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Lecture 1 Fundamentals ofMetal Forming

Course Hour: 3Basic 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 workingEmphasis: classification of forming processes and temperature in metal working, Temperature in metal working, friction and lubrication in metal forming processesDifficulties: Mechanics of metal working, Residual stressHome work: Read the textbook from pages 287-297

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Metal Forming

Plastic Deformation to Change Shape

No Volume Change Stresses > Yield Good Forming Properties

Low Yield Strength

High Ductility

Elevated temperature low strain

rate and lubrication can Help

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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

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Forging

Extrusion

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Drawing

Sheet Metal

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Bulk Deformation Significant Deformations Massive Shape Changes (w/o Waste) “Blacksmith” Work in Plastic Region Flow Stress

Yf= Kn

Flow Stress Curve

Material Behavior – Flow StressMaterial Behavior – Flow Stress

= K = K nn

Concept of Concept of flow stressflow stress, Y, Yff – the instantaneous stress required to deform the material – the instantaneous stress required to deform the material

YYf f = K = K nn

Process force considerations: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

K and n depend on working temperature, characterized by 3 ranges: Cold working, Warm working, K and n depend on working temperature, characterized by 3 ranges: Cold working, Warm working, Hot workingHot working

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Cold Working

Advantages

Better Accuracy, Closer Tolerances; Better Surface Finish; Increased Strength and Hardness

Disadvantages

Higher Forces, Power; Limited Deformation; Annealing May Be Required

Warm Working

Below Recrystallization Temp. Advantages Over Cold Working

Lower Forces and power; More Intricate Geometries; Reduced Annealing Requirements

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Hot Working

Above Recrystallization Temp. (>0.5Tm) Advantages

Substantially Lower Force, Power Needed

Significant Deformations Possible

n Approaches Zero

No Work Hardening (Strengthening)

Isotropic Properties

Extended Material Applications Disadvantages

No Strengthening

Lower Accuracy

Lots of Heat Energy Required

Severe Surface Oxidation

Poor Surface Finish

Higher Tool Wear

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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 temperatureNote: Strain rate a strong function of working temperature

(high values -> 1000 s-1)where where

v = speed of testing headv = speed of testing headh = instantaneous height of part being workedh = instantaneous height of part being worked

Strain rate equation:Strain rate equation:

C = strength constantC = strength constantm = strain-rate coefficientm = strain-rate coefficient

hv

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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…)

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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 0.005 － 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 －10000mm2

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