cad-cam power point presentation
TRANSCRIPT
-
8/12/2019 CAD-CAM Power Point Presentation
1/102
1
Numerical control(NC)
NC is a form of programmable automation inwhich the mechanical actions of a machine tool orother equipment are controlled by a program
containing coded alphanumeric data.The data represent relative positions between the
tool and a workpart as well as other instructionsneeded to operate the machine.
When the current job is completed, the programof instructions can be changed to process a newjob.
The capability to change the program makes NC
suitable for low and medium production.
-
8/12/2019 CAD-CAM Power Point Presentation
2/102
2
Numerical control(NC) (Cont.)
Numerical control can be applied to awide variety of processes. The applicationscan be divided into two categories:
Machine tool applications, such asdrilling, milling, turning, and other metalworking.
Non-machine tool applications, such asassembly, drafting, and inspection.
-
8/12/2019 CAD-CAM Power Point Presentation
3/102
3
Basic Components of an NC System
An NC system consists of three basic
components:
a program of instructions,
a machine control unit, and
processing equipment.
The general relationship among the three
components is illustrated in Figure 6.1.
-
8/12/2019 CAD-CAM Power Point Presentation
4/102
4
NC Part Program
The program of instructions is the detailed step-by-step commands that direct the actions of the
processing equipment.
In machine tool applications, the program of
instructions is called apart program.
The individual commands refer to positions of a
cutting tool relative to the worktable on which the
workpart is fixtured. Additional instructions are usually included, such
as spindle speed, feed rate, cutting tool selection,
and other functions.
-
8/12/2019 CAD-CAM Power Point Presentation
5/102
5
NC Part Program (Cont.)
The program is coded on a suitable medium forsubmission to the machine control unit.
For many years, the common medium was 1-inchwide punched tape, using a standard format that
could be interpreted by the machine control unit.
Today, punched tape has largely been replaced bynewer storage technologies in modern machine
shops. These technologies include magnetic tape, diskettes,
and electronic transfer of part programs from a
computer.
-
8/12/2019 CAD-CAM Power Point Presentation
6/102
6
Machine control unit (MCU)
MCU consists of a microcomputer andrelated control hardware that stores theprogram of instructions and executes it byconverting each command into mechanical
actions of the processing equipment, onecommand at a time.
The related hardware of the MCU includes
components to interface with the processingequipment and feedback control elements.
The MCU also includes one or more readingdevices for entering part programs into
memory.
-
8/12/2019 CAD-CAM Power Point Presentation
7/102
7
Computer numerical control
(CNC)
Because the MCU is a computer, the termcomputer numerical control (CNC) isused to distinguish this type of NC from its
technological predecessors that were basedentirely on hard-wired electronics.
Today, virtually all new MCUs are based on
computer technology; hence, when we referto NC in this chapter and elsewhere, we
mean CNC.
-
8/12/2019 CAD-CAM Power Point Presentation
8/102
8
Computer numerical control
Figure: Schematic diagram of a CNC machine tool
-
8/12/2019 CAD-CAM Power Point Presentation
9/102
9
Processing Equipment
It accomplishes the processing steps totransform the starting workpiece into a
completed part.
Its operation is directed by the MCU,which in turn is driven by instructions
contained in the part program.
In the most common example of NC,machining, the processing equipmentconsists of the worktable and spindle aswell as the motors and controls to drive
them.
-
8/12/2019 CAD-CAM Power Point Presentation
10/102
10
NC Coordinate Systems
There are two axis systems used in NC, one forflat and prismatic workparts and the other for
rotational parts.
Both axis systems are based on the Cartesian
coordinate system.
The axis system for flat and prismatic partsconsists of the three linear axes (x, y, z) in the
Cartesian coordinate system, plus three rotationalaxes (a, b, c), as shown in Figure 2a.
The x-and y-axes are used to move and positionthe worktable, and the z-axis is used to control
the vertical position of the cutting tool.
-
8/12/2019 CAD-CAM Power Point Presentation
11/102
11
Coordinate systems used in NC
Coordinate systems used in NC: (a) for flat andprismatic work and (b) for rotational work.
a) b)
C di d i NC
-
8/12/2019 CAD-CAM Power Point Presentation
12/102
12
Coordinate systems used in NC
(Cont.)
The a-, b-, and c-rotational axes specifyangular positions about the x-, y-, and z-axes, respectively.
Clock wise rotation looking from the originof the axis indicate a positive direction.
The coordinate axes for a rotational NC
system are illustrated in Figure 2(b).These systems are associated with NC
lathes and turning centers, where the y axis
is not used.
-
8/12/2019 CAD-CAM Power Point Presentation
13/102
13
Coordinate systems used in NC (Cont.)
Figure: Direction of Axes in Vertical Milling
-
8/12/2019 CAD-CAM Power Point Presentation
14/102
14
Coordinate systems used in NC (Cont.)
Figure: Direction of Axes in Lathe Machines
-
8/12/2019 CAD-CAM Power Point Presentation
15/102
15
Coordinate systems used in NC
(Cont.)
Figure: Direction of Axes in Horizontal Milling
Machines
-
8/12/2019 CAD-CAM Power Point Presentation
16/102
16
Origin of the Coordinate axis
The part programmer must decide wherethe origin of the coordinate axis systemshould be located.
This decision is usually based onprogramming convenience.
For example, the origin might be located
at one of the corners of the part. If the workpart is symmetrical, the zero
point might be most conveniently defined
at the center of symmetry.
-
8/12/2019 CAD-CAM Power Point Presentation
17/102
17
Target point
At the beginning of the job, the operator mustmove the cutting tool under manual control tosome target point on the worktable, where the tool
can be easily and accurately positioned.
The target point has been previously referencedto the origin of the coordinate axis system by thepart programmer.
When the tool has been accurately positioned atthe target point, the operator indicates to theMCU where the origin is located for subsequenttool movements.
-
8/12/2019 CAD-CAM Power Point Presentation
18/102
18
Motion Control Systems
The different types of movement required formachining are accomplished by the motion control
system.
Motion control systems for NC can be divided into two
types: point-to-point and
continuous path
Point-to-point systemsmove the worktable to aprogrammed
location without regard for the path taken to get to that
location.
-
8/12/2019 CAD-CAM Power Point Presentation
19/102
19
Point-to-Point System
Figure 3 Point-to-point (positioning)
control in NC. Ateach x-y position,table movementstops to perform the
hole-drillingoperation.
-
8/12/2019 CAD-CAM Power Point Presentation
20/102
20
Continuous Path System
Continuous path systems generally refer tosystems that are capable of continuoussimultaneous control of two or more axes.
The system is able to generate angularsurfaces, two-dimensional curves, or three-dimensional contours in the work part.
This control mode is required in many millingand turning operations.
A simple two-dimensional profile millingoperation is shown in Figure 4 to illustratecontinuous path control.
-
8/12/2019 CAD-CAM Power Point Presentation
21/102
21
Continuous Path System (Cont.)
Figure 4:Continuous path(contouring)control in NC
system. (Note thatcutting tool pathmust be offsetfrom the part out-
line by a distanceequal to itsradius).
-
8/12/2019 CAD-CAM Power Point Presentation
22/102
22
Interpolation Methods
One of the important aspects of contouring is
interpolation.
The paths that a contouring-type NC system is
required to generate often consist of circulararcs and other smooth nonlinear shapes.
Some of these shapes can be defined
mathematically by relatively simple geometric
formulas (e.g., the equation for a circle is x2+y2 = R2).
Others cannot be mathematically defined
except by approximation.
-
8/12/2019 CAD-CAM Power Point Presentation
23/102
23
Interpolation Methods (Contd.)
To cut along a circular path, the circlemust be divided into a series of straightline segments that approximate the curve.
The tool is commanded to machine eachline segment in succession so that themachined surface closely matches thedesired shape.
The maximum error between the nominal(desired) surface and the actual(machined) surface can be controlled bythe lengths of the individual line
segments, as explained in Figure 5.
-
8/12/2019 CAD-CAM Power Point Presentation
24/102
24
Interpolation Methods (Contd.)
Figure 5Approximation of acurved path in NC bya series of straightline segments. In (a)the tolerance isdefined on only theinside of the nominalcurve. In (b) thetolerance is definedon only the outside of
the desired curve. In(c) the tolerance isdefined on both theinside and outside ofthe desired curve.
-
8/12/2019 CAD-CAM Power Point Presentation
25/102
25
Interpolation Methods (Contd.)
A number of interpolation methods areavailable to deal with the various problemsencountered in generating a smoothcontinuous path in contouring. Theyinclude:
Linear interpolation,
Circular interpolation,
Helical interpolation,
Parabolic interpolation
Cubic interpolation.
-
8/12/2019 CAD-CAM Power Point Presentation
26/102
26
Interpolation Methods(Contd.)
Linear interpolation:This is the mostbasic and is used when a straight linepath is to be generated in continuouspath NC. Two-axis and three-axis linear
interpolation routines are sometimesdistinguished in practice, butconceptually they are the same. Theprogrammer specifies the beginningpoint and end points of the straight lineand the feed rate to be used along thestraight line. The interpolator computesthe feed rates for each of the two (orthree) axes to achieve the specified
feed rate.
-
8/12/2019 CAD-CAM Power Point Presentation
27/102
27
Interpolation Methods(Contd.)
Circular interpolation:This methodpermits programming of a circular arcby specifying the followingparameters: (1) the coordinates ofthe starting point, (2) the coordinatesof the endpoint, (3) either the centeror radius of the arc, and (4) the
direction of the cutter along the arc. The generated tool path consists of a
series of small straight line segments(see Figure 5) calculated by the
interpolation module.
-
8/12/2019 CAD-CAM Power Point Presentation
28/102
28
Interpolation Methods (Contd.)
Helical interpolation:This method combines
the circular interpolation scheme for two axesdescribed above with linear movement of athird axis. This permits the definition of ahelical path in three-dimensional space.
Applications include the machining of largeinternal threads, either straight or tapered.
Parabolicand cubic interpolationsThese
routines provide approximations of free form
curves using higher order equations. Theygenerally require considerable computationalpower and are not as common as linear andcircular interpolation.
b l l
-
8/12/2019 CAD-CAM Power Point Presentation
29/102
29
Absolute Versus Incremental
Positioning
Another aspect of motion control is concernedwith whether positions are defined relative to theorigin of the coordinate system or relative to the
previous location of the tool.
The two cases are called absolute positioningand incremental positioning.
In absolute positioning, the workhead locations
are always defined with respect to the origin ofthe axis system.
In incremental positioning, the next workheadposition is defined relative to the present
location. The difference is illustrated in Figure 6.
Ab l t V I t l
-
8/12/2019 CAD-CAM Power Point Presentation
30/102
30
Absolute Versus IncrementalPositioning
Figure 6: Absolute versus
incremental positioning.
The work head is
presently at point (20, 20)
and is to be moved to
point (40, 50). In absolute
positioning, the move is
specified by x = 40, y =
50; but in incrementalpositioning, the move is
specified by x = 20, y=30.
C N i l C l
-
8/12/2019 CAD-CAM Power Point Presentation
31/102
31
Computer Numerical Control
Computer numerical control (CNC) is defined
as an NC system whose MCU is based on adedicated microcomputer rather than on a hard-wired controller.
Computer NC systems include additional
features beyond what is feasible withconventional hard-wired NC.
These features include the following:
Storage of more than one part program
Various forms of program input
Program editing at the machine tool
Fixed cycles and programming subroutines
C t N i l C t l
-
8/12/2019 CAD-CAM Power Point Presentation
32/102
32
Computer Numerical Control
(Cont.)
InterpolationPositioning features for setup
Cutter length and size compensation
Acceleration and deceleration calculations
Communications interface: most modern CNCcontrollers are equipped with a standard RS-232 or othe communications interface. This isuseful for various applications, such as:
down loading part programs from a central data file.
interfacing with peripheral equipment, such asrobots.
collecting operational data such as workpiece
counts, cycle times, and machine utilization.
Th M hi C t l U it f
-
8/12/2019 CAD-CAM Power Point Presentation
33/102
33
The Machine Control Unit for
CNC
The general configuration of the MCU in a CNCsystem is illustrated in Figure 7.
The MCU consists of the following componentsand subsystems:
central processing unit,
memory,
I/O interface,
controls for machine tool axes and spindle
speed, sequence controls for other machine tool
functions.
These subsystems are interconnected by meansof a system bus, as indicated in the figure 7.
Th M hi C t l U it f CNC
-
8/12/2019 CAD-CAM Power Point Presentation
34/102
34
The Machine Control Unit for CNC
(Cont.)
Figure 7: Configuration of CNC Machine
Control Unit
Memory:
ROM - Operating
system
RAM - Part programs
Central Processing
Unit (CPU)
Input/Output
interface
Operator panel
Tape reader
Machine tool controls
Position control
Spindle speed control
Sequence controls
Coolant
Fixture clamping Tool
changer
The Machine Control Unit for CNC
-
8/12/2019 CAD-CAM Power Point Presentation
35/102
35
The Machine Control Unit for CNC
(Cont.)
Central Processing Unit: CPU is the brain of the
MCU. It manages the other components in the MCUbased on software contained in main memory.
The CPU can be divided into three sections:
control section,
arithmetic-logic unit,
immediate access memory.
The control section retrieves commands and data from
memory and generates signals to activate other
components in the MCU. The arithmetic-logic unit (ALU) consists of the
circuitry to perform various calculations.
The immediate access memoryprovides a temporary
storage for data being processed by the CPU.
ersona omputers an t e
-
8/12/2019 CAD-CAM Power Point Presentation
36/102
36
Two basic configurations are beingapplied:
the PC is used as a separate front-endinterface for the MCU,
the PC contains the motion control boardand other hardware required to operate themachine tool.
In either configuration, the advantage of
using a PC for CNC is its flexibility toexecute a variety of user software inaddition.
ersona omputers an t eMCU.
-
8/12/2019 CAD-CAM Power Point Presentation
37/102
37
NC Software
There are three types of software programs used in CNCsystems:
machine interface software,
application software.
operating system software,
The principal function of the operating system software isto interpret the NC part programs and generate thecorresponding control signals to drive the machine toolaxes and is stored in ROM in the MCU.
The machine interface software is used to operate thecommunication link between the CPU and the machinetool to accomplish the CNC auxiliary functions.
The application software consists of the NC partprograms.
-
8/12/2019 CAD-CAM Power Point Presentation
38/102
38
Direct Numerical Control (DNC)
The first attempt to use a digital computer todrive the NC machine tool was DNC. This was
in the late 1960s before the advent of CNC.
As initially implemented, DNC involved the
control of a number of machine tools by a
single (mainframe) computer through direct
connection.
Instead of using a punched tape reader to enterthe part program into the MCU, the program
was transmitted to the MCU directly from the
computer, one block of instructions at a time.
-
8/12/2019 CAD-CAM Power Point Presentation
39/102
39
Direct Numerical Control (DNC)
This mode of operation was referred to by thename behind the tape reader (BTR).
The DNC computer provided instruction blocks
to the machine tool on demand.
As each block was executed by the machine, the
next block was transmitted.
The general configuration of a DNC system is
depicted in Figure 8.
-
8/12/2019 CAD-CAM Power Point Presentation
40/102
40
Figure 8: The general configuration of a DNCsystem
Direct Numerical Control (DNC) (Cont.)
-
8/12/2019 CAD-CAM Power Point Presentation
41/102
41
Direct Numerical Control (DNC) (Cont.)
The system consisted of four components: central computer,
bulk memory at the central computer site,
set of controlled machines, and
telecommunications lines to connect the machines tothe central computer.
Advantages claimed for DNC in the early 1970s included:
high reliability
elimination of the tape and tape reader,
control of multiple machines by one computer;
improved computational capability for circularinterpolation;
part programs stored magnetically in bulk memory,
etc.
-
8/12/2019 CAD-CAM Power Point Presentation
42/102
42
Distributed Numerical Control
As the number of CNC machine installations grewduring the 1970s and 1980s, DNC emerged once again,
but in the form of a distributed computer system, or
distributed numerical control (DNC).
The configuration of the new DNC is very similar tothat shown in Figure 8 except that the central computer
is connected to MCUs, which are themselves
computers.
This permits complete part programs to be sent to themachine tools, rather than one block at a time.
It also permits easier and less costly installation of the
overall system.
-
8/12/2019 CAD-CAM Power Point Presentation
43/102
43
Distributed Numerical Control
There are several ways to configure aDNC system.
F igure 9, 10illustrates two types of
DNC configuration: switching network and
LAN
-
8/12/2019 CAD-CAM Power Point Presentation
44/102
44
Distributed Numerical Control
F igure 9:Switching network DNC system
Di t ib t d N i l C t l
-
8/12/2019 CAD-CAM Power Point Presentation
45/102
45
Distributed Numerical Control
F igure 10:LAN type DNC system
-
8/12/2019 CAD-CAM Power Point Presentation
46/102
46
Appl icat ionso f NC
The operating principle of NC has manyapplications.
The applications divide into two categories:
machine tool applications
non-machine tool applications.
Machine Tool Applications
The most common applications of NC are inmachine tool control. Machining was the
first application of NC
-
8/12/2019 CAD-CAM Power Point Presentation
47/102
47
Appl icat ionso f NC (Cont.)
The common NC machine tools are:
NC lathe
NC boring mill, horizontal and
verticalspindle
NC drill press
NC milling machine
NC cylindrical grinder
-
8/12/2019 CAD-CAM Power Point Presentation
48/102
48
Appl icat ionso f NC (Cont.)
Figure 11: Turning Operation
-
8/12/2019 CAD-CAM Power Point Presentation
49/102
49
Appl icat ionso f NC (Cont.)
Figure 12: Drilling Operation
-
8/12/2019 CAD-CAM Power Point Presentation
50/102
50
Appl icat ionso f NC (Cont.)
Figure 13: Milling Operation
-
8/12/2019 CAD-CAM Power Point Presentation
51/102
51
Appl icat ionso f NC (Cont.)
Figure 14: Four-axis CNC horizontalmilling machine
-
8/12/2019 CAD-CAM Power Point Presentation
52/102
52
NC Application Characteristics
In general, NC technology is appropriate for lowto-medium production of medium-to-high variety product.
The following part characteristics have come to be
identified as being most suited to the application of
NC: Batch production
Repeat orders
Complex part geometry
Much metal needs to be removed from the workpar t
Many separate machining operations on the part
The part is expensive
f h l ki
-
8/12/2019 CAD-CAM Power Point Presentation
53/102
53
NC for Other Metalworking
Processes
In addition to the machining process NC
machine tools have also been developed for the
following metal working processes:
Punch pressesPresses for sheet metal bending
Welding machines
Thermal cutting machines, such as oxy-fuelcutting, laser cutting, and plasma arc cutting
Tube bending machines
-
8/12/2019 CAD-CAM Power Point Presentation
54/102
54
Other NC Applications
Some of these machines with NC-type controlsthat position a workhead relative to an object
being processed are the following:
Electrical wire wrap machines
Component insertion machines
Drafting machines
FDM Machines
Coordinate measuring machine
Tape laying machines for polymer composites
Filament winding machines for polymer
composites, etc.
-
8/12/2019 CAD-CAM Power Point Presentation
55/102
55
Advantages of NC
Nonproductive time is reduced
Greater accuracy and repeatability
Lower scrap rates
Inspection requirements are reduced
More-complex part geometries are possible
Engineering changes can be accommodatedmore gracefully
Simpler fixtures are needed
Shorter manufacturing lead times
Reduced parts inventory
Less floor space required
Operator skill-level requirements arereduced
-
8/12/2019 CAD-CAM Power Point Presentation
56/102
56
NC Part programming
NC part programming consists of planning anddocumenting the sequence of processing steps to
be performed on an NC machine.
The traditional input medium dating back to the
first NC machines in the 1950s was 1-inch widepunched tape.
More recently, the use of magnetic tape and
floppy disks have been growing in popularity as
storage technologies for NC.
The advantage of these input media is their much
higher data density.
-
8/12/2019 CAD-CAM Power Point Presentation
57/102
57
NC Cod ing Sys tem
The program of instructions is communicatedto the machine tool using a coding system
based on binary numbers.
This NC coding system is the low-level
machine language that can be understood by
the MCU.
When higher level languages are used, such as
APT, the statements in the program areconverted to this basic code.
-
8/12/2019 CAD-CAM Power Point Presentation
58/102
58
NC Cod ing Sys tem (Con t.)
Part programming can be accomplished
using a variety of methods, which are:
manual part programming
computer-assisted part programming,
part programming using CAD/CAM, and
manual data input.
Binary Numbers and the Binary
-
8/12/2019 CAD-CAM Power Point Presentation
59/102
59
a y u be s a d t e a yCoded Decimal System
In the binary number system, each digit cantake on either of two values, 0 or l.
The meaning of consecutive dig its in thebinary system is based on the number 2 raised
to successive powers. Starting from the right, the first digit is 20
(which equals 1), the second digit is 21(which equals 2), and so forth.
The two numbers, 0 or l, in successive digitpositions, indicate the presence or absence ofthe value. For example, the binary number0101 is equal to the decimal number 5.
Binary Numbers and the Binary
-
8/12/2019 CAD-CAM Power Point Presentation
60/102
60
Binary Numbers and the Binary
Coded Decimal System (Cont.)
The conversion from binary to decimal operates
as follows:
(0x23)+(1x22)+(0x21)+(1x2)=(0x8)+(1x4)
+(0x2)+ (IxI) = 4+1 = 5 Conversion of the 10 digits in the decimal number
system into binary numbers is shown in Table 1.
Four binary digits are required to represent the tensingle-digit number in decimal.
To encode the decimal value 125 in the binary numbersystem requires a total of 11 digits: 10011100010.
Another problem with the binary number system is thecoding of decimal fractions.
-
8/12/2019 CAD-CAM Power Point Presentation
61/102
Binary Numbers and the Binary
-
8/12/2019 CAD-CAM Power Point Presentation
62/102
62
Binary Numbers and the Binary
Coded Decimal System (Cont.)
First 0001 1000
Second 0010 200
Third 0101 50
Fourth 0000 0
Sum 1250
Number
sequence
Binary number Decimal
value
Binary Numbers and the Binary Coded
-
8/12/2019 CAD-CAM Power Point Presentation
63/102
63
Binary Numbers and the Binary Coded
Decimal System (Cont.)
Table 2:Comparison of Binary and Decimal Numbers
0000 0 0101 5
0001 1 0110 6
0010 2 0111 7
0011 3 1000 8
0100 4 1001 9
Binary Decimal Binary Decimal
EIA d ISO C di St d d
-
8/12/2019 CAD-CAM Power Point Presentation
64/102
64
EIA and ISO Coding Standards
In addition to numerical values, the NC codingsystem must also provide for alphabeticalcharacters and other symbols.
Eight binary digits are used to represent all of
the characters required for NC partprogramming.
There are two standard coding systemscurrently used in NC:
the Electronics Industry Associatic (EIA) and
the International Standards Organization (ISO).
The complete listings of EIA and ISO (ASCII)codes for are shown in Table 7.
EIA and ISO Coding Standards
-
8/12/2019 CAD-CAM Power Point Presentation
65/102
65
g
EIA d ISO C di St d d
-
8/12/2019 CAD-CAM Power Point Presentation
66/102
66
EIA and ISO Coding Standards
EIA d ISO C di St d d
-
8/12/2019 CAD-CAM Power Point Presentation
67/102
67
EIA and ISO Coding Standards
Figure: Dimensions of a punched tape
-
8/12/2019 CAD-CAM Power Point Presentation
68/102
68
EIA and ISO Coding Standards (Cont.)
Both EIA and ISO coding schemes weredeveloped when punched tape was the pre-dominant medium for storing NC part
programs.Although punched tape has been largely
superseded by more modern media, it is stillwidely used in industry, if only for backup
storage.To ensure the correctness of the punched tape,
the eight binary digits in the EIA and ISO codesinclude aparity check.
EIA and ISO Coding Standards (Cont )
-
8/12/2019 CAD-CAM Power Point Presentation
69/102
69
EIA and ISO Coding Standards (Cont.)
In the EIA system, the tape reader is
instructed to count an odd number ofholes across the width of the tape.Whenever the particular number or
symbol being punched requires an evennumber of holes, an extra hole ispunched in column 5, hence making thetotal an odd number.
For example, the decimal number 5 iscoded by means of holes in columns 1and 3. Since this is an even number ofholes, a parity hole would be added.
-
8/12/2019 CAD-CAM Power Point Presentation
70/102
70
EIA and ISO Coding Standards (Cont.)
The difference between the EIA and ISOsystems is that the parity check in the ISOcode is an even number of holes, called an
even parity. The EIA system uses an oddparity.
Also, whereas the parity hole is in the fifth-digit position in the EIA coding system, it isin the eighth position in the ISO system.
These differences can be seen in Table 4.
EIA d ISO C d f NC
-
8/12/2019 CAD-CAM Power Point Presentation
71/102
71
EIA and ISO Codes for NC
A binary digit is called a bit. In punched tape, the values 0 or 1 are represented
by the absence or presence of a hole in a certainrow and column position.
Out of one row of bits a character is formed.A character is a combination of bits
representing a numerical digit (0-9), an alphabeticalletter (A-Z), or a symbol (Table 4).
Out of a sequence of characters, a word is formed.A word specifies a detail about the operation,
such as xposition, y-position, feed rate, or spindlespeed.
How Instructions Are Formed ?
-
8/12/2019 CAD-CAM Power Point Presentation
72/102
72
How Instructions Are Formed?
Out of a collection of words, a block isformed.
A block is one complete NC instruction.
It specifies the destination for the move,the speed and feed of the cuttingoperation, and other commands thatdetermine explicitly what the machine tool
will do.
For example:
G02 G17 X088.0 Y040.0 F30 EOB
T F t
-
8/12/2019 CAD-CAM Power Point Presentation
73/102
73
Tape Formats
Different formats have been developed over theyears to specify words within an instruction block.
These are often referred to as tape formats,
More generally, they are known asblock
formats.
Block formats are briefly described in Table 5,with two lines of code for the drilling sequence
shown in Figure 16.The word address format with TAB separation
and variable word order has been standardized byEIA as RS-274. It is the block format used on all
modern controllers.
T F t (C t )
-
8/12/2019 CAD-CAM Power Point Presentation
74/102
74
Tape Formats (Cont.)
Word address format uses a letterprefix to identify the type of word.
Repeated words can be omitted. The
words run together, which makes thecode difficult to read (for humans).
Example:
N001 GOOX0700OY0300OM03N002YO6000
-
8/12/2019 CAD-CAM Power Point Presentation
75/102
75
Tape Formats (Cont.)
The standard sequence of words in a block is:N_, G_, X_, Y_. Z_, I_, J__, K_, F _. S_. T_, M_
where
N is the identification number. G are the preparatory commands
X are the coordinates along the x axis,
Y are the coordinates along the y axis, Z are the coordinates along the z axis,
I, J, and K specify the arc center of circular tool
motion, usually provided with algebraic signs,
T F t (C t )
-
8/12/2019 CAD-CAM Power Point Presentation
76/102
76
Tape Formats (Cont.)
F is the feed rate,
S is the spindle speed,
T is the tool number, and
M are the miscellaneous commands given in
Table 11.3.Thus the following is an example of a word
address NC code:
N040 GOO X0 Y0 Z300 TO 1 M06
Omitted words are assumed to be zero or to bethe same as the value previously defined. The Fand S words were omitted from the example.
T F t (C t )
-
8/12/2019 CAD-CAM Power Point Presentation
77/102
77
Tape Formats (Cont.)
Word address format with TABseparation and variable word order isthe same format as the previous,except that words are separated by
TABs, and the words in the block canbe listed in any order.
Example:
N001 GOO X07000 Y03000 M03N002 Y06000
-
8/12/2019 CAD-CAM Power Point Presentation
78/102
78
Tape Formats (Cont.)
Figure 15: Example drilling sequence forblock formats described in Table 5.Dimensions are in millimeters.
Word Prefixes Used in Word
-
8/12/2019 CAD-CAM Power Point Presentation
79/102
79
Word Prefixes Used in WordAddress Format
Word
N N01
G G21
X, Y, Z X75.0
U, W U25.0
A, B, C A90.0
R R100.0
Prefix Example
Word
Prefix Example
I, J, K 132 J67
F G94 F40
S S0800
T T14
D D05
P P05 R15.0
M M03
Word Prefixes Used in WordAddress Format
-
8/12/2019 CAD-CAM Power Point Presentation
80/102
80
Address Format
or re xes se n orAddress Format
-
8/12/2019 CAD-CAM Power Point Presentation
81/102
81
Address Format
G Codes and Their Functions
-
8/12/2019 CAD-CAM Power Point Presentation
82/102
82
G Codes Functions
G Codes and Their Functions (Cont.)
-
8/12/2019 CAD-CAM Power Point Presentation
83/102
83
G Codes Functions
M Codes and Their Functions
-
8/12/2019 CAD-CAM Power Point Presentation
84/102
84
M Codes Functions
G Codes and Their Functions (Cont.)
-
8/12/2019 CAD-CAM Power Point Presentation
85/102
85
M Codes Functions
MANUAL PART PROGRAMMING
-
8/12/2019 CAD-CAM Power Point Presentation
86/102
86
Instructions in Word Address Format:
Instructions in word address format consist of a series
of words, each identified by a prefix label.
In preparing the NC part program, the part
programmer must initially define the origin of the
coordinate axes.
This is accomplished in the first statement of the part
program.
origin of the coordinate system can be located at any
desired position.
An example of part program manuscript is shown in
the next Table.
MANUAL PART PROGRAMMING
MANUAL PART PROGRAMMING
-
8/12/2019 CAD-CAM Power Point Presentation
87/102
87
MANUAL PART PROGRAMMING
Part name
Part numberSheetRemarks
MANUSCRIPT
CONTOURINGPROGRAM
Prepared by Date
Checked by DaleMachineTape number
n G X Y Z I J K F S T M Remarks
MANUAL PART PROGRAMMING
-
8/12/2019 CAD-CAM Power Point Presentation
88/102
88
MANUAL PART PROGRAMMING
The operator is instructed to move the toolto this position at the beginning of the job.
With the tool in position, the G92 code is
used by the programmer to define theorigin as follows:
G92 XO Y-050.0 ZO10.0
where the x, y, and z values specify thecoordinates of the tool location in the
coordinate system.
MANUAL PART PROGRAMMING
-
8/12/2019 CAD-CAM Power Point Presentation
89/102
89
MANUAL PART PROGRAMMING
a more-complete instruction block wouldbe the following:
G21 G92 XO Y-050.0 ZO10.0
where the G21 code indicates that the
subsequent coordinate values are inmillimeters.
Motions are programmed by the codes
GOO, G01, G02, and G03.GOO is used for a point to-point rapid
traverse movement for example,
GOO X050.0 Y086.5 Z 100.0
MANUAL PART PROGRAMMING
-
8/12/2019 CAD-CAM Power Point Presentation
90/102
90
MANUAL PART PROGRAMMING
Linear interpolation is accomplished by the G0lcode. This is used when it is desired for the
tool to execute a contour cutting operation
along a straight line path. For example, the
commandG0I G94 X050.0 Y086.5 Z 100.0 F40 S800
Selection of the desired plane is accomplished by
entering one of the codes, G17, G18, or G19,respectively. Thus, the instruction
G02 G17 X088.0 Y040.0 R028.0 F30
-
8/12/2019 CAD-CAM Power Point Presentation
91/102
MANUAL PART PROGRAMMING
-
8/12/2019 CAD-CAM Power Point Presentation
92/102
92
MANUAL PART PROGRAMMING
In contouring motions,it is almost alwaysdesirable that the pathfollowed by the center
of the tool beseparated from theactual surface of thepart by a distanceequal to the cutterradius, as shown inFigure 17.
MANUAL PART PROGRAMMING
-
8/12/2019 CAD-CAM Power Point Presentation
93/102
93
MANUAL PART PROGRAMMING
For a three-dimensional surface, the shape of theend of the cutter would also have to be consideredin the offset computation. This tool path
compensation is called the cutter offset.
Modern CNC machine tool controllers performthese cutter offset calculations automatically when
the programmer uses the G40, G41, and G42 codes.
The G40 code is used to cancel the cutter offsetcompensation. The G41 and G42 codes invoke thecutter offset compensation of the tool path on theleft- or right-hand side of the part, respectively.
MANUAL PART PROGRAMMING
-
8/12/2019 CAD-CAM Power Point Presentation
94/102
94
MANUAL PART PROGRAMMING
The instruction for profile milling thebottom edge of the part, assuming that thecutter begins along the bottom left corner,would read:
G42 G01 X100.0 Y040.0 D05
where D05 indicates that the radius offsetdistance is stored in the number 5 offset
register in the controller.This data can be entered into the controller in
either of two ways: (1) as manual input or
(2) as an instruction in the part program.
MANUAL PART PROGRAMMING
-
8/12/2019 CAD-CAM Power Point Presentation
95/102
95
MANUAL PART PROGRAMMING
When the offset data is entered as a partprogram instruction, the statement has theform:
G 10 P05 R10.0where G10 is a preparatory word indicatingthat cutter offset data will be entered; P05
indicates that the data will be entered intooffset register number 05; and R10.0 is the
radius value, here 10.0 mm.
Part Programming Examples
-
8/12/2019 CAD-CAM Power Point Presentation
96/102
96
Part Programming Examples
To demonstrate manual part programming, twoexamples using the sample part shown in Figure18 are taken up.
The first example is a point-to-point program todrill the three holes in the part.
The second example is a two axis contouringprogram to accomplish profile milling around the
periphery of the part.
Part Programming Examples
-
8/12/2019 CAD-CAM Power Point Presentation
97/102
97
Part Programming Examples
Figure 18: Samplepart to illustrate NC partprogramming. Dimensions are in millimeters.
Part Programming Examples
-
8/12/2019 CAD-CAM Power Point Presentation
98/102
98
Part Programming Examples
EXAMPLE 1:Point-to-Point Drilling.N001 G21 G90 G92 X0 Y-050.0 Z010.0; Define origin of axes.
N002 G00 X070.0 Y030.0; Rapid move to first hole location.
N003 G0l G95 Z-15.0 F0.05 S1000 M03; Drill first hole.
N004 G01 Z010.0; Retract drill from hole.N005 G00 Y060.0; Rapid move to second hole location.
N006 G01 G95 Z-15.0 F0.05; Drill second hole.
N007 G0l Z010.0; Retract drill from hole.
N008 G00 X120.0 Y030.0; Rapid move to third hole location.
N009 G01 G95 Z-15.0 F0.05; Drill third hole.
N010 G01 Z010.0; Retract drill from hole.
N01 l G00 X0 Y050.0 M05; Rapid move to target point
N012 M30; End of program, stop machine.
Part Programming Examples
-
8/12/2019 CAD-CAM Power Point Presentation
99/102
99
Part Programming Examples
EXAMPLE 2:Two-Axis MillingThe axis coordinates are shown in Figure
18.
The part is fixtured so that its top
surface is 40 mm above the surface ofthe machine tool table.
Thus, the origin of the axis system willbe 40 mm above the table surface.
A 20-mm diameter end mill with fourteeth will be used.
The cutter has a side tooth engagementlength of 40 mm.
Part Programming Examples
-
8/12/2019 CAD-CAM Power Point Presentation
100/102
100
The bottom tip of the cutter will be
positioned 25 mm below the part topsurface, since the part is 10 mm thick.
The cutter will be operated at a
spindle speed = 1000 rev/min and a
feed rate = 50 mm/min (which
corresponds to 0.20 mm/tooth).
The tool path to be followed by the
cutter is shown in Figure 19.
Part Programming Examples
-
8/12/2019 CAD-CAM Power Point Presentation
101/102
101
Part Programming Examples
Figure 19:Cutter path for profile millingoutside perimeter of sample part.
Part Programming Examples
-
8/12/2019 CAD-CAM Power Point Presentation
102/102
Part Programming Examples
NC Part Program Code:
N001 G21 G90 G92 X0 Y-050.0 Z010.0; Define origin of axes.
N002 G00 Z-025.0 S1000 M03; Rapid to cutter depth, turnspindle on.
N003 G01 G94 G42 Y0 D05 F40; Engage part, start cutter offset.N004 G01 X160.0; Mill lower part edge.
N005 G01 Y060.0; Mill right straight edge.
N006 G17 G03 X130.0 Y090.0 R030.0; Circular interpolationaround arc.
N007 G0l X035.0; Mill upper part edge.N008 G01 X0 Y0; Mill left part edge.
N009 G40 G00 X-040.0 M05; Rapid exit from part, cancel offset.
N01 G00 X0 Y050.0; Rapid move to target point.