[Aluminium.com] Despite careful design and manufacturing of molds, continuous improvement of technical levels, and even the use of CAD/CAM systems, the company strives to design and manufacture as perfect tooling as possible, but due to the increasing number and complexity of cross-sectional shapes of extruded profiles, Due to the increasing requirements for dimensional accuracy and the influence and variation of various production process factors in extrusion production, the profiles produced by the molds produced by the design and manufacture can still exhibit defects of one kind or another.

Hollow aluminum profiles are a common decorative material and industrial profiles. For hollow profiles, the quality of the weld directly affects the quality of the aluminum profile itself. If the quality of the weld does not pass, there will be a black belt or color difference after the surface treatment of the aluminum, which will cause the product to be scrapped and cause irreversible damage. Therefore, the analysis of the formation mechanism of the hollow aluminum profile welds is carried out to ensure the weld quality of hollow aluminum profiles.

First, the formation mechanism of the weld metal through the split hole into several strands reassembled in the welding room, due to the existence of the diversion bridge, the bottom of the bridge will inevitably form a rigid metal flow, so that the diffusion of metal atoms at the combination of slower speed, The density of the metal decreases. Therefore, the use of split-flow composite die extrusion will inevitably exist; but a good weld can make the profile in the surface treatment to avoid or reduce the phenomenon of black belt. To ensure the quality of the weld, the metal in the weld of the weld chamber must be fully diffused and bound. Otherwise, loose, coarse particles, and non-uniform microstructure with other parts will be formed. Therefore, the degree of deformation must be larger, especially welding. The amount of metal deformation in the chamber is large to form a large hydrostatic pressure.

When extruding, the uneven flow of the metal can cause a great deal of additional stress in the profiled product, resulting in various defects. Such as welding line, dimensional instability, length and length of multiple profiles and so on. In order to overcome the defects caused by the uneven flow of metal, it is necessary to study how to make the metal flow rate on the profile section uniform. The factors that affect the velocity of the metal out of the die hole can be summarized as the following two basic factors:

1 The appropriate distribution of metal in each section of the supply profile. That is, the ratio of the ratio of the cross-sectional area of ​​each section of the profile to the amount of metal of the corresponding supply section is equal.

2 When the metal flow is affected by the frictional resistance, the more the amount of metal supplied to a certain part of the profile, the smaller the frictional resistance, the faster the exit velocity of the die hole in the section, and vice versa.

2.1 The distribution ratio of metal supply is mainly determined by mold design and manufacturing. When the mold is manufactured, the proportion of metal is basically fixed.

2.2 For most molds, it is apparent that the metal distribution has been determined, but the frictional resistance between the metal and the mold can be improved. In order to achieve the purpose of adjusting the metal flow rate.

3 The friction between the metal and the mold consists of three parts:

3.1 Contact friction between metal and mold F1

F1=μ? ρ? S

Where: μ: friction coefficient ρ: unit pressure MPa

S: Contact friction area between metal and die surface mm2

It can be seen from the above equation: ρ and S are fixed values, and the impact on the friction force F1 is μ. Therefore, to improve the friction between the metal and the mold surface, it can play a role in adjusting the metal flow rate.

3.2 Contact Friction Between Metal and Die Hole Working Belt

F2=μ? ρ? ∑S=μ? ρ? ∑L1H1

In the formula: ∑S: area of ​​the contact portion of the die hole working part of each section of metal and profile section mm2

L1: working belt circumference of the contact part mm

H1: Phase contact working width mm

It can be seen from the equation that ρ and L1 are fixed values ​​that have an effect on friction. The friction coefficient μ and the operating band width H1, as long as the μ and H1 are adjusted, can achieve the purpose of adjusting the metal flow rate. 3.3 Metal-to-metal relative Friction of movement F3

F3=f?ρ/ц

Where: f: friction coefficient of metal and metal ρ: unit pressure MPa

ц: Metal flow rate mm/min

From the above formula, f is a variable value, with the temperature change, the faster the metal flow speed, the smaller the F3 value under the same unit pressure, then the role played by F1 and F2 becomes more obvious.

Therefore, in the extrusion process, reasonable control of the extrusion temperature and extrusion speed can significantly change the metal flow rate.

Second, the cause of severe quilting 1 extrusion pressure is too low, the welding power is low. The factors causing the low extrusion force are comprehensive, and there are some factors on the mold as well as the process. There are several situations:

1.1 When the extrusion is relatively low, the welding force of the mold can be increased: the thickness of the upper mold is increased, and the shunt hole is appropriately reduced;

1.2 According to the profile size and cross-sectional shape, adjust the extrusion temperature 10 ~ 20 °C.

1.3 Select the appropriate extruder, that is, arrange the extrusion on a larger model.

1.4 deepen the welding room (the method of "sinking" the diversion bridge). However, it should be noted that the Shen Bridge will also reduce the pressing force, so use this method according to the specific circumstances. In the production process, along with the wear of the mold, the wall thickness of the profile also increases, the extrusion ratio also decreases, and the wear to a certain extent, the seriousness of the weld will affect the surface quality of the profile.

2 The design of the splitter hole is too large (especially for profiles with low extrusion ratio), which reduces the pressing force and thus reduces the welding force.

2.1 The welding chamber is too shallow or the volume is too small to form enough hydrostatic pressure. It is reasonable to increase the volume of the welding chamber under the premise of ensuring the rigidity and strength of the core. It may be to increase the cross-sectional area of ​​the welding chamber or to increase the height of the welding chamber.

2.2 The layout of the shunt hole is irrational, and the design and processing of the shunt bridge are unreasonable. Should try to make the weld to the corner or non-decorative surface, and the use of drip-type shunt bridge and a reasonable welding angle, so that the solder joint falls on the plane of the welding chamber (ie, the preformed area).

3 Influence of the production process 3.1 The internal defects of the cast rod are likely to appear on the weld of the hollow profile (hard-to-deform zone). Excessive amounts of Mg and Si and excessively high Fe content will aggravate welding defects. It is recommended that the ratio of Mg to Si be approximately in the range of 1.2 to 1.4, and the Fe content of less than 0.20% can obtain better weld quality.

3.2 Extrusion Temperature and Extrusion Speed ​​The high temperature of the aluminum rod is conducive to the diffusion bonding of metals, but the phenomenon of metal bonding die is intensified. At the same time, the rod temperature is high, the metal grain growth and growth speed is accelerated, and the weld seam structure Thick. Extrusion speed is too fast, the metal deformation work increases, metal temperature rises more. In addition, the extrusion temperature is too high, the pressing force will be reduced, which in turn reduces the welding force. Therefore, the bar temperature and mold should be controlled during extrusion to reduce the impact of other factors on the profile.

3.3 Reasonable selection of the temperature of the ingot barrel for extrusion. For thick-walled profiles, it is recommended that the temperature of the extrusion cylinder be slightly increased by about 5°C. However, in the case of thin-walled profiles and excessively large orifices, the temperature may be appropriately reduced by about 5°C. On the other hand, it is necessary to clear the squeezing tube at regular intervals, and there is more oxidized scale, or the extruding tube has been deformed like a drum, and the gap between the extruding tube and the pressing pad is too large, which all affect the quality of the weld.

3.4 Uneven cooling of quenching will also affect the quality of the weld. When the material slides out of the station and uses graphite products, the side contacted with graphite is not timely dissipated, and the temperature rises locally, thereby accelerating the growth of the grain at the surface weld, and the appearance of the black strip after the oxidation is also prone to occur. However, if the cooling capacity of the equipment is sufficient, this phenomenon can also be avoided. Therefore, it is better to use a high-temperature felt to slide out of the table, and it is not easy to wipe the flowers.

3.5 Effect of Alkaline Oxidation To reduce the influence of the weld on the surface quality, it is also possible to relatively adjust the alkali etching time and temperature.

Concluding Remarks To solve the problem of welding quality of hollow profiles, it is necessary to “diagnose” the mold first, and then select a reasonable process or adjust the extrusion process according to the conditions of the mold. The result of poor welding or severe weld seams is that after the anodized surface treatment of the profile, color bands such as black bands and chromatic aberrations occur, affecting the quality of use.

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