manufacturing processes - fitstaff.fit.ac.cy/eng.os/microsoft powerpoint - lecture11.pdf ·...

1

5/2/2009 AMEM 201 - Manufacturing Processes 1

MANUFACTURINGMANUFACTURINGPROCESSESPROCESSES

-- AMEM 201 AMEM 201 ––

Lecture 11:Lecture 11: COMPUTER INTEGRATED MANUFACTURINGCOMPUTER INTEGRATED MANUFACTURING

5/2/2009 AMEM 201 - Manufacturing Processes 2

COMPUTER INTEGRATED COMPUTER INTEGRATED MANUFACTURINGMANUFACTURING

1.1. NUMERICAL CONTROLNUMERICAL CONTROL

2.2. CAD/CAM SYSTEMSCAD/CAM SYSTEMS

2

5/2/2009 3AMEM 201 - Manufacturing Processes

Numerical ControlNumerical Controlnn A form of programmable automation in which A form of programmable automation in which

the mechanical actions of a piece of equipment the mechanical actions of a piece of equipment are controlled by a program containing coded are controlled by a program containing coded alphanumeric data alphanumeric data

nn NC operating principle is to control the motion NC operating principle is to control the motion of the of the workheadworkhead (tool) relative to the workpart (tool) relative to the workpart and to control the sequence of motionsand to control the sequence of motions


What Is Numerical ControlWhat Is Numerical Control??An automated manufacturing process in

which a machine tool is controlled; – In an ordered sequence– Along a predetermined path– To require dimensions– At a specific feed and speed rate– Done through a group of alphanumeric

instructions

3


CNC or Part ProgramCNC or Part Programnn Example command for linear motion:Example command for linear motion:

N10 G01 X70 Y85.5 F175 S500N10 G01 X70 Y85.5 F175 S500 wherewhere

NN10 = a sequence number;10 = a sequence number;G01 Linear motionG01 Linear motionXX and Y= and Y= xx and and yy coordinate positions (mm) coordinate positions (mm) F = feed rate (175 mm/min)F = feed rate (175 mm/min)S = spindle speed (500 rev/min) S = spindle speed (500 rev/min)

nn Complete part program consists of a sequence Complete part program consists of a sequence of commands of commands


MACHINE UNIT

NUMERICAL CONTROLLER

NUMERICAL DATA

(NC CODE)

MANUFACTURINGOPERATOR

PROCESSED PART

Drive Control

4


ObjectivesObjectives

1. Increased production 2. Reduced labor costs 3. Make production more economical 4. Make production jobs easier 5. Do production jobs that are impossible

without numeric control 6. Increased accuracy on duplicate parts


Types of Numerical ControlTypes of Numerical Control

nn Conventional Numerical Control (NC)Conventional Numerical Control (NC)nn Direct Numerical Control (DNC)Direct Numerical Control (DNC)nn Computer Numerical Control (CNC)Computer Numerical Control (CNC)

5


Conventional Conventional Numerical Numerical Control (NC)Control (NC)

Data is sent to the machine tool by means of punch cards or tapes. The reader at the machine performs no calculations or interpolations.


Direct Numeric Control (DNC)Direct Numeric Control (DNC)

Is a method where a single computer controls many numerical control machinetools. These machine tools may or may not be of a similar nature

6


Computer Numerical Control Computer Numerical Control (CNC)(CNC)

The idea of computer numerical control is to position a computer right at the machine tool. Most, if not all machine tools that are numericaly controlled are CNC machine tools.


Basic Elements of a CNC SystemBasic Elements of a CNC System

COMPUTER

MACHINETOOL

MACHINE CONTROL UNIT

7


NC Coordinate SystemNC Coordinate System

nn Consists of three linear axes (X, Y, Z) of Cartesian Consists of three linear axes (X, Y, Z) of Cartesian coordinate system, plus three rotational axes (coordinate system, plus three rotational axes (aa, , bb, , cc))

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

nn Most NC systems do not require all six axesMost NC systems do not require all six axes


Coordinate systems used in numerical control:(a) for flat and prismatic work.

NC Coordinate Systems

8


Coordinate systems used in numerical control:(b) for rotational work.

NC Coordinate Systems


Two Types of PositioningTwo Types of Positioning

nn Absolute positioning Absolute positioning nn Locations are always defined with respect to origin Locations are always defined with respect to origin

of axis system of axis system

nn Incremental positioning Incremental positioning nn Next location is defined relative to present locationNext location is defined relative to present location

9


The workhead is presently at point (2,3) and is to be moved to point (6,8). In absolute positioning, the move is specified by x = 6, y = 8.In incremental positioning, the move is specified by x = 4, y = 5.

Absolute vs. Incremental Positioning


Motor and leadscrew arrangement in a NC positioning system.

NC Positioning System

Converts the coordinates specified in the NC part Converts the coordinates specified in the NC part program into relative positions and velocities between tool program into relative positions and velocities between tool and and workpartworkpart

10


AdvantagesAdvantages

o Improved accuracyo Reduced human erroro Greater manufacturing

flexibility

o Reduces actual machining time

o Less setup time o Simpler fixtures


LimitationsLimitations

o High initial investmentMachine 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

11


Industries Most Affected by Industries Most Affected by Numerical ControlNumerical Control

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


Machine Tool ApplicationsMachine Tool Applicationsnn NC widely used for machining operations such as NC widely used for machining operations such as

turning, drilling, and millingturning, drilling, and milling

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

nn Other NC machine tools: Other NC machine tools: nn Grinding machines, Sheet metal pressworking Grinding machines, Sheet metal pressworking

machines, Bending machines machines, Bending machines

12


Numerically Controlled Machine ToolsNumerically Controlled Machine ToolsFunctionally the same as a conventional machine tool. The difference is in the way in which the various machine functions and slide movements are controlled.The functions and motions such as;

n turning the spindle on and offn setting cutting speedsn setting feed raten turning coolant on and offn moving tool with respect to work part

are performed by Machine Control Unit (MCU) in NC machine tools.


Computer Numerical Control (CNC)Computer Numerical Control (CNC)

13


NC Horizontal Machining CenterNC Horizontal Machining Center


NC Part Programming NC Part Programming TechniquesTechniques

1.1. Manual part programmingManual part programming2.2. CAD/CAMCAD/CAM-- assisted part programmingassisted part programming

nn Common features: Common features: nn Points, lines, and surfaces of workpart must be Points, lines, and surfaces of workpart must be

defined relative to NC axis system defined relative to NC axis system nn Movement of cutting tool must be defined Movement of cutting tool must be defined

relative to these part featuresrelative to these part features

14


Manual Part ProgrammingManual Part Programming

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

nn Suited to simple machining jobs such as drilling Suited to simple machining jobs such as drilling operations and simple profile cuttingsoperations and simple profile cuttings


CAD/CAMCAD/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.

15


CAD/CAMCAD/CAM

nn With CAD/CAM, programmer receives visual With CAD/CAM, programmer receives visual verification as each statement is enteredverification as each statement is enterednn Errors can be corrected immediately rather than Errors can be corrected immediately rather than

after entire program has been written after entire program has been written nn If part design prepared on CAD, then CAD If part design prepared on CAD, then CAD

model can be used for part programming, model can be used for part programming, making geometric definition unnecessarymaking geometric definition unnecessary

manufacturing processes - fitstaff.fit.ac.cy/eng.os/microsoft powerpoint - lecture11.pdf ·...

Documents