Show
Both reaming and tapping are internal
machining processes, why the tapping is
more difficult?
Tapping produces a significant amount of
chips and their removal through the hole being
tapped can be difficult as they can get clogged
(and can cause tap fracture). Control of
processing parameters and use of effective cutting
fluids are thus important.
Describe the difference between up milling
and down milling.
In up milling, the cutter speed
direction is opposite the feed direction; in
down milling, the direction of cutter rotation
is the same as the feed direction.
What are the advantages of helical teeth
over straight teeth on cutters for slab milling?
When the helical teeth is used for slab milling, there
are always multiple teeth in contact with workpiece, and
each the tooth is partially engaged with workpiece as it
rotates. Therefore, the transition in contact from one
tooth to another is smooth. This will produce the following
advantages: Lower impact loads and periodic forcing functions (and
associated vibration and chatter) from the cutting operat
ion. Lower cutting force and torque.
List few strategies to reduce the surface
roughness during face milling.
Surface roughness can be improved by:
reducing the feed per tooth increasing the corner radius of the insert
correctly positioning the wiper blade using corner flat insert
The wiper insert is designed with a short, flat edge
e that is located between the straight edge and the corner radius.
Which of the following are examples of generating the
workpart geometry in machining, as opposed to
forming the geometry (two best answers): (a) contour
turning, (b) drilling, (c) profile milling, and (d)
thread cutting?
Answer:
(a) and (c).
Reaming is used for which of the following functions
(three correct answers): (a) accurately locate a hole
position, (b) create a stepped hole, (c) enlarge a drilled
hole, (d) improve surface finish on a hole, (e) improve
rove tolerance on hole diameter, and (f) provide an internal thread?
Answer:
(c), (d), and (e).
The difference between up milling and down milling
is that in down milling the direction of motion of
the cutter teeth is opposite the feed direction when the
teeth cut into the work: (a) true or (b) false?
Answer:
(b).
A vertical milling machine is more appropriate than
a horizontal milling machine for performing which of
the following types of operations (three best answers):
(a) end milling, (b) face milling, (c) peripheral milling,
(d) plain milling, (e) slab milling, and (f) surface
contouring?
Answer:
(a), (b), and (f)
What is the difference between a closed
loop control system and an open loop
control system?
. The difference is that a closed
loop control system includes feedback of
data related to the output of the process that
is used to make control adjustments. An
open loop system does not have this
feedback loop.
Identify and briefly describe the three basic
components of a numerical control system.
The three basic components are: (1) part
program, (2) machine control unit, and (3) processing
equipment. The part program is the detailed set of
commands to be followed by the processing equipment.
The machine control unit in modern NC technology is a
microcomputer that stores the program and executes it by
converting each command into actions by the processing
equipment, one command at a time. The processing
equipment accomplishes the sequence of processing steps to
transform the starting workpart into a completed part.
What is the difference between point-to-point and
continuous path in a motion control system? Give
examples for application of point-to-point motion
control system
In point-to-point, the motion is from one
location in space to the next with no regard for the
path taken between starting and final locations. In
continuous path, the trajectory of the movement is
controlled.
Drilling and punching, cut-off during turning, 3D
printing, laser beam cutting, water-jet cutting
What is the difference between absolute
positioning and incremental positioning?
In absolute positioning, the
locations are defined relative to the origin of
the axis system. In incremental positioning,
each succeeding location is defined relative
to the previous location.
What is the difference between an open
loop positioning system and a closed loop
positioning system?
In a closed loop system,
measurements of the output (position) are
fed back to verify that it corresponds to the
desired input value. In an open loop
system, there is no feedback of the output
value.
Under what circumstances is a closed loop
positioning system preferable to an open loop system?
When there is a significant
reaction force resisting the motion of the
positioning system, a closed loop system is
preferred.
Explain why the CNC machine produces
part with high accuracy.
Closed-loop control
Use servomotor (high torque capability)
Feedback sensor to check the machine’s actual position and speed
Use of ball lead screws
Precision ball bearings roll between the nut and the
screw, which eliminates the backlash in the
movement screws by greatly reducing friction.
Rigid construction
Resist vibration
What is the function of the ball leadscrew in
CNC machine.
Ball leadscrew eliminates the backlash in
the movement screws by greatly reducing friction.
This is accomplished by creating a rolling motion
design in which precision ball bearings roll
between the nut and the screw, which allows for
higher precision positioning with greater
repeatability, and positioning at higher speeds with
less wear.