Hot-pressing apparatus

Abstract

This invention relates to a hot-pressing method and a hot-pressing apparatus capable of quenching a workpiece at a sufficient cooling rate. In a hot-pressing step, a hot-pressing apparatus presses and cools a workpiece at the same time. The hot-pressing apparatus includes a lower die and an upper die whose forming surfaces face each other. A top surface of the lower die is provided with a plurality of beads so that a part of the workpiece difficult to come in contact with the forming surface of the lower die and the forming surface of the upper die positioned at the bottom dead center is formed into a stepped shape.

Description

TECHNICAL FIELD [0001]The present invention relates to a hot-pressing method and a hot-pressing apparatus for pressing and cooling a heated workpiece at the same time.BACKGROUND ART [0002]Conventionally, a hot-press forming is widely known in which a pressing machine to which a pair of dies (an upper die and a lower die) are attached presses a workpiece, such as a steel plate, heated to above a temperature at which an austenite structure appears, and at the same time, brings the dies into contact with the workpiece to quench the workpiece.[0003]A technique on the hot-press forming is publicly known which enables the dies to suitably cool the workpiece during the quenching by forming water channels through which cooling water flows inside the dies to cool the dies (for example, see Patent Literature 1).[0004]However, when the workpiece is quenched, clearances are formed between the workpiece and the dies because of variation in the thickness of the workpiece caused by the press worki...

AI Technical Summary

Benefits of technology

[0011]The present invention makes it possible to quench a workpiece at a sufficient cooling rate, and to prevent hardness of some parts in the workpiece from being smaller than a predetermined value.

Problems solved by technology

However, when the workpiece is quenched, clearances are formed between the workpiece and the dies because of variation in the thickness of the workpiece caused by the press working, a precision error in the forming surfaces of the dies caused when the dies are manufactured, flexure of the dies during the press working, and the like.

Consequently, a part of the workpiece where the clearance between the part and the dies is larger than a predetermined size has decreased contact areas with the forming surfaces of the dies when the workpiece is quenched, which causes a problem that the part is cooled at an insufficient cooling rate, and hardness of the part is smaller than a predetermined value,

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