1 Lecture 1 Fundamentals of Metal Forming  Course Hour: 3  Basic requirements: Recalling the principles and concepts of the course “Metal forming: mechanics and principles” Acquainting with classification of forming processes, Acquainting with temperature in metal working, hot working, cold working, strain rate effects, metallurgical structure, hydrostatic pressure, workability, residual stresses; acquainting with friction and lubrication in metal forming processes mechanics of metal working  Emphasis: classification of forming processes and temperature in metal working, Temperature in metal working, friction and lubrication in metal forming processes Difficulties: Mechanics of metal working, Residual stress  Home work: Read the textbook from pages

2 Metal Forming l Plastic Deformation to Change Shape l No Volume Change l Stresses > Yield l Good Forming Properties Low Yield Strength High Ductility Elevated temperature low strain rate and lubrication can Help

3 Bulk forming ◆ Characterized by significant deformations and massive shape changes ◆ "Bulk" refers to workparts with relatively low surface area-to-volume ratios ◆ Starting work shapes include cylindrical billets and rectangular bars Rolling

4 Forging Extrusion

5 Drawing Sheet Metal

6 Bulk Deformation l Significant Deformations l Massive Shape Changes (w/o Waste) l “Blacksmith” l Work in Plastic Region Flow Stress Y f = K  n Flow Stress Curve Material Behavior – Flow Stress  = K  n Concept of flow stress, Y f – the instantaneous stress required to deform the material Y f = K  n Y f = K  n Process force considerations: * during compression, determine instantaneous force from Y f * max force is often all that is required, typically at end of stroke * force analysis may be based on average stresses and strains K and n depend on working temperature, characterized by 3 ranges: Cold working, Warm working, Hot working

7 Cold Working l Advantages Better Accuracy, Closer Tolerances; Better Surface Finish; Increased Strength and Hardness l Disadvantages Higher Forces, Power; Limited Deformation; Annealing May Be Required Warm Working l Below Recrystallization Temp. l Advantages Over Cold Working Lower Forces and power; More Intricate Geometries; Reduced Annealing Requirements

8 Hot Working l Above Recrystallization Temp. (>0.5T m ) l Advantages Substantially Lower Force, Power Needed Significant Deformations Possible n Approaches Zero No Work Hardening (Strengthening) Isotropic Properties Extended Material Applications l Disadvantages No Strengthening Lower Accuracy Lots of Heat Energy Required Severe Surface Oxidation Poor Surface Finish Higher Tool Wear

9 Temperature & Strain Rate Fig 20.5 We will mostly assume that strain rate is negligible at room temperature! Note: Strain rate a strong function of working temperature (high values -> 1000 s -1 )where v = speed of testing head h = instantaneous height of part being worked Strain rate equation: C = strength constant m = strain-rate coefficient

10 Friction * undesirable * retards metal flow (residual stresses & defects) * increases force and power requirements * wears tooling * high temperature stick Lubricants * 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…)

11 l Metal forming products of our country 产品 名称 尺 寸 范 围 金属材料产品 的外形特征 基本塑性 加工方法 板材 0.3 － 80×500 － 2500×1000 － 10000mm 长度一定，较短， 块状或片状 平辊轧制 带材 0.1 － 2×20 － 600mm 厚度较薄，长度大， 卷状 平辊轧制 条材 宽度较窄，长度一定平辊或型辊轧制 箔材 － 0.15×10 － 1200mm 厚度很薄、长度大， 卷状 平辊轧制 管材 Φ1 － 420×0.1 － 50mm 断面圆环形中空，直 条状 挤压、拉拔、轧 制 棒材 Φ50 － 300mm 断面圆形实心，直条 状 型轧、挤压、拉 拔 型材断面积为 20 － 10000mm 2 断面为非圆实心或中 空， 直条状 挤压、轧制 线材 Φ0.001 － 5.0mm 断面细小，成卷拉拔 锻件形状复杂预锻件、普通锻件、 模锻件等 自由锻、模锻、 辊锻、旋锻等 板料 冲压 形状复杂冲裁件、弯曲件、深 冲件等 剪切、冲孔、拉 深、辊弯成形等

12 部分微丝样品照片