Aluminum cans forming process and mould

1 Introduction Aluminum cans occupy a considerable proportion of beverage packaging containers. The manufacture of cans combines the advanced technologies of many industries such as metallurgy, chemical industry, machinery, electronics, and food, becoming a microcosm of aluminum deep processing. With the ever-increasing competition in the beverage packaging market, for many can-making companies, how to minimize sheet thickness, reduce the quality of single cans, increase material utilization, and reduce production costs in the production of cans is an important part of the company’s pursuit. aims. For this reason, technological transformation and technological innovation characterized by light-weighting are quietly emerging. The lightweighting of cans involves many key technologies, of which the can forming process and mold technology are very important aspects.
2 Tank Manufacturing Process and Technology 2.1 Tank Manufacturing Process The main manufacturing process flow of CCB-1A tank tank is as follows: coil transportation → coil lubrication → blanking, stretching → tank forming → trimming → Cleaning/drying→stacking/unloading→coating background→drying→color printing→priming→drying→internal spraying→internal drying→lubricant lubrication→constriction→screw compression neck.
In the process flow, blanking, drawing, can forming, trimming, shrinking, and screwing/flanging processes require mold processing. Among them, blanking, drawing and forming processes and molds are the most important. The level of technology and the level of mold design and manufacturing directly affect the quality and production costs of cans.
2.2 Can manufacturing process analysis (1) blanking a stretching composite process. During drawing, the material at the edge of the blank forms a cup in the radial direction, so that the unit body in the plastic flow region is in a biaxially stressed and uniaxially pulled three-dimensional stress state, as shown in FIG. 1 . Due to the effect of the arc of the punch and the arc of the drawing die, the thickness of the lower part of the cup is reduced by about 10%, while the thickness of the cup is increased by about 25%. The size of the arc at the corner of the cup has a great influence on the subsequent process (formation of the can body). If the control is not good, the broken can easily occur. Therefore, the blanking process must consider the following factors: diameter and draw ratio of the cup, circular arc of the punch, arc of the drawing die, clearance of the die, die, mechanical properties of the aluminum material, frictional performance of the die surface, and material Surface lubrication, tensile speed, lug rate, etc. The production of the lug is mainly determined by two factors: one is the performance of the metal material, and the other is the design of the drawing die. The lugs appear at the highest point and the thinnest point of the cup, which will affect the forming of the cans, resulting in incomplete edging and an increase in the rejection rate.
Based on the above analysis, it was determined that the draw ratio selected in the stretching step was m=36.55%, the blank diameter Dp=140.20±0.01 mm, and the cup diameter Dc=88.95 mm.

(2) Tank forming process.
Thinning process analysis. A typical aluminum can drawing and thinning drawing process is shown in FIG. 2, and a thinning drawing process is shown in FIG. 3. During the stretching process, the metal concentrating in the conical portion in the die mouth is the deformation region, and the force transmission region is the cylinder wall and the housing bottom after passing through the die. In the deformation zone, the material is in the three-axial stress state of axial tension, tangential compression, and radial compression. Under the action of triaxial stress, the grain refinement and strength increase, accompanied by work hardening. In the force-transmitting zone, the stress conditions of the various parts of the material are not the same. Among them, the stress on the metal in the corner area of ​​the punch is the worst, and it is subjected to axial and tangential two-direction tension and radial compression. The trend of thinning is severe, and metal tends to break from here, causing failure of stretching. Comparing the stress state of metal in deformed zone and force-transmitting zone, it can be known that whether the thinning tensile process can proceed smoothly mainly depends on the tensile stress of the metal in the corner of the tensile punch, when the tensile stress exceeds the material strength limit. It will cause breakage, otherwise the stretching process can proceed smoothly. Therefore, reducing the tensile stress during the stretching process is the key to ensure the smooth progress of the stretching.

The selection of thinning tensile ratio is: re-stretching: 25.7%, first thinning stretching: 20% to 25%, second thinning stretching: 23% to 28%, third Thinning stretch: 35% to 40%.
In the forming process, there are many factors that affect the tensile stress inside the metal, including the die angle. The value of the value is directly related to the flow characteristics of the metal in the deformed zone, which in turn influences the size of the forming force required for stretching. Therefore, whether the numerical value is reasonable or not has an important influence on the implementation of the process. When α is small, the range of the deformation zone is relatively large, the metal flows easily, and the distortion of the grid is small. With the increase of α, the range of the deformation zone decreases, the metal deformation concentrates, the flow resistance increases, and the grid divergence becomes serious. Moreover, as the taper angle of the die increases, the strain of the material in the deformed zone increases accordingly. This indicates that when the taper angle of the die is large, not only the deformation range of the metal is concentrated, but also the amount of deformation rapidly increases, thereby making the metal in the deformed zone processed. Hardening is aggravated, causing stress inside the metal to rise, which has a detrimental effect on stretching. On the other hand, if the α is too large or too small, the tensile force will increase. The reason is that when α is too large, the metal flow is sharp, the work hardening effect of the material is significant, and with the increase of the taper angle, the concave The part of the tapered surface that blocks the flow of metal increases, so the required tensile force increases; When the temperature is too small, although the turning of the metal flow is small, the total frictional resistance on the tapered surface is large due to the long contact cone between the metal in the deformed region and the concave surface. Therefore, although the grid distortion is small, the total tensile force increases.
It can be seen that the rational determination of the cone angle of the die should take into account the deformation characteristics of the material in the deformation zone and the friction between the die and the workpiece. The determination of the reasonable range of the die angle of the die has a direct impact on the drawing process. The process test shows that, for the aluminum material 3104H19 for CCB-1A cans, the reasonable value of the concave cone angle is appropriate at α=5°~8°.
Bottom forming process analysis. The formation of the bottom of the can occurs at the end of the stroke of the punch, using a reverse redrawing process. Fig. 4 is a schematic diagram of the forming condition of the bottom of the can. The bottom forming force mainly depends on the nature of the friction force and the size of the blank holder force. Generally, the thickness and strength of the material are a contradiction. The thinner the material, the lower the strength. Therefore, the lightweight technology requires a reduction in the diameter of the tank bottom and a special shape of the tank bottom. The process test shows that if the angle α1 of the outer wall of the tank bottom groove is greater than 40°, the pressure resistance at the tank bottom will be greatly reduced. Taking into account the metal formability, the punch arc R can not be less than 3 times the material thickness. However, if R is too large, it will reduce the intensity. The radius R1 of the spherical surface and the bottom wall of the tank bottom ditch is at least 3 times the material thickness, and usually R1 takes 4~5 times the material thickness. Reducing the angle α2 of the inner wall of the tank bottom ditch will increase the strength, and most of the production uses 10° or less.

There are two failure points at the bottom of the tank: one is the bottom spherical surface; the other is the arc R at the bottom of the tank connecting the spherical surface and the side wall. The strength of the bottom spherical surface of the can depends on several factors: the elastic modulus of the material, the diameter of the bottom, the strength of the material, the radius of the sphere, and the degree of thinning of the metal when formed at the bottom. The radius of the bottom of the tank is usually determined by the formula R ball = d1/0.77. Actually, the R ball = 45.72mm.
3 mold design and manufacturing 3.1 tank stretching mold tank stretching process is actually the cylindrical part of the stretching process, the tension process, the flange of the material under the influence of compressive stress tends to lose stability, leading to Wrinkle, so must consider setting to prevent wrinkling of the crimping device. When the material passes through the die, the corner of the die is a transition zone. The deformation of the die is complex. In addition to the radial and tangential compression, it is also subject to bending, so the choice of die radius is particularly important. After the material passes through the corner of the die, it is in tension. Because the tensile force comes from the punch pressure, it passes through the corner of the punch. The material at the corner of the punch becomes the most severe and becomes the most vulnerable Dangerous section.
Blanking a tensile mold structure shown in Figure 5.

(1) mold material: convex, concave molds are selected carbide material.
(2) Deformation: In the can industry, the drawing ratio δ is generally used to indicate the amount of deformation, δn=(dn−1−dn)/dn−1×100%. According to this formula, the calculation is as follows:
The first stretching takes δ1=(d0−d1)/d0×100%=(140.2001—88.951)/140.2004×100%=36.6%.
Restretching takes δ2=(d1−d2)/d1×100%=(88.951−66.015)/88.951×100%=25.8%.
General requirements 2 total stretch ratio δ ≤ 64%, δ1 ≥ δ2 ≥ ...... ≥ δn, δ1 ≤ 40%.
(3) Edge-pressing device: a waveform blankholder, 0.2-0.3MPa compressed air is used as a power source.
(4) Working Parameters of Drawing Die
Corner radius:
The radius rA of the drawing die is 3.556mm, and the radius rA of the drawing die is 1.78mm.
The draw punch radius rB takes 2.921mm, and then the punch fillet radius takes rB2.286mm.
gap:
When the tensile modulus of convex and concave die is larger than Z/2 on one side, the friction is small, and the tensile force can be reduced. However, the gap is large and the precision is not easy to control. The zigzag clearance between the convex die and the concave die is small when Z/2 is small. Large, increase tensile force.
The unilateral gap Z/2 can be calculated by the following formula:
Z/2=tmax+Kt
In the formula tmax - the maximum material thickness, take 0.285 +0.005mm
t - nominal thickness, take 0.285mm
K——coefficient, when t<0.4mm, take 0.08
Then Z/2=0.290+0.08*0.285=0.313mm.

3.2 Thin Stretching Dies The forming of the can body is actually a combined process that combines re-stretching and three-pass thinning. The design of the thinning die is now described as follows:
(1) mold material. Punch: Base material is alloy tool steel, punch material is M2, heat treatment hardness is 60~62HRC, and TiN is plated. Die (thinning stretch ring): The base material is an alloy tool steel and the die material is cemented carbide (designated as VALENITEVCID-H.L.D. or KE-84KENNAMETAL).
(2) Deformation. The formula for thinning the draw ratio is: δ=(tn-tn-1)/tn×100%, where tn, tn-1 are n times and n—1 times. Calculated: δ1=(0.285-0.225)/0.285×100%=21.05%; δ2=(0.225-0.170)/0.225×100%=24.44 %; δ3=(0.170-0.106)/0.170×100%=37.65%.
Can making factories often according to the given material thickness, thickness of the can body, thin wall requirements, stretching ring and punch size, stretching machine precision and other conditions, the preparation of tensile ring and punch matching table for technical personnel, mold maintenance Personnel and operators choose punches and pull rings.
(3) Working part parameters of the mold. Punch: Punch arc R1.016±0.025mm, re-extend punch arc R2.286mm, tank bottom groove arc R10.478±0.013mm. Thinning stretch ring: concave cone angle α = 5 °, working band width h = 0.38 + 0.25mm.
3.3 Can bottom mould The bottom mould structure is shown in Figure 6.

Tank bottom punch material alloy tool steel Crl2MoV, heat treatment hardness 60 ~ 64HRC, its contour shape should be consistent with the tank design. The bottom side die material is alloy tool steel Cr5MoV, heat treatment hardness 58 ~ 60HRC, its contour shape should match with the punch.
4 Conclusions (1) The important factors considered in the stretching process are: stretch ratio, convexity, radius of concave arc, convexity, gap of die, aluminum mechanical properties, lubrication, and operating parameters.
(2) Thinning taper angle in the stretching process. The size of the metal is related to the flow properties of the metal in the deformed zone, the magnitude of the stress, and the force of the mold. A reasonable range of values ​​is α = 5° - 8°.
(3) The appropriate can type design is the key to the implementation of lightweight technology. The research shows that for the CCB-1A tank, the design parameters are as follows: the angle of the outer wall of the bottom groove is α1=32°, the angle of the inner wall of the bottom groove of the tank is α2=5°, the arc of the convex mold is 1.016 mm, the spherical surface and the bottom groove The inner wall arc R1 = 1.524mm and the bottom spherical surface radius R ball = 45.72mm, which can greatly increase the strength of the tank body.