Metalworking Processes Chapter 4 PDF

Metalworking Processes Chapter 4 AMT 4136 – Aircraft Mechanical Processes Prepared by: Asst. Prof. Sherwin R. Trinidad, LPT, MEAM Session Objective At the end of the session, you will be able to: a. explain the principles and applications of hot working, cold work...

Metalworking Processes Chapter 4 AMT 4136 – Aircraft Mechanical Processes Prepared by: Asst. Prof. Sherwin R. Trinidad, LPT, MEAM Session Objective At the end of the session, you will be able to: a. explain the principles and applications of hot working, cold working, and extrusion in aviation; b. describe the methods and benefits of annealing, normalizing, hardening, and tempering; and c. discuss the critical properties of metals used in aviation and evaluate different quenching media. Metalworking Processes SLIDE 2 Introduction In aviation, materials must be lightweight, strong, and durable enough to withstand the extreme stresses of flight. Metalworking and heat treatment processes are vital in transforming raw metals into highly reliable aircraft components. These processes are designed to improve the strength, toughness, and fatigue resistance of metals while minimizing risks such as brittleness and corrosion. Metalworking Processes SLIDE 3 Metalworking It is the process of shaping and reshaping metals to create individual parts, assemblies, or large structures. Three methods of metalworking: 1. Hot Working 2. Cold Working 3. Extrusion Metalworking Processes SLIDE 4  Hot Working It involves shaping metals at temperatures above their recrystallization points, making the material more malleable and less likely to crack. Process: Steel is typically hot worked from ingots. When stripped from its mold, an ingot has a solid surface but a molten interior. Ingots are placed in soaking pits to equalize temperature and solidify the interior. After soaking, ingots are rolled to intermediate sizes for easier handling. Metalworking Processes SLIDE 5  Hot Working When Rolled: Bloom: Square section with dimensions 6 inches × 6 inches or larger. Billet: Square section with dimensions less than 6 inches × 6 inches. Slab: Rectangular section with width greater than twice its thickness. Applications: These shapes are further rolled into various uniform cross-sectional shapes like sheets, bars, channels, angles, and I- beams. Hot-rolled materials are often finished by cold rolling or drawing for precise dimensions and smooth surfaces. Metalworking Processes SLIDE 6  Hot Working When not rolled: Forging: Performed at temperatures above the critical range to shape the metal. Pressing: Used for large, heavy parts. slow- acting, uniformly transmits force, affecting both interior and exterior grain structure. Hammering: Suitable for small pieces. Quick force application, affecting only a small depth. Requires heavy hammer or repeated blows for thorough working. Smith Forging: Produces small, high-grade parts. Operator controls pressure and finishing temperature. Saves machining time and material. Metalworking Processes SLIDE 7  Hot Working After hardening: Tempering: Involves heating steel to a specified temperature and cooling it in air, oil, water, or special solutions. Relieves internal strain and reduces brittleness. Enhances hardness and toughness. Metalworking Processes SLIDE 8  Hot Working If it’s too hard: Annealing: Involves heating to a prescribed temperature, holding, and slow cooling. Relieves internal stresses, softens metal, increases ductility, and refines grain structure. Maximum softness achieved by very slow cooling; some metals require furnace cooling, others air cooling. Metalworking Processes SLIDE 9  Hot Working For iron base metals: Normalizing: Involves heating to the proper temperature, holding, and cooling in still air. Used to relieve stresses in metals. Metalworking Processes SLIDE 10  Cold Working Cold working takes place below the recrystallization temperature, resulting in harder, stronger metals with improved surface finishes. Benefits: Increases tensile strength and improves fatigue resistance, essential for components subjected to repeated stress, such as aircraft fuselage and wings. Limitations: Excessive cold working can make metals brittle, which may necessitate additional heat treatment to relieve stresses​ Metalworking Processes SLIDE 11  Extrusion A process where metal is pushed through a die to produce long, continuous sections of a fixed cross-sectional shape. Applications: Used to create components like tubes and channels that are lightweight but durable, vital for aircraft construction​ Metalworking Processes SLIDE 12  Heat Treatment Heat treatment is essential for adjusting the mechanical properties of metals, such as hardness, toughness, and ductility. The process involves heating and cooling metals under controlled conditions to optimize their performance. Broadly includes processes like annealing, normalizing, hardening, and tempering for steels. Metalworking Processes SLIDE 13  Heat Treatment Problem: Subjected to shock and fatigue stresses. Fatigue occurs from frequent reversals of loading or repeated loads, leading to cracks and eventual failure. Resistance to shock and fatigue is crucial for critical parts.. Metalworking Processes SLIDE 14  Heat Treatment Purpose: Change mechanical properties to make metals more useful, serviceable, and safe. Can make metals harder, stronger, more impact-resistant, or softer and more ductile. No single heat-treating operation can produce all desired characteristics; some properties improve at the expense of others (e.g., hardening can make metal brittle). Metalworking Processes SLIDE 15 Heat Treatment Restrictions: Heat treatment results depend on metal structure and changes during heating and cooling. Pure metals cannot be hardened by heat treatment due to minimal structural change. Alloys respond to heat treatment as their structures change with heating and cooling. Metalworking Processes SLIDE 16 Heat Treating Equipment Requires close control over heating and cooling factors. Proper equipment selection is crucial (furnace size/type, quenching equipment, handling/cleaning/straightening tools). Furnace atmosphere affects heat-treated parts. Metalworking Processes SLIDE 17  Furnaces Various types and sizes designed for specific temperature ranges. Using furnaces beyond rated temperatures can reduce lifespan and require repairs. Fuel-fired furnaces need air for combustion; usually muffler type to avoid direct flame impingement. Electric furnaces use wire or ribbon heating elements; additional elements at high heat loss points. Common maximum temperatures: electric furnaces up to 2,000°F, resistor bar furnaces up to 2,500°F. Metalworking Processes SLIDE 18  Salt Baths Salt baths for tempering or hardening; temperature range 325°F to 2,450°F. Lead baths temperature range: 650°F to 1,700°F. Faster heating in lead or salt baths compared to furnaces. Metalworking Processes SLIDE 19  Pyrometers Pyrometers measure furnace temperature using thermocouples. Pyrometer components: thermocouple, extension leads, meter. Furnaces for tempering may have gas/electric heating and fans for hot air circulation. Thermocouples: copper-constantan (up to 700°F), iron-constantan (up to 1,400°F), chromel-alumel (up to 2,200°F), platinum- rhodium alloys (up to 2,800°F). Metalworking Processes SLIDE 20  Pyrometers Thermocouple life affected by maximum temperature and furnace atmosphere. Encased in metallic/ceramic tubes to protect from furnace gases. Accurate control requires placing thermocouple close to the work. Automatic controllers help maintain desired temperature. Metalworking Processes SLIDE 21  Pyrometers Indicating type: direct temperature reading. Recording type: permanent temperature record via inked stylus on calibrated paper/chart. Metalworking Processes SLIDE 22  Heating Objective: Transform pearlite to austenite by heating steel through the critical range. Requires slow heating to prevent rapid transition. Cold steel inserted at 300°F to 500°F below hardening temperature. Temperature estimation methods: commercial crayons, pellets, paints, or observing color changes. Steel color changes with temperature: dull red at 1,000°F, progressing to white. Protect steel from oxidation and decarburization using atmosphere control or covering with cast iron borings/chips. Vacuum furnaces used for annealing to maintain non-oxidized surfaces. Metalworking Processes SLIDE 23  Soaking Maintain constant furnace temperature during soaking. Soaking temperatures vary by steel type and part size. Small parts soaked at lower range, heavy parts at upper range. Typical soaking period: 30 minutes to 1 hour. Metalworking Processes SLIDE 24  Cooling Cooling rate through critical range determines steel’s final form. Cooling media: still air (slow), liquids (fastest). Common quenching liquids: brine (strongest), water, oil (least strong). Oil quench for alloy steels, brine or water for carbon steels. Metalworking Processes SLIDE 25 Quenching Media Quenching solutions cool steel without chemical action. Common media: water, inorganic salt solutions, oils. Cooling rates: rapid in brine, less rapid in water, slow in oil. Brine: 5-10% salt solution, effective in removing scale. Metalworking Processes SLIDE 26 Quenching Media Water and brine should be kept cold (below 60°F). Quenching oils: straight mineral oil with Saybolt viscosity of about 100 at 100°F. Oils have greatest cooling velocity at 100- 140°F. Metalworking Processes SLIDE 27 Quenching Process Film forms on hot steel surface, reducing heat abstraction. Agitation or pressure spray quench needed to dislodge vapor films. Recommendations to reduce warping: 1. Avoid throwing parts into quenching bath. 2. Agitate parts to destroy vapor coating. 3. Immerse irregular parts with heavy end first. Metalworking Processes SLIDE 28 Quenching Equipment Properly sized quenching tank with circulating pumps and coolers. Maintain constant temperatures during large- scale quenching. Rapid transfer from furnace to quenching medium is crucial. Use guard sheets to retain heat during transfer. Rinse tank to remove salt after quenching. Metalworking Processes SLIDE 29  References Aircraft Systems. (n.d.). Metalworking Processes and Heat Treatment of Metals. The Piping Mart. (2024). Heat Treatments for Aviation Parts and Tools. Aviation Metals. (n.d.). Metal Treatment and Services. Metalworking Processes SLIDE 30 THANK YOU FOR LISTENING! PREPARED BY: Asst. Prof. Sherwin R. Trinidad, LPT, MEAM (02) 8872-7041 or (02) 8871-0639 loc. 103/216 [email protected]