Abstract

Use

of plastics in structural and non- structural applications is increasing

rapidly. The material used for manufacturing horn should have high fatigue

strength and low acoustic losses. The horn is the only part of the ultrasonic

insertion system which is unique to each process. The resonant frequency of

horn is usually determined numerically using Finite Element Method (FEM). Block

horns used in ultrasonic insertion process have more weight and the amplitude

of vibrations transmitted is uneven. Slotted block horns provide an advantage

by having less weight and the longitudinal direction. The required slots can

introduce additional problems, although these can be reduced through careful

design. Also, the temperature at the interface of the thermoplastic component

and the metal insert is very important in order to obtain the rigid parts. In

this work, the ultrasonic horn will be fabricated for the optimized results

using Aluminium for multiple insertions at a time. Modal and harmonic analysis

of the horn is done using CAE software. Optimization is done by RSM method. The

temperature at the interface of the thermoplastic component and the metal

insert will be calculated by using the numerical calculations. This will be

compared with the results of thermal analysis done using ANSYS software.

Finally, the components will be fabricated and the experiment is carried out in

the ultrasonic plastic welding machine using the fabricated horn.

Keywords

Ultrasonic

Welding, Thermal Analysis, Metal Insertion, Slotted Horn, Finite Element

Method.

1. INTRODUCTION

Ultrasonic insertion is the process of embedding or

encapsulating a small metal component into a thermoplastic part. This process

replaces the costly, time consuming, conventional method of injection molding

plastic around the metal component known as insert molding. An endless variety

of part configurations can be inserted through this process like flat, round,

etc.; the most common configuration is round, threaded inserts. In ultrasonic

insertion, a hole slightly smaller than the insert diameter is either molded or

drilled into the plastic part. This hole provides a certain degree of

interference and guides the insert into place. The metal insert is usually designed

with exterior knurls, undercuts, or threads to resist loads imposed on the

finished assembly. Ultrasonic insertion can be accomplished by two methods, one

method is about the horn can touch the insert, driving it into the plastic part

and in the another method the horn can touch the plastic part, driving it over

the insert.

2. LITERATURE REVIEW

Several types of ultrasonic horns were developed so

far. Models based on different approaches and techniques have been constructed

to enhance the process performance and efficiency. In order to find out the

optimized set of input parameters and also to identify the effect of each

towards a particular output, researchers have been trying for years together. A

brief review on literature on ultrasonic horn designing and modal, harmonic

simulation by ANSYS also development of mathematical model is needed for the

optimization of the ultrasonic horns for insertion process. Anand and Elangovan 1have tried to

optimize the ultrasonic inserting parameters to achieve maximum pull out

strength of ultrasonic insertion process. Cardoni et al 2investigated the design requirements of block

horns which operate as intermediate components in ultrasonic systems. Patrick et al 3investigated the effect of manual and ultrasonic

insertion of standardized class I inlays using three composite resin materials

of different viscosity. Roopa Rani et al 4

have developed different ultrasonic horns from materials a made a study on

thermo-elastic heating of the horns used in ultrasonic plastic welding. Safe

stress levels were predicted by modal and harmonic analysis followed by stress analysis

using ANSYS software. Roopa Rani

and Rudramoorthy 5 have tried computational modeling and experimental

studies of the dynamic performance of ultrasonic horns. Suresh et al 6 have done the modeling and of temperature

distribution in ultrasonic welding of thermoplastics for various joint designs.

Lin 7derived an equation for

the resonance frequency for the design of the longitudinal-torsional composite

ultrasonic exponential horns. Ganeshamoorthi

et al 8 have studied about the optimizing technique used in ultrasonic

metal welding of copper sheet and copper wire.

Ioan-Calin et

al 9 have developed the design and characterization of an axisymmetric

ultrasonic horn held by its circumference, with specified working frequency,

amplification factor and nodal point position. Siddiq and Ghassemieh 10 have

attempted to simulate the ultrasonic welding of metals by taking into account

of effects of surface and volume. Elangovan et al 11 have developed a model

for the temperature distribution during welding and stress distribution in the

horn and welded joints. Arthur et al 12

have developed a model for the mechanics (oscillating deformation), heat

transfer including viscoelastic heat generation and friction dissipation, and

degree of adhesion (intimate contact and healing) for the initial transient

heating phase. Numerical resolution was performed using a multi-physical finite

element code. Kaifeng et al 13 have made a study on Effect of interfacial

preheating on welded joints during ultrasonic composite welding. Mantra et al 14 have made a

study on the control parameters like vibration amplitude, weld pressure and

weld time are considered for the welding of dissimilar metals like aluminum

(AA1100) and brass (UNS C27000) sheet of 0.3 mm thickness. Chen and Zhang 15

have developed a three-dimensional finite element model to study the

temperature distribution and heat generation in ultrasonic welding process.

Chunbo and Li 16 have been developed a three-dimensional (3-D) finite element

model to simulate the coupled thermal-mechanical fields in ultrasonic welding

of aluminum foils. Roopa et al 17 have made study on the far field welding of

semi crystalline polymer/high-density polyethylene. Volkov 18 has developed a

hypothesis for the mechanism of heat generation in the ultrasonic welding of

plastics. Volkov 19 has made an investigation on the special features of

joining metallic components with thermoplastics. Kamaleash and Elangovan 20

have studied about the temperature distribution between the metal and the

plastic component during ultrasonic insertion process. Tsujino et al 21 have made a study on the joint

structure of a transducer horn-holder assembly for a wire bonder. Cretu 22

has made an investigation on the behavior of the finite cylindrical rods with

harmonic variation of the cross section. Himanshu and Harshit 23have

considered weld strength as an effective attribute to identify the quality of

ultrasonically welded joints. Volkov and Bigus 24 have developed a specialized welding

machine for the ultrasonic contour welding of ABS plastics.Jingzhou et al 25 investigated the thermal phenomena and to realize production level in-situ

temperature measurement by using micro thin-film thermocouples and thin-film

thermopile arrays at the very vicinity of the ultrasonic welding spot during

joining of three-layered battery tabs and Cu bus bars (i.e., battery

interconnect) as in General Motors Chevy Volt. Micro sensors were first

fabricated on the bus bars. Kaifeng et al

26 have tested the ultrasonic welding of an injection molded short carbon

fiber reinforced composite is to investigate three important weld attributes,

bonding efficiency, weld area, and horn indentation. From the above research

papers, various design and performance of different types of horns, material

vibrational characteristics, welding of thermoplastics, techniques to evaluate

the parameters were studied and understood. Modal, harmonic analyses for the

different horn profiles were done by using ANSYS software are studied. The

finite element method for calculating the interface temperature and the

derivations of thermo-mechanical problem has been studied. In this project, for

the optimized dimensions the horn will be fabricated and the thermal analysis

will be carried out to find the interface temperature thus, the literatures

from the finite element methods are helpful in doing the simulations as well as

compare it with the experimental results.

3. PROBLEM DEFINITION

The process of joining the metals with the plastics

using mechanical fastening method gives low tensile strength and less torsional

resistance, which leads to distortion of the component used. By placing a metal

insert inside thermoplastic component through ultrasonic insertion process,

complexity can be reduced. Block horns, which are used in the ultrasonic

insertion process having more weight and provide uneven vibration transmission.

Slotted block horns will produce high amplitude of vibrations, having less

weight and reduce the transverse coupling. Usually, only one metal insert could

be inserted in the thermoplastic component. To increase the productivity, a

horn is to be designed multiple insertions at a time. Finding out the interface

temperature between the thermoplastic component and metal insert is important

for the insertion process. This will be finding out by thermal analysis using

ANSYS software.

3.1.Objectives

This work consists of several objectives in order to

achieve the temperature developed in the ultrasonic insertion process.

a.

To

understand the mechanism, working and applications of the ultrasonic insertion

process.

b.

To

design and manufacture the thermoplastic component in which the metal insertion

can be done.

c.

To

design a slotted block horn and fabricate it according to the optimized

conditions for ultrasonic insertion of metal inserts into the thermoplastic

components,

d.

To

carry out the thermal analysis for the assembly of metal insert and

thermoplastic component in order to obtain the interface temperature,

e.

To

derive the mathematical equations for the measurement of interface temperature.

f.

To

compare the simulation results with the mathematical results.

4. METHODOLOGY

The metal insert to be inserted is selected first and

the modeling of slotted horn and thermoplastics are done in CREO software. The

simulation is carried out to find out the intermediate temperature between the

plastics and insert. This will be compared with mathematical results. Then the

thermoplastic component and the horn will be manufactured and tuned to machine

frequency and test by the inserting the metal insert into the plastic

component. Based on the objectives, the methodology has been adopted to carry

out the work shown in Fig 4.1.

Fig. 4.1. Flow chart

5. DESIGNING OF HORN

The actual slotted horn will be designed

after the thorough study on the existing horn profiles. The energy of

vibrations is non-uniformly distributed along the length of the horn with

velocity/amplitude being greater at the tip of the horn than at the booster

end. The commonly used horn profiles in the industry are Stepped and

Catenoidal. Along with these horns the Cylindrical, Gaussian and Bezier horn

profiles are considered for the present study. The Cylindrical horn was

included so as to have comparison with low amplitude horns. The performance of

a horn is usually assessed by the amplification factor or ‘gain’ that can be

achieved at the horn face/end. The gain ‘?’ is defined by the ratio of output

amplitude (A2) to input amplitude (A1). The basic requirement for a gain is

when the amplitude factor ‘?’ > 1. Different horn shapes give different gain

depending on the variation of their cross sections. For a cylindrical horn the

gain in amplitude is ‘1’ as it is of uniform cross section. The length of the horns

is measured from the horns available in the laboratory. Usual horn profiles

include cylindrical, Bezier, catenoidal, stepped and block. When a sonotrode or

horn is made for an existing facility, its frequency should be matched. The

length of the sonotrode should be half the wavelength of vibrations through the

material. The end diameters of all horn profiles are taken as 57 mm and 38 mm

at the top and bottom respectively, to suit the machine and the component. The

cylindrical horn has a uniform diameter of 57 mm. Different horn Profiles are

shown from Fig 5.1 – 5.4.

Fig 5.1 Bezier horn Fig 5.2

Catenoidal horn

Fig 5.3 Cylindrical horn Fig 5.4

Stepped horn

Thermoplastic component and slotted horn were also designed and used to

predict the interface temperature using ANSYS software. Which will then compare

with the numerical results. Thermoplastic component and slotted horn are shown

in Fig 5.5 and 5.6.

Fig 5.5 Slotted horn Fig 5.6

Thermoplastic component

5.1. Modal analysis

To determine

the mode shape and natural frequency of a horn, modal analysis could be used.

They are the important parameters in the design of the part for dynamic loading

conditions. Depend upon the applications, horn shape is modeled by using 3D

software package and imported to ANSYS software with parasolid file (.xt). The

model meshed by using Tetra 10 node 187 SOLID element with a fine mesh size of

3. Material mode is then specified as

linear, elastic, isotropic and properties such as young’s modulus, poission’sraio

and density of the material were specified. Mode extraction is carried out in

the frequency range 19 – 21 KHz using Block-Lanchoz option.

5.1.1 Natural frequencies of horn

profiles

The natural frequency of the

longitudinal mode obtained in modal analysis for Stepped horn profile is 19697 Hz,

for Catenoidalhorn profile is 19605 Hz, for Bezier horn profile is 20401 Hz and

for Cylindrical horn profile is 19524 Hz and for slotted horn profile is 20476

Hz. Fig 5.7 – 5.10 represents modal analysis for various horn profiles.

Fig 5.7 Modal analysis of Catenoidal horn

Fig 5.8 Modal analysis of Bezier horn

Fig 5.9 Modal analysis of Cylindrical horn

Fig 5.10 Modal analysis of Stepped horn

Fig 5.11 Modal analysis of Slotted horn

5.2 Harmonic analysis

A harmonic analysis of the horn is carried out to find the displacement

and stresses experienced by the horn in the given frequency range. The

displacement amplitude produced by the machine 23.4 µm. The output is amplified

by the booster which is placed after the transducer. The displacement at the

booster end-23.4 µm is given as the input or the forcing function to the horn

for performing the harmonic analysis. The horn is constrained to longitudinal

movement by locking it to a nut. This

analysis will show the displacement amplitude at the end of the horn which will

be used for insertion process.

5.2.1 Displacement of horn profiles

The maximum stress amplitude obtained

in harmonic analysis for cylindrical horn profile is horn profile is 0.255E-4,

for stepped horn profile is 0.541E-4, for catenoidal horn profile is 0.307E-4,

forbezier horn profile is 0.477E-4 and for slotted horn profile is 0.296E-4.

Fig 5.12 – 5.16 represents modal analysis for various horn profiles.

Fig 5.12 Harmonic analysis of Catenoidal horn

Fig 5.13 Harmonic analysis of Bezier horn

Fig 5.14 Harmonic analysis of Cylindrical horn

Fig 5.15 Harmonic analysis of Stepped horn

Fig 5.16 Harmonic analysis of Slotted horn

5.3 Thermal analysis

Thermal

analysis of the horn profiles was done in ANSYS software. The maximum

temperature obtained for cylindrical

horn profile is horn profile is 107.054°C, for stepped horn profile is196.163°C,

for catenoidal horn profile is 158.03°C, for bezier horn profile is 160.91°C

and for slotted horn profile is 122.36°C.The

simulation results are shown in Fig 5.17 to 5.21.

Fig 5.17 Thermal analysis of Catenoidal horn

Fig 5.18 Thermal analysis of Bezier horn

Fig 5.19 Thermal analysis of Cylindrical horn

Fig 5.20 Thermal analysis of Stepped horn

Fig 5.21 Thermal analysis of Slotted horn

6. CONCLUSION

From this work, the mechanism,

working and principle of ultrasonic insertion process have been studied.

Different horn profiles were designed and the modal and harmonic analysis of

the horns were done. The results of modal and harmonic analysis is shown in

Table 6.1.

Table 6.1

Results of modal and harmonic analysis

Profile

Frequency(Hz)

Displacement(m)

Temperature(°C)

Bezier

20401

0.477E-4

160.91°C

catenoidal

19605

0.307E-4

158.03°C

cylindrical

19524

0.255E-4

107.054°C

Stepped

19697

0.541E-4

196.163°C

Based on the above results the

various profiles of horn were validated successfully and then slotted block

horn profile is simulated through the ANSYS software and obtained natural

frequency of 20476 Hz, displacement of 0.296E-4 and the interfacial temperature

of 122.36°C. This will be then compared with the numerical results and finally

the experimentation will be done.