Resistance Spot Welding of Multi-Sheet Plated Steel Without Internal Cracks
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Solution Overview
Problem
Existing spot welding methods for sets of three or more steel sheets, including plated high-tensile steel sheets, struggle to prevent internal cracks of nuggets and corona bonds, particularly due to the occurrence of LME cracks.
Innovation Solution
A method involving a main energization step with a first current value and compressive force, followed by a subsequent energization step with a gradually decreasing current value and an increased second compressive force, and an electrode holding step maintaining the second compressive force, all while adhering to specific formulae controlling compressive forces, current values, and timing parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spot welding is performed on plated high-tensile steel sheets with conventional methods, then welding can be completed, but internal cracks of nugget and corona bond occur due to LME cracks
Solution Approach 1:
The invention changes the welding parameters by implementing a two-stage energization process with different current values and compressive forces. The first energization uses higher current and compressive force to form the nugget, while the second energization uses reduced current and maintained compressive force to prevent crack propagation, thereby resolving the technical contradiction between achieving weld formation and preventing internal cracks
Solution Approach 2:
The invention applies periodic action through the two distinct energization stages. The welding process is divided into separate phases with different parameter settings: initial high-intensity energization for nugget formation followed by reduced-intensity energization for crack prevention, allowing the system to address both weld formation and crack suppression in sequence
2Reliability
If after-weld holding time is extended to suppress cracks, then welding quality improves, but production efficiency decreases
Solution Approach 1:
The invention changes the temporal parameters of the welding process by implementing a optimized two-stage energization with specific duration ratios. The first energization stage is brief for nugget formation, while the second stage provides just enough holding time for crack prevention, thereby achieving improved welding quality without excessive extension of total process time that would harm production efficiency
3Reliability
If compressive force is increased to prevent nugget contraction, then internal cracks are suppressed, but energy consumption increases
Solution Approach 1:
The invention applies periodic action by dividing the compressive force application into two distinct stages: initial high compressive force during first energization for nugget formation, followed by maintained but optimized compressive force during second energization for crack prevention. This periodic application of varying compressive force levels achieves crack suppression while optimizing energy consumption compared to sustained high compressive force
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 effectively suppresses the contraction of nuggets and reduces tensile stress at welded portions, thereby preventing internal cracks of nuggets and corona bonds in spot welding of three or more plated high-tensile steel sheets.
Implementation Method 1
performing energization with a first current value I1 while compressing the steel sheets with a first compressive force P1 to form a nugget
Implementation Method 2
compressing the steel sheets with a second compressive force P2 greater than the first compressive force P1
Data Source
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AI summary
Provided is a method for producing a resistance-welded member that makes it possible to suppress an internal crack of a nugget and an internal crack of a corona bond during spot welding of a set of three or more sheets including a plated steel sheet. The method comprises: a main energization step for performing energization with a first current value (I1) while compressing the steel sheets with a first compressive force (P1) to form a nugget; a subsequent energization step for performing, after the main energization step, energization such that the current value gradually decreases from the first current value (I1) while compressing with a second compressive force (P2) greater than the first compressive force (PI); and an electrode holding step for holding the electrodes while maintaining the second compressive force (P2) after the subsequent energization. The second compressive force (P2) and a total sheet thickness (t), compression rise delay time (Tdl), and a downslope time (Tds) and an electrode holding time (Tht) satisfy respective predetermined conditions.