Patent Application
20220126361
This application claims priority of Taiwanese Patent Application No. 109137132, filed on Oct. 26, 2020.
The disclosure relates to a molding process, more particularly to a melt-molding metallurgical method.
In order to produce metal workpieces, the most traditional processing method is casting. Casting is a process in which a metal material is melted into liquid at a high temperature, and then the liquid is poured into a mold and cool to solidify. In casting, it is not only necessary to heat the material to a high temperature, but also the temperature of the material must be maintained before being injected into the mold. Further, the mold must also be able to withstand the corresponding high temperature in order to form the material. Moreover, the danger caused by high temperature must also be considered, so that corresponding safety facilities must be set up. Therefore, the technology of “powder metallurgy” was developed in modern times. Powder metallurgy is a process in which metal powder is put into a mold and then press into a blank. The blank is preformed into the appearance of a workpiece, but the structural strength is still quite low. Thus, it is necessary to perform sintering on the blank in order to improve the structural strength thereof. The advantage of using the powder metallurgy is that it is not necessary to heat the metal material to a liquid state, as long as it reaches the recrystallization temperature. Further, the aforesaid problems of maintaining the temperature of the material, the mold being able to withstand the corresponding high temperature, and the danger of high temperature can be eliminated.
In recent years, the technology of powder metallurgy and plastic injection molding are combined to form metal injection molding (MIM). In the metal injection molding process, powdered metal is injected into a mold using an injection machine, and then sinter it after forming in the mold. In comparison with the traditional powder metallurgy, the metal powder used in the metal injection molding is finer, so it has fluidity and can be injected by an injection machine. Further, because of the finer metal powder, a denser metal structure can be obtained after sintering. Therefore, the application of the metal injection molding technology can produce high density, high precision and complex-shaped metal workpieces. However, the metal injection molding still has the disadvantage of not being able to manufacture large workpieces. This is because the fluidity of metal powder is still poor compared to fluid. In addition, based on the characteristics of injection molding, the value of maintaining pressure can only be used as a control parameter to control the injection volume, and it is impossible to accurately adjust the injection volume for different numbers and sizes of mold cavities.
All of the aforesaid technologies require the injection of liquid metal or metal powder. Therefore, the mold must be provided with a sprue or runner. After the material is formed, the material remaining in the sprue or runner will become a scrap. In order to remove the scrap, additional processing must be performed after the material has solidified or sintered. For example, most of the scrap is first removed by cutting, followed by polishing and grinding to obtain a smooth surface. It should be noted that the scrap cannot be cut before sintering. Because the structural strength of the blank before sintering is quite low, if the shearing is performed, other adjacent parts may collapse and disintegrate. On the other hand, the structural strength of the blank after sintering becomes quite high, so that it is quite difficult to remove the scrap.
Therefore, an object of the present disclosure is to provide a melt-molding metallurgical method that has good fluidity, that requires no additional processing and that can precisely control injection volume and injection speed.
Accordingly, a melt-molding metallurgical method of this disclosure includes the following steps: (A) preparing raw material powder and a binder material; (B) mixing the raw material powder and the binder material to obtain pellets; (C) pressing the pellets to pass through an eye mold so as to obtain a solid state material; (D) preparing a molding device, the molding device including a conveying unit disposed downstream of the eye mold for conveying the solid state material along a conveying direction, a heating unit disposed downstream of the conveying unit along the conveying direction, and a molding unit, the heating unit including a main body, a nozzle disposed on a downstream side of the main body, and a heating channel extending through the main body and the nozzle for passage of the solid state material therein, the molding unit including at least two molds that cooperate with each other to define a forming space, the nozzle having an injection port communicating with the heating channel; (E) activating the conveying unit for conveying the solid state material from the eye mold to the heating channel; (F) heating the solid state material to melt a portion of the solid state material that is proximate to a forming space and become a liquid state material; (G) driving the solid state material that has not melted to push the liquid state material into the forming space; (H) cooling the liquid state material in the forming space to solidify the same into a blank; (I) debinding the blank for removing the binder material from the blank; and (J) sintering the blank to obtain a finished product.
Other features and advantages of the disclosure will become apparent in the following detailed description of the embodiment with reference to the accompanying drawings, of which:
Referring to
In step S1, raw material powder and a binder material are prepared. A melting point of the binder material is lower than that of the raw material powder. In this embodiment, the raw material powder is glass powder, but is not limited thereto, and may be metal powder, glass powder or ceramic powder. Further, the binder material is a crosslinking agent. Common crosslinking agents include white wax, polyurethane, acrylate, etc.
In step S2, the raw material powder and the binder material are uniformly mixed to obtain pellets. How to perform mixing and obtain the pellets is well known to the person having a common knowledge in this field, and is not an important aspect of this disclosure, so that a detailed description thereof is omitted herein.
In step S3, the pellets are pressed to pass through an eye mold 1 so as to obtain a solid state material (R). The solid state material (R) has a linear or rod shape. Specifically, the eye mold 1 has a narrow passage 11. When the pellets are pushed by a considerable degree of pressure and pass through the passage 11, they will squeeze each other and heat up, so that the binder material portion in each pellet is softened or melted (while the raw material powder portion in each pellet remains solid), thereby binding the pellets together and form the solid state material (R).
In step S4, a molding device 2 (see
The heating unit 22 includes a main body 221, a nozzle 222 disposed on a downstream side of the main body 221, a heating tube 223 disposed in the main body 221, a heat source 224 embedded in the main body 221, and a temperature sensor 225 adjacent to the heat source 224. The nozzle 222 is connected to the heating tube 223, and cooperates with the same to define a heating channel 226 for passage of the solid state material (R) therein. The heating channel 226 extends through the main body 221 and the nozzle 222. The nozzle 222 has an injection port 233 communicating with the heating channel 226.
It should be noted herein that, in this embodiment, only a portion of the heating tube 223 extends into the main body 221, so that a junction of the nozzle 222 and the heating tube 223 is located inside the main body 221, but is not limited thereto. In other variations, the heating tube 223 may extend through the main body 221, so that a junction of the nozzle 222 and the heating tube 223 is located outside the main body 221.
The molding unit 23 includes two molds 231, 231′ that are mated in an up-down direction and that cooperate with each other to define a forming space 232. The mold 231′ is disposed below the mold 231, and has an insertion hole 236 for insertion therein of the nozzle 222 such that the injection port 233 of the nozzle 222 is immediately adjacent to the forming space 232. The heating channel 226 communicates with the forming space 232 through the injection port 233. In this embodiment, the molding unit 23 includes two molds 231, 231′, but is not limited thereto, and may include three or more molds according to the requirement.
In step S5, the conveying unit 21 is activated to convey the solid state material (R) from the eye mold 1 to the heating channel 226.
In step S6, the heating unit 22 is activated so that the solid state material (R) in the heating channel 226 can be heated by the heat source 224. When the solid state material (R) is heated, a portion of the solid state material (R) that is proximate to the nozzle 222 will melt and become a liquid state material (L). It should be noted that the liquid state material (L) is heated to a temperature between the melting point of the binder material and the melting point of the raw material powder, so that the composition of the liquid state material (L) still contains the raw material powder that has not been melted.
In this embodiment, the size of the heating channel 226 that is proximate to the injection port 233 is gradually reduced. As such, the pressure of the liquid state material (L) will gradually increase as it moves toward the injection port 233, so that it can be injected into the forming space 232 via the injection port 233.
Further, the heat source 224 can be controlled through the temperature sensor 225 so that the solid state material (R) can reach a sufficiently high temperature and melt.
In step S7, after the conveying unit 21 and the heating unit 22 are activated, the solid state material (R) that has not melted is driven by the conveying unit 21 to push the liquid state material (L), so that the liquid state material (L) is injected into the forming space 232 from the injection port 233.
It is worth to mention herein that, in this embodiment, the step of conveying the solid state material (R) to the heating channel 226 in step S5 is first performed, followed by step S6 and step S7 to achieve the state shown in
In step S8, the molding unit 23 is cooled to cool and solidify the liquid state material (L) in the forming space 232 into a blank 3. It should be noted that after cooling, the molds 231, 231′ are separated to expose the forming space 232 to thereby facilitate removal of the blank 3.
In step S9, the blank 3 undergoes a debinding process to remove the binder material from the blank 3. The debinding process may be a process of heating, water washing, solvent washing or a combination thereof. Those skilled in the art may select an appropriate technical means according to different binder materials to achieve the purpose of removing the binder material from the blank 3.
In step 10, the blank 3 is sintered to obtain a finished product. During sintering, the microstructure of the blank 3 will change to improve its structural strength. Specifically, after the debinding process, the blank 3 is mainly composed of the raw material powder, but the microstructure thereof is very loose, and the overall structural strength is weak. When heated above the recrystallization temperature (that is, during sintering), the grain boundary between molecules will disappear, allowing the molecules to rearrange and recrystallize. In this way, the molecules in the blank 3 can produce an integrated microstructure, naturally increasing the strength of the structure of the blank 3, so that the blank 3 can become a finished product for sale.
In this embodiment, because the portion of the solid state material (R) that is proximate to the forming space 232 will melt and become the liquid state material (L), injected into the forming space 232 is also the liquid state material (L). Compared with the prior art, the liquid state material (L) is a fluid so that it naturally has a better fluidity than that of the powder. Therefore, this embodiment can be used to make larger workpieces. Further, the maximum temperature required in this embodiment only needs to reach the recrystallization temperature, no need to reach the melting point of the raw material powder. The problems encountered in the prior art, such as maintaining the material temperature, the mold must be able to withstand the corresponding high temperature, and the danger caused by high temperature, can be avoided.
Furthermore, since the liquid state material (L) is directly injected into the forming space 232 via the injection port 233, the molds 231, 231′ do not need to be provided with sprues or runners. Hence, the blank 3 does not produce any scrap, so that the blank 3 becomes a finished product after sintering, and no additional processing is required.
Moreover, the liquid state material (L) leaving the heat source 224 and going to the injection port 233 is gradually cooled. To prevent the material remaining in the heating channel 226 from solidifying due to the cooling of the molding unit 23, after the injection is completed, the solid state material (R) can be conveyed in a reverse direction of the conveying direction (T) through the conveying unit 21, so that the liquid state material (L) near the injection port 233 can be drawn back and will not be solidified. The liquid state material (L) is pushed again from the heat source 224 toward the injection port 233 in the next processing. Thus, the liquid state material (L) can be properly used and the effect of almost no waste can be achieved. Additionally, keeping the heat source 224 in an activated state not only can maintain the liquid state material (L) at a certain temperature without solidification, but also can facilitate continuous processing.
In addition, in this embodiment, the conveying unit 21 can be used not only to control the force required to push the solid state material (R), but also to control the moving rate of the solid state material (R). In the prior art, the injection volume and the injection speed can only be controlled by the maintaining pressure, so that this embodiment is different from the prior art. Because the solid state material (R) has a linear or rod shape, the injection amount and the injection speed of this embodiment can also be estimated through the length of the solid state material (R) that has been fed. Therefore, in comparison with the prior art, this embodiment can more accurately control the injection amount and the injection speed.
In summary, in the melt-molding metallurgical method of this disclosure, the portion of the solid state material (R) proximate to the forming space 232 will melt and become the liquid state material (L) which has more fluidity than powder. Further, the liquid state material (L) is directly injected into the forming space 232, so that the blank 3 can become a finished product after sintering, and no need for additional processing. Moreover, not only the force required to push the solid state material (R) can be controlled, but also the moving rate of the solid state material (R) can be controlled so as to accurately control the injection amount and the injection speed. Therefore, the object of this disclosure can indeed be achieved.
While the disclosure has been described in connection with what is considered the exemplary embodiment, it is understood that this disclosure is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.
| Number | Date | Country | Kind |
|---|---|---|---|
| 109137132 | Oct 2020 | TW | national |
