###### Abstract  
Ultrasonic welding is a high-frequency method of welding that uses mechanical energy to generate heat. This is a clean welding method and very suitable for plastic welding. In this study, using the Taguchi experimental method, the control factors of an ultrasonic plastic welding machine were optimized to affect the durability of knots of trawl nets made from polyamide (PA) and polypropylene (PP) filaments as an alternative to the traditional mesh knitting method. After optimization, the PA knots had an amplitude of 32 \(\upmu\)m (34%), a welding pressure of 2.5 kg/cm\({}^{2}\) (41%), a hold time of 0.35 s (24%), and a speed of 5.5 mm/s (1%). The knots made of PP filament had relatively stable strength after optimization, with an amplitude of 36 \(\upmu\)m (25%), a welding pressure of 2.0 kg/cm\({}^{2}\) (22%), a hold time of 0.25 s (16%), and a speed of 6.0 mm/s (37%). Finally, validation experiments were conducted to verify the results obtained in this study.  
polyamide; polypropylene; tensile strength; experiment method; knots of trawl; ultrasonic plastic welding +
Footnote †: journal: Applied  
speed and changing the trajectory of the 3D object. Overall, these studies have digitized the interaction of water flow on the net cage structure, rendering the control of the capture and aquaculture process more efficient. However, due to many reasons, such as environment, water flow, or inappropriate selection of nets, the phenomenon of net tearing causing loss of fishery production still occurs [7].  
This study relates to the ultrasonic welding [8] method of bonding of two objects through the generation of heat from high-frequency oscillations; it is a clean method and is very suitable for application to products related to plastic. To have a good weld point, the Taguchi method (a statistical method developed by [PERSON] to improve the quality of manufactured goods) is often applied to optimize the factor variables. In recent years, many researchers have used this method. [PERSON] et al. [9] used the Taguchi method to study the effects of welding factors on the strength of ultrasonic welds and observed that amplitude was the most important parameter of the ultrasonic plastic welding machine, accounting for 62% of the weld quality. This method has been widely applied in engineering and biotechnology. [PERSON] et al. [10] performed methyl-methacrylate polymerization to improve the reciprocation of nanoparticles, and [PERSON] et al. [11] optimized the process factors of the steel turning process using the Taguchi method. [PERSON] et al. [12] optimized the cutting parameters for precision lathes via the Taguchi method. Their study showed that the cutting depth and spindle speed have the greatest impact, and directly affected the surface roughness of the product and the material removal rate. [PERSON] et al. [13] used the Taguchi method and optimized the control factors of the automatic net-wrapper robot arm. Their study determined the appropriate suction pressure for the ideal cake state for commercialization without destroying the relatively brittle structure like a net wrapper.  
In this study, an ultrasonic plastic welding machine (UPWM) [14] was used to create new knots of trawl and raschel nets to replace the traditional knitting method. For this, it was essential to optimize the control factors of the UPWM machine. Using the earlier published method [15], the tensile strength of knots made using the UPWM was tested at different levels and factors on the tensile tester machine (TTM). Then, the three most promising levels of factors are selected for optimization using the Taguchi method to find the parameter set providing the highest efficiency to the tensile strength of the knot. Finally, validation experiments were performed to verify the optimal set of parameters obtained in this study.  
This paper is structured as follows: the experimental procedure is presented after the introduction. Then, the results are discussed, followed by a conclusion.