TPT May 2022


Thermatool Corp

A path to a better high frequency weld par t 2 – toward a method for high frequency weld heat input control By Olexandra Tupalo – manager, Thermatool Labs and Mick Nallen – president, Thermatool Corp

process control was limited to power (kW) control and fixed HF weld frequency. In the second stage (circa 2005) of solid state power electronics development in HF welding, variable control of HF weld frequency became a reality. In the third stage (circa 2012) fully independent control of power (kW) and frequency (kHz) became possible as advanced solid state power electronics were developed. Current HF welder technology includes full load matching capability and precise regulation of both kW and kHz. With Thermatool’s HAZControl™ Technology Welder the abil ity to adjust and stabilise frequency allows the process control required to HF weld different alloy chemistries in various diameter to wall thickness ratios with precise and repeatable results. The frequency can be selected and changed at the operator’s console without shutting down the line. The software allows you to change frequency and HF weld power in ±1-kHz and 1-kW increments, allowing precise heat input control during welding. While power is the method of inducing amperes (the heat) into a workpiece, frequency (the heated width) is a means to control the distribution of the heat. The innovative software (Figure 2) uses a process window format to help an operator optimise power and frequency settings. When the operator enters the setup parameters such as mill speed, vee length, vee angle, tube geometry, and material information into the software, the predictive algorithm determines the initial variable frequency required to weld the tube. An important feature of the software is that it also has a “recipe” database feature which allows process data storage and retrieval for a library of products.

High frequency (HF) welding is a thermomechanical solid state joining process that relies on precise weld heat input for welding advanced and emerging ferrous and non ferrous materials. A review of weld heat input calculated for common welding processes is provided for context, as well as a model for mechanical forming and control of the strip edges being continuously welded. The method to design an algorithm for the simultaneous process control of heating and forging to create a consistently high-quality continuous HF Weld is developed. In the previous article [1] , we discussed the fundamentals of high frequency welding and learned the key process parameters. We learned how to achieve a better weld by optimising the HF weld process variables and how a proper mill setup can affect weld quality. In this second installment, we will focus on HF weld heat input.

Figure 1: HF welding

Figure 2.Thermatool HCT software screen

In HF welding, heat input can be defined as temperature distribution rate per unit time at the strip edges prior to continuous solid-state forge welding. Several process variables such as welder power, frequency, raw material chemistry, and weld area geometric setup parameters can influence HF weld heat input requirements. This work focuses on both process variables and data to optimise precise HF weld heat input. As the industry moves forward and finds better metal alloys to fulfil application needs and to expand the range of product sizes it becomes increasingly important to use the most advanced equipment for the job. During the first stage (circa 1995) of solid-state electronics used in HF welding technology


MAY 2022

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