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外文原文：
MO Jian\|hua LIU Jie HUANG Shu\|huai (State Key Lab of Plastic Forming Simulation and Die & Mould Technology Huazhong University of Science and Technology 430074)
《Journal of Plasticity Engineering》2001-02
1 forming characteristics and main forming obstacles of automobile panel
1. Characteristics of the vehicle cover
The general forming process of automobile panel is shown in Fig. 6. 39. The forming process includes: (a) billet, and the billet has a certain degree of downward bending of; (b) through the edge-holding device because of its self-weight, and at the same time pressing deep-drawing bars; The (c) punch decreases and the sheet metal contacts with the punch. With the expansion of the contact area, the sheet metal gradually fits with the punch and the; (d) punch continues to move downward, and the material is drawn into the mold cavity continuously, and the side wall is formed. (e) convex, concave die, the material is pressed into the die cavity shape; (f) continues to press to make the workpiece set, the punch reaches the dead point; (g) unloading.
As the automobile covering part has the characteristics of complex shape, high surface quality requirement and the like, the automobile covering part has the following characteristics of:
(1) there are many forming processes.
(2) the forming of automobile panel is the compound forming of drawing, bulging, bending, etc. No matter how complex the shape is, one-time forming is often used.
(3) since most of the automobile panels are non-axisymmetric and non-rotating complex curved-shaped parts, which are not uniform, the main deformation obstacles in deep drawing are wrinkling and tensile cracking. For this reason, it is often used to control the deformation by adding the supplementary surface and drawing bar.
(4) for the forming of large automobile panel, a large and stable blank holder force is needed, so the double power press is widely used in deep drawing.
(5) for the sake of easy drawing and forming, the steel sheet with good stamping performance such as 08 steel is used, and the surface quality of the steel plate is good and the dimension precision is high.
(6) the forming process and die design of automobile panel should be based on automobile panel drawing and main model. The main model is a model of the shape of the car, which is made on the basis of the final master drawing plate, the main template and the automobile cover drawing according to the size scale of 1:1. Often made of wood and fiberglass. The main model is a necessary supplement to the automobile panel diagram. Only the main model can truly represent the information of the automobile panel. Due to the popularization and application of CAD/CAM technology, the main model is being replaced by computer virtual entity model. The traditional oil sludge model to the main model of the automotive design process, is being conceptual design, Instead of modern design methods such as parametric design, the design and manufacturing cycle is greatly shortened and the manufacturing precision is improved.
1.2 main forming obstacles to automotive panels
Because the shape of automobile panel is complex, many positions are non-axisymmetric and non-rotating complex curved shape parts, so the deformation of deep drawing is not uniform, so the wrinkling and cracking during forming are the main obstacles to forming.
1. Wrinkle forming and Anti-wrinkle measures of Automobile Panel
In the drawing process of the automobile panel shown in Fig. 6 / 39, compressive stress occurs in the panel when the sheet is in contact with the punch at the beginning of the drawing. As the drawing goes on, when the compressive stress exceeds the allowable value, the sheet will lose stability and wrinkle.
Fig. 6 / 40 shows the relationship between in-plane stress and wrinkling direction. According to the relationship between the stress and the wrinkle direction, the stress and deformation in the sheet surface can be qualitatively judged when the automobile panel is drawn up and wrinkled, and the corresponding measures to reduce the wrinkle and prevent the wrinkle can be worked out.
In production practice, the corresponding anti-wrinkle measures are taken from the structure, forming technology and die design of automobile panel.
For parts that are simpler in shape and easier to deform, or where the relative thickness of the part is larger (because the critical wrinkling stress of the sheet is approximately proportional to the square of the thickness), The wrinkle can be prevented by using a flat edge holder (or without the use of a side holder).
For the parts with complex shape and difficult deformation, the wrinkle can be prevented only by setting up a reasonable process to replenish the surface and drawing the deep reinforcement.
第二外文原文
Cracking and Anti-cracking measures of Automobile Panel during forming
MO Jian\|hua LIU Jie HUANG Shu\|huai (State Key Lab of Plastic Forming Simulation and Die & Mould Technology Huazhong University of Science and Technology 430074)
《Journal of Plasticity Engineering》2001-02
The cracking of automobile panel during forming is due to the large local tensile stress and local bulging deformation. The cracking occurs mainly in the fillet, and the thickness of the crack is very thin. If the contact area between the punch and the billet is too small and the drawing resistance is too large, it may lead to the local bulging deformation and cracking of the material. Also because of the deep drawing resistance is too large, the concave die fillet clearance is too small and so on causes the whole circle to crack.
In order to prevent cracking, the corresponding measures should be taken from many aspects such as the structure, forming technology and die design of automobile panel. The measures that can be taken from the structure of the automobile panel are as follows: the radius of each fillet is the best, the actual depth of the surface shape in the direction of drawing should be shallow, the depth of each depth should be uniform, the shape should be as simple as possible and the change should be as smooth as possible, and so on.
The main measures adopted in the deep drawing process are as follows: the contact area between the punch and the blank is larger as far as possible in the drawing direction, the reasonable shape of the blanking surface and the blank holder force make the resistance of the parts of the blanking surface uniform and moderate, and the drawing depth is reduced. Start art hole and craft cut, etc.
In die design, reasonable drawing bars and large round corners of die can be adopted to make the clearance of punch and concave die reasonable and so on.
Process Design of stamping forming for Automobile Panel
2.1 determination of stamping direction
The stamping process of automobile panel consists of drawing, trimming, flanging and so on. The stamping direction should be determined from the drawing process, and then the stamping direction of each process will be worked out. The stamping direction of each process should be designed to be consistent as far as possible, so that the automobile panel can not be flipped in the production process of the assembly line, it is convenient to work in the assembly line, lighten the labor intensity of the operator, and improve the production efficiency. Also conducive to mold manufacturing.
For some left and right symmetrical automobile panels with small contour size, it is more advantageous to adopt the integral stamping method of the left and right parts.
1. Determination of drawing Direction
The determination of drawing direction not only determines whether or not the satisfactory automobile panel can be drawn out, but also affects the number of supplementary parts of the process and the plan of the follow-up process.
The principle of determining the drawing direction is that when the automobile panel itself has a symmetrical face, the drawing direction is determined by the rotation of the shaft perpendicular to the symmetrical face. The asymmetrical automobile panel is rotated around the two coordinate planes perpendicular to the vehicle position to determine the drawing direction. In addition, the following issues must be taken into account in determining the direction of drawing:
(1) to ensure that all parts of the punch and the face of the concave die can be contacted in order to ensure that the parts can be drawn once, there should be no dead angle or dead zone beyond the contact of the punch, so that all parts of the face between the punch and the concave die can be contacted. The concave shape of the automobile panel shown in figure 6 / 41 determines the drawing direction, and the drawing direction shown in figure (a) indicates that the punch cannot be drawn into the die. Figure (b) shows the drawing direction determined by rotating the same automobile panel at a certain angle so that the punch can be drawn deep into the concave die. Figure 6 / 42 shows a schematic diagram of the drawing direction determined by the anti-drawing of the automobile panel.
(2) the contact area between the punch and the drawing blank is larger when the punch starts drawing, and the contact surface should be as close as possible to the center of the drawing die. Figure 6 / 43 shows a diagram of the contact state of the blank at the beginning of the drawing of the punch.
Fig. 6 / 43 (a) shows that due to the small contact area, the angle α between the contact surface and the horizontal plane is large, and the contact site is prone to stress concentration and rupture. So the top of the punch is preferably flat and horizontal. The contact area can be increased by changing the drawing direction or the shape of the pressing surface.
Figure 6 / (b) shows that the material on both sides of the blank cannot be drawn evenly into the punch during the drawing process due to the departure from the center of the punch at the beginning of the contact, and the wear of the top of the punch is quick due to the possibility that the blank may move through the top of the punch. It also affects the surface quality of automobile panel.
Fig. 6 / 43 (c) shows that since the initial contact points are concentrated and few, the blank may move through the top of the punch during the drawing process, thus affecting the surface quality of the automobile panel. The contact area can also be increased by changing the drawing direction or the shape of the pressing surface.
Fig. 6 / 43 (d) because of the requirement of 90 °side wall on the shape, the drawing direction cannot be changed, only to make the shape of the pressing surface inclined, so that the two places can contact at the same time.
(3) the feed resistance of all parts of the pressing surface should be uniform. If the feed resistance of each part of the pressing surface is different, it is possible for the blank to move through the top of the punch to affect the surface quality in the process of deep drawing, which will result in serious tensile cracking and wrinkling. Fig. 6 / 44 shows the upper section of a miniature double-seated automobile column. If the drawing direction is rotated to 6 °and the two ends of the pressing surface are as high as the two ends of the pressing surface, the feed resistance is uniform. When the punch starts to draw, it is close to the center of the contact position of the drawing blank, and the deep drawing is formed well. In order to make the feed resistance uniform in all parts of the pressing surface, the uniform drawing depth is also the main measure in addition to the reasonable design of the shape of the pressing surface and the drawing bars and so on. Conditions. In addition, the drawing angle of the punch corresponding to both sides of the material should be as equal as possible.
2. Determination of trimming Direction and trimming form
(1) the determination of trimming direction is to cut off the part other than the trimming line of the drawing part. The ideal trimming direction is the direction of motion of the trimming edge perpendicular to the trimming surface.
If trimming is on a deep-drawn surface, the ideal trimming direction is innumerable, which is impossible in the same process. Therefore, the trimming direction must be allowed to have an angle with the trimming surface, the size of which is generally not less than 10 °. If it is too small, the material is not cut off but torn apart, which will seriously affect the trimming quality.
After deep drawing of automobile panel, the stamping direction of trimming and punching process may be different due to the different position of trimming and punching. Since the position of the automobile panel in the trimming die can only be one, if the compound process of trimming and punching is used, there may be two or more stamping directions in the same process.
(2) the trimming form can be divided into three types: vertical trimming, horizontal trimming and sloping trimming, as shown in Fig. 6. 45.
3. Determination of flanging direction and flanging form
The main results are as follows: (1) the determination of flanging direction is the final forming procedure of stamping process for ordinary automobile panels. The quality of flanging and the accuracy of flanging position directly affect the assembly quality of the whole automobile body. A reasonable flanging direction should meet the following two conditions:
(1) the work direction of flanging die is consistent with flanging flange and vertical edge;
2 the direction of motion of the flanging die is perpendicular to the flanging base, or equal to the angle between the flanging base and the flanging base.
(2) the flanging form can be divided into vertical flanging, horizontal flanging and sloping flanging according to the direction of motion of the flanging die, as shown in Fig. 6. Figure (a), (b) shows vertical flanging; figure (d) (e) shows horizontal flanging; figure (c) shows sloping flanging.
2.2 process treatment of drawing process
The process treatment of the drawing part includes determining the shape of the pressing surface, carrying on the process supplement, developing the flanging, punching the hole and the process notch, etc. It is a technological treatment measure to the automobile covering part according to the deep drawing technology.
1. Determination of the shape of pressing Surface
There are two kinds of pressing surface: one is that the pressing surface is part of the automobile panel itself, the other is that the pressing surface is supplemented by the supplementary part of the process. Remove after drawing.
The following points must be taken into account in determining the shape of the feed surface:
The main results are as follows: (1) reducing the drawing depth and reducing the drawing depth is beneficial to anti-wrinkle and crack prevention. Figure 6 / 47 shows a schematic diagram of reducing the depth of drawing. Figure (a) is the shape of the blanking surface that does not consider reducing the depth of drawing, and figure (b) is the shape of the surface of the press which considers the reduction of the depth of drawing.
(2) The convex mold must have a stretching effect on the blank, as shown in FIGS. 6-48 (a), and only if the spreading length A 'B' C'D 'E' of the pressing surface is less than the extended length of the convex mold surface, the stretching effect can be generated.
The shape of the pressing surface shown in figure 6 / 48 (b), although the unfolding length of the pressing surface is shorter than that of the punch surface, the angle β of the pressing surface is smaller than the angle α of the punch surface. As a result, several instantaneous positions in the drawing process are wrinkled by "multi-material". Therefore, when determining the shape of the pressing surface, the α < β < 180 °should also be made.
2. Process supplement
In order to realize the deep drawing of automobile panel, the structure of automobile panel, such as hole, opening and pressing surface, should be processed according to the requirement of drawing procedure, and this treatment is called process supplement.
Fig. 6 / 49 is a supplement to several possible processes depending on the trimming position.
3. Process holes and process notches
It is sometimes difficult to press a large depth of local protrusions or bulges on the workpiece by flowing into the material from the outside, and further drawing will lead to a rupture. In this case, a punching hole or a process notch may be considered to supplement the material from the interior of the deformation zone. Figure 6 / 50 shows a technical cut diagram of the back drawing of the door inner panel window.
2.3 relationship between drawing, trimming and flanging processes
Each process of automobile panel forming is not independent of each other, but is related to each other. When determining the stamping direction of the automobile panel and adding the supplementary parts of the process, the trimming should also be considered. When flanging, the positioning of the parts and the other relations of the parts are discussed.
There are three kinds of positioning of drawing parts in trimming process:
(1) position with the shape of the side wall of the drawing part.
(2) position with drawing rib shape.
(3) Positioning the process holes made by drawing or passing through the drawing depth.
The positioning of the trimming part in the flanging process is generally used in the shape of the working part, the side wall or the positioning hole of the automobile covering piece. In addition, it is necessary to take into account the direction and the way of the discharge of the work piece, the elimination of the trimming waste, the position of each working piece in the die, and the like.
Design of typical structure and main parts of forming Die for Automobile Panel
3.1 drawing Die for Automotive Panel
1. Typical structure of drawing Die
There are single-action press and double-action press for the deep drawing equipment of automobile panel, and the complex automobile panel must be drawn by double-action press. According to the different equipment, the drawing die of automobile panel can also be divided into the drawing die of automobile panel on single-action press and the drawing die of automobile cover on double-action press. Fig. 6 / 51, Fig. 6 / 52 are typical structural diagrams of drawing dies for automotive panels on single-action press and double-action press, respectively.
2. Design of main parts of drawing Die
The deep drawing die of automobile panel is complicated in shape and size, so the main parts such as punch, die, edge holder and so on are made of hollow castings with stiffened bars, and the material is generally HT250, cast iron with Cr-Mo cast iron now, and the main parts such as punch, die, edge holder and so on are all made of hollow castings with stiffened bars.
The main results are as follows: (1) in addition to the special technological requirements, such as the supplement of technology and the development of flanging surface, the outer contour of the punch is the inner contour of the deep drawing part, and its contour size and depth are the product dimensions. The die thickness of the working surface and contour of the punch is larger than that of the other parts, which is generally 70~90mm (see Fig. 6 / 51 and fig. 6-52). To ensure the size of the outside profile of the punch, the straight wall of a 40~80mm along the pressing surface of the punch must be machined (see fig. 6 / 52). In order to reduce the profile and avoid machining, the straight wall is transitioned upward with a 45 °slant surface, reducing the distance to 15? 40. millimeter
(2) the design of the die is that the blank is gradually inserted into the cavity of the die through the round fillet of the die, until the shape of the punch is formed by drawing. Decorative edges, bars, pits, stiffeners, bulges for assembly, pits for assembly, and anti-drawing for deep drawing parts are generally formed once on the drawing die. Therefore, in addition to the die pressing surface and the concave die fillet, the punch or die formed in the concave die is also a part of the concave die structure. The die structure can be divided into closed die structure and open die structure.
The bottom of the die structure of the closed die is closed, and most of them are closed die structure in the deep drawing die. Figure 6. 53 shows a deep drawing die for the automobile top cover, which adopts a closed die structure and directly processes the groove part of the forming reinforcement on the cavity of the die. For example, the groove part of the stiffener is made into an independent die structure in the cavity of the concave model, which is called the closed die structure of the movable ejector.
Fig. 6 / 54 is a drawing die for the inside plate of a car door. The bottom of the die is open, and the die base is added under the through hole, and the back drawing punch is fastened to the die base. The bottom of the die is a through die structure called the opening die structure. The opening die structure is usually used for drawing die with complex shape, more craters and lines. The shape of the outer wheel of the ejector in the die is a part of the shape, and the shape is more complex.
第三外文原文 Design of drawing Bar
MO Jian\|hua LIU Jie HUANG Shu\|huai (State Key Lab of Plastic Forming Simulation and Die & Mould Technology Huazhong University of Science and Technology 430074)
《Journal of Plasticity Engineering》2001-02
As shown in figure 6 / 55, the multi-bar structure on the press surface is the drawing bar. The drawbar can also be set on the die pressing surface, both of which have the same effect on drawing.
There are three types of deep-drawn tendons: circular, semicircular and square. Figure 6 / 56 shows the structure and size of a semicircular drawing bar. The width of drawing rib is 12mm and 16mm.
For some flatter automobile panels with shallow depth and smaller curvature, due to the small value of the radial tensile stress required for deformation, the workpiece has a large springback deformation after the die is released, or can not be tightly attached to the film at all. At this time to use drawing sill to ensure the quality of the drawing part requirements. The sill can also be said to be one of the drawing bars, which can increase the feed resistance stronger than the drawing bars. The profile of the sill is trapezoidal, similar to the threshold, set at the die entrance, and its structure is shown in figure 6 / 57.
3.2 trimming die for automobile panel
Automobile panel trimming die is a special blanking die. The main difference between the blanking die and the common punching die is that the shape of the punch to be trimmed is complex, the position of the edge separating edge of the die may be arbitrary spatial surface, the stamping parts usually have different degrees of elastic deformation, and the cutting edge of the die may be located in an arbitrary space surface. There is usually a large lateral pressure in the separation process. Therefore, when designing the die, the stamping direction, the position of the parts, the straightening of the die, the elimination of the scrap, the removal of the workpiece, the balance of the lateral force and so on should be considered in the process and the structure of the die.
1. Trimming die structure
Automobile panel trimming die can be divided into vertical trimming die, oblique wedge trimming die and vertical oblique wedge trimming die. Figure 6 / 58 is the trimming punch die for the outside plate of the rear door column of the car:
Figure 6 / 59 is a water tank cover trimming die
2. Design of main parts of trimming Die
The main results are as follows: (1) the layout of punch and concave die insert and the structure of fixed trimming die edge have two types: integral type and mosaic type. If the blade material is surfaced on the punch or concave die body, it is called integral. If it is mounted on a punch or concave die in the form of a block structure, it is called a block type. Because of the multi-position irregular space curve of the trimming line of the automobile panel and the long trimming line, in order to facilitate the manufacture, assembly and repair, the punch and the concave die of the trimming die are usually used in the block structure.
The layout principles of the inlay:
1 insert size should be suitable for processing conditions, straight line segment should be appropriate long, complex shape or corner should be as short as possible, as far as possible to take the standard value.
In order to eliminate the verticality error of the joint surface, the width of the joint surface between the two inserts should be as small as possible.
Insert should be easy to process, easy to assemble and adjust, easy to compensate for error, the best should be rectangular block.
(4) when the curve is connected with a straight line, the joint surface should be in the straight line, and there should be a certain distance from the tangent point (generally take 5~7mm). The joint surface should be perpendicular to the trimming line as much as possible to increase the edge strength when inserting blocks on the surface.
(5) the local insert of the punch is used in the corner, the parts which are easy to wear and damage, and the local insert of the die is installed in the corner and the trimming line with protruding grooves. All the insert blocks are assembled and then modeled to ensure the matching requirements of trimming shape and edge clearance.
Fixed block:
For the trimming and concave die of the block structure, the shearing force and the horizontal pushing force acting on the insert block of the cutting edge will cause the insert block to generate displacement and subversion torque in the force direction, and the fixing of the embedded block must be firm to balance the lateral force. FIGS. 6-60 are schematic diagrams of two commonly used block fixing forms, and FIG. (a) is applicable to a block with a material thickness of less than 1. 2 mm or a small variation in the cut height difference. and FIG. (b) is a block suitable for large variation of the thickness of the material of the automobile covering material of more than 1.2mm or the height difference of the cutting edge, and the structure can bear large lateral force, and is convenient to assemble and is widely adopted.
(2) the design of waste cutter the waste material of automobile covering piece is large in shape, and the shape of trimming line is complex, it is impossible to use general unloading ring to unload the material, it is necessary to cut off the waste and then unload the material before it is convenient and safe. Some parts that cannot be positioned with the shape of the parts themselves can be positioned with scrap knives. So waste knife is also one of the contents of trimming die design.
The structure of the waste knife is also an integral part of the trimming block. The insert type scrap knife is to use the fitting face of the trimming concave die insert as a scrap knife edge, and accordingly install the scrap knife outside the trimming punch insert as another scrap knife edge, as shown in figure 6 / 61, figure 6 / 62, as shown in figure 6 / 61, figure 6 / 6 / 62, as shown in figure 6 / 61, figure 6 / 62.
In order to make the waste material easy to fall off, the cutting edge opening angle of the waste knife is usually 10 °, and should be arranged in the right direction, as shown in figure 6 / 63.
In order to make the waste easy to fall, the vertical wall of the waste knife should be avoided relative configuration as far as possible. However, you can change the edge angle when you have to configure it relative, as shown in figure 6 / 64.
When there is a raised part of the trimming line, in order to prevent the scrap from being stuck, a knife should be arranged in the raised part, as shown in figure 6 / 63.
Do not protrude out of the trimming line when chamfering, as shown in figure 6 / 65 (a). The edge of the waste cutter shall be close to the intersection of the radius arc R and the tangent line. As shown in figure 6 / 65 (b), the waste will not be affected.
When angular waste falls by weight, the center of gravity of the waste must be on the outside of Line A shown in Fig. 6 / 65 (b).
