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Magnetic Particle Inspection of Axle Shafts

Axles are fundamental to automobile functionality, transmitting power from the engine to the wheels while supporting the vehicle’s weight. They enable smooth steering, suspension movement, and wheel rotation. Both front and rear axles contribute to stability, control, and overall drive performance, playing a pivotal role in safe and efficient transportation.

Magnetic Particle Inspection (MPI) is vital for axle shafts to enhance safety and reliability. By magnetizing the shafts and applying magnetic particles, surface and near-surface defects become visible. This non-destructive method detects cracks and flaws, crucial for preventing catastrophic failures. It aligns with industry standards, enabling early defect identification, proactive maintenance, and compliance. MPI’s cost-effectiveness, non-destructive nature, and role in manufacturing quality control make it indispensable for ensuring the integrity of axle shafts in various industries.

The axle shaft needs to be magnetized in two directions perpendicular to each other. A circular magnetic field is used to detect longitudinal flaws in the part.

Circular magnetic field is generated by passing a current through the length of the axle.

Calculation of head shot current is done as per the formula given in ASTM standards.

Head Shot Current = 20 X Diameter of shaft (in mm)

In the above formula, the diameter should be taken as the diameter of the shaft and not the flange.

 

Longitudinal magnetic field, required to detect transverse defects is generated by using one or more encircling coils.

As per ASTM standards, the length of the axle shaft magnetized by the coil is equal to the inside diameter of the coil.

To cover the entire length of the axle the coil must be moved to different points along the length of the axle separated by 90% of the coil diameter. This will ensure the 10% overlap specified in the ASTM standards.

Formula for calculation of coil current

Also, in the above formula for current requirement for coil shot, while calculating L/D ratio, L must be equal to the inside diameter of the coil & not equal to the overall length of the axle.

A bench type machine is used to perform magnetic particle testing on axles. The axle is placed on the steady rollers fitted on the head & tailstock of the machine. A pneumatically operated arrangement is used to clamp the axle from both ends. Pneumatic clamping ensures that there is no sparking when high current is passed through the axle. Use of braided copper pads is also recommended to eliminate arcing sparks.

 

Conventional Technique

A two vector PLC based bench type magnetic crack detector machine is used to perform testing on the axles.

 

Axle MPI Testing

Testing Procedure for conventional machines

  • Clean up & dry the axle’s surface before inspecting.
  • The axle is placed on the steady rollers.
  • Now apply magnetic solution bath to the axle.
  • Press the ‘Cycle Start’ button.
  • The axle automatically gets clamped.
  • Stop the flow of bath.
  • Now, the current passes through the axle.
  • It shows up on the digital metering unit.
  • The axle automatically gets de-clamped.
  • Inspect the axle under UV light for longitudinal defects. Rotate on steady rollers.
  • Position the coil to its 1st position.
  • Now, again apply bath to the job.
  • Press the ‘Cycle Start’ button.
  • Stop the flow of bath.
  • Now the current passes through the coil.
  • It shows up on the digital metering unit.
  • Inspect the axle under UV light for transverse defects. Rotate on Rollers
  • Move the coil to next position & repeat the above 6 steps.

Multidirectional Technique

In this tailor made machine, two coils are used. The coils are automatically moved using pneumatic actuators. The automatic movement of coils facilitates the loading of part on the machine. Each coil covers a length of 450mm from each end of the axle. So two coils cover an area of 900mm. Axles upto 900mm length can be checked on this machine

 

For lengths longer than 900mm we have another tailor-made solution where 4 coils are used. This machine can test axles up to 1600mm length in one go.

 

Testing Procedure for conventional machines

  • Clean up & dry the axle’s surface before inspection
  • Place the axle on the steady rollers.
  • Now apply a bath to the axle.
  • Press the ‘Cycle Start’ button.
  • The axle will automatically get clamped & Coils will come into position
  • Stop the flow of the bath.
  • Now the current will pass through the axle& the coils in multidirectional mode.
  • It will show up on the digital metering unit.
  • The axle will automatically get de-clamped.
  • Inspect the axle under UV light for defects in all directions. Rotate on rollers.
  • Demagnetize

suitable products

Standard MPI Machines

Engineered for precision and efficiency, the Standard Bench Type Magnetic Particle Testing Machine is suitable for entry level testing.

PLC Controlled MPI Bench

With PLC Controlled bench type Magnetic Particle Inspection Machine, you can accurately control the process parameters for reilable results.

Multidirectional MPI Bench

The ultimate solution for robust non-destructive testing, this machine offers multi-directional magnetization for inspection in all directions in one shot..

Demagnetizers

Demagnetizers stand as a key tool in maintaining excellence in production, with the flexibility to handle different materials and magnetism levels, coupled with energy-efficient and user-friendly design.

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