Method for joining a plastic workpiece to a further workplace

Abstract

A method that includes: arranging plastic and further workpieces (1, 3) such that an abutment surface (5) of the plastic workpiece (1) is abutted to a first surface (13) on the further workpiece (3) and a projection (7) on the plastic workpiece (1) extends through a through hole (17) in the further workpiece (3); linearly moving a friction tool (23) parallel to its rotational axis (25) such that a friction surface (31) on the tool (23) contacts a front surface (9) of the projection (7); linearly moving the tool (23) along the rotational axis (25) while rotating the tool (23) so that a pin (29) on the tool (23) penetrates and plasticizes the projection (7) as well as drives a portion of the plasticized projection (7) into an undercut (21) formed in the hole (17) of the further workpiece (3); and retracting the tool (23) from the projection (7).

Claims

1. A method for joining a plastic workpiece (1) to a further workpiece (3), the method comprising: providing a plastic workpiece (1) having an abutment surface (5) and a projection (7), wherein said projection (7) projects away from the abutment surface (5) and has a front surface (9); providing a further workpiece (3) having a first surface (13), a second surface (15) opposite to the first surface (13), and a through hole (17) which connects the first surface (13) to the second surface (15) and which is defined by a side wall (19), wherein an undercut (21) is provided in the side wall (19); arranging the plastic workpiece (1) relative to the further workpiece (3) such that the abutment surface (5) of the plastic workpiece (1) abuts on the first surface (13) of the further workpiece (3) and the projection (7) extends through the through hole (17); providing a friction tool (23) that is configured for rotation about an axis of rotation (25), the friction tool (23) having a base surface (27), which extends transversely to the axis of rotation (25), and a pin (29) that extends along the axis of rotation (25) away from the base surface (27), wherein an end of the pin (29) that is disposed furthest from the base surface (27) has a friction surface (31) that extends transversely to the axis of rotation (25), wherein the pin (29) is formed as a frustum of a cone and has a conical lateral surface (33) that connects the friction surface (31) to the base surface (27), wherein the radius of the pin (29) at the level of the friction surface (31) is referred to as r1 wherein the radius of the pin (29) at the level of the base surface (27) is referred to as r2, wherein the radius of the through hole (17) is referred to as R, wherein the distance between the friction surface (31) and the base surface (27) is referred to as h, wherein the thickness of the further workpiece (3) is referred to as t, wherein parameters a, b and c are defined as: a=r1/R, b=r2/R, and c=h/t; wherein the friction tool (23) and the further workpiece (3) are formed such that a value of parameter a is between 0.35 and 0.5, a value of parameter b is between 0.5 and 0.75 and a value of parameter c is between 0.6 and 0.9; rotating the friction tool (23) about the axis of rotation (25); linearly moving the friction tool (23) in parallel to the axis of rotation (25) towards the projection (7) so that the friction surface (31) contacts the front surface (9) of the projection (7); linearly moving of the friction tool (23) along the axis of rotation (25) while rotating the friction tool (23) so that the pin (29) penetrates the material of the projection (7), plasticizes said material, and laterally displaces said material into the undercut (21); and retracting the friction tool (23) from the projection (7).

2. The method according to claim 1, wherein after said material is laterally displaced into the undercut (21), the method further comprises halting rotation of the friction tool (23) and moving the friction tool (23) linearly along the axis of rotation (25) so that the pin (29) further penetrates the material of the projection (7) and laterally displaces said material towards the hole wall (19) and into the undercut (21).

3. The method according to claim 2, wherein prior to retracting the friction tool (23), the method further comprises halting the linear movement of the friction tool (23) such that the friction tool (23) is maintained in a fixed position.

4. The method according to claim 1, wherein the undercut (21) is formed as a counterbore or chamfer which is open to the second surface (15).

5. The method according to claim 1, wherein the undercut (21) is formed as an annular recess.

6. The method according to claim 1, wherein the value of the parameter a is between 0.4 and 0.45.

7. The method according to claim 1, wherein the value of the parameter b is between 0.6 and 0.65.

8. The method according to claim 1, wherein the value of the parameter c is between 0.7 and 0.8.

9. The method according to claim 8, wherein the value of the parameter a is 0.425, the value of the parameter b is 0.625 and the value of the parameter c is 0.75.

10. The method according to claim 6, wherein the value of the parameter b is between 0.6 and 0.65.

11. The method according to claim 10, wherein the value of the parameter c is between 0.7 and 0.8.

12. The method according to claim 6, wherein the value of the parameter c is between 0.7 and 0.8.

13. The method according to claim 7, wherein the value of the parameter c is between 0.7 and 0.8.

14. The method according to claim 1, wherein the pin of the friction tool forms a cavity in the projection and wherein the cavity extends below an exterior surface of the further workpiece that faces away from the plastic workpiece.

15. The method according to claim 14, wherein the cavity extends below the exterior surface of the further workpiece to a first depth that is greater than a second depth of the undercut from the exterior surface of the further workpiece.

Description

DRAWINGS

(1) The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

(2) FIGS. 1a through 1e are sectional views of a plastic workpiece, a further workpiece and a friction tool during various stages of a method performed in accordance with the teachings of the present disclosure;

(3) FIG. 2 is a cross sectional view of the friction tool of FIG. 1a;

(4) FIG. 3 is an enlarged portion of FIG. 2 illustrating a pin of the friction tool in greater detail;

(5) FIG. 4 is a perspective view of the further workpiece of FIG. 1a;

(6) FIG. 5 is a cross sectional view taken along the line A-A of FIG. 4;

(7) FIG. 6a is a schematic cross sectional view of a joint that employs a solid stake;

(8) FIG. 6b is a schematic cross sectional view of a joint that employs a hollow stake produced in accordance with the method of the present disclosure;

(9) FIG. 7 is a collection of four schematic cross sectional views, each of which depicting a joint produced in accordance with the method of the present disclosure, the collection depicting hollow stakes of different weight reduction factors depending on different geometries.

(10) Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

(11) With reference to FIG. 1, an exemplary method for joining a plastic workpiece 1 to a further workpiece 3 according to the teachings of the present disclosure is illustrated, showing five particular method steps or stages in FIGS. 1a to 1e.

(12) A plastic workpiece 1 made of a polymer material can be provided having an abutment surface 5 and a projection 7. The projection 7 projects away from the abutment surface 5 and can have a front surface 9 that can extend in parallel to the abutment surface 5. Further, the projection 7 can have an annular side surface 11 that can extend transversely to the abutment surface 5.

(13) A further workpiece 3, which is formed of metal in the particular example provided, can have a first surface 13, a second surface 15 opposite to the first surface 13, and an annular through hole 17 which connects the first surface 13 to the second surface 15. The through hole 17 is defined by an annular hole wall 19 which comprises an undercut 21. Said undercut 21 in the present embodiment is formed as a counterbore or a chamfer.

(14) The plastic workpiece 1 can be arranged relative to the further workpiece 3 in such a manner that the abutment surface 5 of the plastic workpiece 1 abuts on the first surface 13 of the further workpiece 3 and the projection 7 extends through the through hole 17. The projection 7 can exceed (i.e., can be longer than) the second surface 15 of the further workpiece 3 such that the front surface 9 of the projection 7, when viewed from the plastic workpiece 1, extends further away from the abutment surface 5 than the second surface 15 of the further workpiece 3. The projection 7 and the through hole 17 can be formed such that a minimum gap or no gap is left between the hole wall 19 and the side surface 11 of the projection 7. It will be appreciated, however, the desired joint can also be established when there is a certain gap between the hole wall 19 and the side surface 11.

(15) A friction tool 23 configured for rotation about an axis of rotation 25 is provided. The friction tool 23 can have a base surface 27, which can extend perpendicularly to the axis of rotation 25, and a pin 29 that can extend along the axis of rotation 25 away from the base surface 27. At its end remote from the base surface 27, the pin 29 has a friction surface 31 that can extend perpendicularly to the axis of rotation 25. Further, the friction tool 23 is made of metal material and can have a conical lateral surface 33 that connects the friction surface 31 to the base surface 27 (see FIG. 1a).

(16) As shown in FIG. 1a, the friction tool 23 can be rotated about the axis of rotation 25 and linearly moved in parallel to the axis of rotation 25 towards the projection 7 until the friction surface 31 contacts the front surface 9 of the projection 7. The friction between the friction surface 31 of the pin 29 and the front surface 9 of the projection 7 can cause the plastic material of the projection 7 to plasticize, which permits the pin 29 to penetrate into the plasticized plastic material of the projection 7.

(17) Subsequently, as shown in FIG. 1b, continued rotation and linear movement of the friction tool 23 about and along the axis of rotation 25 permits the pin 29 to penetrate the material of the projection 7 so that the friction tool 23 further plasticizes the material of the projection 7 and laterally displaces the plasticized material of the projection 7 into the undercut 21 formed in the further workpiece 3.

(18) The rotation of the friction tool 23 can be stopped and the friction tool 23 can be pressed and moved further linearly along the axis of rotation 25 so that the pin 29 further penetrates the material of the projection 7 and laterally displaces said material towards the hole wall 19 and into the undercut 21 (see FIG. 1c). This linear movement can be performed until the base surface 27 of the friction tool 23 contacts the second surface 15 of the further workpiece 3 (see FIG. 1d).

(19) If desired, the linear movement of the friction tool 23 can be halted and the friction tool 23 can be held still in a fixed position for a predetermined time until the material of the projection 7 sufficiently solidifies and does not shrink or move undesirably after retracting the friction tool 23 (see FIG. 1d).

(20) As shown in FIG. 1e, the friction tool 23 can be retracted from the plastic workpiece 1 and the further workpiece 3, so that the pin 29 is retracted out of the projection 7. As a result, a joint between the plastic workpiece 1 and the further workpiece 3 can be formed such that the joint comprises a hollow stake 35 which has a flat surface 37 in line with the second surface 15 of the further workpiece 3. The hollow space 39 in the stake 35 can form a recess from said flat and smooth second surface 15. The plastic workpiece 1, the further workpiece 3, and the friction tool 23 are adapted such that the material of the projection 7 which exceeds (i.e., extends beyond) the second surface 15 of the further workpiece 3 and the material of the projection 7 which is displaced by the pin 29 of the friction tool 23 during performance of the method, can be entirely received into the undercut 21, so that the base surface 27 of the friction tool 23 can contact the second surface 15 of the further workpiece 3 and no material of the projection 7 projects up the second surface 15 of the further workpiece 3.

(21) As shown in more detail in FIGS. 2 and 3, the pin 29 of the friction tool 23 can be formed as a frustum of a cone and has a conical lateral surface 33 that can connect the friction surface 31 to the base surface 27. The radius of the pin 29 at the level of the friction surface 31 is referred to as r.sub.1, the radius of the pin 29 at the level of the base surface 27 is referred to as r.sub.2, and the distance between the friction surface 31 and the base surface 27 is referred to as h.

(22) As shown in more detail in FIGS. 4 and 5 the further workpiece 3 comprises an undercut 21 which can be formed as a counterbore or chamfer that is open to the second surface 15. The radius of the through hole 17 in the further workpiece 3 is referred to as R and the thickness of the further workpiece 3 is referred to as t.

(23) In order to provide a best compromise between a strong and reliable joint between the plastic workpiece 1 and the further workpiece 3, and at the same time a possibly high reduction of weight by a possibly large hollow space 39 in the stake 35, i.e. in the deformed projection 7, a certain geometry is determined for the friction tool 23 based on the geometry of the further workpiece 3. Therefore, the three parameters a, b, c are defined in the following manner:

(24) 0$a=\frac{r_1}{R},b=\frac{r_2}{R},\mathrm{and}c=\frac{h}{t},$
wherein in the particular example provided, a is determined as 0.375, b is determined as 0.527, and c is determined as 0.78, which results in a weight reduction factor W.sub.r of 16%.

(25) In FIG. 6a solid stake 41 (see FIG. 6a) as it is known in the art without any hollow space 39 is compared to a hollow stake 35 (FIG. 6b) which is produced according to a method of the present invention. In FIG. 6 V.sub.SS represents the volume of the solid stake 41 which equals the volume of the through hole 17, V.sub.HS represents the volume of the hollow stake 35, V.sub.DM represents the volume of the displaced material, and V.sub.c represents the volume of the undercut 21.

(26) In FIG. 7 four hollow stakes 35 of different weight reduction factors W.sub.r, produced in accordance with a method of the present invention are compared, wherein in FIG. 7a a=0.375, b=0.527, c=0.78, so that the weight reduction factor W.sub.r=16%, wherein in FIG. 7b a=0.577, b=0.697, c=0.75, so that the weight reduction factor W.sub.r=30%, wherein in FIG. 7c a=0.667, b=0.828, c=0.9, so that the weight reduction factor W.sub.r=50%, and wherein in FIG. 7d a=0.833, b=1.0, c=0.9, so that the weight reduction factor W.sub.r=76%.

(27) The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.