ABSTRACT
This paper discusses the heating and heating methods of forging moulds. It is necessary to heat the forging moulds during the forging process, because the forging temperature is related to the strength, structure, performance and process of the forged parts. In order to ensure the quality of the product, we must pay attention to the selection of heating method. In this paper, we will discuss the functions of the heating process and heating methods of forging moulds, analyze the advantages and disadvantages of various heating methods, and give some useful Suggestions on the selection of heating methods.
Keywords: forging mould； heating method； Suggestions
1 Introduction
In the forging process of metal parts, the moulds used in the process are heated according to the requirement of the forging temperature. It is necessary to heat the forging moulds before the next forging step, because the forging temperature is related to the strength, structure, performance and process of the forged parts. If the die temperature is too low, it will cause the metal parts to deform under the mold when cooled, and the mechanical properties of the metal parts may be reduced. On the contrary, if the temperature of the die is not high enough, it will lead to the incomplete filling of metal into the mould, which affects the product quality and even causes other safety accidents. Therefore, it is very important to choose the right heating method.
2 Functions of Heating Process
In the forging process of metal parts, heating the forging moulds has the following functions:
(1) Reduce the viscosity of metal. According to the thermodynamics of die forging process, when the temperature of the metal increases, its viscosity gradually decreases. It makes the plasticity of metal increase and can be filled in the die cavity perfectly.
(2) Improve the lubricity of die. When the die of forging mould is hot, it can reduce the friction between die and metal and make the moulding process easier.
(3) Improve the strength of the mould. When the forging mould is heated, the thermal stress on the mould surface will be reduced, and its strength will be enhanced.
(4) Reduce the fear of internal defect of casting. In the die forging process, the heating of mould can help to eliminate or reduce the impact of internal defects on the quality of the mould.
3 Heating Method of Forging Mould
According to the different heating sources, the heating methods of forging mould can be divided into two types: direct heating method and indirect heating method.
3.1 Direct Heating Method
The direct heating method of forging moulds refers to the heating method of heating the moulds directly by heating the heating sources, including flame heating, electric heating and induction heating.
(1) Flame heating: Flame heating is a kind of direct heat transfer. When more heat is needed, it is the most economical and reliable heating method. The heat efficiency of flame heating is related to the burning fuel, and natural gas and petroleum coke are often used. Flame heating is mainly used in high-temperature forging of carbon steel and low-temperature forging of brass parts.
(2) Electric heating: Electric heating is a kind of direct heat transfer. When compared with flame heating, electric heating has the characteristics of fast speed, good temperature control and accurate heating temperature. It is mainly used in die forging of high-intelligence parts, such as valves, molds and so on.
(3) Induction heating: Induction heating is a kind of electromagnetic heating method, which is to use the induction effect generated by the alternating magnetic field to heat the object directly. It is a very efficient and precise die forging heating method. It is mainly used for high temperature forging of aluminium alloy and die forging of stainless steel parts.
3.2 Indirect Heating Method
The indirect heating method of forging moulds refers to the heating method of heating the moulds indirectly by heating and transferring the heat generated by the heating source to the moulds through the medium, including furnace heating, heat treatment furnace heating and so on.
(1) Furnace heating: Furnace heating is to heat the forging moulds by heating the heating source in the furnace. The heat energy generated by the heating source is transferred to the forging moulds through the medium in the furnace, and then heated by the furnace. It is mainly used in the die forging of parts that require large heating areas, such as flat steel and steel plates.
(2) Heat treatment furnace heating: Heat treatment furnace heating refers to the heating of forging moulds by heating the heat source in the heat treatment furnace. The heat energy generated by the heating source is transferred to the forging moulds through the medium in the heat treatment furnace, and then heated by the heat treatment furnace. It is mainly used for die forging of special shape parts, such as internal and external threads.
4 Advantages and Disadvantages of Heating Methods
The selection of heating methods should be based on the specific conditions of die forging, and consider the advantages and disadvantages of various heating methods. Generally speaking, each heating method has its advantages and disadvantages, and the comparison is shown in the following table.
Table 1 Comparison of advantages and disadvantages of different heating methods
Heating Method Advantage Disadvantage
Flame heating Low cost, high thermal efficiency, and large heating area. Low precision, difficult to control, prone to oxidation.
Electric heating Fast heating, good temperature control, and accurate heating temperature. High cost.
Induction heating Fast heating, good temperature control, high precision, and energy saving. Small power, not suitable for high temperature forging.
Furnace heating Good heat preservation effect and uniform temperature. Low heating efficiency, long heating time.
Heat treatment furnace Good heat preservation effect and uniform temperature. High cost, and need to be used with special equipment.
5 Suggestions on Selection of Heating Methods
The selection of heating method should be based on the specific conditions of die forging. We should choose the heating method according to the requirements of die forging quality, heating parameters and equipment used. Here are some Suggestions for the selection of heating methods.
(1) Flame heating is suitable for high-temperature forging of carbon steel parts and low-temperature forging of brass parts.
(2) Electric heating is suitable for die forging of high-precision parts, such as valves, molds and so on.
(3) Induction heating is suitable for high-temperature forging of aluminium alloy parts and die forging of stainless steel parts.
(4) Furnace heating is suitable for die forging of parts with large heating areas, such as flat steel and steel plates.
(5) Heat treatment furnace heating is suitable for die forging of special shape parts, such as internal and external threads.
6 Conclusion
The heating of forging moulds is a very important process in the die forging process of metal parts. In order to ensure the quality of the forged parts, it is necessary to pay attention to the selection of heating method. We should choose the heating method according to the requirements of die forging quality, heating parameters and equipment used. We should make a comprehensive assessment of the advantages and disadvantages of various heating methods, and choose the most suitable heating method according to the actual needs.
