Hole and thread forming screw

Abstract

A hole- and thread-forming screw (1) with a screw head (2) having a screw drive design and a screw shaft (3) adjoining the head and having a screw tip (6) at its free end, the shaft having a threaded section (4) at least partially provided with a thread and a forming section (5) extending to the screw tip (6) that is at least partially unthreaded, the cross-section of which decreases in the direction of the screw tip (6), characterized in that the forming section (5) has a first partial forming section (51) and a second partial forming section (53), the cross-sections of which each decrease continuously in the direction of the screw tip (6) and between which an intermediate section (52) is arranged, which has a cross-section that increases at least partially in the direction of the screw tip (6).

Description

[0001] The invention relates to a hole- and thread-forming screw, with a screw head having a screw drive design and a screw shaft adjoining it, having a screw tip at its free end, which has a threaded section at least partially provided with a thread and a forming section extending to the screw tip, at least partially unthreaded, the cross-section of which decreases in the direction of the screw tip.

[0002] Hole-forming and thread-forming screws are frequently used for the detachable joining of sheet metal components. DE 3909725 C1 discloses a hole-forming and thread-forming screw with a screw shank that has a threaded section followed by a non-threaded section extending to the screw tip. The non-threaded section consists of a first, cylindrical section followed by a second section whose cross-section decreases continuously towards the screw tip.

[0003] WO 2010 / 003901 A1 proposes designing the unthreaded section such that its cross-section decreases continuously towards the screw tip, starting directly from the end of the threaded section. This threadless section, decreasing in diameter, is called the forming section and is intended to create a channel after a hole has been drilled in a sheet metal part, thus enabling better retention of the thread in the material.

[0004] Against this background, the invention is based on the objective of providing a hole- and thread-forming screw with improved mounting behavior.

[0005] According to the invention, this problem is solved by a hole- and thread-forming screw with the features of claim 1. An improvement in the screw-in behavior is achieved by the forming section having a first partial forming section and a second partial forming section, the cross-sections of which decrease continuously towards the screw tip, and by the fact that an intermediate section is arranged between them, which at least partially has a cross-section that increases towards the screw tip.

[0006] Surprisingly, it has been shown that when a screw according to the invention is screwed into a sheet metal part, the intermediate section influences the flow behavior of the sheet metal material, resulting in an increase in the performance of the assembly process. The term "sheet metal material" is to be understood broadly here, and includes, for example, profile materials or profile structures.

[0007] In this context, a "decreasing cross-section" refers to a reduction in the cross-section, resulting in a reduced cross-sectional area. Conversely, an "increasing cross-section" refers to an enlargement of the cross-section, resulting in an increased cross-sectional area.

[0008] In a further development of the invention, the intermediate section has a first subsection that decreases in cross-section towards the screw tip, which then transitions into a second subsection with a cross-section that increases in cross-section towards the screw tip. This results in a short-term relaxation of the sheet metal material when the screw is screwed in.

[0009] In one embodiment of the invention, the intermediate section is formed by a circumferential groove incorporated into the molded section. This enables simple manufacturing of the intermediate section.

[0010] In a further embodiment of the invention, the groove has an arcuate side contour in the axial direction. This results in improved material flow when the screw is screwed into sheet metal. It also counteracts potential wedging of the screw during the screwing process. Furthermore, this reduces and interrupts cold welding processes that occur between the screw and the sheet metal. While maintaining the advantageous effects of a slim tip geometry on material displacement behavior, an accelerated hole-forming process is achieved. This is due, among other things, to the reduced wedging effect caused by a partial interruption of the continuously increasing cross-section of the forming section towards the screw head.Furthermore, during the hole-forming process, an impulse is introduced into the sheet metal material in the direction of the screw tip, resulting in a beneficial effect of this process, particularly regarding the time until material penetration. In addition, this also reduces the formation of material bulges directed towards the screw tip. Moreover, an expansion of the process limits with regard to the material thickness to be penetrated is to be expected, especially when the sheet metal thickness corresponds to a maximum of the distance between the screw tip and the transition of the intermediate section to the second forming section.

[0011] In a further development of the invention, the minimum cross-section of the second partial mold section is larger than the maximum cross-section of the first partial mold section. This results in a good hole-forming process. Preferably, the smallest diameter of the intermediate section is between 29 / 50 and 17 / 20 of the largest diameter of the first partial mold section.

[0012] In an embodiment of the invention, the outer edges of the thread flanks of the thread section are at least partially inscribed in a prism with rounded corners, in particular with a cross-section in the form of a triangle with rounded corners and convexly curved sides, and the cross-section of the thread core of the thread section of the screw shank has at least partially the form of a polygon, in particular a triangle with rounded corners and convexly curved sides. This facilitates the formation of a thread in the bore produced by the drilling process, thereby preventing an excessive increase in the screw-in resistance during thread forming. In particular, this counteracts the generation of material loss during the thread forming process.

[0013] In a further embodiment of the invention, the forming section has, at least in some areas, a cross-section in the form of a polygon, in particular a triangle with rounded corners and convexly curved sides. This optimizes the through-hole formed by the forming section when inserting the screw into a sheet metal part, with regard to the subsequent thread forming process.

[0014] In a further development of the invention, the lateral surfaces of the first and second partial forming sections lie at least partially on a common body of revolution, the cross-section of which decreases continuously towards the screw tip. This results in a uniform expansion of the opening when the screw is inserted into a sheet metal part, thereby improving the flow behavior of the sheet metal material.

[0015] In this context, a body of revolution is understood to be a curve rotating around the central axis of the screw shaft. This curve lies, at least partially, on one side edge of the longitudinal section of the first and second partial mold sections.

[0016] Advantageously, the side lines of the first and second partial mold sections each exhibit a constant curvature. In this context, the side line of a partial mold section is understood to be a lateral edge of the longitudinal section of that partial mold section. "Constant curvature" in this context refers to a constant curvature achievable within the manufacturing tolerances of the screw production process.

[0017] In an embodiment of the invention, the forming section has a third partial forming section with a constant cross-section following the threaded section. This facilitates a centered insertion of the threaded section into the opening created in the sheet metal by the forming section when inserting the screw into a sheet.

[0018] The term "constant cross-section" should also be understood in the context of taking into account the manufacturing tolerances in the production of a screw.

[0019] Other embodiments and configurations of the invention are specified in the remaining dependent claims. Exemplary embodiments are shown in the following schematic drawings and are described in detail below. They show: Fig. 1. The representation of a hole- and thread-forming screw; Fig. 2 the screw out Fig. 1 in the top view; Fig. 3. Detailed view of section X of the screw shaft. Fig. 1; Fig. 4 the representation of the shape section of the cutout from Fig. 3 a) in cross-section A - A; b) in cross-section B - B; c) in cross-section C - C; d) in cross-section D - D.

[0020] The hole- and thread-forming screw 1, chosen as an exemplary embodiment, has a screw head 2 to which a screw shank 3 is attached, ending at its free end in a screw tip 6. In this exemplary embodiment, the screw tip is rounded. It can also be pointed for easier penetration into sheet metal. The screw head 2 is provided with a recess 21, which serves for the positive-locking reception of a screw tool. Alternatively, the screw head can, for example, be non-circular or have a non-circular recess to form the screw drive. The essential feature is the presence of a recess for positive-locking or force-locking torque transmission.

[0021] The screw shaft 3 comprises a partially cylindrical threaded section 4 provided with a thread 41 and a threadless form section 5 extending to the screw tip 6. The thread 41 terminates in a further section of the threaded section 4, the groove zone 42.

[0022] In the exemplary embodiment, the outer edges of the thread flanks of the thread 41 of the thread section 4 are predominantly inscribed in a cylinder and to a further smaller extent in a prism with a trilobular cross-section, wherein the cross-section of the thread core of this smaller thread section also has a trilobular shape.

[0023] The forming section 5 extends from the screw tip 6 to the threaded section 4 and comprises a first partial forming section 51 provided with the screw tip 6 and a second partial forming section 53, between which an intermediate section 52 is arranged. A third partial forming section 54 adjoins the second partial forming section 53 and borders the threaded section 4.

[0024] The first partial forming section 51 and the second partial forming section 53 each have a cross-section that decreases in the direction of the screw tip 6. The third partial forming section 54 has a constant cross-section.

[0025] The intermediate section 52 is formed in the form of a circumferential groove with an axially arcuate side contour, which is not symmetrical to its circumferential center line (corresponding to line C - C in) which divides the groove horizontally into two halves. Fig. 3). Rather, the intermediate section 52 has a smaller cross-section at its end facing the first partial section 51 than at its end facing the second partial section 53. Towards the screw tip 6, the half of the intermediate section 52 facing the second partial section 53 has a decreasing cross-section, and the half of the intermediate section 52 facing the first partial section 51 has an increasing cross-section.

[0026] In the exemplary embodiment, the partial mold sections 51, 53, 54, as well as the intermediate section 52 of mold section 5, have a trilobular cross-section. The cross-section of the intermediate section 52 can, unlike in the present exemplary embodiment, also be circular. Fig. Figure 4 shows cross-sections of the molded section 5 at different axial positions.

[0027] When the screw 1 is installed in a sheet (or sheets, not shown), it is pressed against the sheet under high pressure and rotated at high speed using a screw tool that engages positively in the recess 21 of the screw head 2. The frictional heat generated makes the sheet plastically deformable, allowing the forming section 5 with the screw tip 6 to penetrate the sheet material. First, the initial forming section 51 penetrates the sheet material, displacing the sheet material surrounding it. As the intermediate section 52 passes, a further radial displacement of the sheet material occurs along its length, reducing stresses in the sheet material surrounding the forming section 5.

[0028] The sheet metal is then pushed outwards again, and the second forming section 53 penetrates the sheet metal, further developing the opening formed by the first forming section. The third forming section 54 now slides through the formed opening, thereby centrally inserting the subsequent threaded section 4 into the opening, with the first thread of the thread 41 engaging in the sheet metal. This creates a forced feed that initiates the subsequent thread forming process.

[0029] The special design of the thread 41, whose outer edges of the thread flanks describe a prism with a trilobular cross-section at least in certain areas, results in a lower tightening torque. This is due to the lower friction occurring not along the entire circumference, but only at the frictional contact points in certain areas. At the same time, the sheet metal material in the threaded bore formed in this way tends to spring back and contract upon cooling, thus creating a self-locking effect and securing the screw connection against unintentional loosening. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 3909725 C1

[0002] WO 2010 / 003901 A1

[0003]

Claims

[1] Hole- and thread-forming screw (1), with a screw head (2) having a screw drive design and a screw shaft (3) adjoining the head having a screw tip (6) at its free end, which has a threaded section (4) at least partially provided with a thread and a forming section (5) extending to the screw tip (6) that is at least partially unthreaded, the cross-section of which decreases in the direction towards the screw tip (6), characterized by , that the forming section (5) has a first partial forming section (51) and a second partial forming section (53), the cross-sections of which each decrease continuously in the direction of the screw tip (6) and between which an intermediate section (52) is arranged which has at least in some areas a cross-section that increases in the direction of the screw tip (6). [2] Screw according to claim 1, characterized by, that the intermediate section (52) has a first subsection cross-section decreasing in the direction of the screw tip (6), which transitions into a second subsection with a cross-section increasing in the direction of the screw tip (6). [3] Screw according to claim 2, characterized by , that the intermediate section (52) is formed by a circumferential groove introduced into the molded section (5). [4] Screw according to claim 3, characterized by that the groove has an arc-shaped side contour in the axial direction. [5] Screw according to any one of claims 2 to 4, characterized by , that the minimum cross-section of the second partial mold section (53) is larger than the maximum cross-section of the first partial mold section (51). [6] Screw according to claim 5, characterized by , that the smallest diameter of the intermediate section 52 is between 40 / 50 and 17 / 20 of the largest diameter of the first partial mold section 51. [7] Screw according to any of the aforementioned claims, characterized by , that the outer edges of the thread flanks of the thread (41) of the thread section (4) are inscribed at least partially in a prism with rounded corners, in particular with a cross-section in the form of a triangle with rounded corners and convexly curved sides, and that the cross-section of the thread core of the thread section (4) of the screw shank (3) has at least partially the form of a polygon, in particular a triangle with rounded corners and convexly curved sides. [8] Screw according to any of the aforementioned claims, characterized by , that the shaped section (5) has at least in some areas a cross-section in the form of a polygon, in particular a triangle with rounded corners and convexly curved sides. [9] Screw according to any of the aforementioned claims, characterized by, that the lateral surfaces of the first partial mold section (51) and the second partial mold section (53) lie at least partially on a common body of revolution, the cross-section of which decreases continuously in the direction of the screw tip (6). [10] Screw according to any of the preceding claims, characterized by , that the side lines of the first partial form section (51) and the second partial form section (53) each have a constant curvature. [11] Screw according to any of the aforementioned claims, characterized by , that the forming section (5) following the threaded section (4) has a third partial forming section (54) with a constant cross-section.

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