[China Aluminum Network] In the aluminum production enterprises, the mold cost accounts for about 35% of the extrusion production costs. The quality of the mold and whether the mold can be properly used and maintained directly determine whether the company can produce normal and qualified profiles. The working conditions of the extrusion die in the production of the profile extrusion are very bad, both need to withstand severe friction and wear under high temperature and high pressure, and also need to withstand the cyclical load. This requires that the mold has high thermal stability, thermal fatigue resistance, thermal wear resistance and sufficient toughness. In order to meet the above requirements, high-quality 4Cr5MoSiV1 (United States grade H13) alloy steels are currently widely used in the country, and vacuum heat treatment quenching and other methods are used to make molds to meet various requirements in the production of aluminum profiles. Pull-Out Faucet,Pull Out Kitchen Taps,Pull Out Kitchen Faucet,Stainless Steel Kitchen Faucet AIHUI Sanitary Ware , https://www.fsaihuisanitary.com
However, in actual production, there are still some molds that fail to reach the predetermined output when they are squeezed. Severely, they even scrape less than 20 bars or scrape less than 2 times before they are scrapped, resulting in the use of expensive mold steel. The mold is far from achieving its expected benefits. This phenomenon is currently prevalent in many domestic aluminum profiles manufacturers. To study its causes, we need to start from the following aspects.
First, the aluminum profiles themselves are ever-changing, and aluminum extrusion industry has developed to today, aluminum alloys have important advantages such as light weight, good strength, and many industries have adopted aluminum profiles instead of the original materials. Due to the special profile of the profile, the mold has a special cross-section and is difficult to design and fabricate. If you still use the conventional extrusion method is often difficult to achieve the rated output of the mold, you must use a special process, strict control of the production process parameters in order to normal production. And some molds due to their own profile section special or the quality of the mold itself, resulting in the mold can not be squeezed to the rated output, which requires the sales staff to contact the technical department and the mold factory to fully communicate. At the same time, the mold design and production department needs to continuously optimize the mold design technology, improve the accuracy of mold production, and improve mold quality.
Second, select the appropriate extrusion machine for production. Before the extrusion production, it is necessary to fully calculate the section of the profile, and determine the tonnage of the extruder according to the complexity of the profile section, the wall thickness and the extrusion coefficient λ. In general, λ>7-10. When λ>8-45, the service life of the die is longer and the profile production process is smoother. When λ>70-80, it is difficult to squeeze the profile, and the die life is generally shorter. The more complex the product structure, the more likely it is that the local rigidity of the mold is insufficient, the metal flow in the mold cavity is difficult to be uniform, and local stress concentration is accompanied. In the production of profiles, plugs and boring cars or twisted waves are easily formed, and the molds are easily deformed by elasticity. In severe cases, plastic deformation occurs and the molds are directly scrapped.
Third, a reasonable choice of billet and heating temperature. It is necessary to strictly control the alloy composition of the extruded ingot. At present, general enterprises require that the grain size of the ingot be up to a standard, so as to enhance plasticity and reduce anisotropy. When there are pores in the ingot, loose tissue, or central cracks, the sudden release of gas during the extrusion process is similar to "spraying guns," causing the local working belt of the mold to suddenly deload and load, resulting in a local huge impact load, which has a great impact on the mold. Big. Qualified companies can homogenize ingots, forced cooling after 550 ~ 570C for 8 hours, extrusion pressure can be reduced by 7-10%, extrusion speed can be increased by 15%.
Fourth, optimize the extrusion process. To scientifically extend the life of molds and use molds reasonably for production is an aspect that cannot be ignored. As the working conditions of the extrusion die are extremely harsh, reasonable measures must be taken in the extrusion production to ensure the organizational properties of the die. (1) Take the appropriate extrusion speed. In the extrusion process, when the extrusion speed is too fast, the metal flow will be difficult to make uniform, the aluminum metal flow and the friction of the inner wall of the mold cavity will intensify, causing the wear of the mold working belt to accelerate, and the mold temperature actually higher. If the residual heat generated by the metal deformation cannot be taken away in time, the mold may fail due to local overheating. If the extrusion speed is appropriate, the above adverse effects can be avoided. The extrusion speed should generally be controlled below 25 mm/s. (2) Reasonably select the extrusion temperature. The extrusion temperature is determined by the mold heating temperature, the temperature of the ingot and the temperature of the aluminum rod. The low temperature of the aluminum rod easily causes the extrusion force to rise or the boring car phenomenon to occur. The mold is prone to local minute traces of elastic deformation, or cracks may occur at stress concentrated sites, leading to early scrapping of the mold. Excessively high temperature of the aluminum rod will soften the metal structure and cause adhesion to the surface of the mold working belt and even block the mold (in severe cases, the mold will collapse under high pressure). The reasonable heating temperature of the ununiform ingot will be 460-520°C and homogenized. The reasonable heating temperature of the ingot is 430-480°C.
Fifth, the use of extrusion mold must be a reasonable surface nitriding process. The surface nitriding treatment can make the mold greatly improve the surface hardness of the mold under the premise of maintaining sufficient toughness, so as to reduce the thermal wear generated when the mold is used. It should be noted that the surface nitriding can not be completed in a single time. During the service of the mold, it must be carried out 3-4 times of repeated nitriding treatment. Generally, the thickness of the nitriding layer should be about 0.15mm. A more suitable nitriding process is to perform the previous nitriding after the mold is inspected. At this point, because the nitrided layer is not yet stable, it should be nitrided again after extruding 5-10 rods. After the second nitriding, 40-80 rods can be extruded. After the third nitriding, no more than 100-120 rods are suitable. Before nitriding, the working belt must be polished, and the mold cavity should be cleaned. Residues of alkali slag or foreign particles must not be left. In general, the nitridation of the mold is not more than 4-5 times, because at this time, if the nitrided layer is not pulled by the working belt, the nitrided layer structure is relatively stable after repeated nitriding and extrusion. It should be noted that when the previous nitriding process is carried out, an appropriate production process is required to perform nitriding, and the number of nitriding times cannot be too frequent. Otherwise, the work belt is easily delaminated.
Sixth, the mold on the machine before the belt must be polished and polished, the work belt generally requires polishing to the mirror. Check the flatness and perpendicularity of the mold working belt before assembling. Nitriding quality to a certain extent determines the polished finish of the work belt. The mold cavity must be cleaned with high-pressure gas and brush, and no dust or foreign matter shall be allowed. Otherwise, it will easily pull down the working belt caused by the metal flow, so that the extruded profile product will have defects such as rough surface or scribe.
VII. Die holding time during extrusion production is generally around 2-3 hours, but not more than 8 hours, otherwise the hardness of the die working layer with nitride layer will decrease, resulting in rough surface of the profile caused by wear on the machine, and serious Scribe and other defects. When using the mold, mold supports, mold sleeves, and support pads must be matched with the mold to avoid that the contact surface between the mold outlet surface and the support cushion is too small due to the large bore in the support cushion, and the mold is deformed or broken. The concentricity of the die, the extrusion tube, and the extrusion shaft is within ±3mm. Otherwise, the eccentric load and the design flow velocity of the various parts of the mold may change, affecting the molding of the profile.
8. Use the correct alkaline wash method. After the mold is unloaded, the mold temperature is above 500°C. If it is immersed in alkaline water immediately, the temperature of the alkaline water is much lower than the mold temperature. If the mold temperature drops rapidly, the mold is prone to cracking. The correct method is to unload the mold, place the mold in air at 100°-150°C, and immerse it in alkaline water. Ordinary shunting molds are used for drafting before unloading, which can greatly reduce the amount of cooking and shorten the cooking time. The specific method is that after the extrusion is completed, the extrusion rod retreats before the extrusion cylinder, the pressure remains in the extrusion cylinder, and then the extrusion cylinder retreats. At the same time, part of the residual aluminum in the die orifice can be pulled out together with the pressure, and then Then boiled. Some shunt modular mold core head is very small, even thinner than the pen, this type of mold extrusion is not allowed after the end of the mold, the mold must be clear before the mold open mold, must wait for the residual aluminum in the mold cavity Basically boil off before you can open the mold. Otherwise it will be a little inattentive and will break the core, causing the mold to be scrapped.
Nine, mold use from low to high and then use the intensity. Immediately after the mold enters the service period, the internal metal structure and performance are still in a floating stage. During this period, a low-strength work program should be adopted to make the mold transition to a stable period. In the mid-use of the mold, due to the various properties of the mold has been basically in a stable state, similar to the car just past the run-in period, the use intensity can be appropriately increased. In the later period, the metal structure of the die has started to deteriorate, and fatigue strength, stability, and toughness have entered the decline curve after long-term production and service. At this time, the intensity of use of the die should be appropriately reduced until the die is scrapped.
X. Strengthen the use and maintenance records of molds in the extrusion production process, and improve the tracking records and management of each mold. Extrusion die from the acceptance of the factory to the end of the use of mold scrapped, this intermediate time is a few months, the long one year or more. Basically, the use record of the mold also records the various processes of the production of the profile. The number of extrusion dies is large and the variety is large. The management of the use process of each set of dies is helpful to help mold clerk administrators, mold users, and mold design and manufacturing personnel to understand the actual conditions of each set of molds. The track record of the mold includes:
(1) Mold manufacturing information, including design drawings, production records, inspection records (accuracy values, hardness values), etc., of each mold.
(2) Process information of each die press on the machine, such as heating time, aluminum rod temperature, mold temperature, extrusion speed, extrusion force, breakthrough pressure, length of aluminum rod, number of qualified products, profile line density, Product rate and so on.
(3) The first three mold-repairing programs for each mold, the nitriding process time, the time for entering and exiting the mold library, the time and reasons for retiring or returning to the mold plant for maintenance, etc. These records are collected to improve mold management, mold costing, and mold optimization. The work of designing and repairing molds, judging the quality of molds, improving the stability of extrusion production, rationally using molds, and determining the lower inventory of molds have a direct impact.
The increasingly fierce competition in the aluminum profile market forces aluminum extrusion companies to invest tremendous effort in the purchase, use, maintenance, and management of extrusion molds. This requires companies to change their ideas while changing the previous extensive production management. Grasping up and doing a good job of statistical analysis and cost management of molds can only adapt to the new market situation and win opportunities in the market.