Two-part core insert and injection moulding tool having two-part core insert
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- FOSTAG FORMENBAU AG
- Filing Date
- 2024-06-04
- Publication Date
- 2026-05-20
AI Technical Summary
Existing injection molding tools face challenges in producing thin-walled, tubular products like blood collection tubes and syringes with uniform wall thickness due to core misalignment and deformation caused by high injection pressure, leading to irregular wall thickness and defective parts.
A two-piece core insert design for injection molding tools, featuring a hard metal core insert and a conventional tool steel core base, with a central conical section and rear cylindrical section, allowing for precise centering and reduced material costs, along with venting grooves for efficient air removal, which enhances the tool's stiffness and cooling properties.
The two-piece core insert design significantly reduces core offset and deformation, enabling the production of tubular products with uniform wall thickness and reduced cycle times, while maintaining cost-effectiveness and improving cooling efficiency.
Smart Images
Figure CH2024050027_16012025_PF_FP_ABST
Abstract
Description
[0001] TWO-PART CORE INSERT AND INJECTION MOLD WITH TWO-PART CORE INSERT
[0002] Technical area
[0003] The invention relates to an injection molding tool with at least one cavity for producing thin-walled, tubular injection-molded products, in particular blood collection tubes, test tubes, syringes or pipette tips, comprising a die holding plate which has at least one cavity-forming die, a core holding plate which has at least one core unit with a cavity-forming core, and at least one stripping ring for stripping the injection-molded product from the cavity-forming core.
[0004] Technical background
[0005] In the production of thin-walled, tubular injection-molded products, in particular blood collection tubes, test tubes, syringes or pipette tips, a uniform wall thickness is of great importance, since even small deviations in the wall thickness can lead to severe deformations during cooling and demolding of the injection-molded products due to volume shrinkage.
[0006] The cavities for such injection-molded products are formed by a mold and a core arranged within it. To achieve a uniform wall thickness, the core must be positioned in a parting plane perpendicular to the mold closing direction so that it is precisely centered with the cavity-forming mold.
[0007] Injection molding tools known from WO2017215801 and WO2020234065 for such thin-walled, container-like injection-molded products comprise a die holding plate in which at least one cavity-forming die unit or die is firmly held, a core holding plate on which at least one cavity-forming core unit or core is held, and a stripping ring movably mounted on the core unit to strip the finished injection-molded product from the core after the tool has been opened. The core or core unit is provided with an adjustable core centering device for setting precise centering in the die.
[0008] With very thin walls, a further problem arises because the injection pressure increases during injection of the plastic melt. This can lead to long, thin cores in particular being pushed out of their centering by the injected plastic melt, resulting in uneven wall thicknesses and ultimately defective injection-molded parts. Therefore, there is a need for high-precision injection molding tools to prevent such core misalignment and produce injection-molded parts with a uniform wall thickness.
[0009] Description of the invention
[0010] One object of the invention is to provide a cavity-forming core unit for a high-precision injection molding tool for producing thin-walled, tubular injection-molded products with a uniform wall thickness. A further object is to reduce cycle times and / or the amount of plastic.
[0011] At least one of the objects is achieved by a cavity-forming core unit for an injection molding tool having the features of claim 1 and an injection molding tool according to claim 13.
[0012] The cavity-forming core unit for an injection molding tool with at least one cavity has a front cavity-forming core, a central conical section, and a rear, preferably cylindrical and optionally stepped, section. The cavity-forming core unit is formed in two parts with a core base and a central core insert, wherein the core insert forms the front cavity-forming core and a central conical section and a rear
[0013] The core insert is connected to the rear
[0014] Fastening section in the core base such that the central conical section of the core insert forms a front part of the central conical section of the core unit.
[0015] The two-part design of the cavity-forming core unit means that the relatively slim central core insert can be made of cemented carbide, while the core base can be made of conventional tool steel. The cemented carbide core is much stiffer than a core made of conventional tool steel, and core offset relative to the die is significantly reduced, even at high injection pressures. This makes it possible to produce tubular injection-molded products with thin walls. The two-part design of the core unit also makes it possible to design the entire core insert to be slim, i.e. with the smallest possible diameter, and despite the higher costs for cemented carbide parts, the overall material costs for the core unit are not significantly increased. This is primarily due to the use of smaller blanks.In addition, machining a slimmer core insert is easier because significantly less material needs to be removed from the blank. The improved cooling properties of the cemented carbide also reduce cycle times during the injection molding process.
[0016] The two parts of the core unit can be manufactured independently and then joined together. No further processing is required. If necessary, the vent gap surface described below can be reground to increase the air gap, which is typically in the range of 5-13 micrometers.
[0017] The core base forms the rear section of the core unit and is thus accommodated in a corresponding recess in the core holding plate. The stripper ring is typically held in a stripper plate located between the die holding plate and the core holding plate. The stripper ring, which serves to strip the injection-molded product from the core unit when the injection mold is opened, has a corresponding opening to precisely accommodate the central conical section of the core unit. A front surface of the stripper ring forms part of the cavity and pushes the finished injection-molded product off the core when the injection mold is opened.
[0018] Preferred embodiments of the invention are set out in the dependent claims.
[0019] In some embodiments, the rear attachment section can have a circumferential collar, a shoulder, or a stop at the rear end. The circumferential collar serves as a stop when joining the two parts (core insert and core foot) to form the finished core unit, ensuring length tolerances are maintained and the conical surfaces of the two parts are precisely aligned. Furthermore, the circumferential collar facilitates the production of the core insert and the removal of material from the remaining area.
[0020] In some embodiments, the core insert can be precisely received and secured with the rear fastening section in a complementary opening in the core base. The fastening can be achieved by screwing, gluing, welding, or shrinking, with a shrink connection being preferred due to its strength and play-free, precise positioning of the two parts.
[0021] In some embodiments, the central conical section of the core insert can have a circumferential venting gap surface, which, when the mold is closed, forms a venting gap adjacent to the cavity together with a scraper ring. When the injection mold is closed, the circumferential venting gap surface, together with the scraper ring, forms a venting gap for venting the cavity during injection of the plastic melt. The venting gap is typically about 5-13 micrometers deep. The circumferential venting gap surface is generally about 1.5 mm long.
[0022] In some embodiments, the central conical section of the core unit can have a first circumferential venting groove, which directly adjoins the circumferential venting gap surface. The air from the cavity passes through the narrow venting gap into the much larger venting groove and can thus efficiently escape into other areas of the tool. The first venting groove can be formed either in the central conical region of the core insert or in the central conical region formed by the core base.
[0023] In some embodiments, the central conical section of the core unit can have at least one axial venting groove, which is connected to the first circumferential venting groove and extends into the rear region of the central conical section of the core unit. The cavity, the venting gap, the circumferential venting groove, and the axial venting groove are fluidly connected to each other for efficient air removal from the cavity to other areas of the tool.
[0024] In some embodiments, at a parting line between the core base and the core insert in the central conical region of the core unit, a shoulder may be formed on the core base, which shoulder forms the first circumferential venting groove or a second circumferential venting groove.
[0025] When designed as a first circumferential venting groove, the central conical section of the core insert consists only of the circumferential venting gap surface, which borders the first circumferential venting groove. The at least one axial venting groove adjoins the first circumferential venting groove. The carbide core insert does not need to be provided with an axial venting groove, which simplifies its machining.
[0026] When designed as a second circumferential venting groove, the central conical section of the core insert has, in addition to the circumferential venting gap surface, the adjacent first circumferential venting groove. In addition, a front part of the at least one axial venting groove is formed in the central conical section of the core insert, which connects the first axial venting groove with the second axial venting groove. A rear part adjoins the second circumferential venting groove. The second circumferential venting groove, which lies in the parting line between the core base and core insert, has the additional function that when the two parts are joined together, the parts of the axial venting groove do not have to be exactly aligned with one another in the axial direction. Even if the two parts are axially rotated, all venting grooves are fluidically connected to one another.
[0027] In some embodiments, the core base can have at least one additional circumferential venting groove, which is connected to the first venting groove and / or the second venting groove via the at least one axial venting groove. If there are multiple circumferential venting grooves, these are each fluidically connected via the at least one axial venting groove.
[0028] In some embodiments, the circumferential and axial venting grooves are approximately 0.5 to 1 mm deep.
[0029] In some embodiments, the at least one axial venting groove may be formed in the core base and in the core insert, or it may be formed only in the core base, for example if the shoulder of the core base forms the first circumferential groove.
[0030] In some embodiments, the core insert may have a bore for cooling.
[0031] In some embodiments, an injection point may be arranged centrally in the region of the tip of the cavity-forming core or laterally with respect to a longitudinal axis of a, preferably tubular, injection-molded product.
[0032] In some embodiments, the core insert may be made of hard metal.
[0033] The invention further relates to an injection molding tool with at least one cavity for producing thin-walled, tubular injection-molded products, in particular blood collection tubes, test tubes, syringes or pipette tips, comprising a die holding plate which has at least one cavity-forming die as described above, a core holding plate which has at least one cavity-forming core unit, and at least one stripping ring for stripping the injection-molded product from the cavity-forming core unit.
[0034] Short explanation of the figures
[0035] The invention will be explained in more detail below using exemplary embodiments in conjunction with the drawing(s). In the drawing(s): Fig. 1 shows a perspective view of a two-part core unit with several circumferential venting grooves;
[0036] Fig. 2 is a sectional view of the core unit of Fig. 1;
[0037] Fig. 3 a section of the sectional view from Fig. 2;
[0038] Fig. 4 is a perspective view of a two-part core unit with a circumferential venting groove;
[0039] Fig. 5 is a sectional view of the core unit of Fig. 4;
[0040] Fig. 6 is a section of the sectional view from Fig. 5.
[0041] Ways to implement the invention
[0042] Figures 1 to 6 show two embodiments of a core unit 3, such as can be used in an injection molding tool for producing thin-walled, tubular injection-molded products, in particular blood collection tubes, test tubes, syringes, or pipette tips. Figures 1 to 3 show a first embodiment, and Figures 4 to 6 show a second embodiment, with some features being interchangeable between the two embodiments.
[0043] In Figures 2 and 5, further elements of the injection molding tool are shown schematically.
[0044] The injection molding tool has at least one cavity 4 and comprises a die holding plate and a core holding plate. At least one cavity-forming die 1 is formed or received in the die holding plate. At least one core unit 3 with a cavity-forming core 31 is received in the core holding plate 2. The cavity-forming die 1 and the cavity-forming core 31 define the cavity 4 into which the plastic melt is injected.
[0045] Furthermore, the injection molding tool has at least one stripper ring 5 for stripping the injection-molded product from the cavity-forming core. The stripper ring 5 also delimits the cavity 4 in an area between the die 1 and the core unit 3. The stripper ring 5 is typically held in a stripper plate arranged between the die holding plate and the core holding plate.
[0046] The core unit 3 is designed in two parts and has a core base 6 and a central core insert 7. The core base 6 is made of conventional tool steel. The central core insert 7 is made of hard metal. The core unit 3 essentially has three sections: a front cavity-forming core 31, a middle conical section 32, 72, and a rear cylindrical or cylindrically stepped section 33. The core unit 3 is received and secured in the core holding plate by the cylindrical section 33. When the injection mold is closed, the cavity-forming core 31 is centered in the die 1 using suitable devices, such as those described in WO2017215801 and WO2020234065. The central conical section 32, 72 is formed by both the core base 6 and the core insert 7 and, when the injection molding tool is closed, is precisely received in a complementary recess of the scraper ring 5.
[0047] The core insert 7 essentially also has three sections: the front cavity-forming core 31, a central conical section 72, which forms part of the central conical section 32 of the core unit 3, and a rear fastening section 73 for fastening the core insert 7 in the core base 6. The fastening section 73 is cylindrical and has a circumferential collar 74 at the rear end. This circumferential collar 74 serves as a stop for the exact positioning of the cavity-forming core 31 and the central conical section 72 relative to the core base 6 when joining the core base 6 and core insert 7. The core base 6 and core insert 7 are preferably joined by means of a shrink connection. In the embodiments shown, the core insert 7 has a bore 76 for cooling during the injection molding process.
[0048] The central conical section 72 of the core insert 7 has a circumferential conical venting gap surface 75 at its front end. This, together with an inner conical surface of the wiper ring 5, forms an air gap when the injection mold is closed, through which air displaced from the cavity during the injection molding process can escape. The air gap is typically 5 to 13 micrometers thick. The length of the air gap or venting gap surface 75 is typically approximately 1.5 millimeters. To further discharge the escaping air, a first circumferential venting groove 8 and at least one axial venting groove 10 are arranged in the central conical region 32 of the core unit 3. The first circumferential venting groove 8 directly borders the venting gap or venting gap surface 75.The axial venting groove 10 borders the first circumferential venting groove 8 and leads axially into the rear region of the central conical section 32 of the core unit 3. In the rear region, the air can escape through further venting means or parting lines in the injection molding tool. The two embodiments of Figures 1 to 3 and 4 to 6 differ essentially in the design of the venting means 8, 9, 10, 62, 75 and the arrangement of the parting line T between the core base 6 and the core insert 7.
[0049] In the embodiment of Figures 1 to 3, several circumferential venting grooves 8, 9, 62 and at least one axial venting groove 10 are present. A first circumferential venting groove 8 is formed directly adjacent to the venting gap surface 75 in the central conical section 72 of the core insert 7. In addition, the rear region of the central conical section 72 of the core insert 7 has a front part of the at least one axial venting groove 10. A second circumferential venting groove 9 is formed by a shoulder 61 at the front end of the core base 6. The dividing line T between the core base 6 and the core insert 7 is positioned such that it ends in the region of the at least one axial venting groove 10. An exact alignment of the core base 6 and the core insert 7 around the longitudinal axis is not necessary, since the axial venting groove 10 is formed by the second circumferential venting groove 9, which is formed on the parting line T.Even if the parts of the axial venting groove 10 on the core base 6 and the core insert 7 are not aligned, the two parts of the axial venting groove 10 are still fluidly connected via the second circumferential venting groove 9.
[0050] Figures 1 to 3 show additional venting grooves 62 in the central conical section 32 of the core base 6. These are optional. Furthermore, the embodiment shown shows two axial venting grooves 10, which are arranged diametrically opposite each other.
[0051] In the embodiment of Figures 4 to 6, only one circumferential venting groove is present, which is formed by a shoulder 61 at the front end of the core base 6. The dividing line T between the core base 6 and the core insert 7 is positioned such that it is aligned with the further end of the venting gap surface 75. After the core base 6 and the core insert 3 are joined together, a first circumferential venting groove 8 is formed directly adjacent to the venting gap surface 75. The first circumferential venting groove 8 is adjoined by at least one axial venting groove 10. In the embodiment shown, two axial venting grooves 10 are shown, which are arranged diametrically. The embodiment can also have further venting grooves (not shown) formed in the core base 6, which are each fluidically connected by the at least one axial venting groove.In this embodiment, an exact alignment of the core base 6 and the core insert 7 around the longitudinal axis is not necessary, since the axial venting groove 10 ends in the first circumferential venting groove 8, which is formed on the parting line T. In addition, the manufacture of the core insert is simplified, since it does not have an axial venting groove 10.
[0052] List of designations
[0053] 1 matrix holding plate, cavity-forming matrix
[0054] 2 core holding plate
[0055] 3 cavity-forming core unit
[0056] 31 anterior cavity-forming core of the nuclear unit
[0057] 32 middle conical section of the core unit
[0058] 33 rear cylindrical section of the core unit
[0059] 4 Cavity
[0060] 5 scraper ring
[0061] 6 core foot
[0062] 61 paragraph
[0063] 62 circumferential ventilation groove
[0064] 7 central core deployment
[0065] 72 middle conical section of the core insert
[0066] 73 rear fastening section of the core insert
[0067] 74 all-round collar
[0068] 75 venting gap area
[0069] 76 bore
[0070] 8 first circumferential venting groove
[0071] 9 second circumferential venting groove
[0072] 10 axial venting groove
[0073] T dividing line
Claims
Patent claims 1. Cavity-forming core unit (3) for an injection molding tool with at least one cavity (4) comprising a front cavity-forming core (31), a central conical section (32) and a rear, preferably cylindrical, section (33); characterized in that the cavity-forming core unit (3) is designed in two parts with a core base (6) and a central core insert (7), wherein the core insert forms the front cavity-forming core (31) and has a central conical section (72) and a rear cylindrical fastening section (73); wherein the core insert (7) is connected to the rear fastening section (73) in the core base (6) is fixed in such a way that the central conical section (72) of the core insert (7) forms a front part of the central conical section (33) of the core unit (3).
2. Cavity-forming core unit (3) according to claim 1, characterized in that the rear fastening section (73) has a circumferential collar (74) at the rear end.
3. Cavity-forming core unit (3) according to one of the preceding claims, characterized in that the core insert (7) with the rear fastening section (73) is received and fastened in a complementary opening in the core base (6) with a precise fit.
4. Cavity-forming core unit (3) according to one of the preceding claims, characterized in that the core insert (7) is fastened in the core base (6) by means of a shrink connection.
5. Cavity-forming core unit (3) according to one of the preceding claims, characterized in that the central conical section (72) of the core insert (7) has a circumferential venting gap surface (75) which, when the tool is closed, together with a scraper ring (5) forms a venting gap adjoining the cavity (4).
6. Cavity-forming core unit (3) according to claim 5, characterized in that the central conical section (32) of the core unit (3) has a first circumferential venting groove (8) which adjoins the venting gap surface (75).
7. Cavity-forming core unit (3) according to claim 6, characterized in that the central conical section (32) of the core unit (3) has at least one axial venting groove (10) which is connected to the first circumferential venting groove (8) and extends into the rear region of the central conical section (32) of the core unit (3).
8. Cavity-forming core unit (3) according to claim 6 or 7, characterized in that at a parting line (T) between the core base (6) and the core insert (7) in the central conical region (32) of the core unit (3) on the core base (6) a shoulder (61) is formed, which forms the first circumferential venting groove (8) or a second circumferential venting groove (9).
9. Cavity-forming core unit (3) according to claim 7 or 8, characterized in that the core base (6) has at least one further circumferential venting groove (62) which is connected to the first venting groove and / or the second venting groove via the at least one axial venting groove (10).
10. Cavity-forming core unit (3) according to one of the preceding claims, characterized in that the core insert has a bore (76) for cooling.
11. Cavity-forming core unit (3) according to one of the preceding claims, characterized in that an injection point is arranged centrally in the region of the tip of the cavity-forming core (31) or laterally with respect to a longitudinal axis of an injection-molded product.
12. Cavity-forming core unit (3) according to one of the preceding claims, characterized in that the core insert (7) is made of hard metal.
13. Injection molding tool with at least one cavity (4) for producing thin-walled, tubular injection-molded products, in particular blood collection tubes, test tubes, syringes or pipette tips, comprising a die holding plate which has at least one cavity-forming die (1), a core holding plate (2) which has at least one cavity-forming core unit (3) according to one of the preceding claims, and at least one scraper ring (5) for scraping the injection-molded product from the at least one cavity-forming core unit (3).