金属成型基础

1、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, s

2、train 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 work

3、ing, friction and lubrication in metal forming processes Difficulties: Mechanics of metal working, Residual stress Home work: Read the textbook from pages 287-297 2 Metal Forming lPlastic Deformation to Change Shape lNo Volume Change lStresses Yield lGood Forming Properties Low Yield Strength High D

4、uctility 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

5、Rolling 4 Forging Extrusion 5 Drawing Sheet Metal 6 Bulk Deformation lSignificant Deformations lMassive Shape Changes (w/o Waste) l“Blacksmith” lWork in Plastic Region Flow Stress Yf= Kn Flow Stress Curve * during compression, determine instantaneous force from Yf * max force is often all that is re

6、quired, typically at end of stroke * force analysis may be based on average stresses and strains 7 Cold Working lAdvantages Better Accuracy, Closer Tolerances; Better Surface Finish; Increased Strength and Hardness lDisadvantages Higher Forces, Power; Limited Deformation; Annealing May Be Required W

7、arm Working lBelow Recrystallization Temp. lAdvantages Over Cold Working Lower Forces and power; More Intricate Geometries; Reduced Annealing Requirements 8 Hot Working lAbove Recrystallization Temp. (0.5Tm) l Advantages Substantially Lower Force, Power Needed Significant Deformations Possible n App

8、roaches Zero No Work Hardening (Strengthening) Isotropic Properties Extended Material Applications lDisadvantages 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

9、 strain rate is negligible at room temperature! (high values - 1000 s-1) Strain rate equation: C = strength constant m = strain-rate coefficient h v 10 Friction * undesirable * retards metal flow (residual stresses & defects) * increases force and power requirements * wears tooling * high temperatur

10、e 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 lMetal 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 8 0 5 0 0 2 5 0 0 1 0 0 0 10000mm 长度一定，较短， 块状或片状 平辊轧制 带材0.1220600mm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0.0050.1510 1200mm 厚度很薄、长度大， 卷状 平辊轧制 管材14200.150断面圆环形中空，直 条状 挤压、拉拔、轧 制 棒材50300mm断面圆形实心，直条 状 型轧、挤压