Method for producing a moulded part by means of a plastics injection moulding machine, moulded part, insert and injection moulding tool for carrying out the method

Abstract

A method for producing a moulded part by means of a plastics injection moulding machine is proposed, the plastics injection moulding machine comprising an injection moulding tool (9) having a cavity (8) that is in the form of a hollow mould and constitutes a negative shape of the moulded part (20, 25). The injection moulding tool (9) is fitted with at least one inlet for a liquid plastics melt and is designed such that, when the liquid plastics melt is being injected into the cavity, at least two flow fronts (16, 17) of the plastics melt form, meeting while the cavity is being filled and forming a weld line (23, 31) as the melt solidifies. While the plastics melt is spreading out in the cavity (8), the flow fronts (16, 17) are influenced such that the surface areas of the flow fronts (16, 17) are enlarged, with the flow fronts (16, 17) having first flow-front portions (18) and second flow-front portions (19), and the plastics melt in the first flow-front portions (18) preceding the plastics melt in the second flow-front portions (19).

Description

[0001] Title: Method for producing a molded part by means of

[0002] Plastic injection molding machine, molded part, insert and injection mold for carrying out the process

[0003] DESCRIPTION

[0004] The invention is based on a method for producing a molded part by means of a plastic injection molding machine, a molded part produced by the method, as well as an insert and an injection molding tool for carrying out the method.

[0005] During plastic injection molding of a molded part, a plastic is liquefied and the liquid plastic melt is injected under pressure into an injection mold. The injection mold has a cavity that determines the shape and surface structure of the molded part to be manufactured. The cavity represents a negative mold of the molded part. In the injection mold, the liquid plastic returns to its solid state through cooling and / or crosslinking and solidifies. Finally, the finished molded part is removed from the injection mold. In this way, molded parts can be produced cost-effectively in large quantities. The molded parts can have almost any shape and surface structure. This also includes molded parts that are designed as hollow bodies and have a molded part wall that defines a molded part cavity.The plastic melt can be injected into the cavity via one or more inlets on the injection mold. As the liquid plastic melt spreads within the cavity, the melt can form multiple flow fronts. When the flow fronts meet, a weld line forms at the boundary. The plastic melt has already partially cooled at the flow front and has a lower temperature than in the areas behind the flow front. This means that the plastic melt does not mix at the meeting flow fronts, or only mixes to a slight extent. Depending on its position on the molded part and the composition of the plastic melt, the weld line is more or less visible on the finished molded part. If the plastic is reinforced with fibers, for example glass fibers, carbon fibers, aramid fibers, or natural fibers, the fibers do not bond at the weld line.Furthermore, the fibers can be aligned along the weld line. This weakens the molded part at the weld line. Only significantly lower forces can be transmitted before cracks, fractures, or general component failure occur.

[0006] The invention is based on the object of providing a method for producing a molded part, a molded part produced by the method, as well as an insert and an injection mold for carrying out the method, which avoid a weakening of the molded part in the region of a weld line and ensure that the flow fronts connect in a reliable manner.

[0007] This object is achieved by a method having the features of claim 1, by a molded part having the features of claim 6, by an insert having the features of claim 13 and by an injection molding tool having the features of claim 17. The method is characterized in that the flow fronts are specifically influenced as the plastic melt spreads in the cavity. This leads to an enlargement of the surfaces of the flow fronts, wherein the flow fronts have first flow front sections and second flow front sections. The plastic melt in the first flow front sections leads the plastic melt in the second flow front sections. The flow fronts therefore do not have a surface that runs essentially perpendicular to the main flow direction of the plastic melt. Instead, the surface of the flow fronts is, for example, wave-shaped or has a sawtooth shape.The flow front sections interlock when they meet. This creates a larger contact area and significantly increases the strength in the entire area where the flow fronts interlock. A sharply defined area of ​​reduced strength is avoided. This allows significantly higher forces to be transferred in the weld line area before a crack, fracture, or general component failure occurs. If the plastic melt contains reinforcing fibers, these are oriented in different directions and do not exhibit a consistent fiber orientation. This also increases the strength in the weld line area.

[0008] According to an advantageous embodiment of the invention, the first flow front sections of a first flow front are opposite the second flow front sections of a second flow front. Furthermore, the second flow front sections of the first flow front are opposite the first flow front sections of the second flow front. When the first flow front meets the second flow front, the first flow front sections of the first flow front meet the second flow front sections of the second flow front, and the second flow front sections of the first flow front meet the first flow front sections of the second flow front. This ensures a tooth-like interlocking of the plastic melt of the first flow front with the plastic melt of the second flow front.

[0009] According to a further advantageous embodiment of the invention, the flow fronts are influenced by first cavity sections and by second cavity sections of the cavity. First and second cavity sections are arranged alternately in the cavity. The first cavity sections have a larger cross-section than the second cavity sections. The liquid plastic melt spreads faster in the first cavity sections than in the second cavity sections. This results in the plastic melt moving faster in the flow direction in the first cavity sections, forming first flow front sections, while in the second cavity sections the plastic melt spreads more slowly in the flow direction, forming second flow front sections.

[0010] According to a further advantageous embodiment of the invention, the flow fronts are influenced by an insert that is inserted into the cavity before the injection mold is closed. The insert is partially or completely overmolded with the liquid plastic melt. The insert has first insert sections and second insert sections, such that the plastic melt spreads more quickly in the cavities defined by the cavity and the first insert sections due to a larger cross-section than in the cavities defined by the cavity and the second insert sections.

[0011] According to a further advantageous embodiment of the invention, the flow fronts are influenced by multi-component injection molding. In this case, a first-injected component of a multi-component injection molding serves to manipulate the flow front of a subsequently injected component. In this case, the geometry required for flow front manipulation is created by the first component on the side that will later be overmolded with a second plastic component. In a second step, the first component is overmolded with the second component, wherein first and second flow front sections of the flow fronts of the second component are formed due to the geometry created with the first component. The molded part according to the invention with the features of claim 6 is characterized in that it comprises a weld line formed by the meeting of two flow fronts, which has first and second weld line sections.The first and second weld line sections form an alternating weld line. The weld line therefore does not follow a straight line.

[0012] According to a further advantageous embodiment of the molded part according to the invention, the first and second sections of the weld line are offset from one another in such a way that the weld line has a wave-shaped course.

[0013] According to a further advantageous embodiment of the molded part according to the invention, it is designed as a hollow body at least in sections.

[0014] According to a further advantageous embodiment of the molded part according to the invention, it is designed as a plate at least in sections.

[0015] According to a further advantageous embodiment of the molded part according to the invention, it has first molded part sections and second molded part sections, wherein the cross section of the first molded part sections is larger than the cross section of the second molded part sections.

[0016] According to a further advantageous embodiment of the molded part according to the invention, it is equipped with an insert which is overmolded with plastic.

[0017] The insert according to the invention with the features of claim 13 is characterized in that it has first insert sections and second insert sections which are designed such that the plastic melt spreads more quickly in the cavities delimited by the cavity and the first insert sections due to a larger cross section than in the cavities delimited by the cavity and the second insert sections.

[0018] According to a further advantageous embodiment of the insert according to the invention, it consists of a material which is dimensionally stable under the influence of the temperature and pressure prevailing in the injection mold.

[0019] According to a further advantageous embodiment of the insert according to the invention, it consists at least partially of plastic with reinforcement made of glass, aramid, carbon, or natural fibers. The plastic can be, for example, a thermoplastic, thermoset, or elastomer. Alternatively, the insert can be made of metal, ceramic, a natural material, or any other suitable material. The insert can be manufactured by injection molding, die casting, embossing, forging, punching, machining, or a combination of the aforementioned processes.

[0020] The injection molding tool according to the invention with the features of claim 17 is characterized in that the cavity of the injection molding tool has first cavity sections and second cavity sections influencing the flow fronts of the plastic melt, wherein first and second cavity sections are arranged alternately in the cavity and the first cavity sections have a larger cross-section than the second cavity sections.

[0021] Further advantages and advantageous embodiments can be found in the following description, the drawings, and the claims. Drawing

[0022] The drawing shows a molded part and a cavity from the prior art and exemplary embodiments of the subject matter of the invention. It shows:

[0023] Figure 1 a cavity partially filled with liquid plastic melt with two flow fronts without influencing the flow fronts according to the invention,

[0024] Figure 1 b Cavity according to Figure 1a in cross section,

[0025] Figure 2a shows a molded part not according to the invention, which is produced in the cavity according to Figures 1 a and 1 b,

[0026] Figure 2b Molded part according to Figure 2a in a side view,

[0027] Figure 3a shows a cavity partially filled with liquid plastic melt with two flow fronts with inventive influencing of the flow fronts,

[0028] Figure 3b Cavity according to Figure 3a in cross section,

[0029] Figure 4a first embodiment of a molded part according to the invention, which is produced with the cavity according to Figures 3a and 3b,

[0030] Figure 4b Molded part according to Figure 4a in a side view,

[0031] Figure 5 injection molding tool for the cavity according to Figures 3a and 3b and for the molded part according to Figures 4a and 4b,

[0032] Figure 6 second embodiment of a molded part according to the invention,

[0033] Figure 7 insert for the molded part according to Figure 6, Figure 8 molded part according to Figure 6 with top view of the weld line.

[0034] Description of the embodiments

[0035] Figures 1a and 1b show a cavity of an injection molding tool with which a plate-shaped molded part according to Figures 2a and 2b can be produced. The cavity 1 forms a hollow mold, which is a negative mold of the molded part 2. According to Figures 1a and 1b, the cavity has the shape of a cuboid. Liquid plastic melt is injected into the cavity 1 at two opposite sides 3, 4 of the cavity 1. Starting from associated inlets, which are not shown in the drawing, the liquid plastic melt spreads out in the cavity 1. This creates two flow fronts 5, 6 that move towards each other. The flow fronts 5, 6 are essentially parallel to each other and run perpendicular to the flow direction of the liquid plastic melt. The flow direction of the liquid plastic melt is shown by arrows in Figure 1.In the illustration according to Figure 1a, the cavity 1 is approximately half filled with liquid plastic melt.

[0036] The plate-shaped molded part 2 produced with the cavity according to Figures 1a and 1b is shown in Figures 2a and 2b. It has a weld line 7. This is formed at the point where the flow fronts 5 and 6 meet. The weld line 7 has a straight line. It extends essentially perpendicular to the flow direction of the liquid plastic melt as it spreads through the cavity, as shown in Figure 1a.

[0037] Figures 3a and 3b show a cavity 8 of an injection molding tool 9 according to the invention as shown in Figure 5. The injection molding tool 9 comprises two tool parts 10, 11 that delimit the cavity 8. In contrast to the cavity 1 according to Figures 1a and 1b, the cavity 8 according to Figures 3a and 3b has first cavity sections 12 and second cavity sections 13. The first cavity sections 12 have a larger cross-section than the second cavity sections. The first cavity sections 12 and the second cavity sections 13 alternate. They are provided alternately in the cavity. Due to the larger cross-section, the liquid plastic melt spreads faster in the first cavity sections 12 than in the second cavity sections 13. The resistance is greater in the second cavity sections.Like the cavity 1 in Figures 1a and 1b, the cavity 8 is equipped on the sides 14 and 15 with an inlet for the liquid plastic melt, not shown in the drawing.

[0038] Starting from these inlets, the liquid plastic melt spreads in the cavity 8 in two flow directions. A first flow front 16 and a second flow front 17 form. The flow direction of the first flow front 16 and the flow direction of the second flow front 17 are shown as arrows in Figure 3a. Since the plastic melt spreads at different speeds in the first cavity sections 12 and the second cavity sections 13, the flow fronts 16, 17 do not have a straight line but rather a wave-like course. In the first flow front sections 18, the plastic melt is faster than in the second flow front sections 19.The first cavity sections 12 and second cavity sections 13 are arranged in the cavity 8 such that the first flow front sections 18 of the first flow front 16 are opposite the second flow front sections 19 of the second flow front 17, and the second flow front sections 19 of the first flow front 16 are opposite the first flow front sections 18 of the second flow front 17. As a result, the first flow front 16 and the second flow front 17 interlock when they meet.

[0039] Figures 4a and 4b show the molded part 20 produced with the injection mold 9. The external shape of the molded part 20 is determined by the first and second cavity sections 12, 13. Accordingly, the molded part 20 has first molded part sections 21 with a larger cross-section and second molded part sections 22 with a smaller cross-section. In the area where the two flow fronts 16, 17 meet during the production of the molded part 20, a weld line 23 forms. This weld line has a wave-shaped shape corresponding to the shape of the flow fronts 16, 17.

[0040] Figures 6 and 8 show a second embodiment of a molded part 25. In contrast to the molded part 20 in Figures 4a and 4b, the regions with different cross-sections in the cavity are created by an insert 26, which is shown in Figure 7. This insert is inserted into a cavity of an injection mold during the production of the molded part 25. This cavity and the associated injection mold are not shown in the drawing. The insert comprises first insert sections 27, which are formed as recesses in the insert and, together with the cavity of the associated injection mold, have a first cross-section. Furthermore, the insert 26 comprises second insert sections 28, which, together with the cavity of the injection mold, have a smaller cross-section. The insert is overmolded in the cavity with the liquid plastic melt.The liquid plastic melt is injected into the cavity in the area which, in the finished molded part 25, corresponds to the first molded part area 29. Starting from this side, the liquid plastic melt spreads along the cylindrical circumference of the second molded part area 30. Two flow fronts form which meet on the side of the second molded part area 30 opposite the first molded part area 29. This creates a weld line 31. This has a wave-shaped course which is determined by the first and second insert sections 27, 28 of the insert 26. The weld line comprises first weld line sections 32 and second weld line sections 33. Since the insert 26 is completely encapsulated by the liquid plastic melt, it is not visible on the molded part 25 from the outside.

[0041] All features of the invention can be essential to the invention both individually and in any combination. Reference numbers

[0042] 1 cavity

[0043] 2 molded part

[0044] 3 Side of the cavity

[0045] 4 Side of the cavity

[0046] 5 Flow front

[0047] 6 Flow front

[0048] 7 Weld line

[0049] 8 Cavity

[0050] 9 Injection mold

[0051] 10 tool part

[0052] 11 Tool part

[0053] 12 First cavity section

[0054] 13 Second cavity section

[0055] 14 Side of the cavity

[0056] 15 Side of the cavity

[0057] 16 First flow front

[0058] 17 Second flow front

[0059] 18 First flow front section

[0060] 19 Second flow front section

[0061] 20 molded part

[0062] 21 First molded part section

[0063] 22 Second molded part section

[0064] 23 Weld line

[0065] 24

[0066] 25 molded part

[0067] 26 inserts

[0068] 27 First insert section

[0069] 28 Second insert section

[0070] 29 First molded part area

[0071] 30 Second molded part section Weld line First weld line section Second weld line section

Claims

A N S P R Ü C H E 1. A method for producing a molded part by means of a plastic injection molding machine, wherein the plastic injection molding machine has an injection molding tool (9) with a cavity (8) designed as a hollow mold, which represents a negative mold of the molded part (20, 25), wherein the injection molding tool (9) is equipped with at least one inlet for a liquid plastic melt, and wherein the injection molding tool (9) is designed such that when the liquid plastic melt is injected into the cavity, at least two flow fronts (16, 17) of the plastic melt are formed, which flow fronts meet when the cavity is filled and form a weld line (23, 31) when solidifying, characterized in that the flow fronts (16, 17) are influenced during the spreading of the plastic melt in the cavity (8) such that an enlargement of the surfaces of the flow fronts (16, 17) occurs, wherein the flow fronts (16,17) have first flow front sections (18) and second flow front sections (19), and the plastic melt in the first flow front sections, (18) of the plastic melt in the second flow front sections (19).

2. Method according to claim 1, characterized in that the first flow front sections (18) of a first flow front (16) are opposite the second flow front sections (19) of a second flow front (17) and in that the second flow front sections (19) of the first flow front (16) are opposite the first flow front sections (18) of the second flow front (17), such that when the first flow front (16) meets the second flow front (17), the first flow front sections (18) of the first flow front (16) meet the second flow front sections (19) of the second flow front (17) and the second flow front sections (19) of the first flow front (16) meet the first flow front sections (18) of the second flow front (17).

3. Method according to claim 1 or 2, characterized in that the flow fronts are influenced by first cavity sections (12) and second cavity sections (13) of the cavity (8), wherein first cavity sections (12) and second cavity sections (13) are arranged alternately in the cavity (8) and the first cavity sections (12) have a larger cross-section than the second cavity sections (13), wherein the liquid plastic melt spreads faster in the first cavity sections (12) than in the second cavity sections (13).

4. Method according to claim 1 or 2, characterized in that the flow fronts (16, 17) are influenced by an insert (26) which is inserted into the cavity before the injection molding tool is closed, wherein the insert (26) is overmolded with the liquid plastic melt and wherein the insert (26) has first insert sections (27) and second insert sections (28) in such a way that the plastic melt in the cavities delimited by the cavity and the first insert sections (27) due to a larger cross-section spreads faster than in the cavities delimited by the cavity and the second insert sections (28).

5. Method according to claim 1 or 2, characterized in that the flow fronts are influenced by multi-component injection molding.

6. A plastic injection-molded part produced by a process according to any one of the preceding claims 1 to 5, characterized in that it comprises a weld line (23, 31) formed by the meeting of two flow fronts (16, 17), which weld line has first weld line sections (32) and second weld line sections (33), the first and second weld line sections (32, 33) forming an alternating course of the weld line (23, 31).

7. Molded part according to claim 6, characterized in that the first weld line sections (32) and the second weld line sections (33) of the weld line (23, 31) are offset from one another in such a way that the weld line (23, 31) has a wave-shaped course.

8. Molded part according to claim 6, characterized in that the first weld line sections (32) and the second weld line sections (33) of the weld line (23, 31) are offset from one another in such a way that the weld line has a sawtooth-like course.

9. Moulded part according to one of claims 6 to 8, characterized in that it is formed at least in sections as a hollow body (25).

10. Molded part according to one of claims 6 to 9, characterized in that it is formed at least in sections as a flat plate (20).

11. Moulded part according to one of claims 6 to 10, characterized in that it comprises first moulded part sections (21) and second moulded part sections (22) wherein the cross section of the first molded part sections (21) is larger than the cross section of the second molded part sections (22).

12. Moulded part according to one of sections 6 to 11, characterized in that it is equipped with an insert (26).

13. Insert for carrying out the method according to claim 4, characterized in that the insert (26) has first insert sections (27) and second insert sections (28) which are designed such that the plastic melt spreads more quickly in the cavities delimited by the cavity and the first insert sections (27) due to a larger cross section than in the cavities delimited by the cavity and the second insert sections (28).

14. Insert according to claim 13, characterized in that it consists of a material which is dimensionally stable under the influence of the temperature and pressure prevailing in the injection mold.

15. Insert according to claim 13 or 14, characterized in that the insert consists at least partially of plastic which is provided with a reinforcement of glass, aramid, carbon or natural fibers.

16. Insert according to claim 13, 14 or 15, characterized in that the insert consists at least partially of metal or ceramic or a natural material.

17. Injection molding tool for a plastic injection molding machine for carrying out the method according to claim 3, characterized in that the cavity (8) of the injection molding tool (9) has first cavity sections (12) and second cavity sections (13) influencing the flow fronts (16, 17) of the plastic melt, wherein the first and second cavity sections (12, 13) are arranged alternately in the cavity (8) and the first cavity sections (12) have a larger cross-section than the second cavity sections (13).

Images