Tuesday, 25 April 2017
Today we will learn about forging defects types, causes and its remedies. Defects are common in every manufacturing process like casting includes casting defects, welding includes welding defects, same as forging consist some defects which are due to both process and human limitations. Forging gives better mechanical properties among all manufacturing process but it also includes some common defects which are described below.
As the name implies in this type of defect some of the forging section remain unfilled. This is due to poor design of die or poor forging technic. This is also due to less raw material or poor heating.
This defect can be removed by proper die design, proper availability of raw material and proper heating.
Cold shut includes small cracks at corners. These defects occur due to improper design of forging die. It is also due to sharp corner, and excessive chilling in forge product.
The fillet radius of the die should be increase to remove these defects.
Scale pits are due to improper cleaning of forged surface. This defect generally associated with forging in open environment. It is irregular deputations on the surface of forging.
It can be removed by proper cleaning of forged surface.
Die shift is caused by misalignment of upper die and lower die. When both these dies are not properly aligned the forged product does not get proper dimensions.
This defect can be removed by proper alignment. It can be done by provide half notch on upper die and half on lower die so at the time of alignment, both these notches will matched.
These are internal cracks occur due to improper cooling of forge product. When the forge product cooled quickly, these cracks generally occur which can reduced the strength of forge product.
This defect can be removed by proper cooling.
This defect occurs due to improper flow of metal in casting which changes predefine grain structure of product.
It can be removed by proper die design
This defect arises due to incomplete forging. it is due to light or rapid hammer blow.
This defect can be removed by proper control on forging press.
Surface cracking occurs due to exercise working on surfaces at low temperature. In this defect, So many cracks arise on work piece.
This defect can be removed by proper control on working temperature.
This defect occurs due to improper cooling of forged part. Too much rapid cooling is main causes of this type of defects.
This can be removed by slow cooling of forged part.
These are all main types of forging defects. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it on social networks. Subscribe our website for more interesting articles.F
Monday, 24 April 2017
Today we will learn about what is forging and types of forging. Further we will discuss about operation, application, advantages and disadvantages of this process. Forging is a metal forming process in which the metal is heated and a force is applied in such a way that a required shape can be obtain. It is basically a hot working process in which the work piece is heated up to plastic stage and the force is applied by manually or by press according to the requirement. This force is compressive in nature which is basic requirement of forging. Sometime forging operation is done without application of heat known as cold forging. Now days, Forging is used in every manufacturing industries.
What is Forging Process?
Mainly forging consist two operations according to the force applied.
1.) Drawing Down:
Drawing down is a process of elongate the length and reduce the cross section area of work piece. Simply in this operation, the length of work piece increases and the cross section area decreases. In this process, a compressive force is applied at perpendicular direction of its length axis. If a tensile force is applied to change its length at parallel to its length axis, this process is known as wire drawing.
Upsetting is just opposite operation to drawing down. In this operation, the length of work piece decreases and its cross section area increases. In this process, a compressive force is applied at parallel direction to its length axis.
Types of Forging:
Forging may be classified into following ways.
1.) According to the Temperature:
a.) Hot Forging:
If the work piece is heated above its recrystallization temperature and then force is applied, the process is known as hot forging. The recrystallization temperature of most of metals is half of its melting temperature.
b.) Warm Forging:
Warm forging done at the temperature about 40 percent of its melting point temperature.
c.) Cold Forging:
Cold forging is done at room temperature. This process gives highest mechanical properties among all forging processes.
2.) According to arrangement of Die:
a.) Open Die Forging:
This forging process uses flat dies or no die. This is mostly hot forging process in which the work piece heated and hammered to obtain desire shape. This process produce rough product.
b.) Close Die Forging:
Close die forging is a process in which a set of impression die is used to produce desire shape on work piece. Mostly these products do not need any finishing process. This process required higher force.
3.) According to the Forging equipment:
a.) Smith forging:
Smith forging is traditional method of metal forming. It is open die forging method in which the work piece is placed on a stationary anvil and a hammer strikes and deform the work piece. The force is applied either by manually or power hammers.
b.) Drop Forging:
Drop forging is done in closed impression dies. An automatic hammer applied the force in series of blow by dropping action. In this type, a sudden applied force is used.
c.) Press Forging:
Press forging is similar to drop forging except it uses continuous squeezing type applied force by the hydraulic press. This process increase the length and decrease its cross section of work piece.
d.) Machine Forging:
Machining forging is an upsetting process in which the cross section of work piece increases and length decreases.
Advantages and Disadvantages:
- Forging gives comparatively tougher product compare to casting.
- The fatigue strength and creep resistance of forge product is higher.
- Forge product has higher mechanical properties.
- Low cost operation.
- This process does not required special skill operator.
- Variety of shapes can be formed by this process.
- Higher initial cost for big forging presses.
- Secondary finishing process required in hot forging.
- It cannot produce complex shapes.
- Size is limited due to size of press.
- Brittle metal cannot be forged.
Application of Forging:
- Mainly forged products are used in every mechanical industry.
- Turbine rotor, generator rotor etc. are forged product.
- It gives higher fatigue strength so most of moving parts like crankshaft, camshaft gears etc. are made by forging operation.
- Cold forging is used to produce chisel, bolts etc.
- These are mostly used in hand tools and hardware manufacturing.
- It is used in ship building in various structure works.
This is all about what is forging process, operation, types, application, advantages and disadvantages. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it with your friends. Subscribe our website for more interesting articles.
Sunday, 23 April 2017
Today we will learn about metal forming process, its types, advantages and disadvantages. To convert a work piece into various shapes many manufacturing process are used like casting, machining, forming etc. Metal forming is one of the most useful processes of converting work piece into desire shape. Metal forming depends on yield strength of material. In this processes, the work piece is subjected under a force such that the stresses induced in work piece material is higher compare to yield strength of material and lower the ultimate strength. The metal forming takes place due to plastic deformation of material. In these process, the metal is either heated or not and the applied forces are either compressive or tensile according to the product requirement. All rolling, extrusion, drawing etc. processes are include in it.
Types of Metal Forming Process:
Mainly these processes can be classified into two types.
Hot Working Process:
When the metal forming process done above the recrystallization temperature of material, it is known as hot working process. The recrystallization temperature is about one third of the melting temperature of most of the metals. In hot working process, the temperature at which deformation takes place is important because further increase in temperature increase grain growth thus decrease mechanical properties.
- Any metal can be shaped above recrystallization temperature.
- Any amount of working can be imparted.
- It requires less force compare to cold working.
- Any grain size can be achieved by proper controlling the working temperature and cooling rate.
- The metals which get brittle at high temperature cannot be worked by hot working process.
- It gives poor surface finish due to scale formation at surface at higher temperature.
- It is difficult to control dimension accuracy at higher temperature.
- Difficult to handle hot work piece.
Also Read : Hot Working vs Cold Working
Cold Working Process:
When the metal forming process done below its recrystallization temperature, it is known as cold working process. This is done with or without actual heating but the achieved temperature should below its recrystallization temperature. This process accomplish with strain hardening due to working process done below recrystalization temperature.
- It increase strength and hardness of the material due to strain hardening.
- This process gives higher fatigue strength and increases corrosion resistance.
- It gives better dimensional accuracy compare to hot working.
- No energy source required for heating.
- Cold worked work piece can be handle easily.
- It provide good surface finish because no oxide form at surfaces.
- The amount of deformation is limited according to the press size.
- These metal forming processes require higher force to deform the work piece.
- Brittle work pieces cannot worked by cold working.
- Higher risk of cracks in cold working.
- It accomplish by internal and residual stresses.
These is all about metal forming process types, advantages and disadvantages. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it on social networks. Subscribe our website for more interesting articles.
Saturday, 22 April 2017
Today we will learn about investment casting working process, application, advantages and disadvantages with its diagram. Investment casting is one of the most important types of casting process which gives high accuracy and surface finish. This process uses wax pattern to create mould. The wax pattern dipped into a refectory material which makes a shell outside the pattern. Now the refectory material heated which melt down the wax and taken out. The molten metal poured into this refectory mould and allows to solidify. When the metal solidified, the ceramic shell broken and casting is removed from it. This casting process gives high surface finish and good dimensional accuracy compare to other casting process. It is mostly used to cast complex shapes like turbine blade etc.
Investment Casting Process:
Its working can be summarized into following point.
- In the beginning of this process, a wax pattern created together with its gating system into a die cavity.
- A tree is prepared from number of such pattern fixed to a wax or plastic runner bar with a suitable ceramic cup to act as pouring basin.
- The tree is then dipped into ceramic slurry (refectory material). This enables the formation of self-supporting ceramic shell mould to be formed around the wax assembly.
- The ceramic shell mould is then heated so that the wax melts and flows out leaving a precise mould cavity.
- The shell is fired between 850 degree centigrade and 1000 degree centigrade to eliminate all the wax and give more strength to the mould.
- The molten metal is poured into the mould while it is still hot and cluster of castings is obtained.
- At the end, ceramic mould is broken and removed the casting.
This process can be easily understandable by following video.
- It is used to cast small size casting having intricate shape.
- These are used to form jewelry surgical equipment.
- It is used to cast complex shapes like turbine blades, bolt and trigger for fire arm etc.
Advantages and Disadvantages:
- High melting point alloys can be cast by this process.
- It gives high surface finish and dimensional accuracy.
- Complex shapes which are difficult to produce by any other casting method can be produce by investment casting because pattern is withdrawn by melting it.
- Thin section with fine details can be cast by this process.
- More than one part can be cast simultaneously.
- The process is normally limited by the size and mass of the casting.
- It is expressive compare to other casting processes.
This is all about investment casting process working, application, advantages and disadvantages. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it on social networks. Subscribe our website for more interesting articles.
Friday, 21 April 2017
Today we will learn about centrifugal casting its working principle, types, application, advantages and disadvantages. Centrifugal casting is one of the most important type of casting process in which mould is rotated rapidly about its central axis during casting is solidified or metal is poured. This process was patent in 20 century to make higher standards hollow castings. The first centrifugal casting machine was invented by a British, A.G. Eckhardt in 1807. This process is widely used for casting hollow pipes, tubes and other symmetrical parts.
It works on basic principle of centrifugal force on a rotating Component. In this process, a mould is rotated about its central axis when the molten metal is poured into it. A centrifugal force acts on molten metal due to this rotation, which forces the metal at outer wall of mould. The mould rotates until the whole casting solidifies. The slag oxide and other inclusion being lighter, gets separated from metal and segregate towards the center.
True Centrifugal Casting:
True centrifugal casting is sometime known as centrifugal casting is a process of making symmetrical round hollow sections. This process uses no cores and the symmetrical hollow section is created by pure centrifugal action. In this process, the mould rotates about horizontal or vertical axis. Mostly the mould is rotated about horizontal axis and the molten metal introduce from an external source. The centrifugal force acts on the molten metal which forces it at the outer wall of mould. The mould rotates until the whole casting solidifies. The slag particles are lighter than metal thus separated at the central part of the casting and removed by machining or other suitable process. This process used to make hollow pipes, tubes, hollow bushes etc. which are axi symmetrical with a concentric hole.
Semi Centrifugal Casting:
This process is used to cast large size axi symmetrical object. In this process mould is placed horizontally and rotated along the vertical axis. A core is inserted at the center which is used to cast hollow section. When the mould rotates, the outer portion of the mould fill by purely centrifugal action and as the liquid metal approaches toward the center, the centrifugal component decreases and gravity component increase. Thus a core is inserted at center to make hollow cavity at the center without centrifugal force. In this process centrifugal force is used for uniform filling of axi symmetrical parts. Gear blanks, flywheel etc. are made by this process.
In this process there are several mould cavities connected with a central sprue with radial gates. This process uses higher metal pressure during solidification. It is used to cast shapes which are not axi symmetrical. This is only suitable for small objects.
- It is widely used in aircraft industries to cast rings, flanges and compressor casting.
- It is used for cast Steam turbine bearing shell.
- Roller for steel rolling mill is another example of centrifugal casting.
- It is used in automobile industries to cast gear blank, cylindrical liners, piston rings etc.
- It is used to cast bearings.
- This process used to cast switch gear components used in electronic industries.
Advantages and Disadvantages:
- It provides dense metal and high mechanical properties.
- Unidirectional solidification can obtain up to a certain thickness.
- It can use for mass production.
- No cores are required for cast hollow shapes like tubes etc.
- Gating system and runner are totally eliminated.
- All the impurity like oxide or other slag particles, segregated at center from where it can easily remove.
- It required lower pouring temperature thus save energy.
- Lower casting defects due to uniform solidification.
- Limited design can be cast. It can cast only symmetrical shapes.
- High equipment or setup cost.
- It is not suitable for every metal.
- Higher maintenance required.
- High skill operator required.
- In this casting process, solidification time and temperature distribution is difficult to determine.
This is all about centrifugal casting working principle, types, application, advantages and disadvantages. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it on social networks. Subscribe our website for more interesting articles.
Thursday, 20 April 2017
Today we will learn about different types of allowance used in pattern making. The pattern is replica of casting but it has slightly large dimension. This change in dimensions in pattern and casting are due to various allowance used in casting. When the cast solidify, it shrink at some extent due to metal shrinkage property during cooling, so a pattern make slightly larger to compensate it. There are another reasons which are due to poor surface finish and casting limitations, casting make slightly larger so it can machine or polish further. So the pattern hence cavity for casting forms slightly larger which can compensate all these drawbacks of casting. The change in dimensions of pattern and casting are known as allowance.
Also Read : Types of Casting
Types of Pattern Allowance:
Allowance can be classified into following types.
Shrinkage is defined as reduce the dimension of casting during solidification or during cooling. This is general property of all materials. Some metal shrinks more, some less but every material shrinks. There are three types of shrinkage.
1. Liquid Shrinkage
2. Solidification Shrinkage
3. Solid Shrinkage
The liquid shrinkage and solidification shrinkage are compensated by suitable riser but solid shrinkage does not compensated by it so the pattern is made slightly larger to compensate shrinkage. This is known as shrinkage allowance.
When the pattern is removed from mould, the parallel surface to the direction at which pattern is withdrawn, damaged slightly and convert into slightly tapered surfaces. To compensate these changes, these parallel surfaces on patterns are made slightly tapered (1-2 degree). This allow easy removal of pattern from mold and does not affect the actual dimension of casting. These are known as draft allowance.
As we known the casting gives poor surface finish and rough surfaces. Also, the Pattern is made manually which does not fixed accurate angles and dimensions of mating parts. But we need a proper finished and dimensionaly accurate casting. To avoid these problems, casting made slightly larger and after solidification machining is done on it for better surface finish and accurate dimensions. This change in dimension of casting is known as machining allowance.
When casting of very thin surfaces like V Shape, U shape etc. it will distort or damage during pattern removal or during casting. To avoid this problem, a chamber is provided on pattern to compensate distortion during pattern removal. This change in casting dimension is known as distortion allowance.
When the pattern is removed from casting, it will slightly increase the dimension of casting. So to compensate this changes, the pattern is made slightly smaller from casting. This change in dimension is known as rapping allowance.
These are all main types of allowance which are considered in pattern making. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it on social networks. Subscribe our website for more interesting articles.
Wednesday, 19 April 2017
Today we will learn about types of pattern used in casting. Pattern is replica or model of object which to be created. It is used to make hollow cavity in sand mold in which molten metal is poured and allow solidifying to create object. The size and shape of cast object is highly depends of shape and size of pattern. Mostly pattern are made by aluminum, wood, wax etc. Metal pattern are used for mass production. The pattern making is most critical work in casting because the object is highly depended on it. A good pattern should follow following requirements.
- Low cost and easy to cast.
- Easy to repair.
- It should light in weight which make it easy to handle.
- It should able to withstand ramming forces without deformation.
- It should does not change its dimensions in presence of moisture.
- It should be easily removable from mould.
- It should have long life without change in its dimensions.
Types of pattern:
As we discussed, casting objects are highly depend on pattern. According to the shape and size of casting and method of making cavity, pattern can be classified as follow.
Single Piece Pattern:
It is simplest type of pattern which is made in single piece. It is used for simple objects. It is either placed into cope or in drag according to the simplicity of operation. It is used to cast stuffing box of steam engines.
Split Pattern or Multi Piece Pattern:
These patterns are made into two or more pieces. The first half of pattern placed into cope and other half into drag. It is used for complex objects where removal of single piece pattern from mould is impossible. When pattern is made in more than three parts cheeks are also used for easy removal.
Cope and Drag Pattern:
These are two piece split pattern as discussed above. It is used for large objects
Match Plate Pattern:
Match plate pattern is a split pattern in which cope and drag section mounted on opposite sides of a plate. The plate is known as match plate. These will make easy to cast any shape with high production rate. Mostly runner, gates etc. are also mounted on same plate which will easy to mould making work. These patterns are used for mass production.
Loose Piece Pattern:
When removal of pattern is impossible due to an extended surface at either upper half or lower half, the extended part made as loose piece so this extended part can be removed first before removal of whole pattern. This will make easy removal of pattern without effect on the cavity. These patterns are known as loose piece pattern.
These are simply more than one looses piece which are attached with a common gating system. These are used for mass production. It is used to produce small size cavities into one mould.
These pattern are used for large rotational symmetrical casting. A sweep is a section of large symmetrical object which is rotated along a edge into sand which make a large symmetrical mould. These patterns makes easy pattern making work of large objects.
These patterns used for large simple castings. In these patterns, skeleton like structure made by using simple pattern sections. These will save both time and material.
Follow Board Pattern:
Follow board is a wooden board which is used to support pattern during moulding. It acts as sit for pattern.
These are all about what is Pattern and types of pattern used in casting. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it on social networks. Subscribe our website for more interesting articles.
Tuesday, 18 April 2017
Today we will learn about what is casting its working process, advantages, disadvantages and main casting terminology. Casting is defined as a manufacturing process in which molten metal pure into a mold or a cavity of desire shape and allow to solidify which form a predefine shape. This process is widely used to manufacture complex parts which cannot be made by other processes. All major parts like bed of lathe machine, milling machine bed, IC engine component etc. are made by this process.
What is Casting:
There are many types of casting which works differently but all these processes involves following steps.
- First metal is melted in a suitable furnace.
- Now molten metal poured into a predefine cavity.
- The molten metal allows to solidify at desire cooling rate.
- Removal of cast part from mould and clean it for further processes like machining, surface finishing polishing etc.
Advantages and Disadvantages:
Casting has following advantages over other manufacturing process.
- It can create any complex structure economically.
- The size of object doesn’t matter for casting.
- The casting objects have high compressive strength.
- All structure made by casting has wide range of properties.
- This can create an accurate object.
- All material can be cast.
- It creates isotropic structure.
- It is cheapest among all manufacturing processes.
- Composite component can be easily made by casting.
Along these advantages, casting has following disadvantages.
- It gives poor surface finish and mostly requires surface finish operation.
- Casting defects involves in this process.
- It gives low fatigue strength compare to forging.
- It is not economical for mass production.
The moulding flask is used to hold the sand mould. The sand mould has desire cavity of object which to be casted. The sand is rammed into the flask to create sand mould in which metal is poured to get desire shape. It is created into minimum two pieces which allows removal of pattern easily.
The upper part of moulding flask is known as cope.
The lower part of moulding flask is known as drag.
When the moulding flask made into more than two parts, the intermediate parts are known as cheeks. These are used in complex casting.
Pattern is replica of object to be created. It is made by either wood, wax or other suitable material. It is placed into moulding flask and sand rammed over it which forms an object cavity into sand.
It is a funnel shape cavity at the top of the mould. The metal is poured into pouring basin from where it is supplied at different parts of mould.
Runner is a horizontal passage of molten metal. It connects sprue to getting system. Normally it is situated at lower half of mould.
Riser is used as reservoir of molten metal when pouring of molten metal has stopped. When the cavity is filled by molten metal, the pouring is stopped which allows solidifying object. During solidification, volumetric shrinkage takes place which reduces the desire size and shape of object. The riser is provided into the mould which supplies the molten metal to remove effect of volumetric shrinkage during solidification. These are further divided into top riser, blind riser, side riser etc.
It is a passage which connects pouring basin to the runner. It controls the flow of molten metal from pouring basin. It is tapered in shape.
It is the entry point through which molten metal enters into the actual mould cavity.
Core is used to cast hollow cavity. It is also a sand structure and placed at right place into mould cavity where hollow part is to be created. The metal poured into mould cavity does not fill the part at which core is placed thus form a hollow cavity.
These are supporting components of core. These used to support and hold the core into mould cavity. These protect the core from various forces encounter in casting.
Chills are generally solid metal pieces which are placed into cavity to increase cooling rate. Mainly it is used to create direction solidification of molten metal. They have high thermal conductivity.
These are small passages made in mould which allow to escape the gases during solidification.
This is all about what is casting, its working process, advantages, disadvantages and terminology used in casting. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it on social networks. Subscribe our website for more interesting articles.