Mechanical Engineer

What is the Mechanical Engineer

Mechanical engineering is a broad field of engineering that involves the use of physical principles for analysis, design, manufacture and maintenance of mechanical systems. Traditionally, it has been the branch of engineering that through the application of physical principles has enabled the creation of useful devices, as tools and machines.

Mechanical engineers use principles such as heat, force and the conservation of mass and energy to analyze static and dynamic physical systems, helping to design objects. Mechanical Engineering is the branch of machinery, equipment and facilities bearing in mind ecological and economic aspects for the benefit of society. To do their job, mechanical engineering analyze needs, formulate and solve technical problems through an interdisciplinary, and relies on scientific developments, translating into elements, machines, equipment and facilities to provide adequate service through the rational use and efficient use of available resources.

Engineering is dedicated to designing, building, negotiation and component maintenance. It required new devices with complex functions in the movement or that withstand large forces, so it was necessary that this new discipline to study the movement and balance. It was also necessary to find a new way of running the machines as originally used by human or animal power. The use of machines that run on energy from the steam, coal, gas and electricity brought great progress.

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Mechatronics

Mechatronics is a word originated in Japan in 1980s to denote the combination of technologies which go together to produce industrial robots.

A formal definition of Mechatronics is “the synergistic integration of Mechanics and Mechanical Engineering, Electronics, Computer technology, and IT to produce or enhance products and systems.’’

The various fields that make up Mechatronics is shown in Fig

Examples of such systems are

• Computers,
• Disk drives,
• Photocopiers,
• Fax machines,
• VCR,
• Washing machines,
• CNC machine tools,
• Robots, etc.

Today’s modern cars are also mechatronics product with the usage of electronic engine management system, collision detection, global positioning system, and others..

The concept of mechatronics is very important today to meet the customers’ ever increasing demands and still remain competitive in the global market. Very often a mechanical engineer without the mechatronics background is considered equivalent to a mechanical engineer without the engineering drawing knowledge.

Mechatronics requires thinking products and processes so transverse. Mechatronics is "burst the walls, with a steering matrix. The pilot at the highest level of the enterprise is essential in this context, to afford in front needs to be implemented.

The design should no longer be sequentially: the mechatronics approach requires thinking about the product as a whole (all skill areas at a time) and not by separating the mechanical part, then electronics, then the sensor – actuators and computers at risk to achieve additional cost prohibitive.

The project manager must master the various areas and not be an expert in one of mechatronics technology: It was necessary to avoid watching the draft with an eye mechanics or electronics. The pilot is here, as elsewhere, the role of a conductor, not a virtuoso.

The phases of integration are sensitive, such that an electronic assembly in a machine shop (or vice versa). There are telescoping and areas of project management and competence, which involves work that is done jointly, to ultimately obtain not a purely mechanical or purely electronic, but a set that combines the advantages of 2, which can not be separated.

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Sintering / Green Compact / Diffusing

The operation of heating the green compact at high temperature in a controlled atmosphere (Reducing atmosphere which protects oxidation of metal powders). The Sintering increases the bond between the particles and therefore strengthens a powder metal compact. Sintering temperature and time of sintering depends on the type of powders and the strength required in a final product. The Sintering temperatures usually 0.6 to 0.8 times the melting point of powders.

Type of powder                                   Sintering Temperature                 Time
Aluminium & Alloys                                   370 – 520 C                                  24 hrs
Copper, Brass, Bronze                                700 – 900 C                                  30 Mins
Iron                                                           1025 – 1200 C                              30 Mins
Stainless Steel                                           1180 C                                       20 – 40 Mins
Tungsten Carbide                                      1480 C                                      20 – 40 Mins   

Spark Sintering:
 

The process of simultaneous pressing & Sintering of metal powders by high energy electric spark. This spark is discharged from capacitor bank & removes the surface contaminants from powder particles. This cause the particles to form a solid cohesive mass. Immediately after spark, the current is continued for about 10 Seconds, with high temperature which further strengthens the bond used for sintering Aluminium, Copper, Iron and Stainless Steel.

 

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Methods of Compacting / Powder Metallurgy

Methods are:

1. Pressing
2. Centrifugal Casting
3. Slip Casting
4. Extruding
5. Gravity Casting
6. Rolling
7. Iso-static Moulding
8. Explosive Compacting
9. Fibre Metal processes

Pressing:
The function principles of the mechanic press machines differ in how to ensure the upper punch main movement by cams, spindles and friction drives, eccentric, knuckle-joints or by the round table principle, independent if the die or lower punch movement is realized by cams  or eccentric systems or other mechanically or hydraulically combined systems. The executions of auxiliary movements are also not decisive for a term-classification. These auxiliary movements can also base on pneumatic and hydraulic principles. In comparison to hydraulic press machines the maximum compaction forces of mechanical powder presses are limited and are placed in the range </= 5000 kN. For the requirements of wet and dry pressing techniques in the field of Technical Ceramics cams, eccentric, knuckle joint as well as round table presses have proved and tested, whereas cam presses especially used for wet-press-techniques of pourable materials. The range of compaction force of mechanical presses for products of the Technical Ceramics is < 2500 kN, what is caused from the less density of the ceramic materials. Normally the upper punch, lower punch and die systems of mechanical presses don’t work on base of multi subdivided punches.



Centrifugal Casting:
It employed for compacting heavy metal powders such as Tungsten Carbide. The powder is twirled in a mould and packed uniformly with pressures up to 3 MPa. The uniform density is obtained as a result of centrifugal force, acting on each particle of powder.

 


Slip Casting:
Green compact of metal powder may be obtained by slip casting. The slurry, consisting of metal powder is poured in to porous mould. the free liquid in a slurry is absorbed by the mould tearing the solid layer of material on the surface of mould. The mould may be vibrated to increase the density of component. The Components are dried and sintered to provide sufficient strength.



Extruding:
It employed to produce the components with high density and excellent mechanical properties.
Both hot and cold extrusion processes are used for compacting special materials. In cold extrusion the powder is mixed with binder and the mixture is often compressed into billet before being extruded. The binder must be removed before or during sintering. In hot extrusion the powder is compacted in to billet and is then heated to extruding temperature in non oxidizing atmosphere.



Gravity Casting:
It used for making sheets having controlled porosity, the powder is poured on a ceramic tray to form a uniform layer and then sintered up to 48 hrs in Ammonia Gas at high temperature. The sheets are then rolled to desired thickness and to obtain a better surface finish. Porous sheets of stainless steel, made by this process are used for filters.

 


Rolling:
It employed for making continuous strips and rods having controlled porosity with uniform mechanical properties. In this method the metal powder is feed in to two rolls, which compress and interlock the powder particles to form a sheet of sufficient strength. It is then sintered, re-rolled and heat treated if necessary. Metal powders which can be compacted in to strips include Copper, Brass, Bronze, Nickel, Monel and Stainless Steel.



Iso Static Moulding:
It used to obtain the products having uniform density and uniform strength in all directions. metal powder is placed in elastic mould (Deformable Mould) which is subjected to Gas pressure (65 to 650 MPa). After pressing the compact is removed.



Explosive Compacting:
It employed for pressing hard particles. The metal powder are placed in water proof bags which are immersed in water. It contained in a cylinder having wall thickness. Due to sudden deformation of change at the end of cylinder the pressure in the cylinder increases. The pressure used to press the metal powders to form green compact.



Fibre Metal Processes:
In this process, the metal fibers (Fine wires of Convenient length) are mixed with a liquid slurry and poured over a porous bottom. The liquid is drawed off leaving the green mat of fibre. The mat in which the fibers are randomly distributed is pressed and sintered. The products are mainly used for Filters, Battery Plates and Damping’s.

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Powder Metallurgy

Definition:
The Process of producing components from metallic powder parts made by powder metallurgy may contain non-metallic constituents to improve the bonding qualities and properties.
Number and variety of products made by powder metallurgy are continuously increasing:

1. Tungsten Filaments for Lamps
2. Contact Point relays
3. Self lubricating bearings
4. Cemented carbides for cutting tools etc.

Characters of Metal Powders:

• Shape:

It is influenced by the way it’s made. The shape may be spherical (atomization) (Electrolysis) flat or angular (Mechanical crushing). The particle shape influences the flow characteristics of powders.

• Particle Size (Fineness) and size distribution:

Particle Size and Distribution are important factors which controls the porosity, Compressibility and amount of shrinkage. Proper particle size and size distribution are determined by passing the powder through a standard sieves ranging from 45 to 150 micrometer mesh.

• Flowability:

The ability of the powders to flow readily and conform to the mould cavity. The flow rate helps to determine to possible production rate.

• Compressibility:

It’s defines as the volume of initial powder (Powder loosely filled in cavity) to the volume of compact part. Depends on particle shape & size distribution.

• Apparent Density:

The Apparent density depends on particle size is defined as the ratio of volume to weight of loosely filled mixture.

• Green strength:

It refer to strength of a compact part prior to sintering. It depends on compressibility and helps to handle the parts during the mass production.

• Purity:

Impurities affects sintering & Compacting Oxides & Gaseous impurities can be removed from the part during sintering by the use of a reducing atmosphere.

• Sintering ability:

It is the ability which promotes bonding of particles by the application of heat.

Powder Metallurgy Process steps:






 
Manufacture of Metal Powders:
Methods:

• Mechanical pulverization:

Machining, Drilling or Grinding of metals is used to convert them to powders.

• Machining:

It Produces coarse particles (Flack form) especially Magnesium powders.

• Milling or Grinding:

It suitable for brittle materials.

• Shorting:

The process of dropping molten metal through a Sieve or small orifice in to water. This produces Spherical particles or larger size. Commonly used for metals of low melting point.
 

• Atomizing:

In this molten metal is forced through a nozzle, and a stream of compressed air, stream or Inert gas is directed on it break up into five particles. Powders obtained in irregular in shapes. Atomization commonly used for aluminium, Zinc, Tin, Cadmium and other metals of low melting point.

• Electrolytic deposition:

It’s used mainly for producing iron and copper powders. These are dense structure with low apparent density. It consists of depositing metal on cathode plate by conventional electrolysis processes. The Cathode paltes are removed and the deposited powder is scraped off. The powder is wasted, dried, screened & oversized particles are milled or ground for fineness. The powder is further subjected to heat treatment to remove the work hardening effect.

• Chemical reduction:

It’s used for producing iron, Copper, Tungsten, Molybdenum, Nickel & Cobalt powder process consists of reducing the metal oxides by means of carbon monoxide or Hydrogen. After reduction, the powder is usually ground & Sized.

Forming to shape:

1. The process of mixing the powders is called Blending.
2. The Loose powders are formed in to shape by compacting.

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Steering Systems - Hydraulic Power Steering Systems - Steering Wheel Parts

STEERING

The steering system in a vehicle is used to move the vehicle in a particular direction. This is a very important sub-system in a car without which it would be impossible for a vehicle to follow its desired path. The steering system can be used to steer all kinds of vehicles like cars, trucks, buses, trains, tanks etc.

The conventional steering system consisted of turning the front wheels in the desired direction. But now we have four wheel steering system mostly used in heavy vehicles, to reduce the turning radius, rear wheel steering system, differential steering system etc.

The basic components of any steering system are:-

                   1. Steering column

                   2. Steering box

                   3. Tie rods

                   4. Steering arms

The main geometry followed in steering is ACKERMANN STEERING GEOMETRY. It shows that while negotiating a curve, the inner wheel needs to follow a smaller path as compared to the outer wheel. This results in different steering angles for the respective tires.

STEERING RATIO is defined as the ratio of the turn of the steering wheel to the corresponding turn of the wheels, both which are measured in degrees. It plays an important role in determining the ease of steering. A higher ratio would mean that a large number of turns of the steering wheel is required to negotiate a small turn. A lower ratio would enable better handling. Sports cars usually have lower ratio while heavier vehicles have a higher steering ratio.

The Different types of steering systems are:-

                    1. Rack and pinion steering system

                    2. Recirculating Ball steering system

                    3. Power Steering

The Rack and Pinion steering system is the most common system found mostly in modern vehicles. It employs a simple mechanism. The parts of this system are steering column, pinion gear, rack gear, tie rods, kingpin. The circular motion of the steering wheel is transmitted to the pinion gear through the steering column and universal joint. The pinion is meshed with a rack which translates the circular motion into linear motion thus providing the necessary change in direction. It also provides a gear reduction, thus making it easier to turn the wheels. This system is preferred because of its compactness, efficiency, ease of operation. But at the same time it gets easily damaged on impact.

 

The Recirculation Ball steering system is employed in SUV’s and trucks. It uses a slightly different principle than the rack and pinion system. Here the motion is translated with the help of a recirculating ball gearbox, pitman arm and a track rod. It can transfer higher forces. But it is heavier and costlier than the rack and pinion system.

The Power steering system employs either one of the above systems and in addition has a hydraulic or electrical system connected to make it easier to steer. This helps in better control of the vehicle.

Other systems like steer-by-wire systems, drive-by-wire systems also exist, but they are not commercially used as of now but are most likely to replace the modern day steering systems in the future.

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Engine Speed Governors - Speed Control Governor - Speed Limiters

The governor is a device which is used to controlling the speed of an engine based on the load requirements. Basic governors sense speed and sometimes load of a prime mover and adjust the energy source to maintain the desired level. So it’s simply mentioned as a device giving automatic control (either pressure or temperature) or limitation of speed.

 

The governors are control mechanisms and they work on the principle of feedback control. Their basic function is to control the speed within limits when load on the prime mover changes. They have no control over the change in speed (flywheel determines change in speed i.e. speed control) within the cycle.

Take an example:

Assume a driver running a car in hill station, at that time engine load increases, and automatically vehicle speed decreases. Now the actual speed is less than desired speed. So driver increases the fuel to achieve the desired speed. So here, the driver is a governor for this system.

So governor is a system to minimise fluctuations within the mean speed which can occur as a result of load variation. The governor has no influence over cyclic speed fluctuations however it controls the mean speed over an extended period throughout that load on the engine might vary. When there’s modification in load, variation in speed additionally takes place then governor operates a regulatory control and adjusts the fuel provide to keep up the mean speed nearly constant. Therefore the governor mechanically regulates through linkages, the energy provided to the engines as demanded by variation of load, so the engine speed is maintained nearly constant.

Types of Governor:

The governor can be classified into the following types. These are given below,

1. Centrifugal governor

a) Pendulum type watt governor

b) Loaded type governor

i) Gravity controlled type

Ø Porter governor

Ø Proell governor

Ø Watt governor

ii) Spring controlled type

Ø Hartnell governor

Ø Hartung governor

2. Inertia and fly-wheel governor

3. Pickering Governor

Purpose of governor:

1. To automatically maintain the uniform speed of the engine within the specified limits, whenever there is a variation of the load.

2. To regulate the fuel supply to the engine as per load requirements.

3. To regulate the mean speed of the engines.

4. It works intermittently i.e., only there’s modification within the load

5. Mathematically, it can express as ΔN.

Terminology used in the governor:

1. Height of the governor (h):

Height of the governor is defined as the vertical distance between the centre of the governor ball and the point of the intersection between the upper arm on the axis of the spindle. The height of the governor is denoted by ‘h’.

2. Radius of rotation (r):

Radius of rotation is defined as the centre of the governor balls and the axis of rotation in the spindle. The radius of rotation is denoted by ‘r’.

3. Sleeve lift (X):

The sleeve lift of the governor is defined as the vertical distance travelled by the sleeve on spindle due to change in equilibrium in speed. The sleeve lift of the governor is denoted by ‘X’.

4. Equilibrium speed:

The equilibrium speed means, the sped at which the governor balls, arms, sleeve, etc, are in complete equilibrium and there is no upward or downward movement of the sleeve on the spindle, is called as equilibrium speed.

5. Mean Equilibrium speed:

The mean equilibrium speed is defined as the speed at the mean position of the balls or the sleeve is called as mean equilibrium speed.

6. Maximum speed:

The Maximum speed is nothing but the speeds at the maximum radius of rotation of the balls without tending to move either way is called as maximum speed.

 

7. Minimum speed:

The Minimum speed is nothing but the speeds at the minimum radius of rotation of the balls without tending to move either way is called as minimum speed.

8. Governor effort:

The mean force working on the sleeve for a given change of speed is termed as the governor effort.

9. Power of the governor:

The power of the governor is state that the product of mean effort and lift of the sleeve is called as power of the governor.

10. Controlling force:

The controlling force is nothing but an equal and opposite force to the centrifugal force, acting radially (i.e., centripetal force) is termed as controlling force of a governor. In other words, the force acting radially upon the rotating balls to counteract its centrifugal force is called the controlling force.

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Bearings - Types Of Bearings

BEARINGS

A bearing is a machine element that constrains relative motion between moving parts to only give the desired motion. The design of bearing may be provide for free linear movement of the moving parts or free rotation around a fixed axis or it may prevent motion by controlling the vectors of normal forces that bear on the moving parts .They are mainly used to minimize the friction between moving parts.

The invention of the rolling bearing, within the sort of wood rollers supporting, or bearing, associate object being affected is of nice antiquity, and may predate the invention of the wheel. The ball bearing was originally described by GALILEO in the 17^th century.

Bearings played a significant role in technological revolution allowing the new industrial machinery to work with efficiency. There are various types of bearings. The most common bearing is plain bearing which uses lubricant between the rubbing surfaces.

Types of bearings:

• Plain Bearing

• Journal bearing
• Sleeve bearing

Rolling element Bearing

Jewel Bearing

Fluid Bearing

Magnetic Bearing

Flexure Bearing

Common motions permitted by bearing are as follows

• Axial Rotation
• Linear Motion
• Spherical Rotation
• Hinge Motion

Bearings are designed on the basis of the following subjects

• Friction
• Speeds
• Loads
• Purpose
• Stiffness
• Life

Maintenance and Lubrication of a Bearing is very important. The external factors that effect a bearing are electrical signals, temperature,exposure to environment. To prevent bearing from these external factors they should be frequently lubricated and maintained properly.

Plain Bearing:

They have rubbing surfaces with lubricants between them .Friction factor depends on the material and construction. Stiffness is good. Life depends on application and also depends on lubrication

Roller Bearing:

Ball or rollers are used between rotating surfaces. This prevent and minimize the friction. Life is moderate and speed changes according to requirements. These kind of bearings are widely used now a days.

Jewel bearing:

Jewel bearing has an off centre bearing rolls in seating. Friction of this bearings is very low.  Speed and life are low.

Fluid Bearing:

In these bearings fluid is forced between two faces and held in by edge seal. Friction is zero at zero speed. Stiffness is very high. Can be used for high speed applications. Life is infinite in some applications.

Magnetic Bearing:

The two faces of bearing are kept separate by magnets. Zero friction at zero speed but eddy currents are often induced. Stiffness is low and there is no practical limit for speed and life.

Flexure Bearing:

These bearings are provided with material flexes to give any constrain movement. Friction is very low. Stiffness is low, and speed can be very high with high life.

Reducing friction in bearings is commonly important for efficiency. It helps to cutback the wear and tear and to facilitate extended use at high speeds and to avoid heating and premature failure of the bearing. Friction of a control depends on its form, material, and fluid used between two surfaces applied on bearings. Completely different bearing operative have different operational speed limits. Plain bearings generally handle only lower speeds. However the gap between the components that are separated by the bearing varies with load. Forces working on the bearing may be radial, axial or bending moments perpendicular to the most axis.

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Ultrasonic Welding Process

Making of Ultrasonic Weld:

Although the theoretical method of manufacturing an ultrasonic weld is uncomplicated, the interactions of the varied weld parameters are vital and may be understood. When manufacturing an ultrasonic weld, there are 3 primary variables that interact;

They are:

• TIME the period of applied ultrasonic vibration

• AMPLITUDE the longitudinal displacement of the vibration

• FORCE the compressive force applied perpendicular (normal) to the direction of vibration

Power needed initiating and maintaining vibration (motion) throughout the weld cycle will be defined as:

P = F x A

Where:

P = Power (watts)

F = Force (psi)

A = Amplitude (microns)

  Force = (Surface Area of the Cylinder) X (Air Pressure) X (Mechanical Advanta

Energy is calculated as:

E = P x T

Where:

E = Energy (joules)

P = Power (watts)

T = Time (seconds)

Thus the complete ‘Weld to Energy’ process would be defined as:

E = (F x A) x T

A well designed ultrasonic metal welding system can compensate for normal variations within the surface conditions of the metals by delivering the required energy value. This is often achieved by permitting time (T) to regulate to suit the condition of the materials and deliver the required energy.

How Ultrasonic Welding Works:

Step 1: The parts to be welded are placed into a locating holder

Step 2: The ultrasonic tool descends to apply a clamping pressure between the weld parts.

Step 3: The tool then vibrates at a frequency 1 – 40 KHz. (The weld parts are thus scrubbed together under pressure causing surface oils and oxides to be dispersed)

Step 4: The base metals are then mechanically mixed causing a metallurgical bond between the parts. The parts are immediately welded. There is no hold time or curing time.

In Ultrasonic welding electrical power supply is applied to a Transducer at a frequency of 50 to 60 Hz, into a high frequency electrical supply operating at 20, 30 or 40 KHz. Here transducer converts electrical energy into mechanical energy. This electrical energy is supplied to the converts, which converts to mechanical energy at ultrasonic frequencies. 

The vibrating energy is then transmitted through the booster that will increase the amplitude of the acoustic wave. The acoustic waves are then transmitted to the horn. The horn is an acoustic tool that transfers the vibrating energy directly to the components being assembled, and it additionally applies a welding pressure. The vibrations are transmitted through the workpiece to the joint area. The parts are “scrubbed” together under pressure at 20000 cycles per second. Here the vibrating energy is converted to heat through friction this then softens or melts the thermoplastic, and joins the components together. As the atoms are combined between the components to be welded, a real metallurgical bond is made.

Welding Temperature Achieved:

Ultrasonic welding produces a localized temperature rise from the combined effects of elastic hysteresis, interfacial slip and plastic deformation. The weld interfaces reach roughly 1/3 the temperatures required to melt the metals. Since the temperature doesn’t reach the melting point of the material, the physical properties of the welded material are preserved. As the ultrasonic welding method is an exothermic reaction, as welding time will increases so does weld temperature.

The ultrasonic welding process has the advantage that since no bulk heating of the work pieces is involved and there is no danger of any mechanical or metallurgical bad effects. Although metals have up to 2.5 mm thick have been welded by this process. It is used mostly for welding foils. This process is suitable only for thermoplastics with the exception of thermosetting resins and Teflons. The process can be used on a variety of metals including the refractory metals. Even dissimilar metals can be welded because there is no fusion. The process can also be used on temperature sensitive materials because temperature rise is limited.

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