Differences of Using Multi-Directional and Uni-Directional

Magnetic particle inspection has long served the NDT industry as one of the most reliable, affordable and versatile methods of non-destructive testing. Multi-directional machines have since improved the capabilities of magnetic particle inspection by increasing the speed of inspection. We are conducting this time trial experiment to quantify just how much part processing speed differs between uni-directional and multi-directional machines.

For a uni-directional mag bench, the operator must magnetize using a circular field, inspect the part, magnetize using a longitudinal field and inspect the part again. The second mag shot will clear the part of any indications highlighted from the first induced field, thereby requiring two separate inspections.

However, multi-directional magnetic particle benches can magnetize a ferrous part using longitudinal and circular fields at the same time. Thus, indications in all directions can be seen with one inspection.

This is beneficial because it allows an operator to magnetize a part, and then inspect the part for indications in both directions with a UV lamp. The uni-directional style mag bench would require two mag shots and two inspections, which adds considerable time to the testing process.

Machine Setup and Test Plan

This experiment was completed using the MD3-2060. This machine can output current through contact pads, auxiliary coil and flux flow coils independently or concurrently, with separate amperage controls to balance the magnetic fields induced. This allows both uni-directional and multi-directional part processing to be simulated with the MD3-2060.

Three parts were chosen to be tested using both methods. This experiment assumes that the correct test parameters are stored in the machine and the fields are balanced.

Uni-Directional Setup

One output (contact, aux coil, flux flow coils) is selected at a time. Only the contact shot output is turned on for first mag shot. Then after UV inspection of the entire part, the auxiliary coil output is selected and contact is turned off. The second shot is sent through the aux coil and the part is inspected in the other direction using a UV lamp. If the part is over 20” long, a second auxiliary coil shot needs to be fired but no parts used for these trials are over 20” long that need more than two shots.

Multi-Directional Setup

All outputs (contact, aux coil, flux flow coils) are selected at a one time. The contact shot output and auxiliary coil output are both turned on initially. Flux-flow coils can be turned on to extend the reach of the magnetic field or replace the auxiliary coil functionality for parts less than 18”. The amperage for each output may need to be adjusted to balance the field, proven with QQI.

Experiment Steps

The steps for one cycle of part processing on each machine are as follows:

Results

These time trials show the benefits of multi-directional capabilities for various parts and applications. With all other variables held constant, the multi-directional machine consistently outperformed a uni-directional machine in terms of pure part processing speed. Given the results of the experiment it can be concluded that the reduction in steps and time show the added value of a multi-directional machine.

Out of 15 trial runs on each machine the average processing time difference is 47%. Meaning that for every hour an operator is processing the same part with a uni-directional machine, they could be wasting approximately a half an hour which could be saved with a multi-directional machine.

 Average time savings is 51%.

Average time savings is 39%.

Average time savings is 51%.

It is important to note that time savings are directly related to the length of the part. This is because the UV lamp inspection requires a majority of the time spent on each cycle. With multi-directional machines, the inspector only needs to look over the full part once as opposed to twice with the uni-directional.

Published July 10, 2018