METHOD AND SYSTEM FOR PRODUCING ALUMINUM ALLOY PARTS

Abstract

In production of aluminum alloy members by a plastic working of a heat-treatable aluminum alloy extrusion, cracking during the plastic working is eliminated or minimized at low cost as compared with techniques including solution treatment or restoration treatment. An aluminum alloy production system includes an extruding press, a cutting device disposed downstream from the extruding press, and a conveyer and a plastic working machine each disposed in parallel with the extruding press. The extruding press hot-extrudes a heat-treatable aluminum alloy to give an extrusion. The cutting device cuts the extrusion to a predetermined length and isolates the extrusion from the extruding press. The conveyer conveys the extrusion to the plastic working machine, where the extrusion has been cut by the cutting device to a predetermined length. The plastic working machine imparts a plastic working to the extrusion conveyed by the conveyer to form the extrusion into an aluminum alloy part.

Claims

1. A method for producing aluminum alloy parts, comprising: hot-extruding a heat-treatable aluminum alloy using an extruding press to give an extrusion; cooling and cutting the extrusion to a predetermined length, the extrusion being extruded from a die of the extruding press and moving forward; conveying the extrusion after cutting to a plastic working machine; imparting a plastic working to the cut extrusion before the extrusion has a yield strength greater than 120 MPa, where the yield strength increases due to natural aging; and imparting a temper aging to the extrusion after the plastic working.

2. The production method according to claim 1, wherein the extrusion extruded from the die and moves forward is quenching by air-cooling or water-cooling.

3. The production method according to claim 1, wherein the extrusion has a hollow section, and wherein the extrusion extruded from the die and moving forward is cooled by inserting a nozzle from front into the cross section of the extrusion and injecting a coolant from the nozzle.

4. The production method according to claim 1, wherein the extrusion is cut while clamping the extrusion at positions downstream and upstream from a cutting position and, is cooled at the cutting position and in areas downstream and upstream from the cutting position.

5. The production method according to claim 1, further comprising: stretching and straightening the extrusion in the cold after the cutting and before the plastic working.

6. A production system for producing aluminum alloy parts, comprising: an extruding press that hot-extrudes a heat-treatable aluminum alloy to give an extrusion; a cutting device that is disposed downstream from the extruding press and cuts the extrusion to a predetermined length, to isolate the extrusion from the extruding press; and a conveyer and a plastic working machine each disposed in parallel with the extruding press, wherein the cutting device including a cutting tool that is movable forward at a speed approximately equal to an extruding speed of the extrusion, the conveyer conveying the extrusion to the plastic working machine, where the extrusion has been cut to a predetermined length by the cutting device, the plastic working machine imparting a plastic working to the extrusion conveyed by the conveyer to form the extrusion into an aluminum alloy part.

7. The production system according to claim 6, further comprising: a cooler is disposed downstream from the extruding press.

8. The production system according to claim 7, wherein the cooler includes a nozzle that injects a coolant, and wherein the nozzle is movable back and forth along an extruding direction of the extrusion.

9. The production system according to claim 6, wherein the cutting device comprises a pair of clamps, and wherein the clamps are disposed immediately downstream and upstream from the cutting tool, grasp the extrusion, and move forward synchronously with the cutting tool.

10. The production system according to claim 9, wherein at least one of the cutting tool and the pair of clamps comprises a cooling mechanism that cools the extrusion.

11. The production system according to claim 9, wherein the cutting device functions as a stretcher that stretches and straightens the cut extrusion, and wherein the cutting device is operable to grasp the rear and front ends of the extrusion by the pair of clamps, to widen the distance between the pair of clamps, and to stretch and straighten the extrusion.

12. The production system according to claim 6, further comprising: a stretcher is disposed downstream from the extruding press, wherein the stretcher stretches and straightens the cut extrusion.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0032] FIG. 1 is a schematic view of a system (and a method) according to an embodiment of the present invention for producing aluminum alloy parts; and

[0033] FIG. 2 is a schematic view of an exemplary conventional system (and a method) for producing aluminum alloy parts.

DESCRIPTION OF EMBODIMENTS

[0034] A system and method according to the embodiment of the present invention for producing aluminum alloy parts will be illustrated below, with reference to the schematic view of FIG. 1.

[0035] The production system illustrated in FIG. 1 includes an extruding press 11; a cooler 12 and a cutting device 13 disposed downstream from the extruding press 11; and a conveyer 14 and a plastic working machine 15 disposed in parallel with the extruding press 11.

[0036] The extruding press 11 is as with conventional one and hot-extrudes a heat-treatable aluminum alloy. Non-limiting examples of the heat-treatable aluminum alloy include 2xxx-series, 6xxx-series, and 7xxx-series aluminum alloys prescribed in Japanese Industrial Standards (JIS) or registered with Aluminum Association (AA).

[0037] The cooler 12 includes at least one of a fan air cooler or a water cooler and forcedly cools and quenches an extrusion 17 which is extruded from the die of the extruding press 11 and moves forward on a table 16. The cooler 12 also includes a nozzle 18 that injects a coolant (such as air or a coolant liquid). The nozzle 18 is supported by a support mechanism 19 movably back and forth along the extruding direction. The rear end (right end in FIG. 1) of the nozzle 18 is coupled to a coolant supply mechanism (not shown). The cooler 12 is dispensable when the heat-treatable aluminum alloy has low quench sensitivity and the extrusion 17 can be sufficiently quenched by natural cooling alone. The nozzle 18 is dispensable when the extrusion 17 can be sufficiently quenched by the fan air cooler or water cooler alone.

[0038] The cooler 12 is used when the extrusion 17 is unquenchable by natural cooling alone. The nozzle 18 is used as needed in combination with the fan air cooler or water cooler when the heat-treatable aluminum alloy has high quench sensitivity, and is advantageously used particularly when the extrusion 17 has a hollow section and includes one or more inner ribs in the cross section. The nozzle 18 goes into the hollow section of the extrusion 17 which is extruded through the die of the extruding press 11 and moves forward. The nozzle 18 injects the coolant from orifices into the hollow section to cool the extrusion 17 from the inside and gets out of the hollow section after the completion of cooling. To uniformly cool the extrusion 17 from the inside of the hollow section, the nozzle 18 may be configured to go into and get out of the hollow section while injecting the coolant.

[0039] The fan air cooler or water cooler may work in combination with the nozzle 18 in the cooler 12, to cool the extrusion 17 both from the inside and the outside. The combination use can reduce the temperature difference and temperature history difference of the entire cross section of the extrusion 17 in cooling process. This configuration allows the extrusion 17 to less deform and to have more uniform material properties in the cross section after temper aging, where the deformation will be caused by thermal shrinkage during cooling. The configuration also allows the extrusion 17 to cool at a higher cooling rate and to be quenched in the entire cross section including the inner ribs, even when the material aluminum alloy is one having high quench sensitivity, such as a high-strength 7xxx-series aluminum alloy. In addition, the configuration can realize a high cooling rate as compared with conventional equivalents, thereby enlarges the controllable range of cooling rates, and enlarges control ranges of size and distribution of precipitates in artificial aging. This promises higher material strength and higher stress corrosion cracking resistance of the extrusion after temper aging.

[0040] The cutting device 13 includes a cutting tool 21 (a circular saw in this example) and a pair of clamps 22, 22. The cutting device 13 also includes a drive mechanism (drive motor) that drives (rotates) the cutting tool 21; a drive mechanism that drives the clamps 22, 22; and a traveling mechanism that moves the cutting tool 21 and the damps 22, 22 back and forth along the extruding direction, where all these mechanisms are not shown. The cutting tool 21, the damps 22, 22, and the mechanisms are disposed typically above the table 16.

[0041] The cutting tool 21 may be another tool such as a chain saw. The damps 22, 22 are disposed immediately downstream and upstream from the cutting tool 21 in the longitudinal direction, grasps the extrusion 17, which is extruded from the die and moves forward, at the rear and front positions (grasping positions), and locates the extrusion 17 with respect to the cutting tool 21. The cutting tool 21 and the damps 22, 22 grasping the extrusion 17 move forward at a speed approximately equal to the extruding speed of the extruding press 11 (traveling speed of the extrusion 17). During this process, the cutting tool 21 works to cut the extrusion 16. The cutting position is determined to allow the extrusion 17 after cutting (extrusion 17a) to have a predetermined length (length corresponding to one aluminum alloy part). The predetermined length is set to be identical to the length of the final product aluminum alloy part along the extruding direction, or to be somewhat larger in consideration typically of a grasp margin in stretching.

[0042] The damps 22, 22 are arranged to grasp the extrusion 17 at a position immediately after extruding (at a position of about 0.5 to about 1.5 m downstream from the die outlet of the extruding press 11). The cutting position and the grasp positions are highly possibly at high temperatures at the time point when the clamps 22, 22 grasp the extrusion 17. To eliminate or minimize the deformation during cutting of the extrusion 17, which will soften at such a high temperature, at least one of the damps 22, 22 and the cutting tool 21 preferably includes a cooling device or mechanism that cools the cutting position and grasp positions of the extrusion 17 (by air cooling or water cooling).

[0043] The cutting device 13 cuts the extrusion 17 while the cooler 12 cools the extrusion 17. However, cooling by the cooler 12 and cutting by the cutting device 13 do not always have to start and end simultaneously.

[0044] Where necessary, the cutting device 13 may function as a stretcher for the extrusion 17a after cutting and cooling, by the working of the pair of damps 22, 22, the drive mechanism that drives the damps 22, 22, and the traveling mechanism that moves the damps 22, 22 back and forth along the extruding direction. The extrusion 17a after cutting can be stretched and straightened by allowing the damps 22, 22 to grasp both ends of the extrusion 17a and widening the distance between the damps 22, 22.

[0045] Instead of allowing the cutting device 13 to function as a stretcher, it is also acceptable to provide a purpose-built stretcher 23 adjacent to the cutting device 13 and to allow the stretcher 23 to stretch and straighten the extrusion 17a after cutting. When the extrusion 17a undergoes tensile bending in the below-mentioned plastic working machine 15, the extrusion 17a also undergoes stretch straightening during process of the tensile bending, and this eliminates the need for preliminary stretch straightening by the damps 22, 22 or the stretcher 23.

[0046] As described above, cutting of the extrusion 17 immediately after extruding to a predetermined length, and cooling concurrently with or in combination with the cutting eliminates the need for such a huge table 7 (see FIG. 2) as in conventional equivalents. The table 16 illustrated in FIG. 1 will do when having a length of, at longest, about 10 min the longitudinal direction. The extrusion 17a after cutting generally has a short length (at longest about 5 m), and this allows the production system to have a small floor space even including the conveyer 14 and the plastic working machine 15.

[0047] The conveyer 14 grasps the cut extrusion 17a and feeds the same to the plastic working machine 15. As described above, the extrusion 17a generally has a short length, and this allows the system to employ, for example, a robot arm equipped with a gripper as illustrated in FIG. 1. This also allows the production system to have a small floor space.

[0048] The plastic working machine 15 imparts, to the extrusion 17a, at least one plastic working such as bending, crushing, shearing (e.g., piercing), burring, swaging, or another press forming in the cold. The plastic working machine 15 includes a necessary apparatus such as a press, according to the type of the aluminum alloy part (the type of plastic working to be imparted to the extrusion 17a). For example, assume that the aluminum alloy part is a bumper reinforcement; and that bending (bend forming) is imparted to the both ends of the extrusion 17a, and then crushing is imparted to a portion in the longitudinal direction. In this case, the plastic working machine 15 includes a bending press and a crushing press.

[0049] The extrusion 17 (17a), which is formed from the heat-treatable aluminum alloy, undergoes natural aging from immediately after cooling and increases in yield strength with time. The plastic working is completed before the yield strength (0.2% yield strength) of the extrusion 17a exceeds 120 MPa. The production method and production system illustrated in FIG. 1 can cut the extrusion 17, which is extruded from the extruding press 11 and moves forward, to a predetermined length in situ without stocking on a table or in another storage area, and feed the cut extrusion 17a to the plastic working machine 15 by the working of the conveyer 14. This enables plastic working of the extrusion 17a to be performed within a short time after cooling (before the yield strength exceeds 120 MPa), and eliminates the need for a reheat treatment such as solution treatment or restoration treatment, which is performed before plastic working in conventional equivalents.

[0050] The extrusion 17a, which has undergone natural aging not so much, has a low yield strength and a high elongation upon plastic working. This allows the extrusion 17a to less suffer from rupture and cracking; to have a small springback, and to give high-precision aluminum alloy parts, even when the extrusion 17a undergoes tough plastic working (such as crushing). The extrusion 17a (aluminum alloy part), as having such a low yield strength in plastic working, can have smaller residual stress imparted by plastic working and have better stress corrosion cracking resistance. The yield stress of 120 MPa in plastic working is a numerical value that serves as an index for the advantageous effects (see Japanese Patent No. 5671422).

[0051] To eliminate or minimize rupture and cracking during the plastic working more surely, the system and method may perform warm pressing or hot pressing typically in the temperature range of 150 C. to 300 C. using a press forming tool equipped with a heater. In this case, reheating of the extrusion 17a can be omitted by controlling the extruding temperature of the extrusion 17 and the temperature fall of the extrusion 17 (17a) in a time period from immediately after extruding to cutting and conveying, and thereby maintaining the temperature of the extrusion 17a during the plastic working within the temperature range. The warm pressing or hot pressing is performed before the yield strength of the extrusion 17a exceeds 120 MPa at the pressing temperature.

[0052] The extrusion 17a after the plastic working receives artificial aging to be an aluminum alloy part. The artificial aging can be performed lot by lot using a heating furnace. As with conventional equivalents, when higher strength is oriented, a T5 treatment (general temper aging) is appropriately selected, whereas, when stress corrosion cracking prevention is oriented, a T7 treatment (over-aging) is appropriately selected. The heating furnace may be disposed in the same floor with the production system as a portion of the system, or may be disposed at another appropriate location.

[0053] The aluminum alloy extrusion as a material for aluminum alloy parts obtained according to the embodiment of the present invention is advantageously, but not limitingly, selected from high-strength 7xxx-series aluminum alloy extrusions, which are susceptible to stress corrosion cracking. Such a 7xxx-series aluminum alloy preferably has a chemical composition typically including Zn in a content of 3 to 8 mass percent, Mg in a content of 0.4 to 2.5 mass percent, Cu in a content of 0.05 to 2.0 mass percent, Ti in a content of 0.005 to 0.2 mass percent, and at least one element selected from the group consisting of Mn in a content of 0.01 to 0.5 mass percent, Cr in a content of 0.01 to 0.3 mass percent, and Zr in a content of 0.01 to 0.3 mass percent, with the remainder being Al and impurities.

[0054] The aluminum alloy extrusion may also be selected from 6xxx-series aluminum alloy extrusions. Such a 6xxx-series aluminum alloy preferably has a chemical composition typically including Mg in a content of 0.35 to 1.1 mass percent, Si in a content of 0.2 to 1.3 mass percent, Ti in a content of 0.005 to 0.2 mass percent, Cu in a content of 0.15 to 0.7 mass percent, and at least one element selected from the group consisting of Zr in a content of 0.06 to 0.2 mass percent, Mn in a content of 0.05 to 0.5 mass percent, and Cr in a content of 0.05 to 0.15 mass percent, with the remainder being Al and unavoidable impurities.

[0055] The aluminum alloy extrusion may also be selected from 2xxx-series aluminum alloy extrusions. Such a 2xxx-series aluminum alloy preferably has a chemical composition typically including Si in a content of 1.3 mass percent or less, Fe in a content of 1.5 mass percent or less, Cu in a content of 1.5 to 6.8 mass percent, Mn in a content of 1.2 mass percent or less, Mg in a content of 1.8 mass percent or less, Cr in a content of 0.10 mass percent or less, Zn in a content of 0.50 mass percent or less, and Ti in a content of 0.20 mass percent or less, with the remainder being Al and unavoidable impurities.

[0056] The present invention is advantageously usable for the production of aluminum alloy parts for collision protectors (energy absorbing members) and body frames of automobiles such as passenger automobiles, light automobiles, and trucks. Non-limiting examples of the parts for collision protectors include bumper reinforcements, door beams, crush boxes (bumper stays), bumper reinforcements with integrated stays, pedestrian leg protection parts, and under-run protectors. Non-limiting examples of the body frame parts include rear and front side members, radiator supports, front upper members, roof rails, rear and front headers, rockers (rocker panels), and floor cross members.

[0057] In addition, the present invention is also usable for the production of body frame parts of motor-bicycles and bicycles, and any other aluminum alloy parts.

[0058] This application claims the benefits of priority to Japanese Patent Application No. 2019-070883, filed Apr. 2, 2019. The entire contents of the above application are herein incorporated by reference.