Hard Material Body Polymer Coating Overmoulding
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Solution Overview
Problem
The existing injection methods for manufacturing ornamental parts from hard materials, such as those used in watchmaking, do not allow for precise dimensions, necessitating costly machining of hard materials, which is difficult and inefficient.
Innovation Solution
A method combining a hard material with a polymer coating, where the polymer coating is applied overmoulding the hard material body, allowing for precise dimensions and reducing the need for direct machining of the hard material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If injection method is used to manufacture hard material parts, then production efficiency is improved, but manufacturing precision deteriorates
Solution Approach 1:
The part is divided into two segments: a hard material body (injected for high productivity) and a polymer coating (injected for precision). The hard material provides mechanical strength and scratch resistance, while the polymer coating provides precise dimensions and functional surfaces. This segmentation allows each material to fulfill its optimal function without compromising the other.
Solution Approach 2:
The invention creates a composite structure combining hard material (ceramic, zirconium oxide, sapphire, or alumina) with polymer material (POM, PA, PUR, PPS, ABS, or PC). The hard material body is coated with polymer material through overmoulding, creating a composite part that exhibits both the hardness and scratch resistance of the hard material and the dimensional precision and machinability of the polymer.
2Manufacturing precision
If machining is applied to hard material to correct dimensions, then manufacturing precision is improved, but manufacturing cost increases
Solution Approach 1:
Instead of machining the expensive hard material, the invention uses a polymer coating that is easier and cheaper to machine. The polymer layer acts as a sacrificial material that can be removed or shaped at low cost, while the valuable hard material body remains intact. This eliminates the need for costly diamond tools and reduces manufacturing expenses.
Solution Approach 2:
The invention changes the material parameter of the surface layer from hard material to polymer material. This parameter change enables easier machining while maintaining the functional requirements. The polymer coating can be machined with standard tools at lower cost, yet still provides the necessary functional surfaces for water resistance and assembly features.
3Ease of manufacture
If polymer coating is deposited on hard material, then ease of manufacture is improved, but material strength may deteriorate
Solution Approach 1:
Different parts of the component have different material properties optimized for their specific functions. The hard material body provides structural strength, mechanical properties, and scratch resistance where needed. The polymer coating provides dimensional precision, ease of machining, and functional surfaces. This local differentiation of material quality ensures that strength is not compromised while gaining the benefits of polymer coating.
Solution Approach 2:
The polymer coating is applied in advance during the injection molding process, before any machining operations. This preliminary action ensures that the hard material body is already protected and dimensioned correctly, and that the polymer layer is in place to provide the functional surfaces and facilitate subsequent low-cost machining operations.
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 reduces manufacturing costs by minimizing the need for hard material machining, while ensuring water resistance and allowing for precise functional surfaces, such as stair-stepped shapes for assembly.
Implementation Method 1
a step of depositing a polymer material coating on one face of the part, the deposition being carried out by moulding on the body, in particular by injection into a mould
Implementation Method 2
a step of sintering said green body in order to form a body of the future part from said hard material
Data Source
AI summary
An ornamental part, for example for a timepiece, jewellery or telephone, in particular a watch case middle, and its manufacturing method, the part at least partly including a hard material having a Vickers hardness greater than 1000 HV, the method including the following main steps: a step of producing a precursor from a mixture of at least one powder material with a binder, a step of injecting the precursor into a mould in order to form a green body, a step of sintering the green body in order to form a body of the future part from the hard material, and a step of depositing a polymer material coating on one face of the part, the deposition being carried out by moulding on the body, in particular by injection into a mould, the coating and the hard material being inseparable.