Friction Stir Joining Metal to Plastic Workpieces
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Solution Overview
Problem
Existing methods for joining metal and plastic workpieces, such as riveting, screws, and traditional welding or adhesives, are inefficient, weight-increasing, and can lead to stress concentration, material alteration, and unsightly appearance, especially in applications like aviation where weight minimization is crucial and thermoplastic materials cannot be welded.
Innovation Solution
A method using a joining tool with a pin and sleeve that generates frictional heat to plasticize the metal workpiece, forming a nub that interlocks with the plastic workpiece without damaging it, creating a combination of a positive and adhesive joint without additional elements or surface treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical connections (rivets or screws) are used to join metal and plastic workpieces, then the connection reliability is improved, but the device weight increases and stress concentration occurs
Solution Approach 1:
The invention extracts and eliminates the additional mechanical connection elements (rivets, screws) from the joining system. Instead of using separate fastening components, the method creates a direct fusion between metal and plastic workpieces through controlled plasticization and adhesion, removing the weight penalty of additional elements while maintaining connection reliability
Solution Approach 2:
The invention replaces the mechanical connection system (rivets/screws) with a thermomechanical process. By applying controlled heat and pressure through the joining tool, the plastic workpiece is plasticized to form an adhesive bond with the metal workpiece, substituting mechanical fastening with a fusion-based connection that eliminates stress concentration points
2Strength
If traditional welding techniques are used for metal components, then the connection strength is improved, but the method cannot be applied to metal-plastic connections and requires high energy input
Solution Approach 1:
The invention applies local quality by concentrating the thermal energy and pressure only at the specific joining interface between metal and plastic workpieces. The joining tool delivers controlled heat and pressure locally to plasticize the plastic material at the contact surface, while the rest of the workpieces remain unaffected. This localized approach enables metal-plastic connection without the high energy input required by traditional welding methods
Solution Approach 2:
The invention changes the physical parameters (temperature and pressure) locally at the joining interface. By controlling the thermal and mechanical parameters through the joining tool, the plastic workpiece transitions to a plasticized state that enables adhesion to metal, then cools and solidifies to form a strong bond. This parameter control allows versatile application to both metal and plastic materials without requiring them to withstand extreme welding conditions
3Reliability
If adhesives are used to connect metal and plastic workpieces, then the connection stability is improved, but toxic gases are produced or additional heat measures are required
Solution Approach 1:
The invention enables the plastic workpiece to serve its own joining function by plasticizing it through controlled heating. The plastic material itself becomes the adhesive medium that bonds to the metal workpiece, eliminating the need for separate chemical adhesives that produce toxic gases. The process uses the plastic material's own properties to create the connection, reducing harmful emissions and additional safety requirements
4Strength
If friction stir welding is used to join metal and plastic workpieces, then the joint strength is improved, but the method requires additional steps such as applying adhesive or drilling holes
Solution Approach 1:
The invention merges multiple functions into a single joining tool that simultaneously provides friction-based heating, pressing, and joining operations. The tool combines the functions of heat generation (through friction), pressure application (to plasticize and bond), and alignment (to ensure proper joint formation) in one integrated device, eliminating the need for separate steps like adhesive application or hole drilling that would reduce productivity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides a strong, reliable, and aesthetically pleasing lap joint that maintains the integrity of both materials, reducing weight and avoiding the drawbacks of traditional methods like adhesives and mechanical fasteners, while ensuring the plastic workpiece's structure remains unchanged.
Implementation Method 1
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
Implementation Method 2
generates frictional heat to plasticize the metal workpiece, forming a nub that interlocks with the plastic workpiece
Implementation Method 3
creating a combination of a positive and adhesive joint without additional elements or surface treatments
Data Source
Figure 1a~1d
Figure 2a~2d
Figure 3
AI summary
The present invention relates to a method for connecting a metal workpiece and a plastic workpiece by means of a joining tool (5), the method comprising the following steps: Positioning the metal workpiece (1) and the plastic workpiece (3); Bringing the front end of the pin (7), the sleeve (9) and the clamping ring (11) in contact with an outer 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; Moving the pin and the sleeve in the axial direction while both 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 and wherein after stopping the axial movement said one of the sleeve and the pin is retracted from the metal workpiece and said other is moved towards the outer surface of the metal surface until the front ends of the pin and the sleeve are on the same level.