Thick Polymer Article Assembly to Avoid Sink Marks and Voids
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Solution Overview
Problem
Existing injection moulding techniques struggle to produce thick section polymer parts with precision due to thermal shrinkage, poor thermal conductivity, and difficulty in maintaining consistent section thickness, leading to deformities like sink marks and voids, especially in complex geometries required for RF products and multi-material assemblies.
Innovation Solution
A method involving a split line design that divides the article into parts with reduced maximum section thickness, using projections and recesses to join them, allowing for assembly into a shaped article with improved properties and minimal deformities, while maintaining the original design shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If injection moulding is used to produce thick section parts, then manufacturing cost is reduced and productivity is improved, but manufacturing precision deteriorates due to shrinkage and thermal conductivity limitations
Solution Approach 1:
The thick section part is divided into multiple separately moulded sections that are subsequently assembled. Each section is moulded with a thickness within the optimal injection moulding range (avoiding the >4mm problematic threshold), ensuring consistent thickness and quality. The segments are joined using welding or mechanical fastening to form the complete thick section component, thereby achieving both productivity benefits and precision requirements.
2Volume of moving object
If section thickness is increased beyond 4mm, then the part can meet functional requirements, but manufacturing precision deteriorates due to sink marks and voids
Solution Approach 1:
Instead of moulding the entire part as a single thick section, the design is segmented into multiple thinner sections that are moulded separately and then assembled. This avoids the sink mark and void problems associated with thick section injection moulding while achieving the required overall thickness through the stacked assembly of segments.
Solution Approach 2:
The solution transitions from a single-dimension approach (moulding one thick section) to a multi-dimensional approach (stacking multiple thin sections in the thickness direction). This dimensional change allows the part to achieve the required thickness while maintaining geometrical tolerance in each individual section.
3Volume of moving object
If multiple separately moulded parts are assembled, then thick section requirements are met, but device complexity increases due to additional assembly steps
Solution Approach 1:
Multiple separately moulded sections are merged into a single integrated component through welding or mechanical fastening. This combining process creates a unified thick section part that functions as a single component, reducing the complexity of downstream assembly operations and integration with other system components.
4Manufacturing precision
If injection moulding tool design is optimized for thick sections, then manufacturing precision improves, but device complexity and cost increase
Solution Approach 1:
Rather than designing a complex injection moulding tool capable of producing thick sections directly, the approach segments the part into multiple thin sections that can be moulded using standard, simpler tools. This avoids the need for specialized thick-section moulding equipment while maintaining high manufacturing precision.
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
Enables the production of thick section shaped articles with high geometrical tolerance, reduced cycle time, and lower manufacturing costs, while avoiding sink defects and maintaining design integrity, suitable for complex RF products and multi-material assemblies.
Implementation Method 1
Thermoplastic polymers tend to suffer significant shrinkage during cooling and solidification from the melt processing temperatures which allow the polymer to adopt the shape of the cavity during the injection moulding process
Implementation Method 2
Injection moulded parts are typically assembled to form a shaped article or product by polymer welding techniques such as ultrasonic welding or vibrational welding. In these techniques, 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
Method of making a shaped article (5) comprising at least two parts (10, 15) wherein the first part comprises at least one projection (20) and the second part comprises at least one recess (22) by preparing said first part and said second part in a moulding process and joining the prepared first and second part together by engaging the at least one projection with the at least one recess to form said shaped article.