Joining Technologies Lecture 1 PDF

Joining Technologies 2024-2025 Lecture #1 Introduction to Joining Oxyfuel Gas Welding (OFW) Rúben Santos What does joining mean? “Joining is the act or process of putting or bringing things together to make them continuous or...

Joining Technologies 2024-2025 Lecture #1 Introduction to Joining Oxyfuel Gas Welding (OFW) Rúben Santos What does joining mean? “Joining is the act or process of putting or bringing things together to make them continuous or to form a unit.” – in Joining of Materials and Structures by Robert W. Messler Lecture #1 – Introduction to Joining 2/30 What is the purpose of joining? “An assembly is a collection of manufactured parts, brought together by joining to perform one or more than one primary function.” – in Joining of Materials and Structures by Robert W. Messler Lecture #1 – Introduction to Joining 3/30 Joining purposes classification TYPES OF PURPOSES STRUCTURAL MECHANIC ELECTRIC AESTHETIC Bear loads/stress Transmit/allow Transmit electrical Surface coatings movement signals Buildings Bridges Engines/motors Integrated circuitry Laminate coatings Dams Gear wheels Printed circuitry Wallpaper Vehicle frames Actuators Motors Aircraft fuselage Generators Transformers Lecture #1 – Introduction to Joining 4/30 Objetives of joining I. Functionality ✓ Transfer/bear loads in static or dynamic structures; ✓ Achieve a complexity unattained by primary manufacture processes; ✓ Achieve a function only performed by combination of materials; ✓ Allow strutcure portability and/or disassembly; II. Manufacturability ✓ Achieve structural efficiency by adding materials and/or details; ✓ Overcome manufacture limitations posed by primary manufacture processes; ✓ Allow construction of parts and/or details elsewhere; Lecture #1 – Introduction to Joining 5/30 Objetives of joining III. Cost ✓ Make available a wider range of materials for a certain application; ✓ Improve raw materials consumption and usage; ✓ Achieve compromises in production costs; ✓ Allow maintenance, repair and/or replacement of parts/components; IV. Decorative ✓ Allow the use of decorative/appealing coatings/covers; ✓ Allow the manufacture of complex and visually attractive shapes; Lecture #1 – Introduction to Joining 6/30 Joining nature classification JOINING NATURE CHEMICAL PHYSICAL MECHANICAL Adhesives/glue Welding Screwing Cements Brazing Riveting Clamping Lecture #1 – Introduction to Joining 7/30 Welding “Welding is a process in which materials of the same basic type or class are joined together through the formation of primary atomic or molecular level bonds under the combined action of heat and pressure.” – in Joining of Materials and Structures by Robert W. Messler Lecture #1 – Introduction to Joining 8/30 Welding 1. Two or more entities become one. 2. Welding does not apply only to metals. 3. Welding results from application of heat and/or pressure. 4. Filler materials of the same type may or may not be necessary. 5. Welding brings components together by joining materials. Lecture #1 – Introduction to Joining 9/30 Welding PRESSURE ASSISTED WITHOUT PRESSURE WITHOUT WITH WITH FILLER AUTOGENOUS MELTING MELTING MATERIALS (without filler materials) HOMOGENEOUS (Similar chemical composition) HETEROGENEOUS (Different chemical composition) Lecture #1 – Introduction to Joining 10/30 Welding – heat sources classification CHEMICAL ELECTRICAL MECHANICAL Gas welding Arc welding Friction welding Aluminothermic Resistence welding welding Beam welding Lecture #1 – Introduction to Joining 11/30 Welding - pros and cons ADVANTAGES LIMITATIONS ✓ Joints with structural integrtity that do  Impossible to dismantle without not fall apart accidentaly; material destruction; ✓ Wide range of processes;  Heat can damage base materials characteristics and/or properties; ✓ Applicable to a wide range of materials;  Non-uniform heat distribution can ✓ Manual and automatic operation; generate residual stresses; ✓ Portability;  Required skilled operation; ✓ Watertight joints;  High costs in some cases; ✓ Fair costs in most cases.  High initial investment for some processes. Lecture #1 – Introduction to Joining 12/30 Typical strutcure of a welded joint Melting-assisted processes (without pressure) Pressure-assisted processes (without melting) Lecture #1 – Introduction to Joining 13/30  Oxyfuel Gas Welding (OFW) Lecture #1 – Oxyfuel Gas Welding (OFW) 14/30  NP EN ISO 4063:2015 Oxyfuel gas wedling (OFW) - nomenclature AWS A3.0:2010 Oxyfuel gas welding Portuguesa/Europeia PT EN ISO 4063:2015 31 Americana AWS A3.0:2010 OFW Oxyacetylene welding Portuguesa/Europeia PT EN ISO 4063:2015 311 Americana AWS A3.0:2010 OAW Oxypropane welding Portuguesa/Europeia PT EN ISO 4063:2015 312 Lecture #1 – Oxyfuel Gas Welding (OFW) 15/30 Working principle Lecture #1 – Oxyfuel Gas Welding (OFW) 16/30 Combustible gases Flame Heating Gas ΔHº temperature power Flamability limits (%) Reaction (kJ/mol) (ºC) (W/cm2) Lower Upper Acetylene 3030 45 1301 2,5 80 C2H2 + 1,1 O2 3087 Propane 2830 11 2219 2,1 12,5 C3H8 + 3,5 O2 2526 Butane 2830 ― 2878 1,8 8,4 C4H10 + 4,5 O2 Natural gas 2730 13 891 5,0 15 CH4 + 1,5 O2 2538 Hydrogen 2480 14 286 4,0 74,2 H2 + 0,25 O2 2660 Lecture #1 – Oxyfuel Gas Welding (OFW) 17/30 Combustible gases - acetylene Oxyfuel gas welding comprises any welding process that uses heat generated by the combustion of a fuel gas with oxygen. The most widely used fuel in OFW is acetylene due to its high flame temperature, giving the name to the process: oxyacetylene welding (OAW). Base and filler material melting in OAW is achieved by the heat generated in two combustion fases. Fase 1 (19 MJ/m3) 𝑪𝟐 𝑯𝟐 + 𝑶𝟐 → 𝟐𝑪𝑶 + 𝑯𝟐 Fase 2 (36 MJ/m3) 𝟐𝑪𝑶 + 𝑯𝟐 + 𝟏, 𝟓 𝑶𝟐 → 𝟐𝑪𝑶𝟐 + 𝑯𝟐 𝑶 Lecture #1 – Oxyfuel Gas Welding (OFW) 18/30 Types of flame Acetylene combustion in air Acetylene combustion in air (without bottled oxygen supply) generates a yellow, low temperature flame, characterised by incomplete combustion and soot formation. Envelope Inner cone Neutral flame 𝑉 𝑜𝑥𝑖𝑔é𝑛𝑖𝑜 A neutral flame appears when the volume ration 𝑎 = allow a complete 𝑉 𝑎𝑐𝑒𝑡𝑖𝑙𝑒𝑛𝑜 combustion in the first fase, when 𝑎 = 1. Lecture #1 – Oxyfuel Gas Welding (OFW) 19/30 Tipos de chama Acetylene feather Reducing flame A reducing flame forms when there is excess of acetylene in the first combustion fase. It is adequate to remove oxide layers on base materials, such as aluminium, magnesium, and and prevent their oxidation during weldind, and also to prevent decarburisation in steels. 𝑎 < 1 Oxydising flame The oxydising flame has excess oxygen and can visually be distinguished from other types of flames for being shorter. In some materials this oxygen excess helps in forming an oxide layer that decreases/prevents the volatilisation of low melting elements. 𝑎 > 1 Lecture #1 – Oxyfuel Gas Welding (OFW) 20/30 Types of flames Lecture #1 – Oxyfuel Gas Welding (OFW) 21/30 Acetylene production Acetylene is produced from calcium carbide. 𝑪𝒂𝑪𝟐 + 𝟐𝑯𝟐 𝑶 → 𝑪𝟐 𝑯𝟐 + 𝑪𝒂(𝑶𝑯)𝟐 The acetylene is stabilised in acetone and stored inside a porous filling material. Acetylene cylinders are identified by their brown colour (RAL 3009). Cylinders can be fully painted or just at the top. Porous filling material Lecture #1 – Oxyfuel Gas Welding (OFW) 22/30 Oxygen production Oxygen is mainly produced by fractional destillation of air. The air (≈21% O2) is liquified and progressivelly heated to be separated from the nitrogen. Oxygen cylinders are identified by the white colour at the top (RAL 9010). Fractional air destillation Lecture #1 – Oxyfuel Gas Welding (OFW) 23/30  EN 1089-3:2011 Cylinders – colour code General purpose gases RAL code Toxic and/or corrosive 1018 Flamable 3000 Oxidising 5012 Inert 6018 Specific gases Acetylene 3009 Oxygen 9010 Argon 6001 Nitrogen 9005 Carbon dioxide 7037 Helium 8008 Lecture #1 – Oxyfuel Gas Welding (OFW) 24/30 Equipment – torches and nozzles The heat generated by combustion processes is mostly used for cutting, heating and brasing nowadays. The usage dictates the type of torch and nozzle. Handle Welding Light the torch: 1) Open fuel valve; Heating 2) Ignite; 3) Opel oxygen valve; 4) Regulate O2 flux for desired Cutting flame type. Extinguish the flame: 1) Turn off fuel valve; 2) Turn off oxygen valve. Flint lighter Chamfer made by oxyfuel gas cutting Lecture #1 – Oxyfuel Gas Welding (OFW) 25/30 Equipment - cylinders, hoses and pressure regulators Oxygen Acetylene Hoses Lecture #1 – Oxyfuel Gas Welding (OFW) 26/30 Flame (flashback) arrestors Flame arrestors are safety valves connected to the hoses to prevent gas/flame reflux to the cylinders. Lecture #1 – Oxyfuel Gas Welding (OFW) 27/30 Operating technique Backhand Forehand Characteristics Characteristics Intermediate thickness, 6 < t < 15 mm Low thickness, < 4 mm Good penetration Excelent melt pool control Quick Good looking welds Granted root weld Lower distortion Adequate for claddings Pentetration control is more difficult Lecture #1 – Oxyfuel Gas Welding (OFW) 28/30  EN 12536:2000 Materials and types of flame Base material Type of flame Cast iron Neutral Low alloy steel Slightly reducing Low carbon steel Neutral Mild steel Slightly reducing High carbon steel Reducing Stainless steel Slightly reducing Aluminium Slightly reducing Copper Neutral Brass Slightly oxidising Bronze Slightly oxidising Cupronickel Reducing Nickel Slightly reducing Nickel silver Reducing Monel Slightly reducing Inconel Slightly reducing Lead Slightly reducing Lecture #1 – Oxyfuel Gas Welding (OFW) 29/30 Pros and cons ADVANTAGES LIMITATIONS ✓ Simplicity;  Low productivity; ✓ Great mobility/portability;  Low heat power; ✓ Low equipment cost;  Limited shielding; ✓ Fair weldability;  For lower thicknesses only; ✓ Versatility;  High level of distortion; ✓ Fair control.  Large HAZ;  Limited (materials) applicability. Lecture #1 – Oxyfuel Gas Welding (OFW) 30/30