CN1194828C - Plate material shaping mould pretreatment technology - Google Patents

Abstract

The mold pretreatment process for sheet metal forming belongs to the auxiliary processing technology related to basic non-cutting metal processing, so that the flow resistance of the flange surface tends to the uniformity required for forming when the mold is used during the sheet metal forming process. , the total forming force tends to be minimized, which overcomes the problem that the existing measures cannot effectively optimize the forming state of plate forming parts with complex shapes. The present invention includes steps in order: (1) determine the region with maximum flow resistance on the pressing surface of the lower mold as the punching area; (2) punch out blind holes arranged in a uniform lattice in the punching area, wherein Φ=2.0 ~10.0mm, h=(1.5~2.0)Φ, R=0.5Φ, γ=0.5~1mm, d ₁ =2Φ+1.5~2.0mm, d ₂ =1.5Φ+1.0~2.0mm. The invention can effectively reduce the flow resistance on the region with the greatest flow resistance on the contact surface of the pressing material, greatly improve the forming performance of the sheet material, and make the parts that can only be formed after the second drawing can be successfully drawn once.

Description

Die Pretreatment Process for Sheet Metal Forming

technical field

The invention belongs to auxiliary processing related to basic non-cutting metal processing, and particularly relates to the processing technology of molds.

Background technique

During the processing of plate forming parts with complex shapes (referring to thin plate parts manufactured by the forming process), the pressure on the binder surface of the mold (corresponding to this is the flange surface where the slab and the binder surface are in contact with each other) The flow resistance is uneven and varies greatly, especially in the transition area between the rounded corner and the straight edge. In order to balance the flow resistance on the binder surface, the prior art is to set one or two drawbeads with higher resistance in the area of less flow resistance, see Jiang Kuihua. Stamping Technology and Die Design. Beijing: Machinery Industry Press, 1997: 188-189. Such as the existing technology of automobile oil sump is exactly like this. As a result of this, on the one hand, the uniformity of the flow resistance on the binder surface meets the forming requirements, and at the same time, the total forming force is very large, resulting in the forming process often being in a critical state close to failure, and it is very difficult during deep drawing. Cracks easily. Therefore, when the performance of the plate has a slightly larger but permissible negative deviation, even the molds that have been produced normally in the past, and under the condition of accurate installation, there will still be a situation where one cracks and the other is pulled, so that stacking occurs. Mountains of waste.

In order to improve the formability of the sheet metal, eliminate the cracking defects in the sheet metal forming process, and make the cracking rate close to zero, many foreign scholars regard the adjustment and optimization of the blank holder force curve as the main direction of attack, see Sanchez L R, Experimental Simillation of the Sheet Metal Response to Clamping During Forming, SAE Paper 940942: 748～745

K Manabe et al. Artificial intelligence identification of process parameters and adaptive control system for deep-drawing process.

D E Hardt et al. Real-time Control of Binder Force During Stamping, Proceedings of the ^16th Biennial Congress of the IDDRG, International Deep Drawing researchgroup, 1990.17-27

R Kergen et al. Computerized control of the blankholder pressure on deep drawing presses. SAE paper, No.920433, Warrendale, PA, 1992.

The basic idea of these studies is to determine the variation curve of the minimum blank holder force without wrinkling during the sheet forming process. The research of Taytan Altan, a well-known American scholar, goes a step further. Relying on a multi-action control press (made in Germany, the price is more than 10 million U.S. dollars), he not only needs to optimize the pressure curve, but also adjusts the intensity of the blank-holding force on the binder surface (unit Binder picture) distribution over the area. See Mustafa AAhmetoglu, Taylan Altan. Improving Drawability by Using Variable Blank HolderForce and Pressure in Deep Drawing of Round and Non-Symmetric parts. SAE Paper930287, P428-435

M A Ahmetoglu, T Altan, G L Kinzel. Improvement of Part Quality in Stampingby Controlling BHF and Pressure. J. of Materials Processing Technology, 1993, 33: 195-214

This kind of press has more than ten auxiliary oil cylinders specially used for blank-holding. By adjusting the oil pressure of each cylinder, the strength of blank-holding force on the pressing surface can be adjusted. Since temperature and humidity have certain influence on the viscosity of the oil, the working state of this press is very unstable. Therefore, although T Altan has achieved some results, it has not been promoted in production. In fact, most of the blank-holding force used in the production of large enterprises engaged in sheet metal processing in my country is generated by air cushions. Even to optimize the blank-holding force curve, it is necessary to develop a fast, stable and reliable pressure adjustment system. Due to the particularity of the sheet metal forming process, the stability of this system is very difficult to guarantee.

Contents of the invention

The present invention proposes a mold pretreatment process for sheet metal forming, so that when the mold is used in the forming process of the sheet metal, the flow resistance on the flange surface tends to the degree of uniformity required for forming, and the overall The forming force tends to be the smallest, which overcomes the problem that existing measures cannot effectively optimize the forming state of plate forming parts with complex shapes.

A mold pretreatment process for sheet metal forming of the present invention comprises the following steps in sequence: (1) determining the area of maximum flow resistance on the pressing surface of the lower die as the punching area; (2) punching out the hole in the punching area. Blind holes arranged in a uniform lattice, blind hole diameter Φ = 2.0 ~ 10.0mm, blind hole depth h = (1.5 ~ 2.0) Φ, blind hole bottom hemispherical arc radius R = 0.5Φ, blind hole mouth transition radius γ =0.5～1mm, center distance of blind holes d ₁ =2Φ+1.5～2.0mm, distance from the centerline of the first row of blind holes to the contour line of the depression d ₂ =1.5Φ+1.0～2.0mm, the two adjacent rows of blind holes face each other The central radial meridian at the rounded corner of the die is evenly staggered.

The mold pretreatment process for sheet metal forming is further characterized in that the area of maximum flow resistance is determined on the pressing surface of the lower die by means of a test, that is, the sheet metal is processed and formed with a mold without blind holes, and when the sheet material The plate sub-area formed by the crack and the nearest edge of the slab corresponds to the punching area.

In the mold pretreatment process for sheet metal forming, after the blind holes are completed, sawdust, graphite powder or porous engineering plastic particles can be filled in the blind holes for storing lubricating oil.

The applicant used the internationally renowned plate forming analysis software eta/DYNAFORM-952-V-32 to perform a numerical simulation on the forming process of a rectangular box-shaped piece with a flange. Numerical analysis results show that this technological measure can significantly reduce the flow resistance on the area of the flange contact surface with the largest flow resistance during the forming process, thereby effectively optimizing the forming state of the sheet metal and greatly improving the formability of the sheet metal , on this basis, even if it is necessary to set drawbeads in the adjacent area, drawbeads with less resistance can also be selected, which can not only balance the flow resistance on the flange surface, but also greatly reduce the overall flow resistance. The forming force effectively optimizes the forming state of the sheet, which can prevent wrinkling and greatly reduce the cracking rate.

In a physical sense, there are three main factors in the optimization mechanism of this new process measure: (1) The contact area between the slab and the binder surface in the perforated area is reduced, thereby reducing the blank holder force on this area and frictional resistance. (2) On the sheet metal, the compression state of some particles located in this area with the same vertical distance from the entrance of the die and adjacent to each other is quite different, resulting in the movement and deformation of these particles during the entire forming process The states are not synchronized, which is also beneficial to reduce flow resistance. (3) The lubrication state of this area is improved to a certain extent, thereby further reducing the frictional resistance of this area.

Now, under the condition that the technology of various CNC machining centers is very mature and relatively popular, it is not difficult to drill hundreds of small and shallow blind holes according to certain rules on the table top of the lower die, that is, on the binder surface. The increased workload and The cost is also very little. At the same time, this new technological measure does not change the structure of the mold in any way, so it will not have any adverse effects on the reliability and stability of the mold work. Combining this new technology with the above-mentioned other technological measures and cooperating with each other can significantly optimize the forming state of the sheet metal, so there are at least two broad prospects in the entire field of sheet forming: (1) It can greatly Reduce the scrap rate in the thin plate forming process, making it close to zero; (2) It can make many thin plate parts that need to be drawn twice to be formed according to the existing technology, and can be processed by one drawing. Taking the automobile oil pan as an example, our country now produces more than two million vehicles every year, and it will continue to increase every year in the future. The oil pan is the most difficult to process among all the plate forming parts of the automobile. Now most ( About 90%) of the oil pan is processed by secondary drawing. If this new technology is used in combination with other technological measures, it is entirely possible to form most of these oil pans with only one deep drawing.

Description of drawings

Figure 1 is a schematic diagram of the perforated area,

Figure 2 is a schematic diagram of the shape of a blind hole,

Figure 3 is a schematic diagram of blind hole arrangement.

Detailed ways

Figure 1 is a schematic diagram of the perforated area. The perforated area 1 and the perforated area 2 are usually located in the transition area between the rounded corner and the straight edge, that is, the area with the greatest flow resistance, and do not cross the outer contour of the initial slab.

Figure 3 is a schematic diagram of the arrangement of holes. The key to the arrangement of blind holes is that the adjacent two rows of holes must be staggered as evenly as possible, and must not be located on the same meridian. Since the length of the perimeter line in the perforated area increases with the increase of its distance from the center of the circle, when the diameter of the hole is constant, the number of holes in the back row will increase by one every few rows.

When determining the punching area, it is generally necessary to go through experiments. Here, firstly, a common and applicable method is given: If the sheet is cracked, and the sub-area of the sheet formed by the crack and the nearest boundary has been If there is no extra material, the corresponding area on the lower mold table where this sub-area is located is the punching area. The specific situations are elaborated as follows:

1) For thin-plate parts of the rotary type, it is only necessary to directly punch holes on the entire table surface of the lower die according to the rules shown in Figure 3. ring.

2) For non-revolving thin-plate parts, the punching area is usually the transition area between rounded corners and straight sides, especially short straight sides, but how big is this area? There is currently no effective method to accurately delineate how far it extends, and debugging methods are usually required. For example, for an automobile oil pan, firstly drill 4 rows of holes in the longitudinal direction at the transition area between the circumference corresponding to the deep bottom and the straight edge, that is, drill 2 rows of holes in the radial direction on both sides of the circumference area, and at the same time Two rows of holes are drilled in the adjacent straight edge area along the longitudinal direction, so that the deep-drawing test is carried out to determine whether to continue drilling in this area according to whether there is any cracking during deep-drawing and the extension direction of the crack when the cracking occurs And in which direction to punch. For each area that needs to be drilled further, it is best to add only one row of holes along each side at a time. Furthermore, during the deep drawing test, the blank holder force should be reduced in time every time a hole is punched, and the reduction value is equal to (0.75~1) multiplied by the area of the newly punched hole and then multiplied by the blank holder force strength. If there are deep-drawing ribs, the height of the deep-drawing ribs should be continuously reduced. When a row of holes is added to the straight-edge area, the height of the deep-drawing ribs (0.1-0.25) mm on the straight-edge area should be reduced at the same time. . And if the cracking only occurs on the cylindrical side wall, 2 rows of holes are first drilled in the circular area near the entrance of the lower die along the transverse (circumferential) direction. However, the arrangement and distribution of these holes and the holes in the transition region follow the rules shown in FIG. 3 . At this time, whether to continue punching can be operated according to the above method.

If the finite element numerical simulation can be carried out in advance, the workload and cycle of debugging can be greatly reduced.

Figure 2 is a schematic diagram of the shape of the blind hole, marked in the figure as: blind hole diameter Φ, blind hole depth h, blind hole bottom hemispherical arc radius R, blind hole mouth transition radius γ, blind hole center distance d ₁ . The following are examples according to the different sizes of the drawn parts:

(1) For small deep-drawing parts, the blind hole diameter Φ=2.0~4.0 (unit is mm, the same below). For example, when drawing a cylindrical piece with a diameter of 90.0, Φ=3.0, h=2Φ, γ=0.5, d ₁ =2Φ+1.5, d ₂ =1.5Φ+1.0 can be taken.

(2) Medium-sized deep-drawing parts, Φ=4.0～6.0. For example, when drawing the oil pan of a car, take Φ=5.0, h=1.5Φ (when Φ≥4.0, take h=1.5Φ), γ=0.5, d ₁ =2Φ+2.0, d ₂ =1.5Φ+ 1.5.

(3) For large deep drawing parts, Φ=6.0～10.0. For example, when drawing the oil pan of a 4T truck, Φ=6.0, h=1.5Φ, γ=0.5, d ₁ =2Φ+2.0, d ₂ =1.5Φ+2.0 can be taken.

Generally speaking, under the condition that the punching area remains unchanged, the smaller the diameter of the blind hole, the more the number of holes, the more obvious the quality and deformation out of sync benefits, and the better the effect, but the mold cost and manufacturing cycle will increase. Therefore, users should comprehensively consider these two factors and flexibly grasp the above specifications. Therefore, for large-scale deep-drawn parts that are very difficult to deep-draw, it is also allowed to take Φ=5.0.

Claims (3)

1. A mold pretreatment process for sheet metal forming, comprising the following steps in sequence: (1) Determine the area of maximum flow resistance on the binder surface of the lower die as the perforating area; (2) Blind holes with a uniform lattice arrangement are punched in the drilling area, the diameter of the blind hole is Φ=2.0~10.0mm, the depth of the blind hole is h=(1.5~2.0)Φ, and the radius of the hemispherical arc at the bottom of the blind hole is R=0.5 Φ, transition radius of blind hole mouth γ=0.5～1mm, blind hole center distance d ₁ =2Φ+1.5～2.0mm, distance from the center line of the first row of blind holes to the contour line of the depression d ₂ =1.5Φ+1.0～2.0 mm, the two adjacent rows of blind holes are evenly staggered relative to the central radial meridian at the rounded corner of the die. 2. The mold pretreatment process for sheet metal forming as claimed in claim 1, characterized in that the area of maximum flow resistance is determined on the pressing surface of the lower mold by means of a test, that is, the sheet metal is processed with a mold without blind holes. In forming, when the sheet is torn, and the sheet sub-area formed by the torn point and the nearest edge of the slab corresponds to the lower die table area is the punching area. 3. The mold pretreatment process for sheet metal forming as claimed in claim 1 or 2, characterized in that after the blind hole is completed, fill sawdust, graphite powder or porous engineering plastic particles in the blind hole for storage and lubrication Oil.

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