Hot-Stamped PHS Trimming Using Localized Soft Zones
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Solution Overview
Problem
Conventional die trimming of press hardenable steel parts results in severe shearing tool wear and high maintenance costs due to the increased strength and hardness of these materials, necessitating expensive and time-consuming laser trimming processes.
Innovation Solution
A method involving hot stamping and die quenching with a quench die containing slow-cooling channels to create localized soft zones with ferritic microstructure and hard zones with martensitic microstructure, allowing for conventional die trimming without excessive tool wear, where the soft zones are die trimmed to form parts with reduced hardness and strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional die trimming is used to trim press hardenable steel parts, then trimming can be performed with standard equipment, but severe shearing tool wear and high maintenance costs occur due to the increased strength and hardness of the material
Solution Approach 1:
The patent applies local quality by creating a localized soft zone through controlled slow cooling in a specific region of the part. This soft zone has different microstructure (lower hardness) compared to the surrounding hard martensitic regions, allowing the trimming operation to occur in the softer area while the rest of the part maintains its high strength properties. The slow cooling channel is positioned to affect only the necessary trimming region, leaving other areas with fast cooling and high strength.
Solution Approach 2:
The patent changes the thermal parameter (cooling rate) in the trimming region by introducing a slow cooling channel. This parameter change transforms the material properties locally, reducing hardness from typical PHS levels (400-500 HV) to a softer state (200-250 HV) that is more amenable to conventional die trimming, while the rest of the part maintains its original high-strength characteristics.
2Reliability
If laser trimming is used to avoid tool wear, then trimming quality is maintained, but the process becomes expensive and time-consuming
Solution Approach 1:
The patent creates a localized soft zone specifically in the trimming region through controlled slow cooling, while the rest of the part maintains its hard martensitic structure. This allows conventional die trimming to be used in the soft zone without excessive tool wear, achieving both cost-effectiveness and acceptable trimming quality without requiring expensive laser trimming for the entire part.
Solution Approach 2:
The patent effectively creates a disposable soft zone that is intentionally designed to be easier to trim. The localized soft zone acts as a sacrificial area that accommodates the trimming operation with minimal tool wear, while the majority of the part (90%+) maintains its high-strength hard zone. This approach replaces the need for expensive laser trimming equipment with a simple thermal modification during the forming process.
3Ease of manufacture
If the entire part is made soft to enable conventional trimming, then trimming is easier on tools, but the overall strength and hardness of the part is reduced
Solution Approach 1:
The patent applies local quality by creating a localized soft zone through controlled slow cooling in a specific region of the part. This soft zone has different microstructure (lower hardness) compared to the surrounding hard martensitic regions, allowing the trimming operation to occur in the softer area while the rest of the part maintains its high strength properties. The slow cooling channel is positioned to affect only the necessary trimming region, leaving other areas with fast cooling and high strength.
Solution Approach 2:
The patent segments the part into two distinct zones: a localized soft zone (5-20% of volume) for trimming and a hard zone (>90% of volume) for structural integrity. This segmentation is achieved through strategic placement of slow cooling channels that affect only specific regions, allowing differential cooling rates and resulting microstructures in different parts of the same component.
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 conventional die trimming of press hardenable steel parts, reducing tool wear and maintenance costs by using localized soft zones with ferritic microstructure, thereby avoiding the need for expensive laser trimming and lowering manufacturing time and costs.
Implementation Method 1
The blank is die quenched with a quench die comprising at least one slow-cooling channel that reduces the cooling rate of a portion or zone of the blank that is adjacent to the slow-cooling channel. The zone of the blank subject to the reduced cooling rate is locally soft (localized soft zone) compared to an adjacent zone that is subjected to an increased cooling rate and is hard.
Implementation Method 2
hot stamping and die quenching a blank to form a die quenched panel
Implementation Method 3
The transfer unit may include a heating unit or heating element for applying heat to the localized soft zone during transfer of the die quench panel
Data Source
AI summary
A method of forming a hot stamped, die quenched, and die trimmed part is provided. The method includes hot stamping and die quenching a blank with a quench die and forming a die quenched panel. The quench die includes at least one slow-cooling channel. The die quenched panel is die trimmed along the at least one localized soft zone that is adjacent a hard zone. The blank may be formed from a press hardenable steel (PHS), and the at least one soft zone may have a ferritic microstructure and the at least one hard zone may have a martensitic microstructure. The at least one localized soft zone may have a microhardness between about 200 HV and about 250 HV and the hard zone may have a microhardness between about 400 HV and about 500 HV.