random virational analysis on milling...

VVRLS Gangadhar* et al ISSN: 2250-3676

[IJESAT] [International Journal of Engineering Science & Advanced Technology Volume-7, Issue-1, 080-092

IJESAT | Jan-Feb 2017 Available online @ http://www.ijesat.org

RANDOM VIRATIONAL ANALYSIS ON MILLING MACHINE STRUCTURE

Dr. VVRLS GANGADHAR1, S SHASHANK

2, GYADARI RAMESH

3, V.P. RAJU

4

1,2,,3& 4 DEPARTMENT OF MECHANICAL ENGINEERNG

PRINCETON COLLEGE OF ENGINEERING & TECHNOLOGY, HYDERABAD, TELANGANA

Abstract

Beds, bases, columns and box type housings are called

“structures” in machine tools. In machine tools, 70-

90% of the total weight of the machine is due to the

weight of the structure. They provide rigid support on

which various subassemblies can be mounted i.e. beds,

bases, provide housings for individual units or their

assemblies like gear box, spindle head, support and

move the work piece and tool relatively, i.e. table,

carriage, tail stock etc.

In this thesis, tool structure of a milling

machine is designed and modeled in 3D modeling

software CREO 2.0. Static analysis is done on the

tool structure by applying weight forces, cutting

forces for different materials Cast Iron, Mild Steel,

Granite and Concrete to determine deformations

and stresses. Modal analysis and Random Vibration

analysis are done to determine frequencies and

stresses produced from frequencies. Analysis is

done in Ansys.

Key words: Cutting Forces, Metal Cutting, Vibration

I.INTRODUCTION

Milling machines were first invented and

developed by Eli Whitney to mass produce

interchangeable musket parts. Although crude,

these machines assisted man in maintaining

accuracy and uniformity while duplicating parts

that could not be manufactured with the use of a

file Development and improvements of the milling

machine and components continued, which resulted

in the manufacturing of heavier arbors and high

speed steel and carbide cutters. These components

allowed the operator to remove metal faster, and

with more accuracy, than previous machines.

Variations of milling machines were also

developed to perform special milling operations.

During this era, computerized machines have been

developed to alleviate errors and provide better

quality in the finished product.

Metal cutting is generally used in the

manufacturing industry to machine, e.g., work

pieces to desired geometries with certain

tolerances. During the machining process, a

number of different machining operations may be

involved. Today, there are many advanced

machines that have several axes and that can

perform complex milling and turning operations

about non-fixed axes by, for example, rotating or

leaning the axis of the spindle. Another example of

the type of advanced operation that modern

machines are capable of is the production of an

oval or ellipsoidal cross-section of a work piece by

controlling the tool motion in the radial direction of

the work piece during turning.

The metal cutting operation may

sometimes produce high server vibration levels.

The cause of these vibrations can be attributed to

many different factors such as the cutting

parameters, the work piece material and shape, the

tooling structure, the insert, and the stability of the

machine. Thus, there are many different parameters

that impudence the stability of the cutting process

in milling operations, and there has been a lot of

research done in this area.




II.LITERATURE REVIEW

In the paper by Mounir Muhammad Farid

Koura, Muhammad LotfyZamzam, Amir Ahmed

Sayed Shaaban, presented an integrated simulation

system that is employed in order to evaluate the

static and dynamic performance of a milling

machine. The paper discusses the design

consideration of the evaluation system, creates the

system based on finite element technique, applies it

to a case study, and discusses the results. Obtaining

such a reliable model could replace many

experimental tests that must otherwise be carried

out each time the parameters affecting cutting

conditions are changed. Modeling and meshing of

various machine elements including the mechanical

structure are carried out, contacts between each

adjacent element are defined, load components

generated from machining process are modeled,

and finally the static and dynamic performance of

the entire machine is evaluated. The machine

performance is identified in terms of static loop

stiffness in both x and y directions, mode shapes,

and frequency response function at tool center

point.

In the paper by F. Haase, S. Lockwood &

D.G. Ford [2], A restriction for large material

removal rates is the tendency of machines to

ch1atter (structural vibration) for large depths of

cut. This work is concerned with improving

machine tool performance by understanding and

ultimately controlling vibration in machine

structures. If vibration due to chatter under load

conditions can be controlled, then component

surface finish can be improved and the life of

components extended. The first step in this research

is to measure and interpret vibration and model the

structures, which are to be controlled. Appropriate

sensors need to be selected and designed to

measure self-excited vibrations. The vibrations of

the investigated machines need to be understood by

analyzing the sensor signals and surface finish.

Recent advances in micro-machining technology

have resulted in a new type of accelerometer that is

an order of magnitude lower in cost than traditional

types. Results have shown that these sensors can be

successfully used to replace their more expensive

counterparts.

In the paper H. Akesson, T. Smirnova, L.

H. akansson, T. Lag¨o and I. Claesson [3], The

vibration level depends on many different

parameters such as the material type, the

dimensions of the work piece, the rigidity of

tooling structure, the cutting data, and the operation

mode. In milling, the cutting process subjects the

tool to vibrations, and having a milling tool holder

with a long overhang will most likely result in high

vibration levels. As a consequence of these

vibrations, the tool life is reduced, the surface

finishing becomes poor, and disturbing sound

appears. In this report, an investigation of the

dynamic properties of a milling tool holder with

moderate overhang has been carried out by means

of experimental modal analysis and vibration

analysis during the operating mode. Both the

angular vibrations of the rotating tool and the

vibrations of the machine tool structure were

examined during milling. Also, vibration of the

work piece and the milling machine was examined

during cutting. This report focuses on identifying

the source/sources of the dominant milling

vibration components and on determining which of

these vibrations that are related to the structural

dynamic properties of the milling tool holder.

In the paper by SiamakPedrammehr –

Mehran Mahboubkhah – Mohammad Reza Chalak

Qazani3 – ArashRahmani – SajjadPakzad [4] ,




Assuming a sinusoidal machining force, the forced

vibration of a machine tools’ hexapod table in

different directions is addressed in the present

study. A vibration model for the hexapod table is

developed and the relevant explicit equations are

derived. In the vibration equation of the table, the

pods are assumed as spring-damper systems and

the equivalent stiffness and damping of the pods

are evaluated using experimental results obtained

by modal testing on one pod of the hexapod table.

The results of the analytical approach have been

verified by FEM simulation. The theoretical and

FEM results exhibit similar trends in changes and

are close to each other. The vibration of the table in

different positions has been studied for rough and

finish machining forces for both down and up

milling. The ranges of resonance frequencies and

vibration amplitudes have also been investigated.

The safe functional modes of the table in terms of

its upper platform’s position have subsequently

been determined

In the paper by Huaizhong Li, Xiubing

Jing, and Jun Wang [5], An experimental study to

understand the characteristics related to chatter

occurrence in micro milling operations is

presented. Accelerometers are used to measure the

vibration signals in the machining process. The

accelerate on signals are then analyzed in the time

domain and the frequency domain. Along with the

onset of chatter, it is found that there is a

characteristic shift of the dominant frequency

components in addition to the change of vibration

amplitude. A modulation of the spindle frequency

around the chatter frequency is also found to be

present in the vibration signal. A dimensionless

chatter indicator based on revolution RMS values is

designed and used to evaluate the stability of the

micro-milling process. It is shown that the

proposed indicator provides a simple, but effective

way to detect chatter onset.

In the paper by K. Reza Kashyzadeh ,

Prof. Dr. M. J. Ostad-Ahmad-Ghorabi [6], Machine

tool chatter is one of the major constraints that limit

productivity of the turning process. It is a self-

excited vibration that is mainly caused by the

interaction between the machine-tool/work piece

structure and the cutting process dynamics. The

frictional and impact chatter are mainly due to the

nonlinearity of the dry friction and the intermittent

contact between the cutting tool and the work

piece. There are some methods that can limit the

chatter. In this paper we introduce and compare

some of these methods.

In the paper by B.V. Subramaniam, A.

Srinivasa Rao, S.V. Gopala Krishna, CH. Rama

Krishna [7], Static and Dynamic analysis of

machine tool structures plays an important role on

the efficiency and job accuracy of the machine tool.

Static analysis is useful for estimating stresses,

strains and deflections, where as dynamic analysis

deals with the prediction of natural frequencies and

corresponding mode shapes, which will inturn,

prevent the catastrophic failure of the machine tool

structures.

1. ANALYSIS ON MILLING MACHINE

TOOL STRUCTURE

The reference paper for the analysis is

taken from “Simulation approach to study the

behavior of a milling machine’s structure during

end milling operation” by Mounir Muhammad

Farid Koura, Muhammad LotfyZamzam, Amir

Ahmed Saied Shaaban, Turkish J EngEnvSci

(2014) 38: 167 – 183, as specified in Reference

chapter as [1].




The material properties are specified in the below

table which are taken from website

www.matweb.com

MATERIAL

Density

(kg/m3)

Young’s

modulus

(Mpa)

Poisson’s

ratio

Mild steel 7850 210000 0.303

Cast iron 7810 240000 0.370

Granite 2660 60000 0.3

2300 30000 0.18

Table 1 - Material Properties

III.STRUCTURAL ANLYSIS

Condition 1- Force 1000 N

MATERIAL – MILD STEEL

Save Creo Model as .iges format

→→Ansys → Workbench→ Select analysis

system → static structural → double click

→→Select geometry → right click → import

geometry → select browse →open part → ok

→→ Select mesh on work bench → right click

→edit

Imported model

Double click on geometry → select geometries →

edit material

Select mesh on left side part tree → right click →

generate mesh →

Meshed model

Select static structural right click → insert → select

Force –1000N

Force

Select fixed support → select required area →

click on apply →

Fixed support

Select solution right click → solve →

http://www.matweb.com/




Solution- right click → insert → deformation →

total

Solution right click → insert → strain → equitant

(von-misses) →

Solution right click → insert → stress → equitant

(von-misses) →

Right click on deformation → evaluate all result

Total deformation

Von-misses stress

Von-misses strain

MATERIAL – CAST IRON

Total deformation

Von-misses stress

Von-misses strain




MATERIAL -GRANITE

Total deformation

Von-misses stress

Von-misses strain

MATERIAL – CONCRETE

Total deformation

Von-misses stress

Von-misses strain




MODAL ANALYSIS

MATERIAL – STEEL

Save Creo Model as .iges format

→→Ansys → Workbench→ Select analysis

system → model → double click

→→Select geometry → right click → import

geometry → select browse →open part → ok

→→Select modal → right click →select edit →

another window will be open

Imported model

Double click on geometry → select geometries →

edit material →Select mesh on left side part tree →

right click → generate mesh →

Meshed model

Select fixed support → select required area → click

on apply → Select solution right click

Fixed support

Solution right click → insert → deformation →

total deformation → model Solution right click →

insert → deformation → total deformation2 →

mode 2

Solution right click → insert → deformation →

total deformation 3→ mode 3

Right click on deformation → evaluate all result

Mode 1




Mode 2

Mode 3


Mode 1

Mode 2

Mode 3


Mode 1




Mode 2

RANDOM VIBRATIONALANALYSIS

MATERIAL – MILD STEEL

Enter frequencies and deformation values

Solution –right click-solve-select solution –right

click –directional deformation

Select solution –right click –shear stress

Select solution –right click –shear strain

Directional deformation

Shear stress

Shear strain






Shear stress

Shear strain

MATERIAL - GRANITE


Shear stress

Shear strain






Shear stress

RESULT & DISCUSSION STATIC ANALYSIS

Force

Material

Deformation

(mm)

Stress

(Mpa)

Strain

1000N

Steel 0.0013823 0.081035 4.264e-7

Cast iron 0.00011753 0.081752 3.7182e-7

Granite 0.00048436 0.081007 1.4928e-6

Concrete 0.0010038 0.08013 3.0505e-6

500N

Steel 6.9117e-6 0.040517 2.132e-7

Cast iron 5.8764e-5 0.040876 1.8591e-7

Granite 0.00024218 0.040504 7.4642e-7

Concrete 0.0005019 0.040065 1.5252e-6

Static analysis results

MODAL ANALYSIS

Materials Modes Deformation

(mm)

Frequency

(Hz)

Mild steel

Mode1 1.1555 47.855

Mode2 1.0219 48.88

Mode3 1.3766 139.59

Cast iron

Mode1 1.1597 50.946

Mode2 1.025 52.593

Mode3 1.3939 149.36

Granite

Mode1 1.985 43.958

Mode2 1.7355 44.878

Mode3 2.3638 128.19

Concrete

Mode1 2.1363 33.967

Mode2 1.8966 34.001

Mode3 2.5022 98.182

Modal analysis results

0

0.0005

0.001

0.0015

500 1000

DE

FO

RM

AT

ION

(m

m)

FORCE (N)

COMPARISON OF

DEFORMATION VALUES AT

DIFFERENT FORCES AND

MATERIALS

Mild Steel

Cast Iron

Granite

Concrete

0.00E+00

1.00E-06

2.00E-06

3.00E-06

4.00E-06

500 1000

STR

AIN

FORCE (N)

COMPARISON OF STRAIN VALUES AT DIFFERENT FORCES AND

MATERIALS

Mild Steel

Cast Iron

Granite

Concrete




RANDOM VIBRATION ANALYSIS RESULT

Material

Directional

deformation

(mm)

Shear stress

(MPa)

Strain

Mild

steel

65.885

507.05

0.0062923

Cast iron

69.797

631.05

0.0072045

Granite

82.628

181.53

0.0078664

IV.CONCLUSION

In this thesis, tool structure of a milling

machine is designed and modeled in 3D modeling

software CREO. Static analysis is done on the tool

structure by applying weight forces, cutting forces

for different materials Cast Iron, Mild Steel,

Granite and Concrete to determine deformations

and stresses. Modal analysis and Random Vibration

analysis are done to determine frequencies and

stresses produced from frequencies. Analysis is

done in Ansys.

By observing the static analysis results,

the stress values for all materials are less than their

respective yield stress values. The deformation and

strain values are less when Cast Iron is used. By

observing the modal analysis results, the

deformation values are less when Cast Iron is used

but the frequencies are less when concrete is used.

Thereby the vibrations on the structure due to

cutting forces will be reduced when Concrete is

used.

By observing Random Vibration analysis,

due to frequencies from modal analysis, the

directional deformation and shear stress values are

less when Concrete is used.

But the strength of the concrete is very

less when compared with that of Steel or Cast Iron.

So using Cast Iron for milling machine tool

structure is better.

REFERENCES

[1] Muhammad Farid Koura, Muhammad

LotfyZamzam, Amir Ahmed Sayed Shaaban,

Turkish J EngEnvSci (2014) 38: 167 – 183 ⃝c

TUB¨ ˙ITAK doi:10.3906/muh-1404-6

[2] F. Haase, S. Lockwood & D.G. Ford,

Transactions on Engineering Sciences vol 34, ©

2001 WIT Press, www.witpress.com, ISSN 1743-

3533

[3] H. Akesson, T. Smirnova, L. H. akansson, T.

Lag¨o and I. ClaessonBlekinge Institute of

Technology Research Report No 2009:07 ISSN:

1103-1581, November, 2009.

[4] SiamakPedrammehr – Mehran Mahboubkhah –

Mohammad Reza Chalak Qazani3 – ArashRahmani

– SajjadPakzad.

[5] HuaizhongLi ,Xiubing Jing, and Jun Wang,

Sydney, NSW 2052, Australia 2 School of

050

100150200

FREQ

UEN

CY

(H

z)

Modes

COMPARISON OF FREQUENCY WITH DIFFERENT MATERIALS AND MODES

Mild steel

Cast iron

Granite

Concrete




Mechanical Engineering, TianJin University,

China.

[6] K. Reza Kashyzadeh , Prof. Dr. M. J. Ostad-

Ahmad-Ghorabi, International Journal of Emerging

Technology and Advanced Engineering. Website:

www.ijetae.com (ISSN 2250-2459, Volume 2,

Issue 4, April 2012)

[7] B.V. Subrahmanyam, A. Srinivasa Rao, S.V.

Gopala Krishna, CH. Rama Krishna, Imperial

Journal of Interdisciplinary Research (IJIR) Vol-2,

Issue-12, 2016 ISSN: 2454-1362

http://www.onlinejournal.in

random virational analysis on milling...

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