modelling and fabrication of geneva mechanism

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MODELLING AND FABRICATION OF GENEVA WHEEL MECHANISM

PRESENT BY

VIGNESHWARAN V B.E

OBJECTIVE

• To Fabricate And Assemble A Working Model Of An Existing

Geneva Wheel Mechanism Model.

• To Design The Geneva Mechanism Model Using Unigraphics-

Nx Cad 9.0

• To Study The Conventional Machines And Cnc Machining Centres.

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METHODOLOGY

GENERATE GENEVA MECHANISM IDEA(AIM)

3D MODELING OF GENEVA MECHANISM

MATERIAL SELECTION

PROCESS PLANING OF GENEVA MECHANISM

ADVANCED MACHINING PROCESS USING CNC PROGRAMMING

FABRICATION OF PARTS

ASSEMBLY

WORKING CONDITION (ACHIEVE THE GOAL)

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INTRODUCTION

• The Geneva mechanism translates a continuous rotation into an intermittent rotary motion.

• The rotating drive wheel has a pin that reaches into a slot of the driven wheel.

• The drive wheel also has a raised circular blocking disc that locks the driven wheel in position between steps

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MODELLING OF GENEVA WHEEL

COMPUTER-AIDED DRAFTING (CAD):

•It is the use of computer systems to assist in the creation,

modification, analysis, or optimization of a design

• To Increase the Productivity Of the Designer

•Improve the Quality Of Design

•Improve Communications Through Documentation

• To Create A Database For Manufacturing

•To Generate the 3-d Model By Using Nx Unigraphics Software.

•Model is a Representation of an object, a system, or an idea in

some form other than that of the entity itself

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`


TWO DIMENSIONAL MODEL OF ROTATOR TWO DIMENSIONAL MODEL OF GENEVA WHEEL


7TWO DIMENSIONAL MODEL OF BASE PLATE

3-D MODELLING OF GENEVA WHEEL

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MATERIAL SELECTION

RAW MATERIAL:

•Rotator circle plate - Aluminium

•Geneva wheel - Aluminium

•Rectangular Base plate - Aluminium

•Bolt (2 nos) - Galvanized iron coating

•Nut(4nos) - Galvanized iron coating

•Bushes (4nos) - Plastic

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MATERIAL SPECIFICATION

S.NO NAME OF THE PART LENGTH(mm)

BREADTH(mm)

THICKNESS(mm)

DIAMETER(mm)

1 Rectangular base plate 270 200 12

2 Rotator circle plate 25 150

3 Geneva wheel Cut From rectangular plate

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PRE MACHINING PROCESS

HACKSAW PROCESS:

A power hacksaw (or electric hacksaw) is a type of

hacksaw that is powered either by its own electric motor

or connected to a stationary engine.

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FILING PROCESS:

Filing helps achieve work piece function by

removing some excess material and deburring the

surface.

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NAME OF THE PART DIMENSION BEFORE FILING AFTER FILING

Rectangular base plate Length 270 mm 268mm

Thickness 12mm 11.5 mm

Breadth 200mm 196 mm

Square plate Length 116mm 115.5mm

Thickness 12mm 11.5 mm

Breadth 116mm 115.5mm


FACING PROCESS:

Machine: Lathe (three jaw chuck)

Workpiece: Geneva Rotator

Cutting Tool: High Speed Steel

Facing is the process of removing metal from the end of a workpiece to produce a flat surface

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WORKPIECE HOLDING ALLEN NUT BOLT

SUPPORT

NAME OF

THE PART

DIMENSI

ON

BEFORE

FACING

AFTER

FACING

Rotator

circular billet

Length 25mm 20mm


TURNING PROCESS:

Machine: Lathe (three jaw chuck)

Workpiece: Geneva Rotator

Cutting Tool: High Speed Steel

Turning is used to reduce the diameter of the workpiece

usually to a specified dimension and to produce a smooth

finish on the metal

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NAME OF THE

PART

DIMENSION BEFORE

TURNING

AFTER

TURNING

Rotator circular

billet

diameter 150 mm 140 mm


MILLING PROCESS:

Machine: Vertical milling machine

Workpiece: Geneva Rotator,wheel,baseplate

Cutter: Facemill cutter

Milling is a cutting process that uses a milling cutter to

remove material from the surface of a workpiece.

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NAME OF THE

PARTDIMENSION

BEFORE

MILLLING

(in mm)

AFTER

MILLING

(in mm)

Geneva wheel

Length 115.5 115

Breadth 115.5 115

Thickness 11.5 10

Rectangular base

plate

Length 268 266

Breadth 196 191

Thickness 11.5 10

MACHINING PROCESS

CNC MILLING PROCESS:

•Computer Numerical Control (CNC) is one

in which the functions and motions of a machine

tool are controlled by means of a prepared

program containing coded alphanumeric data.

•CNC can control the motions of the work

piece or tool, the input parameters such as feed

depth of cut, speed, and the functions such as

spindle on/off, coolant on/off.

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CNC MILLING PROCESS:

PROGRAM STRUCTURE:

• G-Codes

• M-codes

• Absolute coordinate system

• Incremental system

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CNC MILLING PROCESS

NAME OF

THE PARTDIMENSION

BEFORE

MILLLING

(in mm)

AFTER

MILLING

(in mm)

Geneva

wheel

Length 115 113.1

Breadth 115 113.2

Thickness 10 8.1

Rotator Diameter 140 130

Thickness 20 1518

INSPECTION

• Vernier caliper

• Micrometer

• Dial gauge

• Bevel protactor

• Flatness

• Straightness

• Perpendicularity

• Parallelism19

FINSHING PROCESS

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NAME OF THE

PARTDIMENSION

BEFORE

MACHINING

(in mm)

AFTER

MACHINING

(in mm)

Geneva wheel

Length 113.1 113

Breadth 113.2 113

Thickness 8.1 8

Rectangular base

plate

Length 266 265

Breadth 191 190

Thickness 12 10

Rotator Diameter 130 129

Thickness 15 14

ASSEMBELY OPERATION

PARTS:

•DRIVE WHEEL

•DRIVEN WHEEL

•BASE PLATE

•BOLT

•NUT

•BUSHES

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ADVANTAGES OF GENEVA MECHANISM

• Geneva mechanism may be the simplest and least Expensive of all intermittent motion

mechanisms.

• They come in a wide variety of sizes, ranging from those used in instruments, to those used in

machine tools to index spindle carriers weighing several tons.

• They have good motion curves characteristics compared to ratchets, but exhibit more “jerk” or

instantaneous change in acceleration, than better cam systems

• Geneva maintains good control of its load at all Times, since it is provided with locking ring

surfaces.

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DISADVANTAGES OF GENEVA MECHANISM

• The Geneva is not a versatile mechanism.

• The ratio of dwell period to motion is also established Once the no

of dwells per revolution has been selected.

• All Geneva acceleration curves start and end With finite acceleration

& deceleration.

•This means they produce jerk.

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APPLICATIONS OF GENEVA MECHANISM

• Stepper

• Mechanical Watches

• Plotters

• Cnc Machine

• Iron Ring Clock

• Modern film projectors may also use an electronically

controlled indexing mechanism or stepper motor, which allows for

fast-forwarding the film.

• Indexing tables in assembly lines, tool changers for CNC

machines and so on.

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CONCLUSION

The parts namely Geneva wheel, rotator and baseplate were modeled using UNIGRAPHICS-NX

9.0 cad software and subsequently CNC coding were developed manually.

The parts mentioned above were fabricated using conventional lathe, milling, and drilling

machines.

Next stage of the process was carried out using CNC vertical machining centre to achieve the

near to finish dimensions and later the parts were finished using flat file and emery sheet.

Finally the parts (Geneva wheel, Rotator) were assembled to the baseplate using fasteners

(bolt and nut) to complete the Geneva wheel mechanism.

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modelling and fabrication of geneva mechanism

Engineering