Indirect Spot Welding Pressing Force Control
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Solution Overview
Problem
Indirect spot welding methods face challenges in applying a large pressing force and maintaining stability when welding overlapping metal sheets from one side, leading to instability in the current path and difficulty in forming a strong fused joint, especially in closed cross-sectional structures.
Innovation Solution
A drive unit using a servomotor as a drive source, secured to a rigid bracket without elastic bodies, allows for precise control of pressing force within a range of 70 N to 200 N, with an overshoot control of 10% or less, and variable contact speed to prevent excessive force application, ensuring stable and strong spot welds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If indirect spot welding is used to weld overlapping metal sheets from one side in closed cross-sectional structures, then accessibility to welding locations is improved, but pressing force application capability deteriorates
Solution Approach 1:
A rigid bracket is introduced as an intermediary component to transmit pressing force from the drive unit to the spot welding electrode. This mediator enables effective force application even when welding from one side in closed cross-sectional structures where direct two-sided sandwiching is impossible.
2Ease of operation
If conventional indirect spot welding is used with elastic bodies, then ease of operation is improved, but pressing force control precision deteriorates
Solution Approach 1:
Elastic bodies are completely removed from the pressing force transmission path. The rigid bracket replaces the elastic body, eliminating the compliance that caused pressing force control imprecision while maintaining ease of operation through the drive unit mechanism.
Solution Approach 2:
The elastic mechanical body is replaced with a rigid mechanical bracket controlled by a servomotor-driven drive unit. This substitution enables precise electronic control of pressing force while eliminating the inherent imprecision of elastic deformation.
3Strength
If pressing force is increased to ensure stable welding, then weld strength is improved, but electrode sinking into metal sheet worsens
Solution Approach 1:
The drive unit dynamically adjusts the pressing force applied by the electrode based on real-time feedback and pre-set parameters. This dynamic control allows the system to apply sufficient force for strong welding while preventing excessive force that would cause electrode sinking, thereby maintaining electrode position stability.
Solution Approach 2:
The control unit monitors welding parameters and adjusts pressing force in real-time based on feedback from the welding process. This feedback mechanism ensures optimal pressing force is maintained throughout the welding cycle, preventing both insufficient welding and excessive electrode sinking.
4Strength
If two-stage or three-stage control is used to improve weld quality, then weld strength is improved, but device complexity increases
Solution Approach 1:
The drive unit serves multiple functions: it controls pressing force magnitude, regulates pressing force over time (implementing two-stage or three-stage control), and maintains electrode position stability. This multi-functionality achieves improved weld strength without proportionally increasing device complexity.
Solution Approach 2:
The control unit changes pressing force parameters (magnitude and duration) in predetermined stages based on pre-stored programs. This parameter variation approach enables sophisticated welding control while keeping the hardware structure relatively simple, as the complexity is managed through software control logic.
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 approach enables accurate and stable control of pressing force, reducing overshoot and maintaining high work efficiency, resulting in spot welded joints with satisfactory strength even when welding from one side in unsupported states.
Implementation Method 1
a drive unit (30) using a servomotor (31) as a drive source
Implementation Method 2
passing a current between the spot welding electrode (34) and the feeding point (24)
Implementation Method 3
allows for precise control of pressing force within a range of 70 N to 200 N
Data Source
Figure 1(a)~1(c)
Figure 2~3
Figure 4
AI summary
Even in indirect spot welding where a spot welding electrode applies pressure to overlapping metal sheets from only one side to weld a portion whose opposite side is in an unsupported and hollow state, an indirect spot welding apparatus can accurately control a pressing force of the spot welding electrode and stably obtain a welded portion having a satisfactory strength. In the indirect spot welding apparatus, a lower limit in a stable pressing force region where the pressing force of the spot welding electrode against the metal sheets can be controlled within a tolerance of ±10% ranges from 70 N to 200 N and an upper limit in the stable pressing force region ranges from 800 N to 2000 N, and an overshoot OS(%) = (PL-AL)/AL x 100 of the pressing force occurring when the spot welding electrode is pressed against the metal sheets is controlled to be 10% or less. In the equation described above, PL represents a peak pressing force (N) in an overshoot range, and AL represents an average pressing force (N) applied by the electrode.