Coated Metal Mold Structure for Hot Stamping Adhesion Resistance
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Solution Overview
Problem
Conventional coated metal molds used in hot stamping processes for high tensile strength steel sheets, particularly those plated with aluminum or zinc, face issues with early mold life due to adhesion and insufficient wear, heat, and adhesion resistance, especially under heavy load conditions.
Innovation Solution
A coated metal mold with a hard coating configuration featuring a nitride layer (A layer) and a diamond-like carbon (DLC) layer (B layer), where the DLC layer is on the outer surface, and both layers are polished to specific roughness parameters, enhancing durability through improved adhesion and sliding characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional hard coating is applied to the metal mold surface, then wear resistance is improved, but adhesion resistance deteriorates under hot stamping conditions
Solution Approach 1:
The coating is divided into multiple functional layers: a base coat layer providing wear resistance and a top coat layer providing adhesion resistance. This segmentation allows each layer to optimize its specific function without compromising the other, resolving the contradiction between wear resistance and adhesion resistance in hot stamping applications
Solution Approach 2:
The invention uses a composite coating structure combining different material properties - the base coat layer (e.g., CrN, TiN) provides hardness and wear resistance, while the top coat layer (e.g., DLC, amorphous carbon) provides low friction and adhesion resistance. This composite approach enables simultaneous achievement of both wear resistance and adhesion resistance
2Strength
If the coating film is made thicker to improve durability, then wear resistance is improved, but the risk of coating peeling under heavy load increases
Solution Approach 1:
The thick coating is segmented into multiple thinner functional layers. The base coat layer can be relatively thick (e.g., 5-20 μm) to provide wear resistance, while the top coat layer is thin (e.g., 1-5 μm) to maintain flexibility and adhesion. This segmentation prevents peeling while maintaining durability
Solution Approach 2:
Different parts of the coating have different thicknesses and properties optimized for their specific functions. The base coat layer has greater thickness for wear protection, while the top coat layer has controlled thickness for maintaining adhesion and flexibility under heavy load conditions
3Temperature
If a nitride coating layer is applied to provide heat resistance, then heat resistance is improved, but surface roughness increases reducing sliding characteristics
Solution Approach 1:
The coating is segmented into a heat-resistant base layer and a smooth top layer. The nitride base coat layer (e.g., CrN, TiN) provides heat resistance and structural stability, while the DLC or amorphous carbon top coat layer provides excellent sliding characteristics with Ra ≤ 0.2 μm, resolving the contradiction between heat resistance and sliding performance
Solution Approach 2:
The composite coating structure combines the high-temperature stability of nitride materials with the low-friction properties of DLC or amorphous carbon. This allows the mold coating to maintain both heat resistance for hot stamping and excellent sliding characteristics for reduced adhesion
4Manufacturing precision
If physical vapor deposition is used to coat at low temperature, then mold deformation is reduced, but the coating lacks sufficient adhesion resistance for plated steel sheets
Solution Approach 1:
The PVD coating process is segmented into multiple stages: first applying a base coat layer for dimensional stability, then applying a top coat layer for adhesion resistance. This allows low-temperature PVD processing to be maintained while achieving the required adhesion resistance through the functional top layer
Solution Approach 2:
The multi-layer composite structure enables the base layer to provide dimensional stability from low-temperature PVD coating, while the top layer (DLC, amorphous carbon) provides the necessary adhesion resistance for plated steel sheets, resolving the contradiction between manufacturing precision and adhesion resistance
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
The solution significantly enhances the durability and life of the metal mold by providing excellent wear resistance, heat resistance, and adhesion resistance, effectively addressing the challenges faced in hot stamping processes.
Implementation Method 1
coated metal molds in which the working plane is covered with a hard coating by physical vapor deposition (hereinafter, referred to as PVD method)
Implementation Method 2
a B layer formed from a diamond-like carbon coating, wherein the B layer is disposed closer to the outer surface side than the A layer
Data Source
Figure 1~2
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AI summary
The purpose of the present invention is to provide a coated metal mold having superior durability and adhesion resistance over a usage range from cold to warm/hot; and a method for manufacturing the coated metal mold. The coated metal mold is characterized by having a hard coating on a surface, wherein the hard coating includes an A layer formed from a nitride and having a film thickness not smaller than 5 µm, and a B layer formed of a diamond-like carbon coating, the B layer is disposed closer to the outer surface side than the A layer, the surface of the B layer has an arithmetic mean roughness Ra ≤ 0.2 µm, a maximum height Rz ≤ 2.0 µm, and a skewness Rsk < 0.