Designing And Construction Of An Electric AC Arc Welding Machine.

                                                                    ABSTRACT
This project is titled the designing and construction of an electric A.C arc welding machine. Electric Arc Welding Machine of 220/240 Volts and output voltage of 100volts. A core type step-down transformer and choke are essential as the voltage or the arc is usually between 50 and 100volts. The choke is necessary to displace the phase relationship of the voltage and current so that the heat of the arc may be maintained by ensuring that zero points of current and voltage are as far apart as possible. This welding machine is able to deliver a current 15Amps at voltage of 220 volts, the transformer is mounted on a rectangular metal frame and its enclosed by a case which has opening at a regular internal order to provide air for the cooling of the transformer. A double insulation technique is employed for better protection from electric shock and short circuit in the machine or when working in moist environment. An all-purpose electrode holder is connected across one or the output terminal of the transformer so that various size of electrode can be held properly. After the transformer had been constructed, the primary terminals were connected to source of supply. Then the secondary terminal was connected to the welding circuit, as a source of supply, with the aid of welding cable, by which one of the terminal was \connected to the ground clamp and the other to the electrode holder. A.C. Electric Arc Welding Machine uses alternating (AC) current, and consumable or non-consumable electrodes. The welding region is usually protected by some type of shielding gas, vapor, and/or slag.

The aim of this work is to design and construct an electric welding arc that can be used to weld metals.

 TABLE OF CONTENTS

Cover Page

Title Page

Approval Page

Dedication

Acknowledgment

Abstract

Table of Contents

 CHAPTER ONE

1.0      Introduction

1.1      Background of the project

1.2      Aim/objective of the project

1.3      Significance of the project

1.4      Scope of the project

1.5      Limitation of the project

1.6      types of electric arc welding

1.7      other welding processes

CHAPTER TWO

2.0      Literature Review

• Historical background of the project
• Transformer design
• Review of types of arc welding electrode methods:
• Review Of Welding Equipment
• Factors Affect Weld Quality

CHAPTER THREE

3.0      construction methodology

• Block diagram
• Basic principle of arc welding machine
• Theory And Design Of Welding Transformers
• System operation
• Design calculation
• Cost analysis

CHAPTER FOUR

4.0      Result analysis

• Construction procedure
• Casing and packaging
• Assembling section
• System testing
• Design precaution

 CHAPTER FIVE

• Conclusion and Recommendation
  • Conclusion
  • Recommendation
  • References

 CHAPTER ONE

1.0                                                        INTRODUCTION

An Arc welding machine is a type of welding machine that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. The arc welding is a fusion welding process in which the welding heat is obtained from an electric arc struck between the work(or base metal) and an electrode. The temperature of the heat produced by the electric arc is of the order of 6000°C to 7000°C.

They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is usually protected by some type of shielding gas, vapor, or slag. Arc welding processes may be manual, semi-automatic, or fully automated. First developed in the late part of the 19th century, arc welding became commercially important in shipbuilding during the Second World War. Today it remains an important process for the fabrication of steel structures and vehicles.

Arc welding machine has Main cable that receives energy from the source (Usually 3 phase 220 or 440 Volts AC), the starter or switch, the transformer, the controls of tension (Voltage) and current (Amps-or-Amperage), the two secondary wires: one is to ground the machine to the building + structure + part that you are to weld, the other is to put your electrode and produce the welding

The direction of current used in arc welding also plays an important role in welding. Consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. In welding, the positively charged anode will have a greater heat concentration and, as a result, changing the polarity of the electrode has an impact on weld properties. If the electrode is positively charged, it will melt more quickly, increasing weld penetration and welding speed. Alternatively, a negatively charged electrode results in more shallow welds. Non-consumable electrode processes, such as gas tungsten arc welding, can use either type of direct current (DC), as well as alternating current (AC). With direct current however, because the electrode only creates the arc and does not provide filler material, a positively charged electrode causes shallow welds, while a negatively charged electrode makes deeper welds. Alternating current rapidly moves between these two, resulting in medium-penetration welds. One disadvantage of AC, the fact that the arc must be re-ignited after every zero crossing, has been addressed with the invention of special power units that produce a square wave pattern instead of the normal sine wave, eliminating low-voltage time after the zero crossings and minimizing the effects of the problem.

• AIM AND OBJECTIVE OF THE PROJECT

The aim of this work is to design and construct an electric arc machine that can be used to weld irons. To design and construct an electric machine that will create an electric arc between an electrode and the base material to melt the metals at the welding point.

The objective of this work is:

• At the end of the work an electric arc welding is been built with a power source of 240 VAC with 11 a.c output taps ranging from 140VAC to 240VAC which are used to step the arc voltage and current to the required level.

• SIGNIFICANCE OF THE STUDY

AC Arc Welding Transformers are extensively used today in machine building & general purpose maintenance and fabrication work. Light medium and heavy structural work as a Power Source. These are also used as power source for gas shield and welding with tungsten electrode (TIG) for the welding of Aluminum & Aluminum Alloys.

1.3                                           LIMITATION OF THE PROJECT

1) Higher initial setup cost

2) Atmosphere surrounding the welding process has to be stable (hence the shielding gasses), therefore this process is limited to draught free conditions

3) Higher maintenance costs due to extra electronic components

4) The setting of plant variables requires a high skill level

5) Less efficient where high duty cycle requirements are necessary

6) Radiation effects are more severe

• TYPES OF ELECTRIC ARC WELDING

Arc welding can be  direct current (D.C) or alternating current (A.C) arc welding, but the types of arc welding depending upon the type of electrode:

(A): Unshielded arc welding:

When a large electrode or filler rod is used for welding, it is said to be un- shielded arc welding.

(B): Shielded arc welding:

When the welding rods coated with fluxing material are used, then it is called shielded arc welding.

1.4                                                    OTHER WELDING PROCESSES

The following are the various welding processes commonly used in engineering practice.

1: Carbon arc welding

In carbon arc welding, the welding heat is obtained from an electric arc between a carbon electrode and the work. In welding heavy plants, the additional metal is deposited in the weld from a filler rod.

2: Metal arc welding

In metal arc welding, the arc is produced between the metal electrode(also called filler rod) and the work piece. During the welding process, the metal electrode is melted by the heat of the arc and fused with the work piece. The temperature produced by the heat is about 2400° C to 2700° C.

3: Metallic inert gas (MIG) Arc welding:

In MIG welding , the electrode is consumable, the filler metal is deposited by the arc which is completely surrounded by an inert gas.

4: Tungsten inert gas (TIG) arc welding

In TIG welding, the heat is produced from an arc between the non consumable tungsten electrode and the work piece. The welding zone is shielded by an atmosphere of inert gas (such as helium or argon) supplied from a suitable source. The direct current with a straight polarity is used for welding copper alloys and stainless steel. Whereas the reversed polarity is used for magnesium. The alternating current is more versatile in welding for steel, cast iron, aluminum and magnesium.

5: Atomic hydrogen welding

In atomic hydrogen welding, the arc is obtained between two tungsten  electrodes (non consumable) while a stream of hydrogen passes by the arc and envelopes the welding zone.

6: Stud arc welding

It is a direct current arc welding process, and is used for welding metal studs to the flat metal surfaces.

7: Submerged arc welding

In submerged welding, the arc is produced between a bare metal electrode and the work piece. The submerged arc welding is mostly done on low carbon and alloy steels, but it may be used on many of the non-ferrous metals.

8: Thermit welding

In this welding, a mixture of iron oxide and aluminum known as thermit, is used. The mixture is ignited only at a temperature of about 1500°C. A major advantage of the thermit welding is that all parts of the weld section are molten at the same time and the weld cools almost uniformly. This results in a minimum problem with internal residual stresses. The thermit welding is often used in joining iron and steel parts that are too large to be manufactured, such as rails, trucks frames, locomotive frames, other large sections used on steam and rail roads, for stern frames, rubber frames etc. In steel mills, Thermit electric welding is employed to replace broken gear teeth, to weld new necks on rolls and pinions and to repair broken shears.