Pulse Spot Welding for High Thickness-Ratio Laminates
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Solution Overview
Problem
In spot welding of laminates with varying metal plate thicknesses, the existing methods face challenges in preventing expulsion while ensuring nugget growth, particularly when the plate thickness ratio is high, leading to incomplete welding or excessive nugget growth.
Innovation Solution
A spot welding method using pulse current with a specific pulsed waveform, characterized by a peak current value of 10.6 kA or more, a no-peak duration of 4 ms to 13.6 ms, and a peak duration of 0.9 ms or less, which allows for controlled nugget growth and inhibition of expulsion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If increased current values are used for welding laminates with high plate thickness ratio, then welding can be successfully performed, but expulsion easily occurs
Solution Approach 1:
The patent applies periodic pulsed current instead of continuous current. The pulse waveform includes peak current periods for nugget growth and no-peak periods for cooling, creating a rhythmic heating and cooling cycle that prevents excessive nugget growth and expulsion while ensuring successful welding of laminates with high plate thickness ratios.
Solution Approach 2:
The patent dynamically adjusts current parameters by using variable peak current values (10.6 kA or more) and controlling the ratio between peak duration and no-peak duration (1/5 or less). This dynamic control allows the system to adapt to different plate thickness ratios and prevent expulsion while maintaining welding success.
2Object-generated harmful factors
If decreased current values are used for welding laminates with high plate thickness ratio, then expulsion does not occur, but growth of nuggets does not proceed and welding cannot be successfully performed
Solution Approach 1:
The periodic pulsed current provides cumulative heating effect over multiple cycles. Each peak current pulse contributes to nugget growth, and the no-peak periods allow cooling that prevents expulsion. The repetition of this cycle enables nuggets to grow to sufficient size without exceeding expulsion thresholds, resolving the contradiction between nugget growth and expulsion inhibition.
Solution Approach 2:
The patent changes the temporal parameters of current application by setting specific peak current values (10.6 kA or more) and controlling the duration ratios (peak duration 0.9 ms or less, no-peak duration 4 ms to 13.6 ms, ratio 1/5 or less). These parameter changes enable the current to be sufficiently high for nugget growth while being sufficiently low during critical periods to prevent expulsion.
3Manufacturing precision
If continuous energization is used in spot welding, then nugget can grow sufficiently, but nugget may excessively grow and protrude from corona bond causing expulsion
Solution Approach 1:
The patent replaces continuous energization with periodic pulsed energization. The pulse waveform alternates between peak current (for nugget growth) and no-peak current (for cooling and preventing excessive growth). This periodic action ensures nuggets grow to required size within the corona bond while preventing protrusion and expulsion.
Solution Approach 2:
The no-peak periods in the pulse waveform serve as preliminary cooling action before the next peak current pulse. This preliminary cooling prevents the material from reaching expulsion conditions while still allowing nugget growth during subsequent peak pulses, effectively controlling nugget size within safe limits.
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
This method enables successful welding while preventing expulsion, providing a wide welding current range that accommodates errors, making it suitable for continuous welding of car bodies in mass production.
Implementation Method 1
a nugget is generated among the plurality of metal plates to weld the plurality of metal plates
Data Source
AI summary
Provided is a spot welding method by which welding can be successfully performed while inhibiting occurrence of expulsion. First to third metal plates W1 to W3 were welded in which ratio of total thickness to thickness of the first metal plate W1 is 7. In Example 1, peak current value A1 is 14.6 kA, effective current value A2 is 7.8 kA, peak duration T1 is 0 ms, and no-peak duration T2 is 5.9 ms. As a result, in Example 1, lower limit current value A3 is 6.9 kA, upper limit current value A4 is 8.42 kA, difference A5 between upper limit current value A4 and lower limit current value A3 is 1.52 kA, peak duration T1/no-peak duration T2 is 0, effective current value A2/peak current value A1 is 0.53, and rising time T3/falling time T4 is 0.79, furthermore, no expulsion occurs, and welding result was determined to be OK.