US3701378A - Method of injection die casting - Google Patents

Abstract

A method of injecting molten metal into a die cavity in a pressure die casting operation using a die which removably seats on a nozzle fed from an injection pump having a reciprocable plunger movable to cover entry ports in the pump chamber. After the plunger is advanced to close the ports and fill the die cavity, the plunger is locked and pressure by the plunger is maintained for a predetermined time, after which the pressure is released, followed after a further predetermined time by a short retraction and re-locking of the plunger while the die is being retracted from the nozzle.

Description

United States Patent Graham 1 Oct. 31, 1972 [54] METHOD OF INJECTION DIE 1,999,961 v 4/1935 Daesen ..l64/l l9 CASTING 1,618,223 2/1927 Pierce ..l64/3l8 3 270,378 9/1966 Madwed ..164/3l8 [72] Inventor: Eric Purdy Graham, Peterborough,

Ontario, Canada 3,474,854 10/1969 Mace ..164/318 [7 3] Assignee: Fisher Gauge Limited, Peter- Primary Examiner Robert Baldwin omano Canada Assistant Examiner-Joan S. Brown [22] Filed: Sept. 29, 1970 Atwmeywestell & Hanley [21] Appl. No.: 76,558 [57] ABSTRACT I A method of injecting molten metal into a die cavity [30] Forms" Application Priomy D in a pressure die casting operation using a die which 10, 1969 Great Britain 2/69 removably seats on a nozzle fed from an injection pump having a reciprocable plunger movable to cover U-S. 13, entry ports in the pump chamber After the plunger is [51] Int. Cl. ..B22d 27/10 advanced to close the ports and n h i cavity the [58] Field of Search ..164/1l3, 120, 136, 306, 312, plunger is locked and pressure by the plunger is main 164/313 318 tained for a predetermined time, after which the pressure is released, followed after a further predeter- [56] References C'ted mined time by a short retraction and re-locking of the UNITED STATES PATENTS plunger while the die is being retracted from the nozzle. 1,927,384 9/1933 Bauer ..164/318 2,119,242 5/1938 Flammang ..164/119 2 Claims, 1 Drawing Figure PATENTEDHBIQI I972 3 0 378 r lgl 1:! {1:1} I -13 'T"P INVENTOR. ERIC F?! GRAHAM time period until the metal in the die cavity has solidified, after which the plunger retracts and the die is then separated from the injection nozzle. An example of this operation is shown in US. Pat. No. 3,256,572 issued June 21, 196.6 to Fisher Gauge Works Limited, assignee of William F. Fisher.

This known method has several disadvantages,

namely:

a. The plunger, while maintaining pressure, slowly advances causing the molten metal in the injection chamber to creep past the piston and in doing so erodes the piston an shot sleeve very rapidly, greatly reducing the effective life of the injection unit.

b. The time during which the die is in contact with the nozzle is directly proportional to the time period of pressure maintenance and thus the die is being heated excessively while the nozzle is at the same time being chilled excessively. This requires additional external heat to the nozzle to render it hot enough for the next casting cycle. The additional heat causes rapid oxidation of the nozzle resulting in an abbreviated effective life.

c. If the time period of pressure maintenance is shortened at all, the injection plunger will retract before the metal in the die cavity has chilled. In so doing, a vacuum is created which extracts the still molten metal from the die cavity (suck-back") and results in porous castings being produced.

d. The injection portion of the cycle commences with the injection plunger fully retracted and the level of the metal in the gooseneck is at the level of the metal in the melting pot, which means that a portion of the gooseneck chamber is filled with air. Also the nozzle, the gate and the die cavity, are each full of air. As a result, when injection commences these combined volumes of air must be forced into the die cavity and compressed until injection pressure is reached. This compressed air will then appear as a void in the casting unless directed into a gate or a vented area.

e. A further disadvantage in this method is caused by the molten metal receding from the nozzle, causing immediate chilling of the nozzle. This is overcome by additional external heat with the associated problems outlined in item (b) above. It should also be noted that the injection chamber of the pump must be allowed to refill before the die is retracted from the nozzle. If the time is too short, the die will retract from the nozzle as the chamber is filling and the inertia of this inrushing molten metal will carry the metal up the nozzle and out thetip, resulting in drops of metal remaining on the outside of the nozzle tip. This prevents proper die alignment for the succeeding cycle. Too long a time period causes excessive chilling of the nozzle with the same results as those in item (b) above. Also the cycle period is extended resulting in production losses.

The present invention overcomes these disadvantages by providing a method of injecting molten metal into a die cavity using a die which removably seats on a nozzle fed from an injection pump having a plunger reciprocable in a chamber, and closable flow means for entry of molten metal into the chamber. The method in its broadest aspect comprises the steps of, in sequence:

a. seating the die on the nozzle;

b. retracting the plunger and opening the flow means to allow molten metal to fill the chamber;

c. closing the flow means and advancing the plunger V to inject molten metal under pressure through the nozzle into the die cavity;

d. maintaining pressure by the plunger on the molten metal in the chamber for a predetermined time to offset initial maximum shrinkage of metal in the die cavity as the metal in the die cavity solidifies;

e. releasing the pressure by the plunger and locking the plunger in its advanced position in the chamber as the metal in the die cavity continues to solidify; and

f. after a predetermined time, unlocking and retracting the plunger a short distance and re-locking the plunger, at the same time retracting the die from the nozzle.

The accompanying drawing shows, in elevation and partly in cross-section, an example injection pump for use with the invention.

In the drawings, a pump 10 is mounted on a pot 11 containing molten metal 1111. A plunger 12, hydraulically driven by a cylinder-piston assembly I3, moves in a cylinder 14 which has a chamber 15 connected by a gooseneck passage 16 to an injection nozzle 17. A gate 20, leading to a cavity 22 of a die 21 which is mounted on arms 23 is removably seatable on nozzle 17. A plurality of apertures or ports 18, all closable simultaneously by the downward movement of plunger 12, are located circumferentially in the wall of cylinder 14 and open from chamber 15 into the molten metal Ila of pot I].

In the operation of the injection pump, the die first advances to nozzle 17 after which plunger 12 is retracted (upwardly in the drawing) which opens ports 18 and allows chamber 15 to fill with molten metal through the ports from pot 11. When chamber 15 has been filled, plunger 12 is advanced (downwardly in the drawing) to displace molten metal through gooseneck passage 16 and nozzle 17 into the die cavity. After the die cavity has been filled in this manner, the pressure exerted by plunger 12 is maintained for a predetermined time period, after which the pressure is released but plunger 12 remains locked in its advanced position.

After a short period in this locked, non-pressurized position sufficient to allow the sprue in gate 20 to freeze, the-die is retracted from nozzle 17 and plunger 12 is retracted a short distance when it is again locked in position. i

It will be appreciated that when the die locks on nozzle 17 the nozzle is full of molten metal. Retraction of plunger 12 evacuates air from the sprue and die cavities and this reduces the atmospheric pressure in the die cavity until chamber 15 is filled with molten metal entering through ports 18. Now when the mold cavity is filled with molten metal by the advancement of plunger 12, a casting of increased density is obtained, due to less entrapped air.

When the die cavity has been filled, injection pressure is maintained only long enough to overcome initial (and maximum) shrinkage of the metal in the cavity as it solidifies or freezes. Pressure on plunger 12 by cylinder assembly 13 is then released, but plunger 12 is retained in its advanced position by locking, thus eliminating metal creepage past the plunger and resultant excess wear of the plunger.

As the die is retracted from nozzle 17 plunger 12 is retracted a short distance (upwardly in the drawing). By this step the overflow of molten metal from nozzle 17, caused by warming of the molten metal in the nozzle and the expansion of air trapped in gooseneck passage 16 from the previous cycle, is prevented. Also sinceplunger 12 is not retracted fully until the next cycle-the possibility of suck-back of molten metal from the die cavity is eliminated.

in the present method the die spends less time in contact with nozzle 17, which minimizes the undesirable l. A method of injecting molten metal into a die cavity using a die which removably seats on a nozzle fed from an injection pump having a plunger reciprocable in a chamber, and closable flow means for entry of molten metal into the chamber, comprising the steps of, in sequence:

a. seating the die on the nozzle;

b. retracting the plunger and opening the flow means to allow molten metal to fill the chamber;

0. closing the flow means and advancing the plunger to inject molten metal under pressure through the nozzle into the die cavity;

d. maintaining pressure by the plunger on the molten metal in the chamber for a predetermined time to offset initial maximum shrinkage of metal in the die cavity as the metal in the die cavity solidifies;

e. releasing the pressure by the plunger and locking the plunger in its advanced position in the chamber as the metal in the die cavity continues to solidify; and

f. after a predetermined time, unlocking and retracting the plunger a short distance and re-locking the plunger, at the same time retracting the die from the nozzle.

2. A method as claimed in claim 1 in which a plurality of ports opening into the chamber and constituting the flow means are opened by retracting the plunger and closed by advancing the plunger.

Claims (2)

1. A method of injecting molten metal into a die cavity using a die which removably seats on a nozzle fed from an injection pump having a plunger reciprocable in a chamber, and closable flow means for entry of molten metal into the chamber, comprising the steps of, in sequence: a. seating the die on the nozzle; b. retracting the plunger and opening the flow means to allow molten metal to fill the chamber; c. closing the flow means and advancing the plunger to inject molten metal under pressure through the nozzle into the die cavity; d. maintaining pressure by the plunger on the molten metal in the chamber for a predetermined time to offset initial maximum shrinkage of metal in the die cavity as the metal in the die cavity solidifies; e. releasing the pressure by the plunger and locking the plunger in its advanced position in the chamber as the metal in the die cavity continues to solidify; and f. after a predetermined time, unlocking and retracting the plunger a short distance and re-locking the plunger, at the same time retracting the die from the nozzle.

2. A method as claimed in claim 1 in which a plurality of ports opening into the chamber and constituting the flow means are opened by retracting the plunger and closed by advancing the plunger.

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