Magnetic particle inspection(MPI) is a highly effective and sensitive method to reveal surface or near surface discontinuities of metal parts, often used to inspection casting or forging parts. MPI is suitable for ferromagnetic materials, like carbon steels, most alloy steels.
Recently, MPI becomes particularly important because cleaning method like shot blasting, which tends to close surface breaks of casting or forging parts, So It’s hard for QC people to reveal those surface breaks through visual inspection.
Magnetic particle inspection in our Machining Shop
Many China CNC Machining shops do not have MPI equipment, They rely on their supplier to do the magnetic particle inspection. It really saves a lot of costs, But sometimes, lack of MPI equipment will cause a serious quality accident.
Our factory is producing critical components for several industries leading companies, And because many of our products are machining of castings or Forgings, Therefore, We have purchase MPI equipment, We can do MPI by ourselves.
There are 2 kinds of MPI equipment – Dry method and the wet method. We have bought a wet method MPI equipment, which has better performance than the dry method. It can detect a discontinuity with a maximum depth of 6.5 mm, but usually, 1 to 2.5 mm depth is enough.
Usually, we do magnetic particle inspection before machining, Once find serious defects, the castings or forgings is no need to carry on further machining, But for slightly surface breaks, We can polish the parts to remove the surface breaks.
Advantages of Magnetic Particle Inspection:
- It offers immediate warning signs of defects.
- Quick and easy to reveal the defects.
- It shows surface and near-surface defects.
- Small machining shop can install the MPI equipment
- The cost is cheaper compared to X-ray inspection.
- Can inspect Large or small metal parts
- Not necessary to do the cleaning before the inspection
Disadvantages of Magnetic Particle Inspection:
- It is restricted to the ferromagnetic material, – usually carbon steels or most alloy steels, but cannot inspect austenitic stainless steel parts.
- Need a supply of electricity.
- Need an experienced operator to do the inspection, That is because sometimes, It is unclear whether the magnetic field is sufficiently strong to give good indications.
- The method cannot be used if a thick paint coating is present.
Beside MPI inspection, If you need other kinds of Nondestructive testing, such as x-ray inspection. we can let our supplier do such test.
We can also do dimensional inspection, hardness test, surface roughness test in our own machining factory. We have special MPI operator, We can provide quality machined parts to our customer.