TWO-STEEL SCREW WITH AN EXTRUSION CONNECTION AND METHOD FOR PRODUCING SAID SCREW

Abstract

The invention relates to a two-steel screw comprising a top part and a cutting part, the top part consisting of a corrosion-resistant material and having a screw head and a shank portion, and the cutting part consisting of a hardenable material, the top part being permanently connected to the cutting part in the region of the shank portion by way of impact extrusion.

Claims

1. A two-steel screw (10) comprising a top part (12) and a cutting part (14), the top part (12) consisting of a corrosion-resistant material and having a screw head (16) and a shank portion (18), and the cutting part (14) consisting of a hardenable material, wherein the top part (12) is permanently connected to the cutting part (14) in the region of the shank portion (18) by way of impact extrusion.

2. The two-steel screw (10) according to claim 1, wherein the cutting part (14) has a lug-like projection (34) and that the top part (12) has a cup-shaped recess (24) on the shank portion (18), wherein the lug-like projection (34) is arranged in the cup-shaped recess (24) and axially undercuts the top part (12) in the region of the cup-shaped recess (24) at least partially.

3. The two-steel screw (10) according to claim 2, wherein the lug-like projection (34) fills the shape of the cup-shaped recess (24) completely.

4. The two-steel screw (10) according to claim 1, wherein the cutting part (14) is hardened and has at least one drill bit.

5. The two-steel screw (10) according to claim 2, wherein, in cross-section, the cup-shaped recess (24) has an engaging profile (68) with a plurality of, preferably three, engaging segments (72),

6. The two-steel screw (10) according to claim 5, wherein circular segments (70) are provided between the engaging segments (72).

7. The two-steel screw (10) according to claim 5, wherein the engaging segments (72) and the circular segments (70) are arranged at an angle (74) of 120 relative to one another in the circumference of the recess (24).

8. The two-steel screw (10) according to claim 5, wherein the cup-shaped recess (24) has a first radius (76) in the region of the circular segments (70) and has a second reducing radius (78) which is smaller than the first radius (76) in the region of the engaging segments (72).

9. A method for producing a two-steel screw (10) consisting of a top part (12) made of a corrosion-resistant material and having a screw head (16) and a shank portion (18), and a cutting part (14) consisting of a hardenable material, comprising: pressing a cup-shaped recess (24) with a predetermined depth (26) into the top part (12) in the region of the shank portion (18) or forming a lug-like projection with a predetermined length on the shank portion (18); producing the cutting part (14) with a lug-like projection (34) with a length (38) greater than the depth (26) of the recess (24) or pressing a cup-shaped recess into the cutting part (14) with a depth smaller than the length of the lug-like projection of the shank portion (18); introducing the projection (34) into the recess (24) and connecting the top part (12) and the cutting part (14) by means of impact extrusion, so that the lug-like projection (34) completely fills the shape of the cup-shaped recess (24).

10. The method according to claim 9, wherein the cup-shaped recess (24) is pressed into the top part (12) or into the cutting part (14) in an area ratio of approximately 55% to approximately 75% to a cross-sectional area of the shank portion (18).

11. The method according to claim 9 wherein the lug-like projection (34) is produced in a circular cylindrical shape.

12. The method according to claim 9, wherein when the cup-shaped recess (24) is pressed in, an engaging profile (68) with engaging segments (72) is pressed in.

13. The method according to claim 9, wherein after the connection a thread is rolled onto the shank portion (18) and the cutting part (14).

14. The method according to claim 9, wherein the top part (12) and the cutting part (14) are arranged axially in alignment before connection.

15. The method according to claim 9, wherein the production of the cutting part (14) and the connection to the top part (12) are carried out in a multi-stage press.

Description

[0026] In the drawings:

[0027] FIG. 1 shows an impact extruded two-steel screw;

[0028] FIG. 2 shows a top part for the impact extruded two-steel screw according to FIG. 1;

[0029] FIG. 3 shows a cutting part for the impact extruded two-steel screw according to FIG. 1;

[0030] FIG. 4 shows in alignment the head and cutting parts of the two-steel screw according to FIG. 1 before the impact extrusion process;

[0031] FIG. 5 shows a view of a detail of a top part and of a cutting part at the start of an impact extrusion process;

[0032] FIG. 6 shows a view of a detail of an impact extruded connection after the impact extrusion process; and

[0033] FIG. 7 shows a cup-shaped recess of the top part according to FIG. 2.

[0034] FIG. 1 shows a two-steel screw 10, wherein the two-steel screw 10 has a top part 12 and a cutting part. The top part 12 also has a screw head 16 as well as a shank portion 18. The top part 12 and the cutting part 14 are connected to one another in the region of a joint 20 by means of an impact extrusion process.

[0035] FIG. 2 shows the top part 12 of the two-steel screw 10 shown in FIG. 1. In this case, the screw head 16 as well as the shank portion 18 can be seen clearly. The screw head 16 and the shank portion 18 are arranged concentrically with respect to a central longitudinal axis 22. On the side facing away from the screw head 16 the top part 12 has a cup-shaped recess 24. This cup-shaped recess has a depth 26, which extends in the axial direction, that is to say in the direction of the longitudinal axis 22. In FIG. 2, the cup-shaped recess 24 also has a diameter 28. The shank portion 18 of the top part 12 is formed as a circular cylinder and has a diameter 30. The cup-shaped recess 24 is preferably introduced into the shank portion 18 of the top part 12 by means of a pressing process. The cup-shaped recess 24 advantageously has an engaging profile shown in FIG. 7 which is described and explained in greater detail below with reference to FIG. 7.

[0036] FIG. 3 shows the cutting part 14 of the two-steel screw 10 shown in FIG. 1. The cutting part 14 has a diameter 32 which corresponds approximately to the diameter 30 of the shank portion 18 of the top part 12. The cutting part 14 also has a lug-like projection 34. The lug-like projection 34 and the cutting part 14 are arranged concentrically with respect to the longitudinal axis 22. The top part 12 has a diameter 36 in the region of the lug-like projection 34. Furthermore, the lug-like projection 34 has a length 38 in the direction of the longitudinal axis 22.

[0037] The length 38 of the lug-like projection 34 is greater than the depth 26 of the cup-shaped recess 24 of the top part 12. The length 36 of the lug-like projection 34 is smaller than the smallest diameter 28 of the cup-shaped recess 24.

[0038] This can be seen clearly in FIG. 4. FIG. 4 shows a top part 12 and a cutting part, wherein the top part 12 and the cutting part 14 are arranged axially in alignment along the central longitudinal axis 22. In this case, the lug-like projection 34 of the cutting part 14 is inserted into the cup-shaped recess 24 of the top part 12. The insertion of the lug-like projection 34 into the cup-shaped recess 24 can take place in the direction of the arrow 40. It can be seen clearly that the lug-like projection 34 has a greater length 38 than the depth 26 of the cup-shaped recess 24. Furthermore, it can be seen that the cup-shaped recess 24 has a greater diameter 28 than the diameter 36 of the lug-like projection 34. FIG. 4 shows the top part 12 and the cutting part 14 before the impact extrusion process is carried out.

[0039] FIG. 5 shows an enlarged detail of a top part 12, wherein the lug-like projection 34 of the cutting part 14 is introduced into the cup-shaped recess 24 of the top part 34. The two parts, namely the top part 12 and the cutting part 14 are arranged in a die 42 of a multi-stage press and are supported on a circumferential surface 44 of the die 42. FIG. 5 shows the top part 12 and the cutting part 14 at the start of an impact extrusion process. The direction of action of the machine is represented by the arrow 46. If the cutting part 14 is moved further in the direction of the arrow 46 onto the top part 12 beyond the position illustrated in FIG. 4, an end face 48 of the lug-like projection 34 penetrates at least partially into a base surface 50 of the cup-shaped recess 24. Since a further axial deflection in the direction of the arrow 46 is delimited by the base 50 of the cup-shaped recess 24, material of the lug-like projection 34 can flow radially outwards in the direction of the arrow 52, i.e. transversely with respect to the arrow 46, into a hollow space 54 between the top part 12 and the lug-like projection 34 of the cutting part 14.

[0040] FIG. 6 shows an enlarged detail of an impact extruded connection at the end of the impact extrusion process. The top part 12 and the cutting part 14 of the two-steel screw 10 are still arranged in a die 42 of a multi-stage press and are supported on the circumferential surface 44 of the die. The effect of the impact extrusion process in the direction of the arrow 52 can be clearly seen. Material of the lug-like projection 34 can flow transversely with respect to the direction of action of the press, that is to say transversely with respect to the direction represented by the arrow 46. In this case, the material flows into the hollow space 54 shown in FIG. 5 and fills it.

[0041] The movement of a side wall 56 of the top part 12 which forms the cup-shaped recess 24 is delimited by the circumferential surface 44 of the die 42, since the top part and the cutting part 14 are supported on the circumferential surface 44 of the die 42. At the end of the impact extrusion process the lug-like projection 34 fills the cup-shaped recess 24 completely.

[0042] As can be seen in FIG. 6, the lug-like projection 34 has a convexity 58. After the impact extrusion process, the lug-like projection 34 has a diameter 60 in the region of the convexity 58. At a transition region 62 to the lug-like projection 34 the lug-like projection 34 also has a diameter 64. The diameter 60 is greater than the diameter 64, so that the lug-like projection 34 undercuts the cup-shaped recess 24 in the axial direction. Thus a withdrawal of the lug-like projection from the cup-shaped recess 24 in the direction of the arrow 66 is no longer possible.

[0043] Since high torques must also be transmitted during the production of drilled holes, or during the use of two-steel screws 10, the cup-shaped recess of the top part 12 has an engaging profile 68 shown in FIG. 7, as already stated above. The engaging profile 68 is formed from circular segments 70 and between the circular segments 70 arranged engaging segments 72. In FIG. 7, three circular segments 72 are provided in each case, in such a way that they are arranged at an angle 74 of approximately 120 with respect to one another. In the region of the circular segments 70, the cup-shaped recess 24 has a radius 76 which is constant in the region of the circular segments 70. In the region of the engaging segments 72, the cup-shaped recess 24 has a radius 78 which reduces continuously in the region of the circular segments 72. This reducing radius 78 defines the distance which reduces in the region of the engaging segments 72 towards a bulge 77. The engaging segments 72 are formed as reversed circular segments and can also be defined by a radius 79 applied from the exterior.

[0044] If a cutting part 14 or a lug-like projection 34 of a cutting part 14 is introduced into the cup-shaped recess 24 of the top part 12 for the impact extrusion process, it is particularly preferable if the diameter 36 of the lug-like projection is chosen to be smaller than or equal to the smallest diameter of the cup-shaped recess 24 in the region of the center 80 of the engaging segments 72, so that the lug-like projection 34 can be introduced without problems into the cup-shaped recess 24. During the impact extrusion process material of the lug-like projection 34 can then spread into the hollow spaces 54 which are defined by the circular segments 70. Then in addition to the undercuts due to the convexity 58 which ensures a connection in the axial direction, a torque transmission in the radial direction can be provided because of the engaging profile 68.