Fundamentals of Metal Forming ME 482 Manufacturing Systems

Fundamentals of Metal Forming ME 482 - Manufacturing Systems

Fundamentals of Metal Forming Bulk deformation vs Sheetmetal working Bulk deformation Aluminum extrudate – a simple angled shape. The die shown is more complex. * Low surface area to volume ratios * Operations increase surface area to volume ratios Operations are: rolling extrusion forging drawing This group of machines - which are over a half mile long - roll the slab into sheet steel using tremendous pressure. ME 482 - Manufacturing Systems

Fundamentals of Metal Forming Bulk deformation • Rolling characteristics * compressive deformation * 2 or more rolls * strong frictional relationship • Extrusion characteristics * compressive deformation * force metal through die opening * strong frictional relationship * hot and cold working process ME 482 - Manufacturing Systems

Fundamentals of Metal Forming Sheet metalworking Characterized by: * large surface area to volume ratios * little ratio change after process * machines called presses * parts called stampings * tools are punch and die Operations: bending ME 482 - Manufacturing Systems drawing shearing

Material Behavior – Flow Stress s= K e n Concept of flow stress, Yf – the instantaneous stress required to deform the material Yf = K e n Process force considerations: * during compression, determine instantaneous force from Yf * max force is often all that is required, typically at end of stroke * force analysis may be based on average stresses and strains Average flow stress = Yf = K en /(1 + n) ME 482 - Manufacturing Systems

Fundamentals of Metal Forming Temperature and Metal Forming K and n depend on working temperature, characterized by 3 ranges: Cold working Warm working Hot working ME 482 - Manufacturing Systems

Fundamentals of Metal Forming Temperature and Metal Forming – cold working Advantages: * good accuracy and tolerances * better surface finish * strain hardening increases strength and hardness * directional properties * energy economy Disadvantages: * higher forces/power * strain hardening limits deformation * may need to anneal ME 482 - Manufacturing Systems

Fundamentals of Metal Forming Temperature and Metal Forming – warm working Advantages: * above room temp. , but below re-crystallization temp. (0. 3 Tm) * lower forces and power * reduced strain hardening * more difficult geometry * no need for annealing Disadvantages: * more energy * limited geometry ME 482 - Manufacturing Systems

Fundamentals of Metal Forming Temperature and Metal Forming – hot working Advantages: * above re-crystallization temp. (0. 5 Tm < T < 0. 75 Tm) * lower forces and power * no strain hardening * difficult geometry * isotropic properties Disadvantages: * more energy * poorer surface finish * shorter tool life ME 482 - Manufacturing Systems

Flow stress Fundamentals of Metal Forming - Strain Room temp. Rate Note: Strain rate a strong function of working temperature 400º C (high 800º values. C-> 1000 s-1) where 1200º C v = speed of testing head h = instantaneous height. We of will partmostly being assume workedthat strain rate is negligible at 10 temperature! 102 103 104 room m 1. 0 Strain rate equation: Yf = C e 0. 1 Strain rate C = strength constant m = strain-rate coefficient ME 482 - Manufacturing Systems

Friction and lubrication Friction: * undesirable * retards metal flow (residual stresses & defects) * increases force and power requirements * wears tooling Lubricants are usually oil-based, and when * high temperature stiction used in extreme pressure situations, sulfur, Lubricants: chlorine and phosphorus in the lubricant may chemically react with the metal surfaces (tool, chip). The reactions form a surface boundary layer that is more effective than the lubricant itself in reducing friction. Lubricants are most effective at cutting speeds < 400 ft/min. * reduce frictional effects * remove heat and material * lengthen tool life * may react chemically with tool or work * concerns about toxicity, flammability…. (mineral oils, emulsions, oils, graphite, glass. . ) ME 482 - Manufacturing Systems

Example 20. 6 For a metal with K = 50, 000 lb/in 2 and n = 0. 27, determine the average flow stress that the metal experiences if it is subjected to a stress that is equal to its strength coefficient K. Solution: Yf = K = 50, 000 en Thus e = 1 Yf = 50, 000 (1) 0. 27/1. 27 = 39, 370 lb/in 2 ME 482 - Manufacturing Systems

What have you learned? ME 482 - Manufacturing Systems