Quality analysis and control of the hottest precis

2022-08-03
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Quality analysis and control of precision blanking parts

Abstract: starting with the quality of precision blanking parts, this paper lists the relationship between the status of molds and materials and the quality of parts in the process of mass production, analyzes various phenomena, and puts forward corresponding solutions for specific situations

key words: precision blanking parts; Quality

I. overview

precision blanking is a new type of metal pressure machining method, which can replace the machining of flat parts. It has the characteristics of high quality, high efficiency and low consumption. Its technical and economic effects are very significant, and is deeply valued by various industrial departments. Since the German invented this blanking method in 1923, the fine blanking technology has been popularized and popularized all over the world, and has been expanded from instrumentation, office machinery, light industrial machinery and other departments to automobile, agricultural machinery, tractor, transportation machinery, hoisting machinery, textile machinery, military machinery, aircraft and aviation equipment and other manufacturing departments [1]. Especially in the automotive industry, the development is particularly rapid. For example, there are more than 70 kinds of fine blanking parts in a car. The fine blanking process has become one of the important technical measures for the automotive manufacturing industry to reduce costs, improve performance and increase output

Beijing Electromechanical Research Institute has been researching and developing the fine blanking field for decades and has formed a certain scale. It has explored the fine blanking process, deformation mechanism, mold design and manufacturing, lubricants, force and energy parameters, and the development of fine blanking press. In particular, it has accumulated a lot of experience in mold manufacturing and fine blanking parts production. This paper will enumerate the quality problems of the shear plane encountered in the actual production, analyze them and put forward the corresponding solutions

II. Fine blanking deformation mode

in order to suppress the tearing of materials during fine blanking, the fine blanking process requires three forces (blanking force, blank holder force and back pressure). Before blanking, the "V" shaped blank holder presses the material to prevent the material outside the shear deformation zone from flowing with the punch during the shearing process. The clamping effect of the blank holder and the reverse pressing plate, combined with the small gap between the male and female dies (only 5 ‰ ~ 10 ‰ of the thickness of the material to be punched), keeps the material perpendicular to the blanking direction during the blanking process, and tightly presses the material between the dies to prevent brittle fracture caused by the tensile stress caused by the warping of the parts, thus forming the condition of plastic shear. If necessary, in order to increase the three-dimensional compressive stress tensor in the deformation area and improve the plasticity of the material, the cutting edges of punching punch and blanking die can be rounded to reduce the stress concentration at the cutting edge and avoid or slow down the generation of cracks

figure 1

III. quality of fine blanking parts

qualified precision blanking parts have high quality and can be directly used for assembly without subsequent processes, but the key is how to obtain high-quality fine blanking parts? The quality of precision blanking parts includes dimensional accuracy, shear surface quality, angle collapse, burr height and flatness. The quality of fine blanking parts depends on whether the structure of the die is reasonable, the manufacturing accuracy of the die, the condition of the cutting edge, the plasticity and metallographic structure of the punched material, the complexity of the part geometry, process lubricants, force and energy parameters, and the adjustment of the press [2]

it is not easy to obtain high-quality fine blanking parts in actual production. In order to obtain the normal cutting surface as shown in Figure 2, so that there is 100% bright band on the cutting surface, the collapse angle is relatively small, and the burr size is moderate, first of all, the mold must maintain a good working state, the mold clearance is reasonable, the precision of the guide post guide sleeve and the locking pin meets the requirements, and ensure that the mold is aligned up and down, and the cutting edge fillet of the punching element is appropriate

Fig. 2

it is well known that in actual production, it is difficult to keep the mold in the best state at all times. The mold design and production personnel can consider all aspects of factors in detail. The following is an example and analysis of the unqualified quality of fine blanking parts caused by mold and material factors

there are many thin and dense scale cracks on the shear surface of the fine blanking part, as shown in Figure 3. Obviously, the quality of fine blanking parts can not meet the requirements. The mold in this situation can not continue production and must be adjusted. There are many reasons for this phenomenon. Most of the reason is that the impacted material is not suitable, so it is necessary to replace the material with good plasticity, or spheroidize and anneal the raw material to change the metallographic structure of the raw material and improve the plasticity index of the material. The round corners of punching punch and blanking die of the die are too small or uneven, so that the three-dimensional compressive stress cannot be established, and the quality of the parts will also be reduced. When the surface of the cutting edge of the concave mold cavity is too rough, a similar situation will occur for the fine blanking parts. If the demand for lightweight and rigid parts does not increase, which will affect the reasonable clearance of the mold, the mold edge can be polished to reduce friction. It is best to use the high-precision slow wire cutting machine to cut the key parts of the fine blanking mold during mold manufacturing, In order to avoid affecting the quality of the parts due to the low surface quality of the die edge. Inadequate lubrication of the die will also affect the quality of the shear surface of the parts, and will weaken the service life of the die

figure 3

there is a long and deep tear in the middle of the shear plane of the fine blanking part, as shown in Figure 4. In case of this phenomenon, the fine blanking technician should start from the following aspects: check whether the pressure of the "V" type gear ring with strong blank holder is too small, or the tooth shape of the blank holder ring is inappropriate. Improve the structure of the blank holder ring, change the tooth shape size or increase the blank holder force to ensure that a good three-dimensional compressive stress field is formed in the blanking area of the die; Check whether the die fillet is too small or uneven, and reasonably increase the die fillet or make it uniform along the edge edge; Check whether the fine blanking materials are suitable for fine blanking. If the plasticity of the raw materials is poor, the plasticity of the materials will be exhausted. Of course, if this tearing phenomenon occurs in the sharp corners of the part, and the fillet radius is relatively small, or occurs on the shear plane close to other shear planes (i.e., the wall thickness is small), this kind of situation belongs to the product designer's excessive pursuit of certain functions or shapes, which affects the structural manufacturability of the part. The mold designer should negotiate with the product designer, taking into account both aspects, Make it possible to obtain high-quality parts

Fig. 4

when the fine blanking part has the shear surface shown in Fig. 5, the side close to the collapse angle of the fine blanking part on the shear surface is relatively smooth, while the brittle fracture occurs on the side close to the burr. In terms of the quality of the shear surface of the part, it is very similar to the ordinary blanking part. This is mainly caused by the large clearance between the punch and punch. Once this happens in production, there is no other way but to remake the punch or die to improve the clearance of the die

Fig. 5

when the shear surface shown in Fig. 6 appears in the fine blanking part, that is, from the shear surface, the finish is very good. However, the perpendicularity is not good, and it is obvious that the taper appears. The overall dimension of the burr side is larger than that of the chamfer side. This is because the fillet of the die die is too large. More materials are "pulled" into the die. When the parts are pushed out of the die, the situation shown in Figure 6 will occur. The reverse taper phenomenon can be eliminated by re sharpening the concave and jointly developing the new energy all aluminum passenger car model. In addition, if the relative position of the die always changes, this phenomenon will also occur. Then, the mold designers should take a more reliable mold fixing method to fundamentally solve and eliminate hidden dangers

Fig. 6

when the shear surface shown in Fig. 7 appears in the fine blanking part, that is, some insiders speculated that the finish of the shear surface was very good, but the burr on one side of the punch was thick, and the shear surface was conical. This is caused by the small gap between male and female dies, which can be eliminated only by using a reasonable die gap. However, it is necessary to analyze the specific problems, because sometimes this phenomenon occurs even though the clearance between the punch and the die is reasonable when blanking some special quality materials

Fig. 7

when the shear surface shown in Fig. 8 appears in the fine blanking part, a bright band like "water ripple" appears on the shear surface. Facing the light, "water ripple" is more obvious, which is often mistaken for the visual error caused by the lubricating oil adhering to the shear surface. The better the smoothness of the side surface of the punch and die, the easier this phenomenon will occur and the more obvious the contrast will be. This is due to the large fillet of the female die and the small gap between the male and female dies. This phenomenon is often caused by the designer mistakenly regarding the small clearance of fine blanking as that the smaller the die clearance is, the better. When designing the die, the clearance of the die is too small. In addition, the high-precision CNC wire cutting machine tool is easy to ensure that the die clearance of particularly complex shapes is μ Grade accuracy, even 0 clearance, and it is caused by the serious wear of the die edge and the excessive rounded corner during the production of fine blanking parts. From the perspective of deformation mechanism, fine blanking is closer to cold extrusion, with a large gap compared with ordinary blanking. Therefore, when the die clearance is very small and the punch is pressed into the material to be punched, the material near the punch side around the punch has been separated from the material under the punch due to plastic flow, while the material near the die side cannot be separated at the fillet due to the large fillet of the punch. When the punch continues to move downward, Only the material under the punch can be pulled into the cavity of the concave mold, and the material will produce "water ripple" when it rubs with the concave mold. If so, the mold designer should have a good understanding of the fine blanking process and deformation mechanism. The gap of the mold is in a very narrow range and has a certain ratio to the thickness of the material to be punched. Such a mold can punch 100% smooth shear surface, but obtaining 100% smooth fine blanking parts is not the only goal. The service life of the mold and the overall cost of the mold should be considered

figure 8

when the shear plane as shown in Figure 9 appears, the collapse angle on the part is too large. This is caused by the large fillet of the die. If the back pressure is too small to press the material when pressing the material in the punch, when the material is separated at the cutting edge due to plastic flow, the material under the punch is uneven, that is to say, the workpiece is pulled into the concave die in the bending state, and the workpiece not only has too large collapse angle, but also the parts will be uneven. Of course, it is normal for such large angle collapse to occur at sharp corners or at places with relatively small fillet radius

figure 9

when the blanking raw materials are fine blanking without leveling treatment, the original stress state is retained on the fine blanking parts, which affects the flatness of the punched parts, often resulting in "twist fried dough twist" or warping along the length direction. Therefore, the raw materials must be leveled before fine blanking

after years of practice, it is found that there are more and more types of nonconforming products in actual production, which cannot be listed here. In a word, only through careful analysis and summary, can we successfully solve the problem, prolong the service life of the mold, ensure the quality of fine blanking parts, and finally reduce the cost, so that your enterprise can remain invincible in the tide of market competition

references

[1] Tu Guangqi Fine blanking technology Beijing: China Machine Press, 1990

[2] Wang Yanshan et al Application Manual of forging process standards Beijing: China Machine Press, 1998:656 (end)

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