Balance Shaft Pivot Manufacturing with Wire EDM for Non-Magnetic Precision
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Solution Overview
Problem
The production of watch pivot shafts, particularly balance shafts, is complex due to the need for materials that are soft enough for precise machining without premature tool wear, yet hard enough to resist wear during operation, and non-magnetic to avoid disruption from magnetic fields, while achieving micron-level dimensional precision and surface finish.
Innovation Solution
A method using a numerically controlled machine with a wire EDM machining system to shape non-magnetic and electrically conductive materials like austenitic stainless steels, metallic glasses, tungsten-based alloys, or conductive ceramics, involving continuous and incremental rotation to create precise pivot shapes without traditional rolling operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional turning and rolling operations are used to machine pivot shafts, then soft materials with good machinability can be processed, but the material cannot achieve high hardness to resist wear during operation
Solution Approach 1:
The patent replaces traditional mechanical cutting operations (turning, rolling) with wire EDM (electrical discharge machining). This substitution allows the use of harder, non-magnetic materials that would be difficult to machine conventionally, while still achieving precise pivot geometries and surface finishes. The electrical discharge process removes material through controlled erosion rather than mechanical contact, eliminating the trade-off between hardness and machinability.
Solution Approach 2:
The invention changes the material parameters by selecting non-magnetic, electrically conductive materials (such as austenitic stainless steels, titanium alloys, or composite materials) that can be processed by wire EDM. These materials have different physical properties compared to traditional martensitic steels, allowing simultaneous achievement of high hardness, non-magnetic properties, and ease of processing through electrical discharge machining.
2Object-affected harmful factors
If martensitic steels are used for pivot shafts, then good machinability and hardening capacity are achieved, but the material is sensitive to magnetic fields which can disrupt watch operation
Solution Approach 1:
The patent changes the magnetic parameter of the material by selecting non-magnetic or low-magnetic materials (austenitic stainless steels, titanium alloys, composite materials) while maintaining electrical conductivity for wire EDM processing. This parameter change eliminates magnetic sensitivity to field disruptions while preserving manufacturability through electrical discharge machining.
3Manufacturing precision
If multiple processing steps (turning, rolling, polishing) are used to achieve precise pivot shapes and surface finish, then dimensional precision is improved, but the production process becomes complex and time-consuming
Solution Approach 1:
The patent merges multiple traditional processing steps (turning, rolling, polishing) into a single wire EDM operation. The wire EDM process can simultaneously achieve precise pivot geometries, controlled surface finishes, and accurate dimensional tolerances in one continuous process, eliminating the need for sequential operations and reducing overall process complexity.
Solution Approach 2:
By replacing the mechanical system of turning and rolling with wire EDM, the invention simplifies the production process while maintaining or improving dimensional precision. The electrical discharge machining provides direct control over pivot shapes and surface finishes without requiring intermediate rolling operations or extensive polishing.
4Loss of substance
If traditional rolling operations are used to shape pivots, then desired geometry and surface finish are obtained, but additional material abrasion occurs and dimensional control requires intermediate dimensions
Solution Approach 1:
The patent replaces mechanical rolling operations with wire EDM, eliminating the harmful material abrasion and surface degradation caused by rolling. The electrical discharge process removes material cleanly through controlled erosion, achieving precise pivot dimensions and optimal surface finishes without the material loss and dimensional adjustments required by rolling 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
Achieves precise, non-magnetic pivot shafts with excellent surface finish and dimensional control, eliminating the need for subsequent rolling and reducing material abrasion, while enabling the use of materials with high hardness and conductivity.
Implementation Method 1
shaping the bar by wire EDM machining to obtain a pivot shaft comprising a pivot at each end
Data Source
Figure 1
Figure 2
Figure 3a~3c
AI summary
The present invention relates to a method for producing a balance shaft made of non-magnetic and electrically conductive material by means of a machine comprising a rotary gripping member (1) and a wire EDM machining system (2) mounted on a numerically controlled actuator (3). The method comprises the following steps: - providing a bar (4) of said material extending along a longitudinal axis (A), - arranging the bar (4) along its longitudinal axis (A) on the rotary gripping member (1), - shaping the bar (4) by EDM machining to obtain a balance shaft comprising a pivot at each end, this step comprising continuously rotating the bar (4) around its longitudinal axis (A) for shaping said pivots - optionally carrying out a tribological finishing treatment.The invention also relates to a balance shaft, in particular made from a material chosen from the families of austenitic stainless steels, metallic glasses, tungsten-based alloys, intermetallic materials or even conductive ceramics.