class 2 - slides int cnc programm

7/24/2019 Class 2 - Slides Int CNC Programm

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Introduction to CNCIntroduction to CNC

ProgrammingProgramming

Class 2Class 2

Bob LeMaster, Ph.D.Bob LeMaster, Ph.D.

College of EngineeringCollege of Engineering

University of Tennessee at MartinUniversity of Tennessee at Martin


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Operational Features of CNCOperational Features of CNC

MachineMachine

Degarmo, Figure 29-10.

A CNC control system

includes a velocity loop

within an axis drive system

and a position loop external

to the axis drive system.


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Primary Machine ControlPrimary Machine Control

ElementsElements

Parker, Fig. 5.1


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Position Feedback OptionsPosition Feedback Options

Potentiometers Encoders

Linear RotaryLinear Rotary

ResolversResolvers


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What are Potentiometers?What are Potentiometers?

Material with

constantresistance per

unit length

propertiesWiper

V

Vo

LV

V!

o

=L

!

Position can becomputed from

voltage ratios.


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PotentiometersPotentiometers(Examples)(Examples)

www.betatronix.com


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What are Encoders?What are Encoders?A device used to convert linear position

information into an electrical output signal.

Encoder

Physics

Encoder

Physics

Magnetic

(LVDT)

Magnetic

(LVDT)

OpticalOptical ContactingContacting

CapacitiveCapacitive


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How Does a Rotary OpticalHow Does a Rotary Optical

Encoder Work?Encoder Work?

Bateson, Fig. 7.12

Outer track is used to

determine position.

Middle track is used

to measure direction

of rotation.

Inner track is usedto indicate a

complete revolution.

Integrated counter

circuits are used to

count leading or

falling edges of

pulses.


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Incremental EncodersIncremental EncodersIncremental Encoder - Produces equally spaced

pulses from one or more concentric tracks on the

code disk. Position is determined by counting

pulses

Compliments of BMC Buckbee-Mears St. Paul

Incremental Encodermust be calibrated.

Power loss will lead to

loss of position

information unlessbackup power source is

used.


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Absolute EncodersAbsolute Encoders

Compliments of BMC Buckbee-Mears St. Paul

Absolute Encoder produces a binary number

that uniquely identifies each position on the code

disk.

Absolute encoders

do not have to be

recalibrated after apower loss.

Absolute encoders

are more expensivethan incremental

encoders.


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Gray Binary CodeGray Binary Code

Bateson, Fig. 7-15


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How Does a Linear OpticalHow Does a Linear Optical

Encoder Work?Encoder Work?

www.anilam.comPrecision Glass Scale Encoder

Linear instead of

rotary scale.

Glass is used

because of low

sensitivity totemperature changes.


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MTD BridgeportMTD Bridgeport

Acu-lite Glass Scale Encoder

www.theproductfinder.com

in/yd0002.0

or

mm5

Typical Acu-lite

Encoder Accuracy


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Industrial ApplicationsIndustrial Applications

Rotary Encoders are widely used with robotics.

Linear encoders are widely used with machine tools.


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What areWhat are ResolversResolvers??

A resolver is a rotary transformer that produces an

output signal that is a function of the rotor position.

Bateson, Fig. 7.10


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Servomotor withServomotor with ResolverResolver

Parker, Fig. 1-44


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MachineMachine








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Velocity FeedbackVelocity Feedback

TachometersElectrical output is

proportional to rate ofangular rotation.

Encoders,

Resolvers,

Potentiometers

Number of pulses per time is

proportional to rate change of

position.


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Rotary Encoder VelocityRotary Encoder Velocity(Example)(Example)

cNT

60CS =

secondsinterval,mecounter tiT

TintervaltimeduringcounttotalC

revolutionshaftperpulsesofnumberN

rpmspeed,shaftS

c

c

=

=

=

=


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MachineMachine








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CNC Programming MethodsCNC Programming Methods

ManualComputer AidedManufacturing

(CAM)

Main Control UnitMain Control Unit


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Main Controller UserMain Controller User

InterfacesInterfaces


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Types of CNC ProgrammingTypes of CNC ProgrammingLanguagesLanguages

Standard Proprietary(Conversational)

ISO 6983

EIA RS274

Respond to prompts

Typically proprietary

MTD Big Machine MTD Small Machine

Command List


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Who and what is EIA?Who and what is EIA?

www.eia.org/eng/published.htm

Electronic Industries Association

U.S. Manufacturers ofelectronic equipment.


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Who and what is ISO?Who and what is ISO?

www.iso.ch

World wide

standardsorganization

ISO means

one


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ISO 6983 and EIA RS274ISO 6983 and EIA RS274

Standards are very similarEIA in most cases will adopt an ISO

standard with only minor changes

and issue the standard under an EIA

number.CAD/CAM programs support these

standards


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Example of ISO 6983 andExample of ISO 6983 and

EIA RS274 Standard CodeEIA RS274 Standard Code

Nanfara, pg 35

Often referred to as M-code or G-code


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Major Manufacturers of ISOMajor Manufacturers of ISOand EIA Main Controllersand EIA Main Controllers

Fanuc General Electric

Bendix

Cincinnati Milicron

Giddings and Lewis


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Steps in the CNC ProcessSteps in the CNC Process(Manual Programming)(Manual Programming)

1. Review part drawing

2. Decide which machine will produce the

part3. Choose the tooling required

4. Decide on the machining sequence

5. Do math calculations to find part

coordinates6. Calculate the spindle speeds and feedrates

required for the tooling and part material

7. Write the CNC program

8. Prepare setup sheets and tool lists9. Verify the program using a CNC simulator

or the actual machine

10. Edit the program if necessary

11. Run the program and produce the part Nanfara, pg 11.


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Steps in the CNC ProcessSteps in the CNC Process(CAM)(CAM)

1. Develop the three-dimensional geometric

model of the part using CAD

2. Decide which machining operations arerequired to produce the part

3. Choose the tooling to be used

4. Run a CAM software program to generate

the CNC part program, including the setupsheets and list of tools

5. Verify the program on a machine simulator

6. Download thee part program(s) to the

appropriate machine(s)

7. Verify the program(s) on the actual

machine(s) and edit if necessary

8. Run the program(s) and produce the part Nanfara, pg. 11.


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What is a 3What is a 3--D CAD model?D CAD model?

A 3-D cad model is a computer

representation of an actual part.

The computer representation

contains all of the physical

information about the part(material, dimensions, etc.)

The mathematical descriptions

of the models surfaces can beused to create CNC code.


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Integrated Design andIntegrated Design and

ManufacturingManufacturingA good designer must know

how a part will be produced andwhat tooling will be used to

make it.

This part is made using sand casting

technology.

The patterns are machined using a

three-axis CNC mill.Finish machining is done using a

three-axis CNC mill.


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AssignmentAssignment

Review the material from the first two

classes.

There will be an exam at the beginning ofthe next class.


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What will we do next class?What will we do next class?

We will start learning how to program amill using the ISO and EIA standard

commands.

Bring a calculator if you have one.

class 2 - slides int cnc programm

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