Pilot assembly for progressive die machines

An assembly for locating a workpiece in a punch press where the workpiece is progressively moved through successive forming stages of the press, comprising a movable die, a locator pin for engaging pilot holes formed in the workpiece in response to movement of the movable die, means for supporting the locator pin in the movable die to allow retraction movement of the pin relative to the die, and hydraulic means for controlling the retraction movement of the locator pin relative to the movable die, the hydraulic control means including a first chamber into which the pin retracts, said chamber containing hydraulic fluid to normally oppose retraction movement of the locator pin relative to the movable die, a second chamber containing a compressible gas, means for interconnecting the first and second chambers to allow the fluid to flow therebetween, and valve means cooperating with the interconnecting means to normally prevent flow of fluid from the first chamber but to allow the fluid to flow into the second chamber when an excessive force is applied to the locator pin in opposition to movement of the movable die, said valve means also including means to allow a displaced quantity of the fluid to flow back into the first chamber when the force applied to the locator pin decreases.

In a progressive punch press of the type which includes at least one movable ram supporting a plurality of die elements for forming a workpiece from a strip of sheet material in successive forming stages as the sheet material is fed through the press, and a pilot pin movable with the ram for engaging a pilot hole formed in the sheet material to properly locate the sheet material within the press during a forming stage, the improvement comprising a hydraulic assembly including a chamber filled with hydraulic fluid for maintaining said pilot pin in projected position and against retraction by forces occurring in normal operation of the press, and means to release from said chamber fluid displaced therefrom in response to retraction of the pilot pin under excessive force imposed thereon by an abnormal obstruction to its movement with the movable ram.

A method of controlling retraction movement of a normally projected locator pin in a machine in response to opposition to its normal movement for engaging pilot holes in a workpiece, comprising the steps of opposing retraction movement of the locator pin by hydraulic fluid contained in a hydraulic chamber, displacing hydraulic fluid from the hydraulic chamber in response to a high pressure in the hydraulic fluid sufficient to open a first normally closed valve so as to allow the locator pin to retract in response to an external force applied to the locator pin in opposition to its normal movement, containing the displaced hydraulic fluid in a receiving chamber, and returning the displaced fluid to the hydraulic chamber by applying sufficient pressure to the displaced hydraulic fluid in the receiving chamber to open a second normally closed valve when the external force applied to the locator pin decreases.