Confluence of Multidisciplinary Sciences for Polymer Joining

Polymers are chemical compounds containing large molecules joined together to repeat the same type of chains. Polymers are generally termed as plastics in industries. Polymer structure is illustrated basically through a chain.

The physics underlying the polymer joining is autohesion. The formation of stable bonds between two surfaces of specimens in contact is known as autohesion process. Restriction to the peeling of the welded parts at the primary contact surface is offered by the bonds formed. Autohesion method is initially reported in the year of 1935–7 (Dodin MG: The Journal of Adhesion 12 (2):99–111, 1981)[1].

Ultrasonic welding of polymers is an economically viable joining technique which eludes the addition of solvents or adhesives but causes localized heating at the interface by using relatively short cycle times [1]. Ultrasound welding is a high-frequency continuous joining technique. It is appropriate for joining small and larger regions in a sequential manner [2]. It is the technique that offers a good alternative to automotive, medical, packaging, appliance, textile, electronics, and others. The merits of ultrasonically assembled parts reveal clean and reliable bonds to the components. Ultrasonic welding is a swift process wherein a frequency in the range of 18–70 kHz is being used. Output value differs from hundreds of watts to a few kilowatts. Ultrasonic welding machine comprises a booster, transducer, horn, and electrical power supply (generator). The transducer (process controller) receives the electrical signal supply from the generator. Transducer converts electrical signal into mechanical longitudinal vibrations which are transmitted to horn to bond the interface of the material.

Mechanical deformation of the plastics depends on the temperature, time and viscoelastic nature. The duration of the applied stress and the overall stress history are the stages dictating time dependency. Temperature dependent plastics deformation is affected by the thermal properties of the plastics which typically vary for thermoplastics and thermosets. Temperature dependency basically controls the time for plastic deformation. Semicrystalline or glassy plastics exhibits weaker viscoelastic nature at temperatures below their glass transition temperatures (Tg). It is essential to analyze the semicrystalline plastics for time-dependency based analysis owing to their nature. Increased mechanical response during time analysis is recorded due to the increased temperature either by heat provided during deformation or by the external heat fluxes. Plastics reveal significant difference in the deformation mechanism as compared to metals.

Data acquisition (DAQ) is the key sequence in measurement of physical or an electrical phenomenon such as temperature, pressure, sound, voltage, or current using a computer. DAQ system (Fig. 5.1) comprises various sensors for appropriate applications, and the DAQ hardware is integrated with software to be viewed on computer. Compared to conventional measuring devices, computer-based DAQ devices employ the productivity, processing power, display, and connectivity abilities of industry standard computers offering more flexible, powerful, and inexpensive measurement solution.

Amorphous (PC + ABS) polymers are welded using ultrasonic welding process which is the aim of this investigation. Polymer granules are molded into rectangular plates with energy director embedded onto it before welding of polymer specimens. Taguchi method is employed to design the welding parameters in this investigation. Differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA) are performed to examine the thermal behavior of the welded specimens. Weld strength of the polymers is determined using the mechanical testing. Finite element and microscopical analysis are also reported in this study. In the end, RSM and ANOVA techniques are applied and presented.