WO2022042791A1

WO2022042791A1 - Plastic part with an internal thread and method for producing a plastic part

Info

Publication number: WO2022042791A1
Application number: PCT/DE2021/100648
Authority: WO
Inventors: Lukas Jakob; Juergen Gilmer; Sven Hachmann; Robert DRESSEL
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2020-08-27
Filing date: 2021-07-28
Publication date: 2022-03-03
Also published as: DE102020122372B3; EP4204718A1; CN115989101A

Abstract

A tubular plastic part (1) suitable for use in a screw drive has an internal thread (2) designed as a trapezoidal thread, which ends at an end face of the plastic part (1), wherein a termination face (10) is located at the thread end (9), the extension of which termination face in the axial direction of the internal thread (1) corresponds at least to the pitch (P) of said thread, an acute angle (α) being formed between the termination face (10) and an imaginary central plane (ME), in which the central axis (MA) lies and which touches the termination face (10) at the edge (11) thereof facing away from the end face.

Description

Plastic part with an internal thread and method for producing a plastic part

The invention relates to a plastic part which is suitable for use as a component of a movement thread and has an internal thread in the form of a trapezoidal thread. Furthermore, the invention relates to a method for producing such a plastic part with an internal thread by injection molding.

DE 10 2010 005 145 A1 discloses a screw drive which includes metallic components and plastic components. Either the nut or the spindle can be a part that is at least partially made of metal, while the other component of the screw drive is at least partially made of plastic. In both cases, the nut and spindle have trapezoidal threads as components of the screw drive. The flanks of the trapezoidal thread are followed by first curves in the area of the thread crests and second curves in the area of the thread root.

As far as the standardization of trapezoidal threads is concerned, reference is made to the standards DIN 103, ISO 2901, ISO 2903, DIN 380 and DIN 30295. Background information on thread run-outs, including for trapezoidal and buttress threads, can be found in the DIN 76-3 standard.

Plastic parts with an internal or external thread can in principle be produced by primary shaping, in particular injection molding, or by machining. DE 10 2015 225 247 A1 discloses an injection molding device for producing pipes with internal threads. Here, a tool forms an article cavity which is to be filled with a thermoplastic molding compound. Furthermore, in this case a projectile is provided as a displacement body for the molding compound. Another device for injection molding a plastic body with an internal thread is described in DE 197 24 204 A1. The plastic body can be a screw cap. The thread of the plastic body is in the form of individual thread segments.

DE 10 2018 116 216 A1 discloses a device for unscrewing internal threads in injection molded parts using an electrically controlled drive. With the help of limit switch rings, it should be possible to identify whether a threaded core is screwed into a mold or unscrewed from the mould.

The object of the invention is to achieve progress in the injection molding production of plastic parts with an internal thread, with regard to both a rational production process and the durability of the end product.

This object is achieved according to the invention by a plastic part with the features of claim 1, wherein the plastic part can be designed as a tubular part or as a part with any other external contour. The object is also achieved by a method for producing such a plastic part according to claim 7. Embodiments and advantages of the invention explained below in connection with the production method also apply to the device, i.e. the plastic part provided with an internal thread, and vice versa.

The internal thread of the plastic part is designed as a trapezoidal thread and is arranged concentrically to the central axis of the plastic part. The internal thread runs out towards at least one of the two end faces of the plastic part. Optionally, there is also a thread outlet on the opposite end of the plastic part. At the at least one thread run-out of the trapezoidal thread there is an end surface, the extent of which in the axial direction of the internal thread and thus of the entire plastic part corresponds at least to the pitch of the internal thread, with between the end surface and an imaginary central plane in which the Central axis of the internal thread is located and which touches the end surface at the edge facing away from the end face, an acute angle is enclosed.

In particular, the end surface is inclined by at least 15° and at most 75° relative to the central plane, with the end surface, viewed in the longitudinal direction of the tubular plastic part, extending over a tooth and the subsequent root of the thread to the beginning of the flank of the next tooth.

According to a possible configuration, the closing surface, with which the trapezoidal thread ends towards the end face of the tubular plastic part, extends radially outward beyond the trapezoidal thread. In this case, the section of the end surface that extends radially outwards over the end surface can be more extensive in the radial direction of the plastic part than the section of the end surface that lies within the trapezoidal thread.

Irrespective of how the section of the end surface lying radially outside of the trapezoidal thread is dimensioned in relation to the immediately adjoining section of the end surface lying further inside and at least partially describing the thread profile of the trapezoidal thread, the section of the end surface lying radially outside of the trapezoidal thread can be within a tubular Be arranged end piece of the plastic part, wherein the end piece as well as the trapezoidal thread is an integral part of the plastic part.

According to a possible further development, the pitch of the trapezoidal thread is widened at the end of the thread in comparison to the rest of the trapezoidal thread. For example, the widening extends over the last turn of the trapezoidal thread. This widening, which is equivalent to the fact that the distance between two opposite flanks of the trapezoidal thread profile delimiting a tooth gap is increased, production-related shape deviations can be compensated. It is true that the suitability of the trapezoidal thread to absorb axial forces is within the last one, which extends to the end of the thread Reduced thread pitch, but this disadvantage is overcompensated by excluding overloading in the same thread section.

The widening of the last thread can be designed asymmetrically. This means that one of the named flanks continues the contour of the thread profile given in the further course of the thread unchanged, whereas material is removed on the opposite flank in comparison to the rest of the thread. The asymmetrical design of the area of the trapezoidal thread adjoining the end of the thread has the advantage that the full load-bearing capacity of the thread is retained in exactly one axial direction.

In all of the designs explained above, the plastic part can represent a complete spindle nut of a screw drive. Designs are also possible in which the plastic part forms a spindle nut together with other, in particular metallic, components. In any case, the plastic part, which has the trapezoidal thread as an internal thread, can be produced in the following steps:

- Provision of a first, bolt-shaped, in particular multi-part, tool component suitable for plastic injection molding, which has an external thread profiled according to the profile of the trapezoidal thread to be produced on the plastic part, this tool component having an end surface terminating the external thread, the extent of which in the axial direction corresponds at least to the thread pitch of the external thread and thus also corresponds to the trapezoidal thread, and between the end surface and an imaginary central plane in which the central axis of the external thread and thus also of the later trapezoidal thread lies and which touches the end surface at its edge facing the external thread, i.e. the edge facing away from the end face of the tool acute angle is included,

- Provision of a second, typically also multi-part, tool component suitable for plastic injection molding, its inner contour is designed according to the outer contour of the plastic part to be produced,

- Assembling the two tool components to form a cavity for plastic injection molding,

- Primary shaping of the plastic part in the cavity made in the previous step using the injection molding process,

- Separation of the plastic part from the tool components, this separation comprising a spindle removal.

In order to enable plastic injection molding, the first tool component, which is generally bolt-shaped, is preferably composed of several tool parts. One of these tool parts, which together form the first tool component, has a trapezoidal spotting surface that seamlessly continues the end surface and lies in the same plane, which is in planar contact with a second tool part. In contrast to the first tool part, the second tool part has no external thread. The end surface of the first tool specifies the position and shape of the described end surface of the injection-molded plastic part. Unlike the end surface, the spotting surface of the first tool part lies flat against the second tool part within the assembled first tool. This ensures that the spotting surface forms the end of the thread turn of the internal thread of the plastic part during injection molding. The plastic part can be removed from the first, multi-part tool by spindle-boring the first tool part and removing the second tool part in the axial direction from the plastic part without rotating it.

In all cases, the multi-part injection molding tool is designed in such a way that the end of the thread of the plastic part is inclined at an acute angle in the direction of spindle removal. This design has advantages over conventional solutions with a comparatively sharp-edged thread run-out, both with regard to the durability of the tools and the durability of the product manufactured with them. By avoiding sharp edges on the injection molding tool, technically relevant deformations during the use of the tool, which have a direct impact on the Shape of the workpieces produced, ie plastic parts would affect, practically impossible. This also applies in cases where the trapezoidal thread has a particularly low pitch. As far as the plastic part produced in the injection molding process is concerned, the proposed design with an inclined thread end makes a significant contribution to the fact that abrasion when the plastic part is used as a component of a screw drive is largely avoided. Abrasion would not only lead to increased friction, but also to increased wear of other sliding surfaces.

The plastic part, which has an internal thread designed as a trapezoidal thread, can be used, for example, as a rotating component or as a non-rotatable, exclusively displaceable component of a screw drive, ie a movement thread. The associated counter-component provided with an external thread, ie spindle, can also be made either of plastic or of metal. The entire screw drive is part of an electromechanical actuator, for example. Such actuators are used, inter alia, in parking brakes of motor vehicles.

An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. Show in it:

1 a plastic part with an internal thread, namely a trapezoidal thread, in a perspective view,

2 shows the end of the thread of the internal thread of the plastic part in an enlarged view,

3 shows the end of the thread of the internal thread in a sectional view, 4 shows a first, multi-part tool component for the production of the plastic part according to FIG. 1 by injection molding,

5 shows a detail of the tool component according to FIG. 4,

FIG. 6 a simplified representation of a detail of a second tool component for the production of the plastic part according to FIG. 1 by injection molding,

7 individual parts of the tool component according to FIG. 4 in a partially pushed together state,

8 shows a detail of the arrangement according to FIG.

A plastic part identified overall by the reference numeral 1 is provided for use in a screw drive, not shown in any more detail, which is designed as a simple motion thread. The plastic part 1 has a trapezoidal thread as an internal thread 2 and acts as the spindle nut of the screw drive. The associated threaded spindle, not shown, is driven electrically, for example. A lateral surface of the plastic part 1 is denoted by 3 and an end face by 4 . A web 5 extends over the entire length of the lateral surface 3 and serves to prevent the plastic part 1 from rotating within a surrounding structure. In a modified embodiment, not shown, several such webs 5 can be evenly distributed around the circumference of the lateral surface 3 . Overall, the plastic part 1 has a tubular shape; an inner peripheral surface adjoining the end face 4 is denoted by 6 .

Details of the internal thread 2, which is designed as a single thread, are shown in particular in FIGS. Thread flanks 7 and a thread root 8 can be seen. The thread end of the internal thread 2 is total marked with 9. At the end of the thread 9 there is an end surface 10 . An inner edge 11 of the closing surface 10 lies opposite the front edge 12 . The entire thread end 9 is located in an end piece 13 of the plastic part 1 , the outer peripheral surface of the end piece 13 being an integral part of the lateral surface 3 . The two edges 11, 12 are aligned in the radial direction of the tubular plastic part 1, whose central axis is denoted by MA.

In the view according to FIG. 3, the inner edge 11 represents a surface normal of the plane of the drawing. The inner edge 11 lies in a central plane ME, in which the central axis MA also lies. The end surface 10 is inclined relative to the center plane ME by an angle a of less than 75°, in the exemplary embodiment even by less than 45°. The width of the end 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 peripheral surface 6 has a diameter de which, in the exemplary embodiment, is at least one third larger than the nominal diameter d.

A multi-part injection molding tool 14, 18, which is illustrated in FIGS. 4 to 8, is used to produce the plastic part 1. A first tool component 14 , which is composed of two tool parts 21 , 22 , has a bolt-like basic shape and is provided with an external thread 15 which defines the shape of the trapezoidal thread 2 . An end surface 16 can be seen in FIGS. 4, 5, 7, 8, with which the end surface 10 of the plastic part 1 is produced.

The injection molding tool 14, 18 is completed by a second tool component 18, which is outlined in highly abstract form in FIG. In fact, the second tool component 18, like the first tool component 14, is constructed in several parts. A longitudinal groove 19 in the second tool component 18 forms the web 5 of the plastic part 1 . A cavity is formed in the assembled injection molding tool 14, 18, in which case a lateral surface 20 of the first tool tool component 14 can contact an inner peripheral surface of the second tool component 18 .

The multi-part structure of the first tool component 14 is shown in detail in FIGS. According to this, the external thread 15 is located on the outer peripheral surface of the first tool part 21, which is longer in the exemplary embodiment, whereas the second tool part 22, which is comparatively short in the present case, has no thread. In order to assemble the tool component 14 , the first tool part 21 is partially pushed into the second tool part 22 . In the arrangement according to FIG. 7, the tool parts 21, 22 are pulled apart somewhat in order to make geometric details visible.

The end surface 16 is provided by the second tool part 22, which is also referred to as the counter-mold part of the first tool part 21, i.e. the molded part with an external thread. The end surface 16 has, as can be seen in particular from FIG. 8, a touching surface 16 as an integral part of this surface 16, the touching surface 16 lying flat on the tool part 21 within the assembled tool component 14 and is therefore no longer visible in this state. The section of the end surface 16 lying outside of the inking surface 16 is referred to as the open section 24 of the end surface 16 and specifies the shape of the end surface 10 of the plastic part 1 . The spotting surface 16, on the other hand, forms the end of the thread of the trapezoidal thread 2 and is contoured in a trapezoidal manner in accordance with this. Within the trapezoidal thread 2, this surface, the shape of which is specified by the spotting surface 16, is an imaginary surface which adjoins the connection surface 10 and represents the end of the thread turn at the thread outlet 9.

After the cavity formed between the respective multi-part tool components 14, 18 has been filled with heated plastic mass and the plastic has cooled sufficiently, the inner tool component 14 together with the molded plastic part 1 can be removed from the outer tool component 18. The separation of the two tool parts 21, 22 from the plastic part 1 is possible in that the first tool part 21 is screwed out of the trapezoidal thread 2 in the spindle-boring direction AR (FIG. 3), that is, spindled out. The workpiece, ie plastic part 1, can then be separated from the second tool part 22 by the second tool part 22 being pulled off the workpiece 1 in the axial direction. Depending on the overall structure of the tool components 14, 18, the second tool part 22 can also be spindled out and/or pulled off while the plastic part 1 is still in the second tool component 18 or in an individual part of this tool component 18.

The bolt-shaped tool component 14 is designed in such a way that the thread base 8 is in the area of the thread outlet 9 compared to the rest of the internal thread

2 is expanded. A thread flank 7 is indicated in dashed lines in FIG. Compared to the unmodified contour of the trapezoidal thread 2, the thread flank 7 at the thread outlet 9 is offset by an additional width s, so that the thread root 8 is widened accordingly. As a result, the last turn of the thread of the internal thread 2 carries only on one side. If a mold misalignment occurs during injection molding, which corresponds at most to the additional width s, this would have no effect on the functionality of the trapezoidal thread 2, since there would be no impermissible narrowing of the last thread turn. The possibly slightly reduced axial load capacity of the internal thread 2 in a specific direction is accepted.

The diameter gradation given on the end face 4, which is expressed in the form of the inner peripheral surface 6, which lies radially outside the nominal diameter d of the internal thread 2, promotes both the stability of the finished plastic part 1 and the stability of the connection between the tool components 14, 18 during the injection molding production of the plastic part 1 . Reference character list

plastic part

Internal thread, trapezoidal thread

lateral surface

face

web

inner peripheral surface

thread flank

thread root

Thread run-out 0 Closing surface 1 Inner edge of the closing surface 2 Front edge of the closing surface 3 End piece 4 First tool component, bolt-shaped 5 External thread 6 End surface of the shorter tool part 7 Two flats 8 Second tool component 9 Longitudinal groove 0 Lateral surface of the first tool 1 Tool part with external thread 2 Tool part without external thread 3 Marking surface 4 open section of end face a angle

AR Boring direction d Nominal diameter de Diameter of the inner peripheral surface

MA central axis ME midplane

P pitch s extra width

Claims

patent claims

1. Tubular plastic part (1) having a central axis (MA), with an internal thread (2) designed as a trapezoidal thread, which runs out towards one end face of the plastic part (1), with an end face (10) being located at the thread end (9). , whose extension in the axial direction of the internal thread (2) corresponds at least to its pitch (P), whereby between the end face (10) and an imaginary center plane (ME) in which the center axis (MA) lies and which the end face (10) lies on touches the edge (11) facing away from the end face, an acute angle (a) is included.

2. Plastic part (1) according to claim 1, characterized in that the closing surface (10) is inclined by at least 15° and at most 75° relative to the central plane (ME).

3. Plastic part (1) according to claim 1 or 2, characterized in that the closing surface (10) extends radially outward beyond the trapezoidal thread (2) also.

4. Plastic part (1) according to claim 3, characterized in that the section of the end surface (10) extending radially outwards over the end surface (10) is more extensive in the radial direction than the section of the end surface (10) lying within the trapezoidal thread (2). is.

5. Plastic part (1) according to claim 3 or 4, characterized in that the section of the end surface (10) lying radially outside of the trapezoidal thread (2) lies within a tubular end piece (13) of the plastic part (1).

6. Plastic part (1) according to any one of claims 1 to 5, characterized in that the thread pitch of the trapezoidal thread (2) is widened at the thread end (9) compared to the rest of the trapezoidal thread (2).

7. A method for producing a tubular plastic part (1) having a trapezoidal thread (2) as an internal thread, with the following steps: - Provision of a first, bolt-shaped tool component (14) suitable for plastic injection molding, which has an external thread (15) profiled according to the profile of the trapezoidal thread (2) to be produced, this tool component (14) having the external thread

(15) has a closing end surface (16), the extension of which in the axial direction corresponds at least to the thread pitch (P), and wherein between the end surface (16) and an imaginary center plane (ME) in which the center axis (MA) of the external thread (15) lies and which is the end face

(16) touches at the edge facing the external thread (15), an acute angle (a) is included,

- Provision of a second tool component (18) suitable for plastic injection molding, the inner contour of which is designed in accordance with the outer contour of the plastic part (1) to be produced,

- Assembling the two tool components (14, 18) to produce a cavity for the plastic injection molding,

- Primary shaping of the plastic part (1) in the cavity in the injection molding process,

- Separation of the plastic part (1) from the tool components (14, 18). Method according to Claim 7, characterized in that in preparation for the plastic injection molding, the first tool component (14) is assembled from a plurality of tool parts (21, 22), one of these tool parts (21, 22) having a end surface (16) which continues seamlessly in the same Has a level trapezoidal spotting surface (23) which contacts a second tool part (22) over its entire surface. Method according to Claim 8, characterized in that the first tool part (21) is brought into contact with the second tool part (22) in such a way that during injection molding the spotting surface (23) is the end of a thread turn of the internal thread (2) of the plastic part (1) forms. The method according to claim 8 or 9, characterized in that the plastic part (1) from the first, multi-part tool component (14) ent - 15 - in that the first tool part (21) is spindled out and the second tool part (22) is removed from the plastic part (1) in the axial direction.