Rational Use, Maintenance and Management of Aluminum Profile Extrusion Die

In the aluminium profile production enterprises, the die cost accounts for about 35% of the profile extrusion production cost. Whether the die is good or bad and whether the die can be used and maintained reasonably directly determines whether the enterprise can produce profiles normally and qualified. The working conditions of extrusion die in profile extrusion production are very bad. It not only needs to endure severe friction and wear under high temperature and pressure, but also needs to endure periodic load. All these require that the die has high thermal stability, thermal fatigue, thermal wear resistance and enough toughness. In order to meet the above requirements, high quality 4Cr5MoSiV1 (American brand H13) alloy steel is widely used in China. Vacuum heat treatment and quenching are used to make dies to meet the requirements of aluminum profile production.

However, in the actual production, some dies still fail to reach the expected output when extruded, and even less than 20 bars are extruded or scrapped in advance less than two times on the machine. As a result, the dies manufactured with expensive die steels are far from achieving their due benefits. This phenomenon is prevalent in many aluminium profile manufacturing enterprises in China. To investigate its causes, we need to start from the following aspects.

First, the section of aluminium profile itself is changing rapidly, and the aluminium extrusion industry has developed to today. Aluminum alloy has the important advantages of light weight and good strength. At present, many industries have used aluminium profile to replace the original materials. Because of the particularity of some profiles, it is difficult to design and manufacture the die because of the special section of profiles. If the conventional extrusion method is still used, it is often difficult to achieve the rated output of the die, so special technology must be used to strictly control the production process parameters in order to normal production. Because of the special section of the profile or the quality problem of the die itself, some die can not be extruded to the rated output, which requires the salesman to communicate with the technical department and the die factory fully when receiving the order. At the same time, the die design and manufacturing department needs to continuously optimize the die design technology, improve the accuracy of die manufacturing and improve the quality of the die.

2. Choose suitable extruder type for production. Before extrusion production, it is necessary to fully calculate the section of profile, and determine the tonnage of extruder according to the complexity of section, wall thickness and extrusion coefficient. Generally, λ > 7-10. When lambda > 8-45, the service life of the die is longer and the profile production process is smoother. When lambda > 70-80, it is more difficult to extrude profiles, and the general life of the die is shorter. The more complex the product structure is, the more likely it is to lead to insufficient local rigidity of the die, the more difficult the metal flow in the die cavity tends to be uniform, and accompanied by local stress concentration. During the production of profiles, it is easy to plug the die, block the car or form distorted waves. The die is prone to elastic deformation, and even plastic deformation will occur, which will make the die directly scrapped.

3. Reasonable selection of billet and heating temperature. The alloy composition of the extruded ingot must be strictly controlled. At present, general enterprises require the grain size of ingot to reach the first-class standard in order to enhance plasticity and reduce anisotropy. When there are pore, loose structure or central crack in the ingot, the sudden release of gas during extrusion process is similar to "shooting off", which makes the local working band of the die suddenly load-shedding and loading, forming a local huge impact load, which has a great impact on the die. Conditional enterprises can homogenize the ingot billet. After holding for 8 hours at 550-570C, the forced cooling can reduce the breakthrough pressure by 7-10% and increase the extrusion speed by about 15%.

4. Optimizing extrusion process. In order to prolong the life of the die scientifically, the rational use of the die for production is an aspect that can not be ignored. Because the working conditions of the extrusion die are extremely bad, reasonable measures must be taken to ensure the structure and properties of the die in the extrusion production. (1) Take appropriate extrusion speed. In the process of extrusion, when the extrusion speed is too fast, it will cause the metal flow is difficult to be uniform, and the friction between the aluminum metal flow and the inner wall of the die cavity will intensify, which will accelerate the wear of the working belt of the die, and the die temperature is actually higher. If the heat generated by metal deformation can not be taken away in time, the die may fail due to local overheating. If the extrusion speed is suitable, the adverse consequences mentioned above can be avoided, and the extrusion speed should generally be controlled below 25 mm/s. (2) Reasonable selection of extrusion temperature. The extrusion temperature is determined by the heating temperature of the die, the temperature of the ingot barrel and the temperature of the aluminium bar. Low temperature of aluminium bar can easily lead to the increase of extrusion force or the phenomenon of stuffing. The die is prone to local micro-elastic deformation, or cracks in the stress concentration area, leading to the early scrap of the die. The excessive temperature of aluminium bar will soften the metal structure, which will make it adhere to the working belt surface of the die or even block the die (when the die collapses under high pressure in serious cases). The reasonable heating temperature of the non-uniform ingot is 460-520 C, and the reasonable heating temperature of the homogenized ingot is 430-480 C.

Fifth, the reasonable surface nitriding process must be carried out before the extrusion die is used. Surface nitriding treatment can greatly improve the surface hardness of the die while maintaining sufficient toughness, so as to reduce the thermal wear when the die is used. It should be noted that surface nitriding can not be accomplished in one time. Repeated nitriding treatment must be carried out 3-4 times during the service of the die. Generally, the thickness of nitriding layer is required to reach about 0.15mm. The most suitable nitriding process is the first nitriding after the mould is inspected in the factory. At this time, due to the unstable structure of the nitrided layer, nitrogen should be applied again after extrusion of 5-10 bars.

In the aluminium profile production enterprises, the die cost accounts for about 35% of the profile extrusion production cost. Whether the die is good or bad and whether the die can be used and maintained reasonably directly determines whether the enterprise can produce profiles normally and qualified. The working conditions of extrusion die in profile extrusion production are very bad. It not only needs to endure severe friction and wear under high temperature and pressure, but also needs to endure periodic load. All these require that the die has high thermal stability, thermal fatigue, thermal wear resistance and enough toughness. In order to meet the above requirements, high quality 4Cr5MoSiV1 (American brand H13) alloy steel is widely used in China. Vacuum heat treatment and quenching are used to make dies to meet the requirements of aluminum profile production.

However, in the actual production, some dies still fail to reach the expected output when extruded, and even less than 20 bars are extruded or scrapped in advance less than two times on the machine. As a result, the dies manufactured with expensive die steels are far from achieving their due benefits. This phenomenon is prevalent in many aluminium profile manufacturing enterprises in China. To investigate its causes, we need to start from the following aspects.

First, the section of aluminium profile itself is changing rapidly, and the aluminium extrusion industry has developed to today. Aluminum alloy has the important advantages of light weight and good strength. At present, many industries have used aluminium profile to replace the original materials. Because of the particularity of some profiles, it is difficult to design and manufacture the die because of the special section of profiles. If the conventional extrusion method is still used, it is often difficult to achieve the rated output of the die, so special technology must be used to strictly control the production process parameters in order to normal production. Because of the special section of the profile or the quality problem of the die itself, some die can not be extruded to the rated output, which requires the salesman to communicate with the technical department and the die factory fully when receiving the order. At the same time, the die design and manufacturing department needs to continuously optimize the die design technology, improve the accuracy of die manufacturing and improve the quality of the die.

2. Choose suitable extruder type for production. Before extrusion production, it is necessary to fully calculate the section of profile, and determine the tonnage of extruder according to the complexity of section, wall thickness and extrusion coefficient. Generally, λ > 7-10. When lambda > 8-45, the service life of the die is longer and the profile production process is smoother. When lambda > 70-80, it is more difficult to extrude profiles, and the general life of the die is shorter. The more complex the product structure is, the more likely it is to lead to insufficient local rigidity of the die, the more difficult the metal flow in the die cavity tends to be uniform, and accompanied by local stress concentration. During the production of profiles, it is easy to plug the die, block the car or form distorted waves. The die is prone to elastic deformation, and even plastic deformation will occur, which will make the die directly scrapped.

3. Reasonable selection of billet and heating temperature. The alloy composition of the extruded ingot must be strictly controlled. At present, general enterprises require the grain size of ingot to reach the first-class standard in order to enhance plasticity and reduce anisotropy. When there are pore, loose structure or central crack in the ingot, the sudden release of gas during extrusion process is similar to "shooting off", which makes the local working band of the die suddenly load-shedding and loading, forming a local huge impact load, which has a great impact on the die. Conditional enterprises can homogenize the ingot billet. After holding for 8 hours at 550-570C, the forced cooling can reduce the breakthrough pressure by 7-10% and increase the extrusion speed by about 15%.

4. Optimizing extrusion process. In order to prolong the life of the die scientifically, the rational use of the die for production is an aspect that can not be ignored. Because the working conditions of the extrusion die are extremely bad, reasonable measures must be taken to ensure the structure and properties of the die in the extrusion production. (1) Take appropriate extrusion speed. In the process of extrusion, when the extrusion speed is too fast, it will cause the metal flow is difficult to be uniform, and the friction between the aluminum metal flow and the inner wall of the die cavity will intensify, which will accelerate the wear of the working belt of the die, and the die temperature is actually higher. If the heat generated by metal deformation can not be taken away in time, the die may fail due to local overheating. If the extrusion speed is suitable, the adverse consequences mentioned above can be avoided, and the extrusion speed should generally be controlled below 25 mm/s. (2) Reasonable selection of extrusion temperature. The extrusion temperature is determined by the heating temperature of the die, the temperature of the ingot barrel and the temperature of the aluminium bar. Low temperature of aluminium bar can easily lead to the increase of extrusion force or the phenomenon of stuffing. The die is prone to local micro-elastic deformation, or cracks in the stress concentration area, leading to the early scrap of the die. The excessive temperature of aluminium bar will soften the metal structure, which will make it adhere to the working belt surface of the die or even block the die (when the die collapses under high pressure in serious cases). The reasonable heating temperature of the non-uniform ingot is 460-520 C, and the reasonable heating temperature of the homogenized ingot is 430-480 C.

Fifth, the reasonable surface nitriding process must be carried out before the extrusion die is used. Surface nitriding treatment can greatly improve the surface hardness of the die while maintaining sufficient toughness, so as to reduce the thermal wear when the die is used. It should be noted that surface nitriding can not be accomplished in one time. Repeated nitriding treatment must be carried out 3-4 times during the service of the die. Generally, the thickness of nitriding layer is required to reach about 0.15mm. The most suitable nitriding process is the first nitriding after the mould is inspected in the factory. At this time, due to the unstable structure of the nitrided layer, nitrogen should be applied again after extrusion of 5-10 bars.