冲压模具英文原文.doc

Characteristics of Stamping and Properties of Sheet Metal Forming Stamping is a kind of plastic forming process in which a part is produced by means of the plastic forming of the material under the action of a dieStamping is usually carried out under cold state,so it is also called cold stamping.Heat stamping is used only when the blank thickness is greater than 81 00mm.The blank material for stamping is usually in the from sheet or strip,and therefore it is also called sheet metal forming.Some nonmetal sheets(such as plywood,mica sheet,asbestos,leather)can also be formed by stamping. Stamping is widely used in various of the metalworking industry, and it plays a crucial role in the industries for manufacturing automobiles, instruments,military parts and household electrical appliances,etc. The process，equipment and die are the three foundational problems that needed t0 bestudied in stamping. The characteristics of the sheet metal forming are as follows: (1)High material utilization. (2)Capacity to produce thinwalled parts of complex shape. (3)Good interchangeability between stamping parts due to precision in shape and dimension. (4)Parts with lightweight，highstrength and fine rigidity can be obtained. (5)High productivity,easy to operate and to realize mechanization and automatization The manufacture of the stamping die is costly,and therefore it only fits t0 mass production.For the manufacture of products in small batch and rich variety,the simple stamping die and the new equipment such as a stamping machining center,are usually adopted to meet he market demands. The materials for sheet metal stamping include mi ld steel,copper,aluminum,magnesium alloy and high-plasticity alloysteel,etc. Stamping equipment includes plate shear and punching press.The former shears plate into strips with a definite width,which would be pressed later.The later can be used both in shearing and forming.1.1 Characteristics of stamping forming There are various processes of stamping forming with different working patterns and namesBut these processes are similar to each other in plastic deformationThere are following conspicuous characteristics in stamping： (1)The force per unit area perpendicular to the blank surface is not large but is enough to cause the material plastic deformation I t is much less than the inner stresses on the plate plane directionsIn most cases stamping forming can be treated approximately as that of the plane stress state to simplify vastly the theoretical analysis and the calculation of the process parameters (2)Due to the small relative thickness，the anti-instability capability of the blank is weak under compressive stress As a result，the stamping process is difficult to proceed successfully without using the anti-instability device(such as blank holder)Therefore the variety of the stamping processes dominated by tensile stress are more than those dominated by compressive stress (3)During stamping forming，the Inner stress of the blank is equal to or sometimes less than the yield stress of the materialIn this point，the stamping is different from the bulk forming.During stamping forming，the influence of the hydrostatic pressure of the stress state in the deformation zone to the forming limit and the def6nmation resistance is not so important as to the bulk formingIn some circumstances，such influence may be neglectedEven in the case when this influence should be considered，the treating meth()d is also different from that of bulk forming. (4)In stamping forming，the restrain action of the die to the blank is not severe as in the case of the bulk forming(such as die forging) In bulk forming，the constraint forming is proceeded by the die with exactly the same shape of the partWhereas in stamping，in most cases，the blank has a certain degree of freedom， only one surface of the blank contacts with the dieIn some extra cases， such as the forming of the suspended region of sphere or cone，and curling at the end of tube，neither sides of the blank on the deforming zone con-tact with the dieThe deformation in these regions are caused and controlled the die applying an external force to its adjacent area. Due to the characteristics of stamping deformation and mechanics mentioned above，the stamping technique is different from the bulk metal forming： (1)The importance of the strength and rigidity of the die in stamping forming is less than that in bulk forming because the blank can be formed without applying large pressure unit area on its surfaceInstead，the techniques of the simple die and the pneumatic and hydraulic forming are developed. (2)Due to the plane stress or simple strain state in comparison with bulk forming，more research on deformation or force and power parameters has been doneStamping forming can be performed by more reasonable scientific methodsBased on the real time measurement and analysis on the sheet metal properties and stamping parametersby means of computer and some modem testing apparatus research on the intellectualized control of stamping process is also in proceeding (3)It is shown that there is a close relationship between stamping forming and raw material-The research on the properties of the stamping forming，that is，forming ab1ityand shape stabilityhas become a key point in stamping technologyThe research on the properties of the sheet metal stamping not only meets the need of the stamping technology development，but also enhances the manufacturing technique of iron and steel industry。And provides a reliable foundation for increasing sheet metal quality1.2 Categories of stamping forming Many deformation processes can be done by stamping。the basic processes of the stamping can be divided into two kinds：cutting and forming Cutting is a shearing process that one part of the bank is cut from the otherIt mainly includes blanking·punching，trimming，parting and shavingwhere punching and blankmg are the most widely usedForming is a process that one part of the blank has some displacement from the otherIt mainly includes deep drawing，bending，local forming，bulging，flanging，neckingsizing and spinning In substance，stamping forming is such that the plastic deformation occurs in the deformation zone of the stamping blank caused by the external forceThe stress state and deformation characteristic of the deformation zone are the basic factors to decide the properties of the stamping formingBased on the stress state and deformation characteristics of the deformation zone，the forming methods cart be divided into several categories with the same forming properties and to be studied systematically The deformation gone in almost all types of stamping forming is in the plane stress stateUsually there is no force or only small force applied on the blank surfaceWhen it is assume that the Stress perpendicular to the blank surface equals to zero，two principal stresses perpendicular to each other and act on the blank surface produce the plastic deformation of the materialDue to the small thickness of the blank，it is assumed approximately that the two principal stress distribute uniformly along the thickness directionBased on this analysis，the stress state and the deformation characteristics c，the deformation zone in all kinds of stamping forming on be denoted by the points in the coordinates of the plane principal stresses(diagram of the stamping stress)and the coordinates of the corresponding principal strains(diagram of the stamping strain)The different points in the figures of the stamping stress and strain possess different stress state and deformation characteristics(1)When t he deformation zone of the stamping blank is subjected to the plane tensile stresses，it can divided into two cases ,that isand I n both cases，the stress with the maximum absolute value is always a tensile stressThese two cases are analyzed respectively as followsIn the case thatand.according to the integral the relationships between stresses and strains are：where, are the principal strains of the radial，tangential and thickness directions of the exial symmetrical stamping feinting； , and are the principal stresses of the radial tangential and thicken directions of the axial synmletrical stamping forming；is the average stress, k is a contant. In plane stress,Equation1.1is rewritten as the following form; Since >>0,so >0 and>0.,In indicates that in plane stress state with two axial tensile stresses, if the tensile stress with the maximum absolute value is ,the principal strain in this direction must be positive, that is，the deformation belongs to tensile formingIn addition，because>>0,therefore<0 and<0.the station in the thickness direction of the blank is negative，that is，the deformation belongs to compressive forming，and the thickness decreasesThe deformation condition in the tangential direction depends on the values of and ,when =2,=0;when>2,<0;and when <2,<0,when<2, >0. The range of is 0. In the equibiaxial tensile stress state =, according to Equation 12 =>0 and <0 . I n the uniaxial tensile stress state =0，accordingto Equation 12，=/2. According to above analysis，it is known that this kind of deformation condition is in the region AON of the diagram of the stamping strain(see Fig11)，and in the region GOH of the diagram of the stamping stress.2)when >>0 and =0,according to equation 1.2 2 >>0,and >0.this result shows that for the plane stress state with two tensile stresses，when the absolute value of is the maximum，the strain in this direction must be positive，that is，it must be in the state of tensile formingAlso because >>0, therefore <0 and <0. The strain in the thickness direction of the blank of is negative，or in the state of compressive forming，and the thickness decreasesFig11 Diagram of stamping strain Fig12 Diagram of stamping stress The deformation condition in the radial direction depends on the values of and . when =2,=0;when >2,<0.The range of is >>0,when =,=>0, that is in equibiaxial tensile stress state，the tensi1e deformation with the same values occurs In the two tensile stress direct ions；when =0 , =/2<0 .that isin uniaxial tensile stress state，the deformation characteristic in this case is the same as that of the ordinary uniaxial tensile This kind of deformation is in the region AON of the diagram of the stamping strain(see Fig1.1)，and in the region GOH of the diagram of t he stamping stress(see Fig1.2) Between above two cases of stamping deformation，the properties of and and the deformation caused by them are the same，only the direction of the maximum stress is different These two deformations are exactly the same for isotropic homogeneous material (2)When the deformation zone of the stamping blank is subjected to two compressive stresses and ( =0), it can also be divided into two cases，which are 2<0 , =0 and <<0, =0.1)W hen <<0.， =0, according to Equation 12，2<0 and <0.This result shows that in the plane stress state with two compressive stamping，if the stress with the maximum absolute value is <0 ,the strain in this direction must be negative，that is，in the state of compressive forming Also because <<0 ,therefore >0 and >0The strain i n the thickness direction of the blank is positive，and the thickness increases The deformation condition in the tangential direction depends on the values of and . When =2,=0;when >2 and <0; and when <2, and >0. The range of is <<0 .When =it is in equibiaxial tensile stress state hence =<0,when =0 it is in uniaxial tensile stress state，hence =/2. This kind of deformation condition is in the region EOG of the diagram of tile stamping strain(see Fig1.1)，and in the region COD of the diagram of t he stamping stress(see FigI2)2)When <<0 and =0 according to Equation1.2， 2<0 and <0.This result shows that in the plane stress state with two compressive stresses. if the stress with the maximum absol ute value is ，the strain in this direction must be negative，that isIn the state of compressive formingAlso because <<0,therefore >0 and >0 The strain in the thickness direction of the blank is positive, and the thickness increasesThe deformation condition in the radial direction depends on the values of and .when =2,=0;when >2,<0.The range of is <<0,when = ,it is in equibiaxial tensile stress state，hence =<0;when =0.it is in uniaxial tensile stress state，hence =/2>0 .This kind of deformation is in the region GOL of the diagram of the stamping strain(see Fig11)，and in the region DOE of the di -agram of t he stamping stress(see Fig12)(3)The deformation zone of the stamping blank is subjected to two stresses with opposite signs，and the absolute value of the tensile stress is larger than that of the compressive stressThere exist two cases to be analyzed as follows：1)When >0, <0 and >,according to Equation 1.2 2->0 and >0.This result shows that in the plane stress state with opposite signs，if the stress with the maximum absolute value is tensile，the strain in the maximum stress direction in positive，that is, in the state of tensile forming Also because>0, <0 and >, therefore<0.The strain in the compressive stress direction is negative，that is，in the state of compressive formingThe range of is 0>>.when =.then>0, <0,and =;when =0, then >0, <0,and =/2,it is the uniaxial tensile stress state .this kind of deformation condition is in the region MON of the diagram of the stamping state ,this kind of deformation condition is 1n the region Of the diagram the stamping strain(see Fig11)，and in the region FOG of the diagram of the stamping stress(See Fig12) 2)When>0<0， =0, > ,according to Equation 12 ,by means of the same analysis mentioned above，>0，that is，the deformation zone is in the plane stress state with opposite signsIf the stress with the maximum absolute value is tensile stress ，the strain in this direction is positive，that is，in the state of tensile formingThe strain in the radial direction is negative . that is ,in the state of compressive forming The range of is 0一When= -，then >0,<0 and =;when=0，then >0，<0，and =/2This kind of deformation condition is in the region COD of the diagram of t he stamping s rain(see Fig11)，and in theregion AOB of the diagram of the stamping stress(see Fig12) Although the expressions of these two cases are different，their deformation essences are the same (4)The deformation zone of the stamping blank is subjected to two stressesWith opposite signs, and the absolute value of the compressive