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(11) | EP 0 131 891 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Die casting method and the apparatus therefor |
| (57) A die casting method for obtaining a complex material of a basic metallic material
and an additive by injecting the basic material to the additive to have the additive
instantly mix with the basic material and to form the resultant product by that basic
material with the additive uniformly distributed therein. The die casting apparatus
includes a mixing cavity [5] upstream of a product cavity [3], and a means [6] for
holding the additive in said mixing cavity for distributing the additive completely
in the mixing cavity by the molten metal to be injected, the basic material with the
additive uniformly distributed therein being introduced into the product cavity thereafter. |
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method for die casting a product and the apparatus therefor, particularly a method to obtain a complex material of metal by a die casting process.
[0002] In the past, high-pressure-solidification molding process has been studied to obtain a complex metallic material, however this method requires a pre-heating step for the additive to be added to the basic material and the step to mix the additive and the basic material. Therefore in this conventional method, the productivity is not very high because of the special step required as mentioned above to result in the high producing cost of the product expected. Moreover in the conventional method, the additive is not necessarily distributed uniformly throughout the basic material, especially when the familiarity of the additive to the basic material is poor, it is difficult to obtain a complex material of high quality.
SUMMARY OF THE INVENTION
[0003] The present invention purposes to obtain a complex material at a low cost and at a high productivity rate, where the additive and basic material are uniformly mixed for the best performance.
[0004] One of the primary objects of the present invention is to mix the additive with the molten metal material by utilizing a high agitating energy obtained through the molten metal injected by an injection plunger.
[0005] Another object of the present invention is to form a product cavity, a mixing cavity and a gate positioned between those two cavities as well as a means to hold the additive at the upstream portion to said gate, thereby to first mix the additive with the basic material in the mixing cavity and then introduce the mixture into the product cavity through the gate, thus obtaining a complex material uniformly distributed with the additive in the product cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006]
Fig. 1 is a cross-sectional view showing an embodiment of the die casting apparatus of the present invention,
Fig. 2 is a partial cross-sectional view showing the main part of the die casting apparatus shown in Fig. 1,
Fig. 3 is a front view showing the arrangement of product cavities, mixing cavity and other nearby parts of the dicasting apparatus shown in Fig. 1,
Figs. 4 and 5 show a partial cross-sectional and front view of the means to hold an additive as shown in Fig. 1,
Figs. 6 and 7 show a cross-sectional and front views of another embodiment to hold the additive in the dicasting apparatus shown in Fig. 1,
Fig. 8 shows a partial cross-sectional view of the main part of the die casting apparatus of a further embodiment of the present invention, and
Figs. 9 and 10 are pictures showing micro structures of the material obtained in the die cavity of the die casting apparatus of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0007] In Fig. 1, numeral 28 designates a fixed base secured to the floor in the factory by a bolt. Numeral 17 desitnates a fixed platen supported on the base 28. As is apparent there is another fixed platen opposite to the platen 17 shown in the drawing, those two fixed platens making a couple to form the whole die casting machine. Between those two fixed platens 17 is there provided a tie bar 18. Along this tie bar 18 a movable platen 21 is slidably formed. Therefore the movable platen 21 slides between the two fixed platens 17 by the force of a piston to be moved upon the application of oil pressure. The movable platen 21 moves with the parts explained below as indicated by an arrow K.
[0008] Numeral 9 designates a fixed block secured to fixed platen 17, 10 a fixed die provided in the fixed block 9. The fixed block 9 and the fixed die 10 form a fixed die arrangement 29. Numeral 20 designates a die base secured to the movable platen 21, 12 a movable block secured to the die base 20, and 11 a movable die provided in the movable block 12. The die base 20, movable block 12 and movable die 11 form a movable die arrangement 30. The fixed die 10 and the movable die 11 are made of tool steel (SKD 61).
[0009] When the movable die arrangement 30 is moved close to the fixed die arrangement 29, there are formed a few cavities and gates between those two dies 10 and 11, i.e. a product cavity 3, a mixing cavity 5 and a gate 4 connecting those two cavities. A runner 8 and a mixing gate 7 which is placed to connect the runner 8 and the mixing cavity 5 are also formed. In addition to the above cavities, there is also formed an overflow cavity 1, which is connected with the product cavity 3 via an overflow gate 2.
[0010] The details of this main part of the die casting machine are disclosed in Figs. 2 and 3. As is shown in Fig. 3 especially, there are formed to product cavities 3 in this embodiment. There is formed a single mixing cavity 5 and that is connected to those two product cavities 3. There are also to mixing gates 7 as is also shown in Fig. 3, each of which is connected with the mixing cavity 5. Each of the gates 4 is formed in such a place that none of the mixing gates 7 faces directly to one of the gates 4. Therefore when the molten metal is introduced from each of the main gates 7, the molten metal makes turburances in the mixing cavity 5, thus preventing the molten metal from being introduced directly to the gates 4. Numeral 6 designates a pin provided to be exposed into the mixing cavity 5. The pin 6 is inserted into a hole 10a formed in the fixed die 10, and it is mounted into the apparatus when the fixed die 10 is secured to the fixed block 9.
[0011] When the movable die arrangement 30 is moved to open the mixing cavity 5, an amount of an additive 23 is fixed to the pin 6. The additive 23 is secured to the pin 6 as shown in Figs. 4 and 5, or it is held or supported between two pins 6 as shown in Figs. 6 and 7.
[0012] The additive 23 use in this embodiment is powder alumina (Al2O3), and also the power alumina is wrapped by a thin film of an aluminum alloy, the thickness of which is from 0.01 - 0.1 mm. Therefore the powder alumina wrapped by this thin film of aluminum alloy 23a is grasped, inserted between the two dies, and then secured at the pin 6.
[0013] The volume Vl of the product cavity 3 is smaller than the volume V2 of the mixing cavity 5, and in this embodiment V2 is 1.5 - 2.0 times larger than V1. In this embodiment, Vl means a total volume of the two product cavities 3. Numeral 13 designates push pins for pushing out the product and the nearby parts solidified in the cavities in accordance with the movement of a plunger 22 via a push plate 19. The plunger 22 moves as indicated by an arrow U.
[0014] In Fig. 1, numeral 14 designates an injection sleeve connected to the runner 8, and in the injection sleeve 14 an injection plunger 16 is slidably provided. Numeral 15 designates a mouth opening to the injection sleeve 14, and through this mouth 15 a molten metal is poured. In this embodiment, aluminum-copper-silicon alloy (ADC 12) or high silicon aluminum alloy (A 390) is used as the basic metallic material. Next, the die casting method of the present invention is explained in association with the construction above explained. When the movable die arrangement 30 and the fixed die arrangement 29 are opened with each other, a separator liquid is sprayed onto the product cavity 3 and the mixing cavity 5. Then the additive 23 is fixed to the pin 6. In this embodiment the additive 23 is about 3 - 30% in weight of the molten metal to be filled in the product cavities 3 and the mixing cavity 5. When alumina is used as the additive 23, the amount of less than 3 wt% does not improve the wear resistant performance, and on the other hand the amount of more than 30 wt% deteriorates the strength of the product to be molded because of the nonuniform mixing of the additive to the basic metallic material. Then, the movable die arrangement 30 moves close to the fixed die arrangement 29 to form the cavities 3 and 5. After that molten aluminum alloy of about 630 °C to about 700 °C is poured through the mouth 15, and then the molten metal in the injection sleeve 14 is injected by an injection plunger 16 so that the molten metal flows into the runner 8 as indicated by an arrow T. At this time the injection plunger 16 moves slowly at first to allow the air remaining in the product cavity 3 to flow into the overflow cavity 1. When the injection plunger 16 is moved in such a position that the molten metal is about to enter into the mixing cavity 5, the injection plunger 16 is actuated fast. Since the molten metal is throttled at the mixing gate 7, the velocity of the molten metal after the mixing gate 7 becomes very high, such as 30 to 70 m/s. The molten metal collides to the additive 23 at this speed, and by the energy at this collision the thin film 23a is instantly and completely broken into fragments by the blow of the molten metal to scatter the additive 23 in the mixing cavity 5 within the basic metallic material 5.
[0015] The thin film 23a is mechanically broken into fragments by the injection pressure, rather than being molten by the effect of the high temperature of the molten metallic material. Therefore the thin film 23a must not necessarily be a metallic material of low melting point, lower than that of the basic metallic material, i.e. magnesium, copper and other metallic materials are also usable as the thin film 23a.
[0016] By this agitating operation, the additive 23 uniformly mixes with the molten basic metallic material in the mixing cavity 5, and then the material is introduced into the product cavity 3 via a gate 4. The air partly remaining in the product cavity 3 is pushed by the molten metal and introduced into the overflow cavity 1 with the molten metal material. The arrow A shows the movement of the molten metal above.
[0017] Since the volume V2 of the mixing cavity 5 is larger than that of the product cavity 3 in this embodiment, there still remains part of the molten metal with the additive uniformly distributed in the mixing cavity 5 after the product cavity 3 is completely filled with the molten metal. Therefore the basic material of aluminum alloy itself or that material with the additive distributed nonuniformly does not enter into the product cavity 3, even if it is the case. In other words, the molten material introduced into the product cavity 3 is the molten material with the additive uniformly distributed in every part thereof.
[0018] When the volume V2 of the mixing cavity 5 is below 1.5 times of the product cavity 3, there remains a possibility that a nonmixed molten metal material is introduced into the product cavity 3, and on the other hand when it is more than two times larger than the volume of the product cavity 3, it results in an excessively large mixing cavity 5, which wastes the molten metal.
[0019] In this embodiment the injection pressure by the injection plunger 16 is about 800 - 1200 kg/cm2, therefore the additive is completely united with the basic material. Therefore even after the molten metal is cooled down, the additive 23 does not peel off or separate from the basic- metal material.
[0020] When the cavities 1, 3 and 5 are filled with the molten metal, the apparatus is kept as it stands at that high pressure for a while to wait for the solidification of the metal in the cavities 1, 3 and 5. When the solidification is completed, the movable die arrangement 30 is separated from the fixed die arrangement 29, and then the solidified product is pushed out by the push pins 13 in accordance with the movement of the plunger 22.
[0021] The product and the nearby parts taken out from apparatus are cut at the overflow gate 2 and the gate 4 to take only the product corresponding to the product cavity 3. The product thus obtained shows a high hardness and anti-wear performance because of the appropriate combination of the additive and the basic aluminum material. The product thus obtained is usable as a part of a bearing and a housing of a compressor.
[0022] Fig. 9 shows a picture of the micro structure of the product solidified in the product cavity 3, and Fig. 10 shows a picture of the metal solidified at the outlet of the mixing gate 7 as indicated by n in the drawing. As is evident from the pictures, there are some portions made only by aluminum alloy at the mixing cavity 5, although the picture taken at the product cavity 3 shows an aluminum alloy with the additive distributed throughout the product uniformly.
[0023] Although the present invention is explained in accordance with the embodiments shown in the drawings, the present invention is not limited to those limited examples, but rather be construed to cover all the variations around the embodiments.
[0024] Although alumina is used in the embodiments above, it is basically true that all other powder materials can be used in this invention. For example other metal oxides than alumina, particles of inorganic materials, fibers of inorganic materials, metal, glass and carbon, and whiskers, and any combination of the above materials are also usable in this invention.
[0025] Moreover in the embodiments above, the additive 23 is wrapped by a thin film 23a for an easy handling, however the additive 23 may be put on a supporter 25 as disclosed in Fig. 8. In this embodiment, the additive 23 is inserted into the dies and put on the supporter 25 when the movable die arrangement 30 is opened from the fixed die arrangement 29. Numeral 26 in Fig. 8 designates a rod which moves the supporter 25 by the operation of the piston 27. An arrow Y designates the direction of the operation of the piston 27. Therefore when the movable die arrangement 30 is moved, the supporter 25 is also moved to form the mixing cavity 5 with the fixed die arrangement 29.
[0026] In the embodimentd above a single mixing cavity 5 is formed in the apparatus, however when more mixing performance is required at the mixing cavity 5, another mixing cavity may be provided in series with the mixing cavity 5 shown in the drawing.
[0027] In the embodiments above the means to hold the additive 23, i.e. the pin 6 and the supporter 25 is provided in the mixing cavity 5, however the means may be provided at an another upstream portion than the mixing cavity 5, e.g. in the runner 8. The important thing in this invention is to put the additive at such a position that the injected molten metal directly collides thereto.
[0028] As explained above, the present invention utilizes the energy of the injected molten metal to agitate the additive with the basic material, thus enabling a uniform distribution of the additive in the basic material. The mixing operation in the mixing cavity contributes to the high quality of the product obtained in this invention, which derives from the fact that the mixing gates 7 are not directly aligned with the gates 4.
1. A die casting method comprising the steps of;
placing a movable die apart from fixed die, said movable die and fixed die forming a product cavity in a die cavity to be formed when both dies are moved close to each other,
placing an amount of an additive on one of said movable and fixed dies upstream of said product cavity,
moving said movable die to said fixed die to form said product cavity with said additive placed upstream thereof,
injecting an amount of molten metal by an injection plunger to have said molten metal collide to said additive so that said additive is uniformly distributed in the molten metal injected,
introducing said molten metal with said additive distributed into said product cavity at the end of said injecting step, and
removing the resultant die cast product from said dies.
2. A die casting method as claimed in Claim 1, wherein said injection step is carried
out by bursting said additive by said molten metal for said uniform distribution of
said additive.
3. A die casting method as claimed in Claim 2, further comprising the step of wrapping
said amount of additive by a thin film of substantially the same metal as said molten
metal, said wrapping step being carried out before said additive placing step.
4. A die casting apparatus having a fixed die and a movable die for forming a die
cavity therebetween into which an amount of molten metal is injected by an injection
plunger comprising;
means for forming a product cavity in said die cavity for the product to be die casted, means for forming a mixing cavity in said die cavity upstream of said product cavity, a gate positioned between said product cavity and said mixing cavity to introduce said molten metal into said product cavity from said mixing cavity, means positioned in said mixing cavity for holding an amount of an additive to be uniformly distributed into said molten metal when said molten metal passes through said mixing cavity, a mixing gate positioned upstream of said mixing cavity for introducing said molten metal into said mixing cavity, and an injection sleeve for injecting said molten metal in association with said injection plunger.
5. A die casting apparatus comprising an injection sleeve, an injection plunger positioned
in association with said injection sleeve for injecting an amount of molten metal
from said injection sleeve, a mixing gate positioned downstream of said injection
sleeve for blowing said molten metal therethrough, means for holding an amount of
an additive to said molten metal at a position downstream of said mixing gate for
being bursted by the blow of said molten metal from said mixing gate, a mixing cavity
formed in association with said additive holding means for uniformly mixing said additive
with said molten metal therein, a gate positioned downstream of said additive holding
means and said mixing cavity for introducing said molten metal with said additive
therethrough, and a product cavity formed downstream of said gate for receiving the
molten metal with said additive to form a resultant die casted product therein.
6. A die casting apparatus as claimed in Claim 5, wherein said mixing gate is so positioned
that said molten metal injected directly collides into said additive, and said gate
is positioned in such a position that said gate does not receive said molten metal
delivered from said mixing gate directly, so that said molten metal and said additive
are uniformly mixed in said mixing cavity before the mixture is carried to said gate
leading to said product cavity.
7. A die casting apparatus as claimed in Claim 6, wherein said additive is held by
a pin exposed into said mixing cavity, said pin holding said additive in such a position
that at least a portion of said additive receives a direct supply of said molten metal
from said mixing gate.
8. A die casting apparatus as claimed in Claim 7, wherein a volume of said mixing
cavity is larger than a volume of said product cavity.
9. A die casting apparatus as claimed in Claim 8, wherein said mixing cavity is 1.5
to 2.0 times larger than aid product cavity in volume.
10. A die casting apparatus as claimed in Claim 9 further comprising an overflow cavity
connected with said product cavity via an overflow gate.
11. A die casting apparatus as claimed in Claim 10, wherein said molten metal is of
an aluminum alloy and said additive is of alumina.
12. A die casting apparatus as claimed in Claim 11, wherein said additive of alumina
is of powder shape and said power shaped alumina is wrapped by a thin film of said
aluminum alloy.