JPH067877A - Forging method for aluminum alloy - Google Patents

Abstract

PURPOSE:To provide a forged scroll product having an excellent shape characteristic and no underfill and unequal thickness, etc., by softening a work hardened material in the state set in a die. CONSTITUTION:When the scroll having a ratio H/T >=5 of tooth height H to tooth thickness T is forged, almost entire target shape of the product is formed by pressing the maternal up to a specific pressure P1 determined by the ratio H/T. The material set in the die is held for a specific time t1-t2 keeping the load applied on it and softened by working heat. Then, after a little reduction of pressing force from P1 to P2, the material is formed in the final shape by increasing the load again. Thus, since the work hardened material is softened utilising working heat in the state set in the die, a scroll product having a complex shape is manufactured without requiring high pressure and intermediate annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a product having a complicated shape by forging an aluminum alloy.

[0002]

2. Description of the Related Art In a scroll incorporated in a compressor, as shown in FIG. 1, a disc-shaped flange 1 is integrally formed with a helical wrap portion 2. The wrap portion 2 has a thin and long shape with a height of more than 20 mm and a width of about 4 mm. Further, in order to obtain a low coefficient of thermal expansion, high strength, wear resistance, etc. required for this type of component, a high Si aluminum alloy is used.

When a component having a complicated shape as shown in FIG. 1 is to be obtained by forging a high Si aluminum alloy, forging becomes an extremely difficult work due to the high frictional resistance derived from the shape and the deformation resistance derived from the material. . As means for facilitating forging, generally, forging is performed in a state where the deformation resistance of the material is reduced by improving the lubricant or hot working. However, in the forging of an aluminum alloy that is significantly deformed locally, it is necessary to take the forging taking into account the deformation rate. From these points, a method of using a graphite-based lubricant and pressurizing an aluminum alloy held at a high temperature of 400 ° C. or higher to a final pressure at a relatively slow ram speed of about 18 to 66 m / min is adopted. There is.

[0004]

Particularly when a product having a complicated shape is to be obtained, the conventional forging method is apt to cause lack of thickness, uneven thickness and the like. This is because sufficient plastic flow of the material to the tip of the wrap 2 does not occur during forging.

For example, as shown in FIG. 2, the flange 1
When the distance L ₁ from the end face 1a to the wrap 2a is sufficiently large, the meat is supplied to the tip of the wrap 2a. In this case, the meat is spread over the entire mold cavity corresponding to the wrap 2a, and the wrap 2a having the desired shape is formed. On the other hand, the wrap 2b located at a distance L ₂ near the flange end face 1b, supply from the flange 1 of the meat is not sufficient, the underfill occurs. The height and the wall thickness of the wrap 2 are insufficient in the part where the meat is cut. This kind of flesh is the beginning of the wrap 2 2s
It tends to occur at the end of winding and 2e, and the tooth height is 5 compared to the tooth thickness.
It is noticeable when scrolling more than twice.

It is conceivable to thin the flange 1 in order to replenish the lap 2 with the meat from the flange 1 to avoid the lack of thickness. However, an extremely large load is required to reduce the thickness of the flange 1. That is, the wrap 2 in the other part
The mold cavity corresponding to (3) is already filled with the plastically flowed meat from the flange 1, and deformation cannot be expected even if the load is further increased. Under this circumstance, it is practically impossible to try to replenish the wrap 2 such as the winding start 2s and the winding end 2e for removing the thickness of the wrap 2 from the thinned flange 1 by pressing force.

The work-hardened material can be softened by intermediate annealing. However, when the intermediate annealing is adopted, it is necessary to take out the material being processed from the mold and set the softened material in the mold again. As a result, the number of man-hours required for working increases significantly, leading to a drop in workability and productivity. The present invention has been devised to solve such a problem, and by performing forging in two stages without taking out the material from the die during forging, the meat is filled in every corner of the die cavity. The purpose is to obtain a product with excellent shape characteristics without lacking thickness, uneven thickness, and the like.

[0008]

In order to achieve the object, the forging method of the present invention has a tooth height H and a tooth thickness T of H / T ≧ 5.
Almost all of the target shape is formed by setting the aluminum alloy material in the mold that has the cavity corresponding to the scroll of the shape and pressurizing to a predetermined pressure determined by the material of the material, the shape of the product, the processing temperature, etc. A first forging step, a holding step of holding the raw material at the pressing position as it is, and a second forging step of forming the final shape by increasing the pressing force again after the pressing force has slightly decreased. Characterize.

[0009]

[Working] The load applied to the die when the aluminum alloy material is set in a die having a cavity corresponding to the scroll having a tooth height H and tooth thickness T of H / T ≧ 5 and the forging of the scroll is performed. Changes as shown in FIG. The load is increased at a substantially constant rate until time t ₁ . With respect to the same material, at point A when the pressing force P ₁ determined by the ratio H / T is reached, the material is plastically flowed to almost the entire mold cavity. This material is work hardened by the introduction of many dislocations. Therefore, it is difficult to further increase the load, and the material is in a state of being difficult to deform. On the other hand, if the ratio H / T ≧ 5, the formability at the beginning and the end of the winding becomes poor. Therefore, even if the load is increased above the point A, defects such as lack of thickness and uneven thickness cannot be eliminated.

If the pressing position at point A is kept as it is, a phenomenon in which the load is slightly lowered is observed. This phenomenon is
It is speculated that this is due to the fact that the material heats up and softens due to the processing heat. In the process in which the load is reduced to the pressing force P ₂ , the dislocation is recovered as the material softens. as a result,
The material reaching point B has a low deformation resistance and is easy to process.

The holding times t _{1 to} t ₂ vary depending on the ratio H / T, and it is necessary to set the holding time longer as the ratio H / T increases. For example, when the ratio H / T is in the range of 5 to 7, the holding time t _{1 to} t ₂ is appropriately set in the range of 10 to 12 seconds. Further, in order to effectively progress the softening of the material, it is preferable to maintain the material in the meantime in the temperature range of 450 to 470 ° C. The load is further increased to point C for the softened material, and it is forged into the final shape. In this second forging step, the deformation resistance of the portion that was difficult to deform in the first forging step is reduced, and the material plastically flows to every corner of the mold cavity. Therefore, even if it has a complicated shape such as the scroll shown in FIG. 1, it is possible to obtain a product excellent in shape characteristics without lacking thickness or uneven thickness. Boosting time t ₂
Although not particularly restricted to the present invention, t ₃ to t ₃ can be set to a time such that, for example, the point C is reached at the same pressurizing speed as in the first forging step.

That is, in the present invention, the working heat generated in the first forging step is used for raising the temperature and softening the material, and the second stage forging is performed with the material set in the die. Manufactures products with complex shapes with good workability. In this respect, in the conventional forging method involving intermediate annealing, the material reaching point A is once removed from the mold, softened by heat treatment, and then set in the mold again for forging. When compared with this conventional method, it is obvious that the two-step forging according to the present invention is excellent in workability, thermal economy and the like. Also, in the second forging step for forming the final shape, it is possible to forge with a relatively small load, so that a small press can be used and the life of the die is extended. The decrease in load during the holding process is easily detected by measuring the load on the press. Therefore,
When a sequence of increasing the load again when the load is reduced is performed, the working process can be substantially the same as that of the normal one-step forging.

The applied pressures P ₁ and P ₂ and the times t _{1 to} t ₃ are
It varies depending on the material quality, product shape, forging temperature, etc., and cannot be specified unconditionally. However, the pressing force P ₁ is determined on the basis that almost the entire product shape is molded. Further, the pressing force P ₂ and time t _{1 to} t ₂
Is determined with the aim of reducing the deformation resistance of the work-hardened material by the first stage forging and facilitating the second stage forging. The pressing force P ₂ which is the maximum ultimate load in the second forging step is not particularly limited, but it is preferable that it is substantially the same as the pressing force P ₁ when considering the capability of the press. If the work hardening is severe even by the forging in the second stage, the forging is repeated after passing through the holding step again. By repeating forging with this holding step in between, even a product having a complicated shape can be finished with excellent shape characteristics without defects such as lack of thickness or uneven thickness.

[0014]

EXAMPLES Si: 10.5%, Mn: 0.5%, Cu:
A 25 mm thick material was cut out from an extruded rod (diameter 125 mm) of an aluminum alloy containing 3.0%, Mg: 0.5% and Sb: 0.2%. After applying a graphite-based lubricant to the surface of the material, a heat treatment of heating to 450 ° C. was performed and the mold was set in advance at 250 ° C. Then, the pressing force P ₁ = 600 tons (50 kg / mm ² ) and P
By forging with a load of ₂ = 500 tons (40 kg / mm ² ), the wrap 2 having a tooth thickness T = 5 mm, a tooth height H = 35 mm and a length 520 mm is spirally formed on one surface of the flange 1 having a thickness of 12 mm and a diameter of 130 mm. A scroll having a boss 3 formed on the other surface of the flange 1 was manufactured. The shortest distance L ₂ (see FIG. 2) from the end surface 1b of the flange 1 to the fin 2b was set to 7 mm.

The time t ₁ when reaching the point A was set to 20 seconds, the pressure was increased at a substantially constant speed, and the first forging step was completed. The material after the first forging step was taken out of the mold and its shape was observed. A blank portion 2e ′ shown by a dotted line in FIG. 4 (a) occurs in the material at the winding end 2e of the wrap 2, and FIG.
A flesh portion 2s' indicated by a dotted line was generated in the winding start 2s. In the thickness-reduced portion 2s', the height of the end portion is 20 mm, which corresponds to 2/3 of the target dimension, and the height of the wrap 2 is insufficient over a range of 15 mm along the longitudinal direction. The thickness of the flesh portion 2e 'was 25 mm, which was significantly lower than the target height, and the height of the wrap 2 was insufficient over the range of 15 mm in the longitudinal direction.

Therefore, the material for which the first forging step was completed was held in the pressing position as it was until the time t ₂ = 32 seconds without being taken out from the die. With respect to the material in the holding step, the temperature change of the material temperature was examined by a thermocouple embedded in the mold. As a result, it was found that the material was kept at a high temperature of 470 ° C. or higher during the time t _{1 to} t ₂ = 12 seconds. In this holding process, the load of the press is also P ₁ = 600
It fell from ton to P ₂ = 500 ton. The decrease in the pressing force indicates that the material softens and the deformation resistance decreases due to the increase in the material temperature.

Next, at time t ₃ = 37 seconds, the pressing force P ₁ =
The load is increased again to reach 600 tons and the second
Staged forging was performed. After the second forging step, the load applied to the press was released, and the forged product was taken out of the mold. When the shape of the forged product is observed, FIGS. 4 (a) and 4 (b)
As shown by the solid line, neither the winding end 2e nor the winding start 2s showed the lacked portion 2e 'and the lacked portion 2s'. In the obtained scroll, the wrap 2 was formed with high precision and with the intended thickness of 5 mm and height of 35 mm. That is, it can be seen that the material softened in the holding step plastically flows in the second forging step, and the meat is replenished in the mold cavities hitting the lacking portion 2e 'and the lacking portion 2s'.

[0018]

As described above, in the present invention, the forging is divided into two stages, and the holding process is provided in the middle, whereby the heat of working is utilized to soften the material by heating.
Therefore, the material with reduced deformation resistance is subjected to the second stage forging, and the meat can be supplied to every corner of the mold cavity. Therefore, it is possible to obtain a forged product having excellent shape characteristics even if the shape is complicated. Moreover, since the material set in the same die is forged only by adjusting the load without the need for intermediate heat treatment or the like, the forging operation itself becomes easy. Further, since a large load is not required, a compact press can be used and the life of the mold is extended.

[Brief description of drawings]

Fig. 1 Scroll for compressor as an example of product with complicated shape

FIG. 2 is a diagram illustrating a problem when the scroll is manufactured by forging.

FIG. 3 is a graph showing a change in applied pressure with time according to the present invention.

FIG. 4 is a diagram specifically showing the operation and effect of the present invention.

[Explanation of symbols]

1 Flange 1a, 1b End face of flange 2, 2a, 2b Wrap 2s Wrap winding start 2e Wrap winding end 2s ', 2e' Notched portion 3 Boss

Claims (1)

[Claims] 1. An aluminum alloy material is set in a mold having a cavity corresponding to a scroll having a tooth height H and a tooth thickness T of H / T ≧ 5, and the material of the material, the shape of the product, and the processing temperature. The first forging step of forming almost the entire target shape by pressing to a predetermined pressure determined by the above, the holding step of holding the raw material in the press position as it is, and the pressing force being slightly decreased again. A forging method for an aluminum alloy, characterized by comprising a second forging step of raising to form a final shape.