Threads are one of the most important mechanical machining processes in industrial applications, as they allow different components of a finished product to be joined together.
The absence, incompleteness, or presence of defects inside a threded bore can compromise both the production process and the quality of finished products. This is why 100% of the production must be checked.
There are three important checks required to control a thread:
- thread presence check
- thread guality control
- dimensional specifications of the thread
By using eddy currents technology, we can perform the first two checks quickly and directly on the production line, intercepting non-complying parts.
Eddy currents’ technology can be used to check if the threading has been performed and if there are any faults inside the threads quickly and directly in production lines.
THREAD PRESENCE CHECK
The thread presence check with eddy currents is used to ensure that the threading has been performed on blind or through holes. That is done with a simple sensor which analyses the presence of the machining, on the end part of the machining.
The Marposs E70T electronic unit identifies non-threaded or partially threaded bores and immediately blocks the production process upstream. This is done in order to check the causes that led to the missing threads.
The eddy current ND sensors are constructed in a plastic material with a frontal protective capsule made from hard steel; this is done to protect the sensor from any collisions or rubbing against the internal surface of the thread. The sensors are usually fitted on a recoiling protection system, prevents damages in case the tapping pre-bore has not been performed or if the bore is blocked by a broken male (for example). The thread check sensors are available from the M4 diameter.
The thread is checked by simply inserting an eddy current sensor inside the hole. The quantity of material inside a threaded hole, by changing the magnetic field produced by the eddy current sensor, affects the result of the measurement. The considerable difference in material between threaded holes and smooth holes makes the inspection particularly effective, safe, and quick. This type of process check controls whether the threading has been performed, without providing information on the geometry of the thread itself.
THREAD QUALITY CONTROL
After checking that the thread has been machined, an additional check is required to ensure that there are no defects inside the threaded bore that could compromise its mechanical specifications. Usually defects inside a threaded bore can be divided in two large families:
- porosity caused by the casting process of the base material;
- cracks caused by the mechanical boring and tapping machining processes that, especially on narrow walls, can lead to its failure.
The Marposs E59N electronic unit identifies the presence of porosity and cracks. This is done with an eddy current rotating probe that, by combining the rotation of the ND sensor and the movement along the axis of the hole, checks the whole threaded surface.
The cracks and pore presence check is available for threaded bores with sizes equal to or greater than M8.