MEM05051A Select Welding Processes - Learner Guide

MEM05 Metal and EngineeringTraining Package PL E MEM05051A Select welding processes Learner guide SA M Version 1 Training and Education Support Industry Skills Unit Meadowbank Product Code: 5721 MEM05051A Select welding processes Acknowledgments The TAFE NSW Training and Education Support Industry Skills Unit, Meadowbank would like to acknowledge the support and assistance of the following organisations and people in the production of this learner guide. Capral Aluminium Blue Scope Steel CIGWLED Hardface Technology Harris Product group (Australia) Lincoln Electric Company (Australia) Silverwater Welding Supplies Welding Industries of Australia Western Safety Wear Writer: (Updated from existing TAFE Publications) E Reviewers: Project Manager: Stephen Davies Education Programs Manager TAFE NSW SA M Enquiries PL John Anderson (Hunter Institute) Ed Harkness (Illawarra Institute) Enquiries about this and other publications can be made to: Training and Education Support Industry Skills Unit, Meadowbank Meadowbank TAFE Level 3, Building J, See Street, MEADOWBANK NSW 2114 Tel: 02-9942 3200 Fax: 02-9942 3257 © TAFE NSW (Training and Education Support, Industry Skills Unit Meadowbank) 2012 Copyright of this material is reserved to TAFE NSW Training and Education Support, Industry Skills Unit Meadowbank. Reproduction or transmittal in whole or in part, other than for the purposes of private study or research, and subject to the provisions of the Copyright Act, is prohibited without the written authority of TAFE NSW Training and Education Support, Industry Skills Unit Meadowbank. ISBN 978-1-74236-431-5 © TAFE NSW (Training & Education Support Industry Skills Unit, Meadowbank) 2012 MEM05051A Select welding processes Table of Contents Introduction.................................................................................... 7 1. General introduction.............................................................................. 7 2. Using this learner guide.......................................................................... 7 3. Prior knowledge and experience.............................................................. 9 4. Unit of competency overview.................................................................. 9 Topic 1: Properties of metal.......................................................... 13 Review questions.................................................................................... 16 Topic 2: Carbon steels................................................................... 17 Review questions.................................................................................... 21 E Topic 3: Alloy steels...................................................................... 23 Review questions ................................................................................... 31 PL Topic 4: Non ferrous metals.......................................................... 33 Review questions.................................................................................... 38 Topic 5: Fusion welding processes................................................ 41 SA M Review questions.................................................................................... 48 Topic 6: Pressure welding processes............................................. 53 Review questions.................................................................................... 57 Topic 7: Low temperature welding processes................................ 59 Review questions.................................................................................... 62 Topic 8: Welding safety................................................................. 65 Review questions.................................................................................... 71 Topic 9: Fillet and butt joint terminology....................................... 73 Review questions.................................................................................... 83 Topic 10: Fillet and butt weld defects............................................ 87 Review questions.................................................................................... 91 Topic 11: Distortion control........................................................... 93 Review questions...................................................................................102 Resource Evaluation Form........................................................... 105 © TAFE NSW (Training & Education Support Industry Skills Unit, Meadowbank) 2012 MEM05051A Select welding processes Topic 1: Properties of metal All metals exhibit different properties which make them unique in their own right. A metals properties are important as they influence how they perform in a given industrial environment. Metal properties can be classified as being either physical or mechanical. For example, aluminium is soft, light and has a low melting point whereas carbon steels are harder, heavier and has a much higher melting point. These are typical examples of physical properties of a metal. Due to these differences it is important that metal fabricators have a basic understanding of the properties of metals. A number of common physical and mechanical properties are briefly outlined below. Physical properties Refers to a metals mass per unit volume. For example, steel is heavier than aluminium and therefore has a greater density. Colour: Iron or steel exhibits are silvery colour, copper is red, brass is yellow. The colour of a metal can quickly provide the operator with an idea of the type of material they are dealing with. Thermal expansion: Metals expand when heated. The amount of expansion per degree (°C) rise in temperature is an important measurement and is expressed as the metals co-efficient of thermal expansion. For example, stainless steel will exhibit a greater degree of expansion than carbon steel for the same heat input. SA M PL E Density: Thermal conductivity: Refers to the ease by which heat travels through a metal and how far heat will travel over a given time. Copper and aluminium are excellent thermal conductors whereas stainless steel is a poor conductor. Electrical conductivity: Relates to how easily electricity travels through the metal. Copper and aluminium are excellent conductors of electricity. Steel on the other hand has a much higher resistance and therefore is a poor conductor. Corrosion: Some metals corrode easily, others are more resistant. For example, stainless steels and aluminium are resistance to corrosion whereas steel will rust. Melting point: This is the temperature at which a metal melts. Some metals have a high melting point such as carbon steel (approx 1500°C) while others such as aluminium (approx 660°C) are lower. Magnetism: Ferrous metals (iron based) are magnetic while, almost without exception non-ferrous metals are not. For example carbon steels are attracted to a magnet whereas aluminium, copper and brass are not magnetic. © TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012 Page 13 of 108 MEM05051A Select welding processes Mechanical properties Refers to the ability of a material to be hammered into shape without cracking. Aluminium is extremely malleable whereby cast iron is not. Ductility: Is to the ability of a metal to withstand deformation by bending, rolling and/or folding without cracking. For example, low carbon steel is very ductile, cast irons are not. Yield Strength: This property is the ability of a metal to resist permanent deformation (bending) when a force is applied. When a metal is bent, rolled or pressed it has “yielded” and therefore becomes permanently deformed. Brittleness: Is a weakness in a metal and will crack or break when force is applied. Brittle materials such as cast iron or high carbon, steels are not used for fabrication purposes for this reason. Hardness: Refers to a metal's ability to resist indentation by a given force or load. For example, it is easy to make a “pop mark” on low carbon steels but near impossible to make one on heat treated high carbon steel. Impact strength: This property refers to the amount of energy a metal will absorb due to a sudden blow without cracking or breaking. High impact strength gives a measure of material toughness. A low toughness measure shows the metal to be brittle. For example, low carbon steels resist impact whereas cast iron or high carbon steel are much less resistant. SA M PL E Malleability: Fatigue strength: This refers to a metal’s ability to resist breaking or cracking when subjected to stressful load cycles. A load cycle can be described as forcing a metal in one direction and then in the opposite direction. Weldability: Refers to the ease by which a metal can be welded. For example, low carbon steels are easily welded and therefore have good weldability. A hardened material such as high carbon steel has poor weldability and will crack unless special precautions are taken. Page 14 of 108 ©TAFE NSW(Training&EducationSupport,IndustrySkillsUnitMeadowbank)2012 PL E MEM05051A Select welding processes SA M Weld bend test of determine ductility © TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012 Page 15 of 108 MEM05051A Select welding processes Review questions These questions have been included to help you revise what you have learnt in Topic 1: Properties of metal. 1. List six (6) physical properties of a metal. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ E _______________________________________________________________ PL 2. List six (6) mechanical metal properties of a metal. _______________________________________________________________ _______________________________________________________________ SA M _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 3. What mechanical property is used to describe a metals ability to withstand deformation by hammering, rolling or bending without fracturing? _______________________________________________________________ 4. Name the property of a metal that resists stretching or pulling apart when subjected to stress by two opposing forces. _______________________________________________________________ 5. What is meant by the term "weldability”. _______________________________________________________________ 6. What property is used to determine a metals density or weight? _______________________________________________________________ Page 16 of 108 ©TAFE NSW(Training&EducationSupport,IndustrySkillsUnitMeadowbank)2012 MEM05051A Select welding processes Topic 2: Carbon steels Introduction Metals are produced from mined materials called an ore. Some metals are used in their pure form however; most have other elements added to them to form an alloy. Alloying elements are normally added to pure metals to improve their physical and mechanical properties and industrial applications. Steels are produced by extracting the iron from the ore by a process called steelmaking which involves placing iron ore into a heated blast furnace to separate the iron (Fe) content from the impurities in the ore. E Once the iron content is extracted it is further processed and refined in a basic oxygen steelmaking furnace (BOS). The BOS stage of steel production is a very important one as it removes excess carbon and other impurities in the material. Once this stage is complete the steel is formed into the desired shape by rolling which also improves the strength and toughness of the material. Steel is the most common metal used in fabrication and allied engineering industries and is commercially available in sheet, coil, plate, tube, pipe and structural sections. Lower it's melting point Increase tensile strength of the steel (within limits) Lower ductility Increase hardness and brittleness Increase the capacity of the steel to harden through heat treatment Reduce weldability. SA M • • • • • • PL Small amounts of manganese, silicon and carbon remain in the processed steel to give it strength and toughness. Carbon in steel is very important as the metal depends on its carbon content to give it specific properties. The effect of retaining measured amounts of carbon will have a direct effect on its properties. For example, the effects of increasing the carbon content in plain steel will: Types of carbon steel Carbon steels can be divided into three (3) main groups. The groups are influenced by the percentage (%) range of carbon they contain. The three groups are classified as: 1. Low carbon steels. 2. Medium carbon steels 3. High carbon steels. Low carbon steel Low carbon steels have carbon content of ranging from 0.01% and 0.30%. Steels with a carbon content of 0.15% or less, are soft and ductile. Steel containing 0.23% to 0.27% carbon is used where greater strength is needed. © TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012 Page 17 of 108 MEM05051A Select welding processes Applications Low carbon steels are ductile and readily welded materials. For these reasons they are widely used for: • • • • • Deep drawing and deep pressing applications. Sheet, plate and rolled sections (angle, beam, columns). Car and truck bodies. Sheetmetal cabinets and assemblies. Ship building. Medium carbon steel Medium carbon steels have a carbon content ranging from 0.3% to 0.5%. These steels will harden if allowed to cool too quickly. Special precautions are needed if they need to be welded to slow the cooling rate and reduce hardening. The increased carbon content can cause hard and brittle areas to form in the weld joint. E Applications Steel rails - railways, tramways and overhead crane tracks Hand tools such as cold chisels Machine parts Agricultural equipment parts. SA M • • • • PL Medium carbon steels contain higher carbon contents than low carbon steels. As a result they are more susceptible to hardening and cracking due to rapid cooling. Medium carbon steels have higher strengths and are much stronger than low carbon steels and therefore require careful attention when they need to be welded to avoid cracking or excessive hardness forming in the weld zone. Typical applications for this group of steels include: High carbon steel High carbon steels have a carbon content ranging from 0.5% to 1.2%. If they are heated special precautions need to be observed to prevent these steels becoming extremely hard and brittle. High carbon steels are not normally welded (except for repair purposes) as they are often used for wear-resistant parts, and for the manufacture of some cutting tools. Applications • • • • • • Cutting tools Springs Carbon steel cutting edges Wire cables Dredging equipment Files. Page 18 of 108 ©TAFE NSW(Training&EducationSupport,IndustrySkillsUnitMeadowbank)2012 MEM05051A Select welding processes Additional Elements in Carbon Steel Carbon steels contain additional elements other than iron and carbon. Some elements have been deliberately added to the steel to improve its properties while others are considered impurities that cannot be completely removed during the steelmaking process. The level of impurities must be strictly controlled otherwise the required properties of the steel will be severely compromised. The effects of various elements in steel are as follows: Manganese - Produces a hardening effect - Helps produce a fine grain structure - Acts as a mild deoxidiser or “scavenger” against the harmful effects of sulphur. In most carbon steels the manganese content is kept within 0.3% to 0.8%. - Acts as a deoxidising agent or scavenging agent. Normally silicon in carbon steels is kept to within 0.1% to 0.35%. Sulphur - - Considered an impurity in steels and kept to a maximum of 0.05%. Excessive amounts of sulphur combines with iron to form a harmful compound called iron sulphide which can cause a condition called "hot-short", cracking at elevated temperatures. PL E Silicon SA M Phosphorus - Considered an impurity in steels and kept to a maximum of 0.05%. Excessive amounts of phosphorus combines with iron to form a harmful compound called iron phosphide which can cause an undesirable condition called "cold-short”, cracking at normal working temperatures. Surface treatments for steel Plain carbon steels readily oxidise (rust) when exposed to the atmosphere therefore exposed surfaces must be protected from corrosion. Common methods used to protect steel structures from corrosion include: • • • • • Painting Powder coating Galvanizing (zinc) Mill scale Sheetmetal is supplied with factory painted “Colorbond” or with a sacrificial metal coating of zinc based galvanised or zincalume coating. Galvanised zinc surface Coil of zincalume © TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012 Page 19 of 108 E MEM05051A Select welding processes SA M PL Mining iron ore Hot rolling steel Page 20 of 108 ©TAFE NSW(Training&EducationSupport,IndustrySkillsUnitMeadowbank)2012 MEM05051A Select welding processes Review questions These questions have been included to help you revise what you have learnt in Topic 2: Carbon steels. 1. List four (4) properties affected by increasing the carbon content in steel. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ E 2. State the carbon range (%)for the following: Low carbon steels:________________________________________________ PL Medium carbon steels:_____________________________________________ High carbon steels:_______________________________________________ 3. Give two (2) typical industrial applications for each of the following: SA M Low carbon steels: _______________________________________________________________ _______________________________________________________________ Medium carbon steels: _______________________________________________________________ _______________________________________________________________ High carbon steels: _______________________________________________________________ _______________________________________________________________ 4. Briefly explain the effect of having too much sulphur in steel. _______________________________________________________________ _______________________________________________________________ © TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012 Page 21 of 108 MEM05051A Select welding processes 5. List three (3) methods used to protect steel surfaces from corrosion. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ True/False questions (circle the correct response) 6. An excessive amount of phosphorus in carbon steel can cause hot cracking at normal operating temperatures. True False 7. Small amounts of silicon is added to steel as a deoxidiser. True False E True PL 8. Manganese is added to steel to improve and refine the grain structure. False SA M 9. The sulphur content in most carbon steels is kept within 0.1% to 0.8%. True False 10. Medium carbon steels are heat treatable and will harden if allowed to cool too quickly. True False 11. Increasing the carbon content in steel increases ductility. True Page 22 of 108 False ©TAFE NSW(Training&EducationSupport,IndustrySkillsUnitMeadowbank)2012