AECH 1103 Topic 6c Metal Manufacturing PDF

Topic 6 Metal Manufacturing Process AECH 1103 Industrial Process Overview  Metal Forming and Stresses Plastic deformation is used to change the shape of metal workpieces. The tool, usually called a die, applies stresses that exceed the yield strength of the metal. T...

Topic 6 Metal Manufacturing Process AECH 1103 Industrial Process Overview  Metal Forming and Stresses Plastic deformation is used to change the shape of metal workpieces. The tool, usually called a die, applies stresses that exceed the yield strength of the metal. The metal takes a shape determined by the geometry of the die. Stresses to plastically deform the metal are usually compressive Examples: rolling, forging, extrusion However, some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and compressive) Still others apply shear stresses (shear spinning) 2  Material Properties in Metal Forming Desirable material properties: Low yield strength High ductility These properties are affected by temperature: Ductility increases and yield strength decreases when work temperature is raised Other factors: Strain rate and friction 3  Basic Types of Deformation Processes 1. Bulk deformation Characterized by significant deformations and massive shape changes Rolling "Bulk" refers to work parts with relatively low surface Forging area-to-volume ratios Extrusion Wire and bar drawing Forming and related operations performed on metal sheets, 2. Sheet metalworking strips, and coils Bending High surface area-to-volume ratio of starting metal, which distinguishes these from bulk deformation Deep drawing Often called pressworking because presses perform these Cutting operations Parts are called stampings Usual tooling: punch and die 4  Bulk Deformation Processes Rolling: Forging: Extrusion: Wire and Bar Drawing: 5  Rolling Uses rollers Thick metals passed in between rollers Makes metals thin Types of rolling: Hot rolling (high Temp > 900oC) Cold rolling (Room Temp) 6  Metal extrusion Image result for metal extrusion gif Metal Extrusion is a metal forming manufacturing process in which a cylindrical billet inside a closed cavity is forced to flow through a die of a desired cross section. These fixed cross sectional profile extruded parts are called “Extrudates” and pushed out using either a mechanical or hydraulic press. Reference: https://www.youtube.com/watch?v=Y75IQksBb0M 7  Sheet metalworking Bending Deep drawing Shearing 8  Metal drawing Metal drawing is a manufacturing process that forms metal work stock by reducing its cross section. This is accomplished by forcing the work through a mold, (die), of smaller cross sectional area than the work. This process is very similar to metal extrusion, the difference being in the application of force. In extrusion the work is pushed through the die opening, where in drawing it is pulled through. 9  Drawing process 1. Performed in cold conditions. (better accuracy) 2. Hardened beforehand 3. Surface cleaned (shot blasting or submersion) 4. Washed and dried 5. Conditioning (application of different chemicals for lubrication) 10  Video Metal Forming (Part 1: What is metal forging) Video: https://www.youtube.com/watch?v=gKz7FFIduYc https://www.youtube.com/watch?v=GHFtbHix-WU https://www.youtube.com/watch?v=GI9ePdzt-YI https://www.youtube.com/watch?v=wSbywBfXlHg Rolling: https://www.youtube.com/watch?v=btzgKAjncSo https://www.youtube.com/watch?v=pkJxrZPeP_0 11  Temperature in Metal Forming Any deformation operation can be accomplished with lower forces and power at elevated temperature Three temperature ranges in metal forming: Cold working Warm working Hot working 12  1. Cold Working Performed at room temperature or slightly above Many cold forming processes are important mass production operations Minimum or no machining usually required Advantages: Better accuracy, closer tolerances Better surface finish Strain hardening increases strength and hardness No heating of work required Disadvantages: Higher forces and power required in the deformation operation Ductility and strain hardening limit the amount of forming that can be done In some cases, metal must be annealed to allow further deformation In other cases, metal is simply not ductile enough to be cold worked 13  2. Warm Working Performed at temperatures above room temperature but below recrystallization temperature Dividing line between cold working and warm working often expressed in terms of melting point: 0.3Tm, where Tm = melting point (absolute temperature) for metal Advantage: Lower forces and power than in cold working More intricate work geometries possible Need for annealing may be reduced or eliminated Low spring back Disadvantage: 1. Scaling of part surface 14  3. Hot Working Deformation at temperatures above the recrystallization temperature Recrystallization temperature = about one-half of melting point on absolute scale In practice, hot working usually performed somewhat above 0.6Tm Metal continues to soften as temperature increases above 0.6Tm, enhancing advantage of hot working above this level Advantages of Hot Working Workpart shape can be significantly altered Lower forces and power required Metals that usually fracture in cold working can be hot formed Strength properties of product are generally isotropic No work hardening occurs during forming Disadvantages of Hot Working Lower dimensional accuracy in case of bulk forming Higher total energy required (due to the thermal energy to heat the workpiece) Work surface oxidation (scale), poorer surface finish Shorter tool life 15  Impact of Cold Work As cold work is increased Yield strength (y) increases. Tensile strength (TS) increases. Ductility (%EL or %AR) decreases. Adapted from Fig. 8.20, Callister & Rethwisch 4e. 16  Yield strength (y) increases. Tensile strength (TS) increases. Ductility (%EL or %AR) decreases. low carbon steel Adapted from Fig. 8.20, Callister & Rethwisch 4e. 17