A mold structure for solving the problem of local weld lines of injection molded products
By using a mold structure with blind holes for inserting heat-conducting blocks and inclined heating, the problem of weld lines was solved, the uniformity of melt temperature was achieved, the production cycle was shortened, and the product appearance was improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA HUALU PANASONIC AVC NETWORKS
- Filing Date
- 2023-09-21
- Publication Date
- 2026-05-12
AI Technical Summary
Existing high-gloss molds are difficult to effectively improve weld lines when processing products with many holes or limited by mold structure. Furthermore, large-area heating leads to excessively high overall mold temperature, affecting product production cycle and appearance quality.
A heat-conducting block is inserted into a blind hole on the fixed mold core. The heat-conducting block transfers heat to the melt confluence area through its lower surface. A heat insulation sleeve is provided on the outer periphery of the heat-conducting block. The lower surface of the heat-conducting block is provided with an inclined surface for gradual heating. Combined with a heater and a thermocouple to monitor the temperature, the uniformity of the melt temperature is ensured.
It effectively reduces mold cooling time, shortens production cycle, improves weld lines, avoids flow marks on product surface, and improves product quality.
Smart Images
Figure CN117183232B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of molds, and in particular to a mold structure for solving the problem of local weld lines in injection molded products. Background Technology
[0002] Excessive inserts, holes, and openings on plastic parts cause changes in the flow rate, streamlines, and temperature of the molten material as it flows through these features. When the molten material converges, weld lines and flow marks are easily formed, affecting the product's safety and appearance. Conventional high-gloss molds can improve weld lines in most products, but they are not suitable for products with too many holes or those limited by mold structure (conventional high-gloss molds use straight-through pipes with parallel mold cores for steam heating; when the core spacing is less than 20mm, straight-through pipes cannot be used).
[0003] For products where conventional high-gloss molds are not suitable, existing technologies typically use large-area heating to increase the temperature of the mold core in order to improve weld lines by making the melt temperature as uniform as possible. This results in an excessively high overall mold temperature, and the fitting precision of various mold components is easily affected by thermal expansion. At the same time, it requires more time for cooling during the manufacturing process, which not only increases the production cycle of the product, but also does not achieve the desired effect of removing weld lines. Summary of the Invention
[0004] This invention provides a mold structure to solve the problem of local weld lines in injection molded products, thereby improving weld lines in products that are not suitable for high-gloss molds.
[0005] To achieve the above objectives, the technical solution of the present invention is as follows:
[0006] A mold structure for solving the problem of local weld lines in injection molded products includes: a heater, a heat-conducting block, a heat insulation sleeve, and a fixed mold core;
[0007] The fixed mold core has a cavity on one side that mates with the moving mold core, and a blind hole for inserting a heat-conducting block on the other side of the fixed mold core. The blind hole is located at the melt confluence part of the product inside the cavity.
[0008] The heat-conducting block is equipped with a heater. One end of the heat-conducting block inserted into the blind hole has a lower surface that abuts against the bottom of the blind hole. A heat insulation sleeve is provided between the outer periphery of the heat-conducting block and the side wall of the blind hole.
[0009] The heat-conducting block has a first inclined surface and a second inclined surface arranged opposite to each other on the end of its lower surface, with the first inclined surface and the second inclined surface located on both sides of the lower surface, respectively.
[0010] The first inclined plane is inclined along the melt flowing toward the side where the first inclined plane is located, and the second inclined plane is inclined along the melt flowing toward the side where the second inclined plane is located.
[0011] Furthermore, the width δ of the lower surface is obtained according to the following formula:
[0012] δ=10a
[0013] In the above formula: a is the peak value of the melt flow front;
[0014] The angle between the first inclined plane and the bottom of the blind hole and the angle between the second inclined plane and the bottom of the blind hole are both acute angles θ. The acute angle θ is obtained from the thermal expansion Δl of the heat-conducting block, which is calculated according to the following formula:
[0015] Δl=(T-T1)×h×ɑ
[0016] In the above formula: T is the temperature of the heat-conducting block, T1 is the temperature of the fixed mold core, h is the height of the heat-conducting block, and α is the thermal expansion coefficient of the heat-conducting block material;
[0017] The acute angle θ is obtained according to the following formula:
[0018] θ=arctan(2Δl / (w-δ))
[0019] In the above formula: w is the width of the heat-conducting block.
[0020] Furthermore, both the first and second inclined surfaces are textured with a leather-like finish.
[0021] Furthermore, the depth of the texture is 5 μm.
[0022] Furthermore, it also includes thermocouples, which are disposed within the heat-conducting block.
[0023] The beneficial effects of this invention are:
[0024] This invention provides a mold structure for solving the problem of local weld lines in injection molded products. By opening blind holes in the fixed mold core corresponding to the molten metal confluence area of the product, a heat-conducting block with a heater is inserted into the blind hole. The heat-conducting block transfers heat to the molten metal confluence area of the product through its lower surface abutting against the bottom of the blind hole to improve weld lines. By providing a heat insulation sleeve between the outer periphery of the heat-conducting block and the side wall of the blind hole, the heat is concentrated at the bottom of the blind hole and the heat does not diffuse from the side wall of the blind hole to the entire fixed mold core. Compared with the large-area heating method in the prior art, this can effectively reduce the cooling time of the fixed mold core and shorten the production cycle of the product.
[0025] By setting a first inclined surface and a second inclined surface on the end of the heat-conducting block with a lower surface, respectively located on both sides of the lower surface, the heat-conducting block initially transfers heat to the melt fusion area only through the lower surface. As the overall temperature of the heat-conducting block rises, thermal expansion occurs, and the first and second inclined surfaces abut against the bottom of the blind hole. The temperature gradually rises from the center of the bottom of the blind hole to both sides. This gradual heating ensures that the melt, which gradually cools during the flow process, reaches a temperature as uniform as possible after heating, allowing the melt to completely fuse after fusion. This effectively improves weld lines and avoids flow marks on the surface of the product caused by uneven temperature distribution. Attached Figure Description
[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0027] Figure 1 This is a schematic diagram of a mold structure disclosed in this invention for solving the problem of local weld lines in injection molded products;
[0028] Figure 2 This is a schematic diagram of a heat-conducting block for a mold structure that solves the problem of local weld lines in injection molded products, as disclosed in this invention.
[0029] Figure 3 This is a schematic diagram of melt convergence in a mold structure that solves the problem of local weld lines in injection molded products, as disclosed in this invention.
[0030] Figure 4 This is a schematic diagram of melt flow simulation of a mold structure for solving the problem of local weld lines in injection molded products, as disclosed in this invention.
[0031] Figure 5 for Figure 4 Flow wall thickness profile;
[0032] Figure 6 This invention discloses a mold structure for solving the problem of local weld lines in injection molded products, and provides schematic diagrams of weld lines in different designs.
[0033] In the picture:
[0034] 1. Heater; 2. Thermocouple; 3. Heat-conducting block; 31. First inclined surface; 32. Second inclined surface; 33. Lower surface; 4. Heat insulation sleeve; 5. Fixed mold core; 6. Product; 7. Moving mold core. Detailed Implementation
[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0036] This embodiment provides a mold structure for solving the problem of local weld lines in injection molded products, such as... Figure 1 As shown, it includes: heater 1, heat-conducting block 3, heat insulation sleeve 4, and fixed mold core 5;
[0037] The fixed mold core 5 has a cavity on one side that mates with the moving mold core 7, and the fixed mold core 5 has a blind hole for inserting the heat-conducting block 3 on the other side. The blind hole is located at the melt confluence part of the product 6 inside the cavity.
[0038] The heat-conducting block 3 is provided with a heater 1. One end of the heat-conducting block 3 inserted into the blind hole is provided with a lower surface 33 that abuts against the bottom of the blind hole. A heat insulation sleeve 4 is provided between the outer periphery of the heat-conducting block 3 and the side wall of the blind hole.
[0039] like Figure 2 As shown, the heat-conducting block 3 has a first inclined surface 31 and a second inclined surface 32 arranged opposite to each other on the end of the lower surface 33. The first inclined surface 31 and the second inclined surface 32 are respectively located on both sides of the lower surface 33.
[0040] The first inclined surface 31 is inclined along the melt flowing toward the side where the first inclined surface 31 is located, and the second inclined surface 32 is inclined along the melt flowing toward the side where the second inclined surface 32 is located;
[0041] This embodiment provides a mold structure for solving the problem of local weld lines in injection molded products. By opening blind holes on the fixed mold core 5 corresponding to the melt junction of the product 6, a heat-conducting block 3 with a heater 1 is inserted into the blind hole. The heat-conducting block 3 transfers heat to the melt junction of the product 6 through its lower surface 33 against the bottom of the blind hole to improve weld lines. By providing a heat insulation sleeve 4 between the outer periphery of the heat-conducting block 3 and the side wall of the blind hole, the heat is concentrated at the bottom of the blind hole and the heat does not diffuse from the side wall of the blind hole to the entire fixed mold core 5. Compared with the large-area heating method in the prior art, this can effectively reduce the cooling time of the fixed mold core 5 and reduce the production cycle of the product.
[0042] By providing a first inclined surface 31 and a second inclined surface 32 on the ends of the heat-conducting block 3 with a lower surface 33, respectively located on both sides of the lower surface 33, the heat-conducting block 3 initially transfers heat to the melt fusion area only through the lower surface 33. As the overall temperature of the heat-conducting block 3 rises, thermal expansion occurs, and the first inclined surface 31 and the second inclined surface 32 abut against the bottom of the blind hole. The temperature gradually rises from the center of the bottom of the blind hole to both sides. The gradual heating makes the temperature of the melt that is gradually cooled during the flow as uniform as possible after heating, so that the melt can be completely fused after fusion, thereby effectively improving the weld line and avoiding flow marks on the surface of the product caused by uneven temperature distribution.
[0043] In a specific embodiment, the width δ of the lower surface 33 is obtained according to the following formula:
[0044] δ=10a
[0045] In the above formula: 'a' represents the peak value of the melt flow front; (plastic melt is a typical non-Newtonian fluid, such as...) Figure 3 As shown, the flow of the melt in the mold cavity approximates a parabolic shape, with the peak value of its flow front being 'a'. The value of 'a' is determined by the material and wall thickness of the plastic and can be obtained through simulation.
[0046] The angle between the first inclined surface 31 and the bottom of the blind hole and the angle between the second inclined surface and the bottom of the blind hole are both acute angles θ. The acute angle θ is obtained from the thermal expansion Δl of the heat-conducting block 3. The thermal expansion Δl is obtained according to the following formula:
[0047] Δl=(T-T1)×h×ɑ
[0048] In the above formula: T is the temperature of the heat-conducting block 3, T1 is the temperature of the fixed mold core 5, h is the height of the heat-conducting block 3, and α is the coefficient of thermal expansion of the material of the heat-conducting block 3;
[0049] The acute angle θ is obtained according to the following formula:
[0050] θ=arctan(2Δl / (w-δ))
[0051] In the above formula: w is the width of the heat-conducting block 3.
[0052] In a specific embodiment, both the first inclined surface 31 and the second inclined surface 32 are processed with a leather texture;
[0053] During the thermal expansion of the heat-conducting block 3, the presence of texture makes the surfaces of the first inclined surface 31 and the second inclined surface 32 uneven, causing the contact area between the first inclined surface 31 and the second inclined surface 32 and the bottom of the blind hole to gradually increase with thermal expansion, resulting in a more gradual heating rate, a more uniform melt temperature distribution, and better product molding effect.
[0054] To better illustrate the effectiveness of the mold structure disclosed in this invention for solving the problem of local weld lines in injection molded products, an ideal model is established in Moldflow. Although non-Newtonian fluids are often non-uniform polyphase dispersion systems or non-uniform multiphase mixtures at the microscopic level, in the analysis, the system is considered to be a uniform or pseudo-uniform dispersion system. The plastic material is ABS, and the wall thickness of the product is 2.5mm. Figure 4 and Figure 5 As shown, the peak value of the melt flow front obtained from the simulation is a = 1.36 mm. The melt temperature for mold flow analysis is taken as 260℃ (the melt temperature during injection molding is generally 250℃-270℃), the shear stress is taken as 0.3 MPa, and the maximum shear rate is taken as 50000 s. -1 Initial mold flow analysis revealed severe weld lines. The original mold design employed a rapid cooling and heating high-gloss mold structure, with a fixed mold core temperature of 75℃, a moving mold core temperature of 50℃, and a steam temperature set at 140℃ in the straight-through pipe. Even after trial molding, the finished product still exhibited noticeable weld lines. Figure 6 As shown in (1);
[0055] exist Figure 6 (1) Based on the mold structure used, the straight pipe was removed, blind holes were opened in the fixed mold core, and heat-conducting block 3 and heater 1 were added. After trial molding, the weld lines of the product were improved, such as Figure 6 (2) is shown;
[0056] exist Figure 6 (2) Based on the mold structure used, a first inclined surface 31 and a second inclined surface 32 were added to the heat-conducting block 3. After trial molding, the weld lines of the product were further improved, such as Figure 6 As shown in (3).
[0057] exist Figure 6 (3) Based on the mold structure used, a textured surface is added to the first inclined surface 31 and the second inclined surface 32. After trial molding, the weld lines of the product are almost invisible, such as... Figure 6 As shown in (4).
[0058] In a specific embodiment, the depth of the texture is 5μm. At this depth, the temperature rises gradually and the heating rate adapts to the production cycle.
[0059] In a specific embodiment, a thermocouple 2 is also included, which is disposed inside the heat-conducting block 3 to measure the temperature of the heat-conducting block 3.
[0060] The present invention provides a mold structure for solving the problem of local weld lines in injection molded products. It is suitable for producing products made of engineering plastics such as ABS, PC+ABS, and PP, and for which there are high requirements for safety performance or appearance and weld lines are not allowed.
[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A mold structure for solving the problem of local weld lines in injection molded products, characterized in that, include: Heater (1), heat-conducting block (3), heat insulation sleeve (4) and fixed mold core (5); The fixed mold core (5) has a cavity on one side that mates with the moving mold core (7), and the fixed mold core (5) has a blind hole for inserting the heat-conducting block (3) on the other side. The blind hole is located at the melt confluence part of the product (6) inside the cavity. The heat-conducting block (3) is provided with a heater (1), and the end of the heat-conducting block (3) inserted into the blind hole is provided with a lower surface (33) that abuts against the bottom of the blind hole. A heat insulation sleeve (4) is provided between the outer periphery of the heat-conducting block (3) and the side wall of the blind hole. The heat-conducting block (3) has a first inclined surface (31) and a second inclined surface (32) arranged opposite to each other on the end of the lower surface (33). The first inclined surface (31) and the second inclined surface (32) are located on both sides of the lower surface (33). The first inclined surface (31) is inclined along the melt flowing toward the side where the first inclined surface (31) is located, and the second inclined surface (32) is inclined along the melt flowing toward the side where the second inclined surface (32) is located; The width δ of the lower surface (33) is obtained according to the following formula: δ=10a In the above formula: a is the peak value of the melt flow front; The angle between the first inclined plane (31) and the bottom of the blind hole and the angle between the second inclined plane and the bottom of the blind hole are both acute angles θ. The acute angle θ is obtained by the thermal elongation Δl of the heat-conducting block (3). The thermal elongation Δl is obtained according to the following formula: Δl = (T - T1) × h × ɑ In the above formula: T is the temperature of the heat-conducting block (3), T1 is the temperature of the fixed mold core (5), h is the height of the heat-conducting block (3), and α is the coefficient of thermal expansion of the heat-conducting block (3). The acute angle θ is obtained according to the following formula: θ=arctan(2Δl / (w-δ)) In the above formula: w is the width of the heat-conducting block (3).
2. The mold structure for solving the problem of local weld lines in injection molded products according to claim 1, characterized in that, Both the first inclined surface (31) and the second inclined surface (32) are processed with a leather texture.
3. The mold structure for solving the problem of local weld lines in injection molded products according to claim 2, characterized in that, The depth of the texture is 5 μm.
4. The mold structure for solving the problem of local weld lines in injection molded products according to claim 1, characterized in that, It also includes a thermocouple (2), which is disposed inside the heat-conducting block (3).