69 Questions
What is the major difference between metal forming processes and metal cutting processes?
Amount of material removed
What is the primary objective of machining in the manufacturing process?
To achieve desired dimensions and surface finish
Why is preforming like casting or forging insufficient for engineering components like gears and screws?
It doesn't provide the desired accuracy and finish
Which term best describes the gradual removal of excess material from a preformed blank to achieve the desired dimensions and surface finish?
Machining
What characteristic differentiates metal cutting processes from metal forming processes?
Generation of chips
Why do components like gears and bearings require good surface finish?
To reduce friction and wear
What is the primary purpose of machining a work?
To produce jobs of desired size, shape, and surface finish
What is the function of cutting fluid in machining?
To ease machining by cooling and lubrication
Which type of machine tool is a vertical axis milling machine classified as?
Vertical
What is the main difference between non-automatic and automatic machine tools?
Degree of automation
Which classification of machine tools is based on the number of spindles they have?
According to number of spindles
What is a salient feature used for specifying a center lathe machine tool?
Maximum diameter and length of accommodated jobs
In machining, what are the physical functions of a machine tool?
To firmly hold the blank and the tool
What differentiates heavy-duty machine tools from small-duty ones?
Size and power capacity
What differentiates single spindle lathes from multi spindle lathes?
Number of spindles present
What is the purpose of rake angle in cutting tools?
To reduce cutting force and power requirement
Which classification of cutting tools includes milling cutters and hobs?
Multipoint cutting tools
In the Machine Reference System (ASA system), how are the angles of cutting tools expressed?
With respect to planes and axes of the machine tool
What is the main role of clearance angle in cutting tools?
To avoid rubbing of the tool with the machined surface
Why might a cutting tool have a positive rake angle?
To help reduce cutting force
What is the classification of cutting tools that involve drills?
Double point cutting tools
Which system visualizes only the salient features of cutting tools without providing quantitative information?
Tool-in-Hand System
In the context of cutting tools, what does the term 'multi-point' refer to?
'Multi-point' means having more than two major cutting edges.
Which type of rake angle design is chosen to increase edge-strength and tool life?
Negative rake angle
What is the function of clearance angle in cutting tools?
To avoid rubbing of the tool with the machined surface
What is the main factor that determines the pattern and extent of total deformation of machining chips?
Work material
Which experimental method involves the study of running chips using a high-speed camera with a low magnification microscope?
Study of running chips with a high-speed camera
What is the mechanism of chip formation generally observed in machining ductile materials?
Yielding
What happens at the sharp crack-tip during machining of brittle materials?
Stress concentration occurs
What kind of chips are typically produced when machining ductile materials?
Flat, curved or coiled continuous chips
Which parameter is used to quantify the pattern and degree of deformation during chip formation?
Chip reduction coefficient
What does the chip thickness ratio compare in machining processes?
Thickness of uncut layer to chip thickness ratio
In machining ductile materials, what contributes to the increase in chip thickness compared to uncut chip thickness?
Lamellar sliding effect
Which parameter defines the axial travel of the tool per revolution of the job?
Feed rate
What characteristic behavior do semi-ductile or semi-brittle materials exhibit under compressive forces at the cutting zone during machining?
Ductile behavior under compressive forces
What is the role of the rake angle and friction at the chip-tool interface on chip reduction coefficient?
Affect the value of the chip reduction coefficient
How is chip thickening usually expressed in terms of the chip thickness?
$a1 / a2$
What does a larger value of the chip reduction coefficient (rc) indicate?
More effort required for machining
What does equation 1.8 suggest about the relationship between chip velocity (Vf) and cutting velocity (VC)?
$Vf$ is always less than $VC$
What is the relationship between shear angle and chip reduction coefficient according to equation 1.10?
Shear angle increases with an increase in chip reduction coefficient
Which parameter affects the value of the cutting strain during machining?
Tool rake angle
How can chip reduction coefficient be reduced desirably?
By using lubricant to reduce friction
What happens to shear angle with an increase in tool rake angle?
Increases
What type of material favors the formation of continuous chips without Built-Up Edge (BUE) chips?
Ductile
Which of the following cutting velocities is favorable for the formation of continuous chips?
High
What type of chips are commonly formed when cutting brittle materials like cast iron?
Segmental chips
Which rake angle is conducive to the formation of continuous chips?
Positive and large
Which cutting fluid type is recommended for the formation of continuous chips?
Both cooling and lubricating
In machining, what are segmental chips characterized by?
Fracturing like segments or fragments
What is chip flow deviation angle denoted by in the text?
c
In pure orthogonal cutting, what angle is typically equal to 900?
f
What does BUE stand for in metal machining?
Built-Up-Edge
What encourages and accelerates the formation of Built-Up-Edge (BUE)?
High cutting velocity
Why does Built-Up-Edge (BUE) form in machining ductile materials?
Adhesion due to high stress and temperature
What can happen if the force exerted on Built-Up-Edge (BUE) exceeds its bonding force?
BUE is broken or sheared off
How does high cutting velocity affect Built-Up-Edge (BUE) formation?
Favors BUE formation initially, then hinders it at very high speeds
What harmful effect does Built-Up-Edge (BUE) have on cutting forces?
Increases cutting forces by changing the rake angle
What kind of chips form in machining when the metal is separated without any discontinuity and moves like a ribbon?
Continuous chips without Built-Up-Edge (BUE)
What influences the type of chips formed in metal machining?
Type of cut and work material
Why does Built-Up-Edge (BUE) formation deteriorate surface finish?
By causing an increase in cutting forces
What is the designation (Signature) of a tool geometry with angles 6, 7, 8, 6, 5, 7 and a nose radius of 0.1 in the ASA System?
6, 7, 8, 6, 5, 7, 0.1
Which geometry angle in the ASA System is measured on the machine transverse plane Y?
Back rake angle (y)
What is the surface against which the chip slides upward in a single point cutting tool?
Face
In the ASA System for tool geometry, which plane is perpendicular to both the machine longitudinal plane X and the reference plane R?
Machine transverse plane Y
What does the term 'shank' refer to in relation to a single point cutting tool?
The portion of the tool bit not ground to form cutting edges
Which angle provides strengthening to the tool nose and better surface finish in a single point cutting tool?
Nose radius
What is the role of an inclination angle in relation to the direction of chip flow in metal cutting processes?
Causes chip flow along orthogonal plane
Which type of metal cutting process involves only two forces and simpler analysis?
Orthogonal cutting process
'Auxiliary flank' is associated with which surface in a single point cutting tool?
'Flank'
Study Notes
Theory of Metal Cutting
- Metal cutting is a process of gradual removal of excess material from the preformed blanks in the form of chips with the help of cutting tools moved past the work surface(s).
- The purpose of machining is to impart required dimensional and form accuracy and surface finish to enable the product to fulfill its basic functional requirements, provide better or improved performance, and render long service life.
Types of Cutting Tools
- Cutting tools can be classified according to the number of major cutting edges (points) involved:
- Single point: e.g., turning tools, shaping, planning, and slotting tools, and boring tools.
- Double (two) point: e.g., drills.
- Multipoint (more than two): e.g., milling cutters, broaching tools, hobs, gear shaping cutters, etc.
Geometry of Single Point Cutting Tools
- The concept of rake angle and clearance angle will be clear from some simple operations:
- Rake angle: Angle of inclination of rake surface from the reference plane.
- Clearance angle: Angle of inclination of clearance or flank surface from the finished surface.
- Rake angle may be positive, zero, or negative, depending on the machining operation.
- Clearance angle is essentially provided to avoid rubbing of the tool (flank) with the machined surface.
Systems of Description of Tool Geometry
- Tool-in-Hand System: Only the salient features of the cutting tool point are identified or visualized.
- Machine Reference System (ASA system): The geometry of a cutting tool refers mainly to its several angles or slopes of its salient working surfaces and cutting edges.
- Tool Reference System: Orthogonal Rake System (ORS) and Normal Rake System (NRS).
- Work Reference System (WRS): The planes and axes used for expressing tool geometry in ASA system for turning operation.
Mechanism of Chip Formation
- In machining ductile materials, the chip forms through a process of gradual compression, shear deformation, and slip.
- Piispannen's model explains chip formation using a card analogy.
- The geometry of chip formation is influenced by:
- Work material
- Material and geometry of the cutting tool
- Levels of cutting velocity and feed
- Machining environment or cutting fluid
- Machining of ductile materials generally produces flat, curved, or coiled continuous chips.
Chip Thickness Ratio
- Geometry and characteristics of chip forms are assessed and expressed by some factors, the values of which indicate about the forces and energy required for a particular machining work.
- The chip thickness ratio (a2/a1) is a significant parameter in chip formation.
- The reasons for the chip thickness ratio being greater than unity are:
- Compression of the chip ahead of the tool
- Frictional resistance to chip flow
- Lamellar sliding according to Piispannen### Chip Reduction Coefficient
- The chip reduction coefficient (rc) is the ratio of chip thickness after cutting (a2) to chip thickness before cutting (a1)
- rc = a2 / a1
- Larger values of rc indicate more thickening, requiring more force or energy to accomplish machining
- Desirable to reduce rc without sacrificing productivity (metal removal rate, MRR)
Factors Affecting Chip Reduction Coefficient
- Tool rake angle: larger positive rake angle reduces rc
- Chip-tool interaction: reducing friction by using a lubricant reduces rc
- Equation 1.4: rc = cos(β - γ) / sinβ
Shear Angle
- Shear angle (β) is the angle of inclination of the shear plane from the direction of cutting velocity
- β depends on:
- Chip thickness before and after cutting (rc)
- Rake angle (γ)
- Equation 1.10: tanβ = cos / rc - sin
- Equation 1.11: tanβ = rcos / 1 - rsin
- Increasing rc decreases shear angle, and vice-versa
Cutting Strain
- Cutting strain (ε) is the magnitude of strain that develops along the shear plane due to machining
- Equation 1.12: ε = cotβ + tan(β - γ)
ASA System for Tool Geometry
- The ASA system is used to define tool geometry
- Axes: R, X, Y, Xm, Ym, Zm
- Planes: Reference plane (R), Machine longitudinal plane (X), Machine transverse plane (Y)
- Geometrical features and angles:
- Shank: portion of the tool bit not ground to form cutting edges
- Face: surface against which the chip slides upward
- Flank: surface that faces the work piece
- Heel: lowest portion of the side cutting edges
- Nose radius: conjunction of the side cutting edge and end cutting edge
- Base: underside of the shank
- Rake angles: side rake angle (x), back rake angle (y)
- Clearance angles: side clearance angle (ax), back clearance angle (ay)
- Cutting angles: side cutting edge angle (fs), end cutting edge angle (fe)
Designation of Tool Geometry
- Tool geometry is designated by a series of values of the salient angles and nose radius
- Example: y, x, ay, ax, fe, fs, r (in inch)
Types of Metal Cutting Processes
- Orthogonal cutting process: cutting edge or face of the tool is 90° to the line of action or path of the tool
- Oblique cutting process: cutting edge or face of the tool is inclined at an angle less than 90° to the line of action or path of the tool
Built-up-Edge (BUE) Formation
- Causes of BUE formation:
- High stress and temperature at the chip-tool interface
- Mutual affinity or solubility of the chip-tool materials
- Characteristics of BUE:
- Shape, size, and bond strength
- Depend on work-tool materials, stress, and temperature
- Effects of BUE formation:
- Unfavorably changes rake angle at the tool tip
- Increases cutting forces and power consumption
- Reduces tool life
- Deteriorates surface finish
Types of Chips
- Continuous chips without BUE: formed when the cutting tool moves towards the work piece, and the metal is separated without discontinuity
- Discontinuous chips: formed when the metal is fractured like segments of fragments and passes over the tool faces
- Factors affecting chip formation:
- Type of cut (continuous or intermittent)
- Work material (brittle or ductile)
- Cutting tool geometry (rake, cutting angles)
- Cutting velocity and feed
- Cutting fluid (type and method of application)
This quiz covers the fundamental concepts of metal cutting theory, including the classification of metal working processes and material removal processes. Learn about non-cutting shaping and cutting shaping processes in the context of metal component production.
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