华工成型技术重点第三部分总结

1、46/46Part III 成形（型）部分Forming and Shaping Processes and Equipment 13 Rolling of Metal (轧制） 13.1、IntroductionRolling(轧制)：is the process of reducing the thickness (or changing the cross-section) of a long workpiece by compressive forces applied through a set of rollsPlate(厚板)：which are generally regard

2、s as having a thickness greater than 6 mm, are used for structural applicationsSheet(薄板)：having a thickness less than 6 mm thick; are provided to manufacturing facilities as flat pieces or as strip in coils for further processing into various products. Plate厚板作为结构件，Sheet薄板作为半成品13.2、Flat Rolling（平扎）F

3、lat Rolling（平扎）：A strip （带料 / 条料）of thickness ho enters the roll gap （辊缝 / 辊隙 / 辊间 距离）and is reduced to thickness hf by a pair of rotating rolls, each roll being powered through its own shaft by electric motors （电动机）Vr: The surface speed of the rolls（轧辊的速度）V0: The velocity of the strip at the entran

4、ce（板材入口处的速度）Vf: The velocity of the strip at the exit（板材出口处的速度）neutral point（中性点）or no-slip point(无滑动点) :one point along the contact length where the velocity of the strip is the same as that of the roll.由于速度在中性点前后不一致引起摩擦力的方向在中性点两侧不一致(1) Frictional Forces（摩擦力-平扎中材料前行的驱动力） The rolls pull the material

5、 into the roll gap through a net frictional force（净摩擦力） on the material.摩擦力的危害：1) energy is dissipated in overcoming friction;2) high friction could damage the surface of the rolled productThe maximum possible draft（压下量）, defined as the difference between the initial and final thicknesses, (ho-hf),

6、is a function of the coefficient of friction,and the roll radius, R: ho-hf =R Thus, the higher the friction and the larger the roll radius, the grater the maximum possible draft (and reduction in thickness) becomes.(2) Roll Force（轧制力）：F= L W Yavg减少轧制力的措施：1）reducing friction; 2)using smaller-diameter

7、 rolls ;3)taking smaller reductions per pass;4）rolling at elevated temperatures(3)Spreading现象：对于有高宽厚比的厚板或者薄板的轧制，材料的宽度在轧制过程中基本保持不变，但对于宽厚比较小的厚板或薄板的轧制，材料的宽度在轧制的过程中增加的现象叫做Spreading现象；从左图中Top view俯视图可以看出轧制后宽度变大13.3、Flat Rolling Practice(平扎工艺)(1) Hot rolling(热轧) and Cold rolling(冷轧)：Hot rolling: carried o

8、ut above the recrystallization temperature(再结晶温度) of the metal.The initial breaking down of an ingot or of a continuously cast slab is done by hot rolling. (为什么要用热轧对铸件进行初始的压碎？）1)reduce grain size in metals; 2）breaking up of brittle grain boundaries and the closing up of internal defects, especially

9、porosity;3）improve strength and ductilityCold rolling: carried out at room temperatureCompared to hot rolling, Cold rolling produces sheet and strip with 1) much better surface finish (because of lack of scale); 2) much better dimensional tolerances; 3) much better mechanical properties ( because of

10、 strain hardening).(2) Cast structure(铸造结构) and Wrought structure(锻造结构)：cast structure:1) typically dendritic (树枝状的);2) includes coarse(粗糙的) and nonuniform（不均匀的）grains;3) usually brittle (易碎的) and porous(多孔的) wrought structure:1) finer grains size(细小的晶粒尺寸);2) enhanced strength and ductility（增强的强度和延展

11、性）(3)The product of the hot rolling(热轧产品)：Slab :a slab is usually rectangular in cross-section. slabs are rolled into plates and sheets later.Slab通常是具有长方形截面的厚板或者薄板Bloom：Bloom usually has a square cross-section, at least 150mm on the side. Blooms are processed further, by shaping rolling, into struct

12、ure shapes, such as I-beams and railroad rails.Bloom通常是具有边长大于150mm的正方形截面的结构件，例如I字梁或者铁轨Billets：billets are usually square, with a cross-section area smaller than blooms; they are later rolled into various shapes, such as round rods and bars by the use of shaped rolls.Billets通常是具有边长小于150mm的正方形截面的圆棒或者方

13、棒(4) Scale(热轧中的氧化皮)：Scale is conditioned by various means. Such as:1)use of a torch（火炬）or scaring (火焰表面清理);2) by pickling with acids (acid etching酸洗) ;3) by such mechanical means as blasting with water (水爆);4) grinding(研磨) (5)Packing rolling(叠板轧制)：Pack rolling is a flat-rolling operation in which tw

14、o or more layers of metal are rolled together; this process can improve productivity (记住Packing rolling的目的在于提高生产效率)(6) Defects in Rolled Plates and Sheets(轧制过程中的缺陷)：Undesirable(不利)- Degrade surface appearance（降低表面外观）; Adversely affect the strength（影响强度）Sheet metal defects include: 1) scale（绣皮）rust（氧

15、化皮）scratches（擦伤). gouges（槽）pits(坑)2) Cracks （裂纹）May be caused by impurities and inclusions4) Alligatoring ( 皱裂，鳄纹）complex phenomenon 图(a)是波浪形边缘；图(b)是中心裂纹；图(c)是拉链式边缘裂纹；图(d)是皱裂13.5、Shape-Rolling OperationsStraight and long structure shapes, such as solid bars，channels, I-beams, and railroad rails, are

16、 rolled by passing the stock (原料) through a set of specially designed rolls(特制的轧辊)型轧及平轧的主要区别在于型轧使用特制的轧辊(1) Ring rolling（圆环轧制）：In the ring-rolling process, a thick ring is expanded into a large diameter ring with a reduced cross-section. The ring is placed between two rolls, one of which is driven ,a

17、nd its thickness is reduced by bringing the rolls closer together as they rotate.Since the volume of the ring remains constant during deformation, the reduction in thickness is compensated （补偿） by an increase in the rings diameter.The advantages of this process are 1）short production times, 2） mater

18、ial saving, 3）close dimensional tolerances（精确的尺寸公差）4）favorable（良好的）grain flow（晶粒流线）in the product.(2) Thread-Rolling(螺纹轧制)：The thread rolling process is a cold-forming process by which straight or tapered threads are formed on round rods by passing them between dies. The thread-rolling process has a

19、dvantages such as 1)without any loss of material (scrap) ;2) with a good strength (due to cold working);3)The surface finish is very smooth;4)induces(诱发）compressive residual stresses（残余压应力）on the workpiece surfaces;5)at high rates of production;6) Thread rolling is superior( 更好的）to the other methods

20、 of manufacturing threadsFigure 13.16 (a) Features of a machined or rolled thread. (b) Grain flow in machined and rolled threads. Unlike machining, which cuts through the grains of the metal, the rolling of threads causes improved strength, because of cold working and favorable grain flow.机加工螺纹内部组织被

21、切断，而轧制螺纹由于冷成型加工而保持良好的晶粒流线Review:1. Rolling is the process of reducing the thickness (or changing the cross-section) of a long workpiece by forces applied through a set of rolls. The rolls pull the material into the roll gap through forces on the material. a) compressive b) tensile c) shear d) fricti

22、onal 2. Which one is NOT the characteristic of a cast structure? a) dendritic b) finer grains size c) brittle d) porous 3. Which one is the characteristic of a wrough structure? a) dendritic b) finer grains size c) brittle d) porous 4.Which one of the following is NOT the product of the hot rolling

23、process? a) billet b) ingot c) slab d) bloom 5. Although friction is necessary for rolling materials, energy is dissipated in overcoming friction; thus, increasing friction means increasing forces and power requirements. Furthermore, high friction could damage the surface of the rolled product. A co

24、mpromise has to be made, one which includes low coefficients of friction by using effective lubrication. ( ) 6.In the flat rolling products, sheets are generally regarded as having a thickness greater then 6mm. ( ) SUMMARY 1、Rolling is the process of reducing the thickness or changing the cross-sect

25、ion of a long workpiece by compressive forces applied through a set of rolls. In addition to flat rolling, shape rolling is used to make products with various cross-sections. Products made by rolling include: plate, sheet, foil, rod, seamless pipe(无缝钢管）, and tubing; shaped-rolled products,such as I-

26、beams and structural shapes; and bars of various cross-section. Other rolling operation include ring rolling and thread rolling. 2、Rolling may be carried out at room temperature (cold rolling) or at elevated temperatures (hot rolling). The process involves several material and process variables, inc

27、luding roll diameter (relative to material thickness),reduction per pass, speed, lubrication, and temperature. 3、 Continuous casting and rolling of ferrous and of nonferrous metals(黑色和有色金属） into semifinished products have become a common practice because of its economic benefits. Question： 1、What is

28、 the definition of the rolling? 2、How to classify rolling process? 3、What is the flat rolling? 4、What is the difference between a plate and a sheet? 5、Give some examples of the application of the plates and sheets. 6、Explain the relationship of the velocity between the strip and rolls. 7、Explain the

29、 advantages and disadvantages of the friction during the rolling. 8、Define (a) roll gap, (b) neutral point, ( c )draft 9、Describe the difference between a bloom, a slab , and a billet. 10、List the defects commonly observed after flat rolling 11、What is the hot rolling and cold rolling? 12、What is th

30、e difference between cast structure and wrought structure? 13、What is the difference between hot rolling and cold rolling? 14、 What is scale? 15、 How to remove the scale ? 16、 What is the shape rolling? 17、Make a list of some parts that can be made by shape rolling. 18、Describe types of products tha

31、t can be made by thread rolling 19、What is the advantages of the rolling process ?14 Forging of Metal（锻造） 14.1 、Introduction (1)Forging is a process in which a workpiece is shaped (formed) by compressive forces applied through various dies(模具) and tools(工具). Most forgings, however, require a set of

32、dies and such equipment as a press (压力机) or a forging hammer(锻锤). Characteristics of forged part: Metal flow and grain structure can be controlled, Forged parts have good strength and toughness. They can be used reliably for stressed and critical(关键的) application. Typical forged products: Bolts(螺栓)、

33、Rivets(铆钉)、Connecting rods(连杆)、Gears(齿轮)、Shaft(轴)、Hand tool(手工具)、Structural components(结构组件)铸造件(Casting)有不可避免的缺陷，如晶粒粗大、结构疏松、具有多孔，其组织和性能均较差切削件(Maching)的内部晶粒大小和结构不改变，且其金属纤维组织被切断了，使得零件强度下降锻造件(Forging)在经受了塑性变形和再结晶，粗大的树枝状结晶组织被破碎，疏松和孔隙被压实、焊合，内部组织和性能都得到了提高(2) Classification of ForgingA、depending on tempera

34、ture cold forging(冷锻)：at room temperature hot forging(热锻)：above recrystallization temperature warm forging(温锻)：between room temperature and recrystallization temperatureB、depending on tools Open-Die Forging(自由锻造) Impression-Die Forging(模锻) Closed-Die Forging (闭式模锻) Preicison Forging(精密锻造)(3)Comparis

35、on of Cold Forging to Hot ForgingCold forging: 1) requires greater forces, 2) workpiece materials must have sufficient ductility at room temperature.3) Cold-forged parts have good surface finish and dimensional accuracy. Hot forging: 1）Hot forging requires smaller forces, 2）but it produces dimension

36、al accuracy and surface finish that are not as good14.2 、Open-Die Forging (1)Open-die forging is the simplest forging process. It can be depicted（描述） by a solid workpiece placed between two flat dies and reduced in height by compressing it. Open-die forging is also called upsetting(顶锻，镦粗)or flat- di

37、e forging(平模锻造)(2)Barrel(鼓形现象产生原因及减小措施)：Friction(摩擦的原因)：Barreling is caused primarily by frictional force at the die-workpiece interfaces that oppose the outward flow of the materials at these interfaces. 措施：Barreling caused by friction can be minimized if an effective lubricant is used.使用润滑剂 Temper

38、ature difference(温度差的原因)：Barreling can also occur in upsetting hot workpiece between cold dies. The material at and near interfaces cools rapidly, while the rest of the workpiece remains relatively hot. Thus, the material at the ends of the workpiece has higher resistance to deformation than the mat

39、erial at its center. the central portion of the workpiece expands laterally to a greater extent than do its ends. 措施：Barreling from thermal effects can be reduced or eliminated by using heated dies.加热模具(3) Cogging （开坯或者拔长） , also called drawing out, is basically an open-die forging operation in whic

40、h the thickness of a bar is reduced by successive（连续的） forging steps at specific intervals(时间间隔). Because the contact area per stroke is small, a long section of a bar can be reduced in thickness without requiring large forces or machinery.14.3 、Impression Die (开模锻)and Closed-Die Forging(闭模锻) (1) In

41、 impression-die forging, the workpiece acquires the shape of the die cavities (impressions) while being forged between two shaped dies(Fig. 14.6).Flash(飞边)的作用：Because the thin flash cools rapidly and has higher frictional resistance than die cavity, it subjects the material in the die cavity to high

42、 pressures, thereby encouraging the filling of the die cavity.连杆的开模锻过程：1) Preparing blan(备料)：(a) cutting or cropping from an extruded or drawn bar stock.（从一根挤出或者拉伸棒料上剪切) (b) a preform in operations such as powder metallurgy.用粉末冶金之类的操作方法预成形) (c) casting.（铸造） (d) a preform blank in a prior forging ope

43、ration.(用预锻造操作预成形坯料）2）Preforming processes(预成形)：Preforming processes, such as fullering（压槽） and edging（切 边，修边） (Fig. 14.7b and c), are used to distribute the material into various regions of the blank.fullering-排料,edging-聚料In fullering, material is distributed away from an area. In edging, material

44、is gathered into a localized area3) blocking(粗模锻)：After preform processes, the part is then formed into the rough shape of a connecting rod by a process called blocking （粗模锻）, using blocker dies.4)finishing forging(精模锻)5)trimming operation(剪切)(2) Closed-die forging(闭式模锻)：The example shown in Figs. 1

45、4.6 and 14.7 are also referred to as closed-die forgings. However, in true closed-die or flashless forging, flash does not form and the workpiece completely fills the die cavity. Accurate control of the volume of material and proper die design are essential in order to obtain a closed die forging of

46、 the desired dimensions and tolerances: Undersize(不足的) blanks prevent the complete filling of the die cavity; conversely, oversize(过多的) blanks generate excessive pressures and may cause dies to fail prematurely or to jam.(3) 闭式模锻应用之一 精密锻造（Precision Forging ）Forging generally require additional finis

47、hing operations, such as heat treating（热处理）, to modify properties, and then machining（机加工） to obtain accurate finished dimension. These operations can be minimized by precision forging, which is an important example of the trend toward net-shape or near-net shape forming（净成形或近净成形 ）processes. This tr

48、end significantly reduces the number of operations required, and hence the manufacturing cost to make the final product.特点：1) Precision forging produces parts having greater accuracies than those from impression-die forging and requiring much less machining. 2) The process requires higher capacity e

49、quipment, because of the greater forces required to obtain fine details on the part. 3) Precision forging requires special and more complex dies, precision control of the billets volume and shape, accurate positioning of the billets in the die cavity, and hence higher investment. .4) Less material i

50、s wasted, and much less subsequent machining is required, because the part is closer to the final desired shape应用：1)Because of the relatively low forging loads and temperatures that they require, aluminum and magnesium alloys are particularly suitable for precision forging; 2) Typical precision-forg

51、ed products are gears , connecting rods, housings, and turbine blades.3) The choice between conventional forging and precision forging requires an economic analysis, particularly in regard to the production volume.(4) 闭式模锻工艺应用之二压印（Coining）Coining essentially is a closed-die forging process typically

52、 used in minting coins, medallions and jewelry. The pressures required can be as high as five or six times the strength of the material. Lubricants cannot be applied in coining.14.4、 Related Forging Operations Heading(镦头) is essentially an upsetting operation, usually performed at the end of round r

53、od or wire in order to produce a larger cross-section. The typical parts are the Bolts（螺钉 ）, screws（螺杆）, rivets（铆钉）, nails（钉子） , and other fasteners（紧固件）.Piercing(冲孔) is a process of indenting (压窝）the surface of a workpiece with a punch (but not breaking through) in order to produce a cavity or an i

54、mpression14.7 、Die Materials and Lubrication(锻造材料要求和润滑剂的作用)(1)General requirements for die materials therefore are: 1) strength and toughness at elevated temperature;2) hardenability(淬硬性）and ability to harden uniformly; 3) resistance to abrasive wear, because of the presence of scale in hot forging.

55、(2)Lubricants 1)greatly influence friction and wear, they affect the forces required and the flow of the metal in die cavities; 2)They can act as a thermal barrier between the hot workpiece and the relatively cool dies, slowing the rate of cooling of the workpiece and improving metal flow. 3) Lubric

56、ants serve as a parting agent （脱模剂） which inhibits（抑制） the forging form sticking to the dies and helps in its release from the die. 14.8 、ForgeabilityForgeability is generally defined as the capability of a material to undergo deformation without cracking. 锻造性通常被定义为一种材料经受变形而不开裂的能力Review1 Forging is

57、a process in which the workpiece is shaped by forces applied through various dies and tools. In the impression-die forging, some of the material flows outward and forms a _, which has a significant role in the flow of material in impression-die forging. 2. and are used to distribute the material int

58、o various regions of the forging workpiece. 3、Pack rolling is a flat-rolling operation in which two or more layers of metal are rolled together; this process improves . 3、flat rolling, or simply rolling, where the rolled products are flat and . 4、Which process is was first used to make jewelry, coin

59、s, and various implements by hammering metal with tools made of stone before 4000B.C. A. Stamping B. Rolling C. Forging D. Extrusion 5. Which operation in the following options is not forging processes? A. pancaking B. Piercing C. punch D. Heading 1.The die surfaces in open-die forging always is fla

60、t. . 2.In plastic forming process, the volume of workpiece maintains constant. 3.Barreling is caused primarily by frictional force at the die- workpiece interfaces that oppose the outward flow of the materials at these interfaces. 4.The flash is excess metal that is subsequently trimmed off, so it i