IMLl 425
425E
E: CAM & CNC
CHAPTER 6
Computer Control of Manufacturing Systems
CAM & CNC Programming
• Numerically controlled M/T
• Basics of NC programming
• Manual part programming
• Computer assisted part programming
• CAD/CAM based part programming
HLHL-FA09
1
COMPUTER AIDED MANUFACTURING
IMLl 425
425E
E: CAM & CNC
DEFINITION:
Effective utilization of computer technology in the MANAGEMENT,
CONTROL and OPERATIONS of the manufacturing facility through
either direct or indirect computer interface with the physical and
human resources of the company (after CAMI).
Dominant Operation:
Numerical Control (NC) part programming
Common (and narrower) concept for CAM:
Computer assisted part programming
Logical Starting point:
Manual part programming
HLHL-FA09
2
1
Use of CAM Technology
IMLl 425
425E
E: CAM & CNC
Machining ______________ Milling, Turning, Drilling, Grinding,
Finishing
Nontraditional Processes _ Electric Discharge (EDM: Wire & Plunge),
Electro Chemical (ECM), Water Jet, PCB &
Micro chip Manufacturing
Rapid Prototyping _______ SLA, SLS, FDM, LOM, SGC, Milling
Welding, painting, finish, hoisting and
Robot programming ______ conveying, sheet forming
Measurement &
ReRe-engineering __________
CMM (Computerized Measurement Mach.)
Metal Forming ___________ Sheet blanking and bending in Punch
Press, Plasma Arc Cutting, Sheet bending
in CNC Press Brake, Spinning, etc...
3
HLHL-FA09
CAM in machining operations
IMLl 425
425E
E: CAM & CNC
Basic Advantages
In mass production
•
•
•
•
Better geometric repeatability
Combining many operations in one machine
Flexibility: Many different parts on one machine
Flexibility: Quick and easy implementation of design
modifications
In production of tools, dies and molds
• Quick and hasslehassle-free production of complex 33-D surfaces
• Drastic Time reduction in part programming
• Accurate production of the geometry developed during the
CAD stage and verified in the CAE stage
HLHL-FA09
4
2
IMLl 425
425E
E: CAM & CNC
Realization of a
Product via
Computer Aided
Processes
HLHL-FA09
5
NUMERICAL CONTROL (NC)
IMLl 425
425E
E: CAM & CNC
DEFINITION:
The control of operation of machine tools (M/T) (or other
sheet--working and welding machines) by a series of
sheet
coded instructions called the program, which consists
mainly of alphanumeric characters (numbers and
letters).
Main Characteristics:
Preplanned and predictable
Therefore, NC is a typical form of Programmable
Automation..
Automation
HLHL-FA09
6
3
BRIEF HISTORY OF CAM
IMLl 425
425E
E: CAM & CNC
Time
Characteristic
Description
Early Industrial Revolution
Basic Concept
J.Jackard’s method to control
textile looms by using
punched cards.
2nd World War
2D Manual Applications
Parson’s 22-D Coordinate table
operated by two people
1st modern concept
1947
Parsons’ NC proposal for
milling helicopter rotor blades
1952
1st effectively functioning
version
MIT’s first NC Milling machine
1956
1st industrial contract
USAF’s contract for 100 NC
Milling machines to 8 co.s
1956--1962
1956
Difficult years
Big opposition against NC M/T
in the contractors of USAF
1961
1st industrial success
Point-to
Pointto--point control drill
pressed
1970
1st CNC
Storing the programs on a
computer in add. to tapes.
HLHL-FA09
7
Computer Numerical Control (CNC)
IMLl 425
425E
E: CAM & CNC
CNC was first introduced in 1970 by replacing the hardwired MCU of a
conventional NC system by a microcomputer which accomplishes all
the functions of an MCU with its software.
What is new?
•
•
•
•
•
•
•
•
•
•
•
•
•
•
HLHL-FA09
Feed rate control, buffering, position loop control ...
Ability to edit and store programs
Ability to produce punched (or magnetic) tapes, diskettes etc.
Expanded tool offsets
Expanded control of machinemachine-sequence operations
Digitizing
Circular and more advanced (NURBS etc.) interpolation
Parametric programming
Do loops
Roughnening to a defined shape
Subroutines
Diagnostic capability
OnOn-screen geometric programming
...
8
4
Advantages of NC/CNC
IMLl 425
425E
E: CAM & CNC
• NC M/T ensure positioning accuracy and repeatibility with their
DESIGN, CONSTRUCTION and CONTROLS: Good for making many
of the same part.
• Complex shaped components can be made automatically, with high
precision and reliability.
• Parts that require a long series of operation can be made with minimal
accumulated error.
error.
• NC M/T can operate in hostile and hazardous environments.
• Since most work is shifted to offices from the shop
shop--floor, production can
be monitored by the management directly.
• NC M/T mostly are capable of conducting more than one machining
operation at a time or in a sequence without repeating the part setset-up.
• Minimum idle time and increased productivity.
• Interchangeability of work between different production plants.
HLHL-FA09
9
NC: Limitations
IMLl 425
425E
E: CAM & CNC
Major limitations:
• The relatively high initial cost of the equipment,
• The need and cost for programming and computer
time, and special maintenance requiring trained
personnel.
• Because NC machines are complex systems,
breakdowns can be very costly, so preventive
maintenance is essential.
• However, these limitations are often easily
outweighed by the overall economic advantages of
NC.
HLHL-FA09
10
5
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
11
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
12
6
Elements
of NC
IMLl 425
425E
E: CAM & CNC
• Tape (Media) Reader (electromechanical, electromegnetic, optical etc.)
• Machine Control Unit (MCU, sends conrol signals to servomechanism)
• Servomechanism(s) (amplify signals from the MCU, and send them to servomotors)
• Controlled element (tool, turret, M/T table: the numerically controlled part of M/T)
• Feedback unit (records the achieved tool movement and send them to the MCU)
HLHL-FA09
13
Principles of NC Machines
IMLl 425
425E
E: CAM & CNC
Functional elements in NC:
• Data input
• Data processing
• Data output
HLHL-FA09
14
7
IMLl 425
425E
E: CAM & CNC
Ball
Screw
HLHL-FA09
15
Types of NC Systems
IMLl 425
425E
E: CAM & CNC
Point-to
Pointto--point control system (Numerical positioning control, NPC)
NC Drill presses used in drilling precise patterns of holes.
Straight cut system
Feed rate at each
Axis is controlled
İndependently, one at
A time. Used in face
milling, Pocketing etc.
Contouring system (continuous path system)
Each servo motor can be controlled in varying speeds in coordination to
produce angular lines and curves.
Some simpler systems of this type use the method of breaking down the
curved into smaller linear segments which are connected to each other in a
tiptip-to
to--tail fashion.
HLHL-FA09
16
8
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
17
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
18
9
NC (Part) Programming
IMLl 425
425E
E: CAM & CNC
• Manual Part Programming
(Word Address Programming;
Programming; N-G Codes)
• ComputerComputer-Aided Part Programming
- Programming in APT (Automatically Programmed Tools)
- Professional/commercial CAD/CAM systems
Advantages of Computer Aided Part Programming in APT:
• Use of symbolic language
• Reduced programming time
• Reduced possibility of human error
• Ability to view a machining sequence on the screen for
debugging
• Capability of simple changeover of machining sequence from
machine to machine
• Lower cost because less time is required for programming
HLHL-FA09
19
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
20
10
NC MACHINE MOTIONS
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
21
Manual NC programming for machining
IMLl 425
425E
E: CAM & CNC
Figure shows a 2 in.
square and 0.75 in
thick workpiece that is
machined around its
circumference with an
end mill to a depth of
0.125 in. Before the NC
program is run, the
origin of the axes is set
at the lower left corner
of the part(near D) and
the dimensions are
given in the absolute
dimensioning method.
Also, machining tolerances are not taken into consideration in this example.
The cutter has a diameter of 0.250 in. and starts at a position of
X = -1.500 in., Y = 0, and Z = 1.500 in
HLHL-FA09
22
11
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
23
Milling Slots
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
24
12
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
25
Turning Cycle
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
26
13
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
27
Flowchart
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
28
14
Computer Assisted NC Programming: APT Language
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
29
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
30
15
Basic Geometric Features
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
31
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
32
16
APT Ex.2
Ex.2
IMLl 425
425E
E: CAM & CNC
Drilling the first three
holes:
P0 is where tool is at
rest
GOTO guides on XX-Y
Plane
GODLTA guides the tool
in the z direction
Feed, speed, tool
diameter etc. must be
defined earlier.
HLHL-FA09
33
APT Ex.3
Ex.3
IMLl 425
425E
E: CAM & CNC
L1 to L6, LL and C1 all
defined earlier
Feed, speed, tool diameter
etc. must be defined
earlier.
SP initial point
GORGT and GOLFT for
tool radius compensation
on right and left.
Modifiers:
ON used for direct intersection
TO used in concave path
PAST used in convex path
TANTO used for circular
HLHL-FA09
34
17
APT Ex.4
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
35
APT Ex.4
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
36
18
IMLl 425
425E
E: CAM & CNC
MILL = MACRO / DIA
… definition of macro
(subprogram), DIA is the
variable
CUTTER / DIA
… definition of tool diameter
CALL MILL:
defines the material
removed at each pass
(MILL works as a
subprogram defining the
radius to be compensated.
HLHL-FA09
37
APT Ex.5
IMLl 425
425E
E: CAM & CNC
HLHL-FA09
38
19
IMLl 425
425E
E: CAM & CNC
Generating an
NC Program in a
CAD/CAM System
HLHL-FA09
39
Adaptive Control
IMLl 425
425E
E: CAM & CNC
AC (Adaptive Control) is a system in which the operating parameters
automatically adapt themselves to conform to new circumstances during
the operation.
AC does not only adjust the controller signals but also the controller
mechanism as well.
Objectives:
• Optimize production rate
• Optimize product quality
• Minimize cost
Basic Functions:
• Determine the operating conditions of the process
• Configure the process control (strategy) in response to the operating
conditions
• Continuously monitor the process
ACC (Adaptive Control Constraint) systems
ACO (Adaptive Control Optimization) systems
HLHL-FA09
40
20
CAD/CAM Based NC Programming
IMLl 425
425E
E: CAM & CNC
Integrated CAD/CAM Packages:
CATIA, UG, II-DEAS, ProPro-E, Cimatron
Add-on CAM programs:
AddCAMWorks (on SolidWorks),
HyperMILL on Think Design or Solid Edge
Many others on AutoCAD or MEDesktop
Separate CAM programs:
SurfCAM, MasterCAM, WorkNC, PowerMILL,
Machine Strategist,
M/T Control System programs: ShopMILL, Mazak
HLHL-FA09
Beyond postpost-processors: CNC – BCL
Programming System
HLHL-FA09
41
IMLl 425
425E
E: CAM & CNC
42
21