JP3775159B2 - Extrusion method and die heating method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for manufacturing an extruded profile satisfying a standard value at a high yield while suppressing dimensional variations and wall thickness variations that tend to occur at the beginning of extrusion.
[0002]
[Prior art]
In extrusion molding of aluminum alloy or the like, an extruded profile having a predetermined cross-sectional shape is manufactured by extruding a billet heated at high temperature from a container to a die and passing it through a bearing hole provided in the die.
The die 10 includes a die 12, a baffle plate 13, a back die 14, a die ring 15 and the like in which a bearing hole 11 is formed as shown in FIG. A bolster 16 is set on the exit side of the back die 14 as necessary to adjust the thickness of the die 10. The bolster 16 is also effective in suppressing the bending of the die 10.
The die 10 is mounted on the outlet end portion of the container 20 containing the billet M using a die slide (not shown). When the billet M in the container 20 is pressurized from the entry side in this state, the billet M plastically flows and passes through the bearing hole 11 to obtain an extruded profile S molded into a predetermined cross-sectional shape.
[0003]
When the billet M is extruded, the die 10 is heated to a high temperature around 450 ° C. Since the heating at this time is performed in a die heater maintained in a high temperature atmosphere, the temperature of the die 10 is increased with a uniform temperature distribution. However, the temperature distribution of the die 10 changes as the extrusion process continues. During extrusion, billet M's sensible heat and billet M's processing heat are applied to the die 10, while the bolster 16 is used to transfer heat to the end platen, heat transfer to the die slide, heat dissipation to the outside air, etc. 10 dissipates heat. At this time, the heat input proceeds at the center of the die 10 and is radiated from the outer peripheral direction of the die 10, so that a temperature distribution with a high temperature on the central side and a low temperature on the outer peripheral side is imparted to the die 10 as the extrusion process proceeds. The temperature decrease on the outer peripheral side appears as heat shrinkage that reduces the opening size of the bearing hole 11, and as a result, the extruded profile S becomes thinner with time.
[0004]
[Problems to be solved by the invention]
By suppressing the temperature drop of the die 10 during extrusion molding, it is possible to prevent the extruded shape S from being thinned to some extent with the progress of extrusion molding. For example, in Japanese Patent Laid-Open No. 4-228223, a heat insulating material is incorporated in the middle portion in the thickness direction of the die ring 15 to suppress the die 10 from being cooled from the outer peripheral surface. As a result, it is said that partial temperature reduction of the die 10 is prevented, and occurrence of a defective appearance, a defective shape, a poor accuracy, and the like of the extruded shape member S can be prevented.
Even if the heat insulating material is incorporated in the die ring 15, the temperature drop of the die 10 is delayed by the amount of heat transfer blocked by the heat insulating material. Absent. For this reason, there is a tendency for the extruded shape S to become thinner with time as extrusion is continued.
[0005]
[Means for Solving the Problems]
The present invention has been devised to solve such problems, and it is unavoidable that a temperature distribution that is high on the center side of the die and low on the outer periphery side is unavoidable, and changes due to continuation of extrusion molding. By starting extrusion using a die with a temperature distribution that does not occur, the size fluctuation range of the bearing hole is reduced over the period from the beginning of extrusion to the end of extrusion, and an extruded shape with a stable shape and thickness is manufactured. For the purpose.
[0006]
In order to achieve the object of the extrusion method of the present invention, in the extrusion of an aluminum alloy using a direct extruder, a die having a center temperature higher than a billet temperature used for extrusion and an outer peripheral temperature lower than the billet temperature. And starting extrusion. At the start of extrusion, it is preferable that the temperature decrease rate at the outer peripheral portion is 1.5 ° C./min or less.
The atmosphere in the die heating furnace is divided into a part in contact with the central part and a part in contact with the outer peripheral part, and the atmospheric temperature on the central part side is kept higher than the billet temperature used for extrusion, and the atmospheric temperature on the outer peripheral part side is maintained in the central part atmosphere. By maintaining the temperature lower than the temperature and heating the die, the temperature distribution of the die used for the extrusion can be created.
[0007]
[Action]
Since the temperature of the billet used for extrusion is substantially constant, the temperature at the center of the die (the part in contact with the billet during extrusion) is also substantially constant. However, when the temperature at the center of the die in the initial stage of extrusion is lower than the billet temperature, the opening width of the bearing hole decreases due to thermal expansion accompanying the temperature rise until reaching a constant temperature from the initial temperature. In this case, since the heat is taken away by the die, the billet temperature is lowered at the same time, and when the extrusion pressure is increased, the deflection of the die in the extrusion direction is increased, and the reduction of the opening width is further increased. Therefore, by making the temperature at the center of the die higher than the billet temperature, a rapid increase in the die temperature and a decrease in the billet temperature are prevented from occurring, and a reduction in the opening width is prevented.
On the other hand, the outer peripheral portion of the die is lowered because it is in contact with the atmosphere and the extrusion tool, but when the extrusion molding proceeds to a certain extent, the temperature distribution is balanced and the temperature decrease at the outer peripheral portion becomes very slow.
Equilibration of the temperature distribution is due to the balance between the sensible heat of the billet M given to the die 10 and the processing heat during extrusion molding and the amount of heat dissipated from the outer periphery of the thermoconductive die 10 to the end platen and die slide. it is conceivable that. The shape and thickness of the extruded profile S are determined by the opening size of the bearing hole 11. When the die 10 contracts due to a temperature drop, the opening size of the bearing hole 11 decreases, but the opening size does not substantially change at the stage where the temperature distribution is balanced.
[0008]
The temperature distribution of the die 10 set in the extruder can be estimated from the temperature change on the outer periphery of the die 10. As described above, since the sensible heat and processing heat of the billet M are supplied to the center side of the die 10, it is maintained at a substantially constant temperature during extrusion molding. On the other hand, the outer peripheral side of the die 10 tends to drop in temperature due to heat conduction to the bolster 16, die slide, etc. or heat dissipation to the outside air, but the amount of heat is replenished by heat conduction from the center side of the die 10. When the replenishment heat amount approaches the heat radiation amount, the temperature decreasing rate on the outer periphery of the die 10 becomes slow. This means that the temperature distribution of the die 10 has reached equilibrium when the rate of temperature decrease on the outer periphery of the die 10 set in the extruder becomes gentle.
[0009]
Therefore, in the present invention, the outer peripheral temperature of the die 10 set in the extruder is measured, and extrusion molding is started when the measured temperature decrease rate becomes moderate. The outer peripheral temperature of the die 10 is measured by a thermocouple, an infrared method, a non-contact thermometer or the like. The measurement point P of the outer peripheral temperature has a large influence on the opening dimension of the bearing hole 11 by the temperature distribution in the plane perpendicular to the axis of the die 10 including the bearing hole 11. Is preferably set at a position where the flat surface intersects the outer periphery of the die 10. However, the measurement point can be taken on the outer periphery of the die 10 in consideration of the ease of installation of the temperature measuring element without being restricted by this. In this case, the temperature distribution in the plane in the direction perpendicular to the axis of the die 10 including the bearing hole 11 is calculated from the temperature information obtained at the measurement point.
[0010]
The die 10 is heated to around 450 ° C. and then set in the extruder. Immediately after setting, heat transfer to the bolster 16 and the die slide is active, so it is compared with 2.0 to 3.0 ° C./min. It is cooled at a large cooling rate. However, when a predetermined time elapses, the temperature difference between the die 10 and the outside air, the bolster 16, and the die slide becomes small, and the temperature lowering speed on the outer periphery of the die 10 decreases. A decrease in the temperature drop rate means that the temperature distribution of the die approaches an equilibrium state. Specifically, it is determined that the temperature distribution has reached equilibrium when the rate of temperature decrease is 1.5 ° C./min or less.
[0011]
By starting the extrusion molding in a state where the temperature distribution in the plane perpendicular to the axis of the die 10 including the bearing hole 11 is in an equilibrium state, the influence of cooling shrinkage on the opening size of the bearing hole 11 is eliminated during the extrusion molding. The extrusion is carried out under stable conditions. As a result, the manufactured extruded shape S is a product having a stable shape and thickness over the period from the beginning of extrusion to the end of extrusion.
[0012]
As such a heating method, for example, as shown in FIG. 2, a hot air pipe 21 is applied to a die 10 accommodated in a die ring 15, and the periphery of the bearing hole 11 is concentrated by hot air G fed through the hot air pipe 21. A heating method is adopted. In this case, the temperature of the hot air G is finally set to a temperature higher than the billet temperature, and the temperature on the outer peripheral side is set to a temperature lower than the billet temperature. It is more preferable to set the temperature of the outer peripheral portion to the temperature when the outer peripheral temperature decreasing rate is 1.5 ° C./min or less during the previous extrusion molding. With this heating method, the die 10 is heated with a temperature distribution that is high on the center side and low on the outer peripheral side. When an inert gas or a non-oxidizing gas is used as the hot air G, oxidation around the bearing hole 11 is prevented and the surface state of the obtained extruded shape S is also improved.
[0013]
It is also possible to apply a predetermined temperature distribution to the die 10 by using cooling until the die 10 heated to a uniform temperature distribution by the die heater is set in the extruder. For example, as shown in FIG. 3, the heat insulating material 22 is brought into close contact with the entrance side and / or exit side of the die 10 heated at a high temperature with a uniform temperature distribution until the die 10 is set in the extruder. The outer periphery is cooled by releasing heat to the outside air. The cooling at this time may be either natural convection cooling or forced cooling by blowing cool air.
Furthermore, a predetermined temperature distribution can be given to the die 10 by delaying the time until the extrusion starts. In this case, the die 10 heated at a high temperature with a uniform temperature distribution is placed on the die slide, the container 20 containing the billet M is brought into contact with the die 10, and the billet M is pressed with a stem from the rear, whereby the die 10 Introduce metal inside. In this state, it is left for a predetermined time to lower the temperature of the outer periphery of the die 10, and when the temperature decreasing speed of the outer periphery of the die 10 becomes a set value or less, extrusion molding is started.
[0014]
【Example】
The present invention was applied to manufacturing an L-shaped extruded profile S having a length of 100 mm, a width of 200 mm, and a thickness of 1.45 mm from the billet M. As the billet M, an aluminum alloy JIS A6063 billet having a diameter of 273 mm was used, heated to 470 ° C., and then loaded into the container 20.
[Comparative Example]
After the die 10 was heated to 450 ° C. with a uniform temperature distribution, it was set in an extruder, and extrusion molding was started immediately. Extrusion conditions were set so that the speed of the extruded profile S delivered from the extruder was 40 m / min.
A thermocouple is attached to a measurement point P and a measurement point Q at the center where the plane perpendicular to the axis of the die 10 including the bearing hole 11 reaches the outer periphery of the die 10, and temperature changes at the outer periphery and the center of the die 10 during extrusion molding. investigated. As can be seen from the investigation results in FIG. 4, the outer peripheral temperature of the die 10 decreased to 407 ° C. at the time when 10 minutes passed immediately after the start of extrusion. The temperature lowering rate at this time was 2 ° C./min. In addition, since the die center temperature at the start of extrusion was lower than the billet temperature, the die temperature increased rapidly until 5 minutes passed from the start of extrusion.
When the thickness of the manufactured extruded profile S was measured immediately after the start of extrusion, as shown in FIG. 4, the thickness was increased immediately after the start of extrusion, and the thickness decreased according to the elapsed time from the start of extrusion. It was. The decrease in wall thickness continued for 15 minutes immediately after the start of extrusion, and the wall thickness fluctuation finally stopped when 15 minutes passed.
[0015]
[Invention Example 1]
The periphery of the bearing hole 11 was heated intensively by blowing hot air G (FIG. 2), and the die 10 having a temperature distribution of 500 ° C. in the center and 410 ° C. on the outer peripheral side was set in the extruder. Since the temperature decreasing rate on the outer periphery of the assembled die 10 was 1.5 ° C./min or less, extrusion molding was started immediately.
The temperatures of the outer periphery and the central portion of the die 10 were measured during the extrusion molding, but the outer peripheral temperature hardly decreased as shown in FIG. 5, and the rapid increase in the central portion temperature at the beginning of extrusion was not observed. The thickness of the manufactured extruded section S was 1.48 mm immediately after the start of extrusion, and 1.45 mm when 20 minutes passed immediately after the start of extrusion, and no substantial decrease in thickness was observed. This indicates that a thick extruded shape S satisfying the standard value is produced with a high yield.
[0016]
[Invention Example 2]
The die 10 was inserted into the die heater and heated to 510 ° C. with a uniform temperature distribution. The outer peripheral portion of the die was air-cooled in a state in which a heat insulating material having the same size as the billet diameter was in close contact with the front and rear end faces of the heated die 10. It set to the extruder in the state in which the die outer peripheral part was 410 degreeC. At this time, the temperature of the central portion was 500 ° C. Also in this case, since the temperature decreasing rate on the outer periphery of the incorporated die was 1.5 ° C./min or less, extrusion molding was started immediately. The outer peripheral temperature of the die 10 hardly decreased during the extrusion molding, and neither the shape defect of the manufactured extruded product S nor the tendency to decrease the thickness was observed.
[0017]
【The invention's effect】
As described above, in the extrusion molding method of the present invention, narrowing of the bearing hole accompanying cooling of the die is started by starting the extrusion molding with a predetermined temperature distribution in which the center side of the die is high temperature and the outer peripheral side is low temperature. Thus, the extruded shape whose shape and thickness are stabilized is manufactured. When this method is used, an extruded shape having a thickness that satisfies the standard value and having a good shape is produced at a high yield, so that the production cost is reduced accordingly. Further, it is possible to prevent the production efficiency from being lowered because the thickness of the bearing hole is less than the standard value due to the narrowing of the bearing hole, and the extrusion must be stopped.
[Brief description of the drawings]
FIG. 1 is a diagram showing the internal structure of a die 10 set in an extruder. FIG. 2 is an explanatory diagram of a method of centrally heating the die center. FIG. 3 is an explanatory diagram of partial cooling that gives a predetermined temperature distribution to the die. FIG. 4 is a graph showing that the temperature drop on the outer periphery of the die has an adverse effect on the thickness of the extruded profile. FIG. Graph showing that it is suppressed 【Explanation of symbols】
10: Die 11: Bearing hole 12: Die 13: Baffle plate 14: Back die 15: Die ring 16: Bolster 20: Container 21: Hot air tube 22: Insulation material M: Billet S: Extrusion profile D: Extrusion direction G: Hot air P: Measurement point

Claims (3)

In extrusion of an aluminum alloy using a direct extruder, an extrusion method characterized by starting extrusion using a die having a center temperature higher than a billet temperature used for extrusion and a peripheral temperature lower than the billet temperature. . The extrusion method according to claim 1, wherein the temperature lowering rate of the outer peripheral portion at the start of extrusion is 1.5 ° C./min or less. The atmosphere in the die heating furnace is divided into a part in contact with the central part and a part in contact with the outer peripheral part, and the atmospheric temperature on the central part side is kept higher than the billet temperature used for extrusion, and the atmospheric temperature on the outer peripheral part side is maintained in the central part atmosphere. A die heating method characterized by maintaining the temperature lower than the temperature.

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