Lecture Notes for Subject: CAD/CAM/CIM (ME 804) Given By: … · 2018-10-23 · Visit: 1 Lecture...

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Lecture Notes for

Subject: CAD/CAM/CIM (ME 804)

Given By: Prof. Sunil Pipleya

Introduction of CNC

Computer Numerical Control is the control of a machine tool using numbers and letters.

It is a system in which programmed numerical values are directly inserted and stored on

some form of input medium, and automatically read and decoded to cause a

corresponding movement in the machine which it is controlling.

Advantages of CNC

High degree of quality due to accuracy, repeatability, and freedom from operator-

introduced variations.

Reduced scrap. Errors due to operator fatigue, interruptions, and other factors are

less likely to occur.

Simplified inspection. Once the first piece has passed inspection, minimal

inspection is required on subsequent parts

Lower tooling costs due to less need for complex jigs and fixtures.

Reduced lead time.

Complex machining operations are more easily accomplished due to advanced

machine control.

CNC Disadvantages

Tools on NC machines do not cut metal any faster than conventional machines.

NC does not eliminate the need for expensive tools. There is also a greater initial

cost involved with the NC machine.


NC will not totally eliminate errors. Operators can still fail to push the correct

buttons, make incorrect alignments, and fail to locate parts properly in a fixture.

Selection and training of programmers and maintenance personnel is required.

CNC History

1947 - John Parsons began experimenting with the idea of generating thru-axis

curve data and using that data to control machine tool motions.

1949 - A contract was granted to the Parsons Corporation to search for a speedy

production method.

1952 - MIT successfully demonstrates a model of the NC machine of today. The

machine successfully made parts with simultaneous thru-axis cutting tool movements.

MIT coined the term "numerical control".

1955 - Commercial models of NC machines displayed for customer acceptance.

1957 - NC accepted by industry; several are installed and in use

Prerequisites

Blueprint Reading

Work piece and Fixture setup

Familiarity with machine operations - machine tools, cutting speeds, feed rates,

and depth of cut.

Familiarity with the machine being programmed; its general operating

characteristics; tape, floppy, or network data input; and the machine's control panel

operation.

Understanding of basic computer operations, CNC programming, and data

translations.


CNC Equipment

Milling Machines

CNC Milling Machines use a rotary cutter for cutter motion and linear motion for feed.

The material is pushed into the cutter, or the cutter is pushed into the material, in 3

dimensional straight or curved paths to produce the desired part elements. The finished

part is created by removing all unnecessary material from the workpiece. This process is

called Milling.

Lathes

CNC Lathes rotate the work against a single point tool to produce cutting motion. The

tool is fed along or into the work to produce the feed motion. Machining a part on a lathe

is called Turning.


Machining Centers

Machining Centers are more sophisticated CNC machines that often combine milling and

turning technologies.

EDM Machines

An Electrical Discharge Machine uses electric sparks to make a cavity in a piece of

metal. This process requires an electrode, a power source, a tank, and coolant. The

workpiece is connected to one side of the power supply and placed in the tank. The

electrode, which is made in the shape of the cavity that is desired, is connected to the

other side of the power supply. The tank is filled with coolant. This coolant is a dielectric

material. A dielectric resists the flow of electricity. The electrode is lowered until a spark

jumps between the electrode and the work. When the spark jumps, the dielectric quality

of the coolant has been overcome. The spark dislodges small particles of material that are

carried away by the coolant. A cavity of the same shape as the electrode is created. The

electrode is lowered as the cavity is produced until the proper depth is achieved.


Robots

Industrial Robots are specialized machine tools that are a direct replacement for human

labor. I/Rs are used to consistently perform tasks that are monotonous, repetitive, and/or

hazardous. Some examples are; welding, spray painting, soldering, palletizing, transfer of

materials, and tool and part changers for CNC machines.

CNC Control Panels

CNC Control panels include the controls for all aspects of the machining process. Some

machines also include part programming and tool path verification.


CNC Systems

Point-to-point control is the positioning of the tool from one point to another

within a coordinate system. Most often used for positioning to a point where a manual

machining operation such as drilling or boring would occur.

Straight-cut control has the ability move a tool, while engaged, straight in all axes

of the machine and has the ability to do angles of 45 degrees.

Contouring control systems generate a continuously controlled toolpath by

interpolating intermediate points or coordinates. Interpolating means the ability to

generate the points that make up a path.

Machine Tool Practices

Design and setup of Fixtures

A fixture is a production tool that locates, holds, and supports the workpiece securely so

that the machining operations can be performed exactly the same for duplicate parts (ie.

production runs). Although largely used on milling machines, fixtures are also designed

to work for various operations on most of the standard machine tools. Fixtures vary in

design from relatively simple tools to expensive, complicated devices.


Plate fixtures are the simplest basic fixture made from a flat plate which has a

variety of clamps, locators, or pins to hold and locate a part. Its simplicity and

adaptability make it a popular type of fixture.

Angle-plate fixtures are a variation of the plate fixture that is used to machine the

part at a right angle to its locator point. Most angle-plate fixtures are made at 90 degrees

but they can be made at other angles.

Vise-jaw fixtures are for machining small parts. With this type of fixture the

standard vise jaws are replaced with jaws that are formed to fit the part. These fixtures

are the least expensive type of fixtures to make and their use is only limited by the sizes

of vises available.

Indexing fixtures are used for maching parts which must have machined details

evenly spaced.

Multistation fixtures are used primarily for high-speed, high- volume production

runs where the machining cycle must be continuous.

Duplex fixtures are the simplest form of multistation fixtures. This fixture allows

for the loading and unloading operations to be performed while the machining operations

are in progress. Thus allowing non-stop machining.

Profiling fixtures are used to guide tools for machining contours which the

machine cannot normally follow. CNC Machines do not use these types of fixtures.

Some production operations that use fixtures:

Assembling

Boring

Broaching

Drilling

Forming

Gauging

Grinding

Heat Treating

Honing

Inspecting

Lapping

Milling

Planing

Polishing

Punching

Reaming

Sawing

Shaping

Stamping

Tapping

Testing

Turning

Welding


Various Geometry Producing Tools

A Milling machine boring bar and Lathe tools Endmills and Drill, Ream, Tap, Grinding

wheel and bits


Climb and Conventional Milling

Climb milling or down-milling is when the work is moved in the same direction as the

rotation of the cutter. Full engagement of the tooth is instantaneous. The sliding action of

conventional milling is eliminated resulting in a better surface finish and longer tool life.

Conventional or up-milling is when the work is fed into the rotation of the cutter. The

chips are at a minimun thickness at the start of the cut and are so light that the tool has a

tendency to slide over the work. This sliding, followed by a sudden breakthrough as the

tool completes the cut, causes a rough surface finish.

Cutting Data and Formulas

Here are some of the most common terms used for expressing cutting data:

Spindle speed - Spindle speed is the rotational speed of the spindle and tooling. This

value is usually expressed in RPM. (Revolutions Per Minute)

Feedrate value - The feedrate value is the numerical value at which a tool will traverse

a workpiece. It is usually expressed in either IPM (Inches Per Minute) or IPR (Inches Per

Revolution).

Cutting speed - Cutting speed is the rotational speed of the cutting tool or workpiece.

It can be stated as either RPM or SFM. (Surface Feet Per Minute)

Depth of Cut - Depth of cut is the distance the tool tip is engaged into the workpiece.

It is incorporated into the X, Y, and Z values in a CNC program. Separate from the

program, it can be expressed in inches or mm.

Calculating the cutting data is an important step in the planning of a CNC program.

Several of the most common formulas are explained here.


S.F.M = R.P.M. x Diameter x .262

Example: Find the Surface Feet per Minute of a 1" tool at 600 RPM

SFM = RPM x 1 x .262

SFM = 600 x 1 x .262

SFM = 157.2

R.P.M. = S.F.M. x 3.82 / Diameter

Example: Find the RPM of a 1" tool at 150 SFM.

RPM = SFM x 3.82 / Diameter

RPM = 150 x 3.82 / 1

RPM = 573

I.P.M. = R.P.M x T x F.P.T.

Example: Find the Inches Per Minute of a 1" drill at 500

RPM and .006 FPT. IPM = 500 x 1x .006

IPM = 3.0

F.P.R. = I.P.M. / R.P.M.

Example: Find the Feed (Inches) Per Revolution of a cutter traveling at 200 RPM and 22

IPM.

FPR = 22 / 200

FPR = .11

F.P.T = I.P.M. / T x R.P.M.

Example: Find the Feed (Inches) Per Tooth for a 4 flute 2" cutter traveling at 200 RPM

and 20 IPM.

FPT = 20 / 4 x 200 FPT = .025

Note: A drill is considered a single tooth cutter.


Machine Programming

Program Planning

Blueprint Reading

Blueprint reading is a basic skill in the manufacturing industry that all engineers,

managers, CNC programmers, CNC operator, machinists, and inspectors should know.

Selecting the Proper Machine

Selecting the proper machine for a specific part to be manufactured is the responsibility,

in most companies, of the production manager, machine shop manager, and/or the CNC

manager. In a company with several CNCs, the CNC manager must know:

Each machines envelope (working area)

Each machines options (ie. threading,boring,etc.)

Cutting tools, spindle speeds, feedrates

Fixture design and setup

Machine operations: setup, loading programs,run.


Operations Sheet

The operations sheet, or setup sheet, is used to describe the processes needed to machine

a part on a CNC machine. Each process is written out in the proper machining sequence

and includes the tool to be used and all cutting data.

Programming the outer contour is one operation in the machining of a part. To

accomplish this you must first have a part origin. Then, the points required for machining

would be calculated for the center of the tool to be used, offset the radius of the tool, from

the actual part edge coordinates.

Tooling Requirements

Tooling requirements and selection are based on part restrictions and industry

manufacturing practices. Most of these ideas are common sense thoughts. Good CNC

programmers and operators should be aware of them.

Know the material to be machined and its characteristics.

Use industry standard catalog tooling to cut costs.

Make use of technical services offered by tooling manufacturers.

Quality of the fixture should be based on the number of pieces that will eventually

be produced.


Always use the right tool for the right machining operation.

Keep spares or backups of tooling in the event resharpening is needed or tool

breakage occurs.

Keep an assortment of tooling in case one type does not perform the job as

desired.

Use high speed steel tools on easily machined materials.

Use carbide tools on difficult to cut materials.

Use cobalt or oxide coated tools for exotic alloys.

Use insert type tooling where possible to cut costs.

Consider using reamers, instead of boring bars, on lathe applications where

chatter and chip control may be a problem.

Be aware of the flexing that occurs with long length tools. Extra passes may be

required to eliminate tapering and chattering.

Note: A drill is considered a single tooth cutter.

Tool Motion and Construction Planes

Construction plane codes are used to switch between the coordinate planes for machining

arcs or circles. These codes are G17 (XY), G18 (XZ), and G19 (YZ). Tool Motion must

occur parallel to one of these planes for arcs and circles. The default is G17 (XY).


Unit Systems and Input Modes

Unit Systems are the units of measurement to be used for the CNC program. All

machines understand both English and Metric standards. When programming in english

units you are using inches. And in metric its the millimeter (mm.). The CNC machine

needs to be told which units are being used. Some machines are automatically set-up at

the factory for inches or mm. Normally at the beginning of a CNC program you will see

either; G70 to specify inches or G71 to specify mm..

Input modes refer to the type of coordinate information that is input into the program for

the CNC machine. There are two types.

Absolute input, designated by the G90 code, specifies distances from the origin or

program zero point. Absolute is the most common mode.

Incremental input, designated by the G91 code, specifies distances and directions based

on the previous point as an origin. Incremental input is sometime called point-to-point.

All CNC systems can be switched from absolute to incremental mode and back unlimited

times within a program.

Other input modes such as Helical also exist.


Programming Codes

Letter Code Descriptions

N Sequence Number

G Preparatory Functions

X X Axis Command

Y Y Axis Command

Z Z Axis Command

R Radius from specified center

A Angle ccw from +X vector

I X axis arc center offset

J Y axis arc center offset

K Z axis arc center offset

F Feedrate

S Spindle speed

T Tool number

M Miscellaneous function

Sequence Numbers

Sequence number, also called N code, is the block (line) identification number in a CNC

program. The common code word used begins with N. N is the first code in a block and

normally has a range of N1 through N9999. Many CNCs do not require the use of N

codes which helps to free system memory. Their main benefits are to allow for easy

searches in long programs and the ability to easily restart a program at almost any line

number. Usually the programmer will skip N numbers between blocks to leave space to

insert forgotten or additional blocks later on. For example N5, N10, N15, etc..


Preparatory Functions

Preparatory functions are G codes. G codes are designated by the letter G and a two digit

numeric value. These codes are the most important functions in CNC programming

because they direct the CNC system to process the coordinate data in a particular manner.

Some examples are rapid traverse, circular interpolation, linear interpolation, and drilling.

G codes are somewhat standardized in industry.

Commonly used G Codes

G00 - The Rapid traverse code is used to move the axes quickly between cuts,

tool changes etc. Speeds of 200 IPM (inches per minute) or more are not uncommon.

ex. G00X0Y-.25

G01 - Linear interpolation is used to clear out material by moving the axes in

straight directions along or through the stock. Spindle speed, spindle start, and feedrate

must be specified ,for cutting, before executing this code.

ex. G01x3.125Y0F20

G02 - Circular Interpolation clockwise is used to clear out material by moving the

axes in circular directions along or through the stock. Spindle speed, spindle start, and

feed rate must be specified, for cutting, before executing this code.

ex. G02X.375Y3.I.375J2.5312F20

G03 - Circular Interpolation counter-clockwise is used to clear out material by

moving the axes in circular directions along or through the stock. Spindle speed, spindle

start, and feed rate must be specified, for cutting, before executing this code.

ex. G03X2.625Y3.I2.625J2.5312F20


G00-G99

These codes are not completely standardized

G00 - Rapid traverse positioning.

G01 - Linear tool motion at a specified feed rate.

G02 - Circular tool motion in a clockwise direction.

G03 - Circular tool motion in a counterclockwise direction.

G04 - A temporary dwell, or delay in tool motion.

G05 - A permanent hold, or stopping of tool motion. It is canceled by the machine

operator.

G08 - Smooth acceleration up to the specified feed rate while other machine

functions are occuring (before the tool contacts the workpiece).

G09 - An exact stop of one tool motion before the machine goes on to the next.

(Nonmodal.)

G17 - Selection of the X-Y plane (on machining centers).

G18 - Selection of the X-Z plane (on machining centers).

G19 - Selection of the Y-Z plane (on machining centers).

G20 - Inch data input (on foreign-made machines).

G21 - Metric data input (on foreign-made machines).

G22 - Activation of the stored axis travel limits, which are used to establish a

safety boundary.

G23 - Deactivation of the stored axis travel limits.

G27 - Return to the machine home position via a programmed intermediate point

(a point somewhere between the current location of the tool and the machine home

position). The machine's control will automatically calculate the distance to home

position once the tool has reached this intermediate location.

G28 - Return to the machine home position via a programmed intermediate point

(a point somewhere between the current location of the tool and the machine home

position). The machine's control will automatically cualculate the distance to home

position once the tool has reached this intermediate location.


G29 - Return to the workpiece or fixture from the machine home positon via the

intermediate point that was programmmed in the block containing G28. Any new or old

point on the workpiece of fixture can be programmed, but the tool will first travel to the

intermediate point before going there.

G32, G33 - Thread cutting with a constant lead. If multiple-pass single-point

threading is done, this command will synchronize the start of each pass at exactly the

same point every time so as to avoid the chance of double-threading the workpiece.

G34 - Thread cutting with an increasing lead.

G35 - Thread cutting with a decreasing lead.

G40 - Cancellation of any previously programmed tool radius compensation

(better known as cutter radius compensation, or CRC).

G41 - Application of cutter radius compensation to the left of the workpiece with

respect to the direction of tool travel. This feature allows the finished surface of the

workpiece to be the programmed cutter path, and the tool will automatically be offset to

the left of this path by a distance equal to its radius. On a machining center, G41 is used

in climb milling.

G42 - Application of cutter radius compensation to the right of the workpiece

with respect to the direction of tool travel. On a machining center, G42 is used in

conventional milling.

G43 - Activation of tool length compensation in the same direction of the offset

value (as it is stored in the control's memory). If the dimension stored in the offset

register has a negative value, the tool length compensation will be applied in the negative

axis direction. If the dimension stored in the offset register has a positive value, the tool

length compensation will be applied in the positive axis direction.

G44 - Activation of tool length compensation in the opposite direction of the

offset value (as it is stored in the control's memory). If the dimension stored in the offset

register has a negative value the tool length compensation will be applied in the positive

axis direction. If the dimension stored in the offset register has a positive value the tool

length compensation will be applied in the negative axis direction.


G50 - Establishment of the zero point (absolute zero) in reference to the current

tool positon. This command is commonly used on foreigh-made CNC lathes in place of

G92.

G53 - Indication that all positioning data is that block is in reference to the

machine home positon. It caused the control to temporarily ignore the floating zero

position. (Used in absolute programming.)

G54, G55, G56, G57 - Indication that all positioning data is in reference to the

floating zero position on a particular fixture in a machining operation. For example, G54

would cause all dimensions to refer to the floating zero on the first fixture, G55 would

cause all dimensions to refer to the floating zero on the second fixture, and so on. (Used

in absolute programming)

G59 - Repositioning of the floating zero. The new location is programmed

incrementally from the current zero positon.

G60 - An exact stop of one tool motion before the machine goes on to the next.

(Modal)

G63 - Cancellation of feed-rate override. Used on tapping and threading

operations (in inch-per-minute programmming) where the programmed feed rate must be

maintained in relation to the spindle speed.

G64 - Cancellation of G60. Allows a slight overlap of the different tool motions

so that a smooth blending of contoured surfaces will result. When G60 is used, a dwell

mark will be left by the tool at the intersection of motions.

G70 - Inch data input (on American-made machines).

G70 - Canned cycle for finish turning on a lathe (foreign-made).

G71 - Metric data input (on American-made machines).

G71 - Canned cycle for multiple-pass turning on a lathe (foreign-made).

G72 - Canned cycle for multiple-pass facing on a lathe (foreign-made).

G73 - Canned cycle for multiple-pass pattern repeat on a lathe (foreign-made).

G74 - Canned cycle for pecking in the Z axis on a lathe (foreign-made).

G75 - Canned cycle for pecking in the X axis on a lathe (foreign-made).

G76 - Canned cycle for multiple-pass single-point threading on a lathe (foreign-

made).


G80 - Cancellation of canned cycles on a machining center.

G81 - Canned cycle for basic drilling on a machining center. Causes automatic

feed in, and rapid out.

G82 - Canned cycle for drilling with a dwell on a machining center. Causes

automatic feed in, dwell at the bottom, and rapid out.

G83 - Canned cycle for peck drilling on a machining center. Causes feed in in

multiple pecks and rapid out.

G84 - Canned cycle for basic tapping on a machining center. Causes automatic

feed in, reversal of spindle rotation, and feed out.

G85 - Canned cycle for basic boring on a machining center. Causes automatic

feed in and feed out.

G86 - Canned cycle for alternate boring on a machining center. Causes automatic

feed in, stopping of spindle rotation, and rapid out.


feed in and stopping of spindle rotation. The machine operator then manually retracts the

tool from the hole.


feed in, dwell at the bottom, and stopping of spindle rotation. The machine operator then

manually retracts the tool from the hole.


feed in, dwell at the bottom, and feed out.

G90 - Absolute positioning. All positioning data will be in reference to the current

zero point (also called the absolute zero). (Modal)

G90 - Canned cycle for single-pass turing on a lathe (foreign-made).

G91 - Incremental positioning. All positioning date will be in reference to the

current tool location. (Modal)

G92 - Establishes the zero point (absolute zero) in reference to the current tool

position.

G92 - Canned cycle for single-pass threading on lathe (foreign-made).

G94 - Inch-per-minute programming. The programmed feed rate will be in inches

per minute. G


95 - Inch-per-revolution programming. The programmed feed rate will be in

inches per revolution of the spindle.

G96 - Constant-surface-speed programming. As the diameter turned on a lathe

becomes smaller, the spindle speed will increase to maintain the programmed surface

speed. Inversely, as the diameter turned on a lathe becomes larger, the spindle speed will

decrease.

G97 - Revolutions-per-minute programming. The spindle speed will be

maintained at the same RPM , no matter what diameter is being turned on the lathe.

G98 - Inch-per-minute programming. The programmed feed rate will be in inches

per minute (on foreign-made machines).

G99 - Indication that all positioning data in that block is in reference to the

machine home position. It causes the control to temporarily ignore the floating zero

position (G92). This command is similar to G53. (Used on some American-made

machines.)

G99 - Inch-per-revolution programming. The programmed feed rate will be in

inches per revolution of the spindle (on foreign-made machines).

Miscellaneous Functions

The M code is used for miscellaneous functions such as coolant on-off, spindle on-off

and direction, tape rewind, and program end. M codes range from M00 through M99. M

codes are assigned by the machine builder, but some standardization does exist.

Commonly used M codes

M02 - Program end

M03 - Start of spindle rotation clockwise

M04 - Start of spindle rotation counterclockwise

M07 - Start of mist coolant

M08 - Start of flood coolant


M00-M99

M00 - Program stop. All spindle rotation, tool motion, and coolant flow is off.

M01 - Optional program stop. All spindle rotation, tool motion, and coolant flow

is shut off only if the operator had already activated the "optional stop" switch on the

MCU.

M02 - Program stop and rewind. All spindle rotation, tool motion, and coolant

flow is shut off, and the control prepares to start reading the beginning of the program

again (the program rewind may not occur on some machines). All of the machine's

functions (preparatory, miscellaneous, etc. ) will reset to their default state (the condition

that the machine is in when it is first turned on).

M03 - Start of spindle rotation is a clockwise direction, looking out from the

spindle face.

M04 - Start of spindle rotation is a counterclockwise direction, looking out from

the spindle face.

M05 - Stopping of spindle rotation.

M06 - Change to the next tool in line. This command is used on machines with

sequential tool changers, where the tools are mounted on the turret or tool changer in the

order of their use.

M07 - Mist coolant turned on.

M08 - Flood coolant turned on.

M09 - Coolant turned off.

M10 - Activation of automatic clamping (of machine slides, workpiece fixture,

spindle, etc.)

M11 - Deactivation of automatic clamping (of machine slides, workpiece fixtures,

spindle, etc.)

M12 - Indexing the turret to point halfway between one tool station and the next.

On CNC lathes equipped with two turrets, this command causes one turret to allow tool

travel clearance for the other one.

M13 - Spindle rotation started in a clockwise direction and coolant turned on

(both at the same time).


M14 - Spindle rotation started in a "counterclockwise" direction and coolant

turned on (both at the same time).

M19 - Spindle rotation stopped at a predetermined (oriented) angular position.

M30 - Program stop and rewind. All spindle rotation, tool motion, and coolant

flow is shut off, and the control prepares to start reading the beginning of the program

again. All of the machine's functions (preparatory, miscellaneous, etc.) will reset to their

default state (the condition that the machine is in when it is first turned on). This code

word is similar to M02. It is used on machines where M02 does not have the program

rewind ability.

M31 - Interlock bypass. It temporarily deactivates a normally provided interlock

(restart a program automatically, stop a program on bar machine lathes when the end of

the bar is sensed. etc.).

M40, M41, M42, M43, M44, M45 - Gear range selection. For example, M40

might cause the machine to shift into a low gear range, M41 might cause the machine to

shift into a medium or high gear range, and so on.

M98 - Switch from main program to subroutine program.

M99 - Return from subroutine program to main program.

Special Cycles

Special Cycles or Canned Cycles are a preprogrammed sequences of repetitive tool

motion that are built into the control system for common operations such as drilling,

tapping, boring, and pocketing. Its purpose is to reduce the amount of program code that

would normally have to be written. Canned cycles are G codes that are options purchased

with a CNC, but some are standard equipment depending on the manufacturer.

Drilling cycle (G81, G82 or G83) are used to drill multiple holes without programming

each move separately. Using this cycle reduces the amount of code that would normally

have to be written.


Facing cycle (G77) is used to clean up rough stock material (normally on top of the part)

which can be located within a rectangular area. Using this cycle reduces the amount of

code that would normally have to be written.

Rectangular pocket cycle (G78) is used to clear out material which is located within a

rectangular area. Using this cycle reduces the amount of code that would normally have

to be written.

Circular pocket cycle (G79) is used to clear out material which is located within a

circular area. Using this cycle reduces the amount of code that would normally have to be

written.

Special Codes

Special codes are used to perform functions in the CNC's control and enhance the

programmers ability to write smart programs. Most of these codes are standard in today's

CNCs, others may be optional. The machine builder sets these codes but some

standardization does exist.

/ - Block Delete - A code used in a CNC program to allow the operator to ignore a

given block or blocks of code, depending on the setting of the Block delete switch on the

operators control panel.

EOB - End Of Block - A special character used to signify the end of one block.

Normally this character is the carriage return.

. - Period - A period before a block tells the control to execute system mode

changes during the search mode also.(ie. a line with G70,G90 will have a . in front .)

% - Rewind Stop

= - Execute (or Do) - When looping; or running macros; = means execute.(ie.

=N25/6 - run line number 25 6 times then continue)

E - Rewind Tape

$ - End of Macro - The $ specifies the end of a definition of a macro.

# - The begining of the definition of a macro will have the # sign followed by a

number. (ie. #1)


Part and Tool Change Position

The Part Change Position is a programmed area where the operator can easily remove the

finished part from it's holding device and replace with the blank stock. This is usually an

area clear of cutting tools, fixtures, etc...

The Tool Change position is a programmed or factory set position where the operator or a

robot arm changes the current cutting tool for the next tool needed.

Programming Considerations

Develop a programming style that will be used by all programmers at your

facility.

Proofread all programs for typographical errors before they are sent to the shop.

Keep all programs as simple as possible to perform the desired functions.

Be aware of modal and non-modal codes. Modal codes are commands that remain

in effect until they are cancelled by another code. This makes it possible for you to not

have to repeat them, line after line, for repetitive tasks; such as drilling, boring, etc. .

Choose feeds and speeds that will give you a balance between tool life and short

cycle times.

Use your own previous experience and the experiences of others for programming

feeds, speeds, and depth of cut. But do not guess.


Optimizing cycle time is accomplished after a program has begun producing

dimensionally acceptable parts.

A fully optimized cycle time can be thought of as one that produces the most

finished parts per day.

"Error on the side of caution". In CNC programming, it's a good idea to have

an extra degree of safety. Examples include longer dwell cycles, higher plunge distances

and clearance planes, slower feedrates and lighter depths of cut. Normally this practice

would be used on a new program. Later after the program is proofed, these safeties would

be optimized out for efficiency.

Computer Aided Manufacturing

Computer Aided Manufacturing involves the use of computer programs specifically

designed to create the geometry and tool paths needed for parts to be machined. These

tool paths can then be automatically processed into a program specific for the CNC

machine to be used.

Communications and Data Transfer

Punched Tape


A tape puncher produces holes in paper, mylar, or foil (punched tape) material in such a

manner so as to represent a particular set of data. The standard geometry for this type of

media is EIA RS-227.

A telewriter is a device used to type in CNC programs. As you type in the code, a punch

tape machine would be punching out the punch tape.

Floppy Diskette

Floppy Diskettes are used for the storage of data and to transfer data from one machine to

another. Sometimes floppies are used to transfer programs to CNC machines. Using

floppies to transfer data or for backup copies is sometimes called having a "sneakernet".

RS232

RS-232 is a set of standards specifying various electrical and mechanical characteristics

for interfaces (communications) between computers, terminals, and modems. The

traditional plug has 25 pins but some computers have a newer RS-232 plug that uses only

nine pins.

Some CNCs are connected, via RS-232, to dedicated computers for inputting program

data. These systems accept floppy disks and transfer the program data directly to a

selected CNC. Thus eliminating the need for punch tape or manual data input.


Networks are groups of computers that can communicate with one another and share

date, files, programs, and operations. Most CNC machines are attached to some type of

network. This may eliminate the need for punch tape, floppy disks and MDI. But it also

allows for the creation of the part program at the designer/programmer's CAD/CAM

workstation. Then the file can be electronically sent to the CNC for machining.

Manual Data Input

Manual Data Input is a function of the CNC machine's control that allows for the input of

program instructions directly into the machine's memory.


Machine Setup and Operation

Safety Rules

Eye protection MUST be worn at all times in the machine shop.

Be careful when handling tools and sharp edged workpieces to avoid getting cut.

Cutting tools should be securely fastened in the machine spindle to prevent any

movement during the cutting operation.

Keep loose clothing secured properly.

Use a brush to remove chips from a machine. Don't use your hands.

Avoid scuffling or horseplay.

Wear a short sleeved shirt or roll up long sleeves above the elbow.

Startup

Machine Startup procedures will depend on the particular machine being used. Usually

there is a main power switch or circuit breaker. Some machines also require air pressure

or hydraulics.


Home Position

Most CNCs have a Machine Home Position which allows the control and the machine to

have a preset zero position for all axes. After startup, the machine must be sent to this

location before work can begin. This position will later be changed to a more appropriate

location for machining a particular part.

Tool Length Offsets


The Tool Length Offset value is the distance from the tip of the tool with the spindle in

the home position, to the Z0 plane. TLOs must be set for each tool used in the current

job. They can be set using a height gage, reference tool, fixture location, or on the stock

to be machined. Once the values are determined, they are stored in the controller for use

during program operation.

A more efficient way to set TLOs is to measure from the spindle to each tool tip. This is

better method because the values need only be set once regardless of each different type

and size of part being manufactured. Of course, tool breakage or replacement requires a

reset of the individual TLO when using either method.

Setting up a Part Origin

Setting up a part origin on a CNC machine is basically the same as on a conventional

machine. It involves positioning the axes to a point where the blueprints or programmer

designate as the origin. Many ways are used to locate this position on the blank stock,

fixture or reference point, including: edge finders, wigglers, and magnifying glasses.


Program Loading

Program loading is different for each machine. Some machines have built in tape readers

to input the program into the CNC's memory. Other machines may have internal or

external floppy devices or be connected to networks.

Machining Videos

Face Milling Profile Milling


Center Drilling Drilling

Tool Change Procedure

Some machines require the operator to change tools manually between machining

operations. After a machining operation is complete, the program will move the axes to

the tool change position and display the next tool needed. The operator will remove the

current tool and replace it with the next tool. Most newer machines offer or come

standard with Automated Tool Changers or "Turrets."


Part Setup Considerations

Setup of the raw stock in the holding device requires tooling, such as parallels or clamps

to position the blank stock accurately. Care must always be taken to position the stock as

level and firmly held as possible to produce a rigid setup which will reduce chatter,

increase operator safety, and produce higher quality parts. Acuracy of the finished part

will rely partially on the accuracy of the setup, including parallelism of the vise, fixtures

or jigs, and origin setting and TLO procedures.

Proper procedures must also be followed throughout the production run. Machine

maintenance, coolant and oil levels and the sharpness of tools must be continually

monitored.

Lecture Notes for Subject: CAD/CAM/CIM (ME 804) Given By: … · 2018-10-23 · Visit: 1 Lecture...

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Transcript of Lecture Notes for Subject: CAD/CAM/CIM (ME 804) Given By: … · 2018-10-23 · Visit: 1 Lecture...