18 computer controlled manfctg

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Computer ControlledManufacturing Processes

CHAPTER 18


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I ssues to address.I ntroduction to computer controlledmanufacturing systems.

Automation Types.Numerical Control and ComputerNumerical Control concepts.

Classification of NC systems.

Robotics


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Wh en components can be

manufactured manually w h ywe need computers in Mfg?


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Need for computers in Mfg.

(a)

(b)

(c)

I n w h ich case it is easy to move tool /table on conventional mac h ine?


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Need for Computers in Mfg.How do you Manufacture t h is part?


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With conventional machines.. .


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With Automated machines.


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Need for Computers in Mfg.

I ncreased productivity.

Reduced cost of labor anddependence on labor s h ortages.I ncreased safety or reduced risk of h umans.I mproved quality.


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Need for Computers in Mfg.Reduced manufacturing time.

Reduced in-process inventory.Reduced dependence on

operator skills etc.


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Wh ere else computers can beused in Manufacturing?

Drawing.

Design.I nspection.

Supporting activities of Mfg. likeI nventory control, Sc h eduling etc.


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AutomationAutomation can generally be defined asth e process of following a predetermined

sequence of operations wit h little or noh uman intervention, using specializedequipment and devices t h at perform andcontrol t h e manufacturing process.


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Mec h anization and Automation

M echanization means somet h ing is doneor operated by mac h inery and not byh and.

Automation means a system in w h ichmany or all of t h e processes in t h e

production, movement, and inspection of parts and material are performed undercontrol by self-operating devices called

controllers .


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Types of AutomationF ixed Automation.

Programmable Automation.F lexible Automation.


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Machine control unit

Program

Machine tool

Basic components of NC System


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How NC mac h ine tools work?S tep 1 F eed Numerical Data into t h e NCsystemS tep 2 MCU (Mac h ine Control Unit)reads t h e data, decode it, and c h anges itinto t h e electrical signals and transfer it toth e mac h ine toolS tep 3 Transducers on t h e mac h ine toolconverts t h ese electrical signals into t h eactual movements of t h e mac h ine tool


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How automated mach

ine tools work?


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Wh at does t h e following

information indicate?X+100, Y+50, S+900


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Advantages of NC Systems

Complex mac h ining operationsAccuracyI ncreased productivityF lexibilityGreater operator efficiency


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Advantages of NC SystemsGreater operator safety

Greater mac h ine tool safetyLess inspection required

Need of h

igh

ly skilled/experiencedoperator is avoided


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Disadvantages of NC SystemsRelatively h igh initial investment.

Hig h ly skilled and trained partprogrammer is required.

More complicated maintenance.

Redundancy of labor?


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CONVENT I ONAL VSNC MACH I NES


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Mac h ine tool

operator

I nput MCU Mac h ine tooloperator

Conventional Mac h ining System

Simplified Numerical Control System



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Cost

Skill of operator required.Production rate.

Special tooling.Downtime.Maintenance.



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COORDINATE SYSTEMS

X axis

Z axis

Y ax

is Workpiece

Coordinate system for a prism.


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COORD I NATE SYSTEMS ON A

MACHINE


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or or Program zero point

Alternate locations of program zero point

PROGRAM ZERO POINT


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Program zeropoint X

+50

Z

Y +60

X

Z +3 0

Y

Target pointP

Define t h e coordinate system for a target point P

X + 50, Y+60, Z+30

Defining target point


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Classification of NC SystemsAccording to t h e type of motion control

Point-to-Point (PTP) motion controlContinuous or contouring motion control

According to t h e programming methodsI ncrementalClosed

According to t h e type of control systemsOpen loopClosed loop


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PTP & CONTOUR ING SYSTEM

PTPCONTOUR I NG


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Stepper motor Gear box

Table

InputDesiredosition

Lead Screw

DACDesiredposition Comparator

_

Input+

Table

Feedback Signal

Gear box

Lead Screw Sensor

DCServomoter

Open loop control system

Closed loop control system

CLASS I F I CAT I ON BASED ONCONTROL SYSTEM


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ROBOTICS


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What is a

Robot?

An I ndustrial robot is a general-purpose,reprogrammable mac h ine t h at possessescertain ant h ropomorp h ic, or h umanlike, c h aracteristics. T h e most typicalh uman like c h aracteristics of presentday robots is t h eir movable arm, capableof moving in a t h ree dimensional space.


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Structure of a R obot

An I ndustrial robot is a manipulatorconsisting of several rigid links

connected in series by revolute orprismatic joints. One end of t h e c h ain isattac h ed to a supporting base, w h ile t h eot h er end is free and equipped wit h atool to perform specified tasks or wit h a

gripper to manipulate objects.


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Wrist

JointEnd-effector

ink

A rm

B ase

Structure of industrial robot


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Why to use

Robots ?

I ncreased output compared to

h uman workers.I mproved q uality output.

F ewer rejects.W orking in h ostile environment.


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Why to use

Robots ?

Good profitability in several

applications.Less p h ysical fatigue for operator.

No labor problems.


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Applications of Robots inManufacturing

Mac h ine Loading and Unloadingor Material HandlingHeat Treatment

F orging


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Applications of Robots inManufacturing

Press W ork

W eldingPainting and Coating

Assembly and I nspection etc.


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Robotics scenario in I ndiaI s it true t h at robotics is irrelevantin t h e I ndian context?I f Robots can be used w h ere it canbe used?Interesting statistics for you:I n 1992 Robos in I ndia 100

Japan it was 3,50,000


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Advantages of ComputerControlled Mac h ines

More safety to h uman workers.

Possibility to produce highq uality products at lowest price .Overall increase in productivity .Hig h er q uality .

More leisure time to workers


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Limitations of Computer

Controlled Mac h inesT h ese tec h nologies increase

unemployment problems.I t declines t h e purchasing power of customer.Automation can even disturbth e economy of country as awh ole

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18 computer controlled manfctg