Method for joining metal and plastic workpieces

1. Method for connecting a metal workpiece and a plastic workpiece using a joining tool including a pin movable along an axial direction, a sleeve surrounding the pin and being rotationally driveable and movable with respect to and in the axial direction of the pin, and an outer clamping ring surrounding the sleeve, said method comprising the steps of:

positioning the metal workpiece and the plastic workpiece such that contact surfaces of the workpieces abut on each other;

positioning the joining tool on the metal workpiece so as to bring a front end of the pin, the sleeve, and the clamping ring into contact with an outer surface of the metal workpiece, the outer surface being opposite the contact surface of the metal workpiece;

rotating the sleeve and the pin so as to generate friction between the front ends of the sleeve and the pin and the outer surface of the metal workpiece; and

moving the pin and the sleeve in the axial direction of the pin while both the pin and the sleeve are rotated, one of the sleeve and the pin penetrating into the metal workpiece and the other of the sleeve and the pin being retracted from the outer surface thereof,

wherein the axial movement into the metal workpiece is stopped before said one of the sleeve and the pin reaches the contact surface,

wherein, after stopping the axial movement, said one of the sleeve and the pin is retracted from the metal workpiece and said other of the sleeve and the pin is moved toward the outer surface of the metal workpiece until the front ends of the pin and the sleeve are on the same level.

2. Method according to claim 1 ,

wherein a protrusion is formed on the contact surface of the metal workpiece, the protrusion extending into the plastic workpiece.

3. Method according to claim 1 ,

wherein the sleeve penetrates into the metal workpiece and the pin is retracted from the outer surface of the metal workpiece during the step of axial movement.

4. Method according to claim 1 ,

wherein the penetration depth up to which said one of the pin and the sleeve penetrates into the metal workpiece, is less than 25% of the distance between the outer surface and the contact surface of the metal workpiece.

5. Method according to claim 4 ,

wherein the penetration depth up to which said one of the pin and the sleeve penetrates into the metal workpiece is less than 20% of the distance between the outer surface and the contact surface of the metal workpiece.

6. Method according to claim 1 , further comprising the step of:

cleaning the contact surfaces of the metal workpiece and the plastic workpiece before the step of positioning the joining tool on the metal workpiece.

7. Method according to claim 6 ,

said cleaning step including the step of grinding off the contact surfaces of the workpieces.

8. Method according to claim 1 ,

wherein the contact surface of the metal workpiece is textured.

9. Method according to claim 8 ,

wherein the contact surface of the metal workpiece includes protrusions.

10. Method according to claim 1 , further comprising the step of:

removing the joining tool from the outer surface of the metal workpiece after expiration of a predetermined time period after stopping of the axial movement of the sleeve and the pin.

11. Method according to claim 1 ,

wherein the metal workpiece comprises aluminum.

12. Method according to claim 1 ,

wherein the metal workpiece comprises magnesium.

13. Method according to claim 1 ,

wherein the plastic workpiece comprises polyphenylene sulfide.

14. Method according to claim 1 ,

wherein the plastic workpiece comprises a fiber reinforced material.