2. 1945
▫ First digital electronic computer ENIAC
1952
▫ MIT demonstrated First NC Machine in laboratory
NC Development
▫ Direct Numerical Control DNC
▫ Computer Numerical Control CNC
▫ Distributed Numerical Control DNC
▫ Flexible Manufacturing System FMS
▫ Computer Integrated Manufacturing CIM
2
History of NC
3. 3
Numerical Control ?
A CONTROL Strategy
to
operate a machine tool
using
NUMBERS, LETTERS and SYMBOLS.
6. 6
Why CNC Machining ?
• For the parts
having complex contours
requiring very high accuracy and repeatability
requiring many set-ups and/or the setups very
expensive
subjected to frequent design changes, flexibility
7. • Reduction of Lead Time from Design to Mfg.
• Accurate machining of Complex surfaces/parts
• Excellent repeatability and Interchangeability
• Greater Machine utilization – scrap reduction
• Improved Productivity
• Quick Turn-around for design revisions, Prototyping
7
Advantages of NC Technology
9. Data Processing Unit & Control loop unit
Function
• Reading Program
• Decoding
• Data Computation
• Axis Control Data Creation
• Data transfer to motors, relays
• Feedback control of axes
• Machine control functions
9
Elements of NC tool operation
10. BS 3635
• Motion Control
▫ Point to Point p
▫ Paraxial- Straight Line L
▫ Continuous Path / Contouring C
• Capabilities
▫ No. of Axes controlled Simultaneously
▫ Interpolation
Linear, Circular, Helical, Parabolic
• Axis Definition
• Machine Configurations
▫ 2-5 axis
10
Classification of CNC system
11. 11
Classification of NC system
NUMERICAL CONTROL
FINITE POSITIONING
CONTROLS
POINT TO POINT
SYSTEMS STRAIGHT CUT
SYSTEMS
CONTINUOUS PATH
SYSTEMS
CONTOURING
SYSTEMS
Ex. Drilling, Boring, Robotics Frame Milling, CNC Turning 2,3 axis contouring, SSM
12. • Moving at Maximum Feed rate from point to
point
• Accuracy of the destination is important but not
the path
• Drilling is a typical application
12
Point To Point - PTP
13. • Precise control of both the displacement and
velocity along the path (Both pos. and path
are important)
• Machining of profiles
• Uses Linear and Circular interpolators
13
Continuous Path Control
14. 14
2. Point-to-point(P-T-P) control is applicable in case of
(a) CNC drilling machine
Short Quiz
(b) CNC milling machine (c) CNC lathe (d) None of these
1. There is a stepper motor rotating at 20 rpm and is connected with a table through gear box, lead screw-nut
connection as shown in Fig. 1. The table has single axis of motion and is developing a speed of 20 mm/min
along that axis due to motor rotation. The stepper motor covers one rotation in 200 steps and moves one
step per pulse of the pulse generator. The Basic length unit (BLU) of the drive is (motion of table per pulse of
pulse generator) ?
(a) 0.01mm (b) 0.05mm (c) 0.1mm (d) 0.005mm (e) None of these
3. CNC machining has the following main advantage over conventional automated machining
(a) Ability to employ higher
cutting speed, feed, doc
(b) Flexibility (c) Feedback control (d) None of these
4. An interpolator is definitely present in
(a) A CNC P-T-P control machine (b) A CNC P-T-P control machine with feedback
(c) A CNC continuous control machine (d) All CNC machines
20 rpm 20mm/min
1rev 1mm
1/200 rev 0.005mm
16. 16
CNC Axes Nomenclature
Linear : X, Y, Z (Primary)
U, V, W (Secondary)
P, Q, R (Tertiary)
Rotary : A, B, C
Control : Sequential
Simultaneous
Spindle axis is always Z
22. 22
CNC Program
1. Reading drawing
2. Programming
3. Inputting Program
4. Manufacturing
From the drawing to the workpiece
23. 23
Machine and Part Zero
• Each CNC machine has a built-in location that is called Machine zero.
• Before moving and cutting a block, the CNC machine needs to know where to start, the start
position is the part zero used in programming.
• This location acts as the origin from which all the other dimensions are calculated during the
program and it is usually located on the edge of a workpiece.
24. N010 G20 G40 G80 G90;
N020 S3000 M03;
• Program consists of BLOCKS.
• Each BLOCK has WORDS.
• Each WORD denotes ACTION.
• Program has to EXPLICITLY specify the
ACTION to be done by Tool/Machine.
24
CNC Program
M/c tool action:
• Feed the Tool. Start the Machine. Rotate Spindle.
• Clamp the Job.
• Start the Coolant.
• Stop the Machine.
26. 26
M03
DIRECTION OF ROTATION
(CLOCKWISE)
M04
DIRECTION OF ROTATION
(COUNTERCLOCKWISE)
M06
TOOL CHANGE WITH
AUTOMATIC RETRACTION
M30
END OF PROGRAM
AND
RETURN TO BEGINNING
OF PROGRAM
Word Address Format
(Deckel Maho, Inc.)
M – Miscellaneous code
CNC Command G/M code
NC is a method of automation and nowadays computer is an integral part of that so CNC. NC is a CONTROL Strategy to operate a machine tool using NUMBERS, LETTERS and SYMBOLS. Remember NC is a Control Strategy to operate machine, NOT a machining method. NC machines CANNOT Think, Evaluate, Judge, Decide or Adapt like human beings.
Control Strategy applied to various machine tools,
Parts requiring very tight tolerances. Casting, molding parts need to machine the part and even additive not able to do
MCU: Reading Program, Decoding, Parity Checking, Data Computation, Axis Control Data Creation
BLU: Basic length unit
An interpolator provides two functions: It calculates individual axis velocities to drive the tool along the programmed path at the given feed rate. Controler always takes the shortest path
PTP: Position is more important, path is not
Continuous/contouring: Both pos and path are important. An interpolator provides two functions: It calculates individual axis velocities to drive the tool along the programmed path at the given feed rate. Controler always takes the shortest path
CNC axis system
CNC M/c can be 2-3-4-5 axis. To study that we need to study their axis nomenclature. How they are designated. 3 primary linear axis ,3 additional rotational axis
Here VMC is a 3axis milling m/c. Spindle axis is always Z even in cnc turning center
Why 5 axis is more important why not 3?... Intricate shape where tool can’t reach or require more setup, if we need very high accuracy and complex contours..like here impeller /turbine blade
2 additional rotational axis to 3 linear will configure 5 axis.
VMC- Vertical machining center,
HMC- Horizontal machining center, spindle axis is always Z
Part print analysis, process planning, CAM/manual program via USB derive or R123 cable, finally manufacture the part
Each CNC machine has a built-in location that is called Machine zero. Before moving and cutting a block, the CNC machine needs to know where to start, the start position is the part zero used in programming. This location acts as the origin from which all the other dimensions are calculated during the program and it is usually located on the edge of a workpiece.
Program consists of BLOCKS. Each BLOCK has WORDS. Each WORD denotes ACTION. Program has to EXPLICITLY specify the ACTION to be done by Tool/Machine
Why G/M code used: Provide M/c tool action: Feed the Tool,Start the Machine, Rotate Spindle, Clamp the Job, Start the Coolant. Stop the Machine.
G00: no cutting, fast travel
G01: cutting with slow feed
These are very basic G and M code. We need not to mug up, just understand their application, all will be provided during exams and lab course.
Part Print Analysis: A detail study of Part drawings for the manufacturing of the part is called as Part Print Analysis
CNC( PTP-point to point program): G99-Referencing, G80-Drilling canned cycle, R-referencing level over top of surface
From a rectangular block to make/cut this profile, how can we do that? First analyze the part print, make the process plan and then start writing the program.
CNC Contour Programming, Linear/Circular Interpolation used , Part Surface Programming,Tool Diameter Compensation
Point to Point (PTP) Programming, Canned cycles, Subroutines, Tool Length Compensation