Turning Theory Flashcards
What is the definition of a turning operation?
Metal removal from a revolving work to produce the required shape and size by means of a single pointed cutting tool mounted rigidly in a tool-post.
How should the workpiece be rotated?
Against the cutting edge of the tool to ensure that it do not rub against the tool
What is the definition of depth of cut?
Refers to the depth the tool’s cutting edge engages the workpiece
What is the definition of feed direction?
Refers to the direction of the tool being fed into the workpiece
What are the different types of external operation in turning?
Turning, Facing, Threading, Grooving, Parting
What are the different types of internal operation in turning?
Drilling, Reaming, Boring, Tapping
What is the angle of which tool cutting edge is set to the direction of movement in orthogonal cutting?
90 degree
Chip formation in orthogonal cutting
Form of a clock spring or a flat spiral
Forces present in orthogonal cutting
Axial Force and Tangential Force
What is the angle of which tool cutting edge is set to the direction of movement in oblique cutting?
Any angle other than 90 degree
Chip formation in oblique cutting
Twisted curl chip formation
Forces present in oblique cutting
Radial Force, Axial Force, Tangential Force
Disposal of chips in orthogonal cutting vs oblique cutting
Orthogonal cutting: Present difficulties as chip will stay on top of the tool holder and may damage the workpiece’s surface
Oblique cutting: Greatly improves the surface finish of the workpiece as it allows the chips to move freely away from the area of cutting
Which force is insignificant in oblique cutting?
Radial Force as no motion is associated with it, it does not consume power, but it influences the axial force
What are the 6 factors affecting metal cutting operation?
Cutting conditions, cutting tool material, cutting tool geometry, cutting fluids, workpiece material, machine rigidity
What is the rule of thumb (feedrate, depth of cut, cutting speed) for rough cuts?
Increase feedrate, increase depth of cut, decrease cutting speed
What is the rule of thumb (feedrate, depth of cut, cutting speed) for finishing cut?
Decrease feedrate, decrease depth of cut, increase cutting speed
What are the 6 common cutting tool material?
High Carbon Steel
High Speed Steel
Cast Cobalt Alloys
Cemented Carbide
Cemented Oxide or Ceramic
Diamond
5 reasons why throw-away inserts are becoming popular
- Worn out or broken cutting edge can be easily indexed by unclamping the locking device and rotating the insert to a new cutting tip
- Cutting tips need not be sharpened
- Setting time is minimal
- Proper clamping can be achieved easily
- Relatively cheaper to use and replace throwaway inserts
How does side rake angle affect cutting?
Directs the chip flows away from the cut and it provides for a sharp cutting edge
How does back rake angle affect cutting?
Promotes smooth chip flow and good surface finishes
How does front relief angle affect cutting?
Prevents the tool end from rubbing on the freshly cut workpiece surface
How does side relief angle affect cutting?
Allows the tool to feed into the work material and prevents the tool end from rubbing on the freshly cut workpiece surface
How does side cutting edge angle affect cutting?
Defines orthogonal or oblique cutting. Responsible for turning the chip away from the finished surface. Allows the edge to enter the workpiece without a sudden shock
How does front cutting edge angle affect cutting?
Provides clearance between the trailing edge of the tool and freshly cut workpiece surface
How does nose radius affect cutting?
Influences the surface finish of the workpiece
As positive rake angle increase, tool becomes_______,
Tool becomes weaker and therefore the cutting force and power should be reduced.
Increasing positive rake angle will ______ the machined surface finish.
Improve. It also provides a sharper edge and thus increases tool life
As negative rake angle decreases, the cutting area will be _________
Strengthened. Thus the cutting forces are well supported by the tool body. These tools are used for higher cutting speeds. The surface finish from these tools are very poor.
Chip formation from negative rake angle tools
More plastic and thin continuous chip. Cutting is so rapid that the heat generated by the chip does not have time to pass to the tool and almost all the heat is concentrated in the chip.
Two important functions of cutting fluids
Cooling and for lubrication
When is oil with water emulsions preferred?
When cooling action is more important
When is neat oil used
When lubrication is significantly needed
5 functions of cutting fluids
- Improvement of surface finish quality and dimension
- Flushing away of chips from the cutting zone
- Increase of tool life
- Prevention of chip welding, corrosion of the machine
- Permits the use of higher cutting speed and federate
4 desirable cutting fluids characteristics
- Does not corrode work or machine
- Low evaporation rate
- Stable and not form foam or fume
- Do not injure or irritate the operator, when in contact or inhaled
3 types of chips
Discontinuous chips, continuous chips, continuous chips with a built-up edge
4 factors affecting chip formation
Work material, tool geometry and material, cutting conditions, presence of cutting fluid
Conditions giving rise to discontinuous chips
- Brittle work material
- Small rake angle
- Low cutting speed
- Large depth of cut
- Large feedrate
- Lack of cutting lubricant
Conditions giving rise to continuous chips
- Ductile work material
- Large rake angle
- High cutting speed
- Small depth of cut
- Low feedrate
- Efficient use of cutting lubricant
- Cutting tool material with less pressure-weld tendencies
Conditions giving rise to continuous chips with built-up edge
- Ductile work material
- Low rake angle
- Low cutting speed
- High depth of cut
- High feedrate
- Poor use of cutting lubricant
*BUE also causes the rake angle to change, changing the tool geometry
Symbol for spindle speed
N
rpm
Symbol for cutting speed
V
m/min
Definition of spindle speed (N)
The number of revolutions the workpiece turns in 1 minute and is dependent on the cutting speed and the workpiece diameter
Definition of cutting speed (V)
The rate at which a point in the circumference of the work travels past the cutting tool i.e. the linear speed, and is dependent on the workpiece material and desired finish
Definition of feedrate
The distance the tool bit advances along the work for each revolution of the spindle or per minute. It is dependent on work material, tool material, type of cut
Cutting Speed V equation
V = piDN/1000
Spindle Speed N equation
N = 1000V/piD
Feedrate equation
Fm = Fr x N
