Patent Publication Number: US-2023134954-A1

Title: Cold flake suppression method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Japanese application serial no. 2021-180121, filed on Nov. 4, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to a cold flake suppression method. 
     Description of Related Art 
     It is widely known that injection molding casting is performed by supplying molten metal to a mold to manufacture a molded product, and in such a mold for molding, measures have been proposed to prevent cold flakes from entering the molded product (for example, see Patent Literature 1 (Japanese Patent Laid-Open No. 2004-506515)). 
     In Patent Literature 1, it is proposed to incorporate the flow in the shot sleeve into the model or incorporate the heat exchange between the die and the heat transferring fluid (HTF) into the model in casting of injection molding, so as to improve the accuracy of fluid flow for simulating the flow of fluid in the casting and molding process. 
     In Patent Literature 1, in order to use computer-aided engineering (CAE), there are problems that many parameters are required, it takes a lot of time to specify and input parameters, and it is necessary to secure expensive equipment for calculation and people versed in CAE. 
     SUMMARY 
     The cold flake suppression method of the disclosure is a cold flake suppression method for suppressing occurrence of cold flakes in an injection step in an injection molding device, which includes a sleeve of a cylindrical shape, a tip slidable in an axial direction within the sleeve from one end of the sleeve to the other end, a sprue guide portion which is disposed at the other end of the sleeve and in which a molten metal pressed by the tip in the sleeve and pushed out from the sleeve moves, and a molding die into which the molten metal moving through the sprue guide portion is injected to mold a product, and includes: 
     a contact area estimation step of estimating a contact area between the sleeve and the molten metal per unit time; 
     a total contact area estimation step of estimating an integrated value of the contact area per unit time estimated in the contact area estimation step; 
     a cold flake index estimation step of estimating a cold flake index, which is a value obtained by dividing a total contact area estimated in the total contact area estimation step by a volume of the sprue guide portion; and 
     a shape determination step of determining a shape of at least one of the sleeve and the sprue guide portion so that the cold flake index is equal to or less than a predetermined value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram showing a molding device according to an embodiment of the disclosure. 
         FIG.  2    is a schematic diagram showing a molding device with a tip sliding. 
         FIG.  3    is a schematic diagram showing a molding die, a sprue ring, and a distributer (DB). 
         FIG.  4    is a diagram showing numerical values during casting of the first example and first to sixth comparative examples. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In view of such circumstances, the disclosure is intended to provide a cold flake suppression method, which can easily suppress the inclusion of cold flakes in a molded product. 
     The cold flake suppression method of the disclosure is a cold flake suppression method for suppressing occurrence of cold flakes in an injection step in an injection molding device, which includes a sleeve of a cylindrical shape, a tip slidable in an axial direction within the sleeve from one end of the sleeve to the other end, a sprue guide portion which is disposed at the other end of the sleeve and in which a molten metal pressed by the tip in the sleeve and pushed out from the sleeve moves, and a molding die into which the molten metal moving through the sprue guide portion is injected to mold a product, and includes: 
     a contact area estimation step of estimating a contact area between the sleeve and the molten metal per unit time; 
     a total contact area estimation step of estimating an integrated value of the contact area per unit time estimated in the contact area estimation step; 
     a cold flake index estimation step of estimating a cold flake index, which is a value obtained by dividing a total contact area estimated in the total contact area estimation step by a volume of the sprue guide portion; and 
     a shape determination step of determining a shape of at least one of the sleeve and the sprue guide portion so that the cold flake index is equal to or less than a predetermined value. 
     As a result of intensive studies carried out by the applicant, it has been found that there is a relationship between the cold flake index, which is the value obtained by dividing the total contact area by the volume of the sprue guide portion, and the inclusion of the cold flakes in the molded product, more specifically, it has been found that when the cold flake index is equal to or less than a predetermined value, the inclusion of the cold flakes into the molded product is suppressed. 
     According to the cold flake suppression method of the disclosure, since the shape of at least one of the sleeve and the sprue guide portion is determined to set the cold flake index equal to or less than the predetermined value, it is possible to easily suppress the inclusion of the cold flakes in the molded product. 
     Further, it is preferable that the total contact area estimated in the total contact area estimation step is a total contact area from when the molten metal is poured into the sleeve until a movement speed of the tip which presses and moves the molten metal switches to a high speed. 
     According to this configuration, the residence time of the molten metal in the sleeve can be shortened, and the time required for molding can also be shortened. 
     Further, it is preferable that the sprue guide portion includes a stamp portion, a runner portion, and a gate portion, and a length of the runner portion is changed in the shape determination step. 
     According to the above configuration, since the length of the runner portion is changed in the shape determination step, the cold flake index can be easily set to be equal to or less than a predetermined value. 
     Hereinafter, embodiments of the disclosure are described with reference to the accompanying drawings. 
     As shown in  FIGS.  1  to  3   , a molding device  10  is a device for molding a molded product by, for example, injection molding molten metal M 1  of aluminum. In the embodiment, for example, a casing for a transmission of a vehicle is molded as the molded product. 
     The molding device  10  includes a sleeve  11  of a cylindrical shape and a tip  12  that is slidable in the sleeve  11  in an axial direction (a left-right direction in  FIG.  1   ) from one end (the right end in  FIG.  1   ) to the other end (the left end in  FIG.  1   ). The tip  12  is slid in the left-right direction in  FIG.  1    by a sliding mechanism (not shown), and the driving (sliding) of the sliding mechanism is controlled by a control device  20  that controls the molding device  10  in an integrated manner. The molten metal M 1  is supplied to the sleeve  11  by a supply device (not shown), and the control device  20  controls the driving of the supply device. 
     Further, the molding device  10  includes a sprue guide portion  13  which is disposed at the other end of the sleeve  11  (the left end in  FIG.  1   ) and in which the molten metal M 1  pressed by the tip  12  in the sleeve  11  to be pushed out from the sleeve  11  moves, a molding die  14  which molds a molded product by injecting the molten metal M 1  that has moved through the sprue guide portion  13 , a sprue ring  15 , and a distributer (hereinafter referred to as DB)  16 . 
     The molding die  14  includes a fixed die  14   a  that is fixed and a movable die  14   b  that can move in the left-right direction in  FIG.  1   , and the mold is clamped by moving the movable die  14   b  close to the fixed die  14   a , and the mold is opened by moving the movable die  14   b  away from the fixed die  14   a . In the embodiment, the mold is clamped by moving the movable die  14   b  rightward in  FIG.  1   , and the mold is opened by moving the movable die  14   b  leftward in  FIG.  1   . The movable die  14   b  is moved by a mold moving mechanism (not shown) driven by the control device  20 . 
     The sprue guide portion  13  is formed of a stamp portion  21  also called a biscuit portion, a runner portion  22 , and a gate portion  23  (see  FIG.  3   ). The stamp portion  21  is formed of the sprue ring  15 . The runner portion  22  is formed of the DB  16 , the fixed die  14   a , and the movable die  14   b . The gate portion  23  is formed of the fixed die  14   a  and the movable die  14   b . Further, the two-dot chain line in  FIG.  3    is an imaginary line indicating the boundaries of the respective portions  21  to  23 . 
     [Injection molding] When molding a molded product by the molding device  10 , first, as shown in  FIG.  1   , the control device  20  drives the mold moving mechanism to move the movable die  14   b  to the right side in  FIG.  1    for mold clamping. As a result, a molding portion, which is a hollow portion between the fixed die  14   a  and the movable die  14   b , is formed. 
     Next, the control device  20  drives the supply device to supply the molten metal M 1  of aluminum into the sleeve  11 . In the embodiment, the control device  20  drives the supply device so that the molten metal flows through the sleeve  11  at, for example, 0.1 m/sec. 
     Then, as shown in  FIG.  2   , the control device  20  drives the sliding mechanism to slide the tip  12  leftward. By sliding the tip  12  to the left, the molten metal M 1  in the sleeve  11  passes through the stamp portion  21 , the runner portion  22 , and the gate portion  23  of the sprue guide portion  13  and fills the molding portion of the molding die  14 . 
     After the molten metal M 1  filled in the molding portion of the molding die  14  is solidified, the movable die  14   b  is moved leftward in  FIG.  1    to open the mold. Then, the molded product is removed from the molding die  14 . In this way, a molded product is molded. 
     In the device for injection molding the molten metal M 1  to mold a molded product, if cold flakes are mixed into the molded product, the molded product may become a defective product. 
     As a result of intensive studies, the applicant has found a method for suppressing the inclusion of cold flakes in the molded product. 
     In heat transfer, when heat transfer amount is Q (J), contact area is A (m 2 ), temperature difference is ΔT (K), heat flux is q (W/m 2 ), heat transfer coefficient is h (W/m 2 K), and time is Δt (t), the following Formulas (1) and (2) are established. 
         Q=q×A×Δt    [Formula 1]
 
         q=h×ΔT    [Formula 2]
 
     In the molding device  10  of the embodiment, the molten metal M 1  is controlled to flow through the sleeve  11  at 0.3 m/sec, and when the flow velocity of the molten metal M 1  in the sleeve  11  is 0 to 0.1 m/sec, the heat transfer coefficient h (W/m 2 K) is constant in the sleeve  11 , or if the heat transfer coefficient h (W/m 2 K) changes, the amount of change is small. In this way, the heat transfer coefficient h (W/m 2 K) can be approximated by any constant. 
     In the molding device  10  of the embodiment, the temperature difference at each position in the left-right direction of the sleeve  11  during molding is small. In the molding device  10 , the fluid initial temperature (pouring temperature) is regulated and managed, the temperature of the sleeve  11  on the heat-receiving side (before contact with the molten metal) reaches saturation during continuous casting and becomes constant, and the factor affecting the temperature distribution after contact with the molten metal is whether there is contact between the molten metal and the sleeve. That is, the temperature difference ΔT is replaced by a function of contact between the molten metal and the sleeve=contact area. 
     Thus, q in the above Formula (1) is a function of any constant×the contact area, and the heat transfer amount Q within the sleeve  11  expressed by Formula (1) can be approximated by the contact area per unit time. 
     Further, in the casting process, the control device  20  sequentially calculates the amount of heat transfer that changes continuously from the start of supply of the molten metal M 1  until the tip  12  slides to the position shown in  FIG.  2   , and calculates a total of the amounts as a total amount of heat transfer. Moreover, the control device  20  calculates the volume of the sprue guide portion  13  based on various information (size) about the sprue guide portion  13  input by an operator. 
     As a new index for suppressing the inclusion of cold flakes in a molded product, the cold flake index represented by Formula (3) is to be described. 
       Cold flake index=total amount of heat transfer/volume of sprue guide portion   [Formula 3]
 
     In the above Formula (3), as the total amount of heat transfer increases, the cold flake index also increases, and as the volume of sprue guide portion increases, the cold flake index decreases. 
     In the molding device  10 , the shapes of the sleeve  11  and the sprue guide portion  13  are determined so that the cold flake index is equal to or less than a predetermined value (for example, 0.842). 
     As shown in  FIGS.  1  and  3   , in the embodiment, the thickness of the runner portion  22  is Xl, the length (thickness) of the stamp portion  21  is X 2 , the length of the runner portion  22  is X 3 , and the stroke length of the tip  12  is X 4 . 
     EXAMPLE 
     As shown in  FIG.  4   , experiments of casting by changing the shapes of the stamp portion  21  and the runner portion  22  of the sprue guide portion  13  and the stroke length of the tip  12  (Example 1 and Comparative Examples 1 to 3) were conducted by using the molding device  10 . 
     In the above experiments, the control device  20  drove the supply device and slid the tip  12  at a constant speed from the position shown in  FIG.  1    to the position shown in  FIG.  2   , so that the molten metal flowed through the sleeve  11  at 0.3 m/sec. Further, the control device  20  sequentially calculates the amount of heat transfer that changes continuously from the start of supply of the molten metal M 1  until the tip  12  slides to the position shown in  FIG.  2   , and calculates the total of the amounts as the total amount of heat transfer. Moreover, the control device  20  calculates the volume of the sprue guide portion  13  based on various information (size) about the sprue guide portion  13  input by the operator. 
     In Example 1 and Comparative Examples 1 to 3, whether the cold flake index is equal to or less than 0.842 (condition 1), whether cold flakes do not reach the molding portion of the molding die  14  (condition 2), and whether cold flakes do not reach the molding portion of the molding die  14  under adverse conditions (condition 3) are determined. 
     The adverse condition is, for example, the case where the temperature of the sleeve  11  is lower than a predetermined temperature (for example, 100° C.). A state in which the temperature of the sleeve  11  has cooled due to a long period of casting suspension (for example, from the resumption of casting after the suspension of operation of the factory in which the molding device  10  is installed until the temperature of the sleeve  11  stabilizes after several shots are completed after mold preheating has been completed), the time immediately after the molding device  10  is resumed after being suspended for a short time due to maintenance or the like with a low temperature outside, such as winter, and so on fall under the above adverse conditions. 
     Example 1 
     In Example 1, the thickness of the runner portion  22  was X 1 , the length (thickness) of the stamp portion  21  was X 2 , the length of the runner portion  22  was X 3 ×2.667, the stroke length of the tip  12  was X 4 ×0.907, the volume of the sprue guide portion  13  was X 5 ×1.296, and the total amount of heat transfer was X 6 ×0.936. The above X 1  to X 6  are numerical values used in Comparative Example 1 below. In Example 1, the cold flake index was 0.788, so it was determined that condition 1 that the cold flake index is equal to or less than 0.842 was satisfied, condition 2 that cold flakes do not reach the molding portion of the molding die  14 , was satisfied, and condition 3 that cold flakes do not reach the molding portion of the molding die  14  under adverse conditions, was satisfied. Further, the above length is the length of the left-right direction in  FIG.  1   . 
     Comparative Example 1 
     In Comparative Example 1, the thickness of the runner portion  22  was X 1 , the length (thickness) of the stamp portion  21  was X 2 , the length of the runner portion  22  was X 3 , the stroke length of the tip  12  was X 4 , the volume of the sprue guide portion  13  was X 5 , and the total amount of heat transfer was X 6 . In Comparative Example 1, the cold flake index was 1.044, so it was determined that condition 1 that the cold flake index is equal to or less than 0.842 was not satisfied, condition 2 that cold flakes do not reach the molding portion of the molding die  14  was not satisfied (cold flakes were mixed in the molded product), and condition 3 that cold flakes do not reach the molding portion of the molding die  14  under adverse conditions was not satisfied (cold flakes were mixed in the molded product). 
     Comparative Example 2 
     In Comparative Example 2, the thickness of the runner portion  22  was X 1 ×1.667, the length (thickness) of the stamp portion  21  was X 2 , the length of the runner portion  22  was X 3 , the stroke length of the tip  12  was X 4 , the volume of the sprue guide portion  13  was X 5 ×1.230, and the total amount of heat transfer was X 6 ×1.025. In Comparative Example 2, the cold flake index was 0.907, so it was determined that condition 1 that the cold flake index is equal to or less than 0.842 was not satisfied, condition 2 that cold flakes do not reach the molding portion of the molding die  14  was not satisfied (cold flakes were mixed in the molded product), and condition 3 that cold flakes do not reach the molding portion of the molding die  14  under adverse conditions was not satisfied (cold flakes were mixed in the molded product). 
     Comparative Example 3 
     In Comparative Example 3, the thickness of the runner portion  22  was X 1 , the length (thickness) of the stamp portion  21  was X 2 ×1.65, the length of the runner portion  22  was X 3 , the stroke length of the tip  12  was X 4 , the volume of the sprue guide portion  13  was X 5 ×1.267, and the total amount of heat transfer was X 6 ×1.025. In Comparative Example 3, the cold flake index was 0.881, so it was determined that condition 1 that the cold flake index is equal to or less than 0.842 was not satisfied, condition 2 that cold flakes do not reach the molding portion of the molding die  14  was not satisfied (cold flakes were mixed in the molded product), and condition 3 that cold flakes do not reach the molding portion of the molding die  14  under adverse conditions was not satisfied (cold flakes were mixed in the molded product). 
     Comparative Example 4 
     In Comparative Example 4, the thickness of the runner portion  22  was X 1 , the length (thickness) of the stamp portion  21  was X 2 , the length of the runner portion  22  was X 3 ×2.300, the stroke length of the tip  12  was X 4 ×0.899, the volume of the sprue guide portion  13  was X 5 ×1.233, and the total amount of heat transfer was X 6 ×0.950. In Comparative Example 4, the cold flake index was 0.842, so it was determined that condition 1that the cold flake index is equal to or less than 0.842 was satisfied, condition 2 that cold flakes do not reach the molding portion of the molding die  14  was satisfied, and condition 3 that cold flakes do not reach the molding portion of the molding die  14  under adverse conditions was satisfied. 
     Comparative Example 5 
     In Comparative Example 5, the thickness of the runner portion  22  was X 1 , the length (thickness) of the stamp portion  21  was X 2 , the length of the runner portion  22  was X 3 ×2.117, the stroke length of the tip  12  was X 4 ×0.910, the volume of the sprue guide portion  13  was X 5 ×1.196, and the total amount of heat transfer was X 6 ×0.956. In Comparative Example 5, the cold flake index was 0.871, so it was determined that condition 1 that the cold flake index is equal to or less than 0.842 was not satisfied, condition 2 that cold flakes do not reach the molding portion of the molding die  14  was satisfied, and condition 3 that cold flakes do not reach the molding portion of the molding die  14  under adverse conditions was not satisfied (cold flakes were mixed in the molded product). 
     Comparative Example 6 
     In Comparative Example  6 , the thickness of the runner portion  22  was X 1 , the length (thickness) of the stamp portion  21  was X 2 , the length of the runner portion  22  was X 3 ×2.450, the stroke length of the tip  12  was X 4 ×0.891, the volume of the sprue guide portion  13  was X 5 ×1.259, and the total amount of heat transfer was X 6 ×0.945. In Comparative Example 6, the cold flake index was 0.82, so it was determined that condition 1 that the cold flake index is equal to or less than 0.842 was satisfied, condition 2 that cold flakes do not reach the molding portion of the molding die  14  was satisfied, and condition 3 that cold flakes do not reach the molding portion of the molding die  14  under adverse conditions was satisfied. 
     Thus, by determining the shapes of the sleeve  11  and the sprue guide portion  13 , so that the cold flake index is equal to or less than 0.842, cold flakes do not reach the molding portion of the molding die  14  so the defect rate of the molded product can be reduced. 
     In addition, when the length of the runner portion  22  was increased with respect to Comparative Example 1 to decrease the cold flake index (Example 1, Comparative Example 4, and Comparative Example 6), in comparison with the situation when the thickness of the runner portion  22  was increased with respect to Comparative Example 1 to decrease the cold flake index (Comparative Example 2), and the situation when the length (thickness) of the stamp portion  21  was increased with respect to Comparative Example 1 to decrease the cold flake index (Comparative Example 3), the cold flake index can be greatly reduced. From this, when the shapes of the sleeve  11  and the sprue guide portion  13  are determined, so that the cold flake index is equal to or less than 0.842, it is preferable and effective to increase the length of the runner portion  22  in order to reduce the cold flake index. 
     Further, in addition to the above Example 1, Comparative Example 4, and Comparative Example 6, many experimental results were obtained in which cold flakes did not reach the molding portion of the molding die  14  by setting the cold flake index to be equal to or less than 0.842. Moreover, in addition to Comparative Examples 1 to 3, many experimental results were obtained in which cold flakes reached the molding portion of the molding die  14  by setting the cold flake index to exceed 0.842. As for these experimental results, similar results were obtained with different molding devices for molding different molded products. Furthermore, in addition to Comparative Example 5, many experimental results were obtained in which if the cold flake index was set to slightly exceed 0.842 (approximately 0.87), condition 2 that cold flakes do not reach the molding portion of the molding die  14  was satisfied, but cold flakes reached the molding portion of the molding die  14  under adverse conditions (condition 3 was not satisfied). As for these experimental results, similar results were obtained with different molding devices for molding different molded products. 
     From the above, it has been found that the numerical value of the predetermined value (0.842) is effective when the shapes of the sleeve  11  and the sprue guide portion  13  are determined, so that the cold flake index is equal to or less than the predetermined value (for example, 0.842). Further, the predetermined value may be changed according to the structure and size of the molding device  10 . Also in that case, the same experiments as described above are performed to determine the predetermined value. 
     Although the exemplary embodiment of the disclosure has been described above, as can be easily understood by those skilled in the art, the disclosure is not limited to such embodiment, and may be appropriately modified without departing from the scope of the disclosure. 
     For example, in the above embodiment, the control device  20  sequentially calculates the amount of heat transfer that changes continuously from the start of supply of the molten metal M 1  until the tip  12  slides to the position shown in  FIG.  2   , and calculates the total of the amounts as the total amount of heat transfer. However, data on the total amount of heat transfer under different conditions may be stored in a memory (not shown) as experimental result data, and when the conditions are the same, data on the total amount of heat transfer under the same conditions may be read from the memory without performing the above calculation, and the data may be used as the total amount of heat transfer. 
     In the above embodiment, the control device  20  calculates the volume of the sprue guide portion  13  based on various information (size) about the sprue guide portion  13  input by the operator. However, the volume data of the sprue guide portion  13  obtained in advance may be stored in a memory for each type of information (size) about the sprue guide portion  13 , and in the case of the sprue guide portion  13  with the same information, the volume data of the sprue guide portion  13  of the same information may be read from the memory without performing the above calculation, and the data may be used as the volume of the sprue guide portion  13 . 
     Although the sleeve  11  of a cylindrical shape is used in the above embodiment, any tubular shape, for example, a triangular tubular shape or a square tubular shape, may be used. 
     In the above embodiment, the tip  12  is slid at a constant speed, but the speed may be switched to a high speed on the way. In this case, the total contact area to be calculated is the total contact area from when the molten metal M 1  is poured into the sleeve  11  until the movement speed of the tip  12  switches to the high speed. In the embodiment, the residence time of the molten metal M 1  in the sleeve  11  can be shortened, and the time required for molding can also be shortened. 
     Further, not all of the components shown in the above embodiment are necessarily essential, which may be appropriately selected or omitted without departing from the scope of the disclosure.