Technical Dry Goods | Brief Analysis Of the key points of aluminum extrusion profile die design for new energy vehicle

Abstract: In this paper, in allusion to the new energy resources automobile aluminum products according to the influence of aluminum extrusion profile die design factors are classified according to their structural characteristics, the extrusion process and aluminum extrusion profile die design-related factors are analyzed, and the new energy resources automobile aluminum die design points are introduced in detail.

Keywords: Extrusion coefficient; Extrusion force; Ratio of current distribution; Shunt bridge; Aluminum extrusion profile die

1. Preface

As strategic emerging industries develop and there is a growing emphasis on green, low-carbon, and circular economy, we have been increasingly utilizing aluminum profiles in various fields such as transportation lightweight, new energy materials, and environmental protection industries in recent years.

The product structure of aluminum profiles for new energy vehicles is becoming more and more complex, and the requirements for the mechanical properties of its materials are also getting higher and higher.

Besides the 6063 alloy known for its excellent extrusion performance, we widely use medium-hard alloys like 6061, 6082, and 6005A, which offer higher performance strength.

The following is a detailed description of the key points of Aluminum extrusion profile die design for new energy vehicles.

 

2. Analysis of factors affecting aluminum extrusion profile die design based on structural characteristics of aluminum profiles for new energy vehicles

New energy vehicle aluminum profiles generally comply with the GB/T 14846 high-precision standard, and the size or shape tolerance of each part is higher than the GB/T 14846 high-precision standard.

In addition, the aluminum profile structure of new energy vehicles also has the following characteristics:

(1). Thin-walled base plate profiles, with a minimum wall thickness of less than 2.0 mm and a large width-to-thickness ratio, usually require wide extrusion.

In extrusion production, problems such as excessive flatness and insufficient wall thickness in the middle of the profile often occur.

Commonly used in production is 6063 aluminum alloy. Profiles as shown in Figure 1.

Figure1

Figure 1

(2). Various aluminum profiles have small external dimensions at multi-cavity locations and a large number of internal cavities with small cavities.

There are many cross-ribs and a large wall thickness difference, with a wall thickness between 2.0 and 15.0 mm. They are commonly produced with 6005 and 6061 aluminum alloys.

The presence of cross-ribs and small cavities in the design of aluminum extrusion profile dies reduces the structural strength.

At the same time, the mold’s small male head often deflects, causing the wall to deviate or the small male head to break, which affects the aluminum extrusion profile die service life. Profiles as shown in Figure 2.

Figure 2

Figure 2

(3). Strengthened aluminum profiles have larger dimensions, more cavities, and larger cavities.

There are many ribs inside the fork, and the wall thickness difference is large, with a wall thickness between 3.0 and 18.0 mm.

The performance requirements of aluminum alloys are relatively high, and 6082 aluminum alloy is mostly used for production. In the production process, problems such as verticality flatness tolerance, and wall thickness tolerance often occur.

Verticality and flatness tolerance are not completely related to the mold, perhaps because the large wall thickness difference is related to the flow of quenching water in each part. Profile as shown in Figure 3.

Figure 3

Figure 3

(4). Thick-walled solid and thin-walled hollow composite profiles have a large difference in solid wall thickness, and the metal flow is extremely uneven during the extrusion process.

During the online quenching process, the metal shrinks unevenly due to cooling and deformation, resulting in excessive flatness or verticality.

Frequent thick and thin wall thickness crossings will also cause serious surface shadows and affect surface quality. Profiles as shown in Figure 4.

Figure 4

Figure 4

(5). Thick hollow profiles and thick extruded welds have a great impact on the performance of aluminum alloy products.

The Aluminum extrusion profile die design should arrange the weld position according to the “structural” profile. Profiles as shown in Figure 5.

Aluminum extrusion profile die

Figure 5

(6). In order to reduce automobile manufacturing costs, reduce welding seams, and improve the strength of aluminum frame structures, aluminum extrusion profiles have become more complex, which has brought challenges to extrusion production and aluminum extrusion profile die design. Profiles are shown in Figure 6.

Figure 6

Figure 6

3. Analysis of factors related to extrusion process and die design

In extrusion production, the extrusion ratio λ is closely related to the extrusion pressure.

Extrusion ratio:

λ= F0/ F type——Degree of deformation of metal

F0——Area of ​​extrusion barrel mm²

F type ——Profile area mm²

Extrusion pressure increases with the increase of the degree of metal deformation.

First split ratio: λ1=F0/F type

Split ratio: K=F points/F type

F points——total area of ​​split holes

Extrusion ratio: λ=λ1 ● K= F0/F points ● F points/F type = F0/ F type

When the extrusion ratio λ is constant, the split ratio K increases, and the first split ratio λ1 decreases. Then the split hole decreases, the resistance to the first deformation of the metal increases, the difficulty of metal deformation increases, and the extrusion pressure increases.

Extrusion pressure:

P=βF0σ0lnλ+(1/√3)σ0DL

σ0——Deformation resistance related to extrusion speed, temperature, etc./MPa

D——Extrusion barrel diameter/mm

L——Ingot length after roughening/mm

β——Correction coefficient (1.3~1.5)

λ——Extrusion coefficient; ln20=2.996, ln40=3.69   (3.69-2.996)/2.996=23.13%, the first term of the formula increases by 23.13%.

It can be seen from the formula that the extrusion pressure P is proportional to the natural logarithm of the extrusion coefficient. When the extrusion coefficient increases, the extrusion pressure increases accordingly.

During normal extrusion, P total = P1 + P2 + P3 < SP extruder pressure

P1 – pressure to overcome the friction of the extrusion barrel wall;

P2 – pressure required for the aluminum ingot to deform and enter the die;

P3 – pressure required to overcome the friction in the diversion hole

If: P total = P1 + P2 + P3 > SP

  • Increase the diversion flow to reduce P2
  • Reduce the depth of the die diversion (die thickness) to reduce P2
  • Reduce the length of the working belt to reduce friction P3

In addition, if the extrusion coefficient is large

  • Increase the area of ​​the die diversion hole
  • Reduce the depth of the die diversion (die thickness) to reduce the pressure P2
  • Reduce the length of the working belt to reduce friction P3

If the extrusion coefficient is small

  • Reduce the area of ​​the die diversion hole
  • Increase the depth of the die diversion (die thickness) to increase the pressure P2
  • Increase the length of the working belt or add a secondary welding chamber to increase the pressure P3
  • Increase the volume of the welding chamber to increase the pressure P3

 4. Key points of new energy vehicle aluminum extrusion profile die design

Here we mainly explain the design points of the shunt mold for new energy vehicles.

4.1 Reasonable arrangement of mold diversion holes

 4.1.1 Allocate diversion holes according to the extrusion coefficient

Generally, when the extrusion coefficient of aluminum alloy 6061 and 6082 is large, in order to reduce the extrusion pressure, it is beneficial to profile forming and to ensure the flatness and verticality of the Aluminum Extruded Products, the diversion ratio of the mold should be increased, that is, the area of the diversion holes should be increased.

When the extrusion coefficient is small, the extrusion pressure should be increased, which is beneficial to improving the quality of the metal weld, and the diversion ratio should be reduced, that is, the area of the diversion holes should be reduced.

4.1.2 Reasonable arrangement of welding line position

“Surface” profile weld position   “Structural” profile weld position

“Surface” profile weld position                “Structural” profile weld position

“Structural” profiles need better weld quality to meet the performance requirements of aluminum alloys.

Therefore, the weld position arrangement is different from that of “surface” profiles.

4.1.3 Allocate the flow of the diverter hole according to the distance from the center of the extrusion cylinder

The area allocation principle of the diverter hole: try to make the diverter ratio of each part of the profile equal according to the profile cross-section.

The diverter flow of the outer diverter hole should be increased by 10%. If the diverter hole is larger than the maximum diverter diameter, it should be increased by 20%. The area of the largest diverter hole cannot be greater than 1.5 times the smallest diverter hole.

Maximum flow diameter

Figure 8Figure 8

Figure 8

   

4.1.4 Flow distribution on the inner wall of multiple cavities of profiles

  • Try to reduce the number of connections between the inner ribs and the number of back holes in the back hole, as shown in the figure:

back holes

Figure 9

  • Multiple back holes should be connected together as much as possible, but they cannot go through the center of the mold, otherwise, the mold strength will be greatly reduced, as shown in Figure 10.

Multiple back holes

Figure 10

  • An acceleration slope should be made in the back hole to speed up the metal outflow from the back hole, as shown in Figure 11.

back hole

Figure 11

 4.1.5 Hollow profile diversion solid part

The solid part of the hollow profile should be as far away from the center of the aluminum extrusion profile die as possible. To better control the metal flow rate of the solid part, if it is necessary to place it in the center of the mold, we should position it under the diversion bridge. As shown in Figure 12.

Figure 12

Figure 12

Figure 12

4.2 Principles for calculating mold strength and arranging diverter bridges

4.2.1 Basic principles for arranging mold diverter bridges

(1) The mold bridge must be placed to limit the deformation of the core head

(2) The mold bridge must not affect the flow of aluminum

  • Try not to place the bridge in front of the inner wall
  • Try not to place the bridge in front of the details (screw holes, grooves)
  • Enough space can be left for the diverter hole
  • The mold bridge must be able to withstand the extrusion pressure

4.2.2 Mold Strength Verification

The mold strength is verified to determine the thickness of the upper mold of the diverter mold, and the bending strength and shear strength of the mold are calculated respectively, and the width and span of the diverter bridge are determined to meet the mold strength requirements.

(1) Bending stress verification of the diverter bridge:

Mold Strength Verification

 

4.3 Determination of the size of the mold hole

Before the size of the mold hole is scaled according to the usual ratio, the asymmetric tolerance must be processed first.

    4.3.1 Dimensional tolerance of symmetrical mold holes

The dimensional tolerance of symmetrical mold holes is shown in Figures 13 and 14.

Aluminum extrusion profile die Figure 13

Figure 13

  Dimensional tolerances for symmetrical holes

Figure 14 Dimensional tolerances for symmetrical holes

    4.3.2 Adjust the hole after scaling

After scaling the mold hole size according to the usual ratio, we need to adjust the local size to compensate for the compression deformation that occurs in the mold.

Scaling by ratio

Figure 15 Scaling by ratio

  • For large hollow panels, we perform pre-deformation compensation by adjusting the hole size in the lower model.

Adjust the hole size of the lower model

Figure 16 Adjust the hole size of the lower model

  • Mold core pre-deformation compensation

Adjusting the core size

Figure 17 Adjusting the core size

4.4 Determination of the working zone of the mold hole

(1) Determine the working zone of the mold hole based on the distance between the hole and the mold center

The length of the working belt decreases from the center of the extrusion cylinder to the outside

The length of the working belt decreases from the center of the extrusion cylinder to the outside

Extrusion average speed and distance

Extrusion average speed and distance

(2) Large profiles with different wall thicknesses

First, determine the minimum wall thickness working zone. Given the significant variation in the wall thickness of the profiles, we determine the minimum working zone based on the wall thickness multiple.

For large wall thicknesses, we cannot determine the working zone solely by the wall thickness multiple. Instead, we compensate for the working zone by controlling the metal flow rate, using either a secondary welding chamber or a block to achieve this. An excessively long working zone will cause product surface quality problems.

Aluminum extrusion profile die figure 18

Aluminum extrusion profile die figure 18

Figure 18

(3) Effect of secondary welding chamber on metal flow rate

Effect of secondary welding chamber on metal flow rate

The pocket offset (A) has a significant effect on pressure changes (and aluminum flow velocity)

The pocket offset (A) has a significant effect on pressure changes (and aluminum flow velocity)

Considering the high pressure exerted when the dimension A is less than 1 millimeter, it is comparable to the pressure experienced by the working belt, this similarity allows us to draw insights into the extrusion process dynamics.

1<A<8mm pressure change can handle the aluminum flow

A>8mm pressure is too low and cannot affect the aluminum flow

We effectively utilize the secondary welding chamber to assist the working belt, in accordance with the metal flow law.

5. Conclusion

The above mainly focuses on the relevant factors of aluminum extrusion profile die design in combination with the structural characteristics of new energy vehicle aluminum profiles.

Due to the complexity of new energy vehicle aluminum profiles, which are mostly medium-hard alloys (6005, 6061, 6082) and the complexity of product structure, large extrusion pressure, low extrusion speed, and internal rib rot often occur in the product production process.

To reduce extrusion pressure and increase extrusion speed, we often employ the bridge sinking pressure reduction technique, which significantly enhances mold strength.

Therefore, the strength requirements of new energy vehicle aluminum extrusion profile die are extremely high, and the mold design needs to be more reasonable, the mold manufacturing modeling and processing need to be more precise, and the mold material needs to be high-quality mold steel and optimized mold heat treatment process.

In extrusion production, we require high-quality homogenized alloy materials and a well-planned production process to increase extrusion speed, we adopt this approach to reduce the production costs of aluminum profiles for new energy vehicles and to enhance production efficiency.

References:

[1] Wang Zhutang and Tian Rongzhang, Aluminum Alloy and Its Processing Handbook, Central South University Press, 1989.

[2] Liu Jingan, Aluminum Alloy Extrusion Die Handbook, Beijing: Metallurgical Industry Press, 2012.

 

The content of this article comes from the “2023 Guangdong (Nanhai) Aluminum Processing Industry Technical Conference Proceedings”.

Author profile: Zou Jing (1964.11-), female, senior engineer, engaged in aluminum extrusion profile die design and manufacturing process research.

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