Hole and thread forming screw

Abstract

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, which has a threaded section (4) at least partially provided with a thread and a threadless forming section (5) extending to the screw tip (6), the cross-section of which decreases at least partially 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) having a constant cross-section is arranged.

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 the head having a screw tip at its free end, which has a threaded section provided with a thread at least in some areas and a forming section extending to the screw tip that is at least in some areas unthreaded, the cross-section of which decreases at least in some areas 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. The fact that the forming section comprises a first partial forming section and a second partial forming section, the cross-sections of which decrease continuously towards the screw tip, and between which an intermediate section with a constant cross-section is arranged, significantly reduces the maximum required piercing force, thereby reducing the assembly time of the screw. The piercing force, in this context, is the force required to push (pierce) the forming section of a screw through a material.

[0006] Due to the screw's design according to the invention, the first forming section, which creates the screw tip, fulfills a pre-drilling or piercing function. To penetrate a sheet metal material with the tip formed by the first forming section, a continuous increase in force is required until the intermediate section is reached. The applied force is divided into a depth vector for piercing and a radial vector for expanding the material. During the further course of the process, the diameter in the area of ​​the intermediate section remains constant until the beginning of the expansion area formed by the first forming section. This ensures that the force applied to the screw is used largely in the axial direction for piercing and not in the radial direction for expanding the hole. The intermediate section serves to guide the screw in a centered position and does not itself perform any deformation work.Upon reaching the expansion zone formed by the second forming section, the axial force is again divided into a depth vector for piercing and a radial vector for material expansion. Due to the constant cross-section of the intermediate section, the screw experiences an acceleration—especially with thinner sheet metal—which, upon reaching the second forming section, results in an axial impulse being transferred into the sheet metal.

[0007] In this context, a "constant cross-section" is understood to be a cross-section whose circumference remains constant in the axial direction – within the limits of usual manufacturing tolerances. In the case of a circular cross-section, a constant cross-section describes a cylinder. In the case of a trilobular cross-section, a prism with a trilobular base is described, whose circumference is constant in the axial direction.

[0008] In a further development of the invention, the forming section has at least a partial cross-section in the form of a polygon, in particular a triangle with rounded corners and convexly curved sides (i.e., in the form of a trilobular cross-section). 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.

[0009] In one embodiment of the invention, the mold section in the area of ​​the intermediate section has a circular cross-section. This results in improved guiding behavior of the intermediate section.

[0010] In a further embodiment of the invention, the second mold section, when rotated about its longitudinal central axis, describes a truncated cone; that is, the side lines of the second mold section are straight. This results in improved material expansion.

[0011] In a further embodiment of the invention, the first partial mold section, when rotated about its longitudinal central axis, describes an ellipsoidal segment terminating in a point; that is, the lateral lines of the first partial mold section exhibit an arc-shaped curvature. This facilitates the piercing process. In this context, "arc-shaped curvature" refers to an arc-shaped curvature achievable within the manufacturing tolerances of screw production. Alternatively, the first partial mold section can also be designed in the form of a cone, particularly a cone with a rounded tip.

[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, following the threaded section, has a third forming section with a constant cross-section. This facilitates the centered insertion of the threaded section into the opening created in the sheet metal by the forming section when the screw is inserted. Simultaneously, the third forming section promotes plastic deformation of the opening and thus stabilizes the diameter of the pierced pilot hole. The term "constant cross-section" here also takes into account the manufacturing tolerances in the production of a screw.

[0014] In a further development of the invention, the length of the intermediate section corresponds to at least 40% of the thread core diameter of the threaded section. This further facilitates the piercing process. Advantageously, the diameter of the intermediate section is greater than or equal to 50% and preferably less than or equal to 90% of the thread core diameter of the threaded section.

[0015] In an embodiment of the invention, the length of the third partial forming section corresponds to at least 10% of the thread core diameter of the threaded section. Advantageously, the diameter of the third partial forming section corresponds to 80% or more and 120% or less than the thread core diameter of the threaded section.

[0016] The present invention further relates to a bolted connection arrangement comprising at least two components, in particular at least two sheets, through which a screw of the aforementioned type is guided, wherein the total length of the intermediate section and the first partial forming section corresponds to at least 60 percent, preferably at least 70 percent, and particularly preferably between 80 percent and 95 percent of the total thickness of the at least two components, in particular the at least two sheets. By matching the lengths of the intermediate section and the first partial forming section with respect to the sheet thicknesses, a reduction in the occurrence of incorrect installation is achieved. The tip formed by the first partial forming section should have largely penetrated the sheets before the hole expansion process by the second partial forming section takes place.

[0017] The inventive design of the forming section results in a positive shift in the process limits even when using stronger and thicker sheets at the end user's site.

[0018] 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 schematic representation of a hole- and thread-forming screw a) In side view; b) in top view; Fig. 2. The detailed representation of section Z of the screw shaft. Fig. 1; Fig. 3 the representation of the shape section of the cutout from Fig. 2 a) in cross-section A - A; b) in cross-section B - B; c) in cross-section C - C; Fig. 4. The illustration of a screw connection arrangement for joining two sheets and Fig. 5. Detailed view of section “Y” of the screw connection arrangement from Fig. 4.

[0019] 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 engagement of a screw tool to transmit torque to the screw 1. Alternatively, the screw head can, for example, be non-circular or have a non-circular recess for the screw drive. The essential feature is the presence of a recess for positive-locking or force-locking torque transmission.

[0020] 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.

[0021] 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.

[0022] The forming section 5 extends from the screw tip 6 to the threaded section 4 and comprises a first partial forming section 51, which is provided with the screw tip 6, and a second partial forming section 53, between which an intermediate section 52 is arranged. In the exemplary embodiment, a third partial forming section 54 adjoins the second partial forming section 53, adjoining the threaded section 4 and having a constant cross-section. This partial forming section 54 can also be omitted in this exemplary embodiment.

[0023] 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 intermediate section 52 has a constant cross-section.

[0024] In the exemplary embodiment, the partial mold sections 51, 53, 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, thus giving it a cylindrical shape. Fig. Figure 3 shows cross-sections of the molded section 5 at different axial positions.

[0025] In Fig. Figure 4 shows a screw connection arrangement for joining two sheets 7. When the screw 1 is installed in these sheets 7, it is pressed onto the sheet under high pressure and rotated at high speed by means of a screw tool that engages positively in the recess 21 of the screw head 2. The frictional heat generated in this process 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 (piercing process).

[0026] When passing through the intermediate section 52, no material displacement occurs along its length, meaning that the force applied axially to the screw is largely used in the piercing process of the first partial forming section (cf. Fig. 5).

[0027] Subsequently, the second partial forming section 53 penetrates the sheet metal, further widening the opening formed by the first partial forming section 51. Furthermore, the interaction of the various partial forming and intermediate sections 51, 52, 53, 54 of the forming section 5 results in improved material flow towards the opening 71 on the underside of the lowest sheet 7. This also counteracts excessive material build-up towards the screw head 2.

[0028] The subsequent threaded section 4 is then inserted centrally into the through-hole 71, 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) having at least a portion of its thread and a threadless forming section (5) extending to the screw tip (6), the cross-section of which decreases at least in portion of its 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 a constant cross-section. [2] Screw according to claim 1, 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. [3] Screw according to claim 1 or 2, characterized by , that the shaped section has a circular cross-section at least in the area of ​​the intermediate section (52). [4] Screw according to any of the aforementioned claims, characterized by , that the second partial form section (53) describes a truncated cone when rotated about its longitudinal central axis. [5] Screw according to any of the aforementioned claims, characterized by , that the first partial shape section (51) describes an ellipsoidal section ending in a point when rotated about its longitudinal central axis. [6] 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. [7] Screw according to any of the aforementioned claims, characterized by , that the length of the intermediate section (52) corresponds to at least 40% of the thread core diameter of the thread section (4). [8] Screw according to any of the aforementioned claims, characterized by , that the diameter of the intermediate section (52) is greater than or equal to 50% and preferably less than or equal to 90% of the thread core diameter of the thread section (4). [9] Screw according to any of the aforementioned claims, characterized by , that the forming section following the threaded section (4) has a third partial forming section (54) with a constant cross-section. [10] Screw according to claim 9, characterized by , that the length of the third partial form section (54) corresponds to at least 10% of the thread core diameter of the thread section (4). [11] Screw according to claim 9 or 10, characterized by , that the diameter of the third partial form section (54) is greater than or equal to 80% and less than or equal to 120% of the thread core diameter of the thread section (4). [12] Screw connection arrangement with at least two components, in particular at least two sheets (7), through which a screw (1) according to one of the preceding claims is guided, wherein the total length of the intermediate section (52) and the first partial forming section (51) corresponds to at least 60 percent, preferably at least 70 percent, particularly preferably between 80 percent and 95 percent of the total thickness of the at least two components, in particular the at least two sheets (7).

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