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Posted on Jan 10, 2017 in Other subjects

Which axis is spindle rotating along for
CNC programming? 
Z axis

What is the function of each following block:
(1) N10 G91 G28 X0 (2) N20 G43 H2
Answer:
(1)
Send tool home in in X axis incrementally through
a point 0 distance from the current location
(2)
Turn on the tool length offset, the movement of
the center, end of the cutter is programed in the
work coordinate system (WCS) after G43

Which G code should be used for cutter
radius compensation for down cut if M04 is
in effect? 
G42

Mean temperature with analytical method for
orthogonal cutting:
is the mean temperature rise at the tool-chip interface,
is the mean temperature,

is flow strength of work material,
is specific energy,

 is cutting speed,

 is chip thickness before cut,
is volumetric special heat of work material,
is thermal diffusivity of work material,

What is an orthogonal cutting operation? Why is
the orthogonal cutting model useful in the analysis
of metal machining

Orthogonal cutting involves the use of a wedge shaped

tool in which the cutting edge is perpendicular to the direction

of speed motion the work material

Orthogonal cutting is useful in the analysis of metal
machining because it simplifies the rather complex threedimensional
machining situation to two dimensions. In
addition, the tooling in the orthogonal model has only two
parameters (rake angle and relief angle), which is a
simpler geometry than a single-point tool.

Name and briefly describe the four types of chips
that occur in metal cutting.
The four types are (1) discontinuous, in which the chip is
formed into separated segments; (2) continuous, in which
the chip does not segment and is formed from a ductile
metal; (3) continuous with built-up edge, which is the
same as (2) except that friction at the tool-chip interface ca
uses adhesion of a small portion of work material to the to
ol rake face, and (4) serrated, which are semi-continuous in the
sense that they possess a saw -tooth appearance that is
produced by a cyclical chip formation of alternating high
shear strain followed by low shear strain..
Identify the four forces that act upon the chip in
the orthogonal metal cutting model but cannot be
measured directly in an operation. Identify the two
forces that can be measured in the orthogonal
metal cutting model.

• The four forces that act upon the chip in the orthogonal
metal cutting model but cannot be measured directly are
(1) friction force, (2) normal force to friction, (3) sh
ear force, and (4) normal force to shear.
• The two forces that can be measured in the orthogonal
metal cutting model are (1) cutting force and (2) thrust
force.

What is Merchant equation?

•
The shear plane angle increases when
rake angle is increased and friction angle is

 
decreased.

Which one of the four types of chip would be expected in
a turning operation conducted at low cutting speed on a
brittle work material: (a) continuous, (b) continuous with 
built-up edge, (c) discontinuous, or (d) serrated?
Answer:
(c) discontinuous chip
Which of the following cutting conditions has the
strongest effect on cutting temperature: (a) feed or (b) speed?

Answer: (b) speed

Identify the location of the maximum temperature in
orthogonal cutting, explain it.

The maximum temperature in orthogonal cutting is
located at about the middle of the tool–chip interface as

 shown in the following figure. The chip
reaches high temperatures in the primary shear plane,

and the temperature would decrease from then on.

 If no frictional heat was involved, we would
expect the highest temperature to occur at the shear plane.

State the consequences of high cutting temperatures cutting.

1. Tool wear will be accelerated due to high temperatures.
2. High temperatures will cause dimensional changes in
the workpiece, thus reducing dimensional accuracy.
3. Excessively high temperatures in the cutting zone
can induce thermal damage and metallurgical
changes to the machined surface.
4. Hot chip that is dangerous to machine operator.

Cutting temperature is found to increase with
increase in cutting speed and feed, as
the value of a and b for high-speed steel tools are
higher than for carbides (see the attached table),
explain why.

The magnitudes of a and b depend on the type of cutting tool
as well as the workpiece materials. Factors to be
considered include thermal conductivity and friction at the
tool-chip and tool-workpiece interfaces. Carbides have
higher thermal conductivity than high-speed steels and also
have lower friction. Consequently, these constants are lower for carbides.

Name the three sources of heat generation
during machining of metal. Name the three
mechanisms of heat dissipation in metal
machining, which one carries the most heat?
Answer:  Heat is generated: 
Plastic deformation by shearing in the primary shear zone 
Plastic deformation by shearing and friction in the

second shear zone
Friction between workpiece and tool

on the tool flank 
Heat is dissipated by: 
The discarded chip 
The workpiece acts as a heat sink 
The cutting tool

Explain why the percentage of the total cutting
energy carried away by the chip increases with
increasing cutting speed
As cutting speed increases, the heat generated (particularly that
portion due to the shear plane deformation) does not have enough
time to dissipate into the workpiece (conduction), therefore most of the

heat will stay in the chip and is carried away by the discarded chip