D.Manikandan INTRODUCTION Single reduction gearboxes casing are built

D.Manikandan
1, R.Haridass2, T.Rajeshkumar3,

1 Department of Mechanical engineering, Karpagam College of
engineering, Coimbatore.

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2 Department of Mechanical engineering, Karpagam College of
engineering, Coimbatore.

3 Department of Mechanical engineering, Karpagam College of
engineering, Coimbatore.

 

 

Abstract—

Globoid or double-enveloping gears are the version of general
type worm gears. They differ from single-enveloping worm gears by a higher
load-carrying capacity, especially at great center distances.

The paper considers the technique
of geometrical design of globoid gears modified by increasing the machine-tool
center distance and gear ratio while cutting the worm with respect to the same
parameters of the worm gear.  

Keywords— Globoid worm, generating wheel,
MachineTool     Setting,

                                                                                                                                                             
I.     INTRODUCTION

Single reduction gearboxes casing are
built sturdily with close grained, Cast Iron conforming FG 260 grade. The
gearbox is provided with amply designed fins with suitable fan for adequate
dissipation of heat generated. The entire design is based mainly on BS 721 /
1963 to accuracy class A. BIS Specifications are used wherever possible. The
gearbox design is in such way that is interchangeable with the standard gearboxes.           

The worm is of high quality
casehardening steel very accurately generated and ground finished for the
better performance. The worm wheel is of extremely high quality phosphor bronze
spin cast with a considerably substantial section, rigidly held to a strong hub
with eutectic welding technology / Sandwich Casting.         

Both worm and worm wheel shafts are
mounted on quality tapered roller / angular contact bearings with adequate
safety margin to handle the over-hung loads. Subject to the limitation of oil temperature
of 90°C under full load, the gearbox will give a minimum gear life of 20,000
hrs. Lubrication is positive. MM Gearboxes require absolutely no attention at
all in operation, excepting for the oil level check once in fortnight.

The project involves design and
fabrication of globoid worm gear over the normal worm gear boxes. Globoid or
double-enveloping gears are the version of general type worm gears. They differ
from single-enveloping worm gears by a higher load-carrying capacity,
especially at great center distances. It is caused, first, by a multiple tooth
contact, and, second, by more favorable conditions of a hydrodynamic lubricant
layer generation. In order to get the best of these advantages, the gears
should be modified with respect to the classic Cone gear during the machining
process the worm surface should be generated as if it has been already worn out
after the running-in process

                                                                                                                                                     
II.        
Objective and Scope

A.    Objective

The main objectives of the project are

To collect all information
about Worm & Globoid Worm gears.To achieve high load
transmission. To produce a Globoid Worm Gear
as a product.Machine Building of the
globoid worm gear milling machine.

B.    Scope

Globoid worm gear has a heavy load
carrying capacity than normal worm gears because it has more number of teeth
contact due to its concave profile. In India manufacturing pattern is not
available. And this project is a new methodology in producing Globoid milling
machine as product after the further Development. Also the following are the
benefits of this work.

New product development. i.e.
Globoid worm wheelThereby increasing the power
transmission capacity.More speed reduction with
minimal wear rate can be achieved.Heat distribution area is
more. Lower creep rate.Machine builded for this product
can be used for further applications in which same principle is adopted.

                                                                                                                                               
III.       
Mateials and methods

This chapter deals with design and
calculation of Globoid worm gear, and the conceptual design of pilot model of
Globoid milling machine.

A.    Calculation of double enveloping worm gear

Procedure: First, determine the
horsepower, Input speed, and ratio.

1.      Center
distance – It is necessary to assume a center distance according to Input power

2.      Pitch
diameter of the worm – (Center distance).875/2.2

3.      Pitch
diameter of the gear – 2C-d (or) (No. of gear teeth*pn)/?

4.      Module,
transverse – Axial pitch/?

5.      Calculation
of axial pitch – ?* module

6.      Normal
pressure angle – 20?

7.      Worm
lead angle – tan-1(D/d*mg)

8.      Working
depth –     0.450*pn

9.      Diametrical
pitch, transverse –    ?/px   

10.    Normal
circular pitch –  pn*cos ?

11.    Addendum
– 0.225*pn

12.    Whole
depth – 0.500*pn

13.    Throat
diameter of gear – d+(2*ha)

14.    Throat
diameter of worm – d+(2*ha)

15.    Root
diameter of worm –  d+2ap-2htp

16.    Axial
pressure angle – tan-1((tan ?n) /(cos?))                         

17.    Base
circle diameter – D*sin(?x+?)Where,(?=sin1(px/2D))                   

18.    Face
width of worm – Db-0.03C    

Note: The symbols and formulae from
Dudley’s Hand book of Practical Gear Design (AGMA Standards)

B.    Basic Dimensions

Basic Dimensions

Nomenclatures

Symbols

Values

Center distance

C

4

Pitch diameter of the worm

D

1.5289

Pitch diameter of the gear

D

6.4711

Module, transverse

M

0.1574

Normal pressure angle

?

20deg.

Worm lead angle

?

26.92deg.

Normal circular pitch

pn

0.4411

Working depth

h’

0.1985

Addendum

ha

0.0992

Whole depth

ht

0.2206

Root diameter of worm

dR

1.2861

Axial pressure angle

?x

22.20deg.

Base circle diameter

Db

2.6723

Face width of worm

Fw

2.5523

Gear ratio

mg

50/6

Number of teeth in gear

NG

50

Number of thread in worm

NW

6

Speed of worm

N

1500

Gear face width

F

1.20

Backlash

B

0.09

C.    Standard Backlash

Standard Backlash

Center distance, inches

No. of teeth in gear

Recommended backlash

2.000

24 to 40

.003-.008

2.500

24 to 40

.003-.008

3.000

24 to 50

.003-.008

3.500

24 to 50

.004 -.009

4.000

30 to 50

.004 -.009

5.000

30 to 50

.005-.010

6.000

30 to 50

.006-.012

7.000

30 to 50

.007-.013

8.000

40 to 60

.008-.014

10.000

40 to 60

.010-.017

12.000

40 to 60

.012-.020

15.000

50 to 60

.015-.025

18.000

50 to 60

.015-.025

20.000

50 to 70

.020-.030

22.000

50 to 70

.020-0.30

D.    Composition of Materials

Cpmposition of Materials

Type

Compositions

Uses

Bronze

Cu 88, Sn 10, Zn 2

Spur, Bevel, Worm gears

Phosphor bronze

Cu 89, Sn 10, Pb 0.25

Medium-speed worm gear

Nickel phosphors bronze

Cu 88, Sn 10.5, Ni 1.5, Pb 0.2

Medium-speed worm gear

Lead phosphor bronze

Cu 87.5, Sn 11, Pb 1.5

High-speed worm gear

Aluminum phosphor bronze

Cu 88, Al 10, Fe 1

Spur, Bevel, Low-speed worm gears

 

E.    Conceptual Design

This project deals with company need how
to manufacture Double enveloping worm gear with one new methodology. The
globoid gear manufacturing is not available in India. To start a design one
must have its aspects and calculations, first all collections of calculation
aspects were done and calculation is feed in to Excel sheet are shown in table
3.4 and 3.5. As per the calculations a solid running model of globoid is
created with help of CATIA and SOLID WORKS. An auto generation of 2-D diagrams
of globoid worm gear is generated in SOLID WORKS.

View
of globoid worm assembly

F.    Pilot Model and its Components

For the fabrication of globoid worm shaft there is no existing
manufacturing methods in India. On the normal thread milling machine the
milling cutter traces a linear profile but in case of fabricating globoid worm
shaft  the concave profile need to be
achieved which is not possible in thread milling machine and also it cannot be
fabricated in  NC machines unless a
attachment is provided.  To machine the
globoid worm shaft on the conventional manner, the convention machine for
thread milling must trace a concave thread profile.  In order to get required concave thread a new
pilot model has been designed which meets all the parameters for manufacturing
the globoid worm shaft.

The components used are,

Base plateSupporting plateRectangular boxSpacerBearingBase shaftMain shaftDrive shaftPlummer blockWorm and worm wheel 70:1Spur gear 1:1Worm and worm wheel 10 :1Spur gear 6:1Head chuckKeyMotorFasteners Circlipwork piece          The pilot model of
globoid milling machine is done in order to manufacture globoid worm shaft in
company and to analyze and the proper working of the gear.

Conceptual
3D model created using Solid works

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G.    Working of Pilot model

A model of globoid milling machine is
produced as a working pilot model in this project. A wooden piece is taken as
work piece and slitting wheel is used as module cutter, and it is for fixed
pitch, limited shaft diameter and without lead. This pilot model is a model of
a globoid milling machine not a down size of milling machine. As per the calculations
and design of globoid shafts pitch of shaft is fixed as 86mm and angel to be
rotated by the cutter is 51.48°.

          A
heavy reduction in simple gear train can be achieved only in worm gear, so two
worm gears are chosen. To transfer power between worm gears spur gear of
different ratios are used. In the base plate worm of 70:1 is fixed, this is the
main and base gear in the pilot model. In the wheel of the 70:1 gear cutter
plate, motor and cutter are placed. The cutter along with motor moves in radial
path with respect to 70:1 worm wheel. This radial movement of cutter in this
pilot model is indeed in milling machine to get globoid shape in worm shaft.

          After
fixing the main worm wheel and shaft, from main worm shaft to another worm
shaft power is transmitted through a spur gear of same ratio. This worm shaft
is chosen in the base to link cutter movement to work piece rotation. This worm
reduction is in ratio of 10:1. Feed given to cutter is taken as in put power of
this worm shaft. This worm wheel gives drive a change gear. The change gears
are in sync with the cutter motion. This pilot model has working length of 86mm
as a fixed one. Model of pilot model is shown in Figure.

For a particular angle of movement of a
cutter the work piece has to rotate full complete rotation. In this for 86 mm
of path has a total angle motion of 51.48°. And for a single thread the cutter
has to move about 8.58°. This angle of motion in 70:1 gear wheel is achieved
when shaft is rotated about 10 rotations. This rotation of 10 is directly
transferred directly in to another worm shaft with help of spur gear of same
ratio. This spur is chosen in the base of distance between the two worm shafts.
These spur gears are directly coupled to worms of 10:1. From the worm shat the
rotation is reduced to single rotation. As per the calculation done this single
rotation should be multiplied to 6 rotations. This increase in reduction is not
constant so by changing gears in this set up helps to change the pitch of the
work piece. This 1:6 reduction with a distance 160mm center distance is taken
from the spur gears. The single rotation of worm is multiplied to 6. From the
end spur gear it is taken to holding work piece which is known as head chuck.
The work piece is machined in CNC to get a concave profile before mounting in
the milling process in pilot model.

          The
pilot model is completed with full machining of globoid worm shaft in wood.
After taking it under research and development of the pilot model a complete
globoid milling machine can be manufactured. 

                                                                                                                                               
IV.       
Results and Discussion

The tests are
conducted and the results obtained are analysed to get the concave profile. The
various results obtained by the project, the final picture of the design, the
cost estimation are discussed in this chapter.

Fabricated
pilot model

Work
piece

Slitting
wheel assembly

Finished
globoid worm shaft

                                                                                                                                                                      
V.        
Summary

Globoid worm is a type of worm gear. It
is different from other worm gears by heavy load carrying capacity by more
teeth contact. This gear is not manufactured in India it’s only imported from
other countries. The need of the globoid worm is increased due to load carrying
capacity at heavy reduction then other gears. M.M Gears is a well standard and
ISO holding company working towards mass production worm gears and other gears
in India. They have an idea of implementing the globoid worm gear in India. The
project combines with the company to implement a globoid worm gear.

The globoid worm can be manufactured
only when the cutter must takes a radial path instead of moving in linear path.
To obtain a radial movement in cutter a method is developed in synchronies with
cone drive method. The cutter is placed in a circular plate or gear. This
radial motion should be in connection with work piece rotation. This can be
done only with the help of gear train mechanism.

The project is divided into two phases
one is a design phase and manufacturing phase. In design phase collection of
all dates and basics calculations globoid worm gear are calculated. The
calculations are feed in Ex-cell sheet this calculation is in connection with
center distance. So for changing of each center distance related globoid worm
shafts dimensions are calculated and listed. From the values generated in
Ex-cell sheet a conceptual design of globoid shaft is drawn in 2D and also in
solid model with the help of solid works and catia. The 2D drawing of globoid
shaft is drawn in solid works software. With the help of equation and
configuration in solid works an auto generation of 2D drawing is obtained. But
the solid model of the globoid shaft cannot be created only in solid works
software. The base shaft and teeth profile is generated in catia and the
remaining are created in solid works software. After the real model generated
in software the assembly of shaft and wheel is done using same solid works
software. From the assembly the meshing of shaft and wheel are analyzed. A
running assembly model is done with the motion study in sold works. After the
design of globoid worm gears the design phase is completed and it leads second
phase of manufacturing globoid worm shaft.

To manufacture a globoid worm shaft a
cutter must moves in a radial path. A pilot model of machining globoid shaft is
manufactured. This pilot model consists of a pair of worm gears in different
ratios and spur gears with different needed ratios. In the pilot model the
cutter moves in radial path were it is attached with a worm gear. The worm gear
which holds the work piece moves in respect with the work piece rotation. The
selection of gear size and gear ratio are chosen with the concept of radial
motion of cutter is related to rotation of work piece. This pilot model
machines the wooden work piece to globoid worm shaft and cutter used in is
slitting wheel. This pilot model can machine a globoid worm shaft with a
constant pitch and without lead angle in it.

Based on the report conducted primary
design parameters have been chosen and analyzed on an existing worm gear. The
above parameters have been converted for Globoid shaft. Design calculations for
the remaining parameters have been calculated in an Excel sheet for globoid
worm shaft.

Verification of the parameters has been
done by meshing using solid works design software. Final results have been
arrived for profile calculation of globoid worm gear.

This project satisfies the company need
to develop a globoid worm gear in their company. A research and development
need to be done in the pilot model to develop a globoid milling machine. In
this pilot model a work piece of constant pitch, limited globoid shaft diameter
and no lead only achieved it can be changed as a feature work. The company is
satisfied with the project done and pilot model manufactured. At further
research and development conducted in pilot model a globoid milling machine
will be manufactured by the company.

                                                                                                                                                                
VI.       
Conclussion

A design of globoid worm gear is done
using modeling software, which is not available in current source.

          The
pilot model of globoid milling machine is manufactured based on calculations
and design aspects.

          Application
products of globoid worm gear are imported to India. After the production of
globoid milling machine this applications are produced in India.

          After
further Research and Development conducted on pilot model a globoid milling
machine will be produced. 

          The
globoid worm gear is imported to India since there is no existing methodology
to produce globoid worm gear. With the help of project methodology globoid worm
can be manufactured in India. By this importing of globoid worm will be
entirely removed.

Acknowledgment

We would like to thank DAIJO
Technologies-Coimbatore for their support in modelling works and Fabrication
works.

References

 

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