Back-Injected Control Key With Web-Free Symbol Gap
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Solution Overview
Problem
Current methods for producing control keys with metallic surfaces in car interiors result in damaged decorative surfaces due to high injection pressures and temperatures, and existing solutions fail to achieve a genuine metallic appearance with precise, web-free connections.
Innovation Solution
A method using back-injection technology to create a plastic-metal composite with a genuine metallic surface, where the inner part is precisely connected to the outer part without separate fixing means, ensuring accurate spacing and preventing pressure marks, using a two-part injection mould with a common lower part for cutting and injection operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixing clips are used to hold metallic surfaces in the injection mould, then the metallic surface can be positioned and fixed, but pressure and scratch marks are caused on the decorative surface
Solution Approach 1:
The harmful fixing clips are completely removed from the system. Instead of using separate fixing means, the metallic inner part is directly integrated into the injection mould cavity, eliminating the need for clips that cause surface damage while maintaining positioning accuracy through the mould structure itself
Solution Approach 2:
The fixing function and the mould cavity are merged into a single integrated structure. The metallic inner part is positioned and fixed directly within the injection mould cavity, combining the support function with the forming function, thereby eliminating separate fixing elements that would damage the surface
2Manufacturing precision
If separate fixing means are used to secure the inner part, then positioning can be achieved, but the production process becomes costly and complex
Solution Approach 1:
The positioning and fixing functions are merged into the injection mould cavity structure itself. The metallic inner part is directly integrated into the cavity, eliminating the need for separate fixing mechanisms, retaining means, or dedicated positioning elements, thereby simplifying the device while maintaining high positioning accuracy
Solution Approach 2:
The injection mould cavity serves multiple functions simultaneously: it forms the outer part, positions the metallic inner part, fixes the inner part during injection, and defines the gap geometry. This multi-functionality eliminates the need for specialized fixing devices and reduces overall system complexity
3Productivity
If high injection pressures are used to fill the mould, then the plastic melt can be injected effectively, but the metallic surface is damaged by pressure marks
Solution Approach 1:
The metallic inner part is removed from the harmful zone of high injection pressure. By positioning it within the injection mould cavity rather than as a separate component subjected to pressure, the system maintains effective injection while protecting the metallic surface from pressure marks
Solution Approach 2:
The injection mould cavity is designed to distribute and cushion the injection pressure before it reaches the metallic inner part. The cavity structure acts as a pressure buffer, allowing effective injection while preventing direct high-pressure contact with the sensitive metallic surface
4Shape
If the inner part is cut out and separately fixed, then the symbol can be formed, but webs and connections remain that prevent clean separation
Solution Approach 1:
The harmful webs and connections are completely extracted from the final product. The metallic inner part is positioned and fixed in such a way that when the plastic is injected, it cleanly fills the gap without creating connecting webs, achieving complete separation between the inner part and outer part
Solution Approach 2:
The injection process uses controlled partial filling to ensure the plastic melt fills the gap space uniformly without overfilling that would create connecting webs. The filling level is precisely controlled to achieve clean separation while maintaining the desired gap geometry
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 control keys with defined gap geometry and back-lightable symbols, ensuring an unmarred surface and precise positioning, allowing for continuous industrial production without damage or displacement, and providing a tactile sensation with varying fill levels.
Implementation Method 1
the lower part of the injection mould with the inner part is moved below the upper part of the injection mould. After the mould has been filled with injection moulding melt
Data Source
AI summary
The invention describes a method for producing a decorative ornamental part, eg a control key, having a symbol in relief that is defined by a clearance gap free as far as possible of webs and connections in the frame of the control key, wherein the decorative ornamental part is back-injected with a plastic melt by the plastic injection moulding process. In order to obtain a surface on the visible side of the inner part which is free of traces of clamping and retaining it is proposed: that the production method consists of a cutting operation to produce the clearance gap, that the stamping punch carrying out the cutting operation remains as a place-holder in the cut contour of the clearance gap during the injection operation, and that the subsequent injection operation producing a bond ensures the exact connection of the contour of the cut free inner part to the frame of the ornamental part.