Double-blank detecting apparatus for press machine and die protecting apparatus for press machine

A double-blank detecting apparatus for a press machine that is provided with a die cushion apparatus and forms blanks one by one automatically and repeatedly, the double-blank detecting apparatus comprising:

• a slide position detector configured to detect a position of a slide of the press machine and output a slide position signal;
• a die cushion load detector configured to detect a die cushion load generated on a cushion pad and output a die cushion load signal;
• and
• a double-blank detector configured to detect a state in which a plurality of blanks are stacked as a double blank based on the slide position signal and the die cushion load signal, wherein
• the double-blank detector holds the slide position signal at a timing when the die cushion load signal rises to a predetermined value as a slide position signal hold value, compares the held slide position signal hold value and an abnormality determination value, and detects the double blank in a case where the held slide position signal hold value is equal to or larger than the abnormality determination value, and
• the predetermined value of the die cushion load signal is a value within a range from 5% or more and 20% or less of a maximum die cushion load of the die cushion apparatus.