throttle spring is made from a cold rolled from a spring winding machine. A central navigation computed is used to roll the spring to a correct ‘k’ constant for mass production||2.8X0.5||1||9287186|
In gate 3 seven parts are analyzed to determine Craftsman’s engineering decisions made while designing each component. In the Impact wrench, all internal force reactions between parts are pneumatic or mechanical. The tool has no electric circuitry such as batteries, resistors, or capacitors. Only the power source supplying pressurized air runs off an electric pump and power source. This will not be considered for further analysis. The impact wrench has eight essential components that are required to convert pneumatic flow energy into a rotational impulse force.
- Impact Wrench body
- Rotational Cylinder
- Front/Rear rotational end plates
- Rotational Wheel/ Blades
- Hammer Cage
- Hammer Dog / Cam / Pin
- Regulator Switch
Impact Wrench Body
The Impact wrench body holds most of the internal tool parts together. It is the main body where pneumatic energy is converted into rotational force. The trigger, rotational and regulator systems are housed inside this part which all have dynamic flows associated with each other in a specific order. The flows associated with this component are listed below.
- User input
- Magnitude of Force/Direction
- Desired TQ output
- Compressed Air
- Exhaust Air
User input, force direction, desired TQ output, and compressed air are flows input into the impact wrench body. The flows output from the systems are torque, rotation, impulse and exhaust air.
The Impact wrench body has a unique shape to contain each mechanical and pneumatic system. It is a three dimensional part that is symmetric about the y-axis. The bottom torso is where compressed air enters and exits. A quick connect air fitting screw s into the bottom to supply pressurized air. This also serves as a handle for the user to grip firmly during operation. The handle has a concave curve that fits nicely in your palm with three front finder contours for comfortable use. Grip marks are indent into the rear part so the tool doesn’t slip out your hand in different working environment conditions. A textured finish also increases controllability of the tool as well. The trigger system is contained in the mid body section. There is a whole drilled out from the trigger indentation to the bottom where air is charged to the throttle valve. The regulator valve lies in the rear mid-section. An aluminum cylinder valve is pressed into the impact wrench body with air ports. These small reamed ports direct pressurized air into the rotation cylinder allowing for a clockwise or counterclockwise rotation. In the upper portion lies the rotational system where air enters, and is converted to rotational energy by spinning the rotator wheel and blades. It is mostly hollow and circular in nature. Four bolt holes go through this entire section to hold the rear back plate and front hammer case together.
The Impact wrench body is made out of a hard composite plastic that is light weight. Total weight was documented at 1.2lbs. Since this model is a part of the Craftsman homeowner line, economic factors contributed to this decision. Plastic is generally cheaper to manufacture parts from, keeping the production cost very low. Although plastic may be cheap it is not biodegradable. If the tool is disposed of properly it will have minimal hazardous effect to the environment. Plastic is less rigid than metal therefore it can absorb shock more effectively. Engineers may have choose a plastic frame to translate less vibration from the body to handle making tool operation more comfortable. The impact wrench body color is black with red accents on the handle. It makes the gun aesthetically pleasing to consumers. This can be considered a social design factor associated with marketing the product for greater sales. A warning sticker is located on the tool. It states “WARNING wear approved eye protection, use only impact/sockets/accessories, 90psi psig maximum air pressure, hearing protection recommended, avoid prolonged exposure to vibration, read operating instructions”. This sticker was used by Craftsman to show society that there are precautions to consider before tool operation. The Impact body is also outfitted with a trademark Craftsman logo. This is a global factor to show consumers the product is manufactured by a quality company.
Length- 3.5 in Width- 1 in Height- 2 in
Main upper body:
Length- 2.75 in Width- 2.5 in Height- 3.25 in Outer thickness- .35 in
Complexity of interactions-
The plastic impact wrench body was assumed to be manufactured through injection molding. In this process, plastic is heated to a pliable liquefied state and injected into a reusable metal mold. Once the plastic is cooled, it’s ejected from the mold ready for the next stage. This process uses two different colors of plastic and infuses them together in the mold to make the black handle with red accents. There are evident mold seam lines along the axis of symmetry where the two molds meet. Ejection indents also exist where the plastic body was extracted once fully cooled down. The plastic handle was then drilled out to create the four crew holes, trigger armature and air supply, exhaust, air way. A tap dye was used to create the female thread pattern on the bottom handle. The regulator port system was pressed into the handle to ensure a tight fit. Lastly the Craftsman logo’s and warning sticker where adhered to the handle after production.
The rotational cylinder contains the rotator wheel and blades. This part is responsible for converting pneumatic energy to rotational force which drives the next system. When assembled the rotator wheel sits off center in the y-axis compared to the cylinder. There is a closer gad on top than on bottom . This allows for the blades to drop down and touch the bottom cylinder walls. There are 2 port holes on the inside bottom cylinder walls Air is forced through one of the 2 holes determined by the forward/reverse control button/valve direction. Air passes through a hole in the mechanism to the rear plate. The rear plate then channels the air into the rotator cylinder where it comes in contact with the rotor blades. The blades sit loosely in the rotor. Gravity causes at least 1 of the 6 blades to extend out of the rotor that catches the airflow. This begins to turn the rotor. Centrifugal force moves the rest of the blades partially out of the rotor where they glide along the inside cylinder. The flows associated with the rotational cylinder are:
- Pneumatic force energy
- Frictional force
- Rotational force
- Exhaust air
Pneumatic force energy describes the pressurized air input into the cylinder. This gets converted to frictional and rotational force while expending air in the process.
The rotational cylinder is circular in nature. It is a three dimensional part that is symmetric about the y-axis. The inner chamber is slightly off set from the outer. Therefore it has a smaller thickness bottom wall than upper. Two metal dowel pins are pressed in on the front and rear top faces. These pins hold the front/ rear endplates in correct alignment. Two port holes are reamed through both upper side walls on either side. These holes all air to pass between end plates into the rotator cylinder. On the bottom cylinder walls exists another two reamed ports. These transmit air into the cylinder depending on the FORWARD/REVERSE CONTROL BUTTON/VALVE direction. The inner cylinder walls and ports have a very smooth finish compared to the outside. This polished surface finish reduces the effects of air turbulence and friction from where the blade edge meets the wall. A smaller coefficient of friction increases tool efficiency output along with total lifespan. This is an economical factor that was evident during the engineering process to prolong tool productivity.
The impact wrench operates at 7400RPM free speed and 400 Ft. Lbs of max torque. The internal forces contained within the tool are very large. The rotational cylinder material composition needs to withstand these factors to operate as designed. Our rotator cylinder is made from metal that is dark grey/gunmetal in color. The part may have been heat treated to strengthen overall hardness . Since the Impact wrench is not a professional model, the raw material must be easy to obtain and isn’t expensive, keeping raw material costs minimal. This is an economical factor engineers analyzed so the part wasn’t built over specifications. Metal can be considered a recyclable material. It has minimal impact on the environment if disposed of properly for re-production.
Inner cylinder dia. - 1.6875 in
Outer cylinder dia. - 1.1875 in
Length - 1.375 in
2 air flow holes dia. - .1875 in
Intake / exhaust hole dia. - .25 in
Pin dia. - .1875 in
Pin Length - .4376
Complexity of interactions-
It is assumed the rotational cylinder is manufactured from a die-casting process. In die casting, molten steel or aluminum is poured into a reusable permanent mold. This method has a high initial cost for mold design and manufacturing . This is an economical method for large production orders . Die casting is good for small to medium size parts with a fine surface finish with good dimensional consistency. Some identifying characteristic are evident on the tool part from the casting process. On the top outer cylinder wall there are riser marks from tapered mold separation edges. After the part was casted a CNC machine was used to finish production. All air intake/exhaust ports were reamed out by a drill since the mold cannot achieve this. The inside cylinder walls were finely brazed to a polished finish to minimize potential frictional forces. Front and rear surfaces were milled flat to ensure a perfect fitment between the front/rear plates.
Rotational wheel/Rotor blade
The rotator wheel and blades are responsible for converting pneumatic energy into rotational force which drives the next system. Six rotor blades rest in slots machined into the wheel assembly. When assembled the rotator wheel sits of center of the y-axis compared to the cylinder. There is a closer gap on top than in the bottom . This allows for the blades to drop down and touch the bottom cylinder walls. There are 2 port holes in the inside bottom cylinder walls. Air is forced through one of the 2 holes determined by the FORWARD/REVERSE CONTROL BUTTON/VALVE direction. Air passes through a hole in the mechanism to the rear plate. The rear plate then channels the air into the rotator cylinder where it comes in contact with the rotor blades. The blades sit loosely in the rotor. Gravity causes at least 1 of the 6 blades to extend out of the rotor that catches the airflow. This begins to turn the rotor. Centrifugal force moves the rest of the blades partially out of the rotor where they glide along the inside cylinder. The flows associated with the rotational cylinder are:
- Pneumatic force energy
- Frictional force
- Rotational force
- Exhaust air
Pneumatic force energy describes the pressurized air input into the cylinder. This gets converted to frictional and rotational force while expending air in the process.
The rotator wheel has a thick diameter mid-section with 6 evenly spaced slots milled to hold the blades. These blade slots extrude through the entire wheel midsection. The front and rear rod is pressed into ball bearings located in each cylinder backing plate. These ball bearings are essential to minimize friction during high speed rotation. The rotational force pneumatically generated is transmitted to the impulse system via a male spline connection. This spline connection fits into a female hub also known as the hammer dog. The part is both axis-symmetric about the y and z axis. The component surface is smooth with clean cut edges, chamfers and splines. This indicates the part was precisely manufactured on CNC equipment. The six rotor blades are all the same general shape. On one side it has a flat surface and the other is slightly curved outwards. the curved surface end sits inside the rotor wheel while the flat side creates continuous contact with the inner cylinder walls. The part is symmetrical about the y and z axis.
The impact wrench operates at 7400RPM free speed and 400 Ft. Lbs of max torque. The internal forces contained within the tool are very large. The rotational wheel and blade material composition needs to withstand these factors to operate as designed. Our rotator wheel is made from metal that is dark grey/gunmetal in color. The part may have been heat treated to strength overall hardness . Since the Impact wrench is not a professional model, the raw material must be easy to obtain and isn’t expensive, keeping raw material costs minimal. This is an economical factor engineers analyzed so the part wasn’t built over specifications. Metal can be considered a recyclable material. It has minimal impact on the environment if disposed of properly for re-production. The six rotor blades also called fibro vanes act as a wind mill blade to turn the rotor wheel. These blades have a life span of 1000 hours, a tensile strength of 10000 Lbs/In, breaking strength of 17500 Lbs/in and an impact strength of 12 kg. cm.
Total Length -
Front rod length -
Rear rod length -
Shaft dia. -
Mid-section dia. -
Blade slot depth -
Blade slot thickness-
Complexity of interactions-
The rotary wheel was manufactured by a CNC (computer numerically controlled) machine process. CNC machining controls cutting paths, work piece, and cutting tools through numerical language. The advantages to this process are high precision and tolerances, good part flexibility. Although these machines are expensive, they require no active involvement or personnel. A skilled operator is needed to run the machine which is a large economic factor for production costs. The machine software can also be expensive to purchase and design a product from.
The trigger allows the user to engage and disengage the device. It does this by pushing down on the trigger spring and releasing the valve to allow air to flow into the gun from the air compressor. The amount of air that goes through the gun depends on how far in the trigger is pulled. Although it is difficult it is possible to not full engage the trigger if need be. This trigger is associated with human energy flow used to pull the trigger, and also with the flow of compressed air from the air compressor. The trigger is located on the exterior of the gun so it will be exposed to whatever environment the wrench is being used in which varies with the customer.
The plastic trigger that the users finger rests on is in the shape of a half moon. So a person’s finger does not easily slide off when engaging the wrench. Off the plastic is the metal rod that presses the trigger spring valve down against the spring. This rod is in a basic cylindrical shape in order to fit uniformly through the wrench’s plastic body. Also located on the rod is a rubber washer, which creates an airtight seal to prevent any backwards airflow. The weight of the whole trigger is so light that it is considered negligible and almost completely irrelevant compared to the weight of the whole wrench. The trigger is colored black to go along with the coloring of the rest of the wrench for a smooth and basic look. The materials that were used to build this trigger are very important because of how they are used in the wrench. The trigger is made out of plastic because it is a very cheap material to use; this is an example of an economical factor. Being in the half moon shape is a global factor in that anybody finger fits and can easily have complete control of the devise. A societal factor that influenced the design of the trigger is that the plastic and metal are both very durable materials and can withstand almost any conditions that a person would be using the wrench in. The rod going from the trigger to the air valve is made out of metal so that the chance of having to repair the wrench is extremely low and this is an environmental factor because it greatly increases the wrenches lifecycle.
The plastic grip on the trigger was made through injection molding. This is clear from the smooth sides and the markings on the inside of the trigger where the two molds came together and left marking of a slight excess of plastic. As far as the manufacturing of the metal rod on the backside of the trigger it was most likely made through die-casting. This is concluded because of the basic shape and the indents that are placed in the medal for proper fit. Then to connect the metal rod to the plastic there is probably a strong adhesive used to hold them together. These processes were chosen likely because they are very cost effective ways to produce basic parts at a high rate and low cost.
Trigger, spring, and valve
The function of the trigger spring and valve are to allow to flow from the air compressor into the gun and to stop the flow of air. It does this through the trigger being pulled which pushes down on the valve and spring, which opens the valve to allow air to flow in and “turn on” the pneumatic wrench. The further that the spring is compressed the more air is allowed to pass the valve and increase the rate at which the wrench runs. Then when the trigger is released the valve is then closed and the airflow stops. This valve component functions in a closed environment with in the wrench’s plastic handle.
The basic shape of this component is a flat valve with a cone shaped spring extending from the bottom of the valve. The valve has its flat side in order to stop the flow of air when the trigger is released. The spring is in the shape of a cone for a proper fit in the wrench handle and for proper resistance for the trigger. A global factor of this design is how the spring is made in the cone shape to allow enough tension on the trigger so it is can not be easily pressed by someone but enough to make it so the average person can press the trigger with one finger. The flat top of the valve is an example of a societal factor because it completely cuts off all airflow so there is no chance of the wrench to accidently go off and possibly hurt the user. The valve and spring are both made out of metal so if they are properly disposed of at the end of the wrenches lifecycle there is no waste, and this is an environmental factor. With the valve and spring quite small it is an economical factor in that it does not cost much to produce these parts in a factory setting.
This spring was made through the drawing process through a basic round hole to get the long strand of metal to then be spun and manipulated into the shape of the spring. And the top valve was most likely made through die-casting because of it basic shape and with the ridged edges it would be very easy to make a mold for it. These processes were most likely used because of their efficiency and cost effectiveness. The drawing process of pulling the metal of the spring through a particular shape would be the most efficient way to make the spring because you could make thousands of strand of metal to be spun into the spring shape in just a few hours using modern factory machines. This translates to a low manufacturing cost for Craftsmen. As for the die-casting of the valve this process would be the fasts way because you could also produce thousands of the valves in just a few hours with their basic shape and small size. The main purpose of these two manufacturing methods would certainly be the cheap cost for Craftsmen. Product Dimensions:
The function of the direction valve is to control the direction in which the air flows when it comes through the valve and trigger system. It can either direct the air to the right or left, which is to tighten (right) or loosen (left). It does this by either sending the compressed air through the left or right hole on the bottom of the rotator cylinder. The inner metal part of the directional valve is in a closed environment within the plastic body of the wrench. While the left/right dial is on the outside for the user to turn is exposed to the outside environment, which varies with the customer’s use.
The basic shape of the directional valve is a basic cylinder with different grooves cut out so when it is turned the air can pass through to the left or the right. There are two rectangular cut outs in the middle of the cylinder and that is where the air passes through when it is turned to the left or to the right. Also on the backside in front of where the plastic switch, there is a small rubber washer applied to create an airtight seal to prevent the loss of any power. The very back where the plastic switch is added on there is a small rod that comes out of the cylinder for the plastic piece to snap on. The approximate weight of this whole component is roughly half a pound. The main metal part of this valve is just natural grey because the user does not see it, but the plastic switch attached to it is red so it is easy to find compared to the black body of the devise. The half-inch length of the plastic switch is considered a global factor because it is a good size for anyone to use and easily be able to turn it from left to right or vise versa. An example of a social factor would be the small amount of resistance that it takes to turn the valve to the different directions. The valve being made out of metal makes it a recyclable material if properly disposed of; this is an example of an environmental factor. The valve being a simple die-cast and the switch being made of plastic is an economical factor because the cost of production of this component is very low.
The manufacturing process that is used to make the metal valve is die casting, and this is clear because of the basic shape of the valve and the ridged edges of each end where the metal would be forced into the mold. Craftsmen would chose to use die casting for the manufacturing of this part because it would be the most efficient way to produce a metal part with the basic features of the directional valve. As for the plastic lever it was most likely made through injection molding. This is evident through the lines bordering the outside of the piece which is where the two molds would come together to form the shape. Craftsmen would choose to use injection molding because they would be able to produces a very large amount of these pieces in a short amount of time which would save them money in lowering manufacturing costs.
Solid Modeled Assembly
The rotational assembly is a key component of the impact wrench that was chosen to be further analyzed on Autocad Software. This system is considered unique because it converts energy in the form of compressed air to produce a rotational force output. Integral parts of this system are the rotator blades, wheel, cylinder and front/rear back plates. When assembled the rotator wheel sits off center from the cylinder. There is a larger gap between the bottom inner cylinder wall and outer edge than on top. This allows for gravity to extend 1 of the 6 rotor blades out from the wheel to catch potential airflow. When the system is charged and trigger is released air enters into the cylinder and its direct path depends on by the FORWARD/REVERSE CONTROL BUTTON/VALVE direction. The front / rear plates channel the air into the rotator cylinder where it comes in contact with the rotor blades. The blades sit loosely in the rotor like a sail ready to catch wind. Centrifugal force moves the rest of the blades partially out of the rotor where they glide along the inside cylinder wall and begin to spin extremely fast.
AutoCad 2012 was choose to solid model the impact wrenches rotational system. This program was used because of past group members experience with the software. This design system will allow us to model each product to further analyze tolerances, internal stresses an finite element analysis. The following products will be modeled on Autocad 2012 Software.
- Rotational cylinder
- Rotator wheel
- Rotator blade
- Front/rear cylinder end plates
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 rests on ball bearings 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 in speed of air 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 stream 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 revision 1-Two way trigger(butterfly trigger)
One way to enhance the Craftsman ½” impact wrench is to create an alternative design for the trigger mechanism. Currently the gun operates off a one way directional trigger that controls the pressurized air flow source. It is composed of a trigger, valve, and throttle spring. To start operation the trigger must be firmly squeezed in and held to continue. Once the trigger lets go it ceases all tool rotation. One way to increase the functionality of this product is to increase its productivity and efficiency. When a tool is simplistic an easy to use, it is commonly more desired by the consumer. Less added headaches from reading lengthy instruction manuals is appreciated by the consumer. We decided to increase the controllability of the impact wrench during tool operation. Currently in order to change tool rotation direction, your hand opposite the controlling one holding the handle has let go of the tool or socket and twist the regulator direction switch. 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. this switch could be operated using your pointer and forefinger. There are a few internal components that would need alterations allowing for this simplistic function. Two directional valve solenoids would be controlled by the two way trigger. This would direct the flow of air 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 12𝑘𝑥2=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 to tool direction cutting down on necessary time needed for repair jobs. 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. This would be an economical factor we have contributed to. One disadvantage to this product is that it also requires a more complex system of solenoids an 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- Rubber handle inserts
Another way to enhance the impact wrenches functionality Is through implementing an alternative handle design to increase tool comfort during extended use. If anyone has ever operated an impact wrench they will know the harsh resultant forces expended from the main body down through handle. The repeated vibrations and impulses causes uncomfortable fatigue in the forearms, wrist and fingers. One way to eliminate this is by utilizing a trigger handle with textured rubber gel inserts that contoured to your hand. These rubber gel inserts will absorb most of the resultant shock during use. The rubber material composition should be soft enough to eliminate most vibrational impulses during operation while maintaining a firm rigidity in the users hand. These rubber insert fit inside two indentations outlined by the red plastic handle and be held in by two screws each. This would allow for the inserts to be removed and preplace if damaged. Different styles, hardness’s, grip textures and material compositions could be offered for added tool customization. This is a societal design factor which allows the impact wrench to be customized depending on the consumer’s needs. The price of altering the grip slightly may increase the retail price because of added features. Price increase is based on economic factors such as grip material cost and added manufacturing expenses. The impact wrench would only be engineered slightly different to fit these grips in place. A .25 inch indentation would exist where the current red handle inserts exist. The grip can placed inside of this and tightened down with small screws. An injection mold process would be used to produce these grips. A high initial start-up expense is associated with developing a new mold with different grip textures and shapes styles. The benefit is that molds can be reused to mass produced impact gun handle grips. This design revision is a desirable feature making the gun grips interchangeable, reducing vibration shock, and decreasing fatigue during operation.
Design revision 3- Regulator
A third change that could be made to our ½” pneumatic impact wrench is to add an intake dial on the bottom on the handle. This dial would change the amount of airflow into the device when engaging the trigger. Currently there is no such dial on the device so when you pull the trigger the wrench is fully engaged, and there is no simple way for a user to try and restrict the amount of airflow into the devise. The dial would work by having a scale 1-4 with 1 being the lowest amount of airflow and 4 being the greatest amount of flow. Sense the amount of air flow is directly connected to the RPM’s of the device and how much torque is outputted the user would be able to directly controller how much output energy he/she would like. Some governing equations that are correlated with this change are:
𝑃𝑣=𝑚𝑅𝑇 𝑖𝑑𝑒𝑎𝑙 𝑔𝑎𝑠 𝑙𝑎𝑤
𝑚=lim∆𝑡→0∆𝑚∆𝑡=𝑑𝑚𝑑𝑡 (𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒)
The user can now control how fast and how power they want their wrench to be. This would be very useful for someone who would like to use the wrench for adding or removing bolt or screws are a lower pressure than say car lug nuts. 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 dial with the basic 1-4 scale is an example of a global factor because numbers are used through out the whole world and anyone who would be buying one of these wrenches would easily understand the scale.