15挤压ok

nullnullChapter 15 Extrusion and Drawing of MetalsContextContext15.1 Introduction 15.2 The Extrusion Process 15.3 Hot Extrusion 15.4 Cold Extrusion 15.5 The Drawing Process 15.6 Drawing Practice15.1 Introduction For Extrusion15.1 Introduction For ExtrusionIn the extrusion process, a billet (generally round ) is forced through a die (Fig. 15.1), in a manner similar to squeezing toothpaste from a tube. Schematic illustration of the direct extrusion process1、What is the extrusion process ?null挤压方向挤压挤压挤压是将金属毛坯放入模具模腔中，在强大的压力和一定的速度作用下，迫使金属从模腔中挤出，从而获得所需形状、尺寸以及具有一定力学性能的挤压件。 挤压加工是靠模具来控制金属流动，靠金属体积的大量转移来成形零件的。nullAlmost any solid or hollow cross-section may be produced by extrusion, which can create essentially semifinished parts . Because the die geometry remains the same throughout the operation, extruded products have a constant cross-section.2、What kind of products can be made by extrusion ? Examples of products made by sectioning off extrusionsnullApplicationApplicationnull建筑幕墙地铁线轨散热器Extrusion Profile (挤压型材)Extrusion Profile (挤压型材)建筑型材 工业型材Profile DrawingProfile Drawing工业型材幕墙型材Profile DrawingProfile Drawing 百叶窗型材 推拉门型材nullDepending on the ductility of the material, extrusion may be carried out at room or at an elevated temperature. Because a chamber（腔，膛） is involved, each billet is extruded individually, and thus extrusion is a batchor semicontinuous（半连续） process. Extrusion is often combined with forging operaions, in which case it is generally known as cold extrusion（冷挤压）. It has numerous important applications, including fasteners and components for automobiles, bicycles, motorcycles, heavy machinery, and transportation equipment.nullTypical products made by extrusion are railings for sliding doors, tubing having various cross-section, structural and architectural shapes, and door and window frames. Extruded products can be cut into desired lengths, which then become discrete parts such as brackets（支架）, gears, and coat hangers（衣架）. Commonly extruded materials are aluminum, copper, steel, magnesium, and lead（铅） (lead pipes were made by extrusion in the eighteenth century ). Other metals and alloys can also be extruded, with various levels of difficulty. Extrusion of plastics is described in section 18.2.5、What is the typical products made by extrusion ?6、What is the common extruded materials ?Typical Extrusion productsTypical Extrusion products型材挤压工艺的过程型材挤压工艺的过程特点：高温 高压 大变形 型材实际挤压过程avi 型材实际挤压过程avi实际型材图实际型材图型材挤压机全景型材挤压机全景15.3 The Extrusion Process15.3 The Extrusion Process 15.3.1、Direct Extrusion 直接挤压，正挤压 15.3.2、Indirect Extrusion 间接挤压，反挤压 15.3.3、 Hydrostatic Extrusion 静水压挤压 15.3.4、 lateral Extrusion 侧向挤压15.3.1 Direct Extrusion15.3.1 Direct ExtrusionDirect also is called forward extrusion, a round billet is placed in a chamber (container) （容器，料筒）and forced through a die opening by a hydraulically-driven(液压驱动） ram or pressing stem.Schematic illustration of the Direct ExtrusionnullThe direction the metal flows is same with that the pressing stem moves toward.Billet Pressing stemnullIn indirect extrusion (reverse, inverted, or backward extrusion), the die moves toward the billet. (Fig. 15.3a)15.3.2、Indirect ExtrusionSchematic Illustration of Indirect ExtrusionnullThe direction the metal flow is opposite to that the pressing stem moves toward. Press stemBillet15.3.3 hydrostatic extrusion15.3.3 hydrostatic extrusionIn hydrostatic extrusion (Fig. 15.3b), the billet is smaller in diameter than the chamber, which is filled with a fluid, and the pressure is transmitted to the billet by a ram. Unlike in direct extrusion, there is no friction to overcome along the container walls.Schematic Illustration of Hydrostatic ExtrusionnullAnother type of extrusion is lateral, or side, extrusion.15.3.4 Lateral Extrusionnull15.3.4 Process variables in extrusion15.3.4 Process variables in extrusion1) The die angle, α, 2) extrusion ratio, R reduction in cross-section(A0/Af) 3)extrusion speed, 4)billet temperature, 5)and lubrication 6)all affect the extrusion pressurenullThus the CCD for a square cross-section is its diagonal（对角线） dimension. **About CCDWhat is CCD ?Circumscribing-circle diameter（外切园直径） , abbreviated CCD, is a parameter describing the shape of the extruded product. It is the diameter of the smallest circle into which the extruded cross-section will fit .Method of determining CCD of an extruded cross-sectionnullThe complexity of an extrusion is a function of the ratio of the perimeter(周长） of the extruded product to its cross-sectional area, known as the shape factor. Obviously, a solid round extrusion has the smallest shape factor, whereas the parts shown in Fig. 15.2 have high shape factors. **Shape Factor （形状因子）The shape factor is used to describe the complexity of an extrusion.What is the shape factor ?15.3.5 Types of metal flow in extruding with square dies15.3.5 Types of metal flow in extruding with square diesFlow pattern obtained at low frictionFlow Pattern obtained at high friction, or with cooling of the outer regions of the billet in the chamberThis type of pattern, observed in metals whose strength increases rapidly with decreasing temperature leads to a defect known as pipe, or extrusion defect.15.4 Hot Extrusion15.4 Hot Extrusion1) alloys do not have sufficient ductility at room temperature, 2) in order to reduce the forces required . As in all other hot working operations, hot extrusion has special requirements because of the high operation temperatures.1、The reason for hot process Hot process: hot rolling, hot forging, hot extrusion2、Extrusion Temperature Ranges for Various Metals2、Extrusion Temperature Ranges for Various Metals ℃ Lead 200-250 Aluminum and its alloys 375-475 Copper and its alloys 650-975 Steels 875-1300 Refractory alloys 975-2200null1、 die wear can be excessive 2、 cooling of the hot billet in the chamber can be a problem which results in highly nonuniform deformation (Fig. 15.7c). 3、The billet may develop an oxide film (氧化膜） unless heated in an inert-atmosphere（惰性气氛）. This film can be abrasive, and it can affect the flow pattern of the material. It also can affect surface finish of extrusion products. 3、Usual Questions in Extrusionnull1、Using extrusion dies preheated to reduce cooling of the billet and to prolong die life, as is done in hot forging operations. 2、 Using the dummy block（挤压垫） made a little smaller in diameter than the container and placed ahead of the ram to avoid the formation of oxide films on the hot extruded product,. 4、How to resolve the questions in extrusion process ?nullAs a result, a thin cylindrical shell (skull), consisting mainly of the oxidized layer, is left in the container. The extruded product is thus free of oxides; the skull is later removed from the chamber. 15.5 Cold Extrusion15.5 Cold ExtrusionDeveloped in the 1940s, cold extrusion is general term often denoting a combination of operations, such as direct and indirect extrusion and forging . Thin arrows indicate the direction of metal flow during extrusionCold extrusion has gained wide acceptance in industry, particularly for tools and for components in automobiles, motorcycles, bicycles, appliances, and transportation and farm equipment.挤压挤压冷挤压是一种少无切削加工工艺。它是在室温下利用模具的压力使模腔内的金属毛坯产生塑性流动（变形），从而获得所需要的形状、尺寸以及具有一定机械性能的挤压件。 根据金属被挤出的方向与凸模运动方向的关系，常用的冷挤压方法包括：正挤压，反挤压，复合挤压。null1）Improved mechanical properties resulting from work-hardening, provided that the heat generated by plastic deformation and friction does not recrystallize the extruded metal. 2）Good control of dimensional tolerances, reducing the need for subsequent machining or finishing operations; 3）Improved surface finish, due partly to lack of an oxide film, provided that lubrication is effective. 4）Elimination of the need for billet heating; 5）Production rates and costs that are competitive with those of other methods of producing the same part; 2、Advantages of Cold Extrusion挤压的另一种分类方法挤压的另一种分类方法Hollow ProfileSolid Profile15.6 The Drawing Process15.6 The Drawing Process1、What is the Drawing ?Drawing （拉拔）is an operation, developed between A.D.1000 and 1500, in which the cross-section of solid rod, wire, or tubing is reduced or changed in shape by pulling(拉） it through a die. 2、What kind of products can be made by drawing ?2、What kind of products can be made by drawing ?Drawn rods are used for shafts（轴）, spindles（转轴）, and small pistons（活塞） and as raw material for fasteners such as rivets（铆钉）, bolts（螺栓）, and screws（螺钉）. In addition to round rods, various profiles can also drawn. The term drawing is also used to refer to making cup-shaped parts by sheet forming operations nullThe distinction between the terms rod and wire is somewhat arbitrary, rod merely being larger in cross-section than wire. Wire’ sizes is down to 0.01 mm (0.0005 in.) for magnet wire（磁线）, and even smaller for use in very low-current fuses（低电流保险丝）. Wire and wire products cover a wide range of applications, such as electrical（电的，电气的） and electronic（电子的） wiring cables, tension-loaded（拉伸负荷） structural members, welding electrodes（电极，焊条）, springs（弹簧）, paper clips（回形针）, spokes(辐条） for bicycle wheels, and stringed（弦） musical instruments. 3、What is the distinction between the terms rod and wire ?null1) the reduction in cross-sectional area 2) the speed of drawing, 3) the temperature, 4) the lubrication. 5) die angle, 6) friction along the die-workpiece interfaces 2、Major Variable in drawingnullDrwaing of Other Shapes. Various solid-sections can be produced by drawing through dies with different profiles. The initial cross-section is usually round or square. Proper die design and the proper selection of reduction sequence per pass required considerable experience to ensure proper material flow in the die, reduce internal or external defects, and improve surface quality. The wall thickness, diameter, or shape of tubes that have been produced by extrusion or by other processes can be further reduced by tube drawing processes (Fig. 15.19). null3、Example of tube-drawing operations, with and without an internal mandrelTubes as large as 0.3m in diameter can be drawn by these techniques. Mandrels（芯模，芯棒） of various profiles are available for these operations. 4、 Drawing Practice 4、 Drawing Practice 1）As in all metalworking processes, successful drawing operations require careful selection of process parameters and consideration of many factors. 2）Drawing speeds depend on the material and on the reduction in cross-sectional area; they may range from 1m/s to 2.5m/s for heavy sections, to as much as 50m/s for very fine wire, such as that used for electromagnets（电磁体）. 3）Because the product does not have sufficient time to dissipate the heat generated, temperatures can rise substantially at high drawing speeds and can have detrimental（有害的） effects on product quality. null4）Reductions in cross-sectional area per pass range from near zero to about 45%; usually, the smaller the initial cross-section, the smaller the reduction per pass. 5）A light reduction, called a sizing pass（精整道次）, may also be taken on rods to improve surface finish and dimensional accuracy. Because they basically deform only the surface layers, however, light reduction usually produce highly nonuniform deformation of the material and its microstructure. Consequently, the properties of the material vary with location within the cross-section. null6）Because of work hardening, intermediate annealing（中间退火） between passes may be necessary to maintain sufficient ductility during cold drawing. 7）High-carbon steel wires for springs and for musical instruments are made by heat treating (patenting) the drawn wire; the microstructure so obtained is fine pearlite（珠光体）. These wires have ultimate tensile strengths as high as 5Gpa (700ksi) and tensile reduction of area of about 20%. nullIt refers to draw many wires (as many as several thousand) simultaneously（同时地）. The bundle Drawing is employed to increase productivity. The wires are separated from one another by a suitable metallic material with similar properties but lower chemical resistance. Bundling produces wires that are somewhat polygonal in cross-section rather than round. 5、 Bundle DrawingWhat is the bundle drawing ?nullThe wires produced can be as small as 4um (0.00016in.) in diameter; they can be made from such materials as stainless steels, titanium, and high-temperature alloys. Applications include electrically conductive plastics（导电塑料）, heat-resistant（耐热的） and electrically conductive textiles, filter media, radar camouflage（伪装）, and medical implants（植入物）. null1、What is the extrusion process ? 2、What kind of products can be made by extrusion ? 3、What is the typical products made by extrusion ? 4、What is the common extruded materials ? 5、What is drawing ? 6、What kind of products can be made by drawing ? 7、What is the distinction between the terms rod and wire ? 8、What is the difference between direct extrusion, indirect extrusion, Hydrostatic Extrusion and lateral Extrusion 9、Describe the process variables in extrusion 10、What is CCD ? Review and Question Review and Question Review and Question 11、What is the shape factor ? 12、Why does a solid round extrusion has the smallest shape factor than other profile ? 13、What causes the dead zone ? 14、Two reason for using hot process 15 Describe usual Questions in Extrusion 16、How to resolve the questions in extrusion process ? 17、Describe the advantages of Cold Extrusion What do major Variables in drawing include ? 19 What is the bundle drawing ?SUMMARY SUMMARY Extrusion is the process of forcing a billet through a die, to reduce its cross-section or to produce a wide range of solid or hollow cross-sections. The process is generally carried out at elevated temperatures, to reduce forces and to improve the ductility of the material. Important factors in extrusion are die design, extrusion ratio, billet temperature, lubrication, and extrusion speed. nullAlthough the term cold extrusion applies to extrusion at room temperature, it is also the name for a process which is combination of extrusion and forging operations. Cold extrusion is capable of economically producing discrete parts in various shapes, with good mechanical properties and dimensional tolerances. Rod, wire, and tube drawing basically involve the process of pulling the material through a die (or a set of dies in tandem). Although the cross-section of most drawn products are round, other shapes can also be drawn. nullDrawing tubular products, to reduce either their diameter or their thickness, usually requires internal mandrels. The die design, the reduction in cross-sectional area per pass, and the selection of die materials and lubricants are all important parameters in obtaining drawn products of high quality and of good surface finish. Both external defects and internal defects (chevron cracking) can develop both in extrusion and in drawing; their minimization depends principally on the die angle, the reduction per pass, and the quality of the workpiece material.TRENDS 发展趋势TRENDS 发展趋势Computer-aided die design and manufacturing are being implemented, to improve material flow in extrusion and in drawing and to reduce defects. Ceramic dies are being used in high-temperature extrusion of small cross-section . Improvemants are taking place in die materials and in coatings to extend die life. KEY TERMSKEY TERMSBamboo defect 竹节状缺陷 Bridge die 空心件挤出模, 桥式孔型挤出模 Bull block 拉丝机 Bundle drawing 捆扎拉拔 Canning 外皮包覆，罐装 Capstan 绞盘，卷筒，主动轮 Center cracking 中心开裂 Chevron cracking 人字形裂纹 Circumscribing-circle diameter 外切圆直径 Ironing 挤拉法，变薄拉深，压平 Jacketing 套筒，套式冷却（加温）nullCold extrusion 冷挤压 Conversion coating 转化涂层 Dead-metal zone 金属死区 Draw bench 拉伸（拉拔）机，拉丝机 Drawing 拉拔，拉伸 Extrusion 挤压，挤出 Extrusion constant 挤出常数 Extrusion defects 挤出缺陷 Extrusion ratio 挤出比 Fir-free cracking 冷杉状裂纹 Hydrostatic extrusion 液力静挤压，静水压挤压nullPatenting 钢丝韧化处理, (线材的)拉拔(拉丝)后的退火处理 Pipe defect 管缺陷 Porthole die 多孔拉拔（挤压）模 Rod 杆，棒材 Seam 接缝 Sejournet process Sejournet工艺 Shear die 剪切模 Sizing pass 定径工艺 Speed cracking 高速开裂 Spider die 异形孔挤压模 Turk’s head 互成直角的四辊轮拉丝模装置 Wire 丝，线材