重庆理工材料成形技术基础课程课件双语PPT之7Sheet-MetalFormingProcesses.ppt

1、Fundamental of Materials Forming,-Sheet-Metal Forming Processes板金成形工艺,INTRODUCTION,Products made by sheet-metal forming processes are all around us;they include metal desks,file cabinets,appliances,car bodies,aircraft fuselages(机身）,and beverage（饮料）cans.Sheet forming dates back to 5000 B.C.,when hous

2、ehold utensils(器具）and jewelry were made by hammering and stamping gold,silver,and copper.,冲压生产场景,Compared to those made by casting and by forging,sheet-metal parts offer the advantages of light weight and versatile（万能的）shape.Because of its low cost and generally good strength and formability charact

3、eristics,low-carbon steel is the most commonly used sheet metal For aircraft and aerospace applications,the common sheet materials are aluminum and titanium.,Outline of Sheet-Metal Forming Processes,Figure 16.1,Characteristics of Sheet-Metal Forming Processes,SHEARING剪切,Before a sheet-metal part is

4、made,a blank of suitable dimensions is first removed from a large sheet(usually from a coil)by shearing;that is,the sheet is cut by subjecting it to shear stresses,typically ones developed between a punch and a die(Fig.16.2a).Typical features of the sheared edges of the sheet and of the slug are sho

5、wn in Figs.16.2b and c,respectively.Note that the edges are not smooth,nor are they perpendicular to the plane of the sheet.,The major processing parameters,The major processing parameters in shearing are the shape of and the materials for the punch and die,the speed of the punching,the lubrication,

6、and the clearance,c,between the punch and the die.The clearance is a major factor in determin-ing the shape and the quality of the sheared edge.,Clearance,Figure 16.3(a)Effect of the clearance,c,between punch and die on the deformation zone in shearing.As the clearance increases,the material tends t

7、o be pulled into the die rather than be sheared.In practice,clearances usually range between 2%and 10%of the thickness of the sheet.(b)Microhardness(HV)contours for a 6.4-mm(0.25-in)thick AISI 1020 hot-rolled steel in the sheared region.Source:H.P.Weaver and K.J.Weinmann.,Punch force,The force requi

8、red to punch is,basically,the product of the shear strength of the sheet metalby the area being sheared.Friction between the punch and the workpiece can,however,increase this force substantially.The maximum punch force,F,can be estimated from the equation F=0.7TL(UTS),where T is sheet thickness,L is

9、 the total length sheared(such as the perimeter of a hole),and UTS is the ultimate tensile strength of the material.As the clearance increases,the punch force decreases,and the wear on dies and punches is also reduced.,Shearing Operations,Several operations based on the shearing process are performe

10、d.We first define two terms.In punching,the sheared slug is discarded(Fig.16.4a).In blanking,the slug is the part and the rest is scrap.Many of the operations described below,as well as those described throughout the rest of this chapter,can now be carried out on computer-numerical-controlled machin

11、es(see Chapter 39)with quick-change toolholders.,Shearing Operations,notching开槽,lancing切缝,Slitting切口,erforating成孔,arting切断,Shearing dies,Fig 16.3(a)Effect of the clearance,c,between punch and die in the deformation zone in shearing.As the clearance increases the material trends to be pulled into the

12、 die rather than be sheared.,Fine Blanking.,Very smooth and square edges can be produced by fine blanking(Fig.16.5a).The fine-blanking operation is usually carried out on triple-action hydraulic presses,where the movements of the punch,of the pressure pad,and of the die are separately controlled.The

13、 process usually involves a part having holes that are punched simultaneously with its blanking.Suitable sheet hardness is typically between 50 and 90 HRB.,Fine Blanking精冲,Figure 16.5(a)Comparison of sheared edges produced by conventional(left)and by fine-blanking(right)techniques.(b)Schematic illus

14、tration of one setup for fine blanking.Source:Feintool U.S.Operations.,Slitting(切口）,Slitting.Shearing operations can be carried out by means of a pair of circular blades(刀片）similar to those in a can opener(Fig.16.6);this process is called slitting.The blades follow either a straight line or a circul

15、ar or curved path.A slit edge normally has a burr毛刺,which may be plastically folded over the sheet surface by rolling the sheet between two rolls.,Figure 16.6 Slitting with rotary knives.This process is similar to opening cans.,steel rule钢尺,Soft metals(as well as paper,leather,and rubber)can be blan

16、ked with steel-rule dies.Such a die consists of a thin strip of hardened steel,bent into the shape to be produced(a concept similar to that of a cookie cutter)and held on its edge on a flat wooden base.The die is pressed against the sheet,which rests on a flat surface,and it shearsthe sheet along the shape of the steel rule.,Laser Welding,Figure 16.7 Production of an outer side panel of a car body,by laser butt-welding and stamping.Source:After M.Geiger and T.Nakagawa.,Examples of Laser Welded P