Design And Construction Of A 5KVA Electric AC Arc Welding Machine.

ABSTRACT
This project is titled the designing and construction of A 5KVA 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 a 5kva electric welding arc that can be used to weld metals.

TABLE OF CONTENT

Title Page

Approval Page

Dedication

Acknowledgement

Abstract

Table of Content

CHAPTER ONE

1.0     Introduction

1.1     Objective of the project

1.2     significance of the project

1.3     problem and limitation of the project

1.4     scope of the project

1.5     application of  the project

1.7     Types Of Arc Welding Electrodes

1.8     welding equipment

1.9     Types Of Arc Welding Processes

1.10    Safety Issues Of Arc Welding

CHAPTER TWO

2.0     Literature review

2.1 Review of History of electric arc welding

2.2   Historical Development of Welding

2.3   Review of Different Types Of Arc Welding Electrode

2.3.1 Electrode Identification

2.3.2 Electrodes and Currents Used

2.3.3 Current Types

2.3.4 Electrode Size and Amps Used

CHAPTER THREE

3.0 Methodology

3.1   Basic Principles of Arc Welding

3.2 theory and design of welding transformers

3.3 Ac Welding Power from Transformer

3.4 Specifications and Features of Winding Transformer

3.5 Concept of Electric Arc Welding

3.6 How Electric Arc Welding Works

3.7

construction of an electric arc machine

CHAPTER FOUR

RESULT ANALYSIS

4.0     Construction Procedure and Testing

4.2   General Precautions

4.3      Cost Analysis

CHAPTER FIVE

5.1 Conclusion

5.2 Recommendation

5.3 References

CHAPTER ONE

1.0                                                        INTRODUCTION

Arc welding is a type of welding 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. They can use either 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.

To supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common classification is constant current power supplies and constant voltage power supplies. In arc welding, the voltage is directly related to the length of the arc, and the current is related to the amount of heat input. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding. In these processes, arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. For example, if the wire and the base material get too close, the current will rapidly increase, which in turn causes the heat to increase and the tip of the wire to melt, returning it to its original separation distance.

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.

Duty cycle is a welding equipment specification which defines the number of minutes, within a 10 minute period, during which a given arc welder can safely be used. For example, an 80 A welder with a 60% duty cycle must be “rested” for at least 4 minutes after 6 minutes of continuous welding.^[5] Failure to observe duty cycle limitations could damage the welder. Commercial- or professional-grade welders typically have a 100% duty cycle.

• OBJECTIVE OF THE PROJECT

The objective of this work is to design and construct an electric arc machine that can be used to weld irons.

1.2               SIGNIFICANCE OF THE PROJECT

There are a number of advantages to using arc welding compared with many other formats:

• Cost –arc welding machine is a well-priced and affordable, and the process often requires less equipment in the first place because of the lack of gas
• Portability – this machine is very easy to transport
• Works on dirty metal
• Shielding gas isn’t necessary – processes can be completed during wind or rain, and spatter isn’t a major concern
• Welding joints have the strength equal to parent metal.
• Welding is economical process compared to riveting or bolting.
• Welded joints are comparatively lighter in construction .
• Repare & modifications of welded joints is easy .
• Surface finish of welded joint is better.
• Entire welding process can be automated, which makes the process highly productive & reliable.

1.3  PROBLEM ANA LIMITATION OF THE PROJECT

There are a few reasons why some people look to other options beyond arc welding for certain kinds of projects. These downsides can include:

• Lower efficiency – more waste is generally produced during arc welding than many other types, which can increase project costs in some cases
• High skill level – operators of arc welding projects need a high level of skill and training, and not all professionals have this
• Thin materials – it can be tough to use arc welding on certain thin metals

1.4                                                SCOPE OF THE PROJECT

It is a type of welding 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. This used alternating (AC) current, and consumable or non-consumable electrodes.

1.5                                         APPLICATION OF THE PROJECT

Arc welding offer many benefits in numerous industries which is as follows:

Construction
Welding processes are a foundational aspect of all large-construction industries, ensuring strong, sustainable connections within buildings, bridges and other infrastructures.

Mechanical
For more rugged applications that involve thicker metal dimensions, arc welding provides the control and effectiveness necessary to firmly bond heavier pieces together. In the automotive industry, arc welds bond heat shields, exhaust systems and hydraulic lines to the chassis. Metal furniture pieces like office desks, file cabinets and shelving units are often welded. Heating, ventilation and air conditioning units are usually constructed using welding processes.

Shipbuilding
Welding has been the traditional shipbuilding construction method used since the advent of the Industrial Age. Ensuring a water-tight surface is essential. Inside the ship, welding processes secure hatches, fluid lines, control panels and many other components critical to a safe and seaworthy vessel.

Equipment
Most, if not all, of today’s industries rely on properly functioning equipment, and welding processes are vital to the success of those machines.

Farm equipment
In agriculture, farm machines that plow, plant, seed and harvest are fundamental to the country’s food supply. Those machines are welded throughout their frames and processes. On the chassis, the cab frame, fenders and brackets are formed by welds. Motor structure and electrical functions are fused, as are the features of specialized tools such as threshers and spreaders.

Lawn and garden

Lawn mowers, trimmers, power saws and other garden equipment have long lives due to the strength of their welded frames. Other metal garden features enhance the enjoyment of outdoor life, such as barbecue grills, enclosures, seating and watering systems.

Highway equipment

Maintenance of safe and passable roads also depends on secure welds. Manhole cover plates and the sewer and utility systems that frequently run under roads are also usually constructed with welding processes.

Institutional equipment

Hospitals, medical facilities, schools and homes all rely on well-functioning appliances to keep food warm or cold, run accurate testing operations and clean clothing or dishes. Virtually every appliance in use today was constructed at least in part with a welding process.

1.6                         TYPES OF ARC WELDING ELECTRODES:

Based on their characteristics, arc welding electrodes can be broadly classified into two types. They are:

1. Consumable electrode
2. Non-consumable Electrode

Consumable Electrode:

If the melting point of an arc welding electrode is less, it melts and fills the gap in the workpiece. Such an electrode is called consumable electrode.

In arc welding, to produce deep weld, consumable electrode is connected to the positive terminal of the power supply (i.e., it is made as anode) while workpiece is connected to the negative terminal of the power supply (i.e., it is made cathode).

This is because, heat concentration is always higher in the anode than in cathode. When consumable electrode is made as anode, it melts faster and easily fills the gap in the workpiece.

Consumable electrodes are usually coated with a flux material. This is done to protect the arc and the weld from the external atmosphere.

Metal inert gas welding is an arc welding technique that uses a consumable electrode.

Non-consumable electrode:

If the melting point of the arc welding electrode is high, it does not melt to fill the gap in the workpiece. Such an electrode is called non-consumable electrode.

If a non-consumable electrode is used, either the workpiece should have a low melting point or filler metal with low melting point should be used, to fill the gap in the workpiece.

As non-consumable electrodes do not melt, heat concentration should be high in the workpiece. Hence, in non-consumable electrode processes, to produce deep weld, the electrode is made cathode and workpiece is made anode.

Tungsten is a non-consumable electrode whose melting point is 3422 °C. It is used in tungsten inert gas welding.

1.7                               WELDING EQUIPMENT

All kinds of arc welding are carried out by means of electric current supplied from the mains to the welding machine. This is an alternating current commonly of 230V. The welding machine is often referred to as a transformer or a rectifier depending on the current that it supplies for the welding process. If the current is direct current – dc -, the welding machines is referred to as a rectifier because it changes – rectifies – the alternating current from the mains into direct current.

This voltage level of the current taken from the mains is dangerous in case the welder touches the uninsulated parts of the electric wires. As a safety measure, regulations state that for manual arc welding the voltage level should be less than 80V ac or 100V dc. This voltage level is commonly called ‘the open circuit voltage’ or ‘the no load voltage’. Welders use the abbreviation OCV for ‘open circuit voltage’. This voltage level is not the same as the voltage level that’s used during welding. The latter voltage ranges between 20 and 25 volts for most types of electrodes. Most welding machines are able to step down and rectify the current to different levels, and they are equipped with switches and dials for this purpose.

1.7                                  TYPES OF ARC WELDING PROCESSES

The term ‘arc welding’ covers a large number of welding processes. What they have in common is the fact that they all use electric current to melt the filler metal and the parent metals.

The term ‘arc welding’ is commonly used only about manual arc welding with a coated electrode. That’s why the process is called ‘Manual Metal Arc welding’ – (MMA).
When referring to other arc welding processes, welders use other terms, such as TIG, MIG or CO₂ welding, for example. In these processes a gas is used to shield – to protect – the weld pool, and that’s why these processes are often referred to as ‘gas-shielded processes’. Gas-shielded arc welding can also be carried out manually, but it is more widely used for automatic or semi-automatic processes.

CONSUMABLE ELECTRODE METHODS

Shielded Metal Arc Welding

One of the most common types of arc welding is shielded metal arc welding (SMAW), which is also known as manual metal arc welding (MMAW) or stick welding. An electric current is used to strike an arc between the base material and a consumable electrode rod or stick. The electrode rod is made of a material that is compatible with the base material being welded and is covered with a flux that gives off vapors that serve as a shielding gas and provide a layer of slag, both of which protect the weld area from atmospheric contamination. The electrode core itself acts as filler material, making a separate filler unnecessary. The process is very versatile, requiring little operator training and inexpensive equipment. However, weld times are rather slow, since the consumable electrodes must be frequently replaced and because slag, the residue from the flux, must be chipped away after welding. Furthermore, the process is generally limited to welding ferrous materials, though specialty electrodes have made possible the welding of cast iron, nickel, aluminium, copper and other metals. The versatility of the method makes it popular in a number of applications including repair work and construction.

Gas Metal Arc Welding (GMAW)

Gas metal arc welding (GMAW), commonly called MIG (for metal/inert-gas), is a semi-automatic or automatic welding process with a continuously fed consumable wire acting as both electrode and filler metal, along with an inert or semi-inert shielding gas flowed around the wire to protect the weld site from contamination. Constant voltage, direct current power source is most commonly used with GMAW, but constant current alternating current are used as well. With continuously fed filler electrodes, GMAW offers relatively high welding speeds, however the more complicated equipment reduces convenience and versatility in comparison to the SMAW process. Originally developed for welding aluminium and other non-ferrous materials in the 1940s, GMAW was soon economically applied to steels. Today, GMAW is commonly used in industries such as the automobile industry for its quality, versatility and speed. Because of the need to maintain a stable shroud of shielding gas around the weld site, it can be problematic to use the GMAW process in areas of high air movement such as outdoors.

Flux-Cored Arc Welding (FCAW)

Flux-cored arc welding (FCAW) is a variation of the GMAW technique. FCAW wire is actually a fine metal tube filled with powdered flux materials. An externally supplied shielding gas is sometimes used, but often the flux itself is relied upon to generate the necessary protection from the atmosphere. The process is widely used in construction because of its high welding speed and portability.

Submerged Arc Welding (SAW)

Submerged arc welding (SAW) is a high-productivity welding process in which the arc is struck beneath a covering layer of granular flux. This increases arc quality, since contaminants in the atmosphere are blocked by the flux. The slag that forms on the weld generally comes off by itself and, combined with the use of a continuous wire feed, the weld deposition rate is high. Working conditions are much improved over other arc welding processes since the flux hides the arc and no smoke is produced. The process is commonly used in industry, especially for large products. As the arc is not visible, it is typically automated. SAW is only possible in the 1F (flat fillet), 2F (horizontal fillet), and 1G (flat groove) positions.

NON-CONSUMABLE ELECTRODE METHODS

Gas tungsten arc welding (GTAW), or tungsten/inert-gas (TIG) welding, is a manual welding process that uses a non-consumable electrode made of tungsten, an inert or semi-inert gas mixture, and a separate filler material. Especially useful for welding thin materials, this method is characterized by a stable arc and high quality welds, but it requires significant operator skill and can only be accomplished at relatively low speeds. It can be used on nearly all weldable metals, though it is most often applied to stainless steel and light metals. It is often used when quality welds are extremely important, such as in bicycle, aircraft and naval applications. A related process, plasma arc welding, also uses a tungsten electrode but uses plasma gas to make the arc. The arc is more concentrated than the GTAW arc, making transverse control more critical and thus generally restricting the technique to a mechanized process. Because of its stable current, the method can be used on a wider range of material thicknesses than can the GTAW process and is much faster. It can be applied to all of the same materials as GTAW except magnesium; automated welding of stainless steel is one important application of the process. A variation of the process is plasma cutting, an efficient steel cutting process.

Other arc welding processes include atomic hydrogen welding, carbon arc welding, electroslag welding, electrogas welding, and stud arc welding.

1.9                        SAFETY ISSUES OF ARC WELDING

Welding can be a dangerous and unhealthy practice without the proper precautions; however, with the use of new technology and proper protection the risks of injury or death associated with welding can be greatly reduced.

Heat and sparks

Because many common welding procedures involve an open electric arc or flame, the risk of burns from heat and sparks is significant. To prevent them, welders wear protective clothing in the form of heavy leather gloves and protective long sleeve jackets to avoid exposure to extreme heat, flames, and sparks.

Eye damage

Auto darkening welding hood with 90×110 mm cartridge and 3.78×1.85 in viewing area

Exposure to the brightness of the weld area leads to a condition called arc eye in which ultraviolet light causes inflammation of the cornea and can burn the retinas of the eyes. Welding goggles and helmets with dark face plates – much darker than those in sunglasses or oxy-fuel goggles – are worn to prevent this exposure. In recent years, new helmet models have been produced featuring a face plate that automatically self-darkens electronically. To protect bystanders, transparent welding curtains often surround the welding area. These curtains, made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc.

Inhaled matter

Welders are also often exposed to dangerous gases and particulate matter. Processes like flux-cored arc welding and shielded metal arc welding produce smoke containing particles of various types of oxides. The size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger. Additionally, many processes produce various gases (most commonly carbon dioxide and ozone, but others as well) that can prove dangerous if ventilation is inadequate. The use of compressed gases and flames in many welding processes also pose an explosion and fire risk; some common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.