Core Process Parameter Optimisation: The ideal set of parameters is found using a single-factor + orthogonal experimental design. Using gold wire ball welding as an example, an average weld ball tensile force of 12.836gf with uniform tensile force distribution, consistent failure modes, and significantly improved bonding strength and reliability can be achieved with an ultrasonic pressure of 20gf, an ultrasonic power step value of 300, a hotplate temperature of 150°C, and an ultrasonic time of 40ms.
In order to prevent excessive energy from causing overheating and brittle breaking or inadequate energy from causing incomplete welds and internal porosity, welding energy is matched with matching power for thermocouple wires of varying diameters.
Optimisation of Welding Method Selection: DC TIG welding is recommended because it entirely avoids weld oxidation and carburisation issues by completing the molten ball under full argon gas protection. It is appropriate for long-term high-temperature cycling circumstances in hot runners because the weld ball is smooth, residue-free, and has welding strength significantly higher than that of standard electric arc and gas welding.
While AC arc welding can be utilised for base metal thermocouples, DC arc welding is recommended for precious metal thermocouples. Brittle fracture and weld contamination might result from using the incorrect welding technique.
Pre-treatment and Post-treatment Control: To avoid contaminants entering the weld ball and creating flaws that immediately lower weld strength, completely remove oxides and oil from the 25–30 mm region of the thermocouple measuring end prior to welding.
To avoid long-term corrosion of the thermocouple wires, which can subsequently result in signal drift and contact breaking, clear off any leftover flux and slag from the weld surface as soon as possible after gas or arc welding.
Process Stability Control: Ensure uniformity in every batch of weld balls by standardising operator procedures to minimise variations in weld quality brought on by human skill fluctuations and fatigue.
To avoid equipment parameter drift that results in unstable weld quality, calibrate the welding equipment's current and time control accuracy on a regular basis.
The durability of hot runner thermocouple weld balls under long-term high-temperature vibration circumstances can be increased by more than 40% thanks to these process optimisations, which greatly reduce flaws such incomplete welds, brittle fracture, and oxidation.
