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 die．Stamping 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 8～1 00mm.The blank material for stamping is usually in the from sheet or strip,and therefore it is also called sheet metal forming.Some non—metal 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 be studied in stamping.

The characteristics of the sheet metal forming are as follows:

(1)High material utilization.

(2)Capacity to produce thin—walled parts of complex shape.

(3)Good interchangeability between stamping parts due to precision in shape and dimension.

(4)Parts with lightweight，high—strength 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 alloy—steel,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 names．But these processes are similar to each other in plastic deformation．There 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 directions．In 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 material．In 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 forming．In some circumstances，such influence may be neglected．Even 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 part．Whereas in stamping，in most cases，the blank has a certain degree of freedom， only one surface of the blank contacts with the die．In 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 die．The 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 surface．Instead，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 done．Stamping forming can be performed by more reasonable scientific methods．Based on the real time measurement and analysis on the sheet metal properties and stamping parameters．by 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 stability．has become a key point in stamping technology．The 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 quality．

1.2 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 other．It mainly includes blanking·punching，trimming，parting and shaving．where punching and blank．mg are the most widely used．Forming is a process that one part of the blank has some displacement from the other．It mainly includes deep drawing，bending，local forming，bulging，flanging，necking．sizing 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 force．The stress state and deformation characteristic of the deformation zone are the basic factors to decide the properties of the stamping forming．Based 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 state．Usually there is no force or only small force applied on the blank surface．When 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 material．Due to the small thickness of the blank，it is assumed approximately that the two principal stress distribute uniformly along the thickness direction．Based 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 is r 0, t 0and r 0, t 0 I n both cases，the stress with the maximum absolute value is always a tensile stress．These two

cases are analyzed respectively as follows

In the case that r 0and t 0.according to the integral the relationships between stresses and strains are：

t r k r m m t m

where r, , t are the principal strains of the radial，tangential and thickness directions of

the exial symmetrical stamping feinting； r, t and are the principal stresses of the radial tangential and thicken directions of the axial synmletrical stamping forming； mis the average stress, k is a contant.

In plane stress,Equation1.1is rewritten as the following form;

3 3 t3 r k 2 r 2 t ( r)

Since r> >0,so 2 r >0 and r>0.,In indicates that in plane stress state with

two axial tensile stresses, if the tensile stress with the maximum absolute value is r,the

principal strain in this direction must be positive, that is，the deformation belongs to tensile forming．

In addition，because r> >0,therefore ( r)<0 and t<0.the station in the

thickness direction of the blank is negative，that is，the deformation belongs to compressive forming，and the thickness decreases．

The deformation condition in the tangential direction depends on the values of r and ,when r=2 , =0;when r>2 , <0;and when r<2 , <0,when r<2 , >0.

The range of is r 0. In the equibiaxial tensile stress state r= , according to Equation 1．2 r= >0 and t<0 . I n the uniaxial tensile stress state =0，according

to Equation 1．2， = r/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 Fig．1．1)，and in the region GOH of the diagram of the stamping stress.

2)when > r>0 and t=0,according to equation 1.2 2 > r>0,and >0.this result shows that for the plane stress state with two tensile stresses，when the absolute value of

the strain in this direction must be positive，that is，it must be in the state is the maximum，

of tensile forming．

Also because > r>0, therefore ( r)<0 and t<0.

The strain in the thickness direction of the blank of is negative，or in the state of compressive forming，and the thickness decreases

Fig．1．1 Diagram of stamping strain Fig．1．2 Diagram of stamping stress The deformation condition in the radial direction depends on the values of r and . when =2 r, r=0;when >2 r, r<0.

The range of r is > r>0,when r= , r= >0, that is in equibiaxial tensile stress state，the tensi1e deformation with the same values occurs In the two tensile stress direct ions；when r=0 , r= /2<0 .that is．in 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 Fig．1.1)，and in the region GOH of the diagram of t he stamping stress(see Fig．1.2)． Between above two cases of stamping deformation，the properties of and rand 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 r( t =0), it can also be divided into two cases，which are 2 r <0 , t =0 and r< <0,

t =0.

1)W hen r< <0.， t =0, according to Equation 1．2，2 r <0 and r<0.This result shows that in the plane stress state with two compressive stamping，if the stress with the maximum absolute value is r<0 ,the strain in this direction must be negative，that is，in the state of compressive forming．

Also because r< <0 ,therefore ( r)>0 and t>0．The strain i n the thickness

direction of the blank t is positive，and the thickness increases．

The deformation condition in the tangential direction depends on the values of r and . When r=2 , =0;when r>2 and <0; and when r<2 , and >0. The range of is r< <0 .When = rit is in equibiaxial tensile stress state

hence = r<0,when =0 it is in uniaxial tensile stress state，hence = r/2. This kind

of deformation condition is in the region EOG of the diagram of tile stamping strain(see Fig．1.1)，and in the region COD of the diagram of t he stamping stress(see Fig．I．2)．

2)When < r<0 and r=0 according to Equation1.2， 2 r<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 is．In the state of compressive forming．

Also because < r<0,therefore ( r)>0 and r>0

The strain in the thickness direction of the blank ris positive, and the thickness increases．

The deformation condition in the radial direction depends on the values of r and

.when =2 r, r=0;when >2 r, r<0.

The range of r is < r<0,when = r,it is in equibiaxial tensile stress state，hence = r<0;when r=0.it is in uniaxial tensile stress state，hence r= /2>0 .This kind of deformation is in the region GOL of the diagram of the stamping strain(see Fig．1．1)，and in the region DOE of the di -agram of t he stamping stress(see Fig．1．2)．

(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 stress．There exist two cases to be analyzed as follows：

1)When r>0, <0 and r> ,according to Equation 1.2 2 - r>0 and r>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 r>0, <0 and > r, therefore <0.The strain in the compressive stress direction is negative，that is，in the state of compressive forming．

The range of is 0> > r.when = r..then r>0, <0,and = r;when =0, then r>0, <0,and r= /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 Fig．1．1)，and in the region FOG of the diagram of the stamping stress(See Fig．1．2)．

2)When >0． r<0，2 ,by means of the t=0, > r ,according to Equation 1．

same analysis mentioned above，that is，the deformation zone is in the plane stress state >0，

with opposite signs．If the stress with the maximum absolute value is tensile stress ，the strain in this direction is positive，that is，in the state of tensile forming．The strain in the radial direction is negative . that is ,in the state of compressive forming

The range of ris 0≥ r≥一 ．When r= - r，then >0, r<0 and = r; when r=0，then >0， r<0，and r= /2．This kind of deformation condition is in the region COD of the diagram of t he stamping s rain(see Fig．1．1)，and in the．region A OB of the diagram of the stamping stress(see Fig．1．2)．

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 stresses．With opposite signs, and the absolute value of the compressive stress larger than that of the tensile stress There exist two cases to be analyzed as follows：

1)W hen r>0， <0 and > r．1，according to Equation 1．2，2 r<0 and <0 this result shows t hat in plane stress state with opposite signs，if the stress with maximum absolute value is compressive stress ，the strain in this direction is negative. Or in the state of compressive forming．

Also because r>0， <0,therefore 2 r >0 and r>0The strain in the tensile stress

direction is positive，or in the state of tensile forming．

The range of is O≥ r≥ ．When r= ，then r>0， <0，and r= ；when r=0，then r>0, <0，and = /2。．This kind of deformation is in the region LOM of the diagram of the stamping strain(see Fig．1．1)，and in the region EOF of t he diagram of t he stamping stress(See Fig.1．2)．

2)When >O， r<0 andr> ，according to Equation 1．2 and by mean of the same analysis mentioned above， r<0．This result shows that in plane stress state with

opposite signs，if the stress with the maximum absolute value is compressive stress r,the strain in this direct on is negative，or 1n the state of compressive forming．The strain in the tensile stress direction 1s positive，or in the state of tensile forming．

The range of is O≥ ≥ r．When = rthen >0, r<0，and = r；when =0，then >0, r<0，and = r/2,Such deformation is in the region DOF of the diagram of the stamping strain(see Fig．1．1)，and in the region BOC of the diagram of the stamping stress(see Fig．1．2)．

The four deformation conditions are related to the corresponding stamping forming methods．Their relationships are labeled with letters in Fig．1．1 and Fig．1．2．

The four deformation conditions analyzed above are applicable to all kinds of plane stress

states，that is，the four deformation conditions can sum up all kinds of stamping forming into two types，tensile and compressive．When the stress with the maximum absolute value inthe deformation zone of the stamping blank is tensile，the deformation along this stress direction must be tensile．Such stamping deformation is called tensile forming．Base on above analysis，the tensile forming occupies five regions M()N，AON，AOB，BOC and COD in the diagram of the stamping strain；and four regions FOG,GOH,AOH and AOB in the diagram of the stamping stress．

When the stress with the maximum absolute value in the deformation zone of t he stamping blank is compressive，the deformation along this stress direction must be compressive．such stamping deformation is called compressive forming. Based on above analysis ,the compressive rotating occupies five regions LOM，HOL．GOH,FOG and DOF in the diagram of the stamping strain；and four regions EOF，DOE，COD and BOC in diagram of the stamping stress．

MD and FB are the boundaries of the two types of forming in the diagrams of the stamping strain and stress respectively．Tile tensile forming is located in the top right of the boundary，and the compressive forming is located in the bottom left 0f the boundary．

Because the stress produced by the plastic deformation of the material is related to the strain caused by the stress，there also exist certain relationships between the diagrams of the stamping stress and strain. There are corresponding locations in the diagrams of the stamping stress and strain for every stamping deformation．According to the state of stress or strain in the deformation zone of the forming blank，and using the boundary line in the diagram of the stamping stress MD or the boundary line in the diagram of the stamping strain FB ,its easy to know the properties and characteristics of the stamping forming．

The locations In the diagrams Of the stamping strew and strain for various stress states and the corresponding relationships of the two diagrams are listed in Table 1.1．I t shows that the geometrical locations for every region are different in the diagrams of the stamping stress and strain，but their sequences in the two diagrams are the same．One key point is that l he boundary line between the tensile and the compressive forming is an inclined line at 45。To the

coordinate axis. The characteristics of the stamping technique for tensile and compressive forming are listed in table 1．2．

Table 1·1 Comparison between states of stress and strain in stamping

Table 1．2 clearly shows that in the deformation zone of the blank．the characteristics of the force and deformation，and the patterns relevant to the deformation for each stamping method are the same．Therefore，in addition to the research on the detail stamping methods ,It is

feasible to study stamping systematically and comprehensively．The characteristic of the systematic research is to study the common principle of all different types of stamping methods．The results of the systematic research are applicable to all stamping methods．The research On the properties and limit of the sheet metal stamping has been carried out in certain extent．The contents 0f the research on the stamping forming limit by using systematic method are shown in Fig．1．3．

1.3 Methods to study stamping forming

The objective of the stamping

forming research is to realize and apply

the principles to solve various engineering

problems through study on the

stamping forming procedure．Recently，

the research on stamping forming

has been carried out in wide range with

various methods．The research can be

summed up substantially into following

types．

The double line arrows in Fig．1．4

denote the procedure of formal theoretical

research．In such research．the actions． Fig．1．4 Diagram of stamping research methods of the equipment and die are decomposed into micro-ingredients of the force and applied on the microstructure of the deformation metal microstructure is then investigated and the deformation of the microstructure to micro-deformation of the sheet metal is summed up. This scientific method is perfect．But current development in mechanics and metallurgy cannot meet such demand ,therefore this kind of formal theoretical research is still in burgeoning，and is not applicable in practice．

Since the formal theoretical research method encounters formidable difficulty．a kind of simplified theoretical method appears in the research field of the stamping forming the characteristic of this kind of research meth(x]is denoted by continuous line in Fig．1．4．which is the main trend of the recent research．this research assumes metal as the ideal homogeneous solid and simplifies the property parameters，the boundary conditions and the blank geometrical parameters of the metal，the stamping process and principle are analyzed and described by mathematical method．Naturally，the assumptions adopted in the analysis would induce some deviation between the real stamping process and its simulation．The result is certainly approximate and does not reflect the real stamping process completely．Especially in analyzing complex stamping forming，this theory is not so valid．I n recent years．

due to the development of the finite element method and computer technology，this kind of theoretical method has greatly progressed，it shows applicable prospect even in analyzing complex stamping forming .the application of this kind of theoretical method mainly focus on same special stamping deformation investigation，and it is expected that more achievements can be obtained in the fundamental principles of stamping forming．On the other hand，due to the simplifications and assumptions，experiments are indispensable to test the validity of this theory．

The third method to study stamping forming is shown by dashed dotted line in Fig.1.4．The characteristic of t his method is that ignoring the deformation process of the blank under the action of the load during stamping forming，trying to build the relationship and rules directly among the original forming conditions(Including the structure of the die the geometrical parameters of the die working portion and the properties of t he stamping equipment)with the final results of the stamping forming．It is a rational empirical method and widely used in stamping technology field in recent years ,this method is intuitional．simple and easy to be adopted by engineers，but it cannot be used to reveal the real procedure

of the stamping deformation，so it is not the radical method to investigate the principles of the stamping forming more thoroughly and its usage is strictly limited．

The fourth method to study stamping forming is denoted by dashed line in Fig．1．4．Based

on the fundamental knowledge of the mechanics and metallurgy，the essential characteristics and principles of the stamping forming are investigated to solve the practical problems in stamping process．In comparison with other plastic processes，the characteristics of the stamping forming，the principles of the sheet metal deformation are unique．So this method has definitely aim and the analysis results can be used directly to solve different problem in stamping. The characteristics and effects of this research method are illustrated by following examples．

(1)The sequence of the stamping process can be decided by the rend rule of the stamping deformation．

(2)According to the rule of uniform velocity distribution in the outer flange of the deformation zone during multi—pass deep drawing for the box parts．the shape and dimension of the blank during process sequence can be calculated．Therefore the calculation for deep box parts of the multi-pass deep drawing technology is based on scientific foundation to improve the technique level of stamping forming．

(3)According t()the research 0n the wrinkle during the sheet metal forming caused by non-uniform tensile and shearing force. A new research field is developed beyond the tradition compressive new instability theory the results obtained oiler an effective measure to cope directly with wrinkle during stamping forming．

(4)the theory of sorting stamping forming based on the characteristics of the stamping deformation and mechanics is an easy approach to systematize the researches of the stamping forming，and can be used to deepen the investigation on stamping forming limit, to point out a clear and definite direction for improving the stamping forming limit．

Above examples indicate that this method is closely relevant to the real stamping forming process．It call be used to analyze and solve the stamping forming problems effectively．Although this method is in the junior stage，mainly focusing 0n the qualitative analysis for stamping forming now. With the constant Progress of this method and combined With modern mechanics．the breakthrough of this method is expected t()further enhance stamping forming technology．

1.4 Raw materials for stamping forming

There are a lot of raw materials used in stamping forming，and the properties of these materials may have large difference, the stamping forming can be succeeded only by determining the stamping method，the forming parameters and the die structures according to the properties and．characteristics of the raw materials．The deformation of the blank during stamping forming has been investigated quite thoroughly．The relationships between the materials properties decided by the chemistry component and structure of the material and the

stamping forming has been established clearly．Not only the proper material can be．Selected stamping forming has been established clearly Not only the Proper material can be selected based on the working condition and usage demand，but also the new material can be developed according to the demands of the blank properties during processing the stamping part．This is an Important domain in stamping forming research the research on the material properties for stamping forming is as follows：

(1)Definition of the stamping property of the material．

(2)Method to judge the stamping property of the material，find parameters to express the definitely material property of the stamping forming，establish the relationship between the property parameters and the practical stamping forming，and investigate the testing methods of the property parameters．

(3) Establish the relationship among the chemical component, structure ， manufacturing process and stamping property．

The raw materials for stamping forming mainly include various metals and nonmetal plate．Sheet metal includes both ferrous and nonferrous metals．Although a lot of sheet metals are used in stamping forming，the most widely used materials are steel，stainless steel．aluminum alloy and various composite metal plates．

1.4.1 Ordinary steel plate

In stamping forming，steel plate is the most widely used material．It is used for products in vehicles including automobile，tractor and train，and for electrical，petrochemical, mechanical and architectural products．Due to the different functions and demands for different products，the types and shapes of the steel plate are also different．Fig.1.5 shows the procedures for manufacturing various steel plates and the variation of the program during manufacturing and logistics．

1．Hot rolled plate

There are two kinds of hot rolled plate available．One is the plate with black oxide coat 10m deep formed directly after hot rolling．The oxide coat is hard and brittle．During stamping forming，especially when peeling exists，the die may be damaged．In order to overcome this problem，the hot rolled plate with its oxide coat acid—washed by superficial treatment is also supplied .the surface of the king of steel plate is rough ,but it also has advantage in easy lubrication and fits for forming process.

The hot rolled plate does not have the texture organization of the cold rolling steel，so its stamping forming property is not as good as the cold one．On the other hand，the thickness and properties of the hot rolling steel fluctuate greatly，which is not beneficial to stamping process．Besides the chemical component，the crystallite size also influences its strength and n value．The properties of the hot rolled plate are usually adjusted by controlling the crystallite size．Due to low price of the hot rolling steel，the steel plate with favorite stamping properties and fitting to deep drawing forming is being developed．

2．Cold rolled plate

The superficial quality and the stamping properties of the cold rolled plate are excellent.The properties and thickness of the plate are also stable．Therefore it is widely used in stamping forming．by adjusting the chemical components，controlling the process of the smelting，with hot and cold rolling as well as annealing，many cold rolled plates with various properties can be obtained through the deformation during rolling and the recrystallization

treatment during annealing，the texture organization with increasing can be obtained，hence improving the deep drawing property of the c01d rolled plate and the die fitting ability during curved part forming．table 1．3 shows an approximate comparison of the qual i ty and properties between cold and hot rolled plate．

Table I．

3 Comparison of the quality and properties between cold and hot rolled plate

There are two kinds of cold rolled plates，aged and non—aged．Usually，in the tensile diagram of the ordinary annealed cold rolling mild carbon steel plate，there is a yield point elongation．The reason is due to discontinuous yield phenomenon formed by C and N atoms．Slip lines of damaging surface smoothness would appear during stamping forming．In order to overcome this unfavorable phenomenon，rolling with certain reduction is applied to steel plate after annealing，called sizing rolling．Although this method is very effective，the effect cannot be sustained for long time．After a period of time．the actions of C and N atoms This kind of steel plate is called aged cold rolling plate. Adding Al or Ti can restrain completely the influence of C and N on dislocation，even eliminate aging phenomenon．In this way the effect of the sizing rolling can be maintained permanent．This kind of steel plate is called non．aged cold roiled sheet．The recently widely used 08Al for stamping forming is one kind of non-aged mild carbon cold rolled plate．

1.4.2 High strength steel plate．

With the increasing of the strength．the thickness of the steel plate can be decreased on conditions of guaranteeing part strength and rigidity．and hence both the weight and cost are decreased．Therefore。both domestic and international investigations focus 013．Producing high．strength steel plate and developing corresponding stamping forming technique·

High-strength steel plate is used more often in automobile industry to meet the demands of the strength，toughness and forming properties．Now many kinds of high-strength steel plate are used successfully in automobile industry to substitute ordinary steel plate for reducing weight and cost．The tensile strength of the ordinary high-strength steel plate is in the range of 350～500MPa．some ultra．high．strength steel plates．with the strength as high

as 1000MPa。have been developed．Recently，high-strength steel plates used in production are listed 85 follows：

1．High-strength steel plate modified with phosphorus

This kind of high-strength steel plate belongs to solution hardening type．It was used rather early in automobile industry。and is well developed, Modifying with phosphorus，the strength increases to 350～440MPa and n are decreased a little，with r=1．4—1·8，n=0．2~0．24 respectively．

2．BH hardening high-strength steel plate

The stamping forming property of this kind of steel plate is very similar to that of mild carbon steel．After stamping forming，spraying painting and low temperature baking .Its strength is increased due to BH hardening and it turn to high-strength steel plate·

3．Biphase- high．strength steel plate

There are mild ferritic and hard martensite organizations in this kind of steel plate．and hence both the strength and plasticity of the plate are rather good．This kind of steel plate is mainly used to manufacture automobile parts，such as pillars and chassis．

1.4.3 Superficial treatment steel plate

In order to prevent the corrosion of the part manufactured by steel plate during utilizing after cold and hot rolling，the steel plate is electroplated or processed by hot dipping in450～500 c corrosion．resistance metal solution，and then the superficial treatment steel plate is made．Tin．plating，zinc．plating and aluminum-plating steel plates are the commonly used superficial treatment steel plate．

Due to the thin coating of the superficial treatment steel plate，the influence of the coating on stamping forming property is small．the property of t he treated plate is roughly similar to t he plate without superficial treatment．Whereas，the influence caused by the different friction properties of the plating surface on stamping Process cannot be neglected. particularly ,in the deep drawing forming when using drawing rib，the forming of the stamping parts is controlled by friction，whether the stamping forming is successful or not may be dependant on its surface friction．Research results show that with the increasing of t he friction coefficient of the superficial treatment steel plate，the formability range of the experimental used vehicle cover panel decreases．In other words，the demands of the forming conditions and parameters tend to be more strict．

1.4.4 Stainless steel plate

The stainless steels used in stamping forming are ferritic (Cr -system) and austenti (Cr-Ni．system)．Since the component and organization are different，their stamping properties are aim different．Although both are called stainless steel，due to vast difference in stamping