Forming process and die of the hottest aluminum ca

2022-08-18
  • Detail

Aluminum can forming process and die

Abstract: the can body drawing process, thinning drawing process and bottom forming process are analyzed, and some key technologies related to these processes in the design and manufacture of dies are studied

key words: cans; Forming process; Mold; Thinning and stretching

1 introduction

aluminum cans account for a considerable proportion in beverage packaging containers. The manufacturing of cans integrates advanced technologies in metallurgy, chemical industry, machinery, electronics, food and many other industries, and has become an epitome of aluminum deep processing. With the increasing competition in the beverage packaging market, for many can making enterprises, how to minimize the thickness of sheet metal, reduce the quality of a single can, improve the utilization of materials, and reduce production costs in the production of cans is an important goal pursued by enterprises. Therefore, technological transformation and technological innovation characterized by light-weighting are quietly rising. The lightweight of cans involves many key technologies, among which the can body forming process and die technology are very important

2 can body manufacturing process and technology

2.1 can body manufacturing process flow

the main manufacturing process flow of CCB-1A can body is as follows: coil conveying → coil lubrication → blanking and stretching → tank body forming → trimming → cleaning/drying → stacking/unloading → base color coating → drying → color printing → primer coating → drying → internal spraying → internal drying → tank mouth lubrication → necking → rotating compression neck

in the process flow, the blanking, stretching, can body forming, trimming, diameter reduction, spinning diameter reduction/flanging processes need mold processing, among which the blanking, stretching and can body forming processes and molds are the most critical, and their process level and mold design and manufacturing level directly affect the quality and production cost of cans

2.2 can body manufacturing process analysis

(1) blanking drawing composite process. During stretching, the material at the edge of the blank forms a cup along the radial direction, so the unit body in the plastic flow area is in a three-dimensional stress state of bidirectional compression and unidirectional tension, as shown in Figure 1. Due to the action of punch arc and drawing concave die arc, the wall thickness of the lower part of the cup is reduced by about 10%, and the thickness of the cup mouth is thickened by about 25%. The arc size at the corner of the cup has a great impact on the subsequent process (can body forming). If it is not well controlled, it is easy to break the can. Therefore, the following factors must be considered in the blanking and drawing process: cup diameter and drawing ratio, punch arc, drawing die arc, punch and die clearance, mechanical properties of aluminum, friction properties of die surface, lubrication of material surface, drawing speed, lug ratio, etc. The production of lug is mainly determined by two factors: one is the performance of metal materials, and the other is the design of drawing die. The lug appears at the highest and thinnest point of the cup, which will affect the formation of the can body, resulting in incomplete trimming and increased scrap rate

based on the above analysis, the drawing ratio m=36.55%, blank diameter dp=140.20 ± 0.0lmm and cup diameter dc=88.95mm are determined for the drawing process

(2) can body forming process

analysis of thinning drawing process. The typical aluminum can stretching and thinning stretching process is shown in Figure 2, and the stress condition in the thinning stretching process is shown in Figure 3. In the process of drawing, the metal concentrated in the conical part of the die mouth is the deformation area, while the force transfer area is the cylinder wall and the bottom of the shell after passing through the die. In the deformation zone, the material is in a three-dimensional stress state of axial tension, tangential compression and radial compression. Under the action of the three-dimensional stress, the metal grain refinement, strength increase, accompanied by work hardening. In the force transmission area, the stress conditions of each part of the material are different, among which the metal located in the punch fillet area is the worst. It is pulled in the axial and tangential directions and pressed in the radial direction, so the thinning trend of the material is serious, and the metal is easy to fracture from here, resulting in tensile failure. Comparing the stress state of the metal in the deformation zone and the force transfer zone, it can be seen that whether the thinning stretching process can be carried out smoothly mainly depends on the tensile stress on the metal at the fillet of the stretching punch. When the tensile stress exceeds the strength limit of the material, it will cause fracture, otherwise the stretching process can be carried out smoothly. Therefore, reducing the tensile stress in the process of using the low-pressure circulating evaporator as the high-pressure circulating condenser is the key to ensure the smooth stretching

the selection of thinning stretching ratio is: re stretching: 25.7%, the first thinning stretching: 20%~25%, the second thinning stretching: 23%~28%, the third thinning stretching: 35%~40%

in the forming process, there are many factors that affect the tensile stress inside the metal, including the cone angle of the die. The value of is directly related to the flow characteristics of the metal in the deformation zone, and then affects the size of the forming force required for stretching. Therefore, whether its value is reasonable or not has an important impact on the implementation of the process. When α When it is small, the deformation area is relatively large, the metal is easy to flow, and the lattice distortion is small. along with α With the increase of, the range of deformation zone decreases, the deformation of metal is concentrated, the flow resistance increases, and the lattice disproportion becomes serious. Moreover, with the increase of the cone angle of the die, the strain of the material in the deformation area increases correspondingly, which shows that when the cone angle of the die is large, not only the deformation range of the metal is concentrated, but also the deformation increases rapidly, which intensifies the work hardening phenomenon of the metal in the deformation area, resulting in the increase of the stress in the metal, which has an adverse impact on the tension. On the other hand, in α Too large or too small will cause the increase of tensile force. The reason is that when α When it is too large, the metal flows rapidly, and the work hardening effect of the material is significant. With the increase of the cone angle, the component force produced by the conical surface of the die that hinders the metal flow increases, so the required tensile force increases; When. When it is too small, although the turning point of metal flow is small, the total friction resistance on the cone is large due to the long contact cone between the metal and the concave in the deformation area. Therefore, although the lattice distortion is small, the total tensile force increases

it can be seen that the reasonable determination of the cone angle of the die should also consider the deformation characteristics of the materials in the deformation area and the demand of the die and the barrier film for flexible packaging of industrial and food. The friction between parts begins to show a continuous upward trend. The determination of the reasonable range of the cone angle of the die has a direct impact on the drawing process. The process test shows that for the aluminum 3104h19 for CCB-1A can, the reasonable value of the female die cone angle is α= 5 ° -8 ° is appropriate

bottom forming process analysis. The forming of the tank bottom takes place at the end of the punch stroke, and the reverse re stretching process is adopted. Figure 4 shows the stress state of tank bottom forming. The bottom forming force mainly depends on the nature of friction and the magnitude of blank holder force. Generally, the thickness and strength of the material are a pair of contradictions. The thinner the material, the lower the strength. Therefore, the lightweight technology requires reducing the diameter of the tank bottom and designing a special shape of the tank bottom. The process test shows that the included angle of the outer wall of the tank bottom ditch is α 1. If it is greater than 40 °, the pressure resistance at the tank bottom will be greatly reduced. Considering the formability of the metal, the punch arc r cannot be less than 3 times the material thickness. But if R is too large, the intensity will be reduced. The circular arc R1 of the spherical surface and the inner wall of the tank bottom ditch is at least 3 times the material thickness, and generally R1 is 4-5 times the material thickness. Reduce the included angle of the inner wall of the tank bottom ditch α 2. The strength will be increased, and most of them are below 10 ° in production

there are two failure points at the bottom of the tank: one is the spherical surface at the bottom; The second is the arc r at the bottom of the tank connecting the spherical surface and the side wall. The strength of the spherical surface at the bottom of the tank depends on the following factors: the elastic modulus of the material, the diameter of the bottom, the strength of the material, the radius of the spherical surface, and the thinning degree of the metal when forming the bottom. The spherical radius of the tank bottom is usually determined by the formula r ball =d1/0.77, and the actual r ball =45.72mm

3 mold design and manufacturing

3.1 tank body drawing die

the tank body drawing process is actually the drawing process of cylindrical parts. During the drawing process, the flange part of its material is easy to lose stability under the action of compressive stress, which leads to 2 The verification method causes wrinkling, so we must consider setting up a crimping device to prevent wrinkling. When the material passes through the die, the fillet of the die is a transition zone, and its deformation is complex. In addition to radial tension and tangential compression, it is also subject to bending, so the selection of the fillet of the die is particularly important. After the material passes through the die fillet, it is in a tensile state. Because the tensile force comes from the punch pressure and is transmitted through the punch fillet, the material at the punch fillet is thinnest, which becomes the most vulnerable dangerous section

the structure of blanking drawing combined die is shown in Figure 5

(1) die material: both male and female dies are made of cemented carbide

(2) deformation: in the can industry, the tensile ratio is generally used δ Represents the amount of deformation, δ n=(dn-1-dn)/dn-1 × 100%. According to this formula, it is calculated as follows:

first stretch δ 1=(d0-d1)/d0 × 100%=(140..951)/140.2004 × 100%=36.6%。

stretch again δ 2=(d1-d2)/d1 × 100%=(88..015)/88.951 × 100%=25.8%。 Generally, it is required to have 2 times of total tensile ratio δ ≤64%, δ 1≥ δ 2≥……≥ δ n, δ 1≤40%。

(3) blank holder: use waveform blank holder, 0 3Mpa compressed air is used as the power source

(4) parameters of the working part of the drawing die:

fillet radius: the fillet radius Ra of the drawing die is 3.556mm, and then the fillet radius Ra of the drawing die is 1.78mm. The fillet radius RB of the stretching punch is 2.921mm, and then the fillet radius rb2.286mm of the stretching punch

clearance:

if the unilateral clearance z/2 of the male and female dies of the stretching die is large, the friction is small, which can reduce the stretching force, but the clearance is large, and the accuracy is not easy to control. What is the system structure of the metal material testing machine? Do you know? Today, StarTech will show you:; If the unilateral clearance z/2 of the male and female dies of the drawing die is small, the friction is large and the drawing force is increased

unilateral clearance z/2 can be calculated according to the following formula:

z/2=tmax+kt

where tmax-- maximum material thickness, take 0.285+0.005mm

t-- nominal material thickness, take 0.285mm

k-- coefficient, when t

Copyright © 2011 JIN SHI