Laser beam welding advantages disadvantages

Laser beam welding is a technique of welding which used to join multiple pieces of metal through the use of laser. It is frequently used in high volume applications using automation, such as in the automotive industries. Let us have a deep insight into the pros and cons of laser beam welding in this article.

Advantages of laser beam welding :

• Welding of complicated joint geometry.
• Precise working with the exact placing of the energy spot done in laser beam welding.
• Low heat application, therefor minor changes in microstructure.
• Low thermal distortion.
• Cavity free welds.
• Low post-weld operation time.
• Large working distance is also possible. 
• Heat input is close to the in a minimum required to fuse the weld metal, thus heat-affected zones are reduced and workpiece distortions are minimized.
• Time for welding thick sections is reduced and the need for filler wires and elaborate joint preparations is eliminated by employing the single-pass laser welding procedures.
• No electrodes are required.  
• LBM being a non-contact process so distortions are minimized and tool wears are eliminated.
• Welding in areas that are not easily accessible with other means of welding can be done by LBM.
• The joining of small spaced components with tiny welds very easily because of a laser beam can focus on a small area.
• Wide variety of materials including various combinations can be welded very easily.
• Thin welds on small diameter wires are less susceptible to burn back than is the case with arc welding. 
• Metals with dissimilar physical properties, such as electric resistance can also be welded by LBW.
• No vacuum or X-Ray shielding is required. 
• Welds magnetic materials also. 
• Aspect ratios mean depth-to-width ratio of the order of 10:1 are attainable in LBM.
• Faster welding rate.
• No flux or filler metal required.
• Single-pass two-sided welding. 
• Shorter cycle and higher up times. 

Disadvantages of laser beam welding :

• The welding equipment is expensive so the cost for this process is high.
• If the filler material is necessary but in this process limited amount produced with the use of filler material so relatively expensive.
• There are also a few post welding operations. 
• Joints must be accurately positioned laterally under the beam.
• The final position of the joint is accurately aligned with the beam impingement point.
• The maximum joint thickness that can be welded by laser beam is somewhat limited. 
• The materials have high thermal conductivity and reflectivity like Al and Cu alloys can affect the weldability with lasers. 
• An appropriate plasma control device must be employed to ensure the weld reproducibility while performing moderate to high power laser welding. 
• Lasers tend to have low energy conversion efficiency less than 10 percent. 
• Some weld-porosity and brittleness can be expected, as a consequence of the rapid solidification characteristics of the LBM. 

Laser beam welding application

Application of laser beam welding :

• Used in aerospace and automotive applications for welding a high-strength aluminium alloys and titanium alloys.
• Used in welding a magnesium alloys parts.
• Welding of non-porous seams in medical technology.
• Precision spot welding in electronics or jewellery industries.
• To welding complete car bodies in the automobile industries.
• To deposit welding in tool and mould-making.
• Pressed components to hydroformed tubes or extrusions.
• Production of node structures in aluminium alloy castings or extrusions.
• Production of stiffened structures consisting of the welded sheet.
• Recent advancements in scanner optical configurations, scanner controls, and real-time interfaces to optical sensors are also application of laser beam welding.

What is linkage

What is linkage :

A linkage is obtained if one of the links of a kinematic link is fixed to the ground.

The action of linking or the state of being linked two links is known as linkage.

In other words, the linkage is a system of links.

What is kinematic pair

Kinematic pair :

A kinematics pair of simply a pair is a joint of two kinematic links that have relative motion with respect to each other. 
When two links in a machine are in contact with each other, they form a pair. Each individual links of a mechanism form a pairing element. 

A degree of freedom of kinematic pair is given by the number of independent coordinates required to completely specify the relative movement between the pair of two links.

Types of kinematic pair :

Kinematic pair can be classified according to :

• The nature of the contact.
• The nature of mechanical constraint.
• The nature of relative motion.

Kinematics pairs according to nature of contact :

• Lower pair 
• Higher pair 

Kinematic pairs according to the nature of mechanical constraint :

• Closed pair 
• Unclosed pair 

Kinematics pair according to nature of relative motion :

• Sliding pair
• Turning pair
• Rolling pair 
• Screw pair
• Spherical pair 

Types of kinematic pairs

Types of kinematic pair :

Kinematic pair can be classified according to :

• The nature of the contact.
• The nature of mechanical constraint.
• The nature of relative motion.

Kinematics pairs according to nature of contact :

Lower pair: A pair of links having surface area contact between the member is known as a lower pair.

In the lower pair, the contact surfaces of the two links are similar.

For example : 

• Nut turning on a screw shaft.
• Shaft rotating in a bearing.
• All pairs of slider-crank mechanism.
• Universal joint.

Higher pair: A pair has a point or line contact between the links is known as a higher pair.

In the higher pair, the contact surfaces of the two links are dissimilar.

For example : 

• Rotating on a surface 
• Cam and follower pair 
• Tooth gear 
• Ball-bearing  
• Roller bearings 

Kinematic pairs according to the nature of mechanical constraint :

Closed pair: When the elements of a pair are held together mechanically it is known as a closed pair.
The two elements are geometrically identical one is solid and full and other is hollow or open. The letter not only envelops the former but also and closed it. 
All the lower pairs and some of the higher pairs are closed pair.
A screw pair belong to the closed pair category also. 
  

Unclosed pair: When two links of a pair are in contact but due to some spring action or force of gravity, they constitute an unclosed pair.
In this, the links are not held together mechanically. 

Kinematics pair according to nature of relative motion :

Sliding pair: If two links have a sliding motion related to each other, they form the sliding pair. 

For example - A rectangular rod in a rectangular hole in a prism

Turning pair: When one link has a turning on revolving motion relative to others, they constituted a turning pair.

They also called revolving pair.

For example - In a slider-crank mechanism all pairs except the slider and guide pair are turning pair.

A circular shaft revolving inside a bearing.

Rolling pair: When the link of a pair has a rolling motion relative to each other, they form a rolling pair.

For example - Rolling wheel on a flat surface

Ball and roller bearing in a ball bearing 

The ball and shaft constitutive and rolling pair where is the ball and the bearing is a second rolling pair.

Screw pair : If two mating links have a turning as well as sliding motion between them, they form of screw pair. This can be achieved by cutting matching threads on the two links.

For example - The lead screw and the nut of a late is a screw pair.

Spherical pair : When one link in the form of sphere turn inside a fixed link, it is a spherical pair.

For example - The ball and socket joint

Types of constrained motion

Types of constrained motion :

• Completely constrained motion 

When the motion between two elements of a pair is indefinite direction irrespective of the direction of the force applied it is known as completely constrained motion.

The constrained motion may be linear or rotary.

Example of completely constrained motion :

• The sliding pair 
• The turning pair 

In sliding pair, the inner prism can only slide inside the hollow prism.

In case of the turning pair, the inner shaft can have only rotary motion due to the collar at the ends. 
In each case of force has to be applied in a particular direction force required motion.

• Incompletely constrained motion 

When the motion between two elements of a pair is possible in more than one direction and depend upon the direction of the force applied that motion is known as incompletely constrained motion. 

Example of incompletely constrained motion :

• The inner shaft may have sliding or rotary motion depending upon the direction of the force applied if the turning pair does not have a collar.

Each motion is independent of the other.

• Successfully constrained motion 

When the motion between two elements of a pair is possible in more than one direction but with the using of some external means motion is made to have only in one direction so that motion is known as successfully constrained motion.

Example of a successfully constrained motion :

• A shaft in a footstep bearing may have vertical motion apart from rotary motion but due to the load applied on the shaft, it is a constraint to move in that direction and thus is successfully constrained motion.
•  A Piston in a cylinder of an internal combustion engine is made to have only reciprocating motion and no rotary motion due to constraining of the piston pin. 
• The value of an IC engine is kept on the seat by the force of a spring.

Types of joints in kinematics

Types of joints :

• Binary joint 
• Ternary joint 
• Quaternary joint 

Binary joint :

If two links are joint at the same connection it is known as a binary joint.

Ternary joint :

If three links are joint at a connection it is known as a ternary joint. 
It is considered equivalent to the two binary joints since fixing of anyone link constitute two binary joints with each of the other two links.

Quaternary joint :

If four links are joint at a connection it is known as a quaternary joint.
It is considered equivalent to three binary joints since fixing of anyone link constitutes three binary joints.

If n number of links are connected at a joint, it is equivalent to ( n -1 ) binary joints. 

What is kinematic link

What is the kinematic link?

A mechanism is made of a number of resistant bodies out some may have motions relative to each other. A resistant body or a group of resistant bodies with rigid connections preventing their relative movement is known as a link.
This link is also known as kinematic link or element.

The link can be classified into binary, ternary and quaternary depending upon the end on which revolute or turning pairs can be placed.

A link may also be defined as a member or a combination of members of a mechanism, connecting other member and having motion relative to them. Thus, a link may consist of one or more resistant bodies. 

For example, a slider-crank mechanism consists of four links: frame and guides, crank, connecting rod and slider. however, the frame may consist of bearings of for the crankshaft. The crank link may have a crankshaft and flywheel also, forming one link having no relative motion of this.

Mechanism and machine

In this article, we will discuss the mechanism and machine.

What is the mechanism :

When one of the links of a kinematic link is fixed, then the chain is known as a mechanism.

A mishmash of a number of bodies assembles in such a way that it causes the constrained and predictable motion to the other is known as a mechanism.
Thus, the function of the mechanism is to transmit and modify a motion.

What is a machine :

Machine is a mechanism which receives energy and transforms it into some useful work.

A collection of mechanisms which, transmits and modifies available mechanical energy into some kind of desired work and also imparting definite motions to the parts is called machine.

It is neither a source of energy nor a producer of work that helps in proper utilization of the same. The motive power has to be derived from external sources.

Example :

A slider-crank mechanism converts the reciprocating motion of a slider into rotary motion of the crank or vice-versa. however, when it is used as an automobile engine by adding valve mechanism it is it becomes a machine which converts the available energy into the desired energy.  

Some other examples of mechanisms are typewriter, clocks, watches, spring toys etc. 
In each of these force or energy provided is not more than what is required to overcome the friction of the path and which is utilized just to get the desired motion of the mechanism not to obtain any useful work.

Some useful notes :

A machine is tangible, but the mechanism is not. Only the effect of the mechanism is observable.

In a simple way, a mechanism is a system that is followed by a machine to achieve the particular function while a machine is a combination of tools and parts that performs specific functions at the expense of energy.

For Example :

We think a car is a machine. It made of various mechanisms such as the wipers, piston and crankshaft, differential.
All this parts are simple a mechanism following below : 

• Wipers is a 4 link crank lever mechanism
• Piston and crankshaft is a slider crank mechanism
• Differential is a gear mechanism. 

Thus a machine is made of number of mechanism to carryout a particular task.

Mechanism and structure

Mechanism :

Linkage is obtained if one of the links of kinematic chain is fixed to the ground. If the motion of any of these movable ink results in definite motion of the other, the linkage is known as the mechanism.

However, this distance between a mechanism and linkage is hardly followed and it can be referred in place of others.

In a mechanism, links are connected with temporary fasteners. The links can move relative to each other.

This is facilitated by the presence of joints between the links. So a degree of freedom is >=1

Structure :

If one of the links of the redundant chain is fix it is known as a structure.
It is also known as a locked system.
To obtain constrain or definite motion of some of the links of linkage, it is necessary to know how many inputs are needed. In some mechanism, only one input is necessary that determine the motion of other links and it is said to have one degree of freedom. While other mechanisms, two inputs necessary to determine to constrain motion of the other links so we said they have two degrees of freedom. 

In a structure again a combination of links connected to each other but no relative motion exists between them. So a degree of freedom is zero.

A structure who have a negative degree of freedom is known as a superstructure.

A mechanism is a force manipulating device, while the structure is a load bearing device.

Degree of freedom in kinematics

Degree of freedom :

Degree of freedom is related to motion possibilities of rigid bodies.

An unconstrained rigid body moving in space can describe the following independent motions :

• Translational motion along any three manual perpendicular axis x y and Z.
• Rotational motion about this axis.

Thus, rigid body processes 6 degrees of freedom.

The concept of degree of freedom in the kinematics of machines is used in three ways :

• A body is relative to a reference frame.
• Kinematic joints
• A mechanism.

The connection of a link with another imposes certain constraints on their relative motion.
The number of restraint can never be zero or six.

Degree of freedom of a pair is defined as the number of independent relative motions, both translational and rotational a pair can have. 

Degree of freedom = 6 -  Number of restraints 

The general equation to find out degrees of freedom of a planar mechanism is given below. This equation is also known as Kuthbach equation.

D.O.F = 3 ( N-1 ) - 2L_p - H_p

Here N = Total number of links in the mechanism. 

L_P and H_P = Number of lower pairs and higher pairs respectively.

If the mechanism is 3 dimensional in nature, you could easily derive an equation for mobility using the same concept. So the equation for the degree of freedom would be following below :

D.O.F = 6 ( N-1 ) - 5P₅ - 4P₄ - 3P₃ - 2P₂ - 1P₁

Where P_n = number of pairs which block 'n' degrees of freedom. 

The main thing here will be the determination of nature of the kinematic pair. 

TCI Vs CDI

TCI and CDI both are improved technology of ignition system used by a different automobile company.  First of all, you should know the full form of these two terms. 

Full form of TCI - Transistorised Coil Ignition

Full form of CDI - Capacitor Discharge Ignition

The main difference between them is capacitor discharge ignition is when a capacitor stored energy is used for ignition while transistor controlled ignition is when the ignition coil current is driven by a transistor. 

Let us have a deep insight into the comparison between transistorised coil and capacitor discharge ignition. 

Difference between TCI and CDI :

• CDI ignition system is independent on time while in TCI ignition system is dependent on time.
• CDI Ignition makes the spark by discharging a capacitor loaded with high voltage about 200 to 450 volt from the ignition coil by using an SCR known Thyristor while TCI Ignition charges the coil with the current before the spark is done. Spark is done when the current is cut suddenly.
• CDI coils have low impedance and inductance is about XL< 1 ohm and can reach high RPM makes high power and short sparks while TCI coils have high impedance is about XL >1 ohm and can reach lower RPM thus spark duration may be longer.

Full form of TCI

What is the full form of TCI?

Answer :

• Transistorized Coil Ignition system

What does TCI mean?

TCI is one type of ignition system that reduces the use of mechanical devices, and its purpose is to improve the efficiency of the ignition system. 

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Submerged arc welding

Introduction :

Submerged are welding is a common arc welding process in which the formation of an arc between a continuously fed electrode and the workpiece. It is mainly used for doing faster welding joints. The arc is produced while the consumable electrode wire is continuously fed into the weld zone as in gas metal arc welding. The welding zone is completely covered by means of a large amount of flux. The arc occurring between the electrode and the workpiece is completely submerged under the flux and is not visible from outside. A part of the flux melts and forms the slag, which covers the weld metal. The unused flux is collected and reused.

How it works?

This welding process may be automatic or semi-automatic. The main principle of this process is the flux starts depositing on the joint to be welded. The power source used with submerged arc welding can either be AC or DC. Both constant-voltage and constant current type machines can e effectively used. The arc may be stuck either by touching the electrode with the workpiece or by placing steel wool between electrode and job before switching on the welding current. The arc is maintained between the end of the bare wire electrode and the weld. The electrode is constantly fed into the arc as it is melted. In all cases, the arc is stuck under the cover of flux. Flux otherwise is an insulator but once it melts due to the heat of arc, it becomes highly conductive and hence the current flow is maintained between the electrode and workpiece through the molten flux. The upper portion of flux is in contact with the atmosphere which is visible and remains unused. The lower portion of flux becomes slag, which is waste material and it is removed after the welding process is done.

The electrode at a constant predetermined speed continuously fed to the joint to be welded. The arc length is also kept constant by using the principle of self-adjusting arc because if the arc length decreases the voltage will increases. Therefore burn off rate will increases. 

In this process also some backing plate of the material like steel or copper may be used for control penetration and to support a large amount of molten metal associated with this process. 

SAW process mainly depending upon the following factor :

• Arc voltage or Arc length 
• Electrode travel speed 
• Electrode stick out or Contact tip to work 
• Current type AC or DC 
• Wire feed speed 

Advantages of submerged arc welding :

• High deposition rate.
• High operating factors in some applications.
• Deep weld penetration so welded joints are strong.
• It prevents hot materials from splattering and splashing onto workers because arc is always covered under the blanket of flux.
• High speed welding for thin plates.
• SAW is suitable for indoor and also outdoor works.
• Single pass welds can be made in thick plates. 
• Most of the flux are reused in this process. 
• Very neat appearance and smooth weld shapes can be got.
• Good ductility and corrosion resistance and good impact strength are formed in joints.
• In this process we did not required to add pressure because it already generated by electrode.

Limitations of submerged arc welding :

• This process is limited to steel, stainless steels and nickel.
• Limited to the 1F, 1G and 2F positions. 
• Limited to high thickness metal plates.
• Flux is subjected to contamination that may caused porosity in welded joints.
• The flux needs replacing on the joint which is not always possible.
• Requires backing strips for proper penetration.
• Flux and slag residue can present a health and safety concern.

Electroslag welding

Introduction :

The electro slag welding process is developed mainly to weld very large metal plates without any edge preparation. This process is most of the cases single-pass process using a consumable electrode for filling the gap between the two heavy plates. The heat required for melting the plates and the electrode is obtained initially by means of an arc so that flux will form the molten slag. Once the molten slag is formed, the arc is extinguished and the heat of welding is obtained by the resistance heating of the slag itself. 

How it works?

First of all, in this process, the gap between the two workpieces is filled with a welding flux. It required to maintain a satisfactory amount of slag is fairly small in the order of 0.2 to 0.3 kg per meter of weld length, irrespective of plate thickness. The welding is initiated by an arc between the electrode and workpiece thus, heat utilized for melting the slag is much less. Most of the heat supplied in electroslag welding it melts the fluxing powder and forms the molten slag. The slag, having low electrical conductivity and is maintained in a liquid state due to the heat produced by the electric current.

By this process, a plate of 200 mm thickness can easily be welded in a single pass. The slag reaches a temperature of about the 1930 ⁰C. This temperature is sufficient for melting the consumable electrode and workpiece edges. Metal droplets fall to the weld pool and join the workpiece.

For effective welding, it is necessary to maintain a continuous slag pool and therefore the best way to maintain it. The slag pool is contained in the groove with the help of two water-cooled copper dam plates which move along with the weld.

Electroslag welding is mainly used for welding the steels.

The quality of weld in this process mainly depends upon :

• Slag depth.
• The ratio of a width of the weld pool and its maximum depth is known as the form factor.
• Weld current and voltage.
• A number of electrodes used.

Advantages of electro slag welding :

• Most of the cases welding are done easily by a single pass.
• If any gas is present easily bubbles out through the slag and therefore, a better weld can be done.
• The heating and cooling of the edge are more gradual.
• Whatever be the thickness of the plate,  no edge preparation is required.
• It is also useful for very thick plates. 
• High deposition rate - up to 45 lbs/h (20 kg/h).
• Low slag consumption and low distortion.

Disadvantages of electro slag welding :

• The coarse grain structure of the weld.
• An only vertical position of the weld is possible.
• Low toughness of the weld. 

Application of electro slag welding :

• Fabrication of high-pressure vessels.
• Frames of heavy mechanical and hydraulic presses. 
• In Rolling mill frames. 
• Ship hulls and locomotive frames.