华工成型技术第三部分总结课案.docx

1、华工成型技术第三部分总结课案Part 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 general

2、ly regards 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 Rol

3、ling（平扎）Flat 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 t

4、he entrance（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

5、 material 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,

6、(ho-hf), 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

7、-diameter 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:

8、carried out 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, es

9、pecially 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 ( b

10、ecause of 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

11、（增强的强度和延展性）(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, in

12、to structure 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

13、形截面的圆棒或者方棒(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

14、 which two 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（

15、绣皮）rust（氧化皮）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 r

16、ails, are rolled by passing the stock (原料) through a set of specially designed rolls(特制的轧辊)型轧与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

17、driven ,and 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,

18、 2） material 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 proc

19、ess has advantages 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 othe

20、r methods 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

21、加工螺纹内部组织被切断，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

22、d) frictional 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

23、 rolling 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 prod

24、uct. A compromise 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 c

25、ross-section 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,s

26、uch as I-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 varia

27、bles, including 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：

28、1、What is 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、Ex

29、plain the 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、W

30、hat is the 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 pro

31、ducts that 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

32、a set of 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)、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