Failure analysis of hot forging dies for automotive components

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Abstract

Influencing variables and causes of hot forging die failures for automotive components are summarized. Characteristics of hot forging die failures are exemplified. An important role of microfractography is stressed in engineering failure analysis for hot forging die failures.

Then failure analyzed examples for hot forging die failures and their countermeasures are presented with influencing variables such as die materials, die design, die manufacturing and forging operations. Finally a couple of recommended works for engineering failure analysis for hot forging die failures for automotive components are touched on briefly.

Introduction

Hot forging die failures for automotive components are caused by inadequacy of variables such as die materials, die design, die manufacturing and forging operations. In order to prevent die failure and to improve die life many efforts have been made so far.

In this paper a couple of important issues on engineering failure analysis of hot forging die failures for automotive components are briefly summarized mainly from the authors’ experimental results. Influencing variables and the cause of die failures for automotive components are classified. Macroscopic characteristics of hot forging die failures for automotive components are exemplified for representative hot forging die for automotive components. An important role of microfractography is stressed in engineering failure analysis for hot forging die. Then failure analyzed examples for hot forging dies and their countermeasures are described with influencing variables such as die materials, die deign, die manufacturing and forging operations. Finally future problems should be solved in engineering failure analysis for hot forging dies for automotive components are briefly described.

Section snippets

Macroscopic characteristics of failed hot forging dies and causes of failures

The most of hot forging die failures are caused by inadequacy of influencing variables such as die materials, die design, die manufacturing and forging operations. The influencing variables and causes of hot forging die failures can be classified as shown in Table 1[1].

The hot forging die frequently fails from the corner where stress concentrate. Fig. 1 shows a typical failure of hot forging die for knuckle. From the macroscopic fracture surface it can be easily judged that a brittle failure

Failure analysis process and a role of microfractography in failure analysis of hot forging dies

Failure analysis process for failed hot forging die is basically same as that of conventional machine components. Investigation process is as shown in Fig. 6 [1]. At first circumstances of hot forging die failure and its related data can be seized. Then a macroscopic observation is conducted for failed hot forging die. Investigations on influencing variables on hot forging die failure are conducted for forging equipments, die manufacturing process and forging die steel, respectively. Detailed

Hot forging die failures caused by forging die steel

One of the important mechanical properties for hot forging die steel is fracture toughness. It is well known that fracture toughness is different with orientation of ingot. In the results of impact tests of hammer forging die steel SKT4 the difference of 2 mm U notched Charpy impact value at 573 K showed 40% at different orientation [1]. Therefore in the hot forging die design die graving direction must be decided by taking forging ratio and flow orientation of die steel into considerations. In

Concluding remarks

In this paper influencing variables and causes of hot forging die failures, characteristics of die failures, analyzed examples of failed hot forging dies and its counter measures are briefly summarized. The hot forging die failure is complicated with various kind of influencing variables such as die material, die design,die manufacturing and forging operations. Of course failure analysis of hot forging die failure must be conducted for each failed hot forging die. Recent progress of die steel,

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