Patent Publication Number: US-11638943-B2

Title: Method for manufacturing cold-forged, extruded aluminum alloy tube

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Taiwanese Patent Application Nos. 108112355 and 108145162, filed on Apr. 9, 2019 and Dec. 10, 2019, respectively. 
     FIELD 
     The disclosure relates to a method for manufacturing a cold-forged, extruded aluminum alloy tube by cold forging and cold extrusion. 
     BACKGROUND 
     Taiwanese Utility Model Patent Publication No. 564857 discloses a connecting structure of an upright tube and a front fork of a bicycle, in which a handlebar is inserted into one end of the upright tube, and the front fork is inserted into the other end of the upright tube. 
     The upright tube is generally made by hot forging and hot extrusion in response to the shape and structural strength requirements. Specifically, a material subjected to hot forging and hot extrusion is first heated in a furnace to a temperature above the recrystallization temperature, followed by a processing step for shaping. Hot forging and hot extrusion not only require a furnace that can withstand high temperature and a material-taking equipment, but also incur a high capital expenditure due to quick wearing of the hot forging and hot extrusion dies and large consumption of energy. 
     SUMMARY 
     Therefore, an object of the present disclosure is to provide a method for manufacturing a cold-forged, extruded aluminum alloy tube that can alleviate at least one of the drawbacks of the prior art. 
     According to the present disclosure, a method for manufacturing a cold-forged, extruded aluminum alloy tube includes the steps of: 
     (A) providing a primary material having a hollow columnar shape and made of an aluminum alloy material, and a first cold extrusion apparatus including a first cold extrusion die, and a first ram and a first plunger corresponding in position to the first cold extrusion die, the first plunger extending downwardly from the first ram; 
     (B) processing the primary material to form a preform that extends along an axis and that has a first end surface and a second end surface opposite to each other along the axis, an inner circumferential surface between the first end surface and the second end surface and defining a central bore, and an outer circumferential surface opposite to the inner circumferential surface, the preform further having an original length extending from the first end surface to the second end surface, and an original outer diameter measured across the outer circumferential surface, each of the first end surface, the second end surface and the outer circumferential surface having a surface roughness controlled at equal to or less than 0.4 μm Ra, each of the original outer diameter and the original length having a tolerance of equal to or less than 0.01 mm; 
     (C) subjecting the preform to a homogeneous annealing which involves heating the preform in a furnace to a temperature of about 410° C. to 510° C., and then removing the preform from the furnace after the furnace is cooled to a temperature of about 160° C. to 200° C. at a cooling rate of 10° C. per hour; 
     (D) testing the hardness of the preform, the hardness being 60±5 degrees measured on Rockwell Hardness F scale; 
     (E) immersing the preform in a tank containing a lubricant for a predetermined time, the lubricant is a lipid having a viscosity index equal to or greater than 170, a flash point equal to or greater than 240° C., a pour point equal to or greater than −24° C., and a fire point equal to or greater than 255° C.; and 
     (F) subjecting the preform to cold extrusion which involves positioning the preform in the first cold extrusion die, after which the first cold extrusion apparatus is operated to strike the first ram against the preform with the first plunger extending through the central bore of the preform to thereby form the cold-forged, extruded aluminum alloy tube, the cold-forged, extruded aluminum alloy tube having a first end surface and a second end surface opposite to each other, an outer circumferential surface between the first end surface and the second end surface of the cold-forged, extruded aluminum alloy tube, and an inner circumferential surface opposite to the outer circumferential surface of the cold-forged, extruded aluminum alloy tube and defining a central bore, the cold-forged, extruded aluminum alloy tube having a length that extends between the first end surface and the second end surface of the cold-forged, extruded aluminum alloy tube and that is longer than the original length of the preform. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present disclosure will become apparent in the following detailed description of the embodiment with reference to the accompanying drawings, of which: 
         FIG.  1    is a flow chart, illustrating the steps involved in a method for manufacturing a cold-forged, extruded aluminum alloy tube according to an embodiment of the present disclosure; 
         FIG.  2    is an exploded cross-sectional view of a preform and a first cold extrusion apparatus of the embodiment; 
         FIG.  3    is a cross-sectional view, illustrating how the preform is formed into the cold-forged, extruded aluminum alloy tube of the embodiment; 
         FIG.  4    is a cross-sectional view of a second cold extrusion apparatus of the embodiment; and 
         FIG.  5    illustrates three different ways of forming a primary material of the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG.  1   , a method for manufacturing a cold-forged, extruded aluminum alloy tube according to an embodiment the present disclosure includes steps A to G. 
     In step A, referring to  FIGS.  2  and  4   , in combination with  FIG.  1   , a primary material  1 , a first cold extrusion apparatus  200  and a second cold extrusion apparatus  300  are provided. The primary material  1  has a hollow columnar shape, and is made of an aluminum alloy material, such as, but is not limited to, AL6066 aluminum alloy, and AL7050 aluminum alloy. The first cold extrusion apparatus  200  includes a first cold extrusion die  210 , a first fixing seat  201  movably disposed above the cold extrusion die  210 , a first ram  202  fixed to the first fixing seat  201 , and a first plunger  203  extending downwardly from the first ram  202 . The first ram  202  and the first plunger  203  correspond in position to the first cold extrusion die  210 . The first cold extrusion die  210  has a top surface  211  and a first die cavity  212  extending inwardly and downwardly from the top surface  211 . In this embodiment, the first die cavity  212  has a stepped shape and tapers from top to bottom. Further, the first plunger  203  also has a stepped shape, and tapers from top to bottom. The step portion and the corner of the first plunger  203  are made arcuate in shape. The second cold extrusion apparatus  300  includes a second cold extrusion die  310 , a second fixing seat  301  movably disposed above the second cold extrusion die  310 , a second ram  302  fixed to the second fixing seat  301 , and a second plunger  303  extending downwardly from the second ram  302 . The second ram  302  and the second plunger  303  correspond in position to the second cold extrusion die  310 . The second cold extrusion die  310  has a second die cavity  311  that extends inwardly and downwardly from a top surface thereof, that has a stepped shape and that tapers from top to bottom. The second plunger  303  also has a stepped shape, and tapers from top to bottom. The step portion and the corner of the second plunger  303  are made arcuate in shape. 
     In step B, with reference to  FIG.  2   , the primary material  1  is processed to form a preform  1 ′ having a hollow cylindrical shape. The preform  1 ′ extends along an axis (L), and has a first end surface  101  and a second end surface  102  opposite to each other along the axis (L), an outer circumferential surface  103  between the first end surface  101  and the second end surface  102 , and an inner circumferential surface  105  opposite to the outer circumferential surface  103  and defining a central bore  104 . The preform  1 ′ further has an original length (l) extending from the first end surface  101  to the second end surface  102 , an original outer diameter (D) measured across the outer circumferential surface  103 , and an original inner diameter (d) measured across the inner circumferential surface  105 . Each of the first end surface  101 , the second end surface  102 , the outer circumferential surface  103  and the inner circumferential surface  105  has a surface roughness controlled at equal to or less than 0.4 μm Ra. Each of the original outer diameter (D), the original inner diameter (d) and the original length (l) has a tolerance of equal to or less than 0.01 mm. 
     In step C, the preform is subjected to a homogeneous annealing which involves heating the preform  1 ′ in a furnace to a temperature of about 410° C. to 510° C., and then removing the preform  1 ′ from the furnace after the furnace is cooled to a temperature of about 160° C. to 200° C. at a cooling rate of 10° C. per hour. 
     In step D, the hardness of the preform  1 ′ is tested. The hardness of the preform  1 ′ should be 60±5 degrees measured on Rockwell Hardness F scale. The testing of the hardness of the preform  1 ′ is performed at multiple points of the outer circumferential surface  103  and at equal intervals along the axis (L), and at multiple points of the inner circumferential surface  105  and at equal intervals along the axis (L). 
     In step E, the preform  1 ′ is immersed in a tank containing a lubricant (not shown) for a predetermined time. In this embodiment, the lubricant used is a lipid which has a viscosity index equal to or greater than 170, a flash point equal to or greater than 240° C., a pour point equal to or greater than −24° C., and a fire point equal to or greater than 255° C. The predetermined time for immersing the preform  1 ′ in the tank containing the lubricant depends on the number of the preform  1 ′. When the number of the preform  1 ′ immersed is one, the predetermined time is 4 to 5 minutes, and when the number of the preform  1 ′ immersed is plural, the predetermined time is 25 to 35 minutes. 
     In step F, referring to  FIG.  3   , the preform  1 ′ that has been immersed in the lubricant is subjected to cold extrusion which is conducted at room temperature and which involves positioning the preform  1 ′ in the first die cavity  212 , after which, the first cold extrusion apparatus  200  is operated to strike the first ram  202  against the preform  1 ′ with the first plunger  203  extending through the central bore  104  of the preform  1 ′ to thereby form the cold-forged, extruded aluminum alloy tube  100 . The cold-forged, extruded aluminum alloy tube  100  has a hollow tubular shape, and extends along the axis (L). The cold-forged, extruded aluminum alloy tube  100  has a first end surface  110  and a second end surface  120  opposite to each other along the axis (L), an outer circumferential surface  130  between the first end surface  110  and the second end surface  120 , and an inner circumferential surface  150  opposite to the outer circumferential surface  130  and defining a central bore  140 . The central bore  140  is parallel to the axis (L), and has a contour corresponding to that of the first plunger  203 . The cold-forged, extruded aluminum alloy tube  100  further has a length (l′) that extends between the first end surface  110  and the second end surface  120  and that is longer than the original length (l) of the preform  1 ′. 
     In step G, as shown in  FIGS.  3  and  4   , the cold-forged, extruded aluminum alloy tube  100  is positioned in the second die cavity  311 , after which the second cold extrusion apparatus  300  is operated to strike the second ram  302  against the cold-forged, extruded aluminum alloy tube  100  with the second plunger  303  extending through the central bore  140  of the cold-forged, extruded aluminum alloy tube  100  to thereby form a patterned cold-forged, extruded aluminum alloy tube  100 ′. 
     Thus, by utilizing the above-mentioned Steps A to G of the present disclosure, the primary material  1  can be cold-extruded to form the patterned cold-forged, extruded aluminum alloy tube  100 ′. The patterned cold-forged, extruded aluminum alloy tube  100 ′ is free from defects caused by metal heating, and has several advantageous characteristics, such as high precision and surface quality, an enhanced hardness and strength, and a large deformation resistance. That is, by processing the primary material  1  to form the preform  1 ′ in step B, the surface roughness of each of the first end surface  101 , the second end surface  102 , the outer circumferential surface  103  and the inner circumferential surface  105  of the preform  1 ′ is controlled to be equal to or less than 0.4 μm Ra, and each of the original outer diameter (D), the original inner diameter (d) and the original length (l) of the preform  1 ′ has a tolerance of equal to or less than 0.01 mm, so that the cold-forged, extruded aluminum alloy tube  100  is not required to undergo precision machining of its surfaces. Further, the first cold extrusion apparatus  200  and the second cold extrusion apparatus  300  are not easily worn out. Followed by the homogeneous annealing in step C, the plasticity of the preform  1 ′ can be improved. By utilizing the subsequent cold extrusion step, that is, step F, residual stress of the cold-forged, extruded aluminum alloy tube  100  can be reduced, and the homogenization of the composition and structure thereof can be improved. Moreover, by utilizing the lubricant in step (B), the preform  1 ′ is provided with an improved lubricating effect for subsequent cold extrusion. 
     Therefore, the method for manufacturing the cold-forged, extruded aluminum alloy tube  100  of the present disclosure does not need to be provided with high temperature hot forging and hot extrusion equipment, and material-taking equipment. In addition, by utilizing the processing step of step B, not only does the cold-forged, extruded aluminum alloy tube  100  achieve a high precision, but also the wear out of the first cold extrusion apparatus  200  and the second cold extrusion apparatus  300  can be reduced so as to extend the service life thereof. Furthermore, overall energy consumption may be reduced, which may result in low capital expenditure. 
     It is worth mentioning that, step G may be omitted when the intended usage of the cold-forged, extruded aluminum alloy tube  100  is achieved. In other words, step G is conducted only when patterning of the cold-forged, extruded aluminum alloy tube  100  is required. 
     Moreover, referring to  FIG.  5   , the primary material  1  provided in step A can be made using one of the following methods: Method A, Method B and Method C. Method A, Method B and Method C are respectively denoted by MA, MB and MC in  FIG.  5   . 
     In Method A (MA), a cylindrical blank  4  is processed using a computer numerically controlled (CNC) machine to make the size and surface roughness of the cylindrical blank  4  reach a predetermined precision. Next, the cylindrical blank  4  is subjected to cold forging using a cold forging apparatus (not shown) to obtain a cold-forged blank  4 ′ having a U-shaped groove  401 ′ with a blind end. Then, the blind end of the groove  401 ′ of the cold-forged blank  4 ′ is cut to obtain the primary material  1  having the hollow columnar shape. 
     In Method B (MB), a hollow cylindrical blank  5  is processed using the CNC machine to make the size and surface roughness of the cylindrical blank  5  reach a predetermined precision. Next, the cylindrical blank  5  is subjected to cold forging using a cold forging apparatus (not shown) to obtain a cold-forged blank  5 ′ having a stepped hole  501 ′. Then, a small diameter portion and a part of a large diameter portion adjacent to the small diameter portion of the stepped hole  501 ′ of the cold-forged blank  5 ′ are cut to obtain the primary material  1  having the hollow columnar shape. 
     In Method C (MC), a cylindrical blank  6  is subjected to a first processing using the CNC machine, Next, the cylindrical blank  6  is subjected to cold forging using a first cold-forging apparatus (not shown) to obtain a first cold-forged blank  6 ′ having a U-shaped groove  601 ′ that is shallow. Then, the first cold-forged blank  6 ′ is subjected to a second processing using the CNC machine to make the size and surface roughness of the cold-forged blank  6 ′ reach a predetermined precision (i.e., size calibration). Afterwards, the first cold-forged blank  6 ′ is subjected to a second cold forging operation using a second cold forging apparatus (not shown) to obtain a second cold-forged blank  6 ″ having a U-shaped groove  601 ″ that is deeper that the groove  601 ′ and that has a blind end. Finally, the blind end of the groove  601 ″ of the second cold-forged blank  6 ″ is cut to obtain the primary material  1  having the hollow columnar shape. 
     In summary, by virtue of the method for manufacturing the cold-forged, extruded aluminum alloy tube  100  of the present disclosure, which has simple processing steps and equipments, and is energy-saving, the capital expenditure thereof can be effectively reduced and the quality of the thus obtained cold-forged, extruded aluminum alloy tube  100  can be improved. 
     While the present disclosure has been described in connection with what is considered the exemplary embodiment, it is understood that this disclosure is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.