德语
Because there are too many factors to consider when designing a tensile die, such as the depth coefficient, whether it reaches the limit of the material, the decision of spring force, the direction of stretching, whether it is stretched upward or downward, it is often not formed at once, and it has to be tried many times to achieve the ideal result, and sometimes there is even the possibility of the mold being scrapped. Therefore, continuous accumulation of experience in practice is of great help to the design of the tensile die.
In addition, the size of the cutting material also plays an important role in the production and trial production of the entire mold. So most of the time, when we design some irregular drawing parts, we often reserve a blank step during the mold design stage.
1. Stretching material
When the customer’s requirements for the material are not very strict and the repeated trials cannot meet the requirements, you can change to a material with good tensile performance and try again. A good material is half the success. For stretching, it must not be ignored. The cold-rolled thin steel plates for stretching mainly include 08Al, 08, 08F, 10, 15, and 20 steels. Among them, the largest amount is 08 steel, which is divided into boiling steel and calm steel. Boiling steel has low price, good surface quality, but serious segregation, and tends to "strain aging". It is not suitable for parts with high requirements for stamping performance, strict appearance requirements, good appearance, and high price. The representative grade is aluminum calm steel 08Al. Foreign steel has been used in Japan's SPCC-SD deep stamping steel, and its tensile performance is better than 08Al.
2. The finish of the mold surface
When deep drawing is performed, the two sides of the die and the edge ring are not polished sufficiently, especially when deep drawing stainless steel plates and aluminum plates, it is more likely to cause deep drawing scars, which in severe cases lead to stretching and rupture.
3. Determination of blank size
Our principle is that there are many wrinkles and fewer cracks. The blank positioning design must be correct. The blank diameter of the rotating body stretching part with a simple shape changes during the unthin stretching. Although the material thickness changes, it is basically very close to the original thickness. It can be calculated based on the principle that the blank area and the area of the stretched part (if there is a trimming, it must add a trimming allowance). However, the shape and process of stretching parts are often complicated, and sometimes they have to be thinned and stretched. Although there are many three-dimensional softwares that can calculate the expansion material, their accuracy cannot meet the requirements by 100%.
Solution: Test.
A production piece requires multiple processes, and the first process is generally a blanking process. First, we need to calculate the unfolding material and have a rough understanding of the shape and size of the blank to determine the overall size of the blanking mold. Do not process the convex die size of the blanking die after the mold design is completed. First, use wire cutting to process the blank (if the blank is large, you can use a milling machine to mill and then repair it). After repeated experiments in the subsequent tensile process, the blank size is finally determined, and then the convex die of the blanking die is processed.
Experience 1
In the reverse process, try the stretching die first and then process the blanking edge size of the blank, which will result with twice the result.
4. Tensile coefficient m
The tensile coefficient is one of the main process parameters in the calculation of the tensile process, and it is usually used to determine the order and number of stretches.
There are many factors that affect the tensile coefficient m, including material properties, relative thickness of the material, stretching method (referring to the presence or absence of a pressing ring), number of stretching times, stretching speed, rounded corner radius of the convex die, lubrication, etc.
The calculation and selection principles of the stretching coefficient m are the key points introduced in various stamping manuals. There are many methods such as estimation, table lookup, and calculation. It is very auspicious. I also choose according to the book. There is nothing new. Please read the book.
Experience 2
The relative thickness, stretching method (referring to the presence or absence of a pressing ring), and stretching times of the material are not easy to adjust during mold revision, so be careful. It is best to ask a colleague to proofread it when choosing the stretching coefficient m.
5. Choice of processing oil
The choice of processing oil is very important. The method to distinguish whether lubricating oil is to remove the product from the mold, if the product temperature is so high that it cannot be touched by hand, the choice of lubricating oil and the lubricating method must be reconsidered, and lubricating oil must be applied to the mold, or a film bag is placed on the thin plate.
Experience 3
When stretching and cracking occurs, apply lubricating oil on the die (do not apply on the die), and cover the workpiece with a plastic film of 0.013-0.018mm on one side of the die.
6. Heat treatment of workpiece
Although it is not recommended, it is still necessary to say that during the stretching process, the workpiece undergoes cold work hardening due to cold plastic deformation, which reduces its plasticity and increases its deformation resistance and hardness. In addition, the mold design is unreasonable, and intermediate annealing is required to soften the metal and restore its plasticity.
Note: Intermediate annealing is not necessary in the general process. After all, it will increase the cost. You have to choose between adding more processes and adding annealing. Use with caution!
Annealing generally uses low temperature annealing, that is, recrystallization annealing. There are two things to pay attention to when annealing: decarburization and oxidation. Here we mainly talk about oxidation. There are oxide scales on the workpiece after oxidation, which has two harmful effects: it makes the effective thickness of the workpiece thinner and increases mold wear.
When the company's conditions are not met, ordinary annealing is generally used. In order to reduce the generation of oxide scale, the furnace should be filled as much as possible during annealing. I have also used ordinary methods:
1. When the workpiece is small, it can be mixed with other workpieces (prerequisite: the annealing process parameters should be basically the same).
2. Put the workpiece in the iron box and weld and seal it before installing it in the furnace. In order to eliminate oxide scale, pickling treatment should be carried out according to the situation after annealing.
When the company's conditions are met, nitrogen furnace annealing, that is, bright annealing, can be used. If you don't look closely, the color is almost the same as before annealing.
Experience 4
For metals with strong cold work hardening or when cracks occur in the trial mold and there is no other way, an intermediate annealing process is added.
7. A few additional points
1. The dimensions on the product drawing should be marked on one side as much as possible to make it clear whether the outer dimensions or the inner cavity dimensions are guaranteed. The inner and outer dimensions cannot be marked at the same time. If there are such problems with the drawings provided by others, you should communicate with them. If they can be unified, unify them. If they cannot be unified, you should know the assembly relationship between the workpiece and other parts.
2. For the last process, when the size of the workpiece is outside, the concave mold is the main one, and the gap is obtained by reducing the size of the punch; when the workpiece size is included, the convex mold is the main one, and the gap is obtained by increasing the size of the concave mold;
3. The radius of the convex and concave molds should be designed as small as possible to facilitate subsequent mold repairs.
4. When judging the cause of workpiece cracking, you can refer to: cracks caused by poor material quality are mostly jagged or irregular shapes, while cracks caused by craftsmanship and molds are generally neat.
5. "More will cause wrinkles, less will cause cracks". According to this principle, adjust the flow of the material. Methods include adjusting the pressure of the blank holder, adding deep drawing ribs, trimming the fillet radius of the convex and concave molds, cutting process openings on the workpiece, etc.
6. In order to ensure wear resistance and prevent stretch scratches, the convex and concave molds and edge rings must be quenched, hard chromium plated, or surface TD treated. If necessary, tungsten steel can be used for the convex and concave molds.
Design of automobile rear suspension spring support plate Mold quick review Master the latest mold knowledge
1. Stamping process analysis
Nowadays, there are more and more friends who are studying mold design. Many people ask me if I have any information and what is a better first book to read. According to your needs, I have classified and managed some mold design information. I hope you can have a bright future in the mold industry.
Figure 1 shows the rear suspension spring support reinforcement plate for automobiles, which is mass produced. The material is SAPH440, and the material thickness is t=2mm. SAPH440 is an automotive structural steel with a carbon content of about 0.20%. The material has a yield strength of 305~395MPa, a tensile strength of 390~470MPa, an elongation of ≥30%, and good formability. It is mainly used for structural parts such as automobile frames and wheels that require high strength. The overall dimensions of the part shown in Figure 1 are 107.5mm × 149mm × 33mm. The surface quality and accuracy requirements are high, and the shape is relatively complex. There are assembly requirements for the φ7+0.1mm hole, and the accuracy level is IT9.
According to the appearance characteristics of the part, the mold is designed as a structure of 1 mold and 2 parts (see Figure 2). The forming of the rear suspension spring support requires blanking, punching, forming, separation and other processes. Since the thickness of the part is 2mm and the surface shape is a complex curved surface, it should be produced by combining a single-process mold and a composite mold.
2. Calculation of blank size
Commonly used blank calculation methods for sheet metal parts include the empirical method, the neutral layer method, and the splicing method. Most of these methods are suitable for parts with specific shapes. However, the surface shape of the rear suspension spring support part is complex. It is neither a standard bent part nor a standard drawn part. The deformed part includes bending, drawing, etc. It is difficult to calculate the accurate blank size using the traditional blank calculation method. The finite element analysis method in UG software was used to calculate the blank size, as shown in Figure 3.
3. Mold structure design
1. Storage block 2. Limiting column 3. Upper mold base 4. Upper mold pad 5. Limiting screw 6. Mold handle 7. Ejector (upper mold pressing plate) 8. Unloading spring 9. Die insert 10. Guide sleeve 11. Guide post 12. Lower die base 13. Unloading plate 14. Lower die pad 15. Pungent insert 16. Limiting screw 17. Unloading spring 18. Hanging rod
The blank blanking die adopts a sliding guide column inversion die, a rigid discharge plate and a cast steel guide column mold base. Its structure is shown in Figure 4. Mold working process: The blank is roughly positioned by the stopper pin and finely positioned by the positioning pin to ensure the feeding accuracy. A workpiece ejector is designed in the concave mold. After the upper and lower molds are closed for punching, the parts are ejected by the ejector, and the blanking waste is ejected from the lower mold by the unloading plate.
1. Storage block 2. Limiting column 3. Guide column 4. Upper mold base 5. Female mold insert 6. Mold handle 7. Positioning pin 8. Guide sleeve 9. Lower mold base 10. Hanging rod 11. Rectangular spring 12. Unloading plate 13. Lower mold pad 14. Punch mold insert 15. Positioning pin 16. Limiting screw 17. Positioning pin
Figure 5 shows the structure of the support forming mold. According to the forming characteristics of the parts and in order to reduce manufacturing costs, the male and female molds adopt an insert structure. The female mold is on the upper mold, and the punch and ejector are on the lower mold. The sheet material is placed on the ejector before forming. During operation, the female mold moves downward and the ejector presses the sheet material under the action of the machine tool ejector force. After forming, the ejector pushes up the part. The forming mold is accurately positioned using self-made positioning pins. Three positioning pins are installed on the lower mold base part ejector, and three positioning pin process holes are processed on the concave template of the upper mold. The unloading device of the mold adopts spring unloading. Since the parts will be wrapped on the punch after being formed, eight SWM40-100 rectangular springs are used to act on the unloading plate to eject the parts wrapped outside the punch insert. The bottom of the spring is in direct contact with the lower workbench with a spring cover.
1. Storage block 2. Guide pillar 3. Upper mold base 4. Unloading plate 5. Punching punch 6. Die handle 7. Punching punch 8. Shoulder punch sleeve 9. Guide sleeve 10. Lower mold base 11. Hanging rod 12. Back support plate 13. Punching and concave mold inserts 14. Guide block 15. Convex and concave molds 16. Screws 17. Limiting screw 18. Rectangular spring 19. Guide pin
Since the parts use a mold structure of 1 mold and 2 pieces, they need to be punched and separated after forming. Figure 6 shows the structure of the part punching and separation composite mold. The mold is mainly composed of an upper mold base, a discharge plate, a punching punch, a blanking punch, a concave mold, and a lower mold base. Due to the high punching accuracy requirements, the punching punch is installed on the shoulder-shaped punch sleeve, and together with the shoulder-shaped punch sleeve, it is installed on the upper mold base through screw connection.
In order to ensure the punching accuracy, an insert is designed on the punching die. The die insert and the die are installed on the die using H7/n6 transition fit. The structure is shown in Figure 7. The separation die consists of two die inserts. In order to ensure the position accuracy during punching, a back support plate is installed on the left and right sides of the lower die base.
Figure 8 shows the structure of separating the punch and the die insert. During punching, the upper die base drives the punch and the pressing plate downward to compress the workpiece. The upper die base and the punch continue to move downward to punch and separate the workpiece. The waste material directly falls from the press table, and the parts are pushed out by the unloading plate.
The stamping process of the automobile rear suspension spring support reinforcement plate was analyzed, a reasonable process plan was formulated, and the work contents of the three processes were clarified. Based on traditional design experience and combined with computer-aided design software UG, three sets of molds for blanking, forming and punching separation of the automobile rear suspension spring support reinforcement plate were designed. After mold debugging and mass production, it has been proven that the mold structure is reasonable, the operation is normal, the quality of the parts is stable and reliable, and it meets the requirements of part accuracy and mass production.
Note: All pictures in the article are reprinted online, and will be deleted if infringed!
