Cycloidal tooth profile

What is cycloid?

The cycloid is defined as the locus of a point on the circumference of a circle that rolls without slipping on a fixed straight line.
In this type, the faces of the teeth are epicycloids and the flanks are the hypocycloids. 

Now one question arises in your mind that what is epicycloids and hypocycloids? Let we check 

What is epicycloid?
An epicycloid is the locus of a point on the circumference of a circle that rolls without slipping on the circumference of another circle. 

What is hypocycloid?
A hypocycloid is the locus of a point on the circumference of a circle that rolls without slipping inside the circumference of another circle. 

Formation of cycloidal tooth :

A circle O₁ rolls inside another circle APB is called pitch circle. At the start, the point of contact of the two circles is at A. As the circle O₁ rolls inside the pitch circle, the locus of the point A on the circle O₁ traces the path ALP which is called hypocycloid. A small portion of this curve near the pith circle is used for the flank of the tooth.  

The line joining the generating point A with the point of contact of the two circles is normal to the hypocycloid when the circle O₁ touches the pitch circle at D, the point A is at C and CD is normal to the hypocycloid ALP. 

In the same way, if the circle O₂ rolls outside the pitch circle, starting from P, an epicycloid PFB is obtained.

A small portion of the curve near the pitch circle is used for the face of the tooth also. 

Some key points :

• The path of approach is equal to the arc of approach. 
• The path of contact is equal to the arc of contact. 
• In case of cycloidal teeth, the pressure angle varies from the maximum at the beginning of the engagement to zero when the point of contact coincides with pitch point and then again increased to a maximum in the reverse direction. 
• Since cycloidal teeth are made up of the two curves, it is very difficult to produce accurate profiles. This has rendered this system obsolete. 

Forms of tooth

Types of tooth :

Two curves of any shape that fulfil the law of gearing can be used as the profiles of teeth. 

In other words, an arbitrary shape of one of the mating teeth can be taken and applying the law of gearing the shape of the other can be determined. Such gear is said to have conjugate teeth. 

However, it will be very difficult to manufacture such gears and the cost will be high. It will be very difficult to replace them with the available gears. Thus, arises the need to standardize gear tooth. 

Common forms of teeth that also satisfy the law of gearing are the following :

• Cycloidal tooth profile
• Involute tooth profile  

Contact ratio of gears

Arc of contact :

The distance travelled by a point on either pitch circle of the two wheels during the period of contact of a pair of teeth is called the arc of contact. 

It is the length of the pitch circle traversed by a point on it during the mating of a pair of teeth. 

Thus, all teeth laying in between the arc of contact will be meshing with the teeth on the other wheel. 

Number of teeth in contact n = Arc of contact / Circular pitch 

As we mentioned above the ratio of the arc of contact to the circular pitch is also the contact ratio, the number of teeth is also expressed in terms of contact ratio. 

For continuous transmission of motion, at least one tooth of one wheel must be in contact with another tooth of the second wheel. Therefore, n must be greater than unity.

If n lies between 1 and 2, the number of teeth in contact at any time will not be less than one and never more than two. 

If n is between 2 and 3, it is never less than pairs of teeth and not more than three pairs, and so on. 

If n is 1.6, one pair of teeth are always in contact whereas two pairs of teeth are in contact for 60% of the time. 

Introduction of gears

Gears are used to transmit motion from one shaft to another or between a shaft and a slide. This is done by successively engaging the teeth. 

Gears use no intermediate link or connector and transmit the motion by direct contact. 

The two bodies have either a rolling or sliding motion. Motion is along with the tangent at the point of contact. No motion is possible along the common normal as that will either break the contact or one body will tend to penetrate into the other.  

To transmit a definite motion of one disc to the other or to prevent slip between the surfaces, projections and recesses on the two-disc can be made which can mesh with each other. This leads to the formation of teeth on the discs and the motion between the surfaces changes from rolling to sliding. The discs with teeth are known as gears or gear wheels. 

Final year project ideas for mechanical engineering

What is a project?

An individual or collaborative enterprise that is carefully planned to achieve a particular aim is called project.

Final year project is more important for students so let we discuss here how to do a good project easily for mechanical engineering students and get a good grade.

My point of view :

When you select the project title or project work for final year students you don't have sufficient time for project particularity. You will find time for that from your academic study. so I will give the advice to select easy and some creative project that will make more impact and completed in time. 

The second thing is that there are many choices for a final year project. It has mainly two category project one is purely based upon research and the second one is to make any small working model. For my point of view all students first think about to make a model but at last very few ends with clearly working model. I don't ask to choose that one but if you choose about the model you will work smart and a little bit of effort will also take. In the case of a research-based project, you have to research on a particular side like upon any material or corrosion-related research for that your work is mainly based on pen paper. You will check the research paper then make literature and then some testing upon that particular research material or component. 

Now we will see some project title that will make a good idea about selecting your project :

Model projects :

Example :

• Auto turning fuel valve
• Anti-theft wheel locking system  
• Solar power air conditioning 

Above some example, you can select any model making project according to your project guide. It seems easy to difficult whatever you want to select. 

Research Projects :

Example :

• Corrosion behaviours of material and prevention
• Pollution related research 

Like we mentioned above you can select any research topic and make a good project with minimum effort. 

Involute gear Vs Cycloidal gear

The involute tooth profile is generally used almost everywhere and given preference over cycloidal tooth profile. First, you should know what is involute and cycloidal gear tooth profile?

What is involute gear? 

All the gear teeth have a top flat portion and two side curves. The side curves for the involute gears are in the form of the involute curve of the circle. 

It can be generated by the locus of an endpoint of an imaginary taut string unwinding from the circle.

What is cycloidal gear?

The cycloidal is a curve generated by a locus of any point on a circle which is rolling around another circle gears whose teeth profile is made of cycloidal curves is called cycloidal gears. 

The produced curve is called epicycloid if the second circle rolls outside the first circle. 

The produced curve is called hypocycloid If the second circle rolls inside the first circle.

Let us have a deep insight into the difference between involute and cycloidal gear. 

Involute gear :

• Pressure angle remains constant throughout the operation this leads to smooth-running operation of the gears. 
• It involves a single curve for the teeth resulting in simplicity of manufacturing.
• Teeth have radial flanks thus are weaker. 
• It is simple to manufacture due to the convex surface and thus are cheaper. 
• The velocity ratio is not affected by a little variation in the centre distance.
• Interference takes place.
• Due to two convex surfaces are in contact, more wear and tear takes place.
• Line of action is straight. 
• Suitable for motion as well as power transmission. 

Cycloidal gear :

• Pressure angle keeps on changing varies from a maximum at the beginning, reduced to zero at the pitch point and again increases to maximum this result leads to less smooth-running operation of the gears.
• It involves a double curve for the teeth resulting in the complication in manufacturing.
• Teeth have spreading flanks thus are stronger.
• It is difficult to manufacture due to the requirement of hypocycloid and epicycloid and thus are costlier. 
• To transmit a constant velocity ratio, an exact centre distance is needed.
• There is no interference.
• Due to concave surfaces are in contact, less wear and tear takes place.
• Line of action is curve. 
• Suitable for motion transmission only. 

What is rope drive

The rope drive is widely used where a large amount of power is to be transmitted. For power transmission by rope, grooved pulleys are used. 

The rope drives use the following two types of ropes :

• Fibre ropes 
• Wire ropes 

The rope is gripped on its sides as it bends down in the groove reducing the chances of slipping. Pulleys with several grooves can also be employed to increase the capacity of power transmission. 

These may be connected in the two ways following below :

• Using a continuous rope passing from one pulley to the other and back again to the same pulley in the next groove, and so on. 
• Using one rope for each pair of grooves.

Number of rope required = Total power transmitted / Power transmitted per rope 

Rope drives are, usually, preferred for long centre distances between the shafts.

Rope drive are cheaper as compared to belt drive.

Difference between heat exchanger and condenser

A condenser is a device which converts vapour into the liquid state whereas a heat exchanger is a device which is used for heat recovery also to transfer heat from two fluids.

Let us have a deep insight into the difference between the heat exchanger and condenser.

Difference : 

• Heat exchanger only heat is transferred without phase change and heat is transferred along with the phase change in the condenser. 
• A heat exchanger is one that extracts heat from one liquid and gives that heat to another liquid which is enclosed whereas condenser is also a heat exchanger in which phase transfer occurs for hot liquid while maintaining the same temperature and at the same time the cold liquid gets heated up. 

What does HVAC stand for

Full form of HVAC is Heating Ventilation and Air Conditioning.

HVAC can stand for a climate-control mechanism for providing thermal comfort and acceptable indoor air quality and regulate the humidity and temperature in a living environment.

It is a sub-discipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, heat transfer and sometimes refrigeration and air conditioning. 

This technology is used for indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality.

There are three types of setting done in HVAC :

Full Heat Setting :

Maximum airflow is directed through the heater core by the blend door to deliver the most heat possible to the main upper vents. 

So in this setting operator has demanded full heat.

Economy Mode Setting :

Maximum airflow is directed around the heater core to allow filtered air at ambient temperature to enter the cabin through the main upper vents. 

Max A/C Setting :

In this setting, the HVAC system takes air from the cabin that has already been cooled once and cools it again instead of trying to cool hot ambient air.

To get the most cooling power in this setting the operator has selected max A/C.

What is slotting machine

The slotting machine was developed by Brunel in the year 1800 much earlier than a shaper was invented. It falls under the category of the reciprocating type of machine tool similar to a shaper or a planer. Both are operated almost on the same principle but the major difference between them is in a slotter the ram holding the tool reciprocates in a vertical axis, whereas in a shaper the ram holding the tool reciprocates in horizontal axes. 

What is slotting machine?

Slotting machine is vertically reciprocating machine tool used for making a mortise or shaping the sides of an aperture, in which ram holding the tool reciprocates in a vertical axis and the cutting action of the tool is only during the return downward stoke.

The slotting machine is used for cutting grooves, keyways and slots of :

• Various shapes
• For making regular and irregular surfaces both internal and external. 

It is also used for handling large and awkward workpieces, for cutting internal and external gears and many other operations which can't be conventionally machined in any other machine tools.

Types of slotter machine :

There are mainly two types of slotter machine :

• Puncher slotter
• Precision slotter 

Puncher slotter :

It is heavy, a rigid machine designed for removal of a large amount of metal from large forging or casting. 

The length of puncher slotter is large it may be as long as 1800 to 2000 mm. 

In this machine puncher slotter, ram is usually driven by a spiral pinion meshing with the rack teeth cut on the underside of ram. The pinion is driven by a variable speed reversible electric motor similar to that of a planer. 

In this machine, feed is also controlled by electrical gear. 

Precision slotter :

It is a lighter machine and is operated at high speeds.

This machine is designed to take light cuts giving an accurate finish. 

By using special jigs, the machine can handle a number of identical works on a production basis. 

This machine is also used for general-purpose work and is usually fitted with a whitworth quick return mechanism. 

Parts of slotter machine :

• Base 
• Column 
• Saddle 
• Cross-slide 
• Rotating table 
• Ram and tool head assembly 
• Ram drive mechanism 
• Feed mechanism 

Now we can see parts in details :

Base or bed :

The base is rigidly and it takes up all the cutting forces and entire load of the machine. 

It is the key parts of the machine that made from cast iron. 

The top of the bed is accurately finished to provide guideways on which the saddle is mounted. The guideways are perpendicular to the column face. 

Column : 

The column is the vertical member which is made up of cast iron. 

The column is assembled with the base and houses driving mechanism of the ram and feeding mechanism. 

The vertical front face of the column is accurately finished for providing ways in which the ram reciprocates up and down. 

Saddle :

The saddle is mounted upon the guideways and may be moved towards or away from the column either by power or manual control to supply longitudinal feed to the work. 

The top face of the saddle is accurately finished to provide guidance for the cross-slide. These guideways are perpendicular to the guideways on the base. 

Cross-slide : 

The cross slide is mounted upon the guideways of the saddle and may be moved parallel to the base of the column.

The movement of the slide may be controlled either by hand or power to supply crossfeed. 

The circular worktable is mounted on the top of the cross-slide.  

Handwheels :

It is provided for rotating the table for the longitudinal and cross traverse.

Rotary table : 

The rotary table is a circular table which is mounted on the top of the cross slide. 

The table may be rotated by rotating a worm which meshes with a worm gear connected to the underside of the table. 

The rotation of the table may be affected either by hand or power. 

The rotary table enables a circular or contoured surface to be generated on the work piece. 

Ram and tool head assembly : 

The run is reciprocating member of the machine mounted on the guideways of the column. 

It supports the tools at its bottom end on a tool head. 

A Slot is cut on the body of the ram for changing the position of the stock. 

In some mechanism, a special type of tool holders is provided to relieve the tool during the return stroke. 

Ram drive mechanism : 

A slotter removes metal during the downward cutting stroke. No metal removed during the upward return stroke.

The usual types of ram drive mechanisms are :

• Whitworth quick return mechanism
• Variable speed reversible motor drive mechanism
• Hydraulic drive mechanism 

The operation performed on slotter machine :

• Machining internal and external flat surfaces.
• Internal recess of circular, semi-circular, concave and convex surfaces.
• Machining internal and external circular surfaces.
• Internal machining of blind holes.
• For shaping internal and external forms or profiles.
• Machining vertical, angular or inclined surfaces.
• Machining irregular surface which is difficult to produce.
• For machining dies and punches.
• To cut slots, grooves, splines and keyways for both internal and external surfaces.
• Machining internal and external gear teeth. 

Cutting speed :

The rate at which the metal is removed during downward cutting stroke is called cutting speed.

It is expressed in meters / minute. 

Depth of cut :

The perpendicular distance measured between the machined surface and the un-machined surface called the depth of cut.

It is expressed in mm. 

Feed :

The movement of the work per double stroke is called feed.

It is expressed in mm.

Cutting speed feed and depth of cut of slotter machine

Cutting speed :

The rate at which the metal is removed during downward cutting stroke is called cutting speed.
It is expressed in meters/minute. 

Feed :

A feed is the movement of the work per double stroke. 
It is expressed in mm.

Depth of cut :

Depth of cut is a perpendicular distance measured between the machined surface and un-machined surface also.
It is expressed in mm. 

Slotting machine operation

There is a different operation performed on the slotting machine because this operation is more economical for certain types of work. 

Let us see the different operation performed on the slotter machine :

• Machining internal and external flat surfaces.
• Internal recess of circular, semi-circular, concave and convex surfaces.
• Machining internal and external circular surfaces.
• Internal machining of blind holes.
• For shaping internal and external forms or profiles.
• Machining vertical, angular or inclined surfaces.
• Machining irregular surface which is difficult to produce.
• For machining dies and punches.
• To cut slots, grooves, splines and keyways for both internal and external surfaces.
• Machining internal and external gear teeth. 

Slotting machine parts

In this article you can see some different parts of a slotting machine which are following below :

• Base 
• Column 
• Saddle 
• Cross-slide 
• Rotating table 
• Ram and tool head assembly 
• Ram drive mechanism 
• Feed mechanism 

Now we can see parts in details :

Base or bed :

The base is rigidly built to take up all the cutting forces and the entire load of the machine. 

It is the key parts of the machine that made from cast iron. 

The top of the bed is accurately finished to provide guideways on which the saddle is mounted. The guideways are perpendicular to the column face. 

Column : 

The column is the vertical member which is made up of cast iron. 

The column is assembled with the base and houses driving mechanism of the ram and feeding mechanism. 

The vertical front face of the column is accurately finished for providing ways in which the ram reciprocates up and down. 

Saddle :

The saddle is mounted upon the guideways and may be moved towards or away from the column either by power or manual control to supply longitudinal feed to the work. 

The top face of the saddle is accurately finished to provide guidance for the cross-slide. These guideways are perpendicular to the guideways on the base. 

Cross-slide : 

The cross slide is mounted upon the guideways of the saddle and maybe moved parallel to the base of the column.

The movement of the slide may be controlled either by hand or power to supply crossfeed. 

The circular worktable is mounted on the top of the cross-slide.  

Handwheels :

It is provided for rotating the table for the longitudinal and cross traverse.

Rotary table : 

The rotary table is a circular table which is mounted on the top of the cross slide. 

The table may be rotated by rotating a worm which meshes with a worm gear connected to the underside of the table. 

The rotation of the table may be affected either by hand or power. 

The rotary table enables a circular or contoured surface to be generated on the work piece. 

Ram and tool head assembly : 

The run is a reciprocating member of the machine mounted on the guideways of the column. 

It supports the tools at its bottom end on a tool head. 

A Slot is cut on the body of the ram for changing the position of the stock. 

In some mechanism, a special type of tool holders is provided to relieve the tool during the return stroke. 

Ram drive mechanism : 

A slotter removes metal during downward cutting stroke only whereas during upward return stroke no metal is removed. 

The usual types of ram drive mechanisms are :

• Whitworth quick return mechanism
• Variable speed reversible motor drive mechanism
• Hydraulic drive mechanism 

Types of slotting machine

There are mainly two types of slotting machine :

• Puncher slotter
• Precision slotter 

Puncher slotter :

It is a heavy, rigid machine designed for removal of a large amount of metal from large forging or casting. 

The length of puncher slotter is large it may be as long as 1800 to 2000 mm. 

In this machine puncher slotter, ram is usually driven by a spiral pinion meshing with the rack teeth cut on the underside of ram. The pinion is driven by a variable speed reversible electric motor similar to that of a planer. 

In this machine, feed is also controlled by electrical gear. 

Precision slotter :

It is a lighter machine and is operated at high speeds.

This machine is designed to take light cuts giving an accurate finish. 

By using special jigs, the machine can handle a number of identical works on a production basis. 

This machine is also used for general-purpose work and is usually fitted with a whitworth quick return mechanism. 

Advantages and disadvantages of friction welding

Friction welding works on the basic principle of friction is used to generate heat at the interference surface this heat is used to join two workpieces by applying external pressure at the surface of the workpiece. The joint is created in this welding is due to thermomechanical treatment. The main advantage of friction welding is the ease with which the joining can take place. Now, let us have a deep insight into the pros and cons of friction welding. 

Advantages of friction welding :

• Oxides and contaminants present would easily be removed during the initial rubbing so that edge cleaning is not a problem.
• Since the joining takes place by diffusion rather than by actual melting, even dissimilar metals can be joined. 
• The heat generated is small and below the melting temperature, there will be no distortion and warping.
• The quality of weld achieved is very high.
• High welding speed.
• Economical in other welding operation.
• No skilled operator is required to work on the friction welding machine since it is completely automatic in operation.
• No possibility of porosity and slag inclusion.
• It is an environmentally friendly process since there is no fumes, gases or smoke is generated.
• No flux, filler metal or gas is required to perform this process.
• No special power supply is required.
• Wide variety of metal can be weld by this process.

Disadvantages of friction welding : 

• This process used for only round bars of the same cross-section. 
• Limited to angular and flat butt joints. 
• Set-up cost is very high. 
• Preparation of workpiece is difficult. 
• Non-forgeable materiel can not be weld.
• It can only be used for smaller parts of machines, big parts are not compatible with it. 

Advantages and disadvantages of projection welding

Projection welding is also called as resistance welding produces coalescence of welding material, the heat generated from electric resistance to current through the workpiece hold together with pressure applied to electrodes. Let us have a deep insight into the pros and cons of projection welding in this article. 

Advantages of projection welding :

• It is possible to weld more than one spot at a given time. The number of welds depends on the number of projections that can come under the tip of the electrode. Up to about 6 welds per cycle can be made which substantially reduces the cost of manufacture.
• The welds may be placed closer than possible in spot welding.
• Because of the large-sized electrodes used, their life is much longer than that of the spot welding electrode. The larger contact area makes for very limited deformation of the welding tip.
• They can help in holding the workpieces together in proper alignment during the welding process.
• Proper heat balance can be easily obtained in projection welding by making the projections in thicker plates while welding sheets of different thickness. 
• For welding dissimilar metals, the projections are to be made on the material having higher electrical conductivity to provide proper heat balance.
• The uniformity and appearance of the weld are much better compared to spot welding.

Disadvantages of projection welding :

• Prior operation of embossing is required before welding.
• Electrodes are often to be specially made for a particular operation. This can only be justified when production rates and volumes are large. 

Atomic hydrogen welding

Introduction :

Atomic hydrogen welding is an arc welding process. In this process the arc used in between two tungsten electrodes in a shielding atmosphere of hydrogen. This process was invented by Irving Langmuir in the course of his studies of atomic hydrogen. When Hydrogen is in its atomic state, is a strong reducing gas which prevents oxidation of weld metal and rapid burning of electrodes. Any oxygen present in the surrounding combines with hydrogen forming water which is converted into steam.

Equipment set up :

Set up of this operation consist of hydrogen cylinder, an AC welding machine and the welding torch to accommodate to tungsten electrons, with provision for changing the distance between them. The normal voltage range of the power supply is between 50 to 75 volt with the current varying from 15 to 150 A. This measure is good enough for an electrode size of 1 to 5 mm.

The path of electron travel between the two electrodes is not a straight path as in other arc welding process. Instead, they travel in the form of a fan. This is because the hydrogen atoms formed by the arc causes a downward force because of with electron flow slightly deviates. This fan shape can be changed by altering the distance between the electrodes and the current level. The DC machines could also be used in atomic hydrogen welding, but because of the electron flow is only in one direction, the wear of electron is particularly high and as a result, only AC power supply is used.

When hydrogen atoms recombine near the workpiece surface, they generate a temperature of the order of the 300 0C. Because of this heat, the molten metal becomes highly fluid and therefore, atomic hydrogen welding is used for the flat position only. Filler metal when needed is melted intermittently in the arc fan for fusing with the base metal.

Working principle :

Atomic hydrogen welding the atomic hydrogen welding is an inert gas welding arc welding process done with non-consumable electrodes. The main difference between tungsten inert gas welding and this process is that in atomic hydrogen welding, the arc is obtained between the two tungsten electrodes rather than between the tungsten electrode and the workpiece. This shielding gas used here is hydrogen, which is reactive in nature compared to argon. The hydrogen molecule (H₂), when passing through the electric arc, get this dissociated into two hydrogen atoms (H+). The hydrogen atoms are highly reactive. They form hydrogen molecule and combine with oxygen if present to form water vapour enters release intense heat for the necessary melting of the joint. Because of its type reactivity, the atomic hydrogen is able to break the oxide on the base metal and thus allow the formation of a clean weld. 

Application :

When properly performed, atomic hydrogen welding gives an extremely clean weld with excellent quality. It is generally used for welding of tool Steels containing tungsten, Nickel and Molybdenum as also for hard surfacing and repairing of moulds, dies and tools. Though it can be used for any job, its high cost prohibits its general usage.

Oxy hydrogen welding

Working principle :

In oxy-hydrogen welding, hydrogen combines with oxygen to generate steam and attains a flame temperature of around 2800⁰C. But the weld pool is not protected from the atmosphere when the oxygen for combustion is completely provided by the torch itself. So, Oxygen is an amount slightly less than that required for complete combustion is provided by the torch, whereas atmospheric oxygen accounts for the burning of the remaining hydrogen. This gives rise to a protective preheating flame that surrounds the main flame. But this reduces the flame temperature to some extent. Because of the lower flame temperature, oxy-hydrogen welding is a generally slow process. It is normally used to weld thin sheets of steels and alloys with low melting temperatures.

Key features :

• Operation is convenient & safe

Oxy hydrogen generator produces oxygen and hydrogen gas that you required and also no gas cylinder is required. There is no risk of explosion.

• Environmental friendly 

In this process, fuel comes from water and there is water vapour after finishing this process so this process is environmentally friendly.

• Welding features 

Welding work is fast, precision, smooth and beautiful welding spot. The oxyhydrogen flame is concentrated up to 2800 ⁰C so it can heat the welding spot to melting point very quickly.

• Energy-saving and low cost 

This process is done with very low electricity and pure water. The cost of electricity and water is reduced by more than 40% compared with LPG and other welding processes.