Threaded Insert Sealing in Injection Moulded Components
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Solution Overview
Problem
Existing injection molding processes face challenges in preventing polymeric material from penetrating threaded inserts during overmolding, which can compromise corrosion protection and require stringent dimensional tolerances, leading to high development costs and potential damage to the thread inserts.
Innovation Solution
A threaded insert with a through hole is sealed using a plug, which can be made of plastic or metal, that is either screwed into the internal thread or has an interference fit, allowing for reversible closure to prevent polymeric material ingress during overmolding, and can be used without modifying existing injection molding tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a threaded insert with a through-hole is used to improve corrosion protection, then corrosion resistance is improved, but polymeric material can penetrate into the threads during overmolding, impairing the function of the threaded insert
Solution Approach 1:
A mandrel is introduced as an intermediary element that temporarily occupies the through-hole of the threaded insert during the injection molding process. The mandrel acts as a barrier preventing polymeric material from penetrating into the threads, while allowing the threaded insert to maintain its through-hole structure for corrosion protection. After molding, the mandrel is removed, leaving the thread functionality intact.
2Object-generated harmful factors
If a mandrel is pushed into the through-hole during overmolding to prevent polymer penetration, then polymer material penetration is prevented, but tight dimensional tolerances are required between the mandrel and threaded insert, increasing device complexity and development costs
Solution Approach 1:
The solution changes the dimensional parameters of the mandrel, specifically increasing its diameter beyond the inner diameter of the threaded insert's through-hole. This creates an intentional interference fit that generates frictional resistance, preventing polymeric material from penetrating into the threads during injection molding, while eliminating the need for tight dimensional tolerances between the mandrel and threaded insert.
3Object-generated harmful factors
If tight dimensional tolerances are enforced between mandrel and threaded insert to ensure sealing, then polymer penetration is prevented, but temperature fluctuations during injection molding cause expansion coefficient differences, compromising the seal
Solution Approach 1:
The mandrel diameter is intentionally increased to create an interference fit that relies on frictional resistance rather than precise dimensional matching. This parameter change makes the sealing effect robust against temperature fluctuations and expansion coefficient differences between the mandrel and threaded insert during the injection molding process.
4Reliability
If the threaded insert is made with a blind hole and coated with corrosion protection layer, then initial corrosion protection is provided, but the coating thickness decreases with increasing depth, leading to insufficient corrosion protection beyond certain depth
Solution Approach 1:
Instead of using a blind hole with decreasing coating thickness from the opening, the solution inverts the approach by using a through-hole structure. This allows the corrosion protection coating to be applied uniformly along the entire length of the threaded insert, including the previously unreachable deep regions, by enabling coating material access from both ends or complete surface coverage.
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 solution effectively prevents polymeric material from entering the threads, maintains corrosion protection, and allows for cost-effective production with larger manufacturing tolerances, ensuring the threaded insert remains functional and durable for applications like air spring pistons.
Implementation Method 1
a plug (5), in particular a rivet, with which the first opening (3) and/or the second opening (4) can be sealed
Implementation Method 2
The production of plastic components using injection molding has long been known
Implementation Method 3
Electroplating processes are typically used for this, with the thickness of the corrosion protection layer decreasing with increasing depth of the blind hole
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a component manufactured by an injection molding process, comprising a threaded insert (2) with a first opening (3) and a second opening (4), wherein the component comprises a polymeric material, the threaded insert (2) being substantially embedded in the polymeric material. The first opening (3) and/or the second opening (4) can be sealed by a plug (5).