This set of CNC Multiple Choice Questions & Answers (MCQs) focuses on “DNC and NC Applications”.
1. One of the objectives of Direct Numerical Control was to achieve _______ communication between machines and central computer.
a) One way
b) Two way
c) Three way
d) Four way
View Answer
Explanation: In a DNC system, the central computer sends data to machines and also receives data back from the machines. This two-way communication helps to track conditions like machine breakdown, cycles completed, machine utilization, etc.
2. Direct Numerical Control operation was also referred by the term ________
a) Beside the tape reader
b) Behind the tape reader
c) Behind paper tape
d) Bypass the paper tape
View Answer
Explanation: In Direct Numerical Control, part programs are transferred to the machine control unit directly from bulk memory. Paper tapes and tape readers are not used. Thus, this mode of operation is also known as Behind the Tape Reader (BTR).
3. In Distributed Numerical Control, part programs are transmitted to the machine tool one block at a time.
a) True
b) False
View Answer
Explanation: In Direct Numerical Control, part programs are transferred to the machine control unit one block at a time. In Distributed Numerical Control, complete part programs can be sent to the machine tool.
4. Direct Numerical Control system consists of which of the following components?
a) Tape readers
b) Punched tape
c) Bulk memory
d) Microcomputers
View Answer
Explanation: There are four components in a DNC system – central computer, bulk memory, set of machines, and telecommunication lines. In the Distributed Numerical Control system, the central computer is connected to CNC machines comprising microcomputers.
5. Which of the following Numerical Control equipment needs the point to point control system?
a) NC lathe
b) NC boring mill
c) NC drill press
d) NC cylindrical grinder
View Answer
Explanation: NC lathe, NC boring mill, and NC cylindrical grinder need two-axis continuous path control. In a Numerical Control drill press, the turret position is programmed to apply different drill bits to the same work-piece during the machine cycle.
6. _______ can perform multiple operations on a work-piece.
a) Machining centre
b) NC milling machine
c) Cylindrical grinder
d) Lathe centre
View Answer
Explanation: Machining center is a machine tool that can perform multiple operations on a work-piece without changing the setup. Automatic tool changing is one of the prominent functions that allows a number of operations in a single set up.
7. The Numerical Control technology is appropriate for which of the following type of production?
a) Medium to high quantity and medium to high variety
b) Low to medium quantity and medium to high variety
c) High quantity and low variety
d) Low to medium quantity and low variety
View Answer
Explanation: Numerical Control Technology is suitable for batch production and complex part geometries. Numerical Control is useful where many operations are to be performed on the same work-piece.
8. Use of Numerical Control reduces which of the following factors?
a) Maintenance effort
b) Accuracy
c) Equipment utilisation
d) Non productive time
View Answer
Explanation: Numerical Control involves fewer setups, short set-up time, and automatic tool changing, which reduces non-productive time. The period for which a machine is not performing any machining operation is known as non-productive time.
9. The investment cost is high in Numerical Control machines due to _____
a) Higher scrap rates
b) The use of more reliable components
c) Less floor space
d) The use of complex fixtures
View Answer
Explanation: Numerical Control uses more reliable components due to high equipment utilization, which are expensive than conventional equipment components. Computer & electronic control cost, software development cost, etc. are also responsible for high investment cost.
10. In an open-loop position system, the angle through which the stepper motor rotates is given by which of the following relations? (If Am denotes angle of motor shaft rotation, n is the number of electric pulses received, a is step angle, ns is the number of step angles of the motor, r is the gear ratio.)
a) Am = n*a
b) Am = n/a
c) Am = 360*a/ns
d) Am = n/r
View Answer
Explanation: Step angle is the angle through which the stepper motor rotates in one pulse. Also, Step angle (a) = 360/number of step angles or a = 360/ns. The angle of screw rotation is given by As = Am/r or As = n*a/r.
11. Linear movement of the table in an open-loop positioning system (using a lead screw and stepper motor) is given by which of the following relations? (If p denotes pitch of lead screw, As is the angle of screw rotation, x denotes linear movement in mm.)
a) x = 360*p/As
b) x = 360*As/p
c) x = p*As/360
d) x = 360/(As*p)
View Answer
Explanation: Pitch is the linear distance covered in one revolution of the screw. As/360 gives the number of screw revolutions. Also, x=p*Am/ (360*r) where Am is the angle of motor shaft rotation and r is the gear ratio.
12. Find the number of electrical pulses needed to move the table by x=100 mm. If the gear ratio is 5:1, the pitch of lead screw (p) is 10 mm per revolution, and the step angle for the stepper motor is 60°?
a) 30000
b) 6000
c) 900
d) 300
View Answer
Explanation: Number of screw revolutions = x/p
The angle of screw rotation is given by,
As = 360*number of screw revolutions
= 360*x/p
= 360*100/10 = 3600°
Angle of motor shaft rotation Am = As*r
Number of pulses to be received,
n = Am/step angle (a)
= As*r/a
= 3600*5/60
= 300 pulses.
Sanfoundry Global Education & Learning Series – CNC.
To practice all areas of CNC, here is complete set of Multiple Choice Questions and Answers.
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