explain please
How to solve this:
Solution for q1 pls...
What is the ratio of isro for no of interview to no of post available in mechanical engineering...
plz discuss
Larger end cutting edge angle __________ tool life.
A.increases
B.decreases
C.does not effect
question no 43. please explain the anwer
http://www.indianshout.com/wp-content/uploads/2012/02/MH-2009.pdf
Som k nptel k kaun se professor k notes or video shi hai???
Aur structure based qus in som from where i can get
NC Machines (Numerically controlled) :
It is a form of programmable automation. The instructions are given to the machine in the form of symbols, letters and numbers. Suitable for low to medium production. The instructions are given by means of punched tapes or magnetic tapes
The program is coded on the punched tapes, which is fed into the control unit that intern directs the machine to perform the tasks. The control unit consists of electronics and control hardware, that reads and interprets the program
Elements of NC machines:
The control unit, the drive unit, feedback unit, magnetic box and manual control
The instructions interpreted by the control unit are sent to the drive unit and to the magnetic box.
The drive unit controls the lengths of travel and the feed rates given to the tool.
The magnetic box is responsible for tool change, spindle speed feed, coolant actuation,etc.
The feedback unit sends the information on the tasks performed by the individual units back to the control unit.
Advantages:
Accuracy obtained is better
Less production cost due to lesser lead time
Improved product quality
High production rates
Less wastage
Disadvantages:
Higher costs of machines
Classification:
Based on control system features
Point to point control, straight line control, contour control.
Based on feed back system
Open loop system, closed loop system
Based on number of simultaneous control of axis
2D, 2 1/2 D. 3D, 4D, 5D, 6D
Depending on the capability of machine tool it can be specified by the control available on the side movements. 2D and 3D refer to the machine having continuous motion of the tool in two and three axis respectively. 21/2D means machine is capable for continuous motion in two axis but only transverse (linear) motion in the third.
Point to point control:
it is a feature of control system
In this case the machining is done at specific positions, work is kept stationary and the tool moves from one point to another. Eg: drilling
Straight line control:
In this case the tool moves continuously at a controlled feed rate in one axis performing the operation continuously. Eg: turning
Contour control:
There are continuous, simultaneous and coordinated motion of the tool and the work piece along different axis. Eg: curved surfaces
Open loop system:
In this case there is no feedback signal to the control unit about the actual position of the tool at any given point
Closed loop system:
In this case the system gives the information on the actual position of the tool and we know the difference between the output and input signals in the form of error
if the volume of moist air with 50% relative humidity is isothermally reduced to half of its original volume, then humidity of moist air becomes
- 25%
- 100%
- 75%
- 60%
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CNC machines (computer numerically controlled):
In CNC machines there is a mini computer which stores all the programs in its memory
Advantages:
Changes can be done easily
No errors in reading program
No need to disrupt the program
The programs can be copied from one machine to the other
Elements of CNC machine:
Input unit: it receives the commands from control unit and operator and machine interface the form of AC DC or analog signals
Memory unit: it stores the data received from the input unit and shares to the output unit. The size of the memory unit depends upon the number of programs needed to be stored.
Control unit: It acts as a mediator between input unit and memory unit. It interprets and manipulates the instructions given one at a time
Arithmetic unit: it performs calculations and makes decisions and the results are stored in memory unit.
Output unit: It takes the data and commands from memory and control units and makes the signals compatible to the output devices
Part programming:
G00: rapid positioning
G01: linear interpolation
G02: circular (CW)
G03: circular (ACW)
G04: dwell
G05: hold
G08: acceleration
G09: retardation
G17: xy plane selection
G18: yz plane selection
G19: zx plane selection
M00: program stop
M01: planned stop
M02: program end
M03: CW spindle
M04: ACW spindle
M05: tool change
M06: coolant on
M07: coolant off
M08: clamped
M09: unclamped
Automobile car bodies curvatures are designed with
- None
- B-spline curve
- Coon’s surface
- Both
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Q)
In an NC machining operation the tool has to be moved from point (1,6) to point (7,0) along a circular path with the center at (1,1). Before starting the operation the tool is at (1,6). The NC code for this motion is ?
Minimum number of points required to draw B-spline Cubic curve is ?
1. NC machines are better suited for ________ (batch/mass) production, because their setup time is ________(larger/smaller) in comparison to special purpose machine tools
Ans plz
a sphere, a cube, and a disc all of the same quality volume and material are heated to 900k and left in air which of this have lowest rate of cooling?
- cube
- disc
- sphere
- all will have same rate of cooling
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Largest shrinkage allowance while making pattern
- Brass
- Aluminium
- Cast iron
- Plain carbon steel
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Hey frnds plzz suggest which professor NPTEL lecture is good??
Aur structure based qus in som from where can i get
Qtn no 32 tnsn/non of these