JP2001225159A - Method for die casting of light metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for die casting of light metals, such as aluminum or aluminum alloys, which is capable of eliminating the problems caused by formation, etc., of small holes and air bubbles, in die cast parts by drastically reducing the occlusion of gas. SOLUTION: Molten metal (20) is introduced into a packing chamber (16) and is poured from this packing chamber (16) into a molding cavity by a piston (24). After the molding cavity (14) is preevacuated, oxygen is filled therein and the evacuation is carried out again after the filling oxygen and before pouring of the molten metal (20). Finally, the molten metal (20) is poured into the hollow molding cavity (14). The tendency to the formation of the small holes and air bubbles is lowered and the manufacture of the die cast products having high quality is made possible by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for charging molten metal into a filling chamber from which a hollow molding cavity is formed by a piston.
The present invention relates to a method for die casting light metals, particularly aluminum and aluminum alloys, to be injected into the cavity.

[0002]

In the known die casting process, molten metal is introduced into a filling chamber and injected from a filling chamber into a hollow molding cavity of a die casting machine by a piston. Most of the gases, such as air and water vapor, are released from the mold cavity by the metal injected into the mold cavity. In a variation on this method, the molding cavity is pre-evacuated to a residual pressure of about 200 mbar to 500 mbar, and in a special ingress die casting method
Evacuate to a residual pressure of less than mbar.

[0003] Molds for die-cast parts with thin walls and large surface areas or complex shapes are difficult to penetrate the melt and have narrow areas where it is practically impossible to remove gas from the molding cavity. There is. High vacuum cannot be obtained when the mold is evacuated before filling. This is due to lack of tightness, cost and time. Depositing gas in the form of pores or air bubbles, while vacuum die casting is much less than conventional die casting, nonetheless, the number of these defects in die cast parts is such Too many parts to be used as safe components in the manufacture of automobiles. This is due to inappropriate mechanical properties.

[0004] A non-perforated die casting method (Pore Free
Die-casting (PFD)),
In the die casting process for casting aluminum, the cavity is filled with oxygen before the metal is injected into the molding cavity. The ultimate pressure is set at or above atmospheric pressure so that the gas in the molding cavity is replaced by oxygen. After the oxygen supplied to the molding cavity flows through the narrow gap or region and fills for a predetermined duration, most of the gas previously in the molding cavity is released from the molding cavity. Therefore, the gas in the atmosphere can be prevented from entering the mold again. Subsequent injection of molten aluminum into the mold causes the aluminum to react with oxygen and
₂ O ₃ is formed, which remains in the die cast part as a dispersion of particulates without significantly altering its properties.

However, even when the pressure in the molding cavity is maintained at or above atmospheric pressure, it is practically impossible to completely remove the gas from the inside of the mold by filling the mold with oxygen. I understand. Residual gases often remain in difficult to fill areas for extended periods of time. Aqueous release agents, for example, require a certain amount of time to dry completely at relatively high ambient pressure. In the case of die casting molds for producing relatively complex shaped die cast parts, there are some areas where oxygen is difficult to reach, so that residual gases such as air and water vapor It is not replaced and remains in the molding cavity as before. During die casting, these residual gases and water vapor from the release agent remaining in the molding cavity are trapped by the metal, forming small holes therein, and air bubbles formed on the surface by a subsequent heat treatment such as a solution treatment. Is generated. Due to these bubbles, many die cast parts cannot be heat treated.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for performing die casting as described at the outset, which greatly reduces gas buildup and reduces die The consequences of the problems mentioned above, such as the formation of pores and bubbles in cast parts, can be eliminated.

[0007]

SUMMARY OF THE INVENTION The purpose of this invention is to pre-evacuate the molding cavity, fill it with oxygen, evacuate it again after filling with oxygen and before injecting the molten metal, and finally remove the molten metal from the molding cavity. Is achieved by the present invention.

An important feature of the present invention is that the well-known die casting method is combined with the PDF method. This method eliminates the disadvantages of the individual processes mentioned above in a simple manner. By pre-evacuating the molding cavity, the residual amount of air and water vapor can be significantly reduced, so that the subsequent filling of the molding cavity with oxygen substantially eliminates residual gas. The method according to the invention gives excellent results even at relatively low vacuum.

For optimal results with respect to the formation of pores and bubbles, the residual pressure is brought to 100 mbar by pre-evacuating the molding cavity before filling with oxygen.

When filling the molding cavity with oxygen,
Usefully, a pressure above atmospheric pressure is maintained.

[0011] It is advantageous to maintain an oxygen atmosphere around the die to prevent gas and water vapor from flowing back into the molding cavity. In this way, in the event of a leak, oxygen is sucked back into the molding cavity instead of air or water vapor.

In the method according to the present invention, the following two embodiments are conceivable. 1. A pre-evacuation step and a filling step with oxygen are performed before filling the filling chamber with molten metal. 2. The molten metal is injected into the filling chamber and the filling chamber is closed with a piston. Thereafter, the three steps performed on the molding cavity, the pre-evacuation step, the filling step with oxygen, and the re-evacuation step, are all performed until the molten metal enters the molding cavity during the first filling phase. Implement one after another. This second aspect can be used particularly for large die casting machines. This is because these machines take a long time in the first filling stage.

With the method according to the invention, it is possible to produce die-cast parts made of aluminum or aluminum alloy with a filling gas quantity of less than 1 cm ³ per 100 g of aluminum. Such die-cast parts have excellent mechanical properties and can be used for functional structural parts such as safety parts in automobile manufacturing. Furthermore, die-cast parts manufactured according to the invention can be subjected to thermal treatment and welding without the risk of bubbles being formed by the filling gas.

A particularly advantageous application of the method according to the invention is that M
By a combination of the FT method or the HQC method, i.e. EP-A-0 759 825 and DE D
It is performed by a die casting method and apparatus as described in the patent document of EC-3002886.

[0015] Other advantages, features and details of the invention will become apparent from the following description of the method, read in conjunction with the accompanying drawings.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A die casting machine 10 shown in FIG.
Has a die cast mold 12 having a hollow molding cavity 14 connected to a filling chamber 16. Molten metal 2
0 is introduced into the filling chamber 16 via the inlet opening 18 and the piston 2
4 into the molding cavity 14. After filling the molding cavity 14 with the molten metal 20, it is cooled and solidified in a shape defining the inner surface of the mold 12. After cooling, the die-cast part produced in this way is removed by a take-out pin 26 of the molding cavity 14.

The vacuum suction pipe 28 is used for the molding cavity 14.
Is connected to a vacuum pump 30. During evacuation of the molding cavity 14 via the suction pipe 28, there is a risk that air and water vapor enter the molding cavity 14 via the extraction pin 26. For this reason, sealing means 32 are provided between the take-out pins 26 and the alignment of these pins and between the two halves of the mold 12. In addition, the inlet opening 18 to the filling chamber 16 prevents air or water vapor from entering the interior of the filling chamber 16 through the inlet opening 18.
Is also closed by the piston 24.

Filling chamber 16 and molding cavity 14
After evacuation, the oxygen nozzle 34 is opened to allow oxygen to enter the interior of the filling chamber 16 and into the molding cavity 14 from this chamber. The oxygen nozzle 34 is connected to an oxygen source 38 via a control valve 36.

The molding cavity 14 is connected to a vacuum suction pipe 28
When evacuated through the mold, air and water vapor form the molding cavity 14 and the filling chamber 1 connected to this cavity.
Do not enter 6. 500 mbar / sec to 800 mb for complex shaped mold cavities 14
By choosing a suction rate in the range of ar / sec,
Residual gas can be removed from the concealed part of the molding cavity 14.

Advantageously, the evacuation is performed for one to two seconds. The inlet opening 18 is, of course, closed by a piston 24. The evacuation time of the method according to the invention is somewhat longer when compared to the conventional vacuum die casting method, where evacuation is completed in less than one second. Due to the relatively long evacuation time, a useful vacuum of less than 100 mbar is created in the mold cavity 14. Water vapor generated from the release agent and attached to the inner surface of the mold 12 evaporates from this surface and is carried out of the molding cavity 14.

By evacuating the molding cavity 14, water vapor is removed more effectively than simply filling the molding cavity with gaseous oxygen.
Flows more quickly into However, the evacuation of the molding cavity 14 is at an insufficient level, ie about 100 mbar.
In the case above, a relatively large amount of residual gas remains. In that case, a large portion of the residual gas remaining in the molding cavity 14 is not replaced by oxygen and often remains trapped in the casting.

After the preliminary evacuation, oxygen is introduced into the molding cavity 14 through the oxygen nozzle 34. The supply of oxygen is maintained until the gas and oxygen leak from the mold cavity 14 through the two halves of the mold 12, preferably for 3 to 4 seconds.

As oxygen flows into the pre-evacuated molding cavity 14, it flows into those narrower parts of the molding cavity 14, so that most of the water vapor from the release agent is carried away by the oxygen.

The piston 24 is moved rearward to the opening of the filling inlet 18, thereby maintaining the supply of oxygen. As soon as the inlet opening 18 opens, the oxygen flows out through the inlet opening 18 as shown in FIG. The outflow of oxygen effectively prevents air and water vapor from entering the charging chamber 16 through the inlet opening 18.

After opening the inlet 18, the molten metal 20 is injected into the filling chamber 16. Oxygen continues to flow out of inlet 18 during the filling process. Therefore, when the filling chamber 16 is filled with the molten metal 20, air and water vapor are prevented from entering the filling chamber 16.

The mold 12 is preferably preheated to a temperature of about 150 ° C. to 200 ° C. to eliminate thermal shock and improve productivity.

When a suitable amount of molten metal 20 has been introduced into the filling chamber 16 for the casting cycle, the inlet opening 18 is plugged with molten metal 20. Since oxygen can no longer be introduced through the opening 18, the supply of oxygen is stopped.

A gas such as air or water vapor is injected into the molding cavity 1
4 and after complete removal from the filling chamber, the piston rod 22 with the piston 24 is moved forward and the molten metal 20 is injected into the molding cavity 14. The metal mass filling the molding cavity 14 is cooled and solidified into a shape that matches the shape of the molding cavity.

As mentioned above, in one embodiment of the method according to the invention, particularly in the case of large die casting machines, the molten metal 20 is introduced into the filling chamber 16 in a first step and the inlet opening 18 Is closed with the piston 24. Thereafter, during the first filling phase of the die-casting process, that is, until the molten metal enters the molding cavity, all three steps are sequentially performed, namely, the pre-evacuation step, the oxygen filling step, and the re-evacuation step. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a die casting machine suitable for performing the method according to the invention.

FIG. 2 is a schematic view of a filling chamber of the die casting machine of FIG. 1 during filling with oxygen.

FIG. 3 is a schematic view of a filling chamber of the die casting machine of FIG. 1 during filling with molten metal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Die-cast machine 12 Die-casting mold 14 Hollow molding cavity 16 Filling chamber 18 Inlet opening 20 Molten metal 22 Piston rod 24 Piston 26 Extraction pin 28 Vacuum suction pipe 30 Vacuum pump 32 Sealing means 34 Oxygen nozzle 36 Control valve 38 Oxygen source

 ──────────────────────────────────────────────────の Continuation of the front page (71) Applicant 591059652 Badische Bahnhofstrasse 16, CH-8122 Neuhausen am Rheinfall, Switzerland

Claims (7)

[Claims] A molten metal (20) is filled in a filling chamber (1).
6) die casting method for light metal such as aluminum and aluminum alloy, wherein said molding cavity (14) is configured to be introduced into said molding chamber (14) by said piston (24) from said filling chamber (16). ) Is pre-evacuated and then filled with oxygen, evacuated again after being filled with oxygen and before the injection of the molten metal (20), and finally with the molten metal (20) in the molding cavity (14). A) die casting method of light metal, characterized by injecting into light metal. 2. The method as claimed in claim 1, wherein the molding cavity is pre-evacuated to a residual pressure of less than 100 mbar before being filled with oxygen. 3. The light metal die-casting method according to claim 1, wherein when the molding cavity is filled with oxygen, the inside of the cavity is maintained at a pressure exceeding atmospheric pressure. . 4. An oxygen atmosphere is maintained around the molding cavity so that gas and water vapor do not flow back into the molding cavity during exhaustion from the molding cavity. Item 6. The light metal die-casting method according to item 1, 2 or 3. 5. The step of pre-evacuating, filling the oxygen, and re-evacuating are performed before introducing the molten metal (20) into the filling chamber (16). The light metal die-casting method according to any one of claims 1 to 4, characterized in that: 6. A first molten metal (20) is introduced into the filling chamber (16) and then continues until the molten metal (20) enters the molding cavity (14).
The pre-evacuating step, the step of filling with oxygen, and the step of re-evacuating are performed during the filling step of claim 1. Die casting method for light metal. 7. The residual gas content is 100 g of aluminum.
2. The method as claimed in claim 1, wherein the number of the holes is less than 1 cm ^3.
An aluminum or aluminum alloy die-cast product manufactured by using the light metal die-casting method according to any one of claims 1 to 6.