Material forming technology - APS

2. Material solidification theory

Definition : 凝固是将固体材料加热到液态, 然后按预定的尺寸, 形状及组织形态再次冷却至固态的过程。

2.1 Properties

1. Shape change
2. Appearance
3. Latent heat of solidification

2.2 Nucleation

1. Solidification start at stable crystal particle – Prokaryote；
2. spontaneous nucleation : no foreign interface and particle uniform melt
3. non-spontaneous nucleation: without above
4. Nucleating agent : Si2O3,V,Nb；
5. Inoculant : FeSi。

2.3 Growth

Segregation : in solidification chemical composition is uneven

1. Micro : inside and outside difference
2. Macro : bigger than the grain

2.4 Defect

step growth : spiral->spiral growth->3d step

2.5 Application

1. Mold filling capacity control

   fill the mold , get the shape complete and figure clear casting

2. shrink control : liquid, solidification, solid

3. Defect control:

   1. sinkhole缩孔(凝固等温线, Inscribed circle内切圆), shrinkage缩松 ( macro, micro), deformation变形, segregation 偏析, 裂纹, Slag Inclusion夹渣, blow hole 气孔, cold shut冷隔

      

      

   2. 方法 : riser冒口, chiller 冷铁 ( 减少部分收缩不均, 同时收缩 )
      

2.6 Ceramic powder alloy

工艺 : raw material ->pressing ->sintering烧结

3. Material forming heat process

Definition : 从热度角度来描述一个材料成形工艺过程 ( 热变化过程 )

3.1.Welding heat process

1. Fusion welding熔焊 : 局部加热升温->熔化->冷却焊接
2. Solid state welding : 局部加热呈塑性状态, 加压冷却焊接
3. Solid and liquid welding ( Soldering ) : welding wire melted, weld on the object

3.2 Fusion welding properties

1. heat source is concentrated
2. welding part has large temperature gradient, heating is uneven
3. heat source is usually moving

3.4 Thermal efficiency & Temperature field

1. Thermal efficiency : $\mu=\frac{Q}{Q_0}$

   有效热量与热源提供热之比

2. welding temperature filed :
   $T=f(x,y,z,t)$

   line : $T=f(x,y,t)​$

   surface : $T=f(x,t)$

3. Influence factor

   1. Source type : electric arc, fire, laser
   2. parameter: speed, and heat power
   3. material : $\lambda,c’=c\rho,a=\frac{\lambda}{c\rho},H比焓,\alpha$
   4. shape

4. Plastic forming

4.1 Cold state plastic forming

4.1.1 intracrystalline plastic deformation(main)

1. Slip : 指晶体crystal在力的作用下, 晶体的一部分沿一定的晶面surface和晶向orientation相对于晶体的另一部分发生的相对移动 ( 滑移面, 滑移方向 )

2. Twinning : 晶体在剪应力shear stress作用下, 晶体的一部分沿一定的晶面和晶向发生均匀切变

4.1.2 Between the crystal deformation

grain slide rotate晶粒之间相互滑动和转动, 当剪应力足以克服晶粒之间阻力时, 发生相对滑动

4.1.3 Influence

1. structure : grain shape, 位向, substructure , metallographic structure
2. property change : work hardening加工硬化 ( 变形后金属硬度, 强度$\uparrow$, 塑性, 韧性$\downarrow$, 纠缠错体, 相变硬化(QP钢, 奥氏体变马氏体)

4.2 Hot state plastic deformation

1. reason : in slip, twin, among slide
2. Soften :
   1. softening :
      1. dynamic recovery
      2. dynamic recrystallization
   2. Residual heat :
      1. static recovery
      2. static recrystallization
   3. in : sub dynamic recrystallization
3. influnece
   1. improve grain structure
   2. estimate defect锻合内部缺陷
   3. break carbide and improve its distribution破碎并改善碳化物和非金属夹杂物在钢中的分布
   4. form fibrous structure

4.3 Stress field (slip line)

5. Consolidation forming

Definition : 金属材料焙化后注入与拟成形零件相适应的模具空腔中, 冷却后获得所需要的零件

• structure凝固组织的形成与控制；
• defect铸造缺陷的防止与控制；
• precision铸件精度控制。

5.1 Metal materials

5.1.1 Cast iron

• Grey

1. general

   抗拉强度<铁, 塑性韧性=0, 不可锻, 焊接差

   铸造性能优良, 切削性能好, 减震, 耐磨, 缺口不敏感

   生产导轨, 滑动轴承

   

2. Ductile iron

   力学约=铁, 近灰口

   阀门, 曲轴齿轮, 可取代钢

   

3. Vermicular graphite cast iron

   耐高温, 导热性好, 抗氧化

   化工管道, 汽车的汽缸, 排气管

   

4. malleable cast iron

   阀门

   

• white cast iron
• mottled cast iron

5.1.2. cast steel

5.1.3. cast non iron alloy

铅Hg, 镁Mg

5.2 Technology

tech, properties, application

5.2.1 Sand casting

• tech

  

• properities

  1. almost all几乎适用于所有大小复杂零件
  2. 可单件小批量可大批量

• designs :

  • pouring position

  • parting surface

  • riser
  • chiller
  • core

• Riser

  1. compensate shrink补偿收缩
  2. adjust temperature distribution调整铸件凝固时的温度分布
  3. sum up air and residue /slag排气集渣
  4. watch filling condition观察充型情况

• Chiller

  1. adjust local chill speed调整局部冷却速度
  2. improve hardness, strength提高强, 硬, 延展
  3. control chill order控制铸件的凝固顺序

5.2.2 Metal mold casting

• Tech

  金属预热$\rightarrow$喷涂料painting $\rightarrow$ 合模$\rightarrow$浇注$\rightarrow$凝固$\rightarrow$抽芯$\rightarrow$开模$\rightarrow$切割浇口$\rightarrow$零件

• Pro:

  1. multiple times
  2. high precision
  3. save place and material

• Use: large amount and complicated shape

5.2.3 Pressure casting

Definition:指在高压下快速将液态半液态金属熔液压入模具中成形方法

• 工艺

  模具预热$\rightarrow$喷涂料$\rightarrow$合模$\rightarrow$压射$\rightarrow$保压凝固$\rightarrow$开模$\rightarrow$取件, 去流道

• Fea

  1. high efficiency
  2. high precision
  3. complicated shape
  4. for different material
  5. expensive

5.2.4 Low pressure casting

• 工艺

  预热$\rightarrow$喷刷涂料$\rightarrow$压缩空气$\rightarrow$保压凝固$\rightarrow$撤压$\rightarrow$开模$\rightarrow$取件

• Fea

1. pressure is adjustable, speed also浇注压力, 速度可调,适用于金属型, 砂型, 熔模型可锻造
2. prevent shrink hole and shrinkage有效防止缩孔, 缩松
3. surface quality > metal mold铸件表面质量>金属型
4. high material utilization材料利用率高达90%

5.2.5 Investment casting

• 工艺

  易熔材料制成模型$\rightarrow$模型涂挂耐火材料fireproofing material $\rightarrow$ 硬化外壳$\rightarrow$模型熔化$\rightarrow$焙烧roasting $\rightarrow$放入砂箱$\rightarrow$浇注$\rightarrow$冷却取件$\rightarrow$后处理

• Fea

1. no parting surface
2. high precision精度和表面质量高
3. alloy 适用于各种合金铸造
4. single or amount可单件可批量
5. high costing, complicate progress材料成本高, 工艺复杂, 生产周期长, 难以实现自动化

• wide application, special for craftsApp面广, 特别适于工艺品

5.2.6 Centrifugal casting

Definition : 利用离心力填充铸型并凝固的方法

• Fea
  1. no core and pouring system可省去型芯和浇注系统
  2. texture compact铸件组织致密
  3. filling well充型能力强, 适合于流动性能差的材料铸造
  4. 便于双金属铸造
  5. the inside hole is rough内孔公差大, 粗糙
• use for round pipe

6. Plastic forming tech

• plasticity of metarial
• judgement
• inside field unkown
• shape information precisely input。

6.1 Volume forming

6.1.1 Forging

Definition : 通过金属体积的转移和分配来获得机器零件毛坯的塑性成形方法

• free forging

  • upsetting锻粗
  • drawing out拔长
  • punching冲孔
  • reaming芯轴扩孔
  • swaging芯轴拔长

• die forging

  

  • open (with fin)
  • closed ( no fin )

• 工艺 ( 开式 ) : 下料$\rightarrow$镦粗/拔长$\rightarrow$预锻$\rightarrow$终锻$\rightarrow​$切边

6.1.2 Pressing

• Type : hot, warm, cold, forward, backward, 复合

  

• 工艺 : 下料$\rightarrow$退火annealing $\rightarrow$制坯$\rightarrow$镀润滑层cladding lubricating layder $\rightarrow$挤压$\rightarrow$去应力destressing

• allowable deformation degress : 在模具强度允许的条件下, 一次挤压加工容许的变形程度

• Influence

  • mold structure, material strength材料强度
  • pressing methode挤压方式
  • blank surface roughneess

6.2 Flat forming - sheet metal forming

6.2.1 Blanking

Definition : 利用模具使板料产生分离的冲压工序

• 冷 : 滑移孪生, 热 : 软化过程

• 落料blanking : 从板料上冲下所需要形状的零件或毛坯

• 冲孔 punching: 在工件上冲出所需要形状的孔

  

• 变形过程 : elastic 弹性变形阶段$\rightarrow$塑性变形阶段$\rightarrow​$fracture断裂阶段

• Stress state

  

  断裂顺序为 : E>A, $\sigma_3$为主动力, E开裂后, $\sigma_3$剧增, A断开

• section feature: 圆角fillet( main孪生 ) , bright band ( 孪生滑移交替 ) , tear tape ( 微裂纹, 撕裂面 ) , glitch

  

6.2.2 Bending

Definition : 将板材, 棒料或型材弯成一定形状和角度的方法

• 弹性$\rightarrow$塑性$\rightarrow$成形
• rebound : positive, 0, negative

6.2.3 Deep drawing

• excess triangle

  

• draw times and coefficient

$$m=\frac{d}{D}=\frac{d_1}{D}\cdot\frac{d_2}{d_1}\cdot\frac{d_3}{d_2}\dots\frac{d}{d_n}=m_1\cdot m_2\dots m_n\cdot m_{n+1}​$$

7. Welding technology

principle, types, feature, app

• deformation (residue stress & residue austenite)；
• defect (crack, 未焠透, air hole, slag inclusion)；

7.1 Typical arc welding

7.1.1 Manual arc welding

• Pro : use electric arc between welding rod and component, make them locally melt and solidify after cooling
• Fea
  1. easy use, and highly compatible,
  2. low cost
  3. high craft required
• Welding rod= covering+welding core
• Covering
  1. Protect from air
  2. remove the S
  3. continuous burning

7.1.2 Submerged arc automatic welding

• Pro : arc under the flux焊丝与焊件之间的电弧是埋在颗粒状助焊剂下
• Fea :
  1. high efficiency
  2. weld good quality
  3. good work environment
  4. mainly use for flat welding, low flexibility

7.1.3 TIG Tungsten Inert gas welding

• Pro : 钨电极在氩气的条件下, 电弧熔化焊接
• Fea
  1. alienate air氩气比重大, 有效隔绝空气, 不参与化学反应, 几乎可以焊接所有金属
  2. stable burning 直流正极性电弧 ( 工件+, 钨极- ) 即使电流很小, 仍能稳定燃烧, 特别适合于薄板燃烧
  3. no slag, good quaility明弧无渣, 可见性好, 焊接质量好
  4. current small钨电极所承受的电流小, 耐热性好
  5. Inert gas is expensive惰性气体较贵, 成本高

7.1.4 GMAW Gas metal arc welding

• Pro : under gas protect welding气体保护下, 连续送进焊丝, 电弧焊接, 常用CO2
• Fea
  1. High efficiency
  2. low costing
  3. low energy cost
  4. wide application
  5. anti corrosion , good quality

7.2 Pressure welding and soldering

• ERW electric resistance welding

• friction welding

• soldering
• spot welding

7.4 Stress and deformation

• Design :
  1. symmetry weld
  2. Misplace
  3. Change welding method
• Crafts :
  1. right melding remove
  2. heat
  3. low energy welding
  4. mechanical method

8. Surface forming and strengthen Tech

Definition : material coverage and satisfy other requirement

一种在零件材料的表层制备一层与其性能不同, 能满足特定使用要求的材料覆盖技术

• design particulate surface texture and structure for requirement
• the method to get this texture
• merging 涂层与机体的结合；
• 涂层的材料与结构。

8.1 Surface failure : fatigue, corrosion

8.2 Thermal spraying

• 工艺 : 金属加热熔化melting $\rightarrow$high speed air spray as small particle以高速气流雾化成极细颗粒$\rightarrow$ high speed spray on component surface 高速喷射到事先准备好的零件表面
• Bonding mechanism
  1. mechanical机械结合
  2. metallic bond金属键结合
  3. small melt 微熔合, 微扩散
• structure Feature
  1. Nonuniformity涂层结构的不均匀性
  2. Porous 涂层的多孔性
  3. Oxidation film涂层中大量的氧化膜
  4. inside stress涂层内应力

8.3 Surface strengthen Principle and App

8.3.1 Solid

• 表面形变强化shape : shot blasting ( work hardening )
• 表面相变硬化phase : 淬火quenching ( martensite )
• 化学热处理chemical heat treatment : 渗碳carburizing, 渗氮nitrizing
• 表面镀层Surface cladding material

8.3.2 Liquid

表面处于液态, fast alloying, 组织成分变化, 提高性能

9.Powder metallurgy forming

9.1 Crafts

• Powder make粉末制取$\rightarrow$forming成形$\rightarrow$致密化compact

  • 成形 : 配料$\rightarrow$熔化$\rightarrow$空气雾化$\rightarrow$过筛$\rightarrow$干燥$\rightarrow$混料$\rightarrow$炉内还原$\rightarrow$粉碎$\rightarrow$过筛$\rightarrow$粉碎$\rightarrow$过筛$\rightarrow$混料$\rightarrow$过筛$\rightarrow$包装

9.2 Make powder

• Physical : shot blasting, atomization
• Chemical : precipitin沉淀, electrolytic process电解
• Mechanical : grind

9.3 Powder forming

• Pressure压力成形 : mold模压, forg锻造, 挤压, 注射
• no pressure无压成形 : 粉浆汽注, 无压充型, 浆料涂覆

9.4 Sintering

机理

• 早期颗粒通过原子扩散粘结在一起
• 原子向颈缩部分大量迁移使烧结长大, 颗粒间隙的通道光滑化, 通道和孔隙封闭成球形空洞
• 较小的空间变小消失, 烧结体收缩, 密度$\uparrow$
• 末期小孔间消失, 大孔之间粗化长大

10.Plastics forming

10.1 Composition , Type和成形方法

• Composition :
  • Resin : 天然树脂, 人工合成树脂
  • Additive : 稳定剂, 填充剂, 增塑剂, 着色剂, 固化剂
• Type : 热塑Thermoplastic, 热固Thermosetting ( 不能加热回收再利用 )
• Forming: pushing molding注射成形 ( 挤出成形, 吹塑成形, 模压成形 )
• 物理化学变化 : 纤维方向 ( 各向异性, 收缩率 )

10.2 Craft and mold

• Craft : 塑料粒子的塑化 $\rightarrow$ 注射充模$\rightarrow$保压凝固$\rightarrow​$开模落料
• 设备 : 注塑机injection molding machine, mold
• 模具结构 : 动模+定模 ( 共6件 : 型腔, 导向机构, 浇注系统, 顶出机构, 侧抽芯机构, 冷却系统 )

10.3 Plastics welding

Thermoplastic ok