CH667405A5 - DIE CASTING METHOD AND CASTING PRESSURE PISTON ARRANGEMENT FOR ITS DESIGN. - Google Patents

Description

DESCRIPTION

The invention relates to a die-casting method with a die-cast plunger arrangement, in which a plunger in a plunger cylinder is moved into the casting chamber of a die-casting machine with the aid of hydraulic medium, hydraulic medium being derived from the front of the plunger.

In such a die-casting process, the plunger is moved into the casting chamber and the casting metal located there is injected into the mold cavity. The cast metal is opposed by a different dynamic pressure determined by the shape of the mold cavity. This different dynamic pressure causes the plunger to retract in a jerky, uneven manner. This jerky retraction of the plunger mixes the cast metal with the air, which at the time was still in the mold cavity. There is a risk of gas absorption by the cast metal. This gas absorption prevents the temperability and the tempering of the die-cast aluminum parts produced in this way.

The object of the present invention is to develop a die-casting method with which the plunger is moved smoothly into the casting metal chamber and thus mixing of the casting metal with the air in the pressing chamber and in the mold cavity is avoided.

This task is solved by building up a defined back pressure in the hydraulic medium in the plunger cylinder on the front of the plunger. By this measure, a counter pressure counteracting the pressing pressure can be built up in the press cylinder, which absorbs the different dynamic pressure of the casting metal in the mold cavity and thus a smooth running of the

Press piston causes. Back pressure control in a range of 0-140 bar has proven to be practical and sufficient. The amount of back pressure depends on the wall thickness of the die-cast part to be cast.

Another object of the invention is to provide a die-cast plunger assembly for carrying out the method according to the invention. This is based on a die-cast plunger arrangement according to the preamble of claim 2.

This object is achieved in that an outlet throttle is arranged in the outlet pipe.

With this measure, a definable dynamic pressure can be opposed to the hydraulic medium running off when the plunger is retracted. This dynamic pressure acts as counter pressure on the side of the press piston facing away from the feed piston, in particular the multiplier piston, and absorbs any build-up impacts that may occur on the press piston rod.

In a further embodiment of the invention it is provided that the discharge throttle is adjustable by a predeterminable opening path within a throttle guide assigned to the discharge pipe. These measures can be used to regulate the flow rate in the discharge throttle. The dynamic pressure in the hydraulic medium can thus be regulated as a function of the wall thickness of the die-cast part to be cast. It is intended

that the discharge throttle is assigned a throttle gap and the throttle gap can be controlled via the opening path of the discharge throttle. A simple design of the discharge throttle provides that the throttle gap is conical.

A device according to the invention is shown as an exemplary embodiment in the accompanying drawing and is described in more detail below; show it:

Figure 1 shows the section through a die-cast plunger assembly with drain throttle in the drain pipe.

FIG. 2 shows a detailed representation of the flow restrictor according to section “A” in FIG. 1.

The die-cast plunger assembly 10 shown in FIG. 1 essentially consists of a press cylinder 12 in which a plunger 11 is arranged to be reciprocable. The plunger 11 is guided on a plunger rod 13 which, in turn, can be moved outside the press cylinder 12 as a plunger into a press chamber (not shown).

The press cylinder 12 is filled on both sides of the press piston 11 in chambers 16a and 16b with hydraulic medium which can be pressed against the press piston 11 by a multiplier piston 14 on the side facing away from the press piston rod 13. The multiplier piston 14 in turn is arranged in a multiplier cylinder 15 so that it can be pushed back and forth. When the multiplier piston 14 is shifted to the left, the hydraulic medium runs out of the chamber 16a through a drain pipe 17 and a valve 18 controlled via a control line 30.

After the end of the injection process, the pressure on the multiplier piston 14 is reduced and the chamber 16a is filled. The plunger 11 is thereby retracted.

To avoid hydraulic impacts, a cone valve 20 is provided in the outlet from the chamber 16a.

According to the detailed illustration shown in FIG. 2, a throttle body 24 is arranged in the drain pipe 17 and is adjustable via an opening path 25. The throttle body 24 forms on its upper side a conical annular throttle gap 26, through which the hydraulic medium flowing out of the chamber 16a is stowed during the pressure casting process and then through outlet openings 27 into the throttle outlet 28 ge2

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

3rd

667 405

will be led. The throttle gap 26 can be finely regulated; For this purpose, the throttle body 24 is guided in a guide 29 and can be moved mechanically or hydraulically via the opening path 25.

With the help of the throttle gap 26, a dynamic pressure is built up in the discharge pipe 17, which is transmitted as counter pressure to the side of the press piston 11 facing away from the multiplier piston 14. This back pressure prevents jerky retraction of the plunger 11 and thus mixing air with the pressed cast metal.

The back pressure can be regulated very finely via the throttle gap 26 in a range of approximately 0-200, preferably 0-140 bar. The back pressure required depends on the wall thickness and the wall thickness changes of the workpiece to be cast.

If the plunger 11 is to be reset to the right in FIG. 1 after the pressure casting process has taken place, the chamber 16a is filled with hydraulic medium via a connection, not shown. So that this filling of the chamber 16a can take place without the hydraulic medium being able to flow out through the line 17, the valve 18 receives a closing signal via the control line 30.

In order to prevent the pressure in the chamber 16a from rising excessively in the event of malfunctions, a pressure relief valve 19 is provided, which is connected via a line 22 and a line 23 to the throttle outlet 28 and, if it exceeds a predetermined pressure in the Chamber 16a opens, representing a short circuit to the throttle gap 26.

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

S

1 sheet of drawings

Claims (5)

667 405 PATENT CLAIMS 1. Die-casting method with a die-cast plunger arrangement, in which a plunger (11) is inserted into the casting chamber of a die-casting machine with the aid of hydraulic medium in a plunger cylinder (12), hydraulic medium (16a) being derived from the front of the plunger (11) is characterized in that a defined back pressure in the hydraulic medium (16a) is built up in the plunger cylinder (12) on the front side of the plunger (11). 2. Die-cast plunger assembly for performing the method according to claim 1, with a hydraulic medium-provided chamber (16b) which is adjacent to the back of the plunger (11) and the front of a feed piston (14), and with a drain pipe (17) for discharging the hydraulic medium (16a) from the front of the press piston (11), characterized in that an outlet throttle (24) is arranged in the outlet pipe (17). 3. Die-cast plunger assembly according to claim 2, characterized in that the discharge throttle (24) is adjustable by a predeterminable opening path (25) within a throttle guide (29) associated with the discharge pipe (17). 4. Die-cast plunger assembly according to claims 2 and 3, characterized in that the discharge throttle (24) is associated with a throttle gap (26) and the throttle gap (26) via the opening path (25) of the discharge throttle (24) is controllable. 5. Die-cast plunger assembly according to claim 4, characterized in that the throttle gap (26) is conical.