Injection molding device and injection molding method using volume expansion mechanism

Abstract

To provide an injection molding apparatus which dramatically reduces the amount of air remaining in a cavity and enables the manufacture of a wax pattern that is more faithful to the shape of the cavity. The injection molding apparatus (10) has an injection section (24) capable of coming into contact with a rubber mold (3), a wax tank (21) for pressurizing and storing wax, a vacuum tank (22) connected to a vacuum pump, a wax valve (31) for opening and closing a passage (21L) connecting the injection section (24) and the wax tank (21), and a first suction valve (32) for opening and closing a passage (22L) connecting the injection section (24) and the vacuum tank (22), and the injection molding apparatus (10) further has a volume expansion chamber (23), a volume expansion mechanism (40) for expanding the volume of the volume expansion chamber (23), and a second suction valve (33) for opening and closing a passage (23L) connecting the injection section (24) and the volume expansion chamber (23).

Description

[Technical field]

[0001] The present application relates to an injection molding apparatus and method for wax used in lost wax casting. [Background technology]

[0002] Ornaments, accessories, and jewelry, mainly made of precious metals, are small, complex, and have precise shapes. There is a demand for mass production of such products, and the lost wax precision casting method has developed in this industry. Of course, it can also be applied to the manufacture of precision industrial parts other than those mentioned above.

[0003] Lost wax precision casting in the jewelry manufacturing industry involves the following steps: The first step is to create the prototype. The second step is to create a rubber mold with a cavity of the same shape as the original. The third step is to inject molten wax into a rubber mold and then remove it to produce a wax mold of the same shape as the original. Generally, multiple wax molds are produced by repeating the third step. The fourth step is to attach the numerous wax patterns produced in the third step in a tree-like shape around the wax rod while melting the runner ends of the wax patterns, and then place this in a cylindrical heat-resistant container and pour plaster into it to create a plaster mold. The fifth process is a firing process in which an electric furnace, gas furnace, or other device is used to melt and drain the wax inside the plaster mold at a low temperature, then completely burn off the wax adhering to the inside of the cavity at a medium temperature, and then the temperature is raised further to give the plaster mold enough strength to withstand the impact when the precious metal is poured in, after which the temperature is lowered to a level suitable for pouring in the precious metal and a waiting period is performed. The sixth step is the casting process, in which precious metals are poured into a plaster mold that has many cavities similar to those of the original model. The seventh step is a finishing process in which, once the precious metal has solidified, the plaster mold is rapidly cooled with water to break the plaster into pieces, the dendrites of precious metal are extracted, the excess parts are cut off, and the precious metal is polished to the same shape as the original.

[0004] The method for manufacturing the rubber mold in the second step will be described with reference to Figure 1. In the second step, a mold (not shown) of a size corresponding to the size of the rubber mold 3 to be created, a master model 1, and a part 2 (a runner 2a and a sprue 2b) are used. The bottom of the mold is closed with a plate, the lower half is filled with pre-vulcanized silicone rubber material, and the master model 1 with the part 2 bonded thereto is placed on top of that, after which the upper half is filled with pre-vulcanized material, the top of the mold is closed with a plate, and the temperature is raised while pressing to vulcanize. Two-component solidifying type silicone rubber may be used instead of vulcanizable rubber.

[0005] Once the silicone rubber has hardened and retained its inherent elasticity, the rubber mold 3 is removed from the frame, a cut 3C is formed, the master 1 and the part 2 attached to it are removed, and the rubber mold 3 is separated into an upper rubber mold 3U and a lower rubber mold 3L. This results in a rubber mold 3 having an internal cavity 3H and injection port 3P of the same shape as the master 1 and the part 2. By making such cuts 3C over the entire separation surface, the upper rubber mold 3U and the lower rubber mold 3L can be accurately aligned when they are brought together, and the shape of the internal cavity can also be accurately reproduced.

[0006] Such cuts 3C also facilitate vacuuming and sealing of the pressurized wax when wax is injected into the rubber mold 3 to create the wax model. When removing the wax model from the rubber mold 3, if the upper rubber mold 3U is separated from the mating surface (cut) 3C and then the removal work is performed while deforming the lower rubber mold 3L, even a wax model with a complex shape can be easily removed without breaking. In some cases, the inside of the rubber mold may be divided into several parts or a core may be inserted.

[0007] Since the masters come in a variety of sizes, the rubber molds also vary in size and thickness to accommodate them. The hardness of the rubber is often also changed depending on the durability of the rubber mold and the difficulty of removing the wax model from inside the rubber mold.

[0008] 2 is a conceptual diagram of a conventional injection molding apparatus 10' used in the third step. The injection molding apparatus 10' includes a main body device 20 and a clamp unit 50.

[0009] The main body device 20 has a wax tank 21 for pressurizing and storing wax, a tank 20T having a vacuum tank 22 connected to a vacuum pump, an injection unit 24 capable of contacting the rubber mold 3, and a switching device 30 for selectively connecting the injection unit 24 to the wax tank 21 and the vacuum tank 22. The wax in the wax tank 21 is heated by a heater 20H.

[0010] The injection unit 24 can be selectively connected to the wax tank 21 and the vacuum tank 22 via a switching device 30. The switching device 30 functions as a valve (wax valve 31) that opens and closes the passage 21L that connects the injection unit 24 and the wax tank 21, and as a valve (first suction valve 32) that opens and closes the passage that connects the injection unit 24 and the vacuum tank 22.

[0011] The clamp unit 50 has a function of clamping the rubber mold 3 and pressing the injection port 3P of the rubber mold 3 against the injection section 24.

[0012] By pressing the rubber mold 3 clamped by the clamp unit 50 against the injection part 24 and opening the first suction valve 32, the air in the cavity 3H can be sucked through the injection part 24 (suction step). After that, by closing the first suction valve 32 and opening the wax valve 31, wax can be injected from the injection part 24 into the cavity 3H (injection step).

[0013] 3(a) and (b) show an exemplary structure of the switching device 30. The switching device 30 has a wax valve 31 and a first suction valve 32. The wax valve 31 opens and closes the passage 21L by moving a wax valve rod 31a, and the first suction valve 32 opens and closes the passage 22L by moving a first suction valve rod 32a.

[0014] Usually, the vacuum level achieved by the vacuum pump performing the suction is quite high, about 10 Pa in absolute pressure. A perfect vacuum is theoretically zero Pa, or -101.325 kpa in gauge pressure. However, since the process passes through several pipe joints, and many seal conditions within the device are involved, and the air in cavity 3H is sucked into the vacuum tank at intervals of several tens of seconds during operation of the injection molding device 10', the vacuum pressure in vacuum tank 22 fluctuates to around -100 kpa, and may even drop to around -95 kpa if not properly managed. Therefore, it is impossible to completely remove the air in cavity 3H in the above suction step, and several percent of the air, converted to atmospheric pressure, will always remain as residual air in the cavity.

[0015] Compared to a resin injection molding device that injects molten resin into a mold at high pressure, an injection molding device that injects wax into a rubber mold, such as that used in jewelry manufacturing, has a much lower injection pressure, making it impossible to completely crush the remaining air. Also, in injection molding using a mold, a fixed amount of resin can be injected using a screw or plunger, so it is possible to provide an air venting mechanism in the mold. In contrast, in injection molding using a rubber mold, wax is injected under constant pressure conditions, so an air venting mechanism cannot be provided. (If an air venting mechanism is provided, wax will get into the air venting mechanism and cause it to become clogged.)

[0016] This causes various problems in the third step of making the wax mold. The rubber mold shown in Figure 1 has the simplest design, but if wax is injected immediately after the cavity is evacuated, the wax passes through injection port 3P and branches in cavity 3H, and the wax rejoins at the point farthest from injection port 3P. Then, the several percent of air mentioned above is collected at this junction and condensed to a pressure that is in equilibrium with the injection pressure.

[0017] The condensed air creates bubbles or wrinkles, which causes a mismatch between the shape of cavity 3H and the wax model, resulting in a problem of reduced quality of the wax model. In particular, in the case of ring-shaped objects such as finger rings as shown in Figure 1, there are often intricately designed decorations at this junction. For example, if there is a protrusion at the junction, the protrusion may become rounded or the wax may not reach the tip, which can cause the above problem to become more pronounced.

[0018] Currently, one way to deal with this problem is to apply baby powder or a similar substance to the rubber mold 3. This creates a very small gap in the cut 3C of the rubber mold, which is expected to allow any remaining air in the cavity to be expelled when the wax is injected.

[0019] Increasing the amount of powder applied increases the effectiveness of discharging the remaining air, but the powder adheres to the surface of the wax mold, making the surface rough. Also, the powder increases the amount of leakage from the gaps in the cuts 3C, reducing the degree of vacuum in the rubber mold 3. Conversely, reducing the amount of powder applied makes it difficult to fully displace the remaining air.

[0020] As described above, it is currently impossible to completely remove the air from cavity 3H, and it is impossible to produce a wax mold that perfectly matches the shape of cavity 3H. In particular, the problem of remaining air becomes more serious when the design becomes complicated. For this reason, adjustments such as shifting the position where the clamping force is applied, changing the injection pressure, and changing the wax temperature have been made, but the problem has not been fully solved, and making such adjustments every time the design is changed requires excessive effort.

[0021] One method for solving the above problem is disclosed in Patent Document 2. In Patent Document 2, the remaining air in cavity 3H that is condensed during the wax injection process is sucked through a wax blocking portion. However, the method of Patent Document 2 cannot be applied to many existing rubber molds. Furthermore, with the method of Patent Document 2, the achievable degree of vacuum in cavity 3H is limited to the degree of vacuum in vacuum tank 22 (see this specification

[0012] ). [Prior art documents] [Patent documents]

[0022] [Patent Document 1] International Publication No. 2017 / 068670 [Patent Document 2] Patent No. 6756958 Summary of the Invention [Problem to be solved by the invention]

[0023] As described above, after evacuation, air equivalent to several percent of the cavity volume remains in cavity 3H when converted to atmospheric pressure.

[0024] Therefore, if the air in cavity 3H can be further sucked out by a means other than the vacuum pump and vacuum tank 22 after the air in cavity 3H has been sucked out by the vacuum pump and vacuum tank 22, a high vacuum can be achieved and the remaining air can be significantly reduced.

[0025] If this could be realized, most of the problems mentioned above would be resolved, and it would be possible to produce rubber molds with more difficult designs. Furthermore, this would encourage the evolution of decorative design. An object of the present invention is to dramatically reduce the amount of air remaining in the cavity. Another object of the present invention is to enable the production of wax molds that are more faithful to the shape of the cavity. Yet another object of the present invention is to enable the production of wax molds with more precise or finer shapes. [Means for solving the problem]

[0026] This application discloses the following invention. <Aspect 1> An injection part capable of contacting the rubber mold; a wax tank for pressurizing and storing wax; a vacuum chamber connected to a vacuum pump; a wax valve for opening and closing a passage connecting the injection unit and a wax tank; a first suction valve that opens and closes a passage that connects the injection part and a vacuum chamber; An injection molding apparatus having A volume expansion chamber; A volume expansion mechanism for expanding the volume of the volume expansion chamber; The injection molding apparatus further comprises a second suction valve that opens and closes a passage that connects the injection section and the volume expansion chamber. <Aspect 2> An injection molding method using the injection molding apparatus of aspect 1, a preparation step of closing the wax valve and the first and second suction valves to bring the rubber mold into contact with the injection part; a first suction step of opening the first and second suction valves following the preparation step; Following the first suction step, a second suction step of expanding the volume of the volume expansion chamber after closing the first suction valve; following the second suction step, a wax injection step of closing the second suction valve and opening the wax valve; The injection molding method according to claim 1, [Brief description of the drawings]

[0027] [Figure 1] A method for manufacturing the rubber mold 3 will be described. [Diagram 2] A conventional injection molding apparatus 10' is shown. [Diagram 3] (a) shows one form of a conventional switching device 30. (b) shows another form of a conventional switching device 30. [Figure 4] 1 shows an injection molding apparatus 10 according to one embodiment of the present invention. [Diagram 5] 1 shows an integrated assembly 70 according to one embodiment of the present invention. [Figure 6] The periphery of the switching device 30 of the integrated assembly 70 is shown. [Figure 7] 2 illustrates the operation of one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] 4 shows a conceptual diagram of the injection molding apparatus 10 of the present invention. The injection molding apparatus 10 of the present invention has a main body device 20 and a clamp unit 50.

[0029] The main body device 20 of the present invention has, in addition to the wax tank 21 and vacuum tank 22 similar to those of the conventional device 10', a volume expansion chamber 23 and a volume expansion mechanism 40 for expanding the volume of the volume expansion chamber 23. Also, the switching device 30 of the present invention has the same functions as the wax valve 31 and first suction valve 32 similar to those of the conventional device 10', and also has a function as a valve (second suction valve 33) that opens and closes the passage 23L that connects the injection part 24 and the volume expansion chamber 23.

[0030] The clamping unit 50 is similar to that of a conventional injection molding apparatus 10 .

[0031] A description will now be given of the operation of the injection molding apparatus 10. First, in a preparation step, the rubber mold 3 is brought into contact with the injection section 24 with all the valves 31, 32, and 33 closed.

[0032] In the subsequent first suction step, the wax valve 31 is closed, and the first suction valve 32 and the second suction valve 33 are opened. This causes the air in the cavity 3H of the rubber mold 3 and the air in the volume expansion chamber 23 to be sucked into the vacuum tank 22. This allows the degree of vacuum in the cavity 3H to reach the same level as in the suction step of the conventional device 10' (see

[0011] ). Since the sucked air flows into the vacuum tank 22, the degree of vacuum in the vacuum tank 22 may drop slightly from the initial value.

[0033] In the subsequent second suction step, the first suction valve 32 is closed and then the volume of the volume expansion chamber 23 is increased.

[0034] If the volume of the rubber mold cavity 3H is V1, the sum of the volume of the passage 23L and the volume of the volume expansion chamber 23 before expansion is V2, and the volume expansion of the volume expansion chamber 23 in the second suction step is V3, then V1+V2 changes to V1+V2+V3 by the second suction step.

[0035] Therefore, by increasing the volume ratio of V3 to V1+V2, the remaining air in cavity 3H mentioned in

[0012] can be significantly reduced. For example, if the volume ratio of V3 to V1+V2 is increased by 10 times, the remaining air in cavity 3H becomes (V1+V2) / (V1+V2+V3)=1 / 11=0.091. If the volume ratio is 20 times, the remaining air becomes 1 / 21=0.048. Normally, the volume V1 of a ring is about 1.5cc, and it is easy to design V2 to be about 1.5cc and V3 to be 30cc or more, and a volume ratio of 10 times or more can be easily achieved.

[0036] In this way, compared to the conventional method, the present invention can dramatically reduce the amount of remaining air in cavity 3H and dramatically increase the degree of vacuum. Also, by injecting wax into cavity 3H with a dramatically increased degree of vacuum, it is possible to manufacture a wax mold that is more faithful to the shape of cavity 3H.

[0037] The integrated assembly 70 will be described with reference to FIGS.

[0038] 5, the integrated assembly 70 includes the switching device 30 and the volume expansion mechanism 40. Preferably, the integrated assembly 70 accommodates the switching device 30 and the volume expansion mechanism 40 in a single housing.

[0039] As shown in FIG. 6, the switching device 30 includes a wax valve 31, a first suction valve 32, and a second suction valve 33.

[0040] The wax valve 31 is for opening and closing the passage 21L that connects the injection part 24 and the wax tank 21. The wax valve 31 has a wax valve stem 31a and a wax valve seat 31b. The wax valve 31 is closed and opened as the wax valve stem 31a seats on and separates from the wax valve seat 31b. The wax valve stem 31a is integrated with a piston 61a of a wax valve cylinder 61 shown in Fig. 5, and can be moved to the left in the figure (in the direction to close the wax valve 31) by the biasing force of a return spring 61b, and can be moved to the right in the figure (in the direction to open the wax valve 31) by the pressure of a port 61c.

[0041] The first suction valve 32 opens and closes the passage 22L that connects the injection part 24 and the vacuum tank 22. The first suction valve 32 has a first suction valve rod 32a and a first suction valve seat 32b. The tip of the first suction valve rod 32a seats on and separates from the first suction valve seat 32b to close and open the first suction valve 32. The first suction valve rod 32a is integral with a piston 62a of a first suction valve cylinder 62, and can be moved downward in the figure (in a direction to close the first suction valve 32) by the biasing force of a return spring 62b, and can be moved upward in the figure (in a direction to open the first suction valve 32) by pressurization of a port 62c.

[0042] The second suction valve 33 opens and closes the passage 23L that connects the injection section 24 and the volume expansion chamber 23 shown in Fig. 5. The second suction valve 33 has a second suction valve rod 33a and a second suction valve seat 33b. The tip of the second suction valve rod 33a seats on and separates from the second suction valve seat 33b to close and open the second suction valve 33. The second suction valve rod 33a is integral with the piston 63a of the second suction valve cylinder 63, and can be moved upward in the figure (in a direction to close the second suction valve 33) by the biasing force of the return spring 63b, and can be moved downward in the figure (in a direction to open the second suction valve 33) by pressurizing the port 63c.

[0043] By selectively opening and closing the wax valve 31, the first suction valve 32 and the second suction valve 33, it is possible to selectively open and close the passages 21L, 22L, 23L connecting the injection section 24 to the wax tank 21, the vacuum tank 22 and the volume expansion chamber 23.

[0044] Further, the injection section 24 has a passage 24L extending from the opening 24a of the injection section 24 toward the switching device 30. The passage 24L is preferably linear. The passage 24L branches into three branches leading to the wax valve 31, the first suction valve 32, and the second suction valve 33 via a cross-shaped intersection portion X. It is preferable that the branch leading to the wax valve 31 is arranged in a straight line relative to the passage 24L, the branch leading to the first suction valve 32 is arranged at a right angle relative to the passage 24L, and the branch leading to the second suction valve 33 is arranged at a right angle relative to the passage 24L.

[0045] As shown in FIG. 5, the volume expansion mechanism 40 has a volume expansion cylinder 41 and a drive cylinder 42.

[0046] The volume expansion cylinder 41 has cylinder chambers 41L and 41R on both sides of the volume expansion piston 41a. The left cylinder chamber 41L is the volume expansion chamber 23 and is connected to the passage 23L. The port 41b of the right cylinder chamber 41R is always exhausted (or open to atmospheric pressure).

[0047] The drive cylinder 42 has cylinder chambers 42L and 42R on either side of the drive piston 42a. Each of the cylinder chambers 42L and 42R has a port 42b and a port 42c.

[0048] The volume expansion piston 41a and the drive piston 42a are connected by a connecting rod 43 so as to move together.

[0049] The cylinder chambers 41L and 41R are sealed by sliding packing on the outer periphery of the volume expansion piston 41a, the cylinder chambers 42L and 42R are sealed by sliding packing on the outer periphery of the drive piston 42a, and the cylinder chambers 41R and 42L are sealed by sliding packing on the outer periphery of the connecting rod 43.

[0050] In the volume expansion mechanism 40, the volume expansion piston 41a and the drive piston 42a can be moved to the left in the figure by pressurizing the port 42b and exhausting the port 42c, and the volume expansion piston 41a and the drive piston 42a can be moved to the right in the figure by exhausting the port 42b and pressurizing the port 42c. The volume of the volume expansion chamber 23 decreases when the volume expansion piston 41a moves to the left, and the volume of the volume expansion chamber 23 increases when the volume expansion piston 41a moves to the right.

[0051] 7 shows the operation of the injection molding apparatus 10 of the above embodiment when the integrated assembly 70 is used. The operation of the injection molding apparatus 10 includes the following steps (1) to (4). (1) Preparation steps (2) First suction step (3) Second suction step (4) Injection step The above preparation step, first suction step, second suction step and wax injection step are preferably carried out in the above order of (1) to (4).

[0052] 7(a) shows the preparation step. In the preparation step, the wax valve 31, the first suction valve 32, and the second suction valve 33 are all closed, and the rubber mold 3 clamped by the clamp unit 50 is pressed against the injection part 24. At this time, it is preferable to move the volume expansion piston 41a to the left to minimize the volume expansion chamber 23.

[0053] 7(b) shows the subsequent first suction step. In the first suction step, the first suction valve 32 and the second suction valve 33 are opened. By the first suction step, the air in the cavity 3H of the rubber mold 3 and the volume expansion chamber 23 is sucked into the vacuum tank 32. This makes it possible to increase the degree of vacuum in the cavity 3H to the same level as that of the conventional injection molding apparatus 10'.

[0054] Fig. 7(c) shows the subsequent second suction step. In the second suction step, the first suction valve 32 is closed, and then the volume of the volume expansion chamber 23 is expanded (Fig. 7(c)). By closing the first suction valve 32, the cavity 3H is connected only to the volume expansion chamber 23 via the passage 23L, and is cut off from the wax tank 21 and the vacuum tank 22. In this state, the volume of the volume expansion chamber 23 is expanded, so that the remaining air in the cavity 3H is sucked into the volume expansion chamber 23. This makes it possible to increase the degree of vacuum in the cavity 3H more significantly than in the conventional injection molding apparatus 10'.

[0055] Fig. 7(d) shows the subsequent wax injection step. In the wax injection step, the second suction valve 33 is closed and then the wax valve 31 is opened (Fig. 7(d)). This causes the wax in the wax tank 21 to be injected into the cavity 3H.

[0056] One cycle of the wax injection process is completed by performing the above preparation step, first suction step, second suction step, and wax injection step. By repeatedly performing multiple cycles of the wax injection process, multiple wax molds can be made.

[0057] The injection molding apparatus 10 may have a control device for controlling the operation of each of the valves 31, 32, 33 and the volume expansion mechanism 40. The control device may include a computer. The control device may automatically perform each of the above steps.

[0058] In the above-mentioned injection molding apparatus 10, the second suction step is performed in addition to the first suction step, thereby significantly reducing the amount of air remaining in the cavity 3H. This improves the production yield of the wax mold, and / or enables the production of a wax mold that is faithful to the shape of the cavity, and / or enables the production of a wax mold with a fine and / or complex shape that is difficult to produce with the conventional technology.

[0059] INDUSTRIAL APPLICABILITY The injection molding apparatus and the injection molding method of the present invention can be used in lost wax casting for manufacturing small items such as jewelry and accessories, industrial products, and the like. [Explanation of symbols]

[0060] 1... Prototype 2. Parts 3. Rubber mold 3C...Depth of cut 3U···Upper rubber mold 3L···Lower rubber mold 3H...Cavity 3P···Injection port 10,10'...Injection molding equipment 20T...Tank 20H···Heater 20...Main unit 21 Wax tank 22...Vacuum chamber 23 Volume expansion chamber 24...Injection part 24a...Aperture 21L,22L,23L,24L...Aisle 30. Switching device 31 Wax valve 32... First suction valve 33 Second suction valve 31a,32a,33a...valve stem 31b,32b,33b...valve seat 40 Volume expansion mechanism 41...Volume expansion cylinder 42 Drive cylinder 43 Connecting rod 41a, 42a Piston 41b, 42b, 42c... Ports 41L, 41R, 42L, 42R, 43L, 43R...Cylinder chamber 50···Clamp unit 51 Table 52 Clamping force generator 53 Clamp plate 54...Pushing mechanism 61 Wax valve cylinder 62...First suction valve cylinder 63...Second suction valve cylinder 61a, 62a, 63a...Piston 61b, 62b, 63b...Return spring 61c, 62c, 63c... Port 70...Integrated Assembly

Claims

1. An injection part capable of contacting the rubber mold; a wax tank for pressurizing and storing wax; a vacuum chamber connected to a vacuum pump; a wax valve for opening and closing a passage connecting the injection unit and a wax tank; a first suction valve that opens and closes a passage that connects the injection part and a vacuum chamber; An injection molding apparatus having A volume expansion chamber; A volume expansion mechanism for expanding the volume of the volume expansion chamber; The injection molding apparatus further comprises a second suction valve that opens and closes a passage that connects the injection section and the volume expansion chamber.

2. An injection molding method using the injection molding apparatus of claim 1, a preparation step of closing the wax valve and the first and second suction valves to bring the rubber mold into contact with the injection part; a first suction step of opening the first and second suction valves following the preparation step; Following the first suction step, a second suction step of expanding the volume of the volume expansion chamber after closing the first suction valve; following the second suction step, a wax injection step of closing the second suction valve and opening the wax valve; The injection molding method according to claim 1,

Images