US3117355A - Apparatus for improvement of die castings by vibration - Google Patents

Description

Jan. 14, 1964 J. A. WEBER 3,117,355

APPARATUS FOR IMPROVEMENT 0F DIE CASTINGS BY VIBRATION Filed June 4, 1962 4 Sheets-Sheet 1 INVENTOR.

QW%M APPARATUS FOR IMPROVEMENT OF DIE CASTINGS BY VIBRATION Filed June 4, 1962 J. A. WEBER Jan. 14, 1964 4 Sheets-Sheet 2 J. A. WEBER Jan. 14, 1964 APPARATUS FOR IMPROVEMENT 0F DIE CASTINGS BY VIBRATION Filed June 4, 1962 4 Sheets-Sheet 3 J. A. WEBER Jan. 14, 1964 APPARATUS FOR IMPROVEMENT 0F DIE CASTINGS BY VIBRATION 4 Sheets-Sheet 4 Filed June 4, 1962 United States Patent M 3,117,355 APPARATUS FQR IMPRGVEMENT OF Dill CASTINGS BY VIBRATIQN John A. Weber, High Point, N.C., assignor to Adamslviillis Qorporation, loint, N.C., a corporation of North Caroline Filed June 4, 1962, Ser. No. 199,770 1 Claim. (Cl. 2268) The present invention relates to apparatus for improvement of die castings by vibration at sonic frequencies.

One of the objects of the invention is the provision of improved apparatus for subjecting the metal in a die casting mold to mechanical vibration of a sonic frequency during the time that the molten die cast metal is being injected into a closed die under pressure and While the casting is soli ifying.

Another object of the invention is the provision of an improved apparatus for making die castings which results in improved physical characteristics of the die castings, such as a marked increase in tensile strength and in the yield strength of the castings.

Another object of the invention is the provision of an improved apparatus which results in the substantial elimination of gas porosity in the metal castings and in an increase of ductility.

The present application is a continuation-in-part of my prior application Ser. No. 70,430, filed November 1, 1960, on Methods of Die Casting.

Another object of the invention is the provision of improved apparatus which bring about a substantial reduction of the grain size and a reduction in the size of dendrites in the castings, which also gives the metal better polishing characteristics.

Another object of the invention is to effect a substantial elimination of microshrinl:age and an increase in density of from 6% to 8% in the metal of the castings.

Another object is the beneficial alteration in the formation of dcndritic openings in the solid solution matrix.

Another object of the invention is to effect a reduction in the number of reject castings and to effect a saving in time and labor by speeding the cycling time of ti e die cast machine.

Another object of the invention is the simplification of the methods of making die castings by reducing to a minimum the complexity of such processes and the accomplishment of the foregoing results with the most simple and economical and effective apparatus.

Another object of the invention is the provision of improved apparatus for vibrating die castings during the injection of the metal and its solidification, which apparatus is simple in construction, adapted to be manufactured economically, which has a minimum number of parts, and which is adapted to effect vibration at different frequencies as required to obtain optimum results by vibrating various alloys at frequencies which are dependent upon the specific gravity of the alloy.

Other objects and advantages of the invention will be apparent from the following description and the accompanying drawings, in which similar characters of reference indicate similar parts throughout the several views.

Referring to the drawings, of which there are four sheets,

FIG. 1 is a fragmentary side elevational view of a die casting machine embodying the invention;

FIG. 2 is a fragmentary view in perspective showing the ejector half of the die With the cover removed;

FIG. 3 is a fragmentary sectional view showing the ejector half of the die with its cavity and the mode of attachment of the vibrator, taken on the plane of the line 33 of FIG. 2;

3,ll?,355 Patented .Fan. 14, l fid FIG. 4 is a. bottom plan view in partial section of the vibrator, taken on the plane of the line 44 of FIG. 7;

FIG. 5 is a fragmentary sectional View taken on the plane of the line 55 of FIG. 7;

FIG. 6 is a fragmentary top plan view of the end of the shaft and the driving gears and eccentric weight;

FIG. 7 is a fragmentary sectional view of the vibrator, taken on the plane of the line 77 of FIG. 4;

FIG. 8 is a perspective view of the vibrator mechanism.

Referring to FIGS. 1 and 2, these are assembly drawings of a die casting machine which is equipped to subject the metal of the die castings to vibration at sonic frequencies according to the invention.

in FIG. 1 29 indicates in its entirety the die casting machine and its equipment, in which 21 indicates the movable die platen and 22 the stationary platen. The stationary platen is supported by the base 23 and carries guides 24 and 24 which support the movable die platen 21 for straight line motion on the stationary platen 22.

25 indicates the mold base, which is carried by the movable die platen and as indicates the ejector half of the die. The cover half of the die is indicated at 27 carried by the stationary platen 22; and the vibrator is indicated at 7:8 and is attached to the ejector half of the die 26.

Referring to FIG. 2, 2 inudicates the vibrator base plate. in FEG. 1 3i? indicates the plunger rod and 31 the plunger piston, which moves in a sleeve bushing 32 for injecting die cast metal into the die cavity. 33 indicates the line to a source of volt 60 cycle AC; and this line exends to a limit switch 34, which is connected to another line 35 extending to the vibrator 28.

The limit switch 34% has an actuating member 36, which is moved to the left by the annular shoulder 37 on the plunger rod fit; when the plunger rod moves in to inject metal; and the limit switch actuating member 36 is spring actuated to return to its position in FIG. 1 when the plunger rod 30 is retracted to this position.

The limit switch 34 is carried by a limit switch bracket 33, which is mounted on a fixed frame member 39 carried by the tie bars at) and at.

The ejector half of the die 26 is carried by the back platen 21 by means of a plurality of screw bolts, the heads of which are located in the counterbores 42; and the cavity of the mold, the shape and size of which varies with each different casting, is indicated at 43 with the inlet 44; and the approximate initial freeze point is indicated at 45'.

Referring to PEG. 3, this is a fragmentary sectional view showing the vibrator 28 attached to the ejector half 26 of the die. The die cavity is indicated at 43. The ejector half 25 is provided with a plurality of threaded bores 47, such as, for example, four bores, each of which contains a bolt 43, the threaded end 4th of which is threaded into the bores 47.

Each of the bolts 48 passes through a base plate 59, comprising a rectangular metal plate having four bores 51 receiving the bolts 48 and four counterbores 52 receiving the heads 53 of the bolts 48.

The vibrator 28 has a base 29 which is securely bolted to the base plate 553 by a plurality of screw bolts 54 passing through the vibrator base and threaded into the threaded bores 55 in the base plate 5% The striker plate 56 is spaced slightly from the ejector half 26 of the die, as indicated by the spacing 5'7; and the striker plate is bolted to the base plate 54} by a plurality of screw bolts 58 threaded into threaded bores 59 and having their heads 68 countersunk in the striker plate.

The vibrator and base plate 50 and the striker plate 56 are urged away from the ejector half 26 of the die by a plurality of helical coil springs 61, which are compressed 89 between the surface 62 of the ejector half of the die and the surface 63 of the base plate.

Thus the vibrator is resiliently mounted on the bolts 48 and it is adapted to impact against the ejector half of the die when the vibrator is operated.

in some embodiments of the invention the base 29 of the vibrator may directly engage the end surface of the head 64 of a vibrator pin which has a cylindrical shank 65 extending through the bores 66, 67 in the base plate and striker plate to its end 68 which extends into the cavity and directly engages the die cast metal in the cavity, thereby subjecting the metal itself to the vibrations of the vibrator.

Referring to FIG. 8, this is a view in perspective of a vibrator having a magnetic field structure 6% having a through bore 70 containing the armature 7 1 rotatably supported upon a shaft 72 carried by ball hearings in the end plate 73.

The shaft 72 drives a gear 74 which in turn drives a second gear 75 that is fixedly secured to the gear '76. The gear 76 drives a pinion 77 which is mounted for free rotation on the shaft 72; and the pinion 77 is secured to a hub 78 supporting an eccentric weight 79 on a ball hearing 80'.

Referring to FIGS. 47, the housing 81 comprises a pair of half housing members 82, 33 clamped on a central band 34 mounted on a magnetic field structure 69.

The motor coils are indicated at 85 and the armature at 71 carried by shaft 72. Through bolts 86 extend through the field structure 69 and mount a pair of end plates 73 and 37 on the field structure; and the plates 87 support ball bearings 80 at each end of the shaft for rotatably mounting the shaft 72.

The gears 74, 75, 76, and 77 are driven from the shaft 72; and the last gear 77 comprises an idler secured to the hub 78, which carries the eccentric weight 79. When the eccentric weight is rotated at a suitable speed, the eccens tric weight causes the vibrator to vibrate upon the bolts 48; and the vibrator impacts aginst the surface 62 of the ejector half by means of the striker plate 55.

The operation of the present apparatus is as follows:

The die is first closed, closing the cavity; and the die cast metal is injected into the cavity through the inlet 44 by the plunger 30, which is actuated by the plunger piston 31.

When the plunger 30 is actuated, it closes the limit switch 36, which connects the vibrator in circuit and starts the vibration, which subjects the die cast mold and the die cast metal in the mold to sonic vibrations.

The vibration continues during the injection and solidification, and is turned off when the plunger is retracted, which shuts off the limit switch 36. During the vibration of the vibrator the vibrator assembly impacts against the mold at the sonic frequency, and thereby employs the entire mass of the vibrator assembly for inducing vibration in the mold and the metal.

By impacting the vibrator assembly against the mold once for each rotation of the eccentric weight shaft, the same frequency is attained in the vibration as the rate of rotation of the off center shaft; and the vibrator is moved in one direction by the spring and in the opposite direction by the eccentric weight on the shaft, which also tends to move the vibrator in the other direction with the spring.

The vibrator and the vibrations are preferably applied to the die cast mold and to the metal therein at a point adjacent the initial freeze point of the metal in the mold; and this is usually opposite the point at which the metal is injected into the mold, since the cooling of the metal starts by its engagement with the cooler wall of the mold; and the metal is reflected from that point into the other parts of the mold, where it spreads and fills the mold, while simultaneously the growth of a dendrite structure takes place in the casting.

Dendrites are the tree-like crystalline growths which occur in the casting and which are initiated as the metal 4 engages the chill wall of the mold. The dendrites grow and interlace into minute pockets containing high solute or unaltered liquid metal; and as the chilling progresses, the high solute and unaltered liquid metal freezes and shrinks.

The sonic vibration of the mold and metal at this time increases the formation of the interlocking dendrites and reduces the size of the dentritic structure, causing formation of dendritic structure throughout the entire mold, thereby reducing the sub-microscopic voids and gas inclusions, and reducing the places Where hot tears may occur between dendrite arms.

By using the present method a better die fill is accomplished and a quicker freezing rate is promoted, resulting in a faster operating cycle and a fine porous-free casting with an exceptional surface condition. The dendrite structure is refined and the grain structure improved; and the density is increased in the metal by elimination of gas porosity.

The vibration according to the present method results in the expulsion of bubbles which tend to form at the inner surface of the mold, where the Waves have their nodes; and the gas expelled has a high percentage of air.

The degassifying action is increased at lower frequencies; and my method includes the provision of vents for permitting the escape of the entrapped gas at the node points; and therefore the mold preferably has bleeders extending from the node points to the perimeter of the die, such as, for example, vents in the form of grooves A" wide by .003" deep.

In order to ascertain where the bleeders should be located, the location of the nodes may be determined after a trial casting; and this may be ascertained by using X-ray or by sectioning the casting and observing the bubble lines.

The vibration is applied during the injection and solidification cycle; and when an electrically driven vibrator is employed, the vibration may be turned on by a limit switch located on the plunger in a cold chamber machine or a limit switch connected in the same circuit as the shot switch for a hot chamber machine when that is employed.

Another limit switch in each case may be employed for turning off the vibration on the return stroke of the piston of the die cast machine. A timing device may also be employed and connected into the wiring of the shot system of the die cast machine for turning on the vibration at the same time the injection takes place and for turning it off after solidification has occurred.

The frequency of the vibrations applied varies with the specific gravity or density of the metal; and the higher the specific gravity the higher the frequency, and the lower the specific gravity the lower the frequency which should be applied.

For example, the frequency preferably employed for various non-ferrous metals and for certain alloys is as follows:

The present apparatus results in a lesser number of reject castings. For example, on one case the number of rejects in which the present apparatus was used amounted to only 2%, While the same zinc part with a number of iron inserts die cast in the conventional manner resulted in rejects.

The present machine results in a definite increase in the number of shots per hour due to the accelerated set-up or freezing time of the metal.

Closer dimensional tolerance can be held and surface hardness and resistance to elongation is increased by the present method. The dwell time may be decreased from 20% to 25%; and the pressures employed may be lowered to a point where the metal enters the die as a stream rather than a spray. The life of the dies may be increased greatly.

The tensile strength of the metal in the resulting castings may be increased greatly, such as, for example, in aluminum alloy No. 380 the tensile strength is increased from 43,000 p.s.i. to 68,00072,000 p.s.i.

In the same alloy the yield strength was increased from 23,000 p.s.i. to 48,'00051,000 p.s.i. The elongation was decreased from 1.0% to 05%. Density was increased by approximately 4.5%.

The present machine for die casting results in marked improvement in the castings and a saving of time and labor; and the results accomplished may be summarized as follows:

(1) Degassificat-ion of metal while metal changes from liquid to solid state;

(2) Elimination of micro shrinkage;

(3) Reduction of grain size;

(4) Altering the formation of dendritic openings in the solid solution matrix;

(5) Reduction of size of dentrites;

(6) Increase in density by 6% to 8%;

(7) Decreased cycle time.

These results produce the following changes in physical characteristics of the castings and operations involved:

(I) Marked increase in tensile strength;

(II) Elimination of gas porosity in metal;

(III) Increase in ductility;

(IV) Speeds the cycling time of die cast machine;

(V) Give better polishing characteristics of metal;

(VI) Reduces rejects.

While I have illustrated a preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details of construction set forth, but desire to avail myself of all changes within the scope of the appended claim.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

A die casting machine, comprising, a supporting base, a fixed die platen carried by the base, guides carried by said fixed die platen, a movable die platen slidably mounted on said guides for translation, a die having an ejector half carried by said fixed platen, said die having a cavity provided with an inlet communicating with a cylinder for receiving a shot of molten casting metal, a shot plunger having a piston in said cylinder, and a solenoid for actuating said shot plunger, an electrically actuated vibrator carried by said die, said vibrator having a body movably mounted on said die, said vibrator body vibrating back and forth relative to said die and causing said die to vli brate during each vibration of said vibrator body, a limit switch for controlling the energization of said vibrator, said limit switch closing the vibrator circuit when the shot plunger is turned on to actuate the shot plunger and inject molten casting metal into the mold, projecting the molten metal aginst the cool wall of the metal mold cavity to initiate freezing action while reflecting the metal from the initial freeze point into other parts of the mold cavity, which is then filled, the said mold having a cylindrical bore extending through the wall of the mold from the cavity in the mold to a point adjacent the vibrator body, a cylindrical metal rod, located in said latter bore and slidably and vibratably mounted in said bore with the inner end of said rod in contact with the molten metal in said cavity and the outer end of the rod having a head engaged by the vibrator body and receiving the vibrations from said vibrator body on vibration of the vibrator body, the vibrator directly vibrating the metal in the mold cavity while the cavity is being filled and while the metal is being solidified, and the limit switch being turned off to stop the vibration when the shot plunger is retracted, the vibration expediting growth of dendrite structure, forming interlocking dendrites, reducing grain size, reducing voids and gas inclusions, increasing density and strength, increasing ductility and surface finish, and reducing the number of rejects.

References Cited in the file of this patent UNITED STATES PATENTS 1,938,276 Bell Dec. 5, 1933 1,994,705 Hill et al Mar. 19, 1935 2,265,333 Wry Dec. 9, 1941 2,284,704 Welblund et a1. June 2, 1942 2,871,535 Nelson Feb. 3, 1959 2,914,822 Nyselius Dec. 1, 1959 3,019,495 Cornell Feb. 6, 1962 FOREIGN PATENTS 259,624 Great Britain Oct. 7, 1926

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