*6.1.9.1 Proposed solution*

The scheduling issue is very important, especially with the rapid development of MAM method. Existing production planning and scheduling approach should be developed based on preliminary heuristic studies and models generated from this heuristic study. The scheduling should include all the sections of manufacturing system ranging from ordering the raw materials to delivering the metal parts to the customers. Based on that, scheduling system related to all sectors of MAM method with forecasting technologies can be used to organize the production line on MAM with optimal results.

### *6.1.10 Energy consumption*

Energy consumption in MAM method is important to keep the sustainability of the MAM printing. However, it is affecting the microstructure and mechanical properties of the printed parts especially with metal 3D printing process that requires high source of energy, such as EBM process. This issue has a significant influence on the quality of the part.

## *6.1.10.1 Proposed solution*

The relationship between energy consumption and printed metal parts with microstructure and mechanical properties should be analyzed to approach the solution of this problem. This solution can be implemented by using variable optimal energy density for every MAM process that depends on factors, such as part size, part geometry, and material used with strategies to reduce this consumption. Then, the variable optimal energy density map can be generated according to the characteristics of the part, 3D printing machine used, and used material. Therefore, the variable optimal energy used can be specified from the CAD model of the part. This can be done by inserting this CAD model on previously created software responsible for calculating the map of optimal energy density for the 3D printed metal part. This method of using the optimal energy might be useful to remove the undesirable mechanical properties and microstructure from metal printed part.

**251**

*6.2.2 Fatigue*

*An Investigation of the Metal Additive Manufacturing Issues and Perspective for Solutions…*

ity of the printed metal parts. Some of these defects will be discussed next.

back previous layer for both PBF and DED MAM categories [11].

Residual stress is a stress stored inside the metallic part in different ways. For example, forging on the surface of some plate creates residual stress which is required to reinforce the plate. Laser peening creates desired compressive residual stress in metal part. Similarly, residual stress is stored in the metal after casting stock material which is mostly undesirable. Therefore, the residual stress can be desirable or undesirable. In the MAM method, one of the main defects is influencing the printed metallic parts with undesirable residual stress which may lead to premature failure. Residual stress in MAM method can lead to distortion failure, changing in tolerance, fracture, fatigue, and delamination. A lot of literature review discussed this problem and it is the focus of leading researchers. Several factors may cause the residual stress in MAM parts, such as rapid heating rate, rapid solidification with high cooling, and melting

It is advantageous to use well maintained heat treatment machine (vacuum furnace) to remove the residual stress from the MAM parts. Based on the author's understanding, melting back of the previous layer is the main issue which generates the residual stress. This melting back can be reduced by reducing the pace of heating while building the next layer. Reducing the melting back can be done by installing a cooling unit to reduce the heat between layers, such as air jet to reduce the heat generated when a new layer is being melted and laying down on the previous one. Also, using variable building direction might help in reducing heat accumulation in one direction. More comprehensive study should be conducted to build inspection system rather than in-situ method. This inspection system is used to analyze the melting back spot and figure out where it exists and assign permanent solution for that. Moreover, post process control (a type of heat treatment control) should be applied on the printed metal parts which contain residual stress after inspection.

Fatigue is a damage in a solid material which causes it to weaken. The main reason for fatigue is fluctuating (cyclic) loads applied on metal parts which causes damage at the end and failure in the parts. Several parameters, such as surface finish, shape and geometry of the part, grain size and direction, functionality of the part, load type, part size, corrosion, temperature, and surface treatment cause fatigue. For the MAM method, the temperature is the most affective parameter to cause fatigue in printed metallic parts. Some literature studies have been performed on this subject, especially on multiaxial fatigue in many industries for small and medium size of metallic parts [1].

The most common challenges and issues that the MAM method faces have been discussed in the previous sections. MAM is a manufacturing process, and every process has its pros and cons. The part produced by MAM also has parameters and defects that may affect the functionality of the part and lead to the failure. These defects are residual stress, fatigue, porosity, variation in mechanical properties, surface oxidation, cracks, delamination, variation in grain size, and heat accumulation. Similarly, parameters such as microstructure, building direction, surface roughness, and powder particle size may lead to these defects or affect the quality and reliabil-

*DOI: http://dx.doi.org/10.5772/intechopen.93630*

**6.2 MAM defects**

*6.2.1 Residual stress*

*6.2.1.1 Proposed solution*

*An Investigation of the Metal Additive Manufacturing Issues and Perspective for Solutions… DOI: http://dx.doi.org/10.5772/intechopen.93630*

## **6.2 MAM defects**

*Concepts, Applications and Emerging Opportunities in Industrial Engineering*

Studies should be developed on the required inspection methods. Internal inspection needs to be performed during the printing process. It will act like a monitoring system during the process. In other words, layer inspection should be performed inherent to comparison with slandered. In layer inspection, the defects can be detected when it occurs. Let us assume that a very expensive and complex part is being printed. If there are some defects like undesired mechanical properties or porosities in the middle of printing, it would be wise to stop the process and fix the problem rather than

While increasing the demand and purchasing the MAM parts, the scheduling and nesting processes of metal parts to be printed plays a major role in manufacturing cost. It is beneficial in different ways, such as reducing the operational cost, reducing the parts price, and increasing profit for factories. This issue is also important in supply chain to schedule delivering or requesting metal parts. A very

The scheduling issue is very important, especially with the rapid development of MAM method. Existing production planning and scheduling approach should be developed based on preliminary heuristic studies and models generated from this heuristic study. The scheduling should include all the sections of manufacturing system ranging from ordering the raw materials to delivering the metal parts to the customers. Based on that, scheduling system related to all sectors of MAM method with forecasting technologies can be used to organize the production line on MAM

Energy consumption in MAM method is important to keep the sustainability of the MAM printing. However, it is affecting the microstructure and mechanical properties of the printed parts especially with metal 3D printing process that requires high source of energy, such as EBM process. This issue has a significant

The relationship between energy consumption and printed metal parts with microstructure and mechanical properties should be analyzed to approach the solution of this problem. This solution can be implemented by using variable optimal energy density for every MAM process that depends on factors, such as part size, part geometry, and material used with strategies to reduce this consumption. Then, the variable optimal energy density map can be generated according to the characteristics of the part, 3D printing machine used, and used material. Therefore, the variable optimal energy used can be specified from the CAD model of the part. This can be done by inserting this CAD model on previously created software responsible for calculating the map of optimal energy density for the 3D printed metal part. This method of using the optimal energy might be useful to remove the undesirable

mechanical properties and microstructure from metal printed part.

rejecting the part after the expensive and time-consuming process is finished.

little literature has addressed this issue since it is still new issue [8].

*6.1.8.1 Proposed solution*

*6.1.9 Scheduling*

*6.1.9.1 Proposed solution*

with optimal results.

*6.1.10 Energy consumption*

*6.1.10.1 Proposed solution*

influence on the quality of the part.

**250**

The most common challenges and issues that the MAM method faces have been discussed in the previous sections. MAM is a manufacturing process, and every process has its pros and cons. The part produced by MAM also has parameters and defects that may affect the functionality of the part and lead to the failure. These defects are residual stress, fatigue, porosity, variation in mechanical properties, surface oxidation, cracks, delamination, variation in grain size, and heat accumulation. Similarly, parameters such as microstructure, building direction, surface roughness, and powder particle size may lead to these defects or affect the quality and reliability of the printed metal parts. Some of these defects will be discussed next.

#### *6.2.1 Residual stress*

Residual stress is a stress stored inside the metallic part in different ways. For example, forging on the surface of some plate creates residual stress which is required to reinforce the plate. Laser peening creates desired compressive residual stress in metal part. Similarly, residual stress is stored in the metal after casting stock material which is mostly undesirable. Therefore, the residual stress can be desirable or undesirable. In the MAM method, one of the main defects is influencing the printed metallic parts with undesirable residual stress which may lead to premature failure. Residual stress in MAM method can lead to distortion failure, changing in tolerance, fracture, fatigue, and delamination. A lot of literature review discussed this problem and it is the focus of leading researchers. Several factors may cause the residual stress in MAM parts, such as rapid heating rate, rapid solidification with high cooling, and melting back previous layer for both PBF and DED MAM categories [11].
