What is CNC Machine - Main Parts, Working, Block Diagram

Let me first introduce you about what is CNC machine, so CNC stands for Computer Numerical Control. When computers are used to control a Numerical Control (NC) machine tool than the machine is called CNC machine. In other words the use of computers to control machine tools like lathe, mills, shaper etc is called CNC machine.


what is cnc machine


The cutting operations performed by the CNC is called CNC machining, in CNC machining, programs are designed or prepared first and then it is fed to the CNC machine. According to the program, the CNC controls the motion and speed of the machine tools.

Block Diagram of CNC Machine

Block diagram of cnc machine

Main parts of CNC Machine

The main parts of the CNC machine are

(i) Input Devices: These are the devices which are used to input the part program in the CNC machine. There are three commonly used input devices and these are punch tape reader, magnetic tape reader and computer via RS-232-C communication.

(ii) Machine Control Unit (MCU): It is the heart of the CNC machine. It performs all the controlling action of the CNC machine, the various functions performed by the MCU are

  • It reads the coded instructions fed into it.
  • It decodes the coded instruction.
  • It implements interpolation ( linear, circular and helical ) to generate axis motion commands.
  • It feeds the axis motion commands to the amplifier circuits for driving the axis mechanisms.
  • It receives the feedback signals of position and speed for each drive axis.
  • It implements the auxiliary control functions such as coolant or spindle on/off and tool change.

(iii) Machine Tool: A CNC machine tool always has a slide table and a spindle to control of the position and speed. The machine table is controlled in X and Y axis direction and the spindle is controlled in the Z axis direction.

(iv) Driving System: The driving system of a CNC machine consists of amplifier circuits, drive motors and ball lead screw. The MCU feeds the signals (i.e. of position and speed) of each axis to the amplifier circuits. The control signals are than augmented (increased) to actuate the drive motors. And the actuated drive motors rotate the ball lead screw to position the machine table.

(v) Feedback System: This system consists of transducers that acts like sensors. It is also called as measuring system. It contains position and speed transducers that continuously monitor the position and speed of the cutting tool located at any instant. The MCU receives the signals from these transducers and it uses the difference between the reference signals and feedback signals to generate the control signals for correcting the position and speed errors.

(vi) Display Unit: A monitor is used to display the programs, commands and other useful data of CNC machine.

How CNC Machine Works

  • First the part program is inserted into the MCU of the CNC.
  • In MCU all the data process takes place and according to the program prepared, it prepares all the motion commands and sends it to the driving system. 
  • The drive system works as the motion commands are send by MCU. Drive system controls the motion and velocity of the machine tool.
  • Feedback system, records the position and velocity measurement of the machine tool and sends a feedback signal to the MCU.
  • In MCU, the feedback signals are compared with the reference signals and if there are errors, it corrects it and sends new signals to the machine tool for the right operation to happen.
  • A display unit is used to see all the commands, programs and other important data. It acts as the eye of the machine. 

Advantages and Disadvantages

Advantages

1. It can produce jobs with highest accuracy and precision than any other manual machine.
2. It can be run for 24 hours of a day.
3. The parts produced by it have same accuracy. There is no variation in the parts manufactured by a CNC machine.
4. Highly skilled operator is not required to operate a CNC machine. A semi-skilled operator can also operate accurately and more precisely.
5. Operators can easily make changes and improvements and reduces the delay time.
6. It has the capability to produce complex design with high accuracy in minimum possible time.
7. The modern design software, allows the designer to simulate the manufacturer of his/her idea. And this removes the need of making a prototype or model and  saves time and money.
8. Fewer workers are required to operate a CNC machine and saves labour cost.

Disadvantages

Despite of having so many advantages, a CNC machine has some disadvantages too. And these are:

1. The cost of the CNC machine is very high as compared with manually operated machine.
2. The parts of CNC machines are expensive.
3. The maintenance cost in the case of CNC is quite high.
4. It does not eliminate the need of costly tools.

Application of CNC Machine

Almost every manufacturing industry uses CNC machines. With increase in the competitive environment and demands, the demand of CNC usage has increased to a greater extent. The machine tools that comes with the CNC are late, mills, shaper, welding etc. The industries that are using CNC machines are automotive industry, metal removing industries, industries of fabricating metals, electrical discharge machining industries, wood industries etc.

This is all about what is CNC machine-parts, block diagram, working, advantages and disadvantages and application. If you find any thing missing than comment us. And if this article looks you informative than don’t forget to share it on Facebook and Google+.

Difference Between Stress and Strain in Strength of Materials

In mechanics of solids, the knowledge of difference between stress and strain is very important. When an external force is applied on a body, it starts to deform. the external force applied on the body induces a resisting force within the body, when this resisting force is taken on unit area is called stress. There is a change in the dimension of the body due to the induced stress. The ratio of this change in dimension with the original dimension of the body is called strain.

Difference Between Stress and Strain in Tabular Form

Difference Between Stress and Strain

S.no
Stress
Strain
1.
Stress is defined as the resisting force per unit area.
Strain is defined as the deformation per unit area.
2.
The ratio of resisting force ( or applied load) to the cross section area of the body is called stress.
The ratio of change in dimension of the body to the original dimension is called strain.
3.
Stress is denoted by the Greek symbol ‘σ’ ( sigma).
Strain is denoted by the symbol ‘e’.
4.
The formula of stress is given by


The formula of strain is given by

5.
The unit of stress is N/m2 or N/mm2.
Strain is a unitless quantity.
6.
Stress can exist without strain.
Strain cannot exist without stress.
 7.
The various types of stress are: tensile stress, compressive stress and shear stress.
The various types of strain are: tensile strain, compressive strain, shear strain and volumetric strain.

Comparison Between Stress and Strain

The various comparison between stress and strain are as follows:
  • Stress is the resisting force per unit area where as strain is the deformation per unit area.
  • The stress is given by the ratio of resisting force to the cross section area of the body. The strain is given by the ratio of change in dimension to the original dimension.
  • The stress is denoted by the symbol ‘σ’ and strain by ‘e’.
  • The unit of stress is N/m2 or N/mm2 whereas the strain does not have units.
  • The stress can exist without strain but the existence of strain without stress in not possible.
This is all about the difference between stress and strain in strength of materials. If you find any suggestion regarding this article than you can comment us. If you found this article informative or useful than don’t forget to share and like.

Difference Between NC and CNC Machine

In this article we will study about the difference between NC and CNC machine. In today’s world every manufacturing industries wants high accuracy products in less time. And this complexity of high accuracy in minimum time can be achieved by use of NC and CNC machine. Most of us do not know the basic difference between these machines. Here we will discuss about the basic differences among them.

Difference Between NC and CNC machine

Difference between NC and CNC Machine


The various difference between NC and CNC machine  in tabular form are as follows:

S.no
NC Machine
CNC Machine
1.
Here NC stands for Numerical Control
CNC stands for Computer Numerical Control.
2.
It is defined as the machine which is controlled by the set of instructions in the form of numbers, letters and symbols. The set of instructions is called as program.
It is defined as the machine which is used to control the motions of the workpiece and tool with the help of prepared program in computer. The program is written in alphanumeric data.
3.
In NC machine the programs are fed into the punch cards.
In CNC machine the programs are fed directly into the computer by a small key board similar to our traditional keyboard.
4.
Modification in the program is difficult.
Modification in the program is very easy.
5.
High skilled operator is required.
Less skilled operator is required.
6.
Cost of the machine is less.
Cost of the CNC machine is high.
7.
Maintenance cost is less
Maintenance cost is high.
8.
The programs in the NC machine cannot be stored.
In CNC machines, the programs can be stored in the computer and can be used again and again.
9.
It offers less flexibility and computational capability.
It offers additional flexibility and computational capability.
10.
 The accuracy is less as compared with the CNC.
It has high accuracy.
11.
It requires more time for the execution of the job.
It takes very less time in the execution of the job.
12.
It is not possible to run it continuously.
It can be run continuously for 24 hours of a day.

Comparison Between NC and CNC Machine

The comparison of NC and CNC machine are:
  • NC stands for Numerical Control whereas CNC stands for Computer Numerical Control.
  • In NC Machine the programs are fed into the punch cards. But in CNC machine the programs are fed directly into the computer with the help of a small keyboard similar to our traditional keyboard.
  • In NC machine if and error occurs in the program than its debugging and modification is not easy. In CNC machine the debugging and modification is very easy.
  • High skilled operator is required to operate the NC machine whereas to operate a CNC machine, a semiskilled operator may work.
  • The cost of the NC machine is less as compared with the computer control machines.
  • The maintenance cost of NC is less whereas it is costly in the case of CNC machine.
  • No programs can be stored in the NC machine. In CNC machine, numbers of programs can be stored and can be used again and again for the production.
  • The accuracy of the NC is less as compared with the CNC.
  • In NC machine the execution of the job takes more time but the CNC machine executes the job without taking much time.
  • NC cannot be run continuously for 24 hours but CNC machine can be run for 24 hours continuously.
This is all about the difference between NC and CNC machine. If you find any modification in this article than comment us. And if you found this article useful than don’t forget to share it.

Types of Chips in Metal Cutting

In this article we will learn about different types of chips in metal cutting. When metals are finished in manufacturing industries through machining process than metal chips are produced. These metal chips may be of different types. The chips formed depend upon the types of materials used and other factors too. Here we will discuss about them in detail.

During the machining process of the workpiece to give it a desired shape, metal chips are produced. The chips formed may be of continuous, discontinuous and continuous with built up edge type. The types of chips formed in machining process depends upon so many factors, we will discuss it later. Basically there are three types of chips produced in the metal machining and these are continuous, discontinuous and continuous with built up edge.

Types of Chips

The various types of chips in metal cutting are

Types of Chips in Metal Cutting

1. Continuous chips 
2. Discontinuous chips &
3. Continuous chips with built up edge (or BUE chips)

Let’s discuss about them one by one

1. Continuous Chips

If the metal chips formed during machining is without segments i.e. without breakage, than it is called as continuous types of chips.

continuous chips in metal cutting


Continuous chips are formed when the ductile material is machined with high cutting speed and minimum friction between the chip and tool face.

The conditions which are responsible for the formation of continuous types of chips are

(i) Ductile material like mild steel is used.
(ii) Bigger rake angle of the tool.
(iii) High cutting speed.
(iv) Minimum friction between the chip and tool interface.
(v) Small depth of cut.

Advantages

The formation of continuous chips during machining process has the following advantages

• Better surface finish to the ductile material.
• Less heat generation due to minimum friction between the tool face and chip.
• Low power consumption.
• Long tool life due to less wear and tear.

2. Discontinuous Chips

If the chips formed during machining process is not continuous i.e. formed with breakage is called discontinuous chips.

Discontinuous chips


Discontinuous types of chips are formed when hard and brittle metals like brass, bronze and cast iron is machined.

Conditions which are responsible for the formation of discontinuous chips are:

(i) Low feed rate.
(ii) Small rake angle of the tool.
(iii) High cutting speed.
(iv) High friction forces at the chip tool interface.
(v) Too much depth of cut.

Advantages

The formation of discontinuous types of chips in brittle materials provides good surface finish, increases the tool life and reduces the consumption of power.

Disadvantages

When discontinuous chips are formed in the ductile materials, the workpiece result in poor surface finish and excessive wear and tear of the tool takes place.

3. Continuous Chips with Built Up Edge

Continuous chips with built up edge is formed by machining ductile material with high friction at the chip-tool interface.

Continuous Chips with Built Up Edge

It is similar to the continuous types of chips but it is of less smoothness due to the built up edge.

How Built Up Edge is Formed?

When the chip is flows in upward direction and high friction is exist in between the interface of the chip and tool. Due to the high friction between the chip and tool a very intense heat is generated at the nose of the tool.  The compressed metal adjacent to the tool nose gets welded to it. This compressed metal welded to the nose is called built up edge. When the chip flows through this built up edge, it gets broken and carried away by the chip and called as built up edge chips, the rest of the built up edge is adhere to the surface of the workpiece and makes it rough.

Due to formation of the built up edge the rake angle of the tool gets changed and so is the cutting force.

The factors which are responsible for promoting the formation of the BUE chips are:

(i) Excessive feed rate.
(ii) Small rake angle of the tool.
(iii) Low cutting speed.
(iv) Lack of coolant and this increase the friction between the chip tool interfaces.

Advantages

The making of the BUE has one advantage i.e. it protects the tool from getting damaged from high friction and temperature generated during machining process and hence the tool life increases.

Disadvantages 

The formation of these types of chips results in rough surface finish, change in the rake angle and cutting forces.

Comparison between Continuous, Discontinues and Continuous Chips with Built up Edge in Tabular Form are:

S.no
Factors
Continuous
Chips
Discontinuous
Chips
Continuous chips with Built Up Edge (BUE)
1.
Material types
Ductile
Brittle, ductile but hard
Ductile
2.
Rake angle
Large
Small
Small
3.
Cutting speed
High
Medium or high
Low or medium
4.
Friction between chip tool interface
Minimum
Maximum
Maximum
5.
Depth of cut
Small
High
Medium

This is all about the different types of chips in metal cutting. If you find anything missing or incorrect than comment us. And if you find this article informative and useful than don’t forget to share it.



Single Point Cutting Tool Geometry, Angles, Nomenclature and Signature

In this article we will study about Single point cutting tool geometry, angles, nomenclature and signature.

What is Single Point Cutting Tool?

As its name indicates, a tool that has a single point for cutting purpose is called single point cutting tool. It is generally used in the lathe machine, shaper machine etc. It is used to remove the materials from the workpiece.

Geometry

Single Point Cutting Tool Geometry


1. Shank: It is that part of single point cutting tool which goes into the tool holder. Or in simple language shank is used to hold the tool.
2. Flank: It is the surface below and adjacent of the cutting edges. There are two flank surfaces, first one is major flank and second one is minor flank. The major flank lies below and adjacent to the side cutting edge and the minor flank surface lies below and adjacent to the end cutting edge.
3. Base: The portion of the shank that lies opposite to the top face of the shank is called base. 
4. Face: It is the top portion of the tool along which chips slides. It is designed in such a way that the chips slides on it in upward direction.
5. Cutting edge: The edge on the tool which removes materials from the work piece is called cutting edges. It lies on the face of the tool. The single point cutting tool has two edges and these are
(i) Side cutting edge: The top edge of the major flank is called side cutting edge.
(ii) End cutting edge: The top edge of the minor flank is called end cutting edge.
6. Nose or cutting point: The intersection point of major cutting edge and minor cutting edge is called nose.
7. Nose radius: It is the radius of the nose. Nose radius increases the life of the tool and provides better surface finish.
8. Heel: It is a curved portion and intersection of the base and flank of the tool. 

Angles

The various angles of the single point cutting tool have great importance. Each angle has its own function and speciality.

1. End Cutting Edge Angle: The angle formed in between the end cutting edge and a line perpendicular to the shank is called end cutting edge angle.
2. Side Cutting Edge Angle: The angle formed in between the side cutting edge and a line parallel to the shank.

End cutting or side cutting edge angle

3. Back Rack Angle: The angle formed between the tool face and line parallel to the base is called back rake angle.
4. End Relief Angle: The angle formed between the minor flank and a line normal to the base of the tool is called end relief angle. It is also known as front clearance angle. It avoid the rubbing of the workpiece against tool.
5. Lip Angle/ Wedge Angle: It is defined as the angle between face and minor flank of the single point cutting tool.


Single Point Cutting Tool Angles



 6. Side Rake Angle: the angle formed between the tool face and a line perpendicular to the shank is called side rake angle.
7. Side Relief Angle: the angle formed between the major flank surface and plane normal to the base of the tool is called side relief angle. This angle avoids the rubbing between workpiece and flank when the tool is fed longitudinally.

Single Point Cutting Tool Angles

Nomenclature

There is three coordinate systems which are most popular in tool nomenclature. And these are
1. Machine Reference System (MRS)
2. Orthogonal Tool Reference System (ORS) or Orthogonal Rake System
3. Normal Reference System (NRS)

Signature

The shape of a tool is specified in a special sequence and this special sequence is called tool signature. The tool signature is given below

(i) Back rake angle
(ii) Side rake angle
(iii) Clearance or End Relief angle
(iv) Side Relief angle
(v) End cutting edge angle
(vi) Side cutting edge angle
(vii) Nose radius

A typical tool signature of single point cutting tool is 0-7-6-8-15-16-0.8. Here this tool signature indicates that the tool has 0, 7, 6, 8, 15, 16 degree back rake, side rake, end relief, side relief, end cutting edge, side cutting edge angle and 0.8 mm nose radius.

For Better Explanation Watch the Video Given Below:



This all about the single point cutting tool geometry, angles,nomenclature and signature. If you find anything missing or wrong than comment us. And if you like this article than don't forget to share on Facebook and google+.


What is Milling Machine - Operation, Parts and Types.

In this article you will able to learn about what is milling machine operation, parts and types. Milling machine is the backbone of the manufacturing industries. Almost it is capable of doing any milling operation whether it is gear milling, thread milling, angular milling etc. Here we will discuss about definition, main parts, types and operations of milling machine. 

What is Milling Machine?

It is a machine which is used to remove metals from the workpiece with the help of a revolving cutter called milling cutter. It is used to machined the flat, rough and irregular surfaces and this is done by feeding the workpiece against a rotating milling cutter.

Main Parts of Milling Machine

The milling machine main parts are:


Main parts of vertical milling machine

Vertical Milling Machine 

Main parts of horizontal milling machine

Horizontal Milling Machine

1. Column & Base

Column including base is the main casting that supports all other parts of milling machine.
  • The column contains an oil reservoir and a pump which lubricates the spindle.
  • The column rests on the base and base contains coolant reservoir and a pump which is used during machining operation that requires coolant.

2. Knee

It is a casting that supports the saddle and table. All gearing mechanism is enclosed within the knee.
  • It is fastened to the column by dovetail ways.
  • The knee is supported and adjusted by a vertical positioning screw (elevating screw).
  • The elevating screw is used to adjust the knee up and down by raising or lowering the lever either with the help of hand or power feed. 

3. Saddle and Swivel Table

Saddle is present on the knee and supports the table. It slides on a horizontal dovetail on the knee and dovetail is parallel to the axis of the spindle ( in horizontal milling m/c).
  • The swivel table (in universal machines only) is attached to the saddle that can be swiveled (revolved) horizontally in either direction.

4. Power Feed Mechanism

It is the knee which contains the power feed mechanism. It is used to control the longitudinal ( left and right), transverse ( in and out) and vertical (up and down) feeds.
  • To get the desired rate of feed on the machine, the feed selection lever is positioned as indicated on the feed selection plates.
  • On some universal knee and column milling machine, the feed is obtained by turning the speed selection handle until the desired rate of feed is indicated on the feed dial.
  • Most of the milling machines have a rapid traverse lever that can be engaged when a temporary increase in the speed of the longitudinal, transverse or vertical feeds is required. For example this lever would be engaged when the operator is positioning or aligning the work.

5. Table

It is a rectangular casting which is present on the top of the saddle.
  • It is used to hold the work or work holding devices.
  • It contains several T-slots for holding the work and work holding devices (i.e. jigs and fixtures).
  • The table can be operated by hand or by power.To move the table by hand, engage and turn the longitudinal hand crank. To move it through power, engage the longitudinal direction feed control lever.

6. Spindle

It is the shaft which is used to hold and drives the cutting tools of the milling machine.
  • Spindle is mounted on the bearings and supported by the column.
  • Spindle is driven by the electric motor through gear trains. The gear trains are present within the column.
  • The face of the spindle which lies near to the table has an internal taper machined on it. The internal taper at the front face of the spindle permits only tapered cutter holder or arbor. It has two keys at the front face which provides positive drive for the cutter holder or arbor.
  • The drawbolt and jamnut is used to secure the holder and arbor in the spindle.

7. Over Arm / Overhanging Arm

It is a horizontal beam present at the top face of the column. It may be a single casting which slides on the dovetail ways present on the top face of the column.
  • The overarm is used to fastened arbor support. It may consist of one or two cylindrical bars which slide through the holes in the column.

8. Arbor Support

It is a casting with bearing that supports the outer end of the arbor. It also helps in aligning the outer end of the arbor with the spindle.
  • It prevents the springing of outer end of the arbor during cutting operations.
  • There are generally two types of arbor supports used in the milling machine. The first one has small diameter bearing hole, 1-inch in maximum diameter. And the other one has large diameter bearing hole, usually upto 23/4 inches.
  • The arbor support has an oil reservoir that lubricates the bearing surfaces. It can be clamped anywhere on the overarm. The arbor support is used only in the horizontal types of milling machine.

9. Ram

The overhanging arm in the vertical machine is called ram. One end of the ram is mounted on the top of the column and on the other end milling head is attached.
  • The ram can be a moved transversally ( in and out) on the column by a hand lever.  

Types of Milling Machine

Types of milling machine


Basically the milling machines are divided into two types first is horizontal milling machine and second one is vertical milling machine. They are further classified as knee-type, ram-type, manufacturing or bed type and planer-type milling machine.

Most of the milling machine classified above has self-electric driven motor, coolant systems, power operated table feed and variable spindle speeds.

1. Horizontal Milling Machine

In horizontal milling machine the axis of rotation of the spindle is horizontal to the table. And due the axis of spindle horizontal, it is called as horizontal milling machine.

2. Vertical Milling Machine

The milling machine in which the spindle axis is perpendicular to the table is called vertical milling machine.

3. Knee-Type Milling Machine

The milling machine which has a knee like projection at the middle is called knee-type milling machine. It is characterised by a vertical adjustable work table resting on a saddle supported by a knee.

4. Ram-Type Milling Machine

A milling machine which has a ram on the top of the column is called ram type milling machine. Generally ram is used in vertical milling machine. It can be moved on the column in transverse direction (i.e. in and out when operated from the knee side.

5. Manufacturing or Bed -Type Milling Machine
6. Planer-Type Milling Machine: 

Milling Machine Operation

The different milling machine operation is:

1. Face Milling

This operation makes flat surfaces at the face of workpiece. This machining operation is done on the surfaces which are perpendicular to the axis of the cutter. The operation is performed by the face milling cutter mounted on stub arbor of the machine.

2. Side Milling

It is the machining process which produces flat vertical surface at the sides of a workpiece. This operation is performed by using side milling cutter.

3. Plain Milling

It is a Process of milling flat surfaces keeping the axis of the cutter parallel to the  surface being milled. It is also called surface milling or slab milling. A plain milling cutter is used for the plain milling.

4. Straddle Milling

it is a process in which two side milling cutter are used to machined two opposite sides of a workpiece simultaneously. The straddle milling operation is shown in the figure given below.

5. Angular Milling

It is a process of milling flat surfaces which are neither Parallel nor perpendicular to the axis of the milling cutter. It is also called as angle milling. A single angle milling cutter is used to perform this operation.

6. Gang Milling

It is the machining process in which two or more milling cutters are used together to perform different milling operation simultaneously. In gang milling the cutters are mounted on the arbor.

7. Form Milling

It is the process of machining special contour (outline) composed of curves, straight lines, or entirely of curves, at a single cut. Formed milling cutters shaped to the contour to be cut are used to perform this operation. This operation is accomplish by using convex, concave and corner rounding milling cutters.

8. Profile Milling: 

This milling operation is used to cut a profile on the workpiece. 

9. End Milling

It is the process of producing flat surfaces which may be horizontal, vertical and at any angle taking worktable as a reference. End milling cutters are used to accomplish this operation.

10. Saw Milling

It is machining process which is used to produce narrow grooves or slots on the workpiece.
  • It is also used for the parting off the workpiece into two equal or unequal parts.
  • This milling operation is performed by using saw milling cutter.
  • The width of the this cutter is very less as compared with the width of the workpiece.

11. Milling Key Ways, Grooves and Slots

This milling operation is used to produce key ways, grooves and slots on the workpiece. 

12. Gear Milling

It is the milling process which is used to cut gears on the workpiece. This operation is done by using formed milling cutters called involute gear cutters.

13. Helical Milling

This milling operation is done to produce objects having helical design such as helical gears, twisted drills etc. it is done on the periphery of the cylindrical workpiece.

14. Cam Milling

It is a machining process which is used to make cams. The cams are used to open and close of the valves in the internal combustion engines.

15. Thread Milling

It is the process of milling used to cut threads on the cylindrical workpiece.

For better explanation on the types of milling machine operation, must watch the video given below:




This is all about what is milling machine-operation parts and types. If you find any improvement in the article please tell us through your valuable comments. And if you find this article informative & useful, please don’t forget to share.