MANUFACTURING TECHNOLOGY

MECHANICAL TIPS AND STUDY MATERIAL


MANUFACTURING TECHNOLOGY is an important part of mechanical and production engineering. It includes basics of manufacturing. It is technology that helps us to process raw material to usable finished goods which we use as per our need.

Manufacturing requires combination of mechanical, production, electrical, electronics and computer integrated technology. Given below are the list of topics which are put under manufacturing technology. Click on the link below to read the topics.

1)  The first step includes knowing of materials ( metal, non-metal) and their properties. In manufacturing, knowing of material is prime importance as it gives basic regarding the use of material. Every metal, non-metal has specific use. Given below are properties of some important material whose properties are important to know.

MATERIAL SCIENCE AND MATERIAL PROPERTIES-CLICK

2)  In manufacturing our prime importance is to give material a useful shape. This is done by cating process. Click on the link below to know casting technology.


1) CASTING TECHNOLOGY AND PATTERN ALLOWANCE-CLICK

2) SPECIAL CASTING PROCESS ( SLUSH, INVESTMENT ETC)

3)  Heat treatment of material is another major step after casting is done. After reading casting we have metal treatment process which is done in order to relieve the material from stress and provide surface hardness/stiffness in order to resist deformation. All heat treatment process is prescribed in link given below.

1) ALL TYPE OF HEAT TREATMENT PROCESS

2) ANNEALING -BRIEF CLASSIFICATION

Machining process

Conventional machining

4) After heat treatment of material the next effort is made to machine the material to required specification. There are various processes ( both conventional and non conventional ) to machine the component to provide exact tolerance and perfect shape. Given below is the link for some conventional machining processes. Click on the link for viewing how they work.

1) TURNING AND BROACHING -CONVENTIONAL MACHINING

2) GRINDING AND DRILLING- CONVENTIONAL MACHINING


Non conventional machining 

5) Non-conventional machining processes includes machining with indirect contact between tool and work piece. These process are widely used in mass production processes and helps to attains high surface finish and accuracy as compared to conventional machining processes.

Please clock on link to view non traditional machining processes.

 NON-CONVENTIONAL MACHINING--COMPLETE NOTES

6) Welding processes are integral part of manufacturing process. Various types of flames used in welding and welding processes are explained below.

1) METAL JOINING PROCESS AND SUBMERGED ARC WELDING

2) METAL INERT GAS WELDING

Read More

ANNEALING AND ITS TYPE -- HEAT TREATMENT PROCESS

MECHANICAL TIPS AND STUDY MATERIAL

ANNEALING OF STEEL

Heating of steel to high temperature (austeniting temperature) and henceforth cooling it slowly is called annealing. Austenite is carbon or ferric carbide in iron that is found in steel at high temperature.

Most important advantage of annealing is to improve the machinability and to enhance ductility. Some other advantage like removal of internal stress, decrease hardness and refinement of grain size is also possible with annealing.

In annealing  after heating, rate of cooling of work piece is slow, out of which alloy steels are cooled at lower rate as compared to C- steels. On an average cooling rate is of order 40 degree/hour. On cooling soft spheroidal carbide is obtained  which counts for good ductility and low hardness.

TYPES OF ANNEALING

• Complete/Full annealing
• Spheroidise annealing
• Diffusion annealing
• Process annealing

1. COMPLETE/FULL ANNEALING

For hypoeutectoid steels ---> Heating it at 70 degrees above upper critical temperature (UCT) and holding it or maintaining it at this temperature for a while so that complete body acquire same temperature and then allowing it to cool. During this time austenite is converted into ferrite and pearlite.

For hypereutectiod steels ---> Heating it at 70 degrees above the lower critical temperature (LCT) and maintaing this temperature for some time so that each and every part acquire same temperature (equilibrium temperature) and henceforth allowing it to cool at slow rate. Here austenite decomposes to form cementite and pearlite.

2. SPHEROIDISE ANNEALING.

Steel is heated above the lower critical temperature  and them slow cooling is actuated.
In all annealing process the basics remain same, the only difference is its application. This process is employed for components which are hard to machine like high carbon steels. Carbides (Spheroids of spherical shape)  are formed on the surface of steel during cooling session.

3. DIFFUSION ANNEALING

For steels having chemical inhomogeneity diffusion annealing is prompt option.Complete refinement of structure is possible in this process. This process is also called HOMOGENIZING. 
On heating the specimen to around 1160 degrees diffusion proceeds. Then it is held at this temperature for small interval followed by cooling the specimen at around 800 degrees and further cooled by air.

4. PROCESS ANNEALING

Heating the specimen below the lower critical temperature. Cold working effects are eliminated and softer  output is achieved. Ductility is also improved. Internal stresses is reduced and plasticity is increased due to recrystalisation. In recrystalisation the deformed grains are re-oriented.

Read More

SPECIAL CASTING PROCESS(SLUSH,INVESTMENT,CENTRIFUGAL,SHELL,DIE CASTING)

SPECIAL CASTING PROCESS

SOME IMPORTANT CASTING PROCESS ARE:-

• Slush casting
• Investment casting
• Centrifugal casting
• Shell casting
• Die casting

SLUSH CASTING:-

This is an open casting method, where molten metal is poured in the casting cavity in open condition. It is allowed to cool for sometime and then mould is inverted. The unsolidified molten metal moves out on inverting the mould and solidified metal retains in mould. By breaking the mould the solid casting can be obtained. This type of casting does not necessarily require cope and drag arrangement. Only drag part is enough to carry out casting.

INVESTMENT CASTING

Being the most ancient casting technique, this process is used to produce those shapes which is difficult to obtain through die casting. The pattern used in investment casting is made up of either wax, ceramics or sometimes may be of steel. Generally wax is used as pattern as it melts easily. In designing mould, care is ought to be taken to overcome shrinkage of wax, ceramics etc.

The casting is closed and hence geometry of cast is complex in nature. Initially pattern of wax is dipped in abrasive slurry which constitutes binders, water and silica. It is dipped till it acquire required thickness over the pattern. Then it is allowed to cool down. After that it is heated in so that wax melts down and we get solid refractory casing.

Now molten metal is poured in the refractory and allowed to solidify. After solidification of metal, the outer refractory material is broken and finally we obtain solid casting.

CHARACTERISTIC
Such casting is generally done for obtaining intricate shape with complexity. Good shape, surface finish can also be obtained with such casting. Close dimensional accuracy is achieved, hence ornaments etc can be casted. Surgical instruments are also casted. Here mould is made out of cement concrete. As we know the thermal conductivity of concrete is higher then that of sand, surface hardening occurs. Highly complex shape with good finishing can be obtained by this process. Good dimensional tolerance with high accuracy is also characteristic of this process. Sections with thin diameter is also possible with this process. But on the other side it is expansive process.

CENTRIFUGAL CASTING

AFTER LEARNING INVESTMENT CASTING NOW WE WILL FOCUS ON CENTRIFUGAL CASTING.

As the name suggest centrifugal casting deals with rotation of mould which causes flow of molten metal in outward direction (away from axis of rotation). The mould is rotated at high speed of about 2800 rpm and at the same time molten metal is poured in the mould. The molten metal under centrifugal action is thrown to the inner wall of cylindrical mould. At high rotational speed the thin grained layer of solidified metal is obtained.                    

When the molten metal is poured in the mould box and the mould box starts rotating about its axis, the molten metal flows in outward direction (away from center). This type of casting provides many benefits over other casting. These castings are not in direct contact with atmosphere hence no environmental effect is there. Second thing is that, any size dimension (length, diameter and thickness) can be obtained. And at the same time one mould can be used for many casting for varying thickness need. Also no cope and drag arrangement is needed in this type of casting. Due to high centrifugal rotation of molten metal, the composition becomes highly homogeneous and uniform, hence good machinability is obtained. In casting it is very difficult to cast thin cylinders, for such purposes centrifugal casting is opted first.

The rotation continues till the molten metal is solidified. The impurities under centrifugal action is thrown to outer diameter which is machined after solidification of cast. The figure below depicts centrifugal casting arrangement.

This method is used to produce large hollow section

The thickness of casting depends on the amount of metal poured in for casting. Such casting is free from casting defects. The density of decreases as we move from outer wall to the center of casting. The figure below depicts the density distribution of product.

Disadvantage:-

• Poor machinability.
• Only cylindrical component can be produced.Limited usage for other shapes.
• Maximum diameter of casting is limited three meter and length of fourteen meter. 

DIE CASTING

AFTER STUDYING CENTRIFUGAL CASTING NOW WE WILL STUDY DIE CASTING.

BASIC CHARACTERISTICS

• Such process is used for non ferrous alloys (zinc, copper etc).
• It is characterized by forcing the molten metal under gravity or under high pressure into the mould cavity.
• Used for high volume of production.
• Cost of casting is high.
• Material used as mould box is metal.

PROCESS OF DIE CASTING:-

THERE ARE TWO METHODS OF DIE CASTING

• GRAVITY DIE CASTING
• PRESSURE DIE CASTING

1. GRAVITY DIE CASTING:-

The molten metal is poured via runner and it enters mould cavity. Since the mould box is made up of metal, the molten metal may adhere to the mould box. To avoid this we sprinkle silica sand (parting sand) on the wall of mould box before pouring molten metal. After the molten metal solidifies, the mould box is separated and casting is obtained. The pouring of molten metal can be controlled by tilting of arrangement to distribute molten metal well.

2. PRESSURE DIE CASTING

As shown in figure, there is a gooseneck through which molten metal is pressurized by hydraulic plunger into the mould cavity against the die. High compression locking of about 550 tonnes is applied on the molten metal in the mould box. The latest technology includes use of computerized system like microprocessor chips which automatically reads cooling time extraction time. The molten metal is allowed to cool down under high pressure and casting is obtained. Fast cycle time is obtained with such die casting.

ADVANTAGES:-

1. Good surface finish
2. Good dimensional accuracy
3. Fast production rate.

Read More

HEAT TREATMENT OF METAL (ANNEALING, NORMALIZING, HARDENING AND TEMPERING) AND FORGING TECHNOLOGY

  HEAT TREATMENT OF METAL

Heat treatment is process in which the metal is heated and cooled. This alters the properties of material significantly.

The process of heating and cooling can be controlled to obtain desired properties of material, depending on industrial need.

These are fallowing reason for which heat treatment is done:-

1. Improve mechanical properties of material. 
2. Reduce the stress from the material by heating and cooling process. 
3. Improve the corrosion properties. 
4. Magnetic properties are enhanced. 
5. For better machinability. 

Important heat treatment processes

• Annealing 
• Normalising 
• Hardening 
• Tempering 

ANNEALING

CLEAR CLASSIFICATION OF ANNEALING-CLICK HERE

The purpose of annealing is to soften the material and to relive the stresses for the inside of the material. This help to improve the machinability. The tensile stress, hardness decreases in this case.

 Annealing is of four type:-

Full annealing

Heated above critical temperature and held for some time and then cooled slowly.

Incomplete annealing

Imparts machinability, heated above room temperature and cooled down slowly. 

Spherodising

lowers down hardness and strength,improves machinability. Also it improves ductility.

Malleabilising

It is controlled annealing process where combined form of carbon in steel splits into carbon. Helps to improve ductility and machinability.

Normalising

It helps to restore the material to its original composition.
During the metal working and casting process the micro structure may get distorted. By this process, mechanical properties are refined and good machining characters can be achieved. It is done 80 degrees above the upper critical temperature and short holding at that temperature.

This process increases tensile strength but ductility decreases.

HARDENING:-

It is mechanical metalworking process which is employed to increase the hardness of material. Since hardness is one of the important property of material as it deals with resistance to plastic deformation. It is process accomplished by heating the metal above the critical temperature of material and then quenching it in water pool.

Hardening process in carried out by heating the steel or other material above the critical temperature and keeping it at that temperature for sometime. Then it cooled at the rate faster then normal cooling. This makes the material stronger and resistant to plastic deformation. There are various hardening process known to us. These are work hardening, age hardening, quenching and tempering.


WORK HARDENING

When material is strained beyond yield strength point then due to permanent straining new dislocation are formed. Since new dislocations are obtained, the density increases. With increase in density the strength increases.

The various types of quenching process are:-

• Single quenching 
• Double quenching 
• Steeped quenching 
• Isothermal quenching 

SINGLE QUENCHING

The specimen is heated above the critical temperature and then suddenly cooled at room temperature. High degree of hardness can be obtained. Due to sudden temperature drop between the core of material and outer surface, cracks may appear.

DOUBLE QUENCHING

The specimen is heated above the room temperature and cooled in two segments. Firstly it is cooled to 320 degrees. Secondly it is cooled to room temperature in less intense medium. Cutters,millers etc are produced by this process.

STEPPED QUENCHING

It is accomplished by cooling the material in hot metal bath. Under such conditions transformation takes place.In this process cooling takes place step by step till the temperature of core and outer surface are same.

ISOTHERMAL QUENCHING

Such quenching gives better ductility to material. Here transformation takes place from austenite to bainite (intermediate form) cracking of grains is minimum here. 

TEMPERING

It is simple heat treatment process where the metal is heated below the critical temperature of metal and holding it for sometime at that temperature and then cooling it at room temperature. Such process eliminates the brittle character of the metal. In other words the martensile structure (brittle form) is converted to more stable form and becomes less brittle.

Reasons why tempering is done:-

1. Reduce thermal stresses which gets induced while heating.
2. Reducing induced strain.
3. Improve mechanical properties like toughness, grain size.
4. Relive the excess of hardness.

Classification of tempering process:-

LOW TEMPERATURE TEMPERING

• Heating takes place up to 160 degree to 280 degrees.
• Retains hardness while heating.
• Reduces internal stresses.

MEDIUM TEMPERATURE TEMPERING

• Heating is carried out between 310 degrees to 460 degrees.
• High toughness is induced.

HIGH TEMPERATURE TEMPERING

• Temperature range is from 500 degrees to 660 degrees.
• Internal stresses are relieved.
• Toughness is enhanced.
• Brittleness is reduced.

FORGING

  
CHARACTERISTICS

The process of deformation of material by application of continuous or uniform force.
The material is kept in between the two dies.
Impact force is applied on the material to be forged.

On the basis of force applied forging can be classified as:-

HAND FORGING in which force is applied by hammer.
MACHINE FORGING in which force is applied by hydraulic/mechanical press.

On the basis of die used forging can be classified as:-

• Open die forging
• Closed die forging
• Semi-closed die forging

OPEN DIE FORGING:-

In open die forging the as shown in above figure the position of specimen is changed continuously and force is imparted by hammer to obtain desired shape.

2. CLOSED DIE FORGING:-

Here the size and shape of material produced is similar to the die shape. The material is held in between the two dies and force is applied by hammer. Even mechanical press can be used to apply force, hence shape is obtained.

3. SEMI CLOSED DIE FORGING:-

Here force is applied in repeated manner by number of blows. The half of die provides the shape of material. By changing the position of body required shape can be obtained.

Read More

CASTING PROCESS AND PATTERN ALLOWANCE

                       THE CASTING PROCESS

What is casting?

It is the most ancient process of manufacturing. In this process the molten metal (liquid form) is poured in the mould cavity.

The shape of casting to be made resembles the mould cavity. The size of the mould cavity is kept slightly greater than that casting to be obtained. This is done for tolerance purpose and for machining to be done after casting solidifies.

As the molten metal is poured in the mould cavity, it takes the shape of mould cavity and solidifies
After solidification we obtain the casting.

 What are various terms related to casting?

 The various terms that relates to casting process are:-

Mould
Pattern
Core
Flask
Baking sand
Facing sand
Gating system 

What is mould?

It is nothing but the cavity in which the molten metal is poured. The size of mould is kept slightly larger than the casting to be obtained. This is done for tolerance purpose and machining allowance purpose. It may be made up of metal or sand.

What is pattern?

What impression is to be obtained in casting is provided by pattern. This pattern consists of various designs that we want on the casting after it solidifies. It may be of wood, metal or plastic (depending upon the need).

 What is core?

When we want to obtain a hollow cavities in a casting .
Metal flow around the core to form cavity.

What is baking sand?

This is generally used or burned sand, it covers most mart of refractory material which is found in mould.

What is gating system?

fig:-gating system

The gating system ensures the total flow of molten metal from starting to the end till it solidifies in mould cavity. The figure shows the gating system.

 The various part of gating system
Pouring cup
Sprue
Runner
Gates
Riser

POURING CUP 

It is nothing but reservoir in which molten metal is poured. Here impurities can be filtered out.

SPRUE

It is the tapered section through which the molten metal flows to the runner. The tapered section provides velocity head to the flow of molten metal.

RUNNER

It is trapezoid section in horizontal direction and connects to in-gates through which molten metal flows to cavity. This provides continuous flow of molten metal to cavity.

GATES

 
It signifies the entry point through which the molten metal enters the cavity.

RISER

After the mould cavity is filled, the excess of molten metal rises in the riser.Hence it signifies that mould cavity is completely filled.

PATTERN ALLOWANCES

As described the casting obtained has same shape as that of pattern. But the size of pattern is kept slightly greater than that of casting.

• Size of pattern = Size of casting + allowance
• Allowance is the tolerance provided.

There are various types of allowance :-

Machining allowance
Distortion allowance
Shrinkage allowance
Draft allowance
Shake allowance

SHRINKAGE ALLOWANCE

In this case the pouring temperature of molten metal is nearly 200 degree above melting point of metal.
The molten metal is solidified in the mould. This happens in three stages Super heated liquid to saturated liquid- evolves sensible heat.
Saturated liquid to solid-freezes and gives latent heat.
Free zed solid to solid at room temp-Gives sensible heat.
The casting as it passes through each and every stage shrinks while cooling.

    2.  MACHINING ALLOWANCE

• In order to provide smooth and fine surface of the casting, machining is done. For this reason some allowance is given so that surface finish can be provided to casting. This is called machining allowance.

• It is usually specified as 2mm/side - 4 mm/side.

     3.  DISTORTION ALLOWANCE

It is process of distorting the pattern in opposite direction. As we know that during cooling of mould stresses are developed in it. This will effect the cast as stresses will be induced in it also.

• When a V-shape or U-shape is casted, there may be distortion in the shape.
• Pattern allowance is done to take care of it.

     4.  DRAFT ALLOWANCE

• This is done in order to avoid the braking of upper surface of the mould.
• After removing the pattern the above surface is still in contact of mould. And due to shake of pattern, mould may break.
• To avoid such problem vertical faces are kept inclined or say tapered section is provided on the upper surface for easy removal of material known as draft angle. More is the complex structure greater is the draft angle.

 

    

                                               

Read More