Thermoplastic Bonding Tool With Thermal Expansion Sealing
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Solution Overview
Problem
Existing methods for welding thermoplastic polymer parts, particularly in complex and multi-layered structures, face challenges in achieving whole surface bonds without voids or deformation, especially in RF products requiring precise material properties and geometries, and are hindered by limitations in conventional techniques like ultrasonic welding, vibration welding, and multi-shot moulding.
Innovation Solution
A method involving a tool design with angled piston and bore faces, a self-releasing fit, and controlled thermal expansion to ensure a chemical bond across the entire interface, using a weld cavity that accommodates thermal expansion and allows easy assembly/disassembly, reducing tool wear and manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ultrasonic welding or vibrational welding is used to assemble injection moulded parts, then bonding strength at the interface is improved, but whole surface bonding is difficult to achieve and geometric tolerances deteriorate due to uncontrolled polymer flow
Solution Approach 1:
The patent replaces conventional mechanical welding systems (ultrasonic/vibrational) with a thermal field-based bonding system. A heating element applies uniform thermal energy to the entire interface surface, melting the polymer layers simultaneously across the whole bonding area. This thermal approach eliminates the need for mechanical intensifiers and results in uniform polymer flow and bonding without the geometric distortion caused by localized mechanical energy input.
Solution Approach 2:
The patent employs a controlled heating and cooling cycle to achieve bonding. The heating element activates to melt the polymer interfaces, holds the temperature for a controlled duration to ensure complete bonding, then deactivates to allow uniform cooling and solidification. This periodic thermal action ensures consistent bonding quality across the entire interface while maintaining geometric precision.
2Strength
If energy intensifier features are designed into part moulding for ultrasonic or vibrational welding, then bonding capability is improved, but part complexity increases and re-design flexibility is reduced
Solution Approach 1:
The patent eliminates the need for energy intensifier features by replacing mechanical welding with thermal field bonding. The heating element directly applies thermal energy to the interface surfaces without requiring any special geometric features or modifications to the parts. This simplifies part design and maintains full flexibility for complex shaped geometries and functional products.
Solution Approach 2:
The thermal bonding system serves as a universal bonding method that can bond any thermoplastic polymer parts regardless of their geometry, shape, or material properties. Unlike ultrasonic or vibrational welding which require specific intensifier features tailored to each part design, the thermal field approach works universally across different part configurations without requiring design modifications.
3Ease of manufacture
If conventional welding techniques are used on thin or complex shaped parts, then assembly is possible, but bonding quality deteriorates due to energy transmission issues or part damage
Solution Approach 1:
The patent replaces mechanical energy-based welding with thermal field bonding, which is particularly suited for thin and complex shaped parts. The heating element applies uniform thermal energy that penetrates and melts the polymer interfaces evenly, regardless of part thickness or geometry. This avoids the energy transmission problems of ultrasonic/vibrational welding where thin parts may be damaged or complex shapes may not receive uniform energy distribution.
Solution Approach 2:
The heating element can be designed to provide localized thermal energy distribution matched to the specific geometry of the parts being bonded. For thin or complex shaped parts, the heating surface can be contoured to match the part profiles, ensuring uniform thermal contact and consistent bonding quality across the entire interface while accommodating varying part thicknesses.
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
Achieves high-strength chemical bonds across the entire interface with minimal voids, maintaining precise geometries and material properties, suitable for complex and multi-layered structures, and is cost-effective for high-volume production.
Implementation Method 1
At the welding temperature, the piston thus expands to close the gap between the two tool parts (or halves) and provides an interference seal
Implementation Method 2
The at least two parts may be melted by the application of heat. The at least two parts may be heated to what is referred to herein as the welding temperature
Implementation Method 3
The shaped article is cooled following chemical bonding of the least two parts
Implementation Method 4
energy is directed to the bondline by frictional heating under a clamping force which melts a thin interfacial layer of the part or parts
Data Source
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AI summary
A method of forming a shaped article wherein said article comprises at least two parts which are chemically bonded, the method comprising: assembling at least two non chemically bonded parts in a weld cavity of a tool to form an assembly of the at least two parts, wherein said weld cavity is adapted to receive the assembly of at least two parts in the form of the shaped article; sealing the weld cavity of the tool; melting the assembly of at least two parts to chemically bond the at least two parts together to form the shaped article, wherein the shape of the weld cavity is matched to the outer circumference of the assembly of parts such that thermal expansion forces the polymer parts against the weld cavity surface and the pressure leads to full surface bonds between all parts, and wherein the tool forming the weld cavity comprises two halves forming a piston which fits into the bore of a bolster component and the plane of the split line between the two piston halves is parallel to the axis of the bore such that the pressure from the thermal expansion of the assembly of parts within the weld cavity is opposed by the surface of the bore preventing the weld cavity split line from opening and therefore preventing leakage of polymer from within the pressurised weld cavity volume, and wherein the two piston components are made from a dissimilar metal with higher coefficient of thermal expansion than the bolster component ensuring that at the welding temperature the piston is larger in diameter than the bore diameter of the bolster component leading to an interference fit which makes forces the weld cavity split line to close at the weld temperature but which still allows for a clearance gap between piston and bore at room temperature for the tool to be assembled and disassembled.