JP3794017B2 - Injection molding method for metal molded products - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for injection molding into a metal molded article by melting a low melting point metal material such as zinc, magnesium or an alloy thereof.
[0002]
[Problems to be solved by the invention]
Die casting is used for casting low melting point non-ferrous metals, but die casting requires a melting furnace that completely melts the metal material, and casting is performed by pumping hot water from the melting furnace or extruding it with a plunger. Therefore, in the same way as in the case of plastic materials, the melting is performed by melting the granular metal material supplied from the rear part of the heating cylinder while moving it forward of the heating cylinder by screw rotation. After accumulating and weighing in the chamber, injection filling from the nozzle at the tip of the heating cylinder into the mold is being performed by the screw advance.
[0003]
When such injection molding is adopted for a metal material, the problem is the difficulty of melting and transferring the metal material by screw rotation and the instability of measurement.
Since most of the melting in the plastic material is due to shear heat generation, the screw is formed to have a larger diameter as it becomes the tip portion, and the screw groove serving as the material flow gap is formed relatively shallow. However, in the case of molten plastic, there is a difference in the coefficient of friction at the boundary surface of the inner wall of the heating cylinder. Therefore, even if the flow gap is narrow, the forward transfer by the screw rotation is performed smoothly.
[0004]
On the other hand, a metal material that has been completely dissolved to a liquid phase has a viscosity that is incomparably smaller than that of a plastic material. Therefore, there is almost no difference in the coefficient of friction at the two boundary surfaces. It is difficult to generate a transfer force due to screw rotation as in the case. In addition, in the low-viscosity liquid phase, the pressure does not increase enough to push the screw backward, so the screw does not easily retreat due to the material pressure, and the amount stored in the front chamber differs only by screw rotation. There are technical difficulties in quantification.
[0005]
Therefore, injection molding is performed in a semi-molten state by limiting the melting temperature to a temperature not lower than the solidus temperature and not higher than the liquidus temperature without completely melting the metal material. In the molten metal in the above temperature range, the structure is said to be in a semi-molten state (thixotropic property), and in this state, flow resistance occurs in the molten metal, and measurement by transfer and retraction by screw rotation is possible. Become. Therefore, molding of a metal molded product by injection molding so far has been based on such a method.
[0006]
However, the molding method is simply an application of plastic material injection molding as it is, and unlike metals, metal has good thermal conductivity and is easy to cool, so the temperature of the molten metal in the heating cylinder can be maintained. There are difficulties. Also in the molding of the metal material, the heating cylinder is heated by the outer peripheral band heater to maintain the set temperature. However, there is no heating means on the screw side, and it is easy to radiate heat from the rear end. For this reason, uneven temperature tends to occur in the molten metal in the screw groove, and in order to prevent this by stirring, rotating the screw is because the screw itself also serves as a molten metal material transfer member. It is considered impossible because of excessive supply of materials.
[0007]
The present invention has been conceived in order to solve the above-described problems in the case of injection molding of a metal material in a semi-molten state, and the object thereof is 3 of melting, transfer and injection which have been indispensable so far. Without adopting a screw having a function, it is possible to stir the molten metal in the melting vessel by combining the stirring means and the injection means that are operated separately, thereby bringing the melting temperature of the metal material within the set temperature range. An object of the present invention is to provide a new injection molding method capable of forming a metal molded product having a thixotropy property in a maintained state.
[0008]
[Means for Solving the Problems]
This invention according to the above object has a metering chamber of a required length communicating with the nozzle opening at the tip, and is provided with a stirring means rotatably inside, and the tip is formed at the injection plunger at the center of the stirring means. A cylindrical melting cylinder, in which the injection means is slidably inserted through the injection means, and the injection plunger is slidably fitted in the measuring chamber, is inclined with the nozzle member at the tip of the melting cylinder facing downward, and the inside of the melting cylinder A granular metal material is supplied continuously or intermittently from the supply port, and the metal material is heated and melted to a temperature equal to or higher than the liquidus temperature by external heat, and is homogenized by the stirring means and accumulated in the melting cylinder. A part of the molten metal material is fed into the measuring chamber by the negative pressure generated by the retraction of the injection plunger and weighed. In the process from feeding into the measuring chamber to injection filling into the mold, Metal material above solidus temperature Cooled to liquidus temperature below the temperature injected and filled into a mold, tissue forming the metal molded article of thixotropic properties, is that.
[0009]
The invention also has an injection means having a metering chamber of a required length communicating with the nozzle opening at the tip portion, the stirring means being rotatably provided therein, and the tip portion being formed as an injection plunger at the center of the stirring means. Is inserted into the measuring chamber so that the injection plunger is slidably fitted into the measuring chamber, and the nozzle member at the tip of the dissolving tube is inclined downward and supplied into the melting tube. A granular metal material is continuously or intermittently supplied from the mouth, and the metal material is heated and melted to a temperature not lower than the solidus temperature and not higher than the liquidus temperature by external heat, and the molten metal material is half-heated by the stirring means. Accumulated in the melting cylinder while maintaining stirring in a molten state (thixotropic state), a part of the semi-molten metal material is sent to the measuring chamber by the negative pressure generated by the retraction of the injection plunger, and is measured. Injection while maintaining a semi-molten state By injection filled in a mold by advancing the plunger, the tissue is formed into a metal molded article of thixotropic properties, is intended to refer.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a molding machine capable of carrying out an injection molding method for a metal molded product according to the present invention.
[0011]
In the figure, 1 is an injection mechanism, 2 is a mold clamping mechanism, both are installed on the upper surface of the machine base 3, 4 is a pedestal 4 installed so as to be able to move forward and backward with respect to the mold clamping mechanism 2, and a gantry 5 whose upper surface is inclined is rear The injection mechanism 1 is installed on the mount 5 so that the nozzle side is inclined downward with respect to the mold clamping mechanism 2.
[0012]
The injection mechanism 1 includes a cylindrical melting cylinder 11 serving as a melting container for a metal material, an agitation and injection means described later, and an injection cylinder 12 provided at a rear end portion of the melting cylinder 11 with a space therebetween. The electric motor 14 for stirring attached to the support leg 13 below the rear end of the melting cylinder 11 and a delivery device 15 for supplying a granular metal material into the melting cylinder. The delivery device 15 includes a horizontal cylinder 15a and an internal screw shaft 15c that is rotated by an electric motor 15b provided at the end of the cylinder. Although not shown in the figure, it has a structure in which a heater for preheating the material can be attached around the cylinder as necessary.
[0013]
The melting cylinder 11 includes a nozzle member 10 at the tip and a band heater 16 on the outer periphery. The inside of the distal end portion of the melting cylinder 11 communicating with the nozzle hole of the nozzle member 10 is formed in a cylindrical measuring chamber 17 having a required length reduced in diameter to be smaller than the inner diameter of the melting cylinder 11. In the illustrated example, the inside of the rear part of the nozzle member 10 attached to the tip of the melting cylinder by the tip member 18 is reduced in diameter to be smaller than the inner diameter of the melting cylinder, and the inside of the rear part is the measuring chamber 17 communicating with the inside of the melting cylinder. Depending on the case, the inner diameter of the tip member 18 may be reduced to form the measuring chamber 17, and a nozzle tip may be attached to the tip member 18.
[0014]
A supply port 19 is opened in the middle upper part of the melting cylinder 11 having such a measuring chamber 17 at the tip, and the delivery device 15 is connected to the supply port 19 by connecting the pipe 20. It is. Further, the rear end of the melting cylinder 11 is in an open state, and a stirring member 21 and an injection member 22 that constitute the stirring and injection means are provided therein.
[0015]
The stirring member 21 includes a rotating shaft in which a plurality of stirring blades 24 and 24 are intermittently formed on the outer periphery of the distal end portion of a hollow shaft portion 23 at a fixed position having a through hole in the center. These stirring blades 24, 24 have an outer diameter substantially equal to the inner diameter of the melting cylinder 11. A partition flange 25 that also serves as a guide and is in contact with the inner peripheral surface of the melting tube 11 is integrally formed around the shaft portion behind the stirring blade 24 of the hollow shaft portion 23.
[0016]
A pulley 26 is fixed to the end of the hollow shaft portion 23 protruding from the opening end of the melting cylinder 11, and a timing belt 28 extends over the pulley 26 and a pulley 27 at the drive shaft end of the electric motor 14. The stirring member 21 is rotated in one direction or reciprocally rotated in the melting cylinder by the electric motor 14, and the molten metal can be stirred by the stirring blades 24, 24. .
[0017]
The injection member 22 is inserted into the through-hole of the hollow shaft portion 23 and is slidably provided in the center of the stirring member 21, and attached to the tip of the injection rod 29 and protrudes from the front surface of the stirring member 21, The injection plunger 30 is fitted in the measuring chamber 17. The injection plunger 30 moves forward and backward without exiting the measuring chamber by the injection rod 29. Further, a ring 29a is formed in multiple stages around the outer periphery of the injection rod 29 above the partition flange 25 to serve as both a rod guide and a back flow prevention of molten metal that has permeated into the clearance.
[0018]
The injection plunger 30 has an outer diameter that can be inserted into the measuring chamber 17 with a sliding clearance, and includes a seal ring 31 on the outer periphery thereof. The seal ring 31 is formed by directly adopting a heat-resistant piston ring made of special steel or the like. Although the details of the seal ring 31 are omitted in the drawing, the diameter is reduced at the time of negative pressure on the measuring chamber side due to the retreat of the plunger, and the clearance is expanded to smoothly suck and transfer the molten metal material into the measuring chamber. In order to prevent the backflow of the molten metal from the clearance by expanding the material pressure on the weighing chamber side at the time of injection, a required gap is fitted between the groove bottom and the groove wall in the annular groove around the plunger. It is.
[0019]
The injection cylinder 12 integrally has a support leg 32 below the front end of the cylinder. The injection cylinder 12 is integrally connected to the melting cylinder 11 with a tie bar 33 disposed on both sides, and a piston 34. Is connected to the rear end of the injection rod 29 protruding from the rear end of the hollow shaft portion 23, and moves the injection rod 29 forward and backward together with the injection plunger 30 at the front end.
[0020]
The injection cylinder 12 and the melting cylinder 11 have support shafts 40 and 40 provided with end portions of the support legs 13 and 32 projecting on both lower sides of the support cylinders 40 and 40 arranged side by side on both sides of the inclined upper surface of the gantry 5. The nozzle member 10 is attached downward and inserted downward, thereby constituting the injection mechanism 1 inclined with respect to the mold clamping mechanism 2.
[0021]
Further, on both sides of the injection mechanism 1, a nozzle touch device 44 including a hydraulic cylinder 42 and a long-axis rod 43 is attached to bearing members 46 on both sides of a nozzle touch block 45 erected at the center of the tip of the base 4. While the tip end is pivotally mounted, the hydraulic cylinder 42 is provided between the rear end of the melting cylinder and the front end of the injection cylinder, and the cylinder rear end is rotatably attached to the injection cylinder. The nozzle touch device 44 also functions as a retracting device for repairing or maintaining the injection mechanism 1.
[0022]
The upper surface of the gantry 5 is formed as an inwardly inclined surface having an angle of about 45 °, and the support shaft 40 is attached to the upper surface with members 41 and 41 at both ends. Although not shown in the figure, the pedestal 5 is pivotally mounted and fixed to a portal-type receiving seat 6 installed on the rear end of the pedestal 4, and extends from the inner center of the receiving seat 6 to the nozzle touch block 45. A nozzle touch device 48 of a nozzle member 47 provided horizontally with a member 52 on the front surface of the nozzle touch block 45 is disposed.
[0023]
The hydraulic cylinder 49 of the nozzle touch device 48 is fixed to a receiving member 50 in the center of the base 4 installed on the machine base 3, and a rod member 51 connected to an internal piston rod (not shown) has a tip thereof. Are connected to the nozzle touch block 45, and the rod member 51 is moved forward and backward to move the base 4 together with the injection mechanism 1 on the upper surface of the gantry 5 so that the nozzle touch of the nozzle member 47 to the mold 7 can be performed. It is.
[0024]
The inner upper portion of the nozzle touch block 45 is formed on an inclined rear surface positioned perpendicular to the axis of the nozzle member 10 of the injection mechanism 1, and a nozzle touch gate is opened on the inclined rear surface. In addition, a hot runner 53 that connects the nozzle member 47 and the nozzle member 10 of the injection mechanism 1 is bent inside the nozzle touch block 45 so that the injection mechanism 1 is inclined with respect to the mold clamping mechanism 2. Even if it is done, the nozzle touch is performed without any gaps, and leakage of molten metal during injection filling is prevented.
[0025]
In order to form a metal molded article, for example, a molded article made of magnesium (AZ91D) by the first injection molding method of the present invention using the molding apparatus having the above configuration, first, the melting tube 11 is moved by the outer band heater 16. Heat to a set temperature above the liquidus temperature (620 ° to 680 ° C.) to bring the inside to a high temperature above the melting temperature. Further, the nozzle touch block 45 and the nozzle member 47 also have a solidus temperature (470 ° C.) or higher and a liquidus temperature (595 ° C.) or lower while the molten metal material passes through the runner and is injected and filled into the mold 7. Although not shown in the figure so as to reach the temperature, it is heated by an external heater. At this time, the space portion in the melting cylinder is made an inert gas atmosphere. Although the supply of the inert gas is omitted in the drawing, for example, a supply pipe for an inert gas cylinder can be connected to the pipe line 20.
[0026]
Next, the hollow shaft 23 is rotated at a set speed by the electric motor 14 to be in a stirring state. Therefore, granular magnesium is supplied as metal material from the supply port 19 into the melting cylinder 11 by the delivery device 15. Since the melting cylinder 11 is inclined downward, the metal material immediately melts at the portions of the stirring blades 24 and 24 rotating together with the hollow shaft portion 23 to become hot water. Furthermore, the continuously supplied metal material falls into the hot water stored therein, is melted by the heat of the hot water, and is mixed into the hot water by the stirring blades 24 and 24. As a result, the molten metal material is homogenized at the same time as melting in a very short time.
[0027]
Further, the molten metal material is stored in the front portion of the melting cylinder 11 as it is when the injection plunger 30 is in the forward position. The amount of storage may be about 10 shots, and continuous molding can be performed without any problem if one shot of material is supplied for each molding.
When a predetermined amount of molten metal material is stored, the injection plunger 30 is moved backward. This backward movement is limited to a range where the seal ring 31 stays in the measuring chamber 17, and a part of the molten metal material stored by the backward movement flows into the measuring chamber 17.
[0028]
The molten metal material flows into the measuring chamber 17 due to a negative pressure generated by the backward movement of the injection plunger 30 in the measuring chamber. This is because the molten metal material previously injected is cooled and solidified at the nozzle port of the nozzle member 47 and remains as a cold plug, the nozzle side of the measuring chamber 17 is blocked, and the inflow from the nozzle port is prevented. When a backward force is applied to the injection plunger 30 at the forward limit in such a state, the measuring chamber 17 that is expanded with the backward movement becomes negative pressure.
[0029]
Due to this negative pressure, the diameter of the seal ring 31 of the injection plunger 30 is reduced, and the molten metal material flows from the clearance around the seal ring into the expanding measuring chamber 17 by the negative pressure and fills the chamber. become. Thus, a large negative pressure that makes it difficult to forcibly retract the injection plunger 30 is not generated in the measurement chamber 17, and material measurement is performed by the smooth movement of the injection plunger 30.
Therefore, if the reverse flow rate due to the forward movement of the injection plunger 30 at the time of injection is anticipated and the measurement completion position is set, and then the process is switched to injection filling and the injection plunger 30 is moved forward to the forward limit, the set amount is always maintained. Injection filling of the molten metal material into the mold 7 becomes possible.
[0030]
Even during injection filling from such material weighing, since the stirring member 21 and the injection member 22 are separate in the melting cylinder, the stirring of the molten metal material by the rotation of the stirring blades 24, 24 continues. Thus, even if a new metal material is continuously or intermittently supplied to the melting cylinder 11, the molten metal material in the melting cylinder can be made uniform.
[0031]
Further, since the injection member 22 does not rotate for the purpose of melting the metal material, it is not necessary to manufacture the injection rod with a large diameter like conventional screws in consideration of the rotational torque. Also, since melting is not performed by shearing heat generation, a large gap can be formed between the inner wall surface of the melting cylinder and the outer surface of the hollow shaft, which makes it difficult to use several screws. Therefore, it is easy to store the molten metal material, and the temperature maintaining effect of the molten metal material is further improved.
[0032]
The molten metal material after measurement is pressurized by the forward movement of the injection plunger 30, pushes away the cold plug that closes the nozzle opening of the nozzle member 47, and reaches the nozzle member 47 from the nozzle touch block 45. After passing through 53, the cavity of the mold 7 is injected and filled.
[0033]
In the process from measurement to injection, the molten metal material having a temperature higher than the liquidus temperature is maintained by heating the nozzle touch block 45 and the nozzle member 47 to a temperature higher than the solidus temperature and lower than the liquidus temperature. Therefore, it passes through the hot runner 53 and is cooled while being injected and filled into the mold 7 so that it is in a semi-molten state. Further, a certain amount of agitation occurs due to the disturbance of the flow due to the flow resistance. The molded product is a product having a thixotropic composition.
[0034]
In the second injection molding method of the present invention, all the temperatures of the melting cylinder 11, the nozzle touch block 45, and the nozzle member 47 are set so that the temperature of the molten metal material is not lower than the solidus temperature and not higher than the liquidus temperature. In this temperature range, the metal material is heated and melted in a semi-molten state and stirred by the stirring member 21 to form a thixotropy state. The measurement by moving the injection plunger 30 while maintaining this state and the gold Injecting and filling the mold 7 is performed. Thus, the molded magnesium article is also a product having a thixotropic structure.
[0035]
In any of the first and second injection molding methods, since the stirring member 21 and the injection member 22 are separate in the melting cylinder 11, the stirring blade 24 is used regardless of the metering and injection steps. 24, the molten metal material is continuously stirred, and even if a new metal material is continuously or intermittently supplied to the melting cylinder 11, the molten metal material is uniformly distributed in the melting cylinder. Can be achieved.
[0036]
Further, since the injection member 22 does not rotate for the purpose of melting the metal material, it is not necessary to manufacture the injection rod with a large diameter like conventional screws in consideration of the rotational torque. Also, since melting is not performed by shearing heat generation, a large gap can be formed between the inner wall surface of the melting cylinder and the outer surface of the hollow shaft, which makes it difficult to use several screws. This makes it easy to store the molten metal material in minutes, eliminates the temperature unevenness of the semi-molten metal material, and facilitates the injection molding of thixotropic metal molded products with better molding accuracy than conventional molding methods. .
[Brief description of the drawings]
FIG. 1 is a schematic vertical side view of a molding machine that enables an injection molding method for a metal molded product according to the present invention to be carried out.
FIG. 2 is a side view showing a part in the same manner.
FIG. 3 is a vertical side view of the distal end portion of the melting cylinder when the injection plunger is retracted.
FIG. 4 is a vertical side view of the distal end portion of the melting cylinder when the injection plunger is advanced.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Injection mechanism 2 Clamping mechanism 10 Nozzle member 11 Melting cylinder 12 Injection cylinder 15 Metal material delivery device 17 Measuring chamber 21 Stirring member 22 Injection member 23 Hollow shaft portion 24 Stirring blade 29 Injection rod 30 Injection plunger 31 Seal ring 45 Nozzle touch Block 47 Nozzle member

Claims (2)

  It has a metering chamber of the required length that communicates with the nozzle port at the tip, and is equipped with a stirring means that can rotate freely, and an injection means that has a tip formed as an injection plunger at the center of the stirring means is inserted in a freely reciprocating manner. Then, a cylindrical melting cylinder in which the injection plunger is slidably fitted in the measuring chamber is inclined with the nozzle member at the tip of the melting cylinder facing downward, and a granular metal is introduced into the melting cylinder from the supply port. The material is supplied continuously or intermittently, and the metal material is heated and melted to a temperature equal to or higher than the liquidus temperature by external heat, and is homogenized and accumulated in the melting cylinder by the stirring means. The measured molten metal material is measured at the solidus temperature in the process from feeding into the weighing chamber due to the negative pressure generated by the retraction of the injection plunger and from filling the metering chamber to injection filling into the mold. Above, cool to a temperature below the liquidus temperature And by injection filled in a mold, injection molding method of a metal molded article organization characterized by forming the metal molded article thixotropic properties.   It has a metering chamber of the required length that communicates with the nozzle port at the tip, and is equipped with a stirring means that can rotate freely, and an injection means that has a tip formed as an injection plunger at the center of the stirring means is inserted in a freely reciprocating manner. Then, a cylindrical melting cylinder in which the injection plunger is slidably fitted in the measuring chamber is inclined with the nozzle member at the tip of the melting cylinder facing downward, and a granular metal is introduced into the melting cylinder from the supply port. The material is supplied continuously or intermittently, and the metal material is heated and melted to a temperature not lower than the solidus temperature and not higher than the liquidus temperature by external heat, and the molten metal material is semi-molten (thixotropic) by the stirring means. ) Is kept in the melting cylinder while maintaining agitation, and a part of the semi-molten metal material is fed into the measuring chamber by the negative pressure generated by the retraction of the injection plunger and measured, and the semi-molten state is maintained after the measurement. While moving the injection plunger More and injection filled in a mold, injection molding method of metal formed article, characterized in that the tissue is formed into a metal molded article thixotropic properties.

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