Resistance Welding Heating Element With Cut-Out Sheet For Uniform Heat
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Solution Overview
Problem
Conventional wire mesh heating elements used in resistance welding of thermoplastic components often entrap air at wire intersections, leading to reduced weld quality due to the 'transversal edge effect' and 'longitudinal edge effect', where edge regions are cooler or hotter than the center, causing uneven heating and decreased shear strength.
Innovation Solution
A heating element with a conductive sheet featuring varying ratios of cut-outs along its transverse and longitudinal directions, optimizing electrical resistance to minimize heat generation at edges and center, ensuring uniform heat distribution and reducing air entrapment by eliminating crossing wires, and optionally using an electrical insulation layer to prevent current leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a wire mesh heating element is used for resistance welding, then heating function is achieved, but air is trapped at wire intersections reducing weld quality
Solution Approach 1:
The heating element is segmented into multiple independent heating zones along the welding path, with each zone having its own cut-out pattern. This segmentation allows independent optimization of heating in different regions while eliminating wire intersections that trap air.
Solution Approach 2:
The harmful wire intersections that trap air are completely removed from the heating element structure. The patent extracts only the essential heating function while eliminating the mesh structure that causes air entrapment, using a solid sheet with cut-outs instead.
2Temperature
If conventional wire mesh is used, then heating is achieved, but edge regions are cooler than center due to air cooling effect
Solution Approach 1:
Different regions of the heating element have different cut-out patterns optimized for their specific thermal requirements. Edge regions have fewer or smaller cut-outs to reduce air cooling effects, while center regions have cut-outs positioned to maintain uniform heating across the welding zone.
Solution Approach 2:
The electrical resistance parameters are varied across different regions of the heating element by changing the cut-out patterns. This allows compensation for the air cooling effect at edges, creating a more uniform temperature distribution across the welding zone.
3Temperature
If wire mesh with crossings is used, then heating function is provided, but the thickness at crossing points is doubled causing increased bending moments
Solution Approach 1:
The wire crossings that cause doubled thickness are completely removed from the structure. The patent uses a solid sheet with cut-outs instead of a mesh, eliminating the geometric complexity that leads to increased bending moments while maintaining the heating function.
4Ease of manufacture
If uniform cut-out pattern is used across the sheet, then manufacturing is simplified, but electrical resistance cannot be optimized for uniform heat distribution
Solution Approach 1:
The cut-out pattern is varied across different regions of the sheet to optimize electrical resistance locally. Different cut-out sizes, shapes, and densities are used in different zones to achieve uniform heat distribution while maintaining relatively simple manufacturing processes.
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 solution enhances weld quality by minimizing air entrapment, reducing overheating, and achieving uniform heat distribution across the welding zone, resulting in improved shear strength and reduced bending moments, while preventing current leakage into thermoplastic components.
Implementation Method 1
The heating element is to be connected to an electric circuit, so that the electrically conductive sheet heats due to the current flowing therethrough
Implementation Method 2
the ratio of cut-outs to electrically conductive sheet changes at least along a transverse direction of the sheet, so that an electrical resistance of the sheet has a maximum at a centre of the sheet
Data Source
Figure 1
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Figure 4
AI summary
Described is a heating element (100) for resistance welding of thermoplastic components (21, 22). The heating element (100) comprises an electrically conductive sheet (105) comprising a plurality of cut-outs (111-113), wherein a ratio of cut-outs (111-113) to electrically conductive sheet (105) changes at least along a transverse direction of the sheet (105), so that an electrical resistance of the sheet (105) has a maximum at a centre of the sheet (105). Further described is a welding kit comprising such heating element (100) and an electrical insulation layer (121, 122), a method of manufacturing such heating element, and a method of employing such heating element for welding two thermoplastic components to one another.