SSG Panjab University Regional Centre Bajwara, Hoshiarpur

SHINE AUTO PVT. LTD.

Submitted to: Department of Mechanical EngineeringSubmitted by: RajkamalSemester: 5th sem, MECHRoll No.: SG7920 ACKNOWLEDGEMENT

It gives me abundant pleasure and sense of satiety to express my profound gratitude to

the esteemed personalities who were keenly associated with the successful

accomplishment of my training.At the very outset i am very earnestly beholden to

Dr. Sarabjeet Singh Kang, for providing me an opportunity to do industrial training

at SHINE AUTOS PVT LTD.

I am extremely thanksful to revered Mr.Narinder Modi( personnel Manager) for offering

me a big exposure in various ventures linked with my field.

I am also thanksful to Mr.Mukesh Sharma( Sr Manager) foroffering me a big exposure in

various ventures linked with my field.under whose guidance i have learnt a lot of things.

There cooperation has invariably and unfaithfully helped me to achieve my desired aim.

This stupendous task would not have been possible without their forth-coming benign

guidance.

there cooperation has invariably and unfaithfully helped me to achieve my desired aim.

this stupendous task would not have been possible without their forth coming benign

guidance.

therefore ,i heartily voice my deepest sense of gratitude and thanksfulness for their

timely cooperation.

DIFFERENT MANUFACTURING OPERATIONS IN LMV

*DRILLING It is a process of making hole in an object by forcing a rotating tool called drill.

*BORING It is a process of enlarging a hole that has already been drilled.

*GRINDING To grind means to abrade to wear away by friction or to sharpen. In grinding the material is removed by a means of a rotating abrasive wheel.It is generally used for sharpening the cutting tool ,for grinding threads,better surface finish etc.

* FACING It is the operation of finishing the ends of the work,to make the ends flat and smooth and to make the piece of required length

*Knurling It is process of embossing a diamond shaped regular pattern on the surface of workpiece using a special knurling tool.

*CHAMFERING It is the operation of beveling the extreme ends of the workpiece.Chamfer is provided for better look/to rough turning: In this operation max metal is removed and very little oversize dimentions are left for further machining.

*UNDERCUTTING It is similar to grooving operation but is performed inside a hole.

*SHAPING It is the process of cutting gears on the shaper is known as shaping. tool used in shaping for teeth cutting is a multipoint cutting tool.

*GROVING It is the operation of turning the groove or check in order to terminate a thread or to provide adequate clearance to enable the nut to pass freely on threaded workpiece to remove burs and to protect the workpiece from being damaged

*BROACHING It is a method of metal removal by a tool that has successively higher cutting edges in a fixed path.

HOBBING: It is the process of cutting teeth on gears and shafts and is performed by rotating tool called hob on the hobbing machine.

FINISH TURNING here min metal is removed and very fine finish is obtained on the work surface.

GEAR TOOTH SHAVING Gear shaving is a metal cutting operation for finishing the gearing process.the process used a helical gear shaped, high speed steel, hardened and ground cutter having tooth flanks with multiple separation that act as a cutting edge.The cutter is meshed and rotated and rotated in crossed axis nterrelation with internal and external or helical gear while th work is reciprocated across the face of of the cutter .The centre distance b/w the cutter and work gear is reduced to remove metal from the work gear toot surface in the form of chips

GEAR HOBBING Hobbing is a process of generating a gear by means of a rotating cutter called a hob.It is a continuous indexing process in which both cutting tool and the work piece rotates in a constant relationship while the hob being fed into the work.A hob resembles a worm, with gashes made parallel to its axis to provide the cutting edges. For involute gears the hob has essentially straight sides as a given pressure angle. The faces of both hob teeth are relieved radials to form clearance b/w the cutting edge .The teeth of the hob cut into the gears blank in successive order and each in a slight different position. Each hob cuts its own profile in the shape of cutter but the form of gear teeth, thus is called a generating process. One rotation completes the cutting of gears upto a certain depth until the gear has a certain wide face,so that it may cut it while moving from up to down.Gear hobbing is generally faster than the milling process this is because in the case of gear hobbing several teeth are cut at a time as compared to one by one in the case of milling.

DEBURRING The process of Deburring is a applied to removethe burr of the job.The burr signifies the unwanted particles or the sharp edges, which remain on the sides of the place on the job where the cut being applied . The deburring of job takes on the FEMCO Twin chucker CNC machine. The deburring tool is applied on the back of taper spline and then on the front of the gear cut. This helps in removing the sharp edges, which may harm the hand of worker while on the job.

MACHINE SPECIFICATIONS

Type, make , broader specifications viz.machine no , make

Industrial Engineering is engineering approach to the detailed analysis of the use and the cost of the resources of an organization .the main resources are men, money ,material, equipment and machinery , the industrial Engg carries out such analysis in order to achieve the objective and policies of an organization .it is not associated with meeting cost factor,but with organization structure ,administration ,technology and human problems etc.

It is the most result oriented department in terms of production , planning, designing,optimization method etc.Some functions involve planning of layouts. All the shops to get maximum benefits of available space setting work, time standards to perform a certain job motion study and implementing standards laid.stress is laid down to reduce the downtime and new techniques are invented or implemented to improve the quality and standard of work piece in minimum breakdowns and downtime.use is made of various type of studies for performing the same job in a better and systematic way,to reduce the overburden on system.

JOB RESPONSIBILITIES

+To set up production norms for all production departments ie to set up time standard for the entire job

+To design/ improve work place arrangements to improve productivity and to create good working conditions and enviorment for work placee.

+To design/ improve material handling systems to make its use and optimize its cost.

+To design material storage system for optimizing utilization and minimizing cost.

+To set up new machines and to make process plan.

+Design formats for management reports like rejection of manpower facilities , production target v/s production efficiency.

+Plant layouts:best optimum utilization of space can be achieves by optimum layout.

+Another imp function of I.E is to get the new machinery installed according to the proposed layout.

FUNCTIONS

-Receiving components and drawings from R&D

-Preparing and releasing of process sheets.

-Assesment of direct labour requirement.

-To make decision for purchasing new machines.

-Installation of new machines at proper places.

-Releasing of jigs,tools and fixture drawings.

-To make operation research.

-Miscellaneous and advisory functions.

TOOL ROOM

In industry various type of tools are used.The tool room caters to the needs for manufacturing of jigs,fixture,gauges,dies ,etc.During machining wear and tear of the tool takes place.The tool room is provided in order to re-sharpen these tools.

FUNCTIONS

+Re-sharpening of the tools-whose wear& tear has taken place. This ensures that there is no delay in production due to blunt tools.

+New jigs & fixture- In other to improve the production rate & quality of the work & to decrease the job setting time, new jigs & fixture are developed in the tool room.

+Maintenance of old jigs & fixture-Old & fixture that lose their accuracy due to breakage or wear & tear are repaired in the tool room.

-New development work-Any modification & development work is carried out in tool room,for eg a new components is to be installed in a tractor, its die assembly is developed in the tool room.

-Manufacturing of measuring tools-certain measuring tools used in the metrology lab for quality check are manufactured in the tool room.

Machines used in the tool room

-Precision Grinding machine.

-Jigs Boring machines.

-Lathe Machines(Re sharpening of tools takes place)

-NC Turning Machines(Here certain measuring tool manufactured)

INTER RELATION WITH OTHER DEPARTMENTS

+Tool room-Requirement of jigs, fixture and cutting tools.

+Maintenance- Attending breakdown and carrying out preventive maintenance of machines tools.

+Industrial engg – provides process charts for machining operations.

+Assembly- Ensuring proper fitment of components,production planning and

control, micro loading of components on day-to-day basis.

Broaching operations

Broaching is a machining process that pushes or pulls a cutting tool (called a broach) over or through the surface being machined. Its high-production, metal-removal process is sometimes required to make one-of-a-kind parts. The concept of broaching as a legitimate machining process can be traced back to the early 1850s. Early broaching applications were cutting keyways in pulleys and gears. After World War 1, broaching contributed to the rifling of gun barrels. Advances in broaching machines and form grinding during the 1920s and 30s enabled tolerances to be tightened and broaching costs to become competitive with other machining processes. Today, almost every conceivable type of form and material can be broached. It represents a machining operation that, while known for many years, is still in its infancy. New uses for broaching are being devised every day.

Figure 1. Cutting action of a broaching tool.

Broaching is similar to planing, turning, milling, and other metal cutting operations in that each tooth removes a small amount of material (Figure 1 ).

Figure 2. Typical push keyway broaching tools and a shim.

The broaching tool has a series of teeth so arranged that they cut metal when the broach is given a linear movement as indicated in figure 1. The broach cuts away the material since its teeth are progressively increasing in height.

Properly used, broaching can greatly increase productivity, hold tight tolerance, and produce precision finishes. Tooling is the heart of broaching. The broach tool's construction is unique for it combines rough, semi-finish, and finish teeth in one tool (Figure 3).

                   Figure 3. Parts of a broaching tool.

There are two types of broaching procedures: internal broaching and external broaching. For exterior broaching, the broach tool may be pulled or pushed across a workpiece surface, or the surface may move across the tool.

Internal broaching requires a starting hole or opening in the workpiece so the tool can be inserted. The tool, or workpiece, is then pushed or pulled to force the tool through the starter hole.

Almost any irregular cross-section can be broached as long as all surfaces of the section remain parallel to the direction of broach travel (Figure 4). Helical cuts can also be produced by twisting the broach tool as it passes the workpiece surface.

Figure 4. Different types of broaches.

In conclusion, it may be said that the broach tool and the broaching process are versatile and important and that anyone who works in the field of metals, woods, or plastics should be familiar with them.

Set-upMaintain a rigid set-up at all times. The workpiece must be solidly fixed or nested perfectly square with the baseplate and ram face. Check to make sure that all square and parallel surfaces on the face of the ram and the baseplate remain true.

AlignmentProper alignment of the broach, workpiece, and ram is the most important factor in all broaching operations. Misalignment can cause drifting, deflection, and even breakage. Alignment Tips--If a keyway broach drifts and cuts a taper, try the following:

1. Reverse workpiece or turn broach so teeth face toward the back of the press.2. Let the bushing protrude above the workpiece to give more support to the back of the broachthereby helping to keep it aligned. If a collared bushing is used, place it upside down underthe workpiece.3. Make sure the broach is centered under the ram at the beginning of the cut. If thebroach moves out of alignment after starting to cut, back off the pressure on the ram and align the broach itself. Repeat during successive cuts to ensure perfectly straight cuts.

BROACHING TOOL COATING and MATERIAL

A coating of titanium nitride (TiN) not only gives broaching tools a golden color, but it also gives broaching a golden opportunity to shine as a premier method of one-step, high-precision metal forming in high-production

applications.

TiN coating gives broaching a new look. For one thing, the broaching tool takes on that distinctive golden color that most shops are familiar with from TiN-coated inserts, end mills and twist drills. For another, the reduced wear and extended tool life this coating provides make broaching a process highly suited for today's manufacturing environment.

A broaching tool, or bar, as it is often called, is in reality three-tools-in-one. It performs roughing, semi-finishing, and finishing operations in just one stroke. With a TiN coating, however, the broach may stay sharp many times longer. Because sharpening a broaching tool is no simple matter, the result is a very significant reduction in machine downtime.

.

Broaching In Review

Broaching is a widely-used metal cutting process in which a special tapered multitoothed cutter is forced through an opening or along an outside edge of the workpiece. The broaching tool or bar either enlarges the opening in the workpiece or changes its contour. There is no faster machining method than broaching because it performs the roughing, semi-finish and finishing operations in just one stroke of the bar.

Each successive pass along the longitudinal axis removes only a predetermined amount of stock and is in cutting contact of the workpiece for only a short period of time. The finishing teeth on the end of the tool are shielded from the heavier roughing teeth by the intermediate or middle teeth. A fine finish results because the surfaces of the teeth can be held to close tolerances. Furthermore, each tooth of a long broaching bar removes only a small portion of metal from the cut, usually only a few thousandths of an inch of material. The finishing teeth remove only that final increment of stock and impart a final finish to the workpiece. In many applications, no other finishing operation needs to be performed.

pitch of the teeth, which is the distance from a point on one tooth to the corresponding point on the tooth behind it, is controlled by three factors. They are the length of the broach, the chip thickness and the kind of material being machined. The chip load cannot be altered by the operator. The pitch determines the chip thickness and ultimately the construction and strength of the entire tool. The pitch and angle of the cut appreciably impact the tool life of the broach. The chip space, or gullet between each tooth, must hold all the metal removed by one tooth through the entire stroke. The pitch, as well as the face angle, affects the surface finish.

There are two principle types of broaching: either external (or surface) and internal.

The internal process requires an opening in the workpiece to allow the broaching bar to be pulled down through the piece. The broach has a built-in feed function; the operator merely reloads the machine. This translates into exceptional precision and repeatability. The high degree of accuracy and the ability of the broach to maintain close finishing tolerances make the application of TiN-coated broaches a very practical option.

Why Coatings Work?

When TiN coating is not used in situations involving the relatively low speeds of the broaching process, heat--due to friction--is found to be the prime factor in premature tool failure. TiN-coated broaches ameliorate heat buildup by exhibiting a high degree of lubricity, higher hardness and reduced coefficient of friction which allows the tool to cut cleaner and with less force. For example, in one documented case involving workpieces of 4140 hardened tool steel, production went from 1,000 or 2,000 pieces-per-grind with uncoated broaches to 10,000 or 20,000 pieces-per-grind using TiN-coated broaches.

The lubricity of the TiN coating means a decrease in the coefficient of friction between the contact surfaces, which improves chip formation. Chips flow away from the tool more readily, which in turn reduces the horsepower required to perform the machining operation. For HSS twist drills, for example, experience with these coatings shows that speeds can be increased by about 25 percent and feed rates by 50 to 100 percent. Cutting force measurements indicate that torque and thrust remain relatively constant over a wide range of speeds, with a 35-percent lower torque and 45-percent reduction in thrust compared to uncoated tools. Broaching also benefits from a reduction in these forces.

Reduced power levels utilizing coated tooling, as opposed to conventional tooling, translates into a decrease of machine power requirements. At John Deere, we recognize that this can be a significant factor in many of today's manufacturing environments which utilize older model machines.

Due to lower operating temperatures, there is less tendency to form built-up edges, thereby retaining sharp teeth lines, which results in tighter tolerances for a longer period of time.

Besides reduced cutting force requirements and less heat buildup, a low coefficient of friction reduces chemical diffusion action. The reduced chemical diffusion results in a smoother cut as well as increased resistance to oxidation, which reflects yet another requirement of hard coating material. Good adhesion properties, increased lubricity of the coating material, and of course, the high hardness all contribute to the maintenance of sharp edge cutting zone between the cutting tool and workpiece.

VERTICAL ONE PASS INTERNAL GEAR CUTTING BORACHING MACHINE

MATERIAL OF BROACH

Almost all broaches are made of high-speed tool steels in monolithic construction.Brazed carbide or disposable inserts are sometimes used for cutting edges, most often on tools used for broaching cast irons.Here is a list of tool steels and the materials that are commonly broached with these steels. (The list is only a sampling.)

M-2 steel:Part hardness should be held under Rc 28. General use, including brass, aluminum, magnesium, and the following steels: 1018, 1020, 1063, 1112, 1340, 1345, B-1113, 4140, 4340, 5140, 8620, (RC26), 347 stainless steel (annealed)

M-3Part hardness should be held under Rc 28. Aluminum castings, cast irons, A-286 and the following steels: 4140, 4337, 8617, 8620, 9840, 403 stainless, Greek Ascoloy, M-252, D-279, 4140, 4337, 4340, 8617, 8620, 9310, 9840, 403 stainless

PM-4 (Powdered Metal):Part hardness should be held under Rc 30. An increasingly popular tool steel used on a wide variety of applications. Has a very high wear resistance. High Silicon Steels, Silicon Bronze, Aluminum Die Casting, Armature Grade Irons, 9250, 9260, All materials listed under M-2 & M-3 above.

T-15 (Powdered Metal):One of the best and most expensive tool steels., Aluminum 2219, A-286 (Rc 32-36), Stellite,

17-22A(S)(Rc 29-34), N-155 (Rc 30-40), WASPOLOY, INCOLOY SOL (Rc 32-36), 4340 (Rc 30-40), 52100, 931- (Rc 26-30), 17-4 PH stainless steel, 416 stainless steel (Rc 35-40), 403 stainless steel (Rc 37-40), Custom 450, High Nickel, 4337 (Rc 29-34), 9310 (Rc 36-38), 9840 (Rc 32-36), Greek Ascoloy

CarbidesMost of the carbide cutters used to broach cast iron are used in flat surface broaching applications, although contoured cast-iron surfaces have been broached successfully. Surface broaching of pine tree slots has been tried with carbides on high-temperature alloy turbine wheels, but with little success. The carbide edges tend to chip on the first stroke.

Carbide-Tipped BroachesCarbide tips are seldom used on conventional steel parts and forgings. One reason is that good performance is obtained from high-speed-steel tools; another is the low cutting speeds of most broaching operations (from 12 to 30 fpm) do not lend themselves to the advantages of carbide tooling. The success of carbide tooling on cast irons is due to carbide's resistance to abrasion on the tool flank below the cutting edge.

Another problem with carbide-tipped tools is that a broaching machine work fixture must be exceptionally rigid to prevent chipping of the cutting edge. Experimental work with extra-rigid tools and workpiece fixtures, however, has shown that tool life and surface finish can be greatly improved with carbide tipped tools, even when used on alloysteel forgings.

Cast high-speed tool steels are almost never used in broaches. One property of the cast tool materials that prohibits their use in monolithic internal pull broaches is low tensile strength. Most cast alloys that can attain a hardness of Rockwell C 60 or higher do not have ultimate tensile strengths much in excess of 85,000 psi.

SURFACE TREATMENT

There are several practical ways of extending the life of a broach tool. One can be the use of surface treatment, such as nitriding, TICN, TIN, oxidation, or hard chrome plating, to increase the surface hardness and wear resistance of the broaching tool workpiece. The return on the investment of coatings must be evaluated on a case by case basis.

COMMONLY BROACHED MATERIALS

Broaches have been used on almost every material at one time or another - most of the known metals and alloys, some plastics, hard rubber, wood, composites, graphite, and so on. Metals and alloys are, by far, the most commonly broached materials. The products made from the other materials are not usually made to the stringent dimensional tolerances, or in the quantities, that make broaching economical.

In general, any material that can be machined can be broached. And the higher the machinability of the material, the easier it is to broach. In steels, machinability correlates closely with hardness. That is why workpieces with a high surface hardness, such as produced by previous work-hardening or scale, require that the first broach tooth cut beneath the scale or hard surface is possible.

The hardness of the workpiece material also influences the allowable cut per tooth. On harder metals, it is customary to take a relatively fine finishing cut; on softer nonferrous metals, a fine surface finish can be achieved w3ith a heavier finishing cut.

Too heavy a cut, however, will tend to overload the broach tool - no matter what material is being broached. Too fine a cut, on the other hand, tends to interfere with free-cutting action and increases the tendency of the material to glaze, gall, or tear. Smaller steps can be used for finishing than for roughing.

Stainless SteelsStainless steels with hardnesses above Rockwell C 35 can be broached. Stainless harder than this, however, tends to dull broach teeth fairly fast, reducing the number of pieces produced between grinds.

The approximate rise per tooth (round broaches) runs from 0.001 to 0.005 in. This range will cover practically all types of stainless steel. Broaches with hook angles between 12 and 18 usually give the best results. Backoff should be held to a minimum; a 2 angle is preferable, but in no case should it exceed 5. Chipbreakers should be used.

Free-Cutting SteelFree-cutting steel will allow a greater cut per tooth, or step, than will a hard or tough steel. However, a step of 0.0005 in. on a broach diameter is practical minimum. Hook angles also vary with the material being cut as was mentioned previously. They range between 15 and 20 for the soft steels and between 8 and 12 for the hard steels. Backoff angles of 2 to 3 on the roughing teeth, 1 on the semi-finishing teeth, and 0.5 on the finishing teeth give good results when broaching steel. Chipbreakers should be used.

Cast and Malleable IronsCast and malleable irons permit a greater rise per tooth than even the free-machining steel. Brittle materials such as cast iron call for small hook angles, usually around 6 degrees to 8 degrees. Backoff angles are the same as for the general run of steels. Usually, a shorter pitch is permissible in broaching cast irons than in broaching steels because less chip room is required for the irons.

BROACH SHARPNER

Broach sharpner is exclusively used in industry for sharpening various types of broach which are tools for various type of metal removing process like internal gear manufacturing by one pass of broach. The cost of broach is far more than its sharpner due to its unique design and difficult and time consuming manufacturing .

usually aluminium oxide or silicon carbide type grinders are used to re sharp the each single point tool in a broach use is made of fluid ie coolin fluid or cutter oils to reduce the heat formation and for long life of abrasive material which is binded by a binder in the form of a wheel or desired shape depending upon the requirement or profile of the broach .hob is generally made of high speed tool steel .( discussed inn detail below) and in order to impart a long tool life ie more than several times of their bare strength a coating of

TITANIUM NITRIDE is done which has a golden lusture and

excellent cutting abilities and are capable of withstanding in high temperature and and all desired

working condition .

The sharpner has twochucks or self centring ends at the end of bed ways one is fixed and other can be swiveled or tilted at desired position an another attachment is there ehich runs parallel to the bed ways holding a powerful motor on which a clamping mechanism is there to securely hold the tool for grinding or sharpening the broach .

Othe attachment like carriage, apron, overhead light ,start ,stop buttons,speed control and handles are there to finish the job in user friendly mode.

The chucks generally independent four limbs is used to hold the job at desired point is there. The job can be rotate by using centring

Live centre and dead centre hold the job and a powerful motor drive is there to to run the live cenre at desired speed .

During sharpening all the teeth need need not to be grinded as only few gets distorted due to hardness or impurities present in the workpiece

The job is loaded and unloaded with the help of portable cranes and guided to the machine again after re sharpening.

Grinding wheel or ring may be of any of the following type material for easy operation

Choices for coatings include: titanium nitride (TiN), titanium carbonitride (TiCN), titanium aluminum nitride (TiAIN), aluminum oxide (Al2Ox3), chromium nitride (CrN), zirconium nitride (ZrN), and diamond.

   

Gear nomenclature

Common abbreviations o n. Rotational velocity. (Measured, for example, in r.p.m.)

o ω Angular velocity. (Radians per unit time.) (1 r.p.m. = π/30 radians per second.)

o N. Number of teeth.

Path of contact. The path followed by the point of contact between two meshing gear teeth.

Line of action, also called 'Pressure line'. The line along which the force between two meshing gear teeth is directed. It has the same direction as the force vector. In general, the line of action changes from moment to moment during the period of engagement of a pair of teeth. For involute gears, however, the tooth-to-tooth force is always directed along the same line -- that is, the line of action is constant. this implies that for involute gears the path of contact is also a straight line, coincident with the line of action -- as is indeed the case. Further note on tooth force56

Axis. The axis of revolution of the gear; center line of the shaft.

Pitch point (p). The point where the line of action crosses a line joining the two gear axes.

Pitch circle. A circle, centered on and perpendicular to the axis, and passing through the pitch point. Sometimes also called the 'pitch line', although it is a circle.

Pitch diameter (D). Diameter of a pitch circle. Equal to twice the perpendicular distance from the axis to the pitch point. The nominal gear size is usually the pitch diameter.

Operating pitch diameters. The pitch diameters determined from the number of teeth and

the center distance at which gears operate.2 Example for pinion:

Pitch surface. For cylindrical gears, this is the cylinder formed by projecting a pitch circle in the axial direction. More generally, it is the surface formed by the sum of all the pitch circles as one moves along the axis. Eg., for bevel gears it is a cone.

Angle of action. Angle with vertex at the gear center, one leg on the point where mating teeth first make contact, the other leg on the point where they disengage.

Arc of action. The segment of a pitch circle subtended by the angle of action.

Pressure angle (ø). The complement of the angle between the direction that the teeth exert force on each other, and the line joining the centers of the two gears. For involute gears, the teeth always exert force along the line of action, which, for involute gears, is a straight line; and thus, for involute gears, the pressure angle is constant.

Outside diameter (Do). Diameter of the gear, measured from the tops of the teeth.

Root diameter. Diameter of the gear, measured from the base of the tooth space.

Addendum (a). The radial distance from the pitch surface to the outermost point of the tooth. a = (Do - D) / 2.

Dedendum (b). The radial distance from the depth of the tooth trough to the pitch surface. b = (D - root diameter) / 2.

Whole depth (ht). Whole depth (tooth depth) is the total depth of a tooth space, equal to addendum plus dedendum, also equal to working depth plus clearance.2

Clearance. Clearance is the distance between the root circle of a gear and the addendum circle of its mate.2

Working depth. Working depth is the depth of engagement of two gears, that is, the sum of their operating addendums.2

Circular pitch (p). The distance from one face of a tooth to the corresponding face of an adjacent tooth on the same gear, measured along the pitch circle.

Diametral pitch (Pd). The ratio of the number of teeth to the pitch diameter. Eg., could be measured in teeth per inch or teeth per centimeter.

Base circle. Applies only to involute gears, where the tooth profile is the involute of the base circle. The radius of the base circle is somewhat smaller than that of the pitch circle.

Base pitch (pb). Applies only to involute gears. It is the distance from one face of a tooth to the corresponding face of an adjacent tooth on the same gear, measured along the base circle. Sometimes called the 'normal pitch'.

Interference. Contact between teeth other than at the intended parts of their surfaces.

Interchangeable set. A set of gears, any of which will mate properly with any other.

Helical Gears:

o Helix angle (ψ). The angle between a tangent to the helix and the gear axis. Is zero in the limiting case of a spur gear.

o Normal circular pitch (pn). Circular pitch in the plane normal to the teeth.

o Transverse circular pitch (p). Circular pitch in the plane of rotation of the gear. Sometimes just called "circular pitch". pn = p cos(ψ).

o Several other helix parameters can be viewed either in the normal or transverse planes. The subscript " n " usually indicates the normal.

Worm gears:

o Lead. The distance from any point on a thread to the corresponding point on the next turn of the same thread, measured parallel to the axis.

o Linear pitch (p). The distance from any point on a thread to the corresponding point on the adjacent thread, measured parallel to the axis. For a single-thread worm, lead and linear pitch are the same.

o Lead angle (λ). The angle between a tangent to the helix and a plane perpendicular to the axis. Note that it is the complement of the helix angle which isusually given for helical gears.

o Pitch diameter (Dw). Same as described earlier in this list. Note that for a worm it is still measured in a plane perpendicular to the gear axis, not a tilted plane.

Gear Hobbing PROCESS

Gear hobbing is considered to be the most productive and viable of all a generating process. With Gear hobbing process toothed wheels of gears are manufactured with high quality and gives excellent performance.

However, Hobbing is only used to produce spur and worn gears. Internal gears or shoulder gear cannot be worked up in Hobbing process. The hobbing process works like this. The hob is applied for generating the involute teeth. The hob is essentially a cylindrical tool which is positioned straight. In hobbing process the hob as well as the workpiece rotate continuously displaying a rotational relationship. A thread having the similar cross section as that of rack tooth is helically wound around the Hob. The Hob is then subsequently rotated. The gear blank is fed onto the hob based on the depth of cut. The helix pattern of a rotating hob is identical to that of a moving rack. Gear hobbing is an efficient process however it comes with complicated process kinematics, and some how difficult tool wear mechanisms.

Advantages of Gear Hobbing Process

High productivity rate Economical and efficient

operation

Accuracy

Close tolerances

Versatility of operations

Smooth finishes

Gear Hobbing Machines There are different varieties of Gear Hobbing Machines. These machinces are used in effective production of accurate Spur, Helical, Worm Gears, Sprockets etc. These machines are manufactured with certain features such as follows

Gears and shafts of Alloy Steel. Oil reservoirs, to ensure proper lubrication of gears and bearings.

Bed and Column of Close Grain Casting, perfectly ribbed with 'V' type guide ways.

Oil reservoirs provided to ensure through lubrication of gears and bearings.

Indexing Worm Wheel made of high grade Bronze material.

Hobbing Machine Setting for Cutting Spur Gears

First of all, the spindle-bore taper as well as the taper of the arbor are cleaned. Then the arbor is fitted into the spindle and locked against the taper by a drawbolt. The hob is then fitted on the arbor along with spacing collars, and the tailstock bracket is brought in position to support the other end of the arbor. The nut is locked for locking the hob and spacing collars together. The runout of the hob is checked on the proof-diameter. This should be within 0.005 (0.0002’).

The work is then mounted on the table. The method of supporting the work piece on the table varies from job to job. However, this should ensure that the job runs true with the table-axis. In one off or batch production, this can be checked for every piece and corrected.

However for mass production, the fixture and blank manufacture should ensure that this runout is repeatedly maintained piece after piece.

Necessary change gears are mounted to select the proper speed ratio between the hob and the work piece. Hob head is then set according to the helix angle of the hob as shown in Fig. 9.11. Speed of the hob is dependent on the material of the blank (and the hob material).

Depending on the feed requirement, - radial, axial or diagonal – feed is selected. Feed rate is also dependent on the material and whether the hobb is being used for roughing or finishing.Now the table is brought towards the hob so as to have the hob just touching the work piece. The dial on the lead screw for the table drive is set to zero. The machine is started without engaging the feed so that the hob makes light tooth markings on the outside diameter of the blank. These will indicate the number of teeth being cut. If these are equal to the required number of teeth to be cut, selection of change gears is correct. Now the feed is engaged. The table is fed to the distance equal to the depth of the tooth. After this setting and cutting the gear, the tooth thickness is measured. To thin the tooth further, if required, the table may be further fed.