Lead-Free CuZn42 Watch Components With Low-Stress Tempering
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Solution Overview
Problem
Current manufacturing processes for lead-free brass alloys, such as CuZn42, do not adequately address the need for extreme precision in watch components due to internal stresses and hardness loss during machining, which are optimized for lead-containing brasses.
Innovation Solution
A manufacturing process for CuZn42 alloy components involves stress-relieving tempering at optimized temperatures between 170°C and 230°C with specific holding times to minimize hardness loss and achieve a hardness of 120-190 HV2, ensuring minimal deformation and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If stress-relieving tempering is performed at conventional temperatures (250-300°C) optimized for lead-containing brasses, then internal stresses are relaxed and dimensional stability is improved, but hardness significantly decreases
Solution Approach 1:
The patent applies parameter changes by modifying the tempering temperature range from the conventional 250-300°C (optimized for lead-containing brasses) to a lower range of 150-250°C for lead-free brass CuZn42. This parameter adjustment allows stress relaxation while preserving hardness, as the lower temperature prevents excessive softening of the lead-free alloy. The holding time parameter is also optimized within 1-10 hours to achieve the desired balance between stress relief and hardness retention.
2Object-affected harmful factors
If lead-free brass CuZn42 is used to eliminate toxicity, then health and environmental safety are improved, but the material exhibits greater hardness loss during conventional tempering processes
Solution Approach 1:
The patent resolves this contradiction by changing the tempering parameters specifically adapted for lead-free brass. The temperature range is set to 150-250°C (lower than conventional 250-300°C) and holding time to 1-10 hours, which creates an optimized process window where lead-free brass CuZn42 undergoes stress relief without significant hardness loss. This parameter optimization maintains the toxicity-free advantage while compensating for the material's greater sensitivity to tempering conditions.
Solution Approach 2:
The patent effectively creates a copied or adapted version of the conventional tempering process specifically for lead-free brass. Instead of directly applying the standard 250-300°C process designed for lead-containing alloys, a modified process with lower temperatures (150-250°C) and extended holding times (1-10 hours) is developed, copying the stress-relief function while adjusting parameters to suit the lead-free material's different thermal response characteristics.
3Ease of manufacture
If higher zinc content in CuZn42 alloy is used to improve machinability, then cutting properties are enhanced, but work-hardening potential increases leading to higher initial hardness
Solution Approach 1:
The patent addresses this contradiction through parameter changes in the tempering process. The higher zinc content (42%) in CuZn42 indeed increases work-hardening and initial hardness, but the optimized tempering parameters (150-250°C for 1-10 hours) are specifically designed to reduce this elevated hardness to a target range of 120-190 HV. This parameter optimization allows the material to maintain its machinability benefits from high zinc content while achieving the desired final hardness through controlled stress-relieving tempering.
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 process achieves minimal deformation of a few tenths of a micron, ensuring flatness and clearance in watch components, with hardness loss limited to less than 30 HV2, thereby maintaining machinability and precision.
Implementation Method 1
Stress-relieving heat treatment of said semi-finished part at a temperature between 170 and 230°C with a holding time at said temperature between 20 minutes and 10 hours
Implementation Method 2
Heat treatment of said semi-finished part, also called stress-relieving tempering, in a temperature range between 170°C and 230°C (inclusive), preferably between 180°C and 220°C, with a holding time in these temperature ranges of between 20 minutes and 10 hours
Data Source
Figure 1~2A
Figure 2B~3
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AI summary
The invention relates to a method for manufacturing a timepiece component (1) made of CuZn42 brass with a hardness of between 120 and 190 HV2, the method comprising the following steps: - providing a semifinished part that has been shaped by deformation, the semifinished part having a hardness of between 130 and 220 HV2 and being made from a CuZn42 brass material, - subjecting the semifinished part to a stress-relieving heat treatment at a temperature of between 170 and 230°C with a holding time at this temperature of between 20 minutes and 10 hours, preferably between 30 minutes and 5 hours, more preferably between 1 hour and 4 hours, - machining and finishing the semifinished part to create the timepiece component (1). The invention also relates to the timepiece component made from a CuZn42 brass.