manufacturing processes - fitstaff.fit.ac.cy/eng.os/amem201_lecture7.pdf6 7/13/2017 amem 201 -...

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7/13/2017 AMEM 201 - Manufacturing Processes 1

MANUFACTURINGPROCESSES

- AMEM 201 –

Lecture 7: CNC MACHINE TOOLS

7/13/2017 AMEM 201 - Manufacturing Processes 2

CNC MACHINE TOOLSTERMINOLOGY

NC – Numerical Control

CNC – Computer Numerical Control

CAD – Computer Aided Design

CAM – Computer Aided Manufacturing

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7/13/2017 3AMEM 201 - Manufacturing Processes

Numerical Control - Definition

A form of programmable automation in which the mechanical actions of a machine are controlled by a program containing coded alphanumeric data


NC OPERATING PRINCIPLENC operating principle is to control the motion of

the tool relative to the workpart

- In an ordered sequence of motions- Following a predetermined path- Respecting the required dimensions- At a specific feed and spindle speed rate

This is achieved through a group of alphanumeric instructions (coded program)

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5CNC MACHINE

NUMERICAL CONTROLLER

NUMERICAL DATA (CODED PROGRAM)

MANUFACTURINGOPERATOR

PROCESSED PART

Drive Control

PROCESSED PART

PROGRAMMING & OPERATION OF A CNC MACHINE


CNC Machine Tools - Types NC widely used for machining operations

such as turning, drilling, and milling

NC has motivated development of machiningcenters, which change their own cutting tools to perform a variety of machining operations

Other NC machine tools: Grinding machines, Sheet metal pressworking

machines, Bending machines

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CNC Machine Tools

CNC Machining center


CNC Machine Tools

Turning center

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CNC Machine Tools Drilling Tapping center


Advantages of CNC Machines Increased machining accuracy Do production jobs that are impossible without

CNC Greater manufacturing flexibility Reduced human error Reduced actual machining time Less setup time Make production jobs easier Increased production

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Limitations of CNC Machineso High initial investment

Machine tools cost $30,000 - $1,500,000

o High maintenance requirementsMaintenance personnel must have both

mechanical and electronics expertise

o Not cost-effective for low-level production on simple parts As geometric complexity or volume

increases CNC becomes more economical


CNC – Application fields

o Aerospace o Machinery o Fabrication o Automotive o Instrumentation o Mold making

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BASIC CNC CONCEPTS

2. REFERENCE POINTS- MACHINE ZERO POINT- WORKPIECE ZERO POINT

1. AXES AND DIRECTIONS OF MOTIONS

3. ABSOLUTE & INCREMENTAL COORDINATES

1. Directions of motion on a 3-axis milling machine

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Positive Directions of axes for a milling machine

Axes of motion for a milling machine

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NC Coordinate SystemConsists of three linear axes (X, Y, Z) of Cartesian coordinate system, plus three rotational axes (a, b, c)

Rotational axes are used to orient workpart or workhead to access different surfaces for machining


Motor and leadscrew arrangement in a NC positioning system.

NC Positioning System

Converts the coordinates specified in the coded program into relative positions and velocities between tool and workpart

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2. Reference Points of the milling machine

Machine Zero Point

Machine Zero Point is a fix position set by Machine Tool Builder. It is the reference of the Machine

2. Reference Points of the milling machine

Workpiece Zero Point

Workpiece Zero Point can be anywhere and is set by the user before the machining process start.

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Setting Workpiece Zero Point

Setting Workpiece Zero Point

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Workpiece Zero Point can be compared to the Origin of Rectangular Coordinate System


3. ABSOLUTE VS. INCREMENTAL POSITIONING

Absolute Mode Tool locations are always defined with

respect to origin of axis system

Incremental Mode Next tool location is defined relative to

present location

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The tool is presently at point (100,30) and is to be moved to point (40,70). In absolute positioning, the move is specified by X = 40, Y = 70.In incremental positioning, the move is specified by X = - 60, Y = 40.

3. Absolute vs. Incremental PositioningEXAMPLE

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3. Absolute vs. Incremental Positioning

EXERCISE

MOTION ABSOLUTE INCREMENTAL

0 → 1 Χ30 Υ20 Χ30 Υ20

1 → 2 Χ50 Υ100 Χ20 Υ80

2 → 3 Χ70 Υ60 Χ20 Υ-40

3 → 4 Χ90 Υ60 Χ20 Υ0

4 → 5 Χ100 Υ80 Χ10 Υ20

5 → 6 Χ140 Υ120 Χ40 Υ40

6 → 7 Χ140 Υ20 Χ0 Υ-100

7 → 8 Χ80 Υ20 Χ-60 Υ0

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CNC Programming Techniques

1. Manual programming

2. CAD/CAM programming


1. Manual Programming

Uses basic numerical data and special alphanumeric codes to define the steps in the process

Suited to simple machining jobs such as simple profile cuttings and drilling

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CNC or Part Program Example command for linear motion:

N10 G90 G01 X70 Y85 F300 S2000where,

N10 - A sequence number;G90 - Abslolute ModeG01 - Linear motionX and Y - Coordinate positions (mm) F - Feed rate (300 mm/min)S - spindle speed (2000 rev/min)

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CNC or Part Program Complete part program consists of a sequence

of commands

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Basic Codes for CNC Programming

CODE MEANING

G Gxx – G code

M Mxx – M code

N Command sequence number

F Feedrate (mm/min)

S Spindle speed (RPM)

T Tool number

X, Y, Z Coordinates (mm)

R Radius (mm)

Commonly used G and M codes

G CODE MEANING M CODE MEANING

G90 Absolute Mode M03 Spindle ON - CW

G91 Incremental Mode M06 T… Tool Change

G20 Units in inches M08 Coolant ON

G21 Units in mm M09 Coolant OFF

G00 Linear Motion - Rapid M30 Program End

G01 Linear Motion - Feedrate

G02 Circular Motion CW

G03 Circular Motion CCW

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APPLICATION EXAMPLE - 1 ABSOLUTETOOL T1 S (rpm) F

(mm/min)Depth

End mill Ø 4 2000 300 4mm

N40 G90 G00 X25 Y25 Z2

N10 G21N20 M06 T1

N30 M03 S2000

PROGRAM 1

N50 G01 Z-4 F300N60 G01 X25 Y75

N70 G01 X65 Y125

N80 G01 X125 Y125

N90 G01 X125 Y65N100 G03 X85 Y25 R40

N110 G01 X25 Y25

N120 G00 Z30

N130 M30

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2

3 4

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APPLICATION EXAMPLE - 1 INCREMENTALTOOL T1 S (rpm) F

(mm/min)Depth


N40 G90 G00 X25 Y25 Z2

N10 G21N20 M06 T1

N30 M03 S2000

PROGRAM 1

N50 G01 Z-4 F300N60 G91 G01 X0 Y50

N70 G01 X40 Y50

N80 G01 X60 Y0

N90 G01 X0 Y-60N100 G03 X-40 Y-40 R40

N110 G01 X-60 Y0

N120 G00 Z30

N130 M30

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3 4

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APPLICATION EXAMPLE - 2 ABSOLUTETOOL T1 S (rpm) F

(mm/min)Depth


N40 G90 G00 X25 Y25 Z2

N10 G21N20 M06 T1

N30 M03 S2000

PROGRAM 2

N50 G01 Z-4 F300N60 G01 X25 Y55

N70 G03 X25 Y95 R20

N80 G01 X25 Y125

N90 G01 X45 Y125N100 G03 X105 Y125 R30

N110 G01 X125 Y125

N120 G01 X125 Y95

N130 G03 X125 Y55 R20

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TOOL T1 S (rpm) F (mm/min)

Depth

End mill Ø 4 2000 300 4mmN150 G01 X105 Y25 N160 G03 X45 Y25 R30

N170 G01 X25 Y25

N140 G01 X125 Y25

APPLICATION EXAMPLE - 2 ABSOLUTE

N180 G00 Z30

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APPLICATION EXAMPLE - 2 INCREMENTALTOOL T1 S (rpm) F

(mm/min)Depth


N40 G90 G00 X25 Y25 Z2

N10 G21N20 M06 T1

N30 M03 S2000

PROGRAM 2

N50 G01 Z-4 F300N60 G91 G01 X0 Y30

N70 G03 X0 Y40 R20

N80 G01 X0 Y30

N90 G01 X20 Y0N100 G03 X60 Y0 R30

N110 G01 X20 Y0

N120 G01 X0 Y-30

N130 G03 X0 Y-40 R20

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TOOL T1 S (rpm) F (mm/min)

Depth

End mill Ø 4 2000 300 4mmN150 G01 X-20 Y0N160 G03 X-60 Y0 R30

N170 G01 X-20 Y0

N140 G01 X0 Y-30

APPLICATION EXAMPLE - 2 INCREMENTAL

N180 G00 Z30

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2. CAD/CAM PROGRAMMING


CAD/CAM

– CAD systems are used to define part geometries

– CAM systems are used to create cutter paths that can be used by the machine tool.

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The structure of a CAD/CAM System

Creates part geometry

CNC FILE

CAM

CAD

-Machining method-Shape to machine-Order of operations-Cutting tools-Cutting path & conditions

CAD FILE

manufacturing processes - fitstaff.fit.ac.cy/eng.os/amem201_lecture7.pdf6 7/13/2017 amem 201 -...

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