Texas MMET 201 Assessment 3 Rated A+
5 advantages of machining processes - ANS-1. Closer dimensional accuracy than
other methods
2. Can produce geometric features other methods can't
3. Can remove distortion and discoloration from heated parts for finishing
4. Can make special surface textures
5. *Can be more economical, esp. if low # of parts needed*
(3) drawbacks of machining processes - ANS-1. Waste material and use more
energy than other methods
2. Removing material is more time consuming
3. Can have adverse effects on integrity of product
Shear angle influences - ANS-Force and power requirements, chip thickness and
temperature
Types of chips - ANS-Continuous chips
Built-up-edge (BUE) chips
Serrated chips - stacked up chips basically
Discontinuous chips
Orthogonal cutting - ANS-Two-dimensional cutting process
Can have a well-defined shear place (where chip breaks cleanly) or a shear zone
(where chips just bending)
Resultant forces on each side must be colinear to balance forces
Factors that contribute to BUE - ANS-Adhesion of the material to the rake face
Growth of successive layers of adhered metal on tool
*Tendency of material for strain hardening*
Ways to decrease BUE - ANS-Increase cutting speed, V
Increase rake angle
Decrease depth of cut, t_o
Decrease tip radius of tool
Apply effective cutting fluid
Discontinuous chips form if (6) - ANS-Material is brittle (i.e. thermosetting plastics
and ceramics)
Contains hard inclusions and impurities
*Very low or very high cutting speed*
Large depth of cut or low rake angle
Tool has low stiffness and poor damping
Lack of effective cutting fluid
,Oblique cutting - ANS-Produces chips at inclination angle, away from material, and
will form tighter spiral chips as the angle increases
Thrust forces are important bc - ANS-Tool holder, devices, etc. needs to be stiff
enough to handle this force and minimize deflections
the force that pushes back on the tool tip
Thrust force is negative ONLY when - ANS-Friction at tool chip interface is low
When rake angle is high
Specific cutting force is the ratio of - ANS-Cutting force to cross sectional area
being cut (width * depth of cut)
Cutting force is increased if (4) - ANS-Increasing strength of workpiece material
Increasing depth of cut
*Increasing tool tip radius*
Decreasing rake angle
Temperature rise in cutting is bad because - ANS-Lowers the strength, hardness,
stiffness and wear resistance of tools
Causes uneven dimensional changes in part
Can change properties of machined surface bc of metallurgical changes
Cutting temperature increases with - ANS-Work piece material strength
Cutting speed
Depth of cut
What are the most important variable associated with tool life, in order? - ANS-1.
Cutting speed
2. Depth of cut
3. Feed, f
Types of tool wear in turning operations - ANS-Flank wear on rake face (avg. is
indicated by VB)
Crater wear on top
Types of tool wear in cutting operations - ANS-Flank wear (corner edges wear off
slightly)
Crater wear
Thermal cracking (distinct lines)
BUE (built up edge)
Crater wear is affected by - ANS-Temperature at interface
Chemical affinity between tool and workpiece materials
Machinability is defined in terms of four factors: - ANS-1. Surface integrity after
2. Tool life effects
, 3. Force and power required
4. *Level of difficulty in chip control*
How to improve machinability of steels - ANS-Add lead, in form of *fine lead, sulfur
and/or phosphorous particles* to produce free-machining steels
(forms tiny chips that break up easily, not continuous)
Machinability of aluminum - ANS-Easy to machine, softer grades tend to form BUE
so their surface finishes are weak af
Machinability of thermoplastics and thermosetting - ANS-Tools need to be sharp,
and cooling is necessary to prevent becoming gummy
Thermosetting plastics are brittle, machinability is similar to thermoplastics
Why is ceramic difficult to machine? - ANS-Matrix composite structures
Cutting tool material must have - ANS-1. Hot hardness (hardness maintained at
high temps.)
2. High toughness and impact strength
3. Thermal shock resistance
4. Wear resistance
5. Chemical stability and inertness
Cutting tool materials include - ANS-High speed steels
Cobalt alloys
Carbides (used heavily for inserts)
Ceramic
Cubic boron nitride
Diamond
As angle of cutting edge gets narrower, - ANS-Strength decreases
Chipping and breaking increases
Coatings on tools should have the following characteristics: - ANS-Hot hardness
(hardness at elevated temperatures)
Chemical stability and inertness
Low thermal conductivity
Good bonding to substrate
Little to no porosity
Types of tool coatings - ANS-Titanium nitride
Titanium carbide
Titanium carbonitrade
Ceramic coatings
Diamond coatings
Some used in combination - *multiphase coatings*
5 advantages of machining processes - ANS-1. Closer dimensional accuracy than
other methods
2. Can produce geometric features other methods can't
3. Can remove distortion and discoloration from heated parts for finishing
4. Can make special surface textures
5. *Can be more economical, esp. if low # of parts needed*
(3) drawbacks of machining processes - ANS-1. Waste material and use more
energy than other methods
2. Removing material is more time consuming
3. Can have adverse effects on integrity of product
Shear angle influences - ANS-Force and power requirements, chip thickness and
temperature
Types of chips - ANS-Continuous chips
Built-up-edge (BUE) chips
Serrated chips - stacked up chips basically
Discontinuous chips
Orthogonal cutting - ANS-Two-dimensional cutting process
Can have a well-defined shear place (where chip breaks cleanly) or a shear zone
(where chips just bending)
Resultant forces on each side must be colinear to balance forces
Factors that contribute to BUE - ANS-Adhesion of the material to the rake face
Growth of successive layers of adhered metal on tool
*Tendency of material for strain hardening*
Ways to decrease BUE - ANS-Increase cutting speed, V
Increase rake angle
Decrease depth of cut, t_o
Decrease tip radius of tool
Apply effective cutting fluid
Discontinuous chips form if (6) - ANS-Material is brittle (i.e. thermosetting plastics
and ceramics)
Contains hard inclusions and impurities
*Very low or very high cutting speed*
Large depth of cut or low rake angle
Tool has low stiffness and poor damping
Lack of effective cutting fluid
,Oblique cutting - ANS-Produces chips at inclination angle, away from material, and
will form tighter spiral chips as the angle increases
Thrust forces are important bc - ANS-Tool holder, devices, etc. needs to be stiff
enough to handle this force and minimize deflections
the force that pushes back on the tool tip
Thrust force is negative ONLY when - ANS-Friction at tool chip interface is low
When rake angle is high
Specific cutting force is the ratio of - ANS-Cutting force to cross sectional area
being cut (width * depth of cut)
Cutting force is increased if (4) - ANS-Increasing strength of workpiece material
Increasing depth of cut
*Increasing tool tip radius*
Decreasing rake angle
Temperature rise in cutting is bad because - ANS-Lowers the strength, hardness,
stiffness and wear resistance of tools
Causes uneven dimensional changes in part
Can change properties of machined surface bc of metallurgical changes
Cutting temperature increases with - ANS-Work piece material strength
Cutting speed
Depth of cut
What are the most important variable associated with tool life, in order? - ANS-1.
Cutting speed
2. Depth of cut
3. Feed, f
Types of tool wear in turning operations - ANS-Flank wear on rake face (avg. is
indicated by VB)
Crater wear on top
Types of tool wear in cutting operations - ANS-Flank wear (corner edges wear off
slightly)
Crater wear
Thermal cracking (distinct lines)
BUE (built up edge)
Crater wear is affected by - ANS-Temperature at interface
Chemical affinity between tool and workpiece materials
Machinability is defined in terms of four factors: - ANS-1. Surface integrity after
2. Tool life effects
, 3. Force and power required
4. *Level of difficulty in chip control*
How to improve machinability of steels - ANS-Add lead, in form of *fine lead, sulfur
and/or phosphorous particles* to produce free-machining steels
(forms tiny chips that break up easily, not continuous)
Machinability of aluminum - ANS-Easy to machine, softer grades tend to form BUE
so their surface finishes are weak af
Machinability of thermoplastics and thermosetting - ANS-Tools need to be sharp,
and cooling is necessary to prevent becoming gummy
Thermosetting plastics are brittle, machinability is similar to thermoplastics
Why is ceramic difficult to machine? - ANS-Matrix composite structures
Cutting tool material must have - ANS-1. Hot hardness (hardness maintained at
high temps.)
2. High toughness and impact strength
3. Thermal shock resistance
4. Wear resistance
5. Chemical stability and inertness
Cutting tool materials include - ANS-High speed steels
Cobalt alloys
Carbides (used heavily for inserts)
Ceramic
Cubic boron nitride
Diamond
As angle of cutting edge gets narrower, - ANS-Strength decreases
Chipping and breaking increases
Coatings on tools should have the following characteristics: - ANS-Hot hardness
(hardness at elevated temperatures)
Chemical stability and inertness
Low thermal conductivity
Good bonding to substrate
Little to no porosity
Types of tool coatings - ANS-Titanium nitride
Titanium carbide
Titanium carbonitrade
Ceramic coatings
Diamond coatings
Some used in combination - *multiphase coatings*
