CNC Machine Constructional features.pdf

CNC machine features

1. 1
Construction Of CNC Machine
Tools

2. 2
Important Construction Parts Of CNC
Machine
Machine Structure
Drives And Guide Ways
Feed Drives
Spindle And Spindle Bearings
Measuring System
Gauging
Tool Monitoring
Controls, Software and Operator Inter Face

3. Important Construction Parts Of CNC
Machine
Machine Structure
Drives and Guide Ways
Feed Drives
Spindle And Spindle Bearings
Measuring System
Gauging
Tool Monitoring
Controls, Software and Operator Inter Face

4. Machine Structure
FollowingareBasicDesignFactors
StaticLoad
DynamicLoad
ThermalLoad
ReasonOfStaticLoad
WeightOfSlidesAndWorkPiece
TheMachineStructureShouldhaveAdequate
StiffnessandAProperStructuralConfiguration

5. Dynamic Load
Dynamicloadistermusedfortheconstantlychanging
forcesactingonthestructurewhilemovementis
takingplacetheseforcescausewholemachinesystem
tovibrate
REASON OF VIBRATION OF MACHINE
(A)Unbalanced Rotating Force
(B)Improper Meshing Gears
(C)Bearing Irregularities
(D)Interrupted Cuts While Machining
The Effect of Vibration On Machine can be
Reduced By Following Different Ways

6. REDUCING THE MASS STRUCTURE
INCREASING THE STIFFNESS OF THE STRUCTURE
IMPROVING THE DAMPING PROPERTIES
THERMAL LOAD
SOME SOURCES OF THERMAL LOAD ARE
1 ELECTRIC MOTOR
2 FRICTION IN MECHANICAL DRIVES AND
GEAR BOX
3 MACHINING PROCESSES
4 TEMPERATURE OF SURROUNDING
OBJECTS

7. Elements Of CNC Machine Tool
In A CNC Machine There Are Three Main Groups Of
Elements
(A)Control And Electronics
(B) Power Units Or Electric Drives (Electromechanical
Drives)
(C) Mechanical Elements(table, Slide, Tool, Holder)
InAdditionThereCanBeHydraulicOrPneumatic
SystemsWhichAreIntegratedWithSystemThe
PrimaryFunctionOfTheDriveIsToCauseMotionOf
TheControlledMachineToolMembersLikeSpindle
SlideEtc.

8. COMPUTER NUMERICAL CONTROL AND
ELECTRONIC SYSTEM
ELECTRIC DRIVES
MACHINE SLIDE , TABLE SPINDLE ETC

9. SPINDLE WORK PIECE
DRIVES IN CNC M/C

10. SPINDLE
DRIVE
MOTOR
FEED DRIVE
MOTOR
SPINDLE
WORK PIECE
Electric drive in
Cnc lathe

11. DRIVES FOR PROVIDING CUTTING
SPEED (SPINDLE DRIVE)
THE MOTOR MUST BE CAPABLE OF PROVIDING
POWER AND HIGH CUTTING SPEED AT THE MAIN
SPINDLE SO THAT CNC M/C USED ELECTRIC MOTOR .
WITH THE DEVELOPMENT IN POWER ELECTRONICS
AND
MICROPROCESSOR SYSTEM VARIABLE DRIVE SYSTEM
HAVE BEEN DEVELOPED THESE ARE SMALLER IN SIZE
HIGH RELIABLE AND MEET ALL THE DEMANDS

12. SPINDLE DRIVE
THE REQUIREMENT OF SPINDLE DRIVE MOTOR ARE
•High rotational accuracy
•Wide constant power band
•Excellent running smoothness
•Compactness
•Fast dynamic response
•Range of rated output from 3.7.-50 kw
•Maximum speed up to 9000-20000 rpm
•High overload capacity

13. TYPES OF SPINDLE DRIVE
DC SPINDLE DRIVE AC SPINDLE DRIVE
Separately excited dc shuntmotor
Controller
Thyristor (scr) amplifier or
Micro processor based self turned
Thyristor amplifier
Speed control
Armature and field control
Dc motor are commonly used
Sqirrel cage induction motor
controller
Microprocessor based
Pulse width modulated(pam)
inverter
(C-axis application) due to
this ac drive are being
Proffered to dc drives
Speed control
Frequency and vector
Control

14. ELECTRICAL DRIVES
SPINDLE
DRIVE
FEED
DRIVE
DRIVES IN CNC M/C
DC SHUNT MOTOR
THREE PHASE
INDUCTION MOTOR
D.C.SERVOMOTOR
AC SERVO MOTOR
STEPPER MOTOR

15. Fluid motors are driven by oil or air under
pressure. The fluid is pressurized by a pump,
which is normally driven at a constant speed by
an alternating current electric motor. As stated
previously, fluid motors are not generally used for
providing the cutting speed. but there are a few
application, such as for milling and drilling
operation on aluminum alloys which use fluid
power for driving the main spindle. One of the
effective applications was on the Molins system
24 machines.
FLUID MOTOR

16. FEED DRIVES
SPECIAL CHARACTERISTICS OF FEED DRIVE
•It consists of feed servo motor and electronic controller.
•* It have constant torque and positioning
•* Fast response in feed drive
•MATCH DYNAMIC characteristics
•Damped servo system so that several feed drive can work
simultaneously
The power unit that provide feed movement do not have to
be so powerful as those used for the
Main spindle 1kw motor are adequate and feed rate are
much slower 5 to 200mm/min during machining an 5m/min
during rapid positioning