Employing Experimental and Analytical Methods to Understand the Ultrasonic Spot Welding Process for Thermoplastic Polymers to Guide Joint Design

The title of the proposed work is “Employing Experimental and Analytical Methods to Understand the Ultrasonic Spot Welding Process for Thermoplastic Polymers to Guide Joint Design.” The work outlined in the proposal explains how a better understanding of the underlying phenomena of ultrasonic spot welding (USSW) will help create better, more consistent welds of thermoplastic materials. Currently, welds are unpredictable and have a wide range of seemingly random temperature fluctuations, causing wide ranges of weld strengths. The proposed work will seek to understand the underlying cause of these temperature fluctuations and the variables that control them. By controlling these variables, the random temperature spikes in the welds will be prevented, leaving a stronger, higher quality joint with accurate and predictable properties. This work will also seek to understand the flow of the heated material at the weld location. Currently, the bond area of a weld varies greatly, and there is no way to predict how the material will flow while undergoing the process of USSW. A highly varied bond may lead to weak spots in the weld, where there is not enough material to create a strong joint. This work will seek to analyze the flow of the material as the result of a three-coupled problem: 1) Vibrational effects of material flow within the weld, 2) Geometry changes of the weld due to fluid mechanics, and 3) Temperature evolution throughout the USSW process. An analytical model of the expected flow and temperature changes within a weld with given parameters will be created. The created model will aid in the design and manufacturing process of welded thermoplastics. By predicting the flow of the welded material, defects in the weld due to bond area variation and degradation caused by high temperatures will be mitigated. Of particular interest is the potential of controlling the temperature of the welded material using given input variables (pressure, time, amplitude, and energy), to discover if thermoplastic materials can be welded after reaching their glass transition temperature, where they become soft and pliable, but before reaching their melting temperature. With the ability to better control the flow and temperature of material within the weld joint, high quality welds with predictable properties will be created without extra processes currently used before or during manufacturing. This advancement will reduce the cost of welding and manufacturing time, allowing for more rapid and cost-efficient production. The future of this work has great potential for USSW. The analytical model of weld flow and temperature evolution will aid in further understanding the controllable parameters that can be used to create welds with specific desired properties. In addition, the discovery of whether thermoplastics can be welded before reached their melting temperature has large implications for USSW. If discovered to be possible, this idea can be applied to novel materials previously thought to be incompatible with USSW such as thermosets, which cannot be melted but have higher strength and temperature resistance than thermoplastics – desirable properties in the aerospace field.

This advancement will reduce the cost of welding and manufacturing time, allowing for more rapid and cost-efficient production. The future of this work has great potential for USSW. The analytical model of weld flow and temperature evolution will aid in further understanding the controllable parameters that can be used to create welds with specific desired properties. In addition, the discovery of whether thermoplastics can be welded before reached their melting temperature has large implications for USSW. If discovered to be possible, this idea can be applied to novel materials previously thought to be incompatible with USSW such as thermosets, which cannot be melted but have higher strength and temperature resistance than thermoplastics – desirable properties in the aerospace field.

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