Method for connecting a surface-structured workpiece and a plastic workpiece

Abstract

A method for connecting a surface-structured workpiece (SSW) and a plastic workpiece using a joining tool with a sonotrode. The method includes: positioning the SSW and the plastic workpiece on an anvil such that a structured contact surface section (SCSS) of the SSW faces a contact surface of the plastic workpiece; positioning the sonotrode in contact with an outer surface of the SSW that is opposite to the SCSS; and applying pressure to the sonotrode and/or the anvil perpendicular to the contact surface to hold the workpieces fixed between the anvil and the sonotrode and applying ultrasonic vibrations to the workpieces by the sonotrode for a predetermined period of time to induce softening of the plastic workpiece and penetrate pin-like elements of the SCSS into the plastic workpiece.

Claims

1. A method for connecting a surface-structured workpiece and a plastic workpiece using a joining tool including a sonotrode, said surface-structured workpiece comprising a structured contact surface section, said structured contact surface section comprising pin-like elements extending away from the structured contact surface section, said method comprising: positioning the surface-structured workpiece and the plastic workpiece on an anvil such that the structured contact surface section faces a contact surface of the plastic workpiece, positioning the joining tool on the surface-structured workpiece so as to bring the sonotrode into contact with an outer surface of the surface-structured workpiece, the outer surface being opposite to the structured contact surface section, and applying a pressure to the sonotrode and/or the anvil perpendicular to the contact surface to hold the workpieces fixed between the anvil and the sonotrode and applying ultrasonic vibrations to the workpieces by the sonotrode for a predetermined period of time, so that softening of the plastic workpiece is induced and the pin-like elements penetrate into the plastic workpiece.

2. The method of claim 1, further comprising removing the pressure and ultrasonic vibrations and retracting of the sonotrode.

3. The method of claim 1, wherein the pin-like elements comprise anchoring elements at their distal ends.

4. The method of claim 3, wherein the anchoring elements of the pin-like elements are designed as conical or spherical or convex or arrow-like or hook-like heads.

5. The method of claim 1, wherein the pin-like elements have a length of 1 to 5 mm in direction perpendicular to the contact surface section.

6. The method of claim 1, wherein the structured contact surface section comprises between 3 to 10 pin-like elements per cm.sup.2.

7. The method of claim 1, wherein the surface-structured workpiece is formed of aluminum or an aluminum alloy.

8. The method of claim 1, wherein the surface-structured workpiece is formed of magnesium or a magnesium alloy.

9. The method of claim 1, wherein the surface-structured workpiece is formed of titanium or a titanium alloy.

10. The method of claim 1, wherein the surface-structured workpiece is produced by: forming a mixture by mixing a metal powder and/or metal alloy powder with a binder; shaping the mixture by injection moulding to give the resulting workpiece at least one structured surface section, with the structured surface section having pin-like elements, and sintering the structured workpiece, to form the shaped surface-structured workpiece having a structured surface section.

11. The method of claim 10, wherein the production of the surface-structured workpiece further comprises: subjecting the structured workpiece to chemical binder removal; and subjecting the structured workpiece which has been subjected to chemical binder removal, to thermal binder removal before sintering the workpiece.

12. The method of claim 1, wherein the plastic workpiece is formed of a fiber reinforced plastic material.

13. A method for connecting a surface-structured workpiece and a plastic workpiece using a joining tool including a sonotrode, said surface-structured workpiece comprising a structured contact surface section, said structured contact surface section comprising pin-like elements extending away from the structured contact surface section, said method comprising: positioning the surface-structured workpiece and the plastic workpiece on an anvil such that the structured contact surface section faces a contact surface of the plastic workpiece, positioning the joining tool on the surface-structured workpiece so as to bring the sonotrode into contact with an outer surface of the surface-structured workpiece, the outer surface being opposite to the structured contact surface section, applying a pressure to the sonotrode and/or the anvil perpendicular to the contact surface to hold the workpieces fixed between the anvil and the sonotrode and applying ultrasonic vibrations to the workpieces by the sonotrode for a predetermined period of time, so that softening of the plastic workpiece is induced and the pin-like elements penetrate into the plastic workpiece; and removing the pressure and ultrasonic vibrations and retracting of the sonotrode; wherein the pin-like elements have a length of 1 to 5 mm in direction perpendicular to the contact surface section; wherein the pin-like elements comprise anchoring elements at their distal ends, wherein the anchoring elements of the pin-like elements are designed as conical or spherical or convex or arrow-like or hook-like heads; wherein the structured contact surface section comprises between 3 to 10 pin-like elements per cm.sup.2; and wherein the surface-structured workpiece is formed of a material selected from the group consisting of: aluminum, aluminum alloy, magnesium, magnesium alloy, titanium and titanium alloy.

14. The method of claim 13, wherein the surface-structured workpiece is produced by: forming a mixture by mixing a metal powder and/or metal alloy powder with a binder; shaping the mixture by injection molding to give the resulting workpiece at least one structured surface section, with the structured surface section having pin-like elements; and sintering the structured workpiece, to form the shaped surface-structured workpiece having a structured surface section.

15. The method of claim 14, wherein the production of the surface-structured workpiece further comprises: subjecting the structured workpiece to chemical binder removal; and subjecting the structured workpiece which has been subjected to chemical binder removal, to thermal binder removal before sintering the workpiece.

16. The method of claim 13, wherein the plastic workpiece is formed of a fiber reinforced plastic material.

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) FIG. 1 is a schematic illustration of a device for performing method in accordance with the teachings of the present disclosure,

(3) FIG. 2 is a schematic illustration of an exemplary method conducted in accordance with the teachings of the present disclosure,

(4) FIG. 3 shows a schematic of a produced joint,

(5) FIG. 4 shows a sectional view of joints realized by different examples of the pin-like elements,

(6) FIG. 5 shows a schematic of a produced joint with an assembly of plastic workpieces,

(7) FIG. 6 shows a first example of the application of the method of the present invention,

(8) FIG. 7 shows a second example of the application of the method of the present invention,

(9) FIG. 8 shows a third example of the application of the method of the present invention,

(10) FIG. 9 shows a fourth example of the application of the method of the present invention,

(11) FIG. 10 shows a fifth example of the application of the method of the present invention and

(12) FIG. 11 shows a sixth example of the application of the method of the present invention.

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

DETAILED DESCRIPTION

(14) As shown in FIG. 1, a device for performing a method in accordance with the teachings of the present disclosure is shown with which a surface-structured workpiece 1 comprising a structured contact surface section 3 with pin-like elements 5 that extend away from the structured contact surface section 3, and a plastic workpiece 7 can be connected with each other.

(15) Optionally, the surface-structured workpiece 1 can be produced by a metal injection molding method, which can comprise the following steps: forming a mixture by mixing a metal powder and/or metal alloy powder with a binder, shaping the mixture by injection molding to give the resulting workpiece at least one structured surface section 3, with the structured surface section 3 having pin-like elements 5, and sintering the structured workpiece to form the shaped surface-structured workpiece 1 having a structured surface section 3.

(16) In particular, this production method may further comprise: subjecting the structured workpiece to chemical binder removal; and subjecting the structured workpiece that has been subjected to chemical binder removal to thermal binder removal before sintering the workpiece.

(17) However it is also conceivable that the surface-structured workpiece 1 is formed of aluminum or an aluminum alloy, magnesium or a magnesium alloy or titanium or a titanium alloy.

(18) Furthermore, the plastic workpiece 7 can be formed of a fiber reinforced plastic material.

(19) The device comprises a sonotrode 9 having a sonotrode tip 10 and an anvil 11, and the workpieces 1, 7 are arranged between the sonotrode 9 and the anvil 11 in such a way that the distal ends of the pin-like elements 5 of the structured contact surface section 3 of the surface-structured workpiece 1 are facing towards a contact surface 13 of the plastic workpiece 7.

(20) Generally the sonotrode 9 is part of an ultrasonic welding system with the main components (not shown in FIG. 1) of an ultrasonic generator, which generates high frequency alternating voltage in a kilohertz-regime, a converter transforming this voltage into mechanical oscillations, usually due to the reversed piezoelectric effect, a booster typically increasing the oscillation amplitude to a range between 5 m up to 50 m, and the sonotrode 9 transferring the ultrasonic mechanical oscillation to the joining zone i.e. by direct contact with the surface-structured workpiece 1.

(21) The method of the present disclosure can be divided into five stages illustrated as in FIG. 2.

(22) Initially the workpieces 1, 7 are fixed between the anvil 11 and the sonotrode tip 10 with the pin-like structures 5 of the surface-structured workpiece 1 on top of the plastic workpiece 7, wherein the pin-like elements 5 touch the contact surface 13 of the plastic workpiece 7 (see Part a) of FIG. 2). The sonotrode tip 9 abuts on an upper surface 15 of the surface-structured workpiece 1 opposite the structured contact surface section 3 of the surface-structured workpiece 1 and a static pressure 17 is applied perpendicularly to the contact surfaces 3, 13 of the workpieces 1, 7, typically pneumatically. This pressure 17 is applied on the sonotrode 9 and/or the anvil 11, so that it presses the overlapping workpieces 1, 7 against each other during the joining process (see Part a) of FIG. 2).

(23) The sonotrode 9 starts to vibrate with ultrasonic frequency 19 with a typical amplitude between 5 m and 50 m in a forward-backward movement parallel to the contact surfaces 3, 13 of the workpieces 1, 7 to be joined as shown in Part b) of FIG. 2. However, the method is not restricted to a vibrational movement parallel to the contact surfaces 3, 13. The method is also applicable with ultrasonic oscillations directed perpendicularly to the contact surfaces 3, 13 or with torsional movement of the sonotrode 9.

(24) Set in motion by the ultrasonic vibration 19, the pin-like elements 5 interact with the contact surface 13 of the plastic workpiece 7 producing frictional heat. The pressure 17 and ultrasonic vibration 19 are maintained during a predetermined period of time, so that softening of the plastic workpiece 7 in the vicinity of the pin-like elements 5 is induced, in particular softening of the polymeric matrix of the fiber reinforced polymer workpiece 7, allowing further penetration of the pin-like elements 5 into the plastic workpiece 7 (see Part c) of FIG. 2).

(25) By adjusting the period of time the sonotrode 9 vibrates, the amplitude of the vibrations and the amount of pressure 17, the frictional heat can be controlled and damage of the plastic workpiece 7 due to high thermal energy transfer can be avoided. Generally, the ultrasonic-based joining process is characterized by a low heat development during the process.

(26) Finally the pressure 17 and ultrasonic vibrations 19 are removed and the sonotrode 9 is retracted from the now joined hybrid workpiece 1, 7 to release the latter (see Part d) of FIG. 2). The joining time can be shortened to typically less than five seconds. This significant reduction of time for direct assembly will also reduce the assembly costs compared to state-of-the-art assembly processes.

(27) Finally, the pin-like elements 5 extend entirely in the plastic workpiece 7 so that the contact surfaces 3, 13 directly abut on each other, as it becomes more evident in FIG. 3. Thus, a bulk connection rather than just a laminar connection is formed and the mechanical stability in particular with respect to loads perpendicular to the contact surfaces 3, 13 is improved.

(28) This effect is even more increased, if the pin-like elements 5 are designed not just with a mere cylindrical shape, but comprise anchoring elements 21 at their distal ends. FIG. 4 shows a sectional view through joined surface-structured-plastic workpieces 1, 7 with different types of anchoring elements 21 such as conical or spherical or convex or arrow-like shape. In such case the strength of the connection is even more improved due to the fact that the polymeric matrix of the plastic workpiece 7 completely encloses the anchoring elements 21 after being softened during the ultrasonic welding process, thereby producing a form fit when the plastic workpiece 7 solidifies.

(29) As it is shown in FIG. 5, the described joining method can also be applied to a stack of plastic workpieces 7, 7. If the size of the pin-like elements 5 is adapted to the thickness of a first plastic workpiece 7 (or a first stack of plastic workpieces) in such a way that they are larger than the thickness of the first plastic workpiece 7 (or stack of plastic workpieces) in the welding region, the pin-like elements 5 can entirely penetrate the first plastic workpieces 7 (or a stack of plastic workpieces) and finally protrude into a lowermost plastic workpiece 7 creating the above-described form fit connection.

(30) The afore-mentioned method according to the present can be used to connect one or more plastic workpieces 7, 7 by means of a surface-structured workpiece 1.

(31) A first example is depicted in FIG. 6 comprising a first plastic workpiece 7 having a T-shaped cross section and a second plastic workpiece 7.

(32) In a second example shown in FIG. 7 a surface-structured workpiece 1 is employed as a reinforcement element for a fiber reinforced plastic workpiece 7 and the workpieces 1, 7 are connected by means of the above-described embodiment of the method of the present invention.

(33) In FIGS. 8 to 11 examples are shown, in which primary structures formed of plastic workpieces 7, 7 are coupled by surface-structured workpieces 1.

(34) In conclusion, those of skill in the art will appreciate that a method according to the teachings of the present disclosure can produce a connection between a surface-structured workpiece and one or more plastic workpieces having a high stability also in the direction perpendicular to the contact surface in a simple and quick manner.

(35) 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.