Semisolid casting/forging apparatus and method as well as a cast and forged product

Abstract

An excellent cast and forged product that is superior in mechanical properties and has a microstructure and which may not only be a thin but also be a thick product can be made without using complicated process steps or equipment. A semisolid casting and forging method is provided in which a metal melt is teemed so that it is supercooled into a lower die in a press so controlled that the metal melt has a rate of solidification as desired, thereby preparing a semisolid slurry; an upper die is brought into contact with the semisolid slurry; and thereafter at least one of the upper and lower dies is moved relatively towards the other at a rate of movement between 0.1 and 1.5 m/sec, thereby compressing the semisolid slurry to mold it into a product. The semisolid slurry preferably has crystal grains of a grain size of 50 m or less.

Claims

1. A semisolid melt casting and forging method, comprising: teeming a metal melt into a cavity of a lower die, and moving at least one of the lower and an upper die relatively towards the other at a rate of movement to perform molding of the metal melt in a semisolid state; wherein said metal melt is formed into a slurry having grains of a grain size of not more than 50 m throughout the slurry, and wherein said molding is initiated at a lapse of time ranging between 0.1 second and 10 seconds following an instant at which the metal melt is teemed.

2. A semisolid melt casting and forging method as set forth in claim 1 wherein said lapse of time between the instant at which the metal melt is teemed and the instant at which the molding is initiated is between 0.1 second and 5 seconds.

3. A semisolid melt casting and forging method, comprising the steps of: teeming a metal melt so that it is supercooled to be teemed into a lower die in a press so controlled that the metal melt has a rate of solidification as desired, so as to make a semisolid slurry having crystal grains of a grain size of not more than 50 m throughout; bringing at least an upper die into contact with the semisolid slurry; and thereafter moving at least one of the upper and lower dies relatively towards the other at a rate of movement between 0.1 and 1.5 meter per second at least after an instant at which the upper die comes in contact with said semisolid slurry, thereby compressing said semisolid slurry to mold it into a product.

4. A semisolid melt casting and forging method as set forth in claim 1, wherein the metal melt as it is teemed is of a temperature higher by 10 to 30 C. than its liquid phase or liquidus temperature.

5. A semisolid melt casting and forging method as set forth in claim 1, wherein the metal melt is cooled passing through a liquidus curve at a rate of cooling of not less than 2 C. per second.

6. A semisolid melt casting and forging method as set forth in claim 1, wherein said lower die is of a temperature of 200 C.100 C.

7. A semisolid melt casting and forging method as set forth in claim 1, wherein said upper die is of a temperature different from that of said lower die.

8. A semisolid melt casting and forging method as set forth in claim 7, wherein the temperature of at least a portion of said upper die is lower than the temperature of said lower die.

9. A semisolid melt casting and forging method as set forth in claim 1, wherein the ratio in mass of a product to a raw material is not less than 0.9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the Drawings:

(2) FIG. 1 is a conceptual view illustrating a molding apparatus that can be used to carry out a method of the present invention;

(3) FIG. 2 is a view of a die (mold) arrangement illustrating a process step (before melt teeming) in Example 1 of the present invention;

(4) FIG. 3 is a view of a die arrangement illustrating a process step (for melt teeming) in Example 1 of the present invention;

(5) FIG. 4 is a view of a die arrangement illustrating a process step (for forging) in Example 1 of the present invention;

(6) FIG. 5 is a view of a die (mold) arrangement illustrating a process step (before melt teeming) in Example 2 of the present invention;

(7) FIG. 6 is a view of a die (mold) arrangement illustrating a process step (before melt teeming) in Example 2 of the present invention;

(8) FIG. 7 is a view of a die arrangement illustrating a process step (for forging) in Example 2 of the present invention;

(9) FIG. 8 carries photographs showing a view of metallurgical structure and a view of appearance of a product, using the forming apparatus shown, and formed in Example 2 by the method, of the present invention; and

(10) FIG. 9 carries graphs illustrating influences exerted by a teeming temperature on a uniformity of thermal distribution of a semisolid slurry.

DESCRIPTION OF REFERENCE CHARACTERS

(11) 10 molding apparatus 12 bed 14 column 20 slide 24 upper die 32 bolster 34 lower die 50d product 51 different member 53 pin rod

Modes for Carrying Out the Invention

(12) FIG. 1 is an entire makeup view that shows one example of molding apparatus to which can be applied a method of forming an aluminum alloy in accordance with the present invention. This apparatus will represent a simplification of the apparatus disclosed in JP 2007-118 030 A.

(13) The molding apparatus shown in FIG. 1 that can, for example, be an oil hydraulic press, has a frame comprising a bed 12, a column 14 and a crown 16, and a slide 20 guided by a guide unit 18 so as to be movable vertically. A first hydraulic cylinder 22 mounted on the crown 16 transmits a driving force to the slide 20 to move it both downwards and upwards as shown in FIG. 1. The slide 20 has its lower end to which is mounted and attached an upper die 24.

(14) On the other hand, a lower die 34 is mounted and attached to a bolster 32 provided on the bed of the molding apparatus 10.

(15) By lowering the slide 20, a molten metal or metal melt, or a semisolid slurry, or a semisolid preformed billet, that is arranged in a space in the lower die 38 can be compressed and worked to form a product.

(16) Design is made of heat capacity of the lower die 34.

(17) Also, so that a specific rate of solidification optionally selected may be had when the lower die and a material of the melt poured or teemed reach their thermal equilibrium state, a heat capacity of the lower die, a heat capacity of the metal melt being teemed and a latent heat thereof are calculate previously, and the size of the lower die, the melt temperature, the temperature of the lower die and the amount of the metal melt are designed so that a thermal balance may be taken at the specific rate of solidification.

(18) When the temperature of the metal melt and the temperature of the lower die becomes equal to each other, it is thought that heat will no longer be transferred and the temperature will change no longer. A temperature T.sub.eq at that time (hereinafter, referred to as equilibrium temperature) can be given below.

(19) $\begin{array}{cc}\left[\mathrm{mathematical}\mathrm{expression}1\right]& \\ T_{\mathrm{eq}}=\frac{T_c+T_m+H_f^{}{f}_s}{1+}& \left(1\right)\end{array}$

(20) where T.sub.c is an initial temperature of the metal melt, T.sub.m is an initial temperature of the lower die, H.sub.f is a semisolid latent heat divided by a specific heat, and f.sub.s is a rate of solidification. And, is a heat quantity required to raise a temperature of the lower die by 1 K, that is divided by a heat quantity required to raise a temperature of the metal melt by 1K, and is given below.
=(.sub.mc.sub.mV.sub.m)/(.sub.cc.sub.cV.sub.c)(2)

(21) where is a density, c is a specific heat and V is a volume, and subscripts .sub.c and .sub.m represent the metal melt and lower die, respectively.

(22) When a metal melt is teemed into the lower die, the melt is teemed from a height from the bottom of the lower die, which is 3.5 times or more of a mean diameter D of the lower die. Note, here, that the mean diameter is assumed to be the half () power of a product area of the lower die.

(23) While product shapes do not matter, the lower die preferably has a flat base. The base if undulating should have a difference of undulation which is preferably not more than , and more preferably , of the thickness of a product. Otherwise, a metal melt tends to accumulate on a lower portion, causing an unbalance in compressibility.

(24) There is no specific limitation of a metal to be cast and forged according to the present invention. Especially, an alloy of low melting point such as an aluminum alloy is effective, however. Alloys of the AlSi (ADC1) series, AlSiMg (ADC3) series, AlSiCu (ADC10, 10Z, ADC12, 12Z, ADC14) series and AlMg (ADC5, 6) series, prescribed by JIS, are suitably used.

(25) Besides these aluminum alloys, such alloys as a magnesium alloy or a zinc alloy are similarly effective.

(26) In general, the higher the rate of solidification, the less the fluidity, requiring higher pressure for injection, it being thought that it becomes harder to fill a thinner portion in the die.

(27) It has been found, however, that a semisolid even if it is of high rate of solidification but if it is of grains having a reduced grain size is ensured of its fluidity and that one rather having a higher rate of solidification is allowed to fill a thinner portion reliably.

(28) A rate of solidification of 30% or more is preferred. Noting that exceeding 60% increases the compression pressure, it has been found on the other hand that 60% or less is preferable.

(29) A rate of cooling of the metal melt when it passes through the liquidus curve is preferably 2 C. per second or more.

(30) A cooling rate not less than 2 C. per second is preferred. When the metal melt is cooled at a cooling rate of 20 C. per second or more, the semisolid will have extremely fine grains (having grain sizes of 2 to 4 m) distributed therein. The existence of such micro grains is deemed to make it possible to produce a die cast product that is thin and which has substantially no gas entangled and no void left.

EXAMPLES OF EMBODIMENT

Example 1

(31) In this Example, a connecting rod is produced.

(32) As a mold or die, use is made of an upper die 24 and a lower die 34 as shown in FIG. 2.

(33) Such that a semisolid slurry may be yielded having an adequate rate of solidification in the mold, optimum conditions are sought in advance, under which a semisolid casting and forging process is performed.

(34) The semisolid casting and forging process has process steps as follows: 1. Setting the temperatures of the metal melt and die; 2. Teeming into the lower die; 3. Movement towards the position at which the dies are to be clamped and closed; 4. Clamping and closing the dies; 5. Filling or packing; 6. Molding completed; 7. Opening the dies; and 8. Taking out a molded product

(35) As shown in FIG. 3, a molten metal or metal melt is teemed into a space in the lower die 34.

(36) Subsequently, the upper die 24 as shown in FIG. 4 is lowered to compress a semisolid slurry and to form a product.

(37) As the molding machine, use is made of a hydraulic servo-controlled press of 20 tons made by Kouei Seisakusho in which both the lower die (at the fixed side) 34 and the upper die (at the movable side) 24 are set at a temperature of 250 C. and the metal melt (AC4CH) is set at a temperature of 620 C.

(38) The metal melt is teemed into the lower die 34 and the upper die 24 is lowered at a rate of movement of 0.1 m/s. The upper die 24 brought into contact with the semisolid slurry is moved as it is at the rate of movement of 0.1 m/s maintained to perform press molding.

(39) A product 50d after it is solidified is taken out from the dies.

(40) Molding conditions are as follows:

(41) Casting and Forging Conditions

(42) Melt material: AC4CH

(43) Liquidus temperature TL: 610-612 C.

(44) Solidus temperature TS: 555 C.

(45) Teeming temperature: 620 C.

(46) Temperature of the upper die: 250 C.

(47) Temperature of the lower die: 250 C.

(48) Clamping rate: 0.1 m/s

(49) Ratio of product mass/raw material mass: 0.9/1

(50) Rate of solidification: 60%

(51) Height of the melt in the lower die: 50 cm high from the cavity base in the lower die

Example 2

(52) In this Example, a product consisting of a composite is produced. Specifically, a connecting rod provided at each of its two ends with a ball 51 embedded therein as a different member.

(53) In this Example as shown in FIG. 5, pin rods 53, each holding a ball 51, are inserted in the upper die 25. The balls 51 are held to the pin rods by magnetic force of attraction. A vacuum or any other chucking force may be substituted for.

(54) As in Example 1, a metal melt is teemed (FIG. 6). Then, the upper die 24 is lowered. The balls 51 are lowered with the upper die 34 lowered and come to be embedded in the semisolid slurry (FIG. 7). Each of the balls 51 is solidified and left at the product side. Then, more than one half of the ball body is left embedded in the body of the product. The ball having a diameter more than a diameter of its entry or exposed portion could not leave the body. When a member of a shape other than a ball is to be embedded in a body of the product, the member suitably bent will prevent it from leaving the body.

(55) Thus, according to the present invention, a member that can be of an intricate shape can be embedded in a body (semisolid slurry) of the product, making it possible to mold a composite member with a firm bond acquired without resort to welding or the like.

(56) FIG. 8 shows a photograph of appearance of a semisolid molded product (connecting rod) and results of observation of its metallographic structure. It has primary crystals a which as those by the conventional semisolid slurry method (NRC, NRF, nano-cast, cup and sleeve techniques) are seen to include ones have a variation and a little unstable in size. But, the structure is found to possess a spherical structure having an average grain size of about 50 m throughout the entirety of a molded product. As a result, the product is excellent having substantially no shrinkage void and no segregation therein.

(57) The spherical crystallographic structure having crystal grains of an average grain size around 50 m in a final product has a grain size smaller than that in its semisolid slurry stage.

(58) A plastic flow has been observed in a high load portion (ball part) of the connecting rod and deemed to form a microstructure expected of an increased strength. To wit, such a portion at it is not only under a high load but also at a low temperature is deemed to solidify and bring about a plastic deformation that provides a forged structure.

(59) Thus, in the present invention, there can be formed a forged structure in a cast structure.

INDUSTRIAL APPLICABILITY

(60) According to the present invention, an excellent cast product can be made having a microstructure and in which there is substantially no shrinkage void and substantially no non-metallic inclusion and which may not only be a thin but also a thick product. Accordingly, the present invention can be utilized not only in the field of electrical and electronic components but only in those, e.g. that of automobile components and others.

(61) The present invention is applicable to all possible shapes of articles other than that of a connecting rod, including, for example, a member H-shaped in cross section, a member I-shaped in cross section, a member in the shape of a kettle or iron pot, a member in the shape of a cross, an aluminum wheel and other products. The applicable industrial field is thus not limited to a particular field of industry.