Resistance Spot Weldingreport

7/27/2019 Resistance Spot Weldingreport

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INDI N INSTITUTE OF TECHNOLOGY DELHI

ADVANCES IN RESISTANCE WELDING

SUBMITED TO: SUBMITED BY:

S. ARAVINDAN AJAY KUMAR 2013MEP8369



Delphi Deformation Resistance Welding (DRW)

Delphi's Deformation Resistance Welding (DRW) enables designers and

engineers to use tube sheet metal instead of stampings as the building blocks for

structures. Compared to conventional welding methods, DRW is quick, costeffective, reliable, and repeatable. This metal-joining technology allows

designers to reduce part count and cost without sacrificing structural integrity or

rigidity. As the name indicates, DRW applies the heat and force of resistance

welding to generate heat, with tooling designed to create the necessary

deformation. This creates atomically bonded, solid-state joints through the

heating and deformation of the two surfaces to be joined. Melted and solidified

weld nuggets may also be obtained through the use of more weld pulses. This

process is easily automated and creates near instantaneous, leak proof jointswith uniform circumferential strength capable of holding fluids and gases.

Using resistance welding rather than TIG or MIG welding, designers can

quickly create dependable joints cost effectively. Resistance welding has

traditionally been used to join overlapping sheet metal members. Theconnection is formed by the solidification of the molten metal where the

members meet. Compared to brazing, tube joining with resistance welding more

quickly and efficiently creates leak-tight joints.



Benefits

Allows the welding of similar or dissimilar material joints efficiently and

economically.

Provides the ability to join different types of metals with solid state bonds

in a variety of configurations, including Tube-to-sheet,Tube-to-tube,

Tube-to-solid.

Creates atomically bonded joints through the heating and deformation of

the mating surfaces Creates a weld in a reliable, repeatable fashion, and at

significantly lower costs when compared to conventional brazing,traditional MIG and TIG welding, and laser welding.

Can be used with tubular structures welded with sheets and/or solids aswell as other configurations.

Costly stampings and adhesives can be eliminated.

No filler material required.

Lowers materials and capital cost.

Strong construction forms near instantaneous, full strength welds and can

create a joint stronger than the original metal.

Creates leak-tight joints with uniform circumferential weld strength

capable of holding fluids and gases. Tubes can be bent into desired shapes by hydroforming,an economical

process in which a tube is placed in a mold and filled with fluid.

Process is easily automated to help cut cost investment in time and

material.

Reduces welding cycle time and cost in manufacturing an array of

structures built with hollow members.

Enhanced design flexibility enabling new structural approaches.

Typical Applications

Delphi's Deformation Resistance Welding can be used for welding operations inmanufacturing and industrial industries for tubular structures and hydro forms to

help eliminate die stamping. It is also viable alternative to conventional brazing.

Potential applications include:

Heat exchangers/chillers

Medical devices

Load-bearing structural applications like bridges

Water heaters



Fluid based mechanical systems including plumbing

Computer cooling systems

DRW can also be used in the transportation industry for frames in motorcycles,

recreational vehicles, bicycles, wheelchairs, and more. It enables quick changes of styles and designs

that benefit from tube

construction, and can be used for the following applications:

Chassis/suspension

Roof frames

Cross-car beams

Exhaust systems

Chassis module assemblies

Three sheet welding

When welding three sheets the configuration becomes more complex because

extra

resistances are introduced. There is one extra sheet with extra bulk resistance

and two extra contact resistances between sheets, with their associated

complications of coatings and contamination. As the distance between theseextra resistances and the water cooled electrodes changes, the point of initial

melting need not be exactly between the two electrodes. If all sheets to be joined are of similar materials then the symmetry in the configuration will lead

to the start of melting in the middle sheet, or on the interfaces between the outer

sheets and the middle sheet. The exact location is dependent upon the distance

to the water cooled electrodes and the thickness of the sheets, as these factors

determine how much heat is conducted away. If the contact resistance between

the sheets is high enough to overcome the shorter distance of the interface

between the sheets to the electrodes compared to the distance between thecentre of the middle sheet and the electrodes, then melting will start at the

interfaces, otherwise melting will start in the centre of the middle sheet. If the

sheets to be joined are of dissimilar materials, as is the usual case, then this

symmetry breaks down and the location of the onset of melting becomes more

complex.The difference in grade introduces three complications:

• differences in strength

• differences in thermal conductivity

• differences in electrical resistivity



Differences in strength will result in the resistance against indentation.

Resistance against indentation translates in differences in true contact area

between electrodes and workpiece.

A soft material will be indented by the electrode more than a hard material. This

will lead to an increase in true contact area, lowering the current density whilstsimultaneously increasing the surface trough which heat can be conducted away

to the electrodes.

Differences in thermal conductivity will lead to differences in the ability of the

materials to accumulate generated heat. The generation of this heat is dependent

on the electrical resistivity of these materials which will differ between different

grades. In general thermal conductivity and electrical resistivity are linked. Thelink between these is not the same for all materials. Especially in advanced high

strength steels, the microstructure of these materials, consisting of multiple

phases, combined with a texture determined by thermomechanical treatment,

the relation between electrical resistivity and thermal conductivity may differ

somewhat from the relation in low carbon steels.Differences in thicknessobviously lead to a breakdown of the symmetry. In the configuration that is the

subject of this case study a thin material is to be joined with



two thicker sheets of materials. Even if the materials would be similar in allother aspects the challenge to create a joint between the thin sheet on the outside

with the middle sheet would be complicated, as the distance between the

interface between these two sheets and the water cooled electrode is so small

that most heat is conducted away, making it hard to accumulate heat. Becausecontact resistance between sheets is generally the highest resistance in aconfiguration, melting generally occurs at the interface between sheets.

Differences in surface conditions, especially coatings, lead to differences in

contact resistance and thus heating conditions.

Resistance welding of thermoplastic composites-an

overview

Introduction

As a result of their growing potential for high performance applications,

continuous fibre reinforced thermoplastic composites (CFRTPCs) are becoming

of greater interest for the industry. Thermoplastics have various advantages like

good toughness, better environmental resistance (high temperature,

moisture,aggressive fluids), shorter processing times, non-flammability and

infinite shelf life Probably Their most important advantage lies in the potential for a low cost, rapid

production. However, due to the limited deformation of the fibre reinforcement,

currently produced thermoplastic components have rather simple geometry,

which implies that for achieving complex structures, joining of the components

is an inevitable process Joining has proved to be a critical step in the process of

manufacturing thermoplastic composite products because it can initiate a

number of irregularities in the structure, which can result in weakening of the properties.

Resistance welding processResistance welding, known also as resistive implant welding, electrical-

resistance fusion or electro-fusion is one of the most attractive welding

techniques for thermoplastics today. It is a rather simple method that useselectrically resistive implant sandwiched between the bonding surfaces of the

laminates to provide the necessary heat to the joint. The principle of the

resistance welding process is schematically shown in the below figure. When

current flows through the heating element, the heat generatet follows the Joule’sLaw, where the energy dissipated from



Fig. Standard welding set up



The resistor is proportional to the resistance, current and elapsed time. When thesupplied energy exceeds the thermal losses in the material and the surroundings,

the temperature of the laminates starts to rise, first in the close vicinity to the

bonding surfaces, and later, if the electrified time allows it, deeper into the

material. It is favourable to keep this so-called heat affected zone (HAZ) asclose to the bonding surface as possible to avoid possible fibre disturbance inthe laminates. When the temperature at the bond line rises to a certain point (Tg

for amorphous or Tm for semi-crystalline polymers), thermoplastic matrix starts

to melt. When nominal melting is achieved, current is switched off and the joint

is allowed to cool while an adequate pressure is maintained. The welding

pressure that has to be applied during the whole welding process enables the

intimate contact between the laminate surfaces and promotes moleculardiffusion in the interface. The heating element remains trapped in the joint.

Resistance welding requires very simple tooling and little or no surface

treatment. The fact that the heating element remains in the weld strongly points

to the possibility of reprocessing if inspection shows flaws or incomplete

bonding.

Surface modification of resistance welding electrodeby electro-spark deposited composite coatings

To improve electrode life during resistance spot welding of Zn-coated steel

sheets, a monolithic TiCP/Ni composite coating was deposited onto the surface

of a Cu – Cr – Zr electrode by an electro-spark deposition process. The coating

was designed as a barrier to prevent electrodes from alloying with the Zn-

coating leading to degradation by pitting or erosion. Some coated electrodes

were also subjected to laser treatment in order to eliminate cracks formed in theas-coated monolithic TiCP/Ni composite coating. In addition, a multi-layer

deposition process has also been proposed to improve the coating quality by

using Ni and TiCP/Ni composite as deposition materials alternately. The

microstructure and mechanical properties of the coatings have been

characterized by scanning electron microscopy,



Advances in the Resistance Welding

Online nugget diameter control system for resistance

spot welding

Introduction Resistance spot welding (RSW) has been widely used in industries where

joining of sheet metal is commonplace such as the automobile industry.However, the process is

Complicated as it involves interactions between electromagnetic, thermal,mechanical, and metallurgical phenomena. The workpieces for welding have

large individual differences, such as surface roughness and/or contamination,

thickness and/or stack-up variation, even in the same batch of workpieces.Hence, real-time control of the resistance spot welding process plays a critical

role in obtaining welds with satisfactory quality. Currently, ensuring weld

quality through process control has been and remains a major challenge and a

worthwhile goal for the modern welding industry. Due to lack of direct

measurements of a weld’s internal information during the welding process, the

quality of the welds cannot be guaranteed. Traditionally, destructive or non-

destructive tests are often employed to obtain information regarding weldsquality. To check the welds quality, these tests are applied on randomly selected

workpieces at the production site. Since the tests are time

Consuming and costly, they can only be done on a sample basis. There is an

increasing demand for a reliable, low-cost, effective technique for predicting

and generating welds of satisfactory quality in real time during the welding

process.

In order to obtain welds of satisfactory quality during actual production, the

mechanism of the RSW process should be analyzed thoroughly and the process

variables and parameters should be accurately monitored. For decades, there has



been an enormous amount of research on RSW in order to precisely obtainonline information about welds quality. Various process variables and

parameters relating to the initial formation and growth of nuggets have been

investigated according to different understanding about the nugget formation

during the welding process. Dynamic resistance and electrode displacement(indentation) are the most

The purpose of this study is to develop an integrated system, which can be used

to control the nugget diameter in real-time operation. The proposed controlsystem is composed of a constant current controller for RSW and an online

nugget diameter estimator. Using the newly developed high resolution real-timedynamic resistance measurement system, the time when the first melting of a

weld occurs can be estimated accurately. With this information and the constantcurrent control strategy, the nugget growth process can be considered as

uniform after the time when the first melting point of the weld appears during

the process. As a result, a mathematical model of the relation between the heatenergy absorbed by the weld and the nugget diameter can be obtained from the

moment the first melting of the weld occurs, while the heat energy absorbed by

the weld starts to be taken into account. Since it is the function of heat energy

absorbed by the weld only, the model is easily realized mathematically. This

model serves as an online nugget diameter estimator. The welding process

ceases once the error between the desired nugget diameter and the estimatednugget diameter is within a given tolerance.



Resistance spot welding of aluminium

The weldability of aluminium alloys used by joining car bodies is very good but

some conditions and rules must be applied. Resistance Spot Welding of

aluminium and its alloys involves applying high power welding guns because

welding current must be 2 – 3 times higher than in case of steel but the welding

time is 1/3 weld time of steel. The main of that is 3 times higher than in case of

steel its thermal and electrical conductivity. It means the electric parameters

(current and voltage) must be controlled more precisely in narrower window of

time. Sometimes the welding guns using for welding steel has not enough

power to ensure required welding current, thus the sources of power are often

designed for resistance spot welding of aluminium.

Electrodes for resistance welding aluminium

An ideal electrode’s material for RSW of aluminium should have high thermaland electrical conductivity and high hardness as well. Moreover it shouldn’ttend to make alloys thus it is very difficult to find a compromise. The pure

electrolytic copper has a conductivity 100% IACS however its hardness is

relativity low (considerably below 100HV) and its tendency to alloying with

aluminium is very high. The main problem connected with electrodes byResistance Spot welding of aluminium and its alloys is relatively short time of

life of electrodes . It can be a crucial problem especially by massive production.

The rapid deterioration of tips surface is the result of high pressure, high

temperature and alloying process during welding. which directly involves

pickup effect, electrode alloying with aluminium, pitting effect and cavitations.

Thus the quality of spot-welds rapidly decreases.

The alloying effect causes increasing resistance of contact tip-sheet. This is thereason the heat is generated in tip-sheet layer, instead sheet-sheet. To ensure the

better contact between electrode and worksheet the lubricants are applied. It wasinvestigated, that some metalworking lubricants extended the electrodes life-

time and directly led to reduction alloying effect and concurrently pitting and

pickup effect. To avoid high costs of electrode’s materials replaceable caps areused and also cleaning after at least 20 spot-welds is required as well. It was

proved, that increasing hardness of electrodes reduces mushrooming of

electrodes. To achieve higher hardness pure copper is alloyed by zirconium,

cadmium, chromium and also dispersion hardened with aluminium oxide is

used. It was investigated that using some special copper alloys especially

alloyed by gold. This way 5 times longer time of life can be achieved.

Resistance Spot Weldingreport

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