In plastic injection molding, when molding operations are being carried out in mass manufacturing, initial failures or random failures can occur at certain probabilities.
In the last course we explained the different failure periods, and this time we will explain what is called the "Mean Time Between Failures (MTBF)".

The average time after a mold has failed until the next failure occurs is called the MTBF. Therefore, the unit of MTBF used is time (hr, min, etc.) or the number of shots.

When the value of MTBF is large, it can be evaluated that the mold is one in which failure is difficult to occur.
On the other hand, if the value of MTBF is small, it can be said that the mold is likely to fail easily, and it is difficult to make a plan of production of stable molding operations.

Let us consider MTBF in a more realistic example. When several repeated molds are manufactured using the same design drawings, although initial failures and random failures are more likely to occur in the first mold, if technical improvements are made in response to such failures, it will be difficult for such failures to occur in the second and subsequent molds. Therefore, the MTBF of second and subsequent molds will be a large number compared to that of the first mold.

When considering the "production cost + maintenance and management cost" of a mold from it is initially produced until it is disposed off, if the cost of a mold is evaluated based only on the fact that the initial cost (initial production cost) of the mold is cheap, in the end it may become an expensive purchase.
MTBF has a lot of importance as an index for evaluating the maintenance and management cost.

On the other hand, as an index for evaluating the ease of repair of molds, there is what is called the Mean Time To Repair (MTTR).
In case a mold fails, the MTTR of that mold has a small value if it is possible to repair it quickly.
As an example, if spare parts are always in stock, and also if the structure is such that it is possible to replace the spare parts from the parting surface even without removing the mold plate of the cavity, then the MTTR will become a small value.
MTTR, also, has a lot of importance as an index for evaluating the maintenance and management cost.