Types Of Dies In Sheet Metal, Die Construction, Tool Making And Tool Engineering

By // No comments:
Hi friends in the previous post we have discussed types of tool die operations. This post is about types of dies used in the manufacturing industry for sheet metal components. In which the function of dies and differences between these dies are mentioned.

Sheet Metal Stamping Dies

Stamping dies are used to produce the high volume production by stamping process. The die will have the ability to provide appropriate stamping force to perform the required operation. In the die there will be two parts, upper half and the lower half. These part can also be referred as male part and female part. Male or female parts can take either the upper position or the lower position. 

Construction of dies

In a tool, the punches of respective operations like blanking and punching is at the ram or at the bed of the plate. The ram will bolted with the bed of the machine.
For example, the figure of bending tool is given. The tool will rest on the bed of tool. And ram part will press the sheet metal component to produce a bend. 

Bending press tool

Types Of Dies

The different types of dies are given below. The difference between them is important to understand.

Simple Dies

Dies which can perform only one operation in one stroke by press are known as simple dies. This operation can be either cutting operation or forming operation.

Combination Die

These dies are also able to perform more than one operation at one machine station. Since compound die can perform only cutting operation, this die can perform bending or drawing operation along with cutting operations. Because of these properties in the die it is called combination die. For example, to produce a cup shaped component the combination die can be used for blanking punching and drawing simultaneously. 

Compound Die

Compound dies are those in which more than one operations can be performed by one stroke of press at a single station. Basically these types of dies are cutting tools. In such dies only cutting operations can be performed. For example a washer can be pressed out by performing blanking and piercing operation at the same station. These type of dies are very accurate than dies of single operation. Mass production by these dies is more economical than single operation die.

Progressive Dies or follow Dies

Die which can perform series of operations is called progressive or follow die. The operation is performed at each station on a work piece during a stroke of press. The work piece is transferred to the next station between the strokes. In every stroke a finished work is completed. For example, if piercing is done on a part in one stroke, the blanking punch tool cut a blank in the metal in which the previous hole is pierced at previous station. That is why after the first stroke, when thw hole will be punched, the finished product will be produced by each stroke of press.

Transfer Dies

In the transfer dies, the metal work piece do not fed progressively from one to another work station, as in the progressive dies. But in these type of dies the already blanked out work-piece is fed mechanically from one station to another station.

Multiple Dies Or Gang Dies

Multiple dies are those which has the ability to produce more than one work pieces in a single stoke of the press. This is also called Gang Dies.  In this die the number of simple dies and punches are combined or ganged together so that it can produced more than one parts at each stroke of the press.

Inverted Dies

In other dies, the punching tool is held in the punch holder plate which is fastened to the ram. On the other side, the die is fitted with die holder which is fastened at the bed of press. In the inverted dies there is a difference. The places of punch and die are interchanged. In this the punch if fastened at the bed of press and die is attached with the ram.



Difference between progressive die, combination die and compound die

Compound die performs one or more operation simultaneously while progressive die performs series of operations and combination die performs two or more operations at one station. Compound die only performs cutting operations and combination dies can perform other operations like bending, drawing etc.

Introduction To Types Of Press Tool Operation ( Cutting And Non Cutting Actions)

By // No comments:
Hi friends in the another post, we have discussed about types of dies used for manufacturing. Basically the types of dies depends on the type of operation in the press machine. So we will discuss the type of operations in the sheet metal component by press machine.

Type of operation in the press machine

There are many operations which can be performed in the sheet metal. They are divided in the two categories i.e. 1) cutting operations 2) non cutting operations.

Cutting operation in press machine

The operations in which sheet metal component is divided into several parts is called cutting operations. Some important cutting operations are given below-

1) Blanking

This is one of the cutting process. In which the punch tool is imposed or pressed in a specimen to cut the material. In blanking the punched part will be the useful product and the remaining will be the scrap part.

Blanking Operation

2) Piercing

This is same process as blanking. In this process the holes are cut by press machine. But in piercing the punched part will be the scrap and remaining would be useful product.

piercing operation

3) Notching

In the notching process the material is removed from the edges of the specimen. The press is applied and scrap is removed by cutting action from the edge of the work piece.

Notching Operation

4) Parting off

In this cutting process material is removed from one specimen to make two useful products by cutting action.

5) Lacing

In this cutting process the material is not removed totally from the specimen. In a rectangular cut three side cutting operation is done. The remaining side is used for bending.

6) Cut off

If the cutting action is done along a line, it is simply referred as cut off.

7) Perforating

In this cutting process, maximum holes are tried to cut in a single stroke of press. This is a kind of piercing process to cut maximum holes.

8) Cropping

This is cutting action to control the movement of the strip.

9) Nibbling

In this process the successive holes are created by punching. The required size of sheet is created through punching. This is done when the die to cut the sheet is not available or the size of required product is large. This process can also be done by drilling the holes in the specimen.

10) Louvering

This process in consist of cutting and forming process. In this one edge is operated with cutting action and three edges are cut by forming operation.

11) Trimming

This process is to remove the extra unwanted material from a drawn component.

12) Shaving

This is a finishing operation to be performed on the blanked or pierced parts.

Non Cutting Operation In The Press Machine

These operation are generally forming operations. In which the shape of material is changed by plastic deformation. Some of these operation is described below

1) Bending

In this operation the sheet metal is pressed to bend at an angle. The bending tool is designed to fix a certain bending angle for mass production.

2) Embossing

Embossing is the process of producing a shallow forming of identical thickness.

3) Drawing

It is process of changing the blanked part into hollow vessel. This definition is regarding sheet metal because Drawing is also a forming operation.

4) Coining

Process of making impressions and/or depressions in the specimen by press machine tool is called coining.

5) Engraving

It is a process to insert a text on the surface of metal sheet. If someone want to write something on the metal sheet, this process is used. The tool will press the metal to dig out a text.

6) Bulging

In this the height of a cup shaped component is decreased. This happens due to the expansion of cup along a narrow band.

7) Seaming

This is the process of forcing the material along to the periphery of a hollow cylinder.

8) Curling

It is the process to turn the edge inside to a segment.

9) Hemming

It is a process to join the two sheets of metal by interlock them with each other.
Sheet metal industry is very big in the field of manufacturing. Most automobile parts are of sheet metal. So every mechanical geek should know about these operations.
This is all about this post if you want to ask something, please let me know in the comment section. If you have some additional information about this post then please mention it in the comment.

What are Type of chips? (Discontinuous or segmental Chips,Continuous Chips,Continuous Chips With Built-Up Edge)

By // No comments:
In a tool room while machining process is performed in a work piece. The material removal takes place. This material removes in the form of chips. These material chips could be of many types. The type of chips determines the nature and properties of material. As this topic is related to machining process so on should fully understand what is machining process.

Machining is a process under which a specimen is shaped in a desired product by removing the material from the specimen. For machining process a machine tool with a cutting tool is necessary. This material will be removed in the form of chips. Machining is a finishing or a semi finishing process while removing the material. Other finishing process can be implemented after machining if better surface finish is required.

The chips formed after machining can be classified into following types.


  • 1. Discontinuous or segmental Chips
  • 2. Continuous Chips
  • 3. Continuous chips with built-up edge

1) What are Discontinuous Or Segmental Chips ?

These types of chips forms while machining the brittle material. The Chips are collected in the form of segments or pieces. A series of rupture occurs to form these segments. The rupture in the material generally takes place perpendicular to the face of the tool. Good surface finish can be achieved in this type of chips with preserving the tool life for longer. Continuous breaking of chips causes the reduction in friction between tool and chips. The discontinuous or segmental chips are easy to handle, transport and dispose or recycle. 

Segmental chips forms when one or more condition given below satisfies

1. Material is brittle
2. Cutting speed is low
3. Large chip thickness
4. Large depth of cut
5. Small Rack angle in the tool

2) What are Continuous Chips ?

This types of chips generates in the form of continuous segment that is why it is called continuous chips. Due to machining in the ductile material like low carbon steel, copper aluminium etc. this types of chips forms. In a high cutting speed machine this type of chips forms. There would be the continuous plastic deformation in the material to form continuous chips by applying the tool. The friction between the job and tool is less during the process. Chips formed continuously would have uniform thickness throughout the length of the chip. 

The continuous chips forms when one or more condition given below satisfies

1. Material is of ductile nature
2. High cutting speed
3. Large rack angle
4. Depth of cut is small
5. Friction between tool and job work-piece is less
6. Using coolant according to type of material.

3) Continuous Chips with Built up Edge

These types of chips are quite similar to the continuous chips. The difference in this type of chips is that it has a built up edge adjacent to the face of the tool. These chips are not as smooth as continuous chips. Ductility of the material is required same as in continuous chips but the high surrounding temperature, high pressure for cutting and high friction between tool and work-piece will cause the chips to stick on the tool edge. Resulting this phenomenon successive layers will be added and a built up edge is formed. When this series of layers become larger the edge will breaks up in parts. The size of built up edge changes during cutting operation. During cutting first the edge increases, then it decreases and again increases. 

The conditions of formation of built up edge is given below-

1. Machining in ductile material
2. High friction at the face of cutting tool.
3. Proper coolant is not used.
4. High pressure and temperature between specimen and tool.

*Non Homogeneous Chips In Machining*

When the hardness of the material to be machined is very high such as titanium and hard alloys, these types of chips generates. Due to high hardness, yield strength of material decreases and temperature between interface increases.

Introduction And Nomenclature Of Single Point Cutting Tool And Tool Signature

By // No comments:
Hello guys, i am back with my new post about single point cutting tool. in this post you ca have all the information about single point cutting tools. Here we will discuss the nomenclature of single point cutting tool, its parts and tool signature. in the post you can also read the types of cutting positions. 

What Is A Single Point Cutting Tool?

Metal cutting tools are used for machining process in the metals. Metal cutting is conventional process of machining. These tools are used with machines. Machining process is used to provide the required shape in specimen by material removal in a work shop or tool room. These tools are of two types – 1) Single point Cutting Tool, 2) Multipoint Cutting Tool.


Single point cutting tool is the cutting tool which has only one cutting edge. These tools are made of High Speed Steel so these tools can be operated at high RPM. In this only one sharp point is able to remove the material from the specimen. This tool is associated with the machine such as lathe and shaper machine. Then it is subjected to the specimen to perform the machining operation. These tools can be used for turning, shaping, planning etc.

What Is Orthogonal Cutting And Oblique Cutting

These are the types of cutting based on the position of the tool with respect to the specimen and the location of the cutting edge.

1) Orthogonal Cutting

In the orthogonal cutting the tool is set as perpendicular to the axis of the work-piece. This position is generally for turning. This is a two dimensional metal removal position of tool.
Orthogonal cutting

2) Oblique Cutting.

This position is generally to provide a taper in the work-piece. In this position of tool the edge of tool is given an angle. It is a three dimensional metal removal process.

Oblique cutting 

Components of single point cutting tool

Shank:This is the extended body of the tool that is used by machine to hold the tool.
 

Face:This surface is very important in the tool design. The chips of the material after cutting will slide on this face and leave the tool after sliding.
 

Cutting Edge:These are the edges on the face of the tool. This is main part of the tool because the material removal is to be done by these edges. There will be two cutting edges on the tool. These are side cutting edge and end cutting edge. These edges intersects at nose. Side cutting  edge is the major cutting edge in the tool. 
 

Flank:Flank is the surface below the cutting edge and above heel is called flank. These are more than one surfaces.
 

Nose:This is the tip of the tool. And it is the actual cutting point in the tool. It is the intersecting point of end cutting edge and side cutting edge.
 

Heel:Heel is the intersecting edge of flank and base of the tool   

Nomenclature of single point cutting tool

1) Side cutting Angle

It is also called lead angle. It is the angle between side cutting edge of the tool and the side of shank. This angle is important for turning operation and also for removal of chips by sliding on the face.

2) End Cutting Edge angle

End cutting edge is the angle between the end cutting edge of the tool and the line normal to the shank of the tool. This angle is important to provide the clearance between specimen and the cutting edge of the tool.

Nomenclature of single point cutting tool

3) Side Relief Angle

Side relief angle is the angle between the part of flank below the side cutting edge and the line normal to the base of the tool at the right angle to the side. This angle is essential to prevent the interface while the tool enters into the work piece.  The angle is provided to enable the relief between the side flank and job work. If the extra side clearance is provided in the tool then that is known as side clearance angle. This angle is the secondary angle just below to the side relief angle.

4) End Relief Angle

End relief angle is the angle between the part of the end flank just below the cutting edge and the line normal to the base of the tool at the right angle to the flank. This angle provides the facility to the tool to cut the material without rubbing on the job work. If the extra clearance is provided on the tool then that is called end clearance angle. This angle is the secondary angle just below to the end relief angle.

5) Bake Rake Angle

Back rake angle is the angle between the face of cutting tool and a line parallel to the base of the tool measures in a normal plane through the side cutting edge of the cutting tool. Back rake angle is helpful for removing the chips after cutting. When the slope face is downward toward the nose, then this is called negative back rack angle. And when the slope is upward towards the nose. It is known as positive back rake angle.

6) Side Rake Angle.

Side rake angle is the angle between the surface of the flank just below the point and the line downward from the point normal to the base. In the single point cutting tool side rake angle is one by which the face of the tool is inclined sideways. This angle is responsible to determine the thickness of tool after the cutting edge of the tool. Side rake angle is provided to provide the clearance between tool and work piece to prevent the rubbing of the job work with the end flake of the tool.

Basics Of Tool Signature

Tool signature is the determination of different angles in the single point cutting tool. There are seven signature in a single point cutting tool. The following order is a standard tool signature-

1) Back rake angle - 0°
 

2) Side rake angle - 7°
 

3) End relief angle - 6°
 

4) Side relief angle - 8°
 

5) End cutting angle - 15°
 

6) Side cutting edge angle - 16°
 

7) Nose radius – 0.8mm

This is all about single point cutting. your queries are welcome in comment section.

What Are Jigs And Fixtures And Difference Between Them With Application ?

By // No comments:
Jigs and fixtures are very important devices used in manufacturing industry. These devices or equipment are used to locate, guide and hold the work piece in the machining process. The main benefit of jigs and fixtures is repeatability. It eliminates the problem of adjusting the work piece again and again in the machine. So production rate can be increased by reducing the setting time of work pieces. The operations which are required the working tool to be guided or to held in a position to get the repeatability and higher production rate are required the properly designed jigs and fixtures.

Jig are used to guide the work piece while fixtures are used to hold the specimen at a specific place. Jigs and fixtures are comes in the category of tools. Nowadays, jigs and fixtures are very important in the manufacturing industry. Because these tools has the ability to provide high precision, interchangeability and accuracy in the operation. These tools can be designed to use in any kind of production process e.g. machining, welding, assembly, quality inspection etc.




Advantages of jigs and fixtures

1) Jigs and fixtures reduces the time required in the operations by the machine and hence the production rate can be improved.

2) Interchangeability is possible with jigs and fixtures.

3) Higher precision and higher repeatability can be gained.

4) Production cost can be controlled by using jigs and fixtures.

5) Installing Automation becomes easy after using jigs and fixtures in a machine. 

6) Complex shaped parts can be manufactured with higher accurately be positioning it in a rigid fixture tool.

7) The machine using jigs and fixtures do not need highly skilled labour.  

8) The operation becomes safer by decreasing operator’s involvement in the machine.

What is the difference between a jig and a fixture?

The main difference is that jigs are able to guide the work piece but fixture are just able to locate or hold the specimen.
In most cases the jigs has less volume while fixtures are heavy in construction.
Jigs are used for drilling, tapping, boring i.e. one directional operations and fixtures can be used for multi directional operations e.g. shaping, milling, cutting, welding, turning etc.

What are Jigs?

Jigs are unidirectional tool which is used to locate, hold and guide the work piece. Jigs should not be confused with fixtures. Fixture cannot guide the tool but jigs can locate as well as guide the tool. Jigs can provide speed in operation, accuracy, repeatability and interchangeability. Jigs are most commonly used in the operations like drilling, boring, reaming, tapping etc.

In the CNC machines, the use of jigs is not necessary because the machine is controlled digitally by programming using computers. There are many types of jigs depending upon the purposes. Drilling jig is most used type of jig. Drill jig repeatedly locate the center on multiple parts by guiding the drill or reaming tool. 

What Are Fixtures (Tool) ?

Fixture is used to hold the work. It do not have the ability to guide the work piece. Although, the fixtures have large area of applications than jigs. Fixtures are multi-directional tool. They are mainly used for turning, milling, shaping etc. These tools are used to hold and support the work piece so that the machining operation can be performed easily with high precision and accuracy. Fixtures enables the interchangeability and quality assurance in the parts. It reduces the need of skilled labour and produced the product of good quality. 





In the design of fixtures, the part to fix and required part after machining should be kept in mind. Various blocks and plugs are inserted as edge finder and hole or center finder.  These blog will make the work piece to be fixed in a unique position.  This unique position will provide great repeatability and accuracy. Most commonly used fixtures are sawing fixtures, welding fixtures, turning fixture, bending fixture etc. Although, the fixture can be used in any type of operation to get repeatability and high rate of production.

The nomenclature of fixture are to be done on the basis of its application and the machine tool in which the respective fixture is to be used.

What Is Demineralizers Or Ion Exchanger

By // No comments:
Demineralizers also called ion- exchangers. Demineralizers are used in power plants which uses fluids. It is used to eliminate the impurities from fluids. This is most common method to remove impurities dissolved in a fluid. This facility increases the overall efficiency of the plant by preventing the corrosion formation and heat loss.
The demineralizers bears the ion exchange resins and also the transportation of fluid through them.

What Is Demineralizer System

Demineralizer is a cylindrical shaped system in which inlet and outlet port is attached. In the cylinder one port for resin is also connected. At the top of the cylinder the inlet port for water and at the bottom of the cylinder the outlet port is situated. There would be the retention elements to keep the resin beads in the demineralizer. The resin can be altered at bottom by the connections. To purify the water, it is forced in the inlet port at the top of the cylinder to flow through the resin beads. Appropriate flow rate should be maintained for better purification. In the flow path the purification process will be processed and the desired result in the form of purified water will come through the outlet of the tank.

There are two types of demineralizer-

1. Single-Bed demineralizer
2. Mixed bed Demineralizer

Single Bed Demineralizers

In the single-bed demineralizer both cation or anion type of resin beads can be used. In a power plant a series of two single-Bed demineralizers can be used. In the series, first cation bed and then anion bed would be placed. Hydrogen ions and hydroxyl ions are used to substitute the impurities from water. The impurities can be exchanged by hydroxyl ions in the cation bed and in the anion bed hydrogen ions are used to replace the impurities. After ion exchange these two ions will be combined mutually to form water.

Single bed Regeneration

In the single bed demineralizer regeneration process completes in three crucial steps
Initially the water is pumped from the bottom and forced to go through resin beads. This will remove any unwanted particles and. This water will be thrown out from the system from the inlet valve at the top of the cylinder. Finally water will be pumped in a vessel called waste container. This first step in the process is called backwash

The next step is about regeneration. In this step the sources of cations and anions will be used. The cation source is acid solution and anion source would be caustic solution. These ion sources will be mixed with water coming from the top. Proper ratio of water and acid or caustic solution should be maintained i.e. these solution should be diluted. This water will pass through the resin beads and drained out from cylinder to the waste container.

In the last step the water would be inserted again in the cylinder from the inlet port at the top and then flows through the resin and exit at the outlet port. This step is just to eliminate any residue particles if available in the cylinder. This last step is called rinsing.

Mixed bed Demineralizer

As the name of the system, it is mixed-bed demineralizer in which both resin beads i.e. cation and anion resin beads are mixed together. The capacity to exchange the ions with impurities in mixed-bed demineralizers is better. The mixed bed demineraliser is same as the two single bed demineralizers in series. The water produced after the process in the mixed-bed demineralizer will the more pure than the single bed demineralizers. But the process of mixed bed demineralizer is complex.

Mixed bed regeneration

Mixed bed regeneration process is complicated than the single bed demineralizer.
Same as the single bed demineralizers, in the mixed bed demineralizer backwash is the first step of the process. The water enters from the bottom and drained out from the top of the cylinder to washout the foreign substances.

The second step is known as regeneration step in which caustic solution would be mixed with the water and bring at the top of the cylinder. Below that the anion bed would be placed. In the same way the acid solution would be bring at the bottom of the cylinder and the cation bed would be placed above the entrance of the acid solution. The flow rate of these solution would be maintained same. These solution should be drained out after the successful use of the solution. If the system is exposed to the radioactive substances then the wastes should also be treated as radioactive waste.

After regeneration, the rinsing would be the further step. In which the water is to be introduced in the vessel. In the mixed bed ion exchanger, the rinsing is a two way process so the water would be introduced from both ends of the vessel and any residual impurity would be eliminated.

What is Cation Exchange resin

the resin which is used to separate the positive ions from the water is called cation exchange. The cation exchanger is to be charged with negative ions to separate the positive ions.

What is Anion Exchange Resin

This resin is charged with positive ion and it is used to eliminate the negative ion impurities from water.

What are the Four Forces act on the aircraft

By // No comments:

We know that there are four type of forces that act on an aircraft. Now we will discuss these forces in detail. In this post we will discuss how these forces generate and how these forces are controlled by the pilot. 
As we know there are mainly four forces acts on the aircraft whose position and direction can be understand by following picture.

In the picture all the forces are shown acting on the aircraft in the different direction.
Before discussing the four forces first we should know the two types of forces in the aircraft. These types are artificial force and natural forces.
Artificial forces are those which would be generated by pilot during flying operation and natural forces are those which is naturally generated.
The four forces of the aircraft are described below-

Lift on the Aircraft

Lift is a force that acts at vertical upward direction. This force is developed through the wings. And it can be manipulated by varying the angle using flaps. When the aircraft has to climb then the lift would be greater than the weight and when the aircraft has to go down then the lift would be less than the weight. So it is an artificial force that can be controlled by pilot. It act opposite to the weight of the aircraft. In cruise condition of the aircraft, the lift force is equivalent to the weight force of the aircraft.

How lift force generates in the airplane

As mentioned above the lift force is generated through the wings. Actually the shape of the aircraft wings is responsible for the development of the lift force. The aerofoil shape of cross section of the wing creates the lift force in the airplane. So to understand the generation of lift one need to understand the concept of aerofoil

Concept of Aerofoil



In the aerofoil, when the air strikes to the leading edge of the wing the air bifurcates. Which means the portion of air goes up and part of air goes lower side of the wing as shown in figure. The part of air which goes upper side of the aerofoil has to travel more distance than the distance travelled by the air at the lower side of the aerofoil. The air at the upper side of the wing has to increase its velocity to reach out to the air at the lower side at the same time while leaving the aerofoil. 
The aerofoil concept is an application of Bernoulli’s theorem. This theorem also tells us about the relation of velocity and pressure. As there is a velocity difference in the aerofoil. So there would also be the pressure difference. The pressure would be less where the velocity is more and the pressure would be more where the velocity is less.  So the pressure at the upper side of aerofoil would be less than the pressure at the lower side of the aerofoil. Because of this pressure difference the system lift to the upper side. So here the process completes to produce the lift force by the aerofoil.

Thrust force in the Aircraft

Thrust force acts horizontally at the direction of the motion of the aircraft. This force is generally generated by the engines and can be controlled by the pilot. So it is an artificial type of force that acts opposite to the direction of the air flow. This force provides the forward motion to the aircraft. To vary the speed of the aircraft this force is very crucial. The thrust force can be manipulated to control the speed of the aircraft. Thrust force opposes the drag force so the in the cruise condition the thrust would be equivalent to the total drag acting on the aircraft.

How thrust force generates

Thrust force generates through the engine of the aircraft. In the engine fuel is used to generate the energy. The fuel is mixed with the air and the combustion of this air fuel mixture would take place to generate the required energy. The energy would be used to produce the forward horizontal force to move the aircraft that is called thrust. 

Weight force

This force is the total weight of the aircraft. It acts vertically downward in the plane. It is a natural force and cannot be manipulated. This force opposes the lift force. So in cruise condition the weight of the aircraft should be equal to the lift produced in the aircraft by pilot. As the weight cannot be varied so the lift would be manipulated by the pilot to control the altitude of the aircraft.

Drag force on the Aircraft

Drag force is a type of frictional force that is generated due to air resistance in the aircraft. This force is partially artificial because it can be partially manipulated but cannot be eliminated completely.
Drag force acts in the plane in many types. The types of drag is given below

Induces drag or lift-induced drag

This type of drag occurs due to the lift generated in the aircraft. This drag is the horizontal component of lift while vertical component is used to lift the aircraft. The drag due vortex generation also comes under category of induced drag.

Parasite drag

This type of drag mainly includes drag due to friction. When solid body moves through a fluid then this type of friction force generates. In the parasite drag many types of drag are included such as form drag and skin friction.
Form drag generates due to viscosity of fluid. The viscosity of fluid creates the pressure drag. And skin friction is the drag due to roughness of solid body.