Sources of Magnetization in Manufacturing Environments
1Mechanical Processes
- Workpieces can become magnetized during machining or forming operations when magnetic tools or fixtures are used.
- Machining may reveal pre-existing magnetized areas deep within the material.
- Steel itself may develop magnetization during forming processes.
2Handling and Operations
- The use of magnetic lifters or clamping devices can magnetize ferromagnetic materials.
- Direct contact between parts and tools over small areas can also cause localized magnetization.
3Storage and Transportation
- When large volumes of steel are stacked, small gaps can lead to magnetic field concentration.
- The orientation of stored steel in relation to the Earth’s magnetic field may induce magnetization.
- Vibrations during transportation can cause magnetization or, conversely, demagnetization.
4Magnetic, Electrical, and Electrochemical Processes
- High-current operations (e.g., welding, EDM) generate strong magnetic fields that can magnetize parts.
- Electrochemical processes (e.g., electroplating) performed under high current conditions can also lead to magnetization.
- PVD processes, which deliberately generate magnetic fields, may likewise result in magnetization of components.
Why Demagnetization Is Necessary?
Effects of Magnetism and Residual Magnetism
1. Adverse Impacts on Manufacturing and Assembly Processes
- Machining: Residual magnetism hinders proper chip removal, leading to surface scratches on the workpiece or tool damage.
- Stamping and Forming: Magnetic attraction of debris can cause tool wear or defects in finished parts.
- Powder Metallurgy: Magnetization may lead to uneven green density, reducing product consistency and quality.
- Product Assembly: Magnetic forces attract fine particles, which can cause malfunctions in sensitive assemblies.
- Welding and Coating: Magnetic blow effects destabilize the welding arc, while coatings may suffer from reduced quality and adhesion.
2. Impacts on Cleaning and Technical Cleanliness
- Residual magnetism attracts ferromagnetic particles, making it difficult to achieve cleanliness standards during cleaning.
- In sensitive components, particle adhesion caused by magnetism significantly increases the risk of functional failure.
- Proper demagnetization reduces cleaning complexity and costs while improving overall product reliability.
Effects of Magnetism on Measurement and Testing Processes
- Eddy Current Testing (ECT): Localized magnetic spots on the surface can generate artifacts or false indications.
- Hall Sensors or Inductive Sensors: Uncontrolled magnetic fields can lead to inaccurate readings.
- Electron Beam Processes: Magnetic interference causes beam deflection, resulting in positional deviations.
- High-Resolution Fluxgate Sensors: In military and aerospace applications, magnetic disturbances may lead to measurement errors.
Demagnetization: Technologies and Methods
1. Pulse Method
- An alternating magnetic field inside the coil rises rapidly to a high amplitude and then gradually decreases to zero.
- Frequency, current, pulse waveform, and pulse duration are precisely controlled by the power module.
- Pulse parameters can be optimized according to specific application requirements.
- This method achieves the highest demagnetization efficiency.
2. Continuous Method
- The alternating magnetic field inside the coil remains constant.
- Demagnetization is achieved by gradually reducing the field effect through increasing the distance between the part and the coil—for example, pulling the component out of the coil or moving it through the coil via a conveyor system.
- Compared to the pulse method, this technique requires lower magnetic field intensity.
- Coil current can be supplied by a power module; for simple applications, it can also be directly powered from the mains.
Controlled low frequency sine pulse for the demagnetization of large, thick walled components.
Short progressive frequency sine pulse (~1300ms pulse duration) for demagnetization of small parts at fast production cycle.