Plastic part with internal thread and method for manufacturing a plastic part

Abstract

A tubular plastic part (1) suitable for use in a threaded drive has an internal thread (2) which is configured as a trapezoidal thread, which internal thread ends towards the end side of the plastic part (1), wherein there is a termination face (10) at the thread tail (9), which termination face has an extension in the axial direction of the internal thread (2) which corresponds at least to the pitch (P) of the internal thread, wherein an acute angle (a) is formed between the termination face (10) and an imaginary centre plane (ME), a centre axis (MA) lying in the imaginary centre plane, and the imaginary centre plane contacting the termination face (10) at an edge (11) of the termination face facing away from the end side.

Description

Technical Field

[0001] This invention relates to a plastic part suitable for use as a transmission thread component, the plastic part having an internal thread in the form of a trapezoidal thread. The invention also relates to a method for manufacturing such a plastic part with an internal thread using injection molding technology. Background Technology

[0002] DE 10 2010 005 145 A1 discloses a threaded drive device comprising metal and plastic components. Here, either the nut or the screw may be a part at least partially made of metal, while other components of the threaded drive device are at least partially made of plastic. In both cases, the nut and screw, as components of the threaded drive device, have trapezoidal threads. On the flank of the trapezoidal thread, a first chamfer is connected in the region of the thread crest and a second chamfer is connected in the region of the thread root.

[0003] Standards DIN 103, ISO 2901, ISO 2903, DIN 380, and DIN 30295 specify the standardization of trapezoidal threads. Background information on thread tails, particularly for trapezoidal and sawtooth threads, can be found in standard DIN 76-3.

[0004] Plastic parts with internal or external threads can, in principle, be produced by molding, especially injection molding, or by machining. DE 10 2015 225 247 A1 discloses an injection molding apparatus for manufacturing tubes with internal threads. Here, a mold forms a product cavity, which can be filled with a thermoplastic molding compound. Furthermore, in this case, a projectile is provided as an extruder for the molding compound.

[0005] DE 197 24 204 A1 describes another apparatus for injection molding a plastic body with internal threads. Here, the plastic body may be a screw cap. The threads of the plastic body are formed in the form of a single threaded segment.

[0006] A device for demolding internal threads in an injection molded part by means of an electrically controlled drive is known from DE 10 2018 116 216 A1. A limit switch ring should be used to indicate whether the threaded core is screwed into or out of the mold. Summary of the Invention

[0007] The objective of this invention is to make progress in the manufacture of internally threaded plastic parts using injection molding technology, which involves both a rational manufacturing process and the load-bearing capacity of the final product.

[0008] According to the invention, the objective is achieved by a plastic part, which can be designed as a tubular part or a part having any other external contour. The objective is also achieved by a method for manufacturing such a plastic part. The design and advantages of the invention explained below in conjunction with the manufacturing method also apply, by way of the meaning, to the device, i.e., the plastic part with internal threads, and vice versa.

[0009] The internal thread of the plastic part is configured as a trapezoidal thread and is concentrically arranged with the central axis of the plastic part. The internal thread terminates toward at least one of the two end sides of the plastic part. Optionally, a thread tail is also present on the opposite end side of the plastic part. A terminating face is present on at least one thread tail of the trapezoidal thread, the terminating face extending in the axial direction of the internal thread, and thus extending in the axial direction of the entire plastic part, at least corresponding to the pitch of the internal thread, wherein an acute angle is formed between the terminating face and an imaginary central plane, the central axis of the internal thread lies in the imaginary central plane, and the imaginary central plane contacts the terminating face at the edge of the terminating face on the opposite end side.

[0010] The terminating surface is inclined at at least 15° and at most 75° relative to the center plane, wherein, when viewed from the longitudinal direction of the tubular plastic part, the terminating surface extends beyond the thread tooth and the root of the thread tooth connected thereto to the beginning of the flank of the next thread tooth.

[0011] The terminating surface extends radially outward, beyond the trapezoidal thread according to a feasible design, the trapezoidal thread terminating with the terminating surface toward the end of the tubular plastic part. Here, the radially outward extension of the terminating surface beyond the terminating surface can be larger in the radial direction of the plastic part than the portion of the terminating surface located within the trapezoidal thread.

[0012] Regardless of how the dimensions of the section of the terminating face located radially outside the trapezoidal thread are designed relative to the section of the terminating face that is directly connected to the section and is more inner and at least partially describes the thread profile of the trapezoidal thread, the section of the terminating face located radially outside the trapezoidal thread can be located within a tubular end piece of the plastic part, wherein the end piece is an integral part of the plastic part as well as the trapezoidal thread.

[0013] According to a feasible improvement, the thread line at the end of the trapezoidal thread is widened compared to the rest of the trapezoidal thread. For example, the widened portion extends beyond the last turn of the trapezoidal thread. This widening can intercept shape deviations caused by manufacturing processes. Similarly, the distance between the tooth flanks of the two opposing, limiting thread clearances in the trapezoidal thread profile is increased. Although the trapezoidal thread's ability to absorb axial forces decreases as it extends to the last turn of the thread, this disadvantage is overcompensated by eliminating overload within the same thread section.

[0014] The widening of the final thread turn can be designed asymmetrically. This means that one of the tooth flanks continues to maintain the profile of the thread shape given in further thread extension, while at the opposite tooth flank, material is removed compared to the rest of the thread. The asymmetrical design of the area of ​​the trapezoidal thread connected to the thread tail has the advantage of preserving the complete load-bearing capacity of the thread in exactly one axial direction.

[0015] In all the structural forms explained above, the plastic part can be a complete screw and nut of a threaded drive. It is also possible for the plastic part to form the screw and nut together with other, particularly metal, components. In any case, a plastic part having a trapezoidal thread as an internal thread can be manufactured in the following steps:

[0016] - A bolt-shaped, particularly multi-part, first mold component suitable for plastic injection molding is provided. The first mold component has an external thread forming the profile of a trapezoidal thread to be produced on the plastic part. The mold component has an end face terminating the external thread, the axial extension of which corresponds at least to the thread pitch of the external thread, and thus to the thread pitch of the trapezoidal thread. An acute angle is formed between the end face and an imaginary central plane, the central axis of the external thread, and consequently the central axis of the trapezoidal thread, also lies in the imaginary central plane. The imaginary central plane contacts the end face at the edge of the end face facing the external thread, i.e., at the edge opposite to the mold end.

[0017] - Provides a typical multi-part second mold component suitable for plastic injection molding, the inner contour of which is designed according to the outer contour of the plastic part to be manufactured.

[0018] - Assemble the two mold components to form a cavity for plastic injection molding.

[0019] - The plastic part is molded in the cavity created in the previous step using an injection molding method.

[0020] - Separating the plastic part from the mold component, wherein the separation includes unscrewing.

[0021] To enable plastic injection molding, the generally bolt-shaped first mold component is preferably assembled from multiple mold parts. One of the mold parts forming the first mold component has a trapezoidal scraping surface in the same plane, ensuring seamless continuity of the end face, which contacts the second mold part. Unlike the first mold part, the second mold part does not have external threads. The end face of the first mold pre-determines the position and shape of the termination face of the plastic part to be injection molded. Unlike the end face, the scraping surface of the first mold part rests against the second mold part on the inner surface of the assembled first mold. This ensures that during injection molding, the scraping surface forms the end of the thread line of the internal thread of the plastic part. The plastic part can be removed from the multi-part first mold by unscrewing the first mold part and removing the second mold part axially from the plastic part without rotating it.

[0022] In all cases, multi-part injection molds are designed such that the threaded end of the plastic part is angled at an acute angle in the screw-out direction. This design offers advantages over traditional solutions with relatively sharp-edged threaded end caps in terms of both mold durability and the durability of the products manufactured using it. By avoiding sharp edges at the injection mold, technically significant deformation during mold use, which directly affects the shape of the manufactured workpiece, i.e., the plastic part, is effectively eliminated. This also applies to trapezoidal threads with particularly small pitches. Regarding plastic parts manufactured by injection molding, the proposed design with angled threaded end caps decisively helps to largely avoid wear when using plastic parts as components of threaded drives. Wear not only leads to increased friction but also to increased wear on other sliding surfaces.

[0023] Plastic parts with internal threads configured as trapezoidal threads can be used, for example, as rotating components of threaded drives or as non-rotatable, movable components. The associated mating component with external threads, the screw, can also be made of either plastic or metal. For example, the entire threaded drive is part of an electromechanical actuator. Such actuators are primarily used for parking brakes in motor vehicles. Attached Figure Description

[0024] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Wherein are shown:

[0025] Figure 1 A perspective view of a plastic part with internal threads, i.e., trapezoidal threads, is shown.

[0026] Figure 2 This is an enlarged view of the thread tail of the internal thread of a plastic part.

[0027] Figure 3A cross-sectional view of the thread tail of an internal thread is shown.

[0028] Figure 4 Showing the method of manufacturing according to injection molding technology Figure 1 The first mold component of the multi-piece plastic parts,

[0029] Figure 5 Showing according to Figure 4 Details of the mold components,

[0030] Figure 6 Showing the method of manufacturing according to injection molding technology Figure 1 A partial schematic diagram of the second mold component for the plastic part.

[0031] Figure 7 The basis for showing the state of being partially pushed together. Figure 4 The various components of the mold parts,

[0032] Figure 8 Showing according to Figure 7 Details of the settings. Detailed Implementation

[0033] The plastic part, generally designated by reference numeral 1, is designed for use in a threaded drive mechanism (not shown) configured as a simple transmission thread. The plastic part 1 has a trapezoidal thread as an internal thread 2 and functions as a screw nut in the threaded drive mechanism. The associated threaded screw (not shown) is, for example, electrically driven. The outer surface of the plastic part 1 is indicated by 3, and the end face by 4. A connecting piece 5 extends along the entire length of the outer surface 3, serving as a torsional stop for the plastic part 1 within the surrounding structure. In a modified design (not shown), multiple such connecting pieces 5 may be evenly distributed around the circumference of the outer surface 3. The plastic part 1 generally has a tubular construction; the inner circumferential surface adjacent to the end face 4 is indicated by 6.

[0034] The details of the internal thread 2, designed as a single-start thread, are particularly evident from... Figure 2 and Figure 3 It is known that the thread flank 7 and thread root 8 can be seen. The thread tail of the internal thread 2 is generally represented by 9. There is a terminating surface 10 at the thread tail 9. Facing the end face 4, the terminating surface 10 is bounded by the end side edge 12. The inner edge 11 of the terminating surface 10 is opposite to the end side edge 12. The entire thread tail 9 is located in the end piece 13 of the plastic part 1, wherein the outer circumferential surface of the end piece 13 is an integral part of the outer surface 3. The two edges 11, 12 are oriented in the radial direction of the tubular plastic part 1, the central axis of which is represented by MA.

[0035] According to Figure 3In the view, the inner edge 11 is the surface normal of the drawing plane. The inner edge 11 lies in the center plane ME, and the central axis MA also lies in the center plane. The terminating surface 10 is inclined relative to the center plane ME at an angle α less than 75°, and in this embodiment even less than 45°. The width of the terminating surface 10, measured in the longitudinal direction of the central axis MA, corresponds to the pitch P of the internal thread 2. The internal thread 2 is a single-start trapezoidal thread with a nominal diameter d. The inner circumferential surface 6 has a diameter d6, which in this embodiment is at least one-third larger than the nominal diameter d.

[0036] Figures 4 to 8 The multi-part injection molds 14 and 18 shown are used to manufacture plastic parts 1. The first mold component 14, assembled from two mold parts 21 and 22, has a bolt-like basic shape and is provided with external threads 15 in the shape of a pre-set trapezoidal thread 2. Figure 4 , Figure 5 , Figure 7 , Figure 8 As can be seen from the end face 16, the termination face 10 of the plastic part 1 is generated using the end face.

[0037] Injection molds 14 and 18 are completed through the second mold component 18. Figure 6 The second mold component is depicted in a very abstract manner. In fact, the second mold component 18, like the first mold component 14, is a multi-piece construction. The longitudinal groove 19 in the second mold component 18 corresponds to the connecting piece 5 of the plastic part 1. A cavity is formed in the assembled injection molds 14 and 18, wherein, in the stated state, the outer surface 20 of the first mold component 14 can contact the inner circumferential surface of the second mold component 18.

[0038] The multi-piece structure of the first mold component 14 Figure 7 and Figure 8 Details are available. Accordingly, the external thread 15 is located on the outer circumferential surface of the longer first mold part 21 in this embodiment, while the shorter second mold part 22 in the present case does not have a thread. For assembling the mold assembly 14, the first mold part 21 is partially pushed into the second mold part 22. According to... Figure 7 In the setup, mold parts 21 and 22 are slightly pulled apart to make geometric details visible.

[0039] The end face 16 is provided via a second mold part 22, which is also referred to as the mating forming part of the first mold part 21, i.e., a forming part with external threads. (See, particularly from...) Figure 8It is understood that the end face 16 has a scraped surface 16 as an integral part of the face 16, wherein the scraped surface 16 is attached to the mold part 21 on the inner surface of the assembled mold part 14, and is therefore no longer visible in the stated state. The portion of the end face 16 outside the scraped surface 16 is called the open portion 24 of the end face 16, and presupposes the shape of the termination face 10 of the plastic part 1. Conversely, the scraped surface 16 forms the termination portion of the thread line of the trapezoidal thread 2, and thus constitutes a trapezoidal profile. Within the trapezoidal thread 2, the surface presupposed by the scraped surface 16 is an imaginary surface, which is connected to the connecting surface 10 and is the end of the thread line at the thread tail 9.

[0040] After the cavity formed between the multi-part mold components 14 and 18 is filled with heated molding compound and the plastic is sufficiently cooled, the inner mold component 14, along with the molded plastic part 1, can be removed from the outer mold component 18. The separation of the two mold parts 21 and 22 from the plastic part 1 is achieved by rotating the first mold part 21 along the ejection direction AR (…). Figure 3 It is feasible to unscrew or unscrew from the trapezoidal thread 2. Subsequently, the workpiece, i.e., the plastic part 1, can be separated from the second mold part 22 by removing the second mold part 22 from the workpiece 1 in the axial direction. Depending on the overall structure of the mold components 14 and 18, the second mold part 22 can also be unscrewed and / or removed while the plastic part 1 remains in the second mold component 18 or in a single part of the mold component 18.

[0041] The bolt-shaped mold component 14 is designed such that the thread root 8 in the area of ​​the thread tail 9 is wider compared to the rest of the internal threads 2. Figure 2 In the diagram, the thread flank 7 is represented by a dashed line, as it exists in the unchanged section of the internal thread 2, away from the thread tail 9. Compared to the unchanged profile of the trapezoidal thread 2, the thread flank 7 is offset by an additional width s at the thread tail 9, causing the thread root 8 to widen accordingly. This results in the last turn of the internal thread 2 being carried on only one side. If a shape offset corresponding to at most the additional width s occurs during injection molding, it will not affect the functionality of the trapezoidal thread 2, as no unacceptable narrowing of the last turn of the thread will result. A slight decrease in the axial load capacity of the internal thread 2 in a given direction is acceptable.

[0042] The diameter gradient provided at end face 4 is beneficial to both the stability of the manufactured plastic part 1 and the stability of the connection between mold components 14 and 18 during the manufacture of the plastic part 1 by injection molding. The diameter gradient is represented in the form of an inner circumferential surface 6, which is radially outside the nominal diameter d of the internal thread 2.

[0043] List of reference numerals

[0044] 1. Plastic parts

[0045] 2. Internal threads, trapezoidal threads

[0046] 3. Outer surface

[0047] 4 end face

[0048] 5 Connecting pieces

[0049] 6. Inner ring circumference

[0050] 7. Thread flank

[0051] 8. Thread root

[0052] 9. Threaded end cap

[0053] 10 Termination Surface

[0054] 11. Inner edge of the termination surface

[0055] 12. End edge of the termination surface

[0056] 13 End components

[0057] 14 First mold component, bolt-shaped

[0058] 15 External thread

[0059] 16. End faces of shorter mold parts

[0060] 17 Dihedral

[0061] 18 Second mold component

[0062] 19 Longitudinal grooves

[0063] 20. Outer surface of the first mold

[0064] 21. Mold parts with external threads

[0065] 22. Mold parts without external threads

[0066] 23 Scraped surface

[0067] 24. Open section of the end face

[0068] α angle

[0069] AR Rotation Direction

[0070] d Nominal diameter

[0071] d6 is the diameter of the inner circumferential surface.

[0072] MA midline

[0073] ME central plane

[0074] P pitch

[0075] s is the extra width.

Claims

1. A tubular plastic part (1) having a central axis (MA), the plastic part having an internal thread (2) configured as a trapezoidal thread terminating toward the end side of the plastic part (1), wherein a terminating face (10) is present at the thread tail (9), the extension of the terminating face in the axial direction of the internal thread (2) corresponding at least to the pitch (P) of the internal thread, wherein an acute angle (α) is formed between the terminating face (10) and an imaginary central plane (ME), the central axis (MA) being located in the imaginary central plane, and the imaginary central plane contacting the terminating face (10) at an edge (11) on the opposite end side of the terminating face.

2. The plastic part (1) according to claim 1, characterized in that The termination surface (10) is inclined at at least 15° and at most 75° relative to the center plane (ME).

3. The plastic part (1) according to claim 1, characterized in that The terminating surface (10) extends radially outward beyond the trapezoidal thread (2).

4. The plastic part (1) according to claim 3, characterized in that The radially outward extension of the terminating surface (10) beyond the terminating surface (10) is greater in the radial direction than the section of the terminating surface (10) located within the trapezoidal thread (2).

5. The plastic part (1) according to claim 3, characterized in that The section of the termination surface (10) located radially outside the trapezoidal thread (2) is located inside the tubular end piece (13) of the plastic part (1).

6. The plastic part (1) according to any one of claims 1 to 5, characterized in that The thread line of the trapezoidal thread (2) at the thread tail (9) is widened compared to the rest of the trapezoidal thread (2).

7. A method for manufacturing a tubular plastic part (1) having a trapezoidal thread (2) as an internal thread, the method comprising the following steps: - A bolt-shaped first mold component (14) suitable for plastic injection molding is provided, the first mold component having an external thread (15) forming a profile according to the profile of a trapezoidal thread (2) to be produced, wherein the first mold component (14) has an end face (16) terminating the external thread (15), the axial extension of the end face corresponding at least to the thread pitch (P), and wherein an acute angle (α) is formed between the end face (16) and an imaginary central plane (ME), the central axis (MA) of the external thread (15) being located in the imaginary central plane, and the imaginary central plane contacting the end face (16) at the edge of the end face facing the external thread (15). - Provide a second mold component (18) suitable for plastic injection molding, the inner contour of the second mold component being designed according to the outer contour of the plastic part (1) to be manufactured. - Assemble the two mold components (14, 18) to create a cavity for plastic injection molding. - The plastic part (1) is formed in the cavity by injection molding. - Separate the plastic part (1) from the mold components (14, 18).

8. The method according to claim 7, characterized in that, In preparation for plastic injection molding, the first mold component (14) is assembled from a plurality of mold parts (21, 22), wherein one of the mold parts (21, 22) has a trapezoidal scraping surface (23) in the same plane that allows the end face (16) to be seamlessly continued, and the scraping surface is in surface contact with the second mold part (22).

9. The method according to claim 8, characterized in that, The first mold part (21) is brought into contact with the second mold part (22) such that during injection molding, the scraping surface (23) forms the end of the thread line of the internal thread (2) of the plastic part (1).

10. The method according to claim 8 or 9, characterized in that, The plastic part (1) is removed from the multi-part first mold component (14) by unscrewing the first mold part (21) and removing the second mold part (22) from the plastic part (1) in the axial direction.

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