Bates Vibration Welding of Continuous Reinforced Composites
This article throws light upon the five main processes used for fabricating composites into desired components. The processes are: 1. Induction Welding 2. Ultrasonic Welding 3. Gas Tungsten Arc Welding (GTAW) 4. Resistance Welding 5. Fusion Bonding.
Process # 1. Induction Welding:
In this process a modified wound toroidal inductor core as shown in Fig. 22.24, is used to transfer magnetic flux through the thermoplastic to a carbon-steel screen placed between the two pieces to be joined. The air gap in the toroid directs the magnetic flux from the toroid to the screen.
The air gap of the toroid is placed on one of the plastic surfaces on either side of the screen to melt and flow into the screen and form the joint. The toroid is moved along the seam at the controlled speed to produce a weld. The power required is 25 – 100 W which can be obtained by the use of a battery or solar power. This process can be used in aerospace, automobile, furniture, and construction industries.
Process # 2. Ultrasonic Welding:
Ultrasonic welding heads employing 20 KHz power signal has been used to weld light weight composite thermoplastics (Gr-Ps) beams in space shuttle. The vibration of the sonotrode quickly heats thermoplastic resin to the viscous fluidic state and the parts are clamped together to weld—a typical weld cycle requires one second for excitation and half a second for cooling. The process appears to have good potentials for future use in the welding of composites.
Process # 3. GTAW:
This process has been used for welding composite materials like Ti-W and Ti-Gr, in square butt configuration both in manual and mechanised modes. In Ti-Gr fibre system carbide formed around each graphite filament as a result of fusion leads to enhancement of tensile strength at the joint.
Results have shown that B-A1 composites can be welded without severely damaging the boron filaments. Filler metal can also be added to intermix with the aluminium matrix to alter its chemical composition significantly. For successful future application of GTAW to B-A1 composites it is essential to find means of controlling reaction products during welding. Manual plasma arc and EBW are not very successful for joining B-A1 composites because of excessive metallurgical reactions between A1 and boron which lead to low joint strength.
Attempts have also been made to weld Al-Gr composites by GTAW but resulted in the formation of Al-carbide on the surface of the fibres.
Process # 4. Resistance Welding:
Resistance spot welding schedules have been developed for welding B- A1 composites with current settings lower than those used for A1 but at approximately double the electrode pressure to prevent expulsion of matrix material. However, for seam welding pressure used is lower to avoid the filament breakage.
Gr-Ps composite can also be spot welded successfully. For a Gr-Ps composite at 36 wt% polysulfone the joint strength attained is around 8.3 MPa.
Gr-A1 composites have been successfully spot welded to each other and to other Al-alloys using 0 08 mm foil of 88 % A1 + 12 % Si as filler material.
Process # 5. Fusion Bonding:
Some fusion bonding techniques have been successfully used for joining fibre-reinforced thermoplastic structures. One such technique employed placing resistance wires at the bond interface to which the desired potential was applied. The heated wire softened the fibre-reinforced polysulfone that fused and formed the joint. In another approach 80 mesh stainless steel screen was used as a resistance heater to affect a bond under a pressure of about 70 MPa.
Diffusion bonding has also been successfully used for joining B-Al to other Al-alloys. Also aircraft turbine-engine fan blades of Ti-6A1-4V have been locally stiffened by diffusion bonding with an inlay of Ti-6A1-4V-50B composite. Future applications of diffusion bonding include composite strictures (filled, laminar, cellular, and metal and/or ceramics) and hybrid structures.
Welding of ceramics is becoming a fascinating field as it has vast potentials for future use. Apart from isostatic compaction method to form ceramics, friction welding has also been successfully used to join metals and ceramics.
Source: https://www.yourarticlelibrary.com/welding/welding-of-composites-5-processes/97837
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