Spot Welding Current Control for Overlapping PWM Waveforms
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Solution Overview
Problem
Existing spot welding methods face issues with inconsistent rising slopes of waveforms when pulse-shaped waveforms overlap, leading to variable heat input and degradation of welding quality.
Innovation Solution
A spot welding method using PWM control to maintain a constant rising slope by setting target rise current values, including a first target current value larger than the rise start current, and an intermediate target current value to stabilize the heat input quantity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pulse-shaped waveforms are used for spot welding, then spatter occurrence is reduced and welding current forms proper nugget size, but waveform overlap occurs when effective value increases to high level, causing inconsistent rising slopes and degradation of welding quality
Solution Approach 1:
The patent applies dynamics by making the PWM pulse width variable rather than fixed. The control device dynamically adjusts the pulse width based on the instantaneous welding current value to maintain a constant rising slope. This is achieved by calculating a target PWM pulse width that corresponds to a predetermined rising slope, thereby adapting the pulse waveform to the actual welding conditions and preventing waveform overlap while maintaining consistent heat input characteristics.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the welding current and using this information to adjust the PWM pulse width. The control device calculates the target PWM pulse width based on the measured welding current value and the desired rising slope, creating a closed-loop control system. This feedback mechanism ensures that even when waveforms overlap, the rising slope remains consistent, maintaining welding quality.
2Productivity
If welding current is controlled by fixed rise time, then current increases to peak state, but waveform overlap causes different rising slopes between first and second waves, leading to variable heat input
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the PWM pulse width parameter based on the welding current value. Instead of using a fixed rise time, the system calculates a target PWM pulse width that maintains a predetermined rising slope. This parameter adjustment ensures that the heat input remains consistent even when waveforms overlap, as the pulse width is optimized for each instantaneous current condition.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method ensures consistent waveform rising slopes even with overlapping waveforms, stabilizing heat input and reducing degradation in welding quality.
Implementation Method 1
electric power is applied between a pair of electrode tips in a state in which a plurality of metal plates are held between the pair of electrode tips to thereby generate a nugget between the plurality of metal plates, so that the plurality of metal plates are welded
Data Source
AI summary
Provided is a spot welding method capable of performing current control that makes a rising slope of waveform constant even in a case where pulse-shaped waveforms overlap with each other. The spot welding method includes, for a welding current L10: setting a target rise current value P for each predetermined PWM pulse when the welding current L10 increases toward a peak current range R1; and setting, as a first target current value A, a target rise current value P that is larger than and the closest to a rise start current value S in a case where an effective value L14 of the welding current reaches a set welding current L23 while the welding current is decreasing toward a bottom current PB.