Decorative Part Bond Seam Using Reaction Plastic Injection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The production of decorative parts for motor vehicles, such as steering wheels, faces challenges in achieving an optically and haptically perfect connection between support parts while maintaining cost-effectiveness, due to complex manufacturing processes, high material viscosity issues with thermoplastics, and the limitations of reaction plastics, including short pot life and adhesion problems.
Innovation Solution
A method where support parts are held at a distance to form a gap, allowing a low-viscosity reaction plastic to fill and cure, then closing to form a bond seam, using latching and centering mechanisms to ensure precise alignment and adhesion without external forces, and employing inserts to manage adhesion and curing outside the mold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermoplastic is used for in mold coating, then the transparent cover layer can be formed, but high injection pressures and temperatures are required which cause the rigid foam to yield and lose dimensional stability
Solution Approach 1:
The patent changes the material parameter from thermoplastic to reaction plastic, which fundamentally alters the injection process parameters. Reaction plastics have lower viscosity and can be injected at lower pressures and temperatures, eliminating the problem of foam yielding while maintaining the ability to form a transparent cover layer.
Solution Approach 2:
The patent uses a composite approach by combining reaction plastic with specific additives (parting agents, catalysts) to achieve the desired properties. The reaction plastic system allows for controlled polymerization after injection, forming the cover layer without requiring high injection pressures that would deform the foam core.
2Productivity
If reaction plastic with short pot life is used to reduce cycle time, then production efficiency improves, but cured particles can enter the mold cavity causing optical impurities and product quality deterioration
Solution Approach 1:
The patent optimizes the pot life parameter of the reaction plastic to be sufficiently long (at least 10 seconds, preferably 15-60 seconds) to allow complete injection and mold filling before curing begins. This parameter adjustment prevents cured particles from entering the mold cavity while still maintaining efficient production cycle times.
Solution Approach 2:
The patent ensures that the injection process is completed entirely before the polymerization reaction significantly progresses. By controlling the pot life to be longer than the injection duration, the system performs the injection action preliminarily while the material remains in a liquid, non-cured state, preventing optical impurities.
3Stress or pressure
If reaction plastic is injected into the mold, then lower injection pressures can be applied, but the plastic material tends to adhere to the mold surface making ejection difficult and preventing out-of-tool surface formation
Solution Approach 1:
The patent introduces a parting agent as an intermediary substance between the reaction plastic and the mold surface. This parting agent prevents direct adhesion of the curing plastic to the mold, enabling easy ejection of the finished part while maintaining the low injection pressure advantage of reaction plastics.
Solution Approach 2:
The parting agent acts as a disposable intermediary layer that facilitates the ejection process. It is applied to the mold surface temporarily for each injection cycle, enabling the reaction plastic to release easily after curing without damaging the mold or the part surface.
4Manufacturing precision
If support parts are connected with complex working steps to achieve neat connection, then optical and haptic quality improves, but production expenditure increases
Solution Approach 1:
The patent merges the connection of support parts with the in mold coating process into a single integrated operation. The reaction plastic is injected to simultaneously form the transparent cover layer and fill the gap between support parts, creating bond seams that connect the parts while providing the protective cover layer, eliminating the need for separate connection operations.
Solution Approach 2:
The reaction plastic serves a dual function as both the bonding agent and the protective cover layer material. This composite approach allows the same material to perform multiple functions: filling gaps, bonding support parts, and providing the transparent protective surface, thereby simplifying the overall manufacturing process.
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 method enables a nearly invisible, gap-free, and stable bond seam, improving the optical and haptic quality of decorative parts with reduced cycle times and lower reject rates, while allowing the use of reaction plastics with longer pot life, thus enhancing cost-effectiveness and productivity.
Implementation Method 1
at least two separate plastic components are mixed in a mixing head arranged directly at the outer side of the injection mold, whereby then a chemical reaction is started that leads to a polymer reaction (polyaddition, polymerization)
Data Source
AI summary
A method is provided for producing a decorative part that has a closed cross-section having an external visible side and that has at least two support parts to be connected along a connecting joint. The support parts are held spaced at a distance from one another such that a gap is formed between the edges of the support parts which adjoin one another at the connecting joint. The support parts are inserted in at least two halves of a molding tool. A reaction plastic is injected into the molding tool, such that the reaction plastic penetrates the gap. The support parts are moved toward each other such that the gap closes while the reaction plastic is still liquid. The support parts are fixed against each other in this position at least until the plastic has sufficiently cured so as to form a bond seam in the connecting joint.