23-09-2014, 03:00 PM
Gear is rolling disc which have cut teeth on its periphery. It is used to transmit power from one shaft to another shaft with change of torque & speed. A gear is a rotating machine part having cut teeth which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source. The most common situation is for a gear to mesh with another gear; however a gear can also mesh a non - rotating toothed part, called a rack, thereby producing translation instead of rotation. Gears are used in tons of mechanical devices. They do several important jobs, but most important, they provide a gear reduction in motorized equipment. This is key because, often, a small motor spinning very fast can provide enough power for a device, but not enough torque. For instance, an electric screwdriver has a very large gear reduction because it needs lots of torque to turn screws,
PROJECT REPORT ON STUDY OF
GEAR MANUFACTURING
INDEX
1. Gear
2. Type of gear
Spur gear
Helical gear
Bevel gear
Worm gear
Rack and pinion
3. How do gear work
4. Gear profile
5. Standard system of gear system
6. Design consideration
7. Selection material
8. Gear material
9. Gear calculation
10. Gear manufacturing
Forming gear teeth
Sand casting
Die casting
Investing casting
Sintering & Powder metallurgy process
Injection molding
Extrusion
Cold drawing
Extension
Precisions forming
Performing
Machining
Form milling
Form milling by disc cutter
Form milling by end mill cutter
Rack generation
Gear shaping
Hobbing
Finishing process
Shaving
Grinding
Brushing
Lapping and honing
Bevel gear generating
Straight teeth gear generator
Spiral bevel gear generator
GEAR
Gear is rolling disc which have cut teeth on its periphery. It is used to transmit power from one shaft to another shaft with change of torque & speed. A gear is a rotating machine part having cut teeth which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source. The most common situation is for a gear to mesh with another gear; however a gear can also mesh a non - rotating toothed part, called a rack, thereby producing translation instead of rotation.
Gears are used in tons of mechanical devices. They do several important jobs, but most important, they provide a gear reduction in motorized equipment. This is key because, often, a small motor spinning very fast can provide enough power for a device, but not enough torque. For instance, an electric screwdriver has a very large gear reduction because it needs lots of torque to turn screws, but the motor only produces a small amount of torque at a high speed. With a gear reduction, the output speed can be reduced while the torque is increased.
Another thing gears do is adjust the direction of rotation. For instance, in the differential between the rear wheels of your car, the power is transmitted by a shaft that runs down the center of the car, and the differential has to turn that power 90 degrees to apply it to the wheels.
There are a lot of intricacies in the different types of gears. In this article, we\'ll learn exactly how the teeth on gears work, and we\'ll talk about the different types of gears you find in all sorts of mechanical gadgets
TYPES OF GEAR
Each type of gear has its own purpose as well as unique advantages and disadvantages.
VARIOUS TYPES OF GEAR
SPUR GEAR:- Spur gear are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used at once to create very large gear reductions.
When two spur gears of different sizes mesh together, the larger gear is called a wheel, and the smaller gear is called a pinion. In a simple gear train of two spur gears, the input motion and force are applied to the driver gear. The output motion and force are transmitted by the driven gear. The driver gear rotates the driven gear without slipping.
Spur gears are used in many devices like the electric screwdriver, dancing monster, oscillating sprinkler, windup alarm clock, washing machine and clothes dryer. But you won\'t find many in your car.
This is because the spur gear can be really loud. Each time a gear tooth engages a tooth on the other gear, the teeth collide, and this impact makes a noise. It also increases the stress on the gear teeth.
To reduce the noise and stress in the gears, most of the gears in your car are helical.
SPUR GEAR
HELICAL GEAR:- The teeth on helical gears are cut at an angle to the face of the gear. When two teeth on a helical gear system engage, the contact starts at one end of the tooth and gradually spreads as the gears rotate, until the two teeth are in full engagement.
Helical gears are very similar to spur gears except the teeth are not perpendicular to the face. The teeth are at an angle to the face giving helical gears more tooth contact in the same area.
This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears. For this reason, helical gears are used in almost all car transmissions.
Because of the angle of the teeth on helical gears, they create a thrust load on the gear when they mesh. Devices that use helical gears have bearings that can support this thrust load.
One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees. Helical gears can also be used on non - parallel shafts to transmit motion.
HELICAL GEAR
BEVEL GEAR:- Bevel gears are useful when the direction of a shaft\'s rotation needs to be changed. They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well. The teeth on bevel gears can be straight, spiral or hypoid. Straight bevel gear teeth actually have the same problem as straight spur gear teeth as each tooth engages, it impacts the corresponding tooth all at once.
Just like with spur gears, the solution to this problem is to curve the gear teeth. These spiral teeth engage just like helical teeth: the contact starts at one end of the gear and progressively spreads across the whole tooth.
On straight and spiral bevel gears, the shafts must be perpendicular to each other, but they must also be in the same plane. If you were to extend the two shafts past the gears, they would intersect. The hypoid gear, on the other hand, can engage with the axes in different planes. This feature is used in many car differentials. The ring gear of the differential and the input pinion gear are both hypoid. This allows the input pinion to be mounted lower than the axis of the ring gear. Since the driveshaft of the car is connected to the input pinion, this also lowers the driveshaft. This means that the driveshaft doesn\'t intrude into the passenger compartment of the car as much, making more room for people and cargo.
STRAIGHT TEETH BEVEL GEAR SPIRAL BEVEL GEAR
WORM GEAR:- Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater. Worm gears are used to transmit power at 90° and where high reductions are required. The worm resembles a thread that rides in concaved or helical teeth. Many worm gears have an interesting property that no other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm. This is because the angle on the worm is so shallow that when the gear tries to spin it, the friction between the gear and the worm holds the worm in place.
This feature is useful for machines such as conveyor systems, in which the locking feature can act as a brake for the conveyor when the motor is not turning. One other very interesting usage of worm gears is in the Torsen differential, which is used on some high - performance cars and trucks. A gear which has one tooth is called a worm. The tooth is in the form of a screw thread. A worm wheel meshes with the worm. The worm wheel is a helical gear with teeth inclined so that they can engage with the thread - like worm. The worm wheel transmits torque and rotary motion through a right angle. The worm always drives the worm wheel and never the other way round. Worm mechanisms are very quiet running.
WORM GEAR
RACK AND PINION:- A rack is basically a straight gear used to transmit power and motion in a linear movement. Rack and pinion gears are used to convert rotation into linear motion and vice versa. A perfect example of this is the steering system on many cars. The steering wheel rotates a gear which engages the rack. As the gear turns, it slides the rack either to the right or left, depending on which way you turn the wheel.
A round spur gear, the pinion, meshes with a spur gear which has teeth set in a straight line, the rack.
Rack and pinion gears are also used in some scales to turn the dial that displays your weight.
RACK AND PINION
HOW DO GEAR WORK?
In the simplest terms a gear is a way to generate speed or power or change the direction of power. Most gears are mounted on shafts, generally an input and output shaft. When two gears are meshing (connected) they are called a transmission.
What do Gears Do?
Gears can be used to do the following things –
§ Increase or Decrease Speed
By connecting two gears together, Gear A with 10 teeth and Gear B with 5 teeth. Gear B will have to turn around much faster to keep up with gear A, however it does so with half as much turning force. The fact that B is turning faster than A is down to the gear ratio
§ Increase decrease torque
To increase the force of gears, the second gear in a pair of gears will have fewer teeth than our first gear. It will turn slower but will do so with more force.
§ Change Direction
When two gears are meshing together, the second gear always turns in the opposite direction to the first gear. So if Gear A is turning clockwise, Gear B will turn anti - clockwise. If you had three gears meshing together A and B would be turning clockwise, whilst B would be turning anti - clockwise.
GEAR PROFILE
There is four diameter of a gear:-
§ Outside diameter - The major diameter of a gear. It is measured from top face of the gear.
§ Pitch circle diameter - The diameter of pitch circle.
§ Root diameter - The diameter of the root circle measured from the base of the tooth
§ Clearance diameter - it is diameter generating from top face of meshing gear (pinion).
Other profiles are-
§ Addendum - The radial distance from the pitch circle to the outside diameter.
§ Dedendum - The radial distance between the pitch circle and the root diameter. Radial distance from the depth of the tooth trough to the pitch surface .
§ Clearance - Distance between the root circle of a gear and the addendum circle of its mate. The amount by which the tooth space is cut deeper than the working depth .
§ Backlash - The amount by which the width of a tooth space exceeds the thickness of the engaging tooth on the pitch circles.
§ Module - A standard or unit of measurement. A scaling factor used in metric gears with units in millimeters whose effect is to enlarge the gear tooth size as the module increases and reduce the size as the module decreases. It is the ratio of pitch circle diameter to the no of teeth. The length in mm of the pitch circle diameter per tooth .
§ Circular thickness - The distance of the arc along the pitch circle from one side of a gear tooth to the other .
§ Circular pitch - The length of the arc of the pitch circle from one point on a tooth to the same point on the adjacent tooth .
§ Whole depth - The total depth of a tooth space equal to the sum of the addendum and dedendum .
§ Working depth - The depth of engagement of two mating gears that is, the sum of their addendum.
§ Pressure angle - The angle between a tooth profile and a radial line at the pitch circle .
§ Chordal addendum - The distance from the top of the tooth to the chord connecting the circular thickness arc.
§ Chordal thickness - The thickness of a tooth on a straight line or chord on the pitch circle.
§ Diametral pitch - The number of gear teeth to each inch of pitch diameter.
§ Center distance - The distance between the centers of the pitch circles.
§ Apex point - It is in bevel gear. The point of intersection of the shafts is called the apex. it is point where pinion and wheel axis intersect this point is called apex point.
SPUR GEAR
§ Mounting distance - distance between resting face of the job and apex point is mounting distance. Mounting Distance of Bevel Gear is the distance from the back end of the gear hub of one gear to the centerline of its mating gear. When properly mounted to this dimension, the ends of the teeth of these gears will be flush with each other. If the mounting distance is too long the gears will not be fully in mesh, thus permitting the load to be concentrated above the pitch line and allowing excessive backlash. When distance is too short, gears may bind causing excessive heat, wear and breakage.
STANDARD SYSTEM OF GEAR TEETH
In a gear drive, two types of curves, the cycloidal and the involute, are generally used. In a gear drive, the shape of the tooth depends upon the pressure angle. Gears of involute profile with 14.5°, 20° full-depth and 20° stub pressure angles are most commonly used in industries. A 20° pressure angle full-depth involute gear tooth has various advantages over the other pressure angles. BIS has recommended the use of 20° pressure angle full depth involute gear tooth.
DESIGN CONSIDRATION
The accuracy of the output of a gear depends on the accuracy of its design and manufacturing. The correct manufacturing of a gear requires a number of prerequisite calculations and design considerations. The design considerations taken into account before manufacturing of gears are:
Strength of the gear in order to avoid failure at staring torques or under dynamic loading during running conditions. Gear teeth must have good wear characteristics. Selection of material combination. Proper alignment and compactness of drive Provision of adequate and proper lubrication arrangement.
Selection of material
The gear material should have the following properties:
§ High tensile strength to prevent failure against static loads
High endurance strength to withstand dynamic loads Low coefficient of friction
PROJECT REPORT ON STUDY OF
GEAR MANUFACTURING
INDEX
1. Gear
2. Type of gear
Spur gear
Helical gear
Bevel gear
Worm gear
Rack and pinion
3. How do gear work
4. Gear profile
5. Standard system of gear system
6. Design consideration
7. Selection material
8. Gear material
9. Gear calculation
10. Gear manufacturing
Forming gear teeth
Sand casting
Die casting
Investing casting
Sintering & Powder metallurgy process
Injection molding
Extrusion
Cold drawing
Extension
Precisions forming
Performing
Machining
Form milling
Form milling by disc cutter
Form milling by end mill cutter
Rack generation
Gear shaping
Hobbing
Finishing process
Shaving
Grinding
Brushing
Lapping and honing
Bevel gear generating
Straight teeth gear generator
Spiral bevel gear generator
GEAR
Gear is rolling disc which have cut teeth on its periphery. It is used to transmit power from one shaft to another shaft with change of torque & speed. A gear is a rotating machine part having cut teeth which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source. The most common situation is for a gear to mesh with another gear; however a gear can also mesh a non - rotating toothed part, called a rack, thereby producing translation instead of rotation.
Gears are used in tons of mechanical devices. They do several important jobs, but most important, they provide a gear reduction in motorized equipment. This is key because, often, a small motor spinning very fast can provide enough power for a device, but not enough torque. For instance, an electric screwdriver has a very large gear reduction because it needs lots of torque to turn screws, but the motor only produces a small amount of torque at a high speed. With a gear reduction, the output speed can be reduced while the torque is increased.
Another thing gears do is adjust the direction of rotation. For instance, in the differential between the rear wheels of your car, the power is transmitted by a shaft that runs down the center of the car, and the differential has to turn that power 90 degrees to apply it to the wheels.
There are a lot of intricacies in the different types of gears. In this article, we\'ll learn exactly how the teeth on gears work, and we\'ll talk about the different types of gears you find in all sorts of mechanical gadgets
TYPES OF GEAR
Each type of gear has its own purpose as well as unique advantages and disadvantages.
VARIOUS TYPES OF GEAR
SPUR GEAR:- Spur gear are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used at once to create very large gear reductions.
When two spur gears of different sizes mesh together, the larger gear is called a wheel, and the smaller gear is called a pinion. In a simple gear train of two spur gears, the input motion and force are applied to the driver gear. The output motion and force are transmitted by the driven gear. The driver gear rotates the driven gear without slipping.
Spur gears are used in many devices like the electric screwdriver, dancing monster, oscillating sprinkler, windup alarm clock, washing machine and clothes dryer. But you won\'t find many in your car.
This is because the spur gear can be really loud. Each time a gear tooth engages a tooth on the other gear, the teeth collide, and this impact makes a noise. It also increases the stress on the gear teeth.
To reduce the noise and stress in the gears, most of the gears in your car are helical.
SPUR GEAR
HELICAL GEAR:- The teeth on helical gears are cut at an angle to the face of the gear. When two teeth on a helical gear system engage, the contact starts at one end of the tooth and gradually spreads as the gears rotate, until the two teeth are in full engagement.
Helical gears are very similar to spur gears except the teeth are not perpendicular to the face. The teeth are at an angle to the face giving helical gears more tooth contact in the same area.
This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears. For this reason, helical gears are used in almost all car transmissions.
Because of the angle of the teeth on helical gears, they create a thrust load on the gear when they mesh. Devices that use helical gears have bearings that can support this thrust load.
One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees. Helical gears can also be used on non - parallel shafts to transmit motion.
HELICAL GEAR
BEVEL GEAR:- Bevel gears are useful when the direction of a shaft\'s rotation needs to be changed. They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well. The teeth on bevel gears can be straight, spiral or hypoid. Straight bevel gear teeth actually have the same problem as straight spur gear teeth as each tooth engages, it impacts the corresponding tooth all at once.
Just like with spur gears, the solution to this problem is to curve the gear teeth. These spiral teeth engage just like helical teeth: the contact starts at one end of the gear and progressively spreads across the whole tooth.
On straight and spiral bevel gears, the shafts must be perpendicular to each other, but they must also be in the same plane. If you were to extend the two shafts past the gears, they would intersect. The hypoid gear, on the other hand, can engage with the axes in different planes. This feature is used in many car differentials. The ring gear of the differential and the input pinion gear are both hypoid. This allows the input pinion to be mounted lower than the axis of the ring gear. Since the driveshaft of the car is connected to the input pinion, this also lowers the driveshaft. This means that the driveshaft doesn\'t intrude into the passenger compartment of the car as much, making more room for people and cargo.
STRAIGHT TEETH BEVEL GEAR SPIRAL BEVEL GEAR
WORM GEAR:- Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater. Worm gears are used to transmit power at 90° and where high reductions are required. The worm resembles a thread that rides in concaved or helical teeth. Many worm gears have an interesting property that no other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm. This is because the angle on the worm is so shallow that when the gear tries to spin it, the friction between the gear and the worm holds the worm in place.
This feature is useful for machines such as conveyor systems, in which the locking feature can act as a brake for the conveyor when the motor is not turning. One other very interesting usage of worm gears is in the Torsen differential, which is used on some high - performance cars and trucks. A gear which has one tooth is called a worm. The tooth is in the form of a screw thread. A worm wheel meshes with the worm. The worm wheel is a helical gear with teeth inclined so that they can engage with the thread - like worm. The worm wheel transmits torque and rotary motion through a right angle. The worm always drives the worm wheel and never the other way round. Worm mechanisms are very quiet running.
WORM GEAR
RACK AND PINION:- A rack is basically a straight gear used to transmit power and motion in a linear movement. Rack and pinion gears are used to convert rotation into linear motion and vice versa. A perfect example of this is the steering system on many cars. The steering wheel rotates a gear which engages the rack. As the gear turns, it slides the rack either to the right or left, depending on which way you turn the wheel.
A round spur gear, the pinion, meshes with a spur gear which has teeth set in a straight line, the rack.
Rack and pinion gears are also used in some scales to turn the dial that displays your weight.
RACK AND PINION
HOW DO GEAR WORK?
In the simplest terms a gear is a way to generate speed or power or change the direction of power. Most gears are mounted on shafts, generally an input and output shaft. When two gears are meshing (connected) they are called a transmission.
What do Gears Do?
Gears can be used to do the following things –
§ Increase or Decrease Speed
By connecting two gears together, Gear A with 10 teeth and Gear B with 5 teeth. Gear B will have to turn around much faster to keep up with gear A, however it does so with half as much turning force. The fact that B is turning faster than A is down to the gear ratio
§ Increase decrease torque
To increase the force of gears, the second gear in a pair of gears will have fewer teeth than our first gear. It will turn slower but will do so with more force.
§ Change Direction
When two gears are meshing together, the second gear always turns in the opposite direction to the first gear. So if Gear A is turning clockwise, Gear B will turn anti - clockwise. If you had three gears meshing together A and B would be turning clockwise, whilst B would be turning anti - clockwise.
GEAR PROFILE
There is four diameter of a gear:-
§ Outside diameter - The major diameter of a gear. It is measured from top face of the gear.
§ Pitch circle diameter - The diameter of pitch circle.
§ Root diameter - The diameter of the root circle measured from the base of the tooth
§ Clearance diameter - it is diameter generating from top face of meshing gear (pinion).
Other profiles are-
§ Addendum - The radial distance from the pitch circle to the outside diameter.
§ Dedendum - The radial distance between the pitch circle and the root diameter. Radial distance from the depth of the tooth trough to the pitch surface .
§ Clearance - Distance between the root circle of a gear and the addendum circle of its mate. The amount by which the tooth space is cut deeper than the working depth .
§ Backlash - The amount by which the width of a tooth space exceeds the thickness of the engaging tooth on the pitch circles.
§ Module - A standard or unit of measurement. A scaling factor used in metric gears with units in millimeters whose effect is to enlarge the gear tooth size as the module increases and reduce the size as the module decreases. It is the ratio of pitch circle diameter to the no of teeth. The length in mm of the pitch circle diameter per tooth .
§ Circular thickness - The distance of the arc along the pitch circle from one side of a gear tooth to the other .
§ Circular pitch - The length of the arc of the pitch circle from one point on a tooth to the same point on the adjacent tooth .
§ Whole depth - The total depth of a tooth space equal to the sum of the addendum and dedendum .
§ Working depth - The depth of engagement of two mating gears that is, the sum of their addendum.
§ Pressure angle - The angle between a tooth profile and a radial line at the pitch circle .
§ Chordal addendum - The distance from the top of the tooth to the chord connecting the circular thickness arc.
§ Chordal thickness - The thickness of a tooth on a straight line or chord on the pitch circle.
§ Diametral pitch - The number of gear teeth to each inch of pitch diameter.
§ Center distance - The distance between the centers of the pitch circles.
§ Apex point - It is in bevel gear. The point of intersection of the shafts is called the apex. it is point where pinion and wheel axis intersect this point is called apex point.
SPUR GEAR
§ Mounting distance - distance between resting face of the job and apex point is mounting distance. Mounting Distance of Bevel Gear is the distance from the back end of the gear hub of one gear to the centerline of its mating gear. When properly mounted to this dimension, the ends of the teeth of these gears will be flush with each other. If the mounting distance is too long the gears will not be fully in mesh, thus permitting the load to be concentrated above the pitch line and allowing excessive backlash. When distance is too short, gears may bind causing excessive heat, wear and breakage.
STANDARD SYSTEM OF GEAR TEETH
In a gear drive, two types of curves, the cycloidal and the involute, are generally used. In a gear drive, the shape of the tooth depends upon the pressure angle. Gears of involute profile with 14.5°, 20° full-depth and 20° stub pressure angles are most commonly used in industries. A 20° pressure angle full-depth involute gear tooth has various advantages over the other pressure angles. BIS has recommended the use of 20° pressure angle full depth involute gear tooth.
DESIGN CONSIDRATION
The accuracy of the output of a gear depends on the accuracy of its design and manufacturing. The correct manufacturing of a gear requires a number of prerequisite calculations and design considerations. The design considerations taken into account before manufacturing of gears are:
Strength of the gear in order to avoid failure at staring torques or under dynamic loading during running conditions. Gear teeth must have good wear characteristics. Selection of material combination. Proper alignment and compactness of drive Provision of adequate and proper lubrication arrangement.
Selection of material
The gear material should have the following properties:
§ High tensile strength to prevent failure against static loads
High endurance strength to withstand dynamic loads Low coefficient of friction