Countermeasures to Prevent Cracks in Forging and Pressing
Abstract
Cracks are one of the most common and potentially dangerous defects during forging and pressing processes. This article discusses the various causes for cracks in forging and pressing processes, provides a variety of preventive measures and suggests possible solutions to reduce the occurrence of cracking.
Introduction
Forging and pressing are two important processes used in the production of all kinds of metal objects, from simple components for consumer products to complex pieces for aerospace. To create a desired shape, the material is forced to flow and deform, either through repetitive hammer strikes or high force pressing in a die.
The forging and pressing processes each have their own specific characteristics and parameters, but both processes can be vulnerable to concerns related to propagation of cracks. Small cracks can result in the product not meeting desired specifications and crippling further machining operations. Large cracks can often result in premature product failure, risk to the operators and even complete destruction of the work piece.
It is thus of utmost importance to understand and anticipate the occurrence of cracks and take preventive measures. This article provides an overview of the possible causes of cracks in forging and pressing and outlines a variety of potential solutions that can be implemented to reduce the likelihood of occurrence.
Causes of Cracking
The cracking of any material is a complex phenomenon, which is dependent on the specific location, material type and the interactions between the material and the environment. In the context of forging and pressing, failure by crack propagation can often be attributed to the material properties, such as metallurgical structure, grain size and inherent impurities, or to external sources such as temperature differences or die misalignment.
Metallurgical Structure
When dealing with forging or pressing operations, microstructural features and the grain size of the material are of utmost importance as they greatly determine the behaviour of the material under high pressure and strain. Furthermore, the microstructural integrity of material is often affected by heat treatments and other treatments applied to the material prior to deformation.
Grain Size
Grain size is also important in determining the behaviour of a material in the forging or pressing process. If the grain size is large enough, the material can become brittle and crack under a high strain. The solution is to use small grain size, which is more resistant to cracking.
Inherent Impurities
Impurities are another cause of failure that can affect the forging or pressing process. Impurities, such as iron and sulphur, can weaken the material, making it more prone to cracking, especially at elevated temperatures.
External Sources
Temperatures play a key role in the forging and pressing processes. If the temperature of the material is not uniform, the material can be strained unevenly due to the different coefficients of expansion, causing a crack to form. Furthermore, temperature differences can cause the die to become misaligned, which can also lead to cracking.
Preventive Measures
When operating forge or press facilities, it is essential to take measures to ensure that the environment and material specifications are ideal for the process. The following are a few preventive measures to help reduce the chance of cracking.
Material Selection
The right material should be selected for the specific job. The metallurgical structure, grain size and purity of the material should all be considered in order to assure the best results in the forging process.
Heat Treatments
Heat treating is a common practice when forging and pressing metal, as it can improve the mechanical properties of the material and help reduce the occurrence of cracking.
Die Alignment
It is important to make sure that the die is properly aligned before each forging or pressing operation. Any misalignment can increase the likelihood of cracking.
Temperature Control
Maintaining a uniform temperature in the entire working area is essential in order to avoid uneven strain due to temperature differences.
Conclusion
The forging and pressing processes are vulnerable to cracking due to a variety of factors, such as material properties, misalignment of the die and temperature differences. It is important to take preventive measures such as careful material selection, heat treatment and die alignment to reduce the severity and occurrence of cracks. By following these preventive measures, the risks associated with the forging and pressing processes can be significantly reduced.
