Comprehensively summarize the influencing factors of additive manufacturing process

Comprehensively summarize the influencing factors of additive manufacturing process

Based on the introduction of additive manufacturing in the first two chapters, namely, Brief Introduction to the Process Method of Metal Additive Manufacturing Technology and Simple Analysis of the Main Factors Affecting Additive Manufacturing Technology, it can be seen that when using additive manufacturing technology to process workpieces, first select the heat source type, power size, scanning speed and other parameters according to the characteristics of the materials, then place the materials in the processing area through the conveying device, and gradually shape them under the effect of the heat source. Additive manufacturing process is a discontinuous process, and the stability and consistency of the process are the key to its success. The stability and consistency of product processing can only be guaranteed by the combined action of materials, heat sources, technological processes and other factors. During additive manufacturing, the type, power and scanning speed of general heat source are constant, that is, the heat source for material forming is stable and consistent during processing. During the processing, the heat source will act with the powder and the matrix in the formed area at the same time. When the powder is fed by powder spreading, the heat source will act more directly on the powder; The effect between heat source and matrix will become more obvious when direct powder feeding is adopted.

No matter which way the powder is placed in the molding area, the total amount of action of heat source on the powder is stable in the same action area and space. When the heat source acts on the material, it is affected by the action mechanism and the state of the material itself (such as particle size, sphericity, surface state). Therefore, the stability of additive manufacturing process is ultimately determined by the stability and consistency of materials. The better the consistency of materials, the more stable the metallurgical changes of materials during processing, so as to ensure that the changes of materials in the scanning path and the final performance are more stable and consistent. For powder materials, the consistency of properties not only includes the consistency of chemical composition, microstructure, mechanical properties and other conventional properties of materials, but also their morphological characteristics, such as particle size, spherical degree and other factors, are important indicators. The most ideal powder for additive manufacturing should have the same particle size and shape. Due to the limitation of production process and method, it is difficult to use completely consistent materials in actual production, and the powder used for processing is generally mixed with powders of various particle sizes. In order to ensure the stability during processing, the metallurgical changes of this mixed powder during processing should be controlled within a reasonable range.

According to the characteristics of additive manufacturing technology, k is a constant. When Q supply/Q demand=1, it is the most ideal processing state, and the material will not be overheated or under heated under the effect of heat source; When Q supply/Q demand>1, it means that the supply of heat source exceeds the demand during processing, and the excess energy will heat the powder to a temperature higher than the required temperature for molding; When Q supply/Q demand<1, it indicates that the energy supply is insufficient. As the smaller the powder diameter is, the larger the ratio of Q supply/Q demand is under the same conditions of other parameters, that is, the greater the excess energy supply is, the easier overheating occurs in the molding process. Excessive heating may cause excessive melting of materials. If the temperature of the molten pool is too high, the flow of the molten metal in the molten pool will become more complex, which may cause splashing of the molten metal. If the temperature is too high, the alloy elements will be burned more easily, and even lead to the reaction between the elements and the protective gas and the introduction of inclusions. The smaller the diameter and the larger the specific surface area of the powder, the easier it is to agglomerate. The agglomerated powder will greatly reduce the transportability of the powder.

After the metal is melted, it is very easy to spheroidize due to the effect of surface tension. Due to the fast cooling speed during forming, the spheroidization may be completely retained, resulting in a decline in the surface quality of the workpiece, which may lead to processing failure in serious cases. In actual production, it is found that the degree of spheroidization in the processing process increases with the increase of the proportion of fine powder in the powder. When the powder diameter is too large, the energy obtained in the heating process cannot fully heat the powder to the ideal molding temperature, which may lead to incomplete metallurgical changes of materials, affect the bonding force between materials, and reduce the compactness of the workpiece. When the powder diameter reaches a critical value, the molding process will be completely impossible. It can be seen from the change law of the function that in the adjacent area with d0 as the middle, the change of the function is relatively gentle. At this time, the ratio of energy supply to demand deviates from the ideal state relatively little, which is conducive to maintaining the stability of the additive manufacturing process. It can be inferred that the particle size distribution of powder materials for additive manufacturing should be within a relatively narrow range. This is consistent with the actual situation that the particle size of powder for additive manufacturing is generally 200~500 meshes.

To sum up, Qinhuangdao zhongwei Precision made the following three conclusions on additive manufacturing technology:

1. Additive manufacturing is a new forming technology, and materials are the main factors that restrict the wide application of additive manufacturing technology.

2. Powder materials for additive manufacturing are essentially the same as powder materials for powder metallurgy, but their particle size distribution requirements are more strict and need to be controlled within a narrow range.

3. The particle size and particle size distribution of powder for additive manufacturing are determined by the type of heat source and molding parameters.

For more information about metal powder metallurgy, please consult Qinhuangdao Zhongwei Precision