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MANUFACTURING PROCESS -1 BASIC MACHINE TOOLS AND METAL CUTTING

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Q-1 Explain the classification of machine tools.

 Ans. 

Machine tools are broadly classified as follows: 

1. According to the direction of major axis :

The direction of the major axis is a horizontal 

• horizontal center lathe, horizontal boring machine etc. 

The direction of the major axis is vertical 

• vertical – vertical lathe, vertical axis milling machine etc. 

The direction of the major axis is inclined 

• For special case (e.g: transfer machines). 

2. According to the purpose of use: 

• General purpose – e.g. center lathes, milling machines, drilling machines etc.

•Single purpose – e.g. facing lathe, roll turning e etc. special purpose – for mass production. 

3. According to the degree of automation: 

• Non-automatic e.g., center lathes, drilling machines etc. 

• Semi-automatic – e.g., capstan lathe, turret lathe, hobbing machine etc.

• Automatic – e.g., single spindle automatic lathe, Swiss type automatic lathe, CNC milling machine etc. 

4. According to size :

Heavy duty 

e.g., heavy-duty lathes (e.g. > 55 kW), boring mills, planning machine, horizontal boring machine etc.

Medium duty 

e.g., lathes – 3.7 – 11 kW, column drilling machines, milling machines etc. 

Small duty 

e.g., table top lathes, drilling machines, milling machines. 

Micro duty 

e.g., micro-drilling machine etc.

 

Q-2 Define a basic machine tool? Classify them what are the general requirements of machine tools?

Ans. 

Machine tool: 

A machine tool is a non-portable power operated and reasonably valued device or system of device in which energy is expended to produce jobs of desired size, shape and surface finish by removing excess material from the preformed blanks in the form of chips with the help of cutting tools moved past the worked surface.

1. According to the direction of major axis : 

Direction of major axis is horizontal 

• horizontal center lathe, horizontal boring machine etc. 

 

Direction of major axis is vertical 

vertical – vertical lathe, vertical axis milling machine etc. 

 

Direction of major axis is inclined 

• For special case (e.g: transfer machines). 

 

2. According to the purpose of use :

• General purpose – e.g. center lathes, milling machines, drilling machines etc.

•Single purpose – e.g. facing lathe, roll turning e etc. special purpose – for mass production. 

3. According to the degree of automation: 

• Non-automatic e.g., center lathes, drilling machines etc. 

• Semi-automatic – e.g., capstan lathe, turret lathe, hobbing machine etc.

• Automatic – e.g., single spindle automatic lathe, Swiss type automatic lathe, CNC milling machine etc. 

4. According to size :

Heavy duty 

e.g., heavy-duty lathes (e.g. > 55 kW), boring mills, planning machine, horizontal boring machine etc.

Medium duty 

e.g., lathes – 3.7 – 11 kW, column drilling machines, milling machines etc. 

Small duty 

e.g., table top lathes, drilling machines, milling machines. 

Micro duty 

e.g., micro-drilling machine etc.

 

The general requirements of machine tools are: 
 
1. The machine tools should be selected that can reduce labor cost and other general charges to a minimum. 
2. The slides should be machined precisely. 
3. They must have high wear resistance and be hardened. 
4. Some auxiliary equipment should be present for minimizing the manufacturing time in bulk productions. 
5. Big and heavy workpieces should be machined in one fixturing. 
6. Safety precautions must be considered and the design of the machine tool is important for the easy working of the employee.

 

Q-3 Define the term machining. 

Ans. 

Machining is an essential process of finishing by which jobs are produced to the desired dimensions and surface finish by gradually removing the excess material from the preformed blank in the form of chips with the help of cutting tools moved past the work surface. It is a removal process.

 

Q-4 Give classification of machining process. 

Ans. 

The classification of machining process is based on type of cutting edge or point as follows:

1. Single Cutting edge (point) process: 

  • • Turning Operation. 
  • Facing Operation. 
  • Grooving Operation. 
  • Shaping Operation. 
  • Planning Operation. 

2. Multi-Cutting edge (point) process: 

  • • Milling Operation. 
  • • Drilling Operation. 
  • Broaching Operation. 
  • Grinding Operation.
  •  Reaming Operation.

 

Q-5 Explain basic elements of machining. 

Ans. 

The basic elements of machining are workpiece, tool and chip. 

For any cutting action, it is necessary to have relative motion between tool and workpiece. 

Unwanted material is removed from workpiece by the cutting action of the tool. 

The type of chips formed is greatly affected by the workpiece material, geometry of cutting tool and method of cutting. 

The chip formed can be continuous, discontinuous or segmental and continuous chips with built up edge. 

Ductile material, High cutting speeds and large rake angle produce continuous chips. 

Mild steel and copper are considered most desirable metals for producing continuous chips. 

Brittle material (cast iron and bronze), low cutting speeds and small rake angles are the main reasons for producing discontinuous chips. 

Continuous chips with built up edge are mainly produced due to high local temperature, high pressure while cutting ductile material.

Q-6 Explain the primary and auxiliary motions with reference to machine tool. 

Ans. 

The parts of the required shape and size can be obtained on a machine tool by imparting coordinated motions to its working member i.e.. the cutting tool should move in a particular manner with respect to the workpiece. 

There are two types of cutting motions. 

1. Primary motion: 

Primary motion includes the cutting motion and feed motion. The primary motion is the main motion provided by a machine tool or manually to cause relative motion between tool and work piece. So that the face of the tool approaches the work piece material. It absorbs most of the power required to perform a machining operation. Primary motion has the purpose of removing the material from the workpiece. The feed motion is a motion that may be provided to a tool or workpiece by a machine tool which, when added to a primary motion, leads to a continuous chip removal and the creation of machined surface of desired geometry. This motion may proceed in steps or continuously. In both the cases usually absorbs small portion of total power required to perform a machining operation. 

2. Auxiliary motion: 

The auxiliary motions do not participate in the process of formation of the required surface but are nonetheless necessary to make the working motions fulfil their assigned functions. Examples of auxiliary motions in machine tools are clamping and unclamping of the workpiece, idle travel of the cutting tool to the position from where cutting is proceed, changing the speed of feed and drive motions, engaging and disengaging of work motions. 

The auxiliary motions may be carried out manually or may also be power operated depending upon the degree of automation of the machine tool. In general purpose machine tools most of the auxiliary motions are executed manually. In automatic machines, all auxiliary motions are automated and performed by the machine tool itself.

 

Q-7 Describe working and auxiliary motions in machine tools. 

Ans. 

For obtaining the required shape on the workpiece, it is necessary that the cutting edge of the cutting tool should move in a particular manner with respect to the workpiece. 

The relative movement between the workpiece and cutting edge can be obtained either by the motion of the workpiece, the cutting tool or by a combination of the motions of the workpiece and cutting tool. These motions which are essential to impart the required shape to the workpiece are known as working motions. 

Working motions can further be classified as: 

1. Drive motion or primary cutting motion. 

2. Feed motion. Working motions in machine tools are generally of two types: rotary & translatory.

Auxiliary motion: 

The auxiliary motions do not participate in the process of formation of the required surface but are nonetheless necessary to make the working motions fulfil their assigned functions. Examples of auxiliary motions in machine tools are clamping and unclamping of the workpiece, idle travel of the cutting tool to the position from where cutting is proceed, changing the speed of feed and drive motions, engaging and disengaging of work motions. 

The auxiliary motions may be carried out manually or may also be power operated depending upon the degree of automation of the machine tool. In general purpose machine tools most of the auxiliary motions are executed manually. In automatic machines, all auxiliary motions are automated and performed by the machine tool itself.

 

Q-8 What is tool signature and tool geometry?

Ans.

Tool Signature: 

The numerical code that describes all the key angles of a given cutting tool. 

A convenient way to specify tool angles by use of a standardized abbreviated system is known as tool signature or tool nomenclature.

Example: 

Total Signature 0-7-7-7-15-15-1/32 

This implies 

  •  Back rake = 20degree
  •  Side rake = 7degree 7degree 
  •  Side relief = 7degree 
  •  End cutting edge angle = 
  •  Side cutting edge angle = 15degree
  •  End relief = 15degree
  •  Nose radius = 1/32″

 Tool Geometry: 

Geometry of a Cutting Tool. the shape and angles to which the cutting portion of a cutting tool are ground. It influences the type of machining process for materials, the efficiency and economy, the quality of the finished part, and the life of the cutting tool.

 

Q-9 Define lip angle. 

Ans. 

It is defined as the angle between face and minor flank of the single point cutting tool. It depends on the rake and clearance angle provided on the tool.

 

Q-10 Identify the following tool signature 8-12-6- 6-6-10-1 in ASA System. 

Ans. 

According to ASA System 

  • Back rake angle – 8 
  • Side rake angle – 12 
  • End relief angle -6 
  • Side relief angle – 6 
  • End cutting edge -6 
  • Side cutting edge -10 
  • Nose radius -1 inch

 

Q-11 In tool signature 8-14-6-6-20-15-4 what is nose radius value. 

Ans. 

The nose radius value is 4 inch.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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