Investigating the causes and remedies for porosity defects in the casting process: A review

1. Introduction

In industries, including aerospace, automotive, and medical, complicated parts and components are produced using casting production, which is a commonly utilized technology. During the procedure, molten metal or other materials are poured into a mold, which is then left to cool and solidify before the finished object is removed. This method of manufacturing is known for its ability to produce parts with intricate geometries and near-net shapes, reducing the need for costly machining and other finishing operations. However, the casting process is not without its challenges, and defects can occur due to several root causes. These defects can significantly affect product quality, increase costs, and reduce productivity. Therefore, in order to recognize and create efficient corrective methods to overcome them, it is essential to have a thorough grasp of the casting process, including its different flaws and related core causes.

The article tries to present a thorough analysis of casting manufacturing, concentrating on its numerous processes, related flaws, and solutions to those flaws. Casting manufacturing has been used for thousands of years, and it continues to play a vital role in modern manufacturing. With advancements in technology, the casting process has become more efficient, cost-effective, and versatile. Today, it is utilized to make parts and components for a variety of industries, including consumer products, aircraft, and the automotive and automotive. Despite its numerous benefits, the casting process can still suffer from defects that can significantly impact product quality and performance. Porosity, for example, can cause structural weaknesses and reduce the mechanical properties of the finished product (1). Shrinkage defects can result in dimensional inaccuracies and warping, while surface irregularities can affect the part’s appearance and function.

Therefore, understanding the root causes of these defects and developing effective remedial measures is critical to the success of casting manufacturing. Remedial measures may involve changes in the design of the casting, the selection of materials, or modifications to the casting process itself. This examination will cover the various casting procedures utilized in contemporary production in addition to analyzing casting flaws and corrective actions. Among the most popular casting techniques are sand casting, investment casting, and die casting, each of which has its own benefits and drawbacks (2). By providing a thorough review of these casting processes and their associated challenges, we hope to offer a better understanding of casting manufacturing as a whole.

1.1. Various casting processes

Many different casting processes are employed in contemporary manufacturing. The criteria for the finished product, the material being used, and additional factors such as cost and production volume all influence the process choice. Here are some of the most commonly used casting processes:

● Sand casting: One of the earliest and most fundamental casting processes is this one. It involves pouring molten metal into a mold that has been made from sand. Sand casting is used for both small and large parts and is particularly useful for producing complex shapes and designs (3).

● Investment casting: It is also referred to as lost-wax casting and is creating a wax or plastic model of the required part, which is then covered in a ceramic shell. The remaining ceramic shell is hollow and filled with molten metal after the wax has been melted out. Investment casting is useful for producing parts with high precision and accuracy and is often used for jewelry and other small, intricate parts (4).

● Die casting: Die casting is applying intense pressure to the molten metal as it is being poured into a steel die. This method is especially helpful for generating lots of precise, accurate parts in huge quantities. Die casting is often used for producing parts for the automotive and aerospace industries (5).

● Permanent mold casting: This procedure, often referred to as gravity die casting, is pouring molten metal into a reusable mold composed of steel or another metal. The mold is made to make it simple to remove the finished product. For the production of highly accurate and precise items, such as engine parts and other mechanical components, permanent mold casting is frequently employed (6).

● Centrifugal casting: In this procedure, molten metal is poured into a spinning mold. The molten metal is distributed evenly throughout the mold because of centrifugal force, producing a part with a high density and fine-grained structure. Pipes, tubes, and other cylindrical pieces are frequently made by centrifugal casting (7).

Each casting process has its own unique advantages and limitations, and manufacturers must carefully consider their options when selecting the appropriate casting process for a given application.

1.2. Casting-associated defects

Casting defects can arise during the casting process and can significantly impact the quality of the finished product. Here are some of the most common casting defects:

● Porosity: Porosity occurs when air pockets or voids are formed within the casting during the solidification process. This defect can result in weakened mechanical properties and reduced structural integrity (8).

● Shrinkage: Shrinkage defects occur when the casting solidifies and cools, causing it to contract and form voids or cavities. This defect can result in dimensional inaccuracies and warping (9).

● Surface irregularities: Surface irregularities can occur due to various reasons, including mold erosion, gas porosity, or improper mold coating. This defect can affect the appearance and function of the finished product (10).

● Inclusions: Inclusions refer to foreign materials or impurities that become embedded within the casting. This defect can result in weakened mechanical properties and reduced product quality (11).

● Cold shut: Cold shut defects occur when two streams of molten metal fail to fuse together, resulting in a part with incomplete fusion lines (12).

● Misruns: This defect happens when the molten metal fails to fully fill the mold cavity, leaving behind components that are either wholly or partially unfinished (13).

Identifying and addressing these defects is crucial to the success of casting manufacturing. Remedial measures may involve changes to the casting design, the selection of materials, or modifications to the casting process itself. By taking steps to address these defects, manufacturers can improve product quality and reduce costs, resulting in more efficient and profitable casting manufacturing.

1.3. Casting remedies to overcome

Casting flaws can be fixed with a variety of solutions, which will also raise the caliber of the final product. The following are some of the most popular treatments for casting flaws.

● Porosity can be minimized by using high-quality mold materials, maintaining proper casting temperature, and minimizing turbulence during casting. The use of vacuum-assisted casting can also help to reduce porosity.

● By modifying the casting process parameters, such as the pouring temperature and cooling rate, shrinkage faults can be reduced to a minimum. Reduced shrinkage faults can also be achieved with the use of chilling and risers.

● Surface irregularities can be addressed by improving mold design and maintenance, controlling mold temperature, and using proper mold coatings. The use of vibratory finishing and other surface treatments can also help to improve surface finish and texture.

● Inclusions can be minimized by using high-quality raw materials, maintaining proper casting temperature, and minimizing turbulence during casting. The use of filters and other process controls can also help to reduce the formation of inclusions.

● Cold shut defects can be minimized by optimizing the gating and riser design, adjusting the casting temperature and speed, and using proper mold coatings.

● Misruns can be minimized by optimizing gating and riser design, using proper mold coatings, and ensuring that the casting temperature and speed are properly controlled.

The key to overcoming casting defects is to carefully analyze the root causes of the defects and implement targeted remedies to address them. By continuously monitoring and improving the casting process, manufacturers can achieve higher levels of product quality, consistency, and efficiency.

1.4. Significance of this study

Defects in casting processes can have significant implications on the quality, reliability, and durability of the final product. Therefore, it is critical to comprehend the underlying reasons for casting process flaws and put those causes into practice in order to prevent or reduce them. Here are some of the key significance of defects, root causes, and their remedies in casting processes:

● Quality improvement: Defects in casting processes can result in poor-quality products that may not meet the required standards. Finding the source of these flaws and putting effective fixes in place might assist to raise the standard of the final product (14).

● Cost reduction: Defects in casting processes can lead to scrap and rework, which can increase production costs. Implementing effective remedies to address root causes can help to reduce these costs (15).

● Increased efficiency: The effectiveness of the casting process can be increased by finding the underlying causes of flaws and putting preventative measures in place. This can result in increased productivity and reduced cycle times (16).

● Safety: Some defects in casting processes can pose safety risks to workers and end users of the final product. Implementing effective remedies can help to eliminate or minimize these risks (17).

● Customer satisfaction: Defects in casting processes can lead to dissatisfied customers, which can have a negative impact on business. By addressing the root causes of defects and improving product quality, customer satisfaction can be increased (18).

Defects, root causes, and their remedies in casting processes are significant because they can impact the quality, cost, efficiency, safety, and customer satisfaction of the final product. By understanding and addressing these issues, manufacturers can improve their products and their bottom line.

1.5. Objectives of this study

Gaining a deeper understanding of the numerous types of defects that can happen during the casting process, their underlying causes, and efficient remedies to treat them is the goal of examining faults, root causes, and their remedies in casting processes. Manufacturers may enhance the quality, dependability, and longevity of their cast products while lowering costs and boosting efficiency by comprehending the underlying causes of problems and putting efficient treatments into place. The review should aim to.

● Recognize the various casting process flaws that could appear, such as shrinkage, porosity, cracking, and deformation, among others.

● Understand the root causes of these defects, such as improper gating and risering, poor design, incorrect pouring temperature, or poor material quality.

● Review the various remedies that can be implemented to address these defects, such as modifying the gating and risering design, adjusting the pouring temperature, improving mold quality, or using different materials.

● Evaluate the effectiveness of these remedies in addressing specific defects and improving product quality.

● Provide recommendations for manufacturers to improve their casting processes, including best practices for defect prevention, root cause analysis, and effective remedy implementation.

By fulfilling these goals, the study will be able to offer manufacturers useful perceptions and suggestions for boosting the quality and effectiveness of their casting operations while lowering costs and raising customer satisfaction.

2. Literature review

For the production of complicated objects with excellent surface polish and dimensional accuracy, casting is a popular manufacturing process. However, there are a number of flaws that can arise during the casting process and seriously affect the performance and quality of the final product. In this review, we examine the root causes of casting defects and various remedies that can be implemented to minimize their occurrence.

Porosity is a common defect in casting that results in air pockets or voids within the casting. Porosity can be caused by a variety of factors, including mold materials, casting temperature, and turbulence during casting (19). Remedies for porosity include using high-quality mold materials, maintaining proper casting temperature, and minimizing turbulence during casting. Additionally, the use of vacuum-assisted casting can help to reduce porosity.

Another factor that contributes to porosity is the casting temperature. The metal may not flow effectively if the temperature is too low, which could lead to trapped gas and porosity. On the other hand, if the temperature is too high, it can cause the release of gas from the mold material, resulting in porosity. Therefore, maintaining proper casting temperature is crucial to reduce porosity defects. Turbulence during casting is another factor that can cause porosity. Turbulence can lead to the entrapment of air pockets within the casting, resulting in porosity. Therefore, minimizing turbulence during the casting process can help to reduce porosity defects.

In addition to the above remedies, vacuum-assisted casting is another effective way to reduce porosity. Vacuum-assisted casting uses a vacuum to remove gas from the mold cavity, which reduces the occurrence of porosity. This technique has been reported to be effective in reducing porosity in aluminum, magnesium, and other metals. Another typical casting flaw that can happen is shrinkage. Factors such as the temperature of the pour and the pace of cooling might result in shrinkage faults. Adjusting the casting process’s variables, such as the pouring temperature and cooling rate, can solve shrinkage faults. Reduced shrinkage faults can also be achieved with the use of chilling and risers.

Pouring temperature is a significant factor in causing shrinkage defects. If the pouring temperature is too high, it can cause rapid cooling, which can lead to shrinkage defects due to the rapid contraction of the metal as it cools. On the other side, if the pouring temperature is set too low, the mold may not completely fill and have shrinkage flaws. Therefore, lowering the pouring temperature to the ideal range can aid in lowering shrinkage flaws. Another important element that can result in shrinkage issues is the cooling rate. Shrinkage flaws may result from the metal contracting too quickly due to an excessive cooling rate. On the other hand, if the cooling rate is too slow, it might result in the creation of coarse-grained structures that are vulnerable to flaws brought on by shrinkage. Therefore, controlling the cooling rate to an optimal level can help to reduce shrinkage defects.

Additionally, helpful treatments for shrinking flaws include chills and risers. Chills are metallic objects inserted into the mold to absorb heat and facilitate rapid cooling, which lessens the metal’s contraction and lowers the likelihood of shrinkage flaws. Risers, on the other hand, are reservoirs of molten metal placed near the casting to compensate for the shrinkage of the metal as it cools (20). Using chills and risers can help to reduce the occurrence of shrinkage defects in casting.

Surface irregularities can also occur during casting, resulting in defects such as mold erosion and gas porosity. Remedies for surface irregularities include improving mold design and maintenance, controlling mold temperature, and using proper mold coatings. Additionally, the use of vibratory finishing and other surface treatments can help to improve surface finish and texture.

Inclusions are a type of defect that refers to foreign materials or impurities that become embedded within the casting. Inclusions can be caused by factors such as raw materials and turbulence during casting (21). Remedies for inclusions include using high-quality raw materials, maintaining proper casting temperature, and minimizing turbulence during casting. The use of filters and other process controls can also help to reduce the formation of inclusions.

Cold shut and misrun are two additional defects that can occur during casting. Remedies for cold shut and misrun defects include optimizing gating and riser design, adjusting the casting temperature and speed, and using proper mold coatings (22).

In addition to the defects and remedies discussed above, there are several other types of casting defects that can occur. For example, sand inclusion is a type of defect that results from sand particles becoming trapped within the casting. Remedies for sand inclusion defects include using high-quality molding sand, controlling the sand moisture content, and maintaining proper molding and core-making practices (23).

Another sort of casting flaw is cracking, which can cause cracks or fractures in the casting. Cracking defects can be caused by factors such as improper cooling, thermal stress, and structural defects. Remedies for cracking defects include optimizing cooling and solidification rates, using stress-relieving treatments, and improving the casting design and material selection.

Cracking faults can be caused by a number of important variables, including improper cooling and solidification rates. Thermal shock and cracking problems can result from overly rapid cooling. On the other side, if the pace of cooling is too sluggish, residual stresses may accumulate in the casting and result in cracking flaws. Therefore, optimizing the cooling and solidification rates to achieve a uniform cooling rate throughout the casting can help to reduce cracking defects.

Another important element that might result in cracking faults is thermal stress. When there is a temperature difference between the interior and exterior of the casting, thermal stress develops and can lead to cracking. Thus, thermal stress can be reduced, and cracking faults can be prevented by stress-relieving processes such as annealing or heat treatment. Cracking problems can also be brought on by structural flaws including porosity, inclusions, or cold closes. In addition to acting as stress concentrators, structural flaws can encourage the start and spread of casting cracks. Thus, enhancing the casting design and material choice can aid in reducing structural flaws and avoiding cracking flaws.

A flaw known as warping refers to the casting’s dimensional distortion or deformation. Thermal stress, poor gating and riser design, and unequal cooling rates are a few examples of the causes of warping flaws. Remedies for warping defects include optimizing gating and riser design, using proper cooling techniques, and implementing stress-relieving treatments. Thermal stress is a significant factor that can cause warping defects in casting. During the cooling process, thermal stress can build up in the casting due to differential cooling rates, which can cause the casting to deform or warp. Therefore, it is essential to use proper cooling techniques to minimize thermal stress and prevent warping defects.

Improper gating and riser design can also cause warping defects in casting. Gating and riser design should be optimized to ensure the even distribution of molten metal during casting, minimizing any localized cooling and stress concentrations. Proper gating and riser design can help to reduce warping defects by ensuring a uniform flow of molten metal throughout the casting. Uneven cooling rates can also lead to warping defects in casting. Therefore, it is essential to use proper cooling techniques, such as directional solidification, to ensure even cooling rates throughout the casting. This can help to minimize thermal stress and prevent warping defects.

Stress-relieving treatments, such as annealing or heat treatment, can also help to reduce warping defects by reducing the residual stresses in the casting. These treatments can help to improve the dimensional stability of the casting and prevent warping defects. Warping defects in casting can be caused by factors such as thermal stress, improper gating and riser design, and uneven cooling rates. Optimizing gating and riser design, using proper cooling techniques, and implementing stress-relieving treatments are effective remedies to reduce warping defects in casting.

Finally, the inclusion of slag is another type of defect that can occur in casting processes that involve molten metal. Remedies for slag inclusion defects include using high-quality raw materials, optimizing the casting process parameters, and using effective slag removal techniques (24).

Casting defects can arise due to a range of factors, including materials, design, and process parameters. However, by implementing targeted remedies and continuously monitoring and improving the casting process, manufacturers can reduce the occurrence of defects and achieve higher levels of product quality and consistency.

Another type of casting defect is shrinkage, which occurs when the casting solidifies and contracts, resulting in voids or cavities in the material. Remedies for shrinkage defects include optimizing the cooling rate, increasing the metal temperature, and modifying the alloy composition (25).

Another typical flaw brought on by trapped gas or air bubbles in the casting is porosity. Porosity problems can be fixed by employing the right degassing procedures, improving gating and riser design, and managing the pouring temperature and rate. The remedies for porosity defects include various techniques that aim to minimize the formation of gas or air bubbles during the casting process (26). One of the most effective ways to prevent porosity is by using proper degassing techniques. Degassing involves removing the gases from the molten metal before pouring it into the mold. This can be achieved by using various degassing agents such as nitrogen or argon, which react with the gas bubbles and form insoluble compounds. Optimizing gating and riser design is another effective way to prevent porosity defects. Gating and riser design should be optimized to ensure a uniform flow of molten metal and minimize turbulence during casting. This can help to prevent the formation of gas or air bubbles in the casting.

It is also essential to regulate the pouring temperature and flow rate to avoid porosity flaws. To guarantee a steady flow of molten metal and avoid the creation of gas or air bubbles owing to abrupt temperature fluctuations, the pouring temperature and pace should be controlled. Porosity defects in casting can be prevented by using proper degassing techniques, optimizing the gating and riser design, and controlling the pouring temperature and speed. These remedies can help to minimize the formation of gas or air bubbles during casting and improve the quality and performance of the casting.

In some cases, surface defects such as roughness, pitting, or scaling can occur due to various factors such as mold or core material, gating and riser design, or post-casting processing. Remedies for surface defects include using proper mold and core materials, optimizing gating and riser design, and implementing appropriate post-casting processing techniques such as cleaning or surface finishing (27).

Finally, in some casting processes, such as investment casting, the presence of cracks or defects in the ceramic mold itself can result in defects in the final casting. Remedies for mold defects in investment casting include using high-quality mold materials, optimizing the mold-making process, and using proper handling and storage techniques (28).

Overall, while casting defects can be caused by a variety of factors, there are a range of remedies that can be implemented to reduce their occurrence and improve casting quality. By continuously monitoring and optimizing the casting process, manufacturers can minimize defects and achieve higher levels of product quality and consistency.

In addition to the specific defects and their remedies, there are also some general strategies and techniques that can be used to improve casting quality. To reduce turbulence and guarantee good mold filling, it is critical to maintain a steady pouring temperature and rate. Additionally, by ensuring uniform and controlled metal flow throughout the casting, optimizing the gating and riser design can help to prevent flaws like porosity or shrinkage (29).

The casted product’s quality also depends on the purity and quality of the metal utilized. The mechanical qualities and general quality of the casting can be impacted by impurities and inclusions in the metal, which can result in flaws such as porosity or cracking. In order to remove any impurities or pollutants, it is crucial to use high-quality metal and follow the right cleaning and preparation procedures.

To prevent these defects, it is important to use high-quality metal that is free from impurities and inclusions. This can be achieved by sourcing metal from reputable suppliers who adhere to strict quality control measures during the production process. Proper cleaning and preparation techniques should also be implemented to remove any impurities or contaminants from the metal before casting. These techniques can include mechanical cleaning, chemical cleaning, and thermal treatments, such as annealing or heat treatment. Additionally, any residual impurities or inclusions during the casting process can be eliminated with the aid of filters and gating devices. While gating systems can be created to stop the flow of pollutants into the mold cavity, filters can be employed to remove solid particles.

To avoid flaws and guarantee the quality of the finished product, the metal used in casting must be of high quality and cleanliness. Choosing high-quality metal for the casting and using the right cleaning and preparation methods will help to get rid of any impurities or contaminants and enhance the casting’s overall quality and performance.

To discover and address any flaws or quality problems, it is crucial to regularly monitor and test the casting process and the finished product. Defects such as porosity, shrinkage, or cracks can be found using methods including X-ray inspection, ultrasonic testing, and visual inspection. Early detection and resolution of these problems by manufacturers can enhance the overall consistency and quality of their castings (30). To guarantee that the castings satisfy the necessary quality requirements, the casting procedure and the finished product must be continuously observed and tested. Manufacturers have access to a variety of testing methods, including visual inspection, ultrasonic testing, and X-ray inspection, which they can use to identify and analyze any flaws or quality problems. These methods can be used to find flaws in the casting, such as porosity, shrinkage, or cracks, and to assess their severity and location. By addressing these issues early on, manufacturers can implement the necessary remedies and improve the overall quality and consistency of their castings. Additionally, regular testing and analysis can help manufacturers to identify any trends or patterns in the defects, which can lead to further optimization of the casting process and improved quality control measures.

In conclusion, while casting defects can be a significant challenge in the manufacturing process, there are a range of remedies and strategies that can be used to minimize their occurrence and improve casting quality. By focusing on factors such as metal quality, gating and riser design, and process monitoring and testing, manufacturers can achieve higher levels of product quality and consistency and ultimately improve customer satisfaction and competitiveness.

Numerous other research and articles examined casting flaws and solutions in addition to the literature reviewed above and examined how to employ grain refiners and inoculants to enhance the mechanical characteristics of cast aluminum alloys while lowering the likelihood of flaws. They discovered that utilizing these materials enhanced mechanical characteristics and decreased porosity and other flaws (31).

Another study looked at how to make casting processes better and have fewer flaws by using computer simulation and optimization approaches. They discovered that by enhancing the gating and riser designs as well as other process variables, they could lessen the incidence of flaws such as porosity and shrinkage and raise the consistency and general quality of the castings (32). The casting process can be analyzed and optimized using computer simulation and optimization techniques, which can help to lower the likelihood of faults and raise the caliber of the finished product. Manufacturers can model the casting process and pinpoint areas for improvement by employing tools such as computer-aided engineering and finite element analysis. Manufacturers can enhance the general quality and uniformity of their castings by optimizing the gating and riser design as well as other process variables such as the pouring temperature and cooling pace.

According to this study, casting problems such as porosity and shrinkage can be less frequently encountered by applying computer modeling and optimization approaches. The flow of the molten metal was improved by identifying and correcting hot spots and by optimizing the riser and gating designs. The use of computer simulation and optimization techniques can also help manufacturers to reduce the number of physical prototypes needed for testing, saving time and costs in the development process. The use of computer simulation and optimization techniques can help to improve the casting process and reduce defects, resulting in higher quality and more consistent castings.

Additionally, there is ongoing research into the use of advanced materials and technologies to further improve casting quality and reduce defects. For example, another study investigated the use of a 3D-printed ceramic core in the investment casting of titanium alloys and found that this approach led to improved surface quality and reduced defects such as surface cracks. This can lead to improved product quality, lower production costs, and increased competitiveness in the market (33). To fully realize the potential of these cutting-edge materials and technologies, however, and to guarantee their scalability and affordability for industrial-scale production, more research and development is required.

Overall, the literature on casting defects and remedies is extensive, and there are many different approaches and techniques that can be used to improve casting quality and reduce defects. By continuing to explore and develop these approaches, manufacturers can improve their competitiveness and meet the growing demand for high-quality, reliable castings in a range of industries.

2.1. Novelty and research gap

The novelty of the proposed research on defects, root causes, and remedies in the casting process lies in its comprehensive review of the literature, which encompasses a wide range of casting defects, their root causes, and various remedies to overcome them. The study aims to identify research gaps in this field and provide insights for further research to overcome these gaps.

One potential research gap that the proposed study could address is the lack of comprehensive studies on the effectiveness of various remedies for specific casting defects. While several studies have investigated the use of process optimization, alloy modification, coatings, and additives as remedies, there is a need for more research that focuses on comparing the effectiveness of these remedies for specific casting defects. This can help identify the most effective remedy for a given defect and provide a more targeted approach to quality improvement in the casting process.

Another potential research gap is the limited research on the use of emerging technologies, such as machine learning and artificial intelligence, to improve casting quality and reduce defects. These technologies have the potential to provide more accurate predictions of casting defects and enable real-time monitoring and adjustment of process parameters. In order to fully explore the potential of these technologies for enhancing casting quality and lowering faults, more research is required.

The proposed study aims to provide a comprehensive review of the literature on casting defects, root causes, and remedies, and identify research gaps that can guide future research in this field.

3. Testing and evaluation of casting defects

Casting defects can be detected and evaluated through various testing methods. The following are some common testing and evaluation techniques used for casting defects.

3.1. Visual inspection

This is the simplest and most common method for detecting casting defects. A visual inspection involves examining the surface of the casting for any irregularities or abnormalities, such as cracks, porosity, or surface roughness. Visual inspection is the most basic and common method of inspecting casting defects. It involves a thorough examination of the surface of the casting using the naked eye or magnifying tools such as magnifying glasses, microscopes, or borescopes. Visual inspection can be performed before or after any post-casting treatments such as machining or surface finishing (34).

During visual inspection, the inspector examines the casting for any visible signs of defects such as cracks, voids, inclusions, shrinkage, or surface roughness. The inspector must have sufficient knowledge of the casting process, material properties, and casting defects to identify any issues. The inspector may also compare the casting to a standard or reference casting to check for deviations from the intended design. Visual inspection can be performed in different lighting conditions and angles to detect surface irregularities. Inadequate lighting or poor surface preparation can make it difficult to detect surface defects, so proper illumination and surface preparations are crucial. The casting’s surface should be clear, dry, and devoid of any dirt or coatings that could conceal flaws (35).

The results of visual inspection are often recorded using visual aids such as photographs, sketches, or written reports. If any defects are found during visual inspection, further testing and evaluation may be necessary to determine the severity and potential impact of the defect on the casting’s performance. Visual inspection is a simple yet effective method of detecting casting defects. It is an essential part of the casting quality control process and should be performed by qualified personnel with adequate training and knowledge of casting defects. Proper illumination and surface preparation are critical to ensure accurate defect detection. The results of visual inspection should be properly documented to ensure traceability and quality assurance.

3.2. Radiographic testing

In radiography, X-rays or gamma rays are used to look for internal casting flaws such as shrinkage, cracks, and porosity. The magnitude and seriousness of the flaws can be determined by examining the radiography pictures. A non-destructive testing technique called radiographic testing is used to find interior flaws in castings. It involves creating a radiographic image of the casting using X-rays or gamma rays. Defects that might not be evident to the human eye, including cracks, inclusions, porosity, and shrinkage, can be found through radiographic examination (36).

Placing the casting between an X-ray source and a film or digital detector is required for radiographic testing. The X-rays pass through the casting and create a shadow image on the detector. The density of the shadow image depends on the thickness and density of the casting material, as well as the presence and size of any defects. The radiographic image is then analyzed by a trained technician or inspector. Any casting flaws can be seen in the photograph, including their location, size, and degree of severity. The technician can compare the results to acceptance criteria and standards by using image analysis tools to quantify the size and depth of any flaws (37). Radiographic testing requires careful preparation and safety precautions to protect personnel from radiation exposure. The casting must be positioned correctly, and the exposure time and radiation intensity must be controlled to produce a clear and accurate image. The radiographic equipment must be calibrated and maintained to ensure consistent and reliable results (38). Radiographic testing is a valuable method for detecting internal defects in castings. It is an essential part of the casting quality control process and should be performed by trained and qualified personnel with adequate knowledge of radiographic testing principles and safety procedures. The results of radiographic testing should be properly documented and analyzed to ensure the casting meets the required standards and specifications.

3.3. Ultrasonic testing

High-frequency sound waves are used in ultrasonic testing to find flaws in internal castings. Small flaws such as porosity and cracks can be found using this procedure, which is extremely helpful. A non-destructive testing technique called ultrasonic testing is used to find internal flaws in castings. It includes penetrating the casting material with high-frequency sound waves in order to find any alterations in the waves’ velocities or amplitude brought on by flaws such as inclusions, porosity, or cracks.

A transducer that sends high-frequency sound waves into the casting material is used in the ultrasonic testing procedure. Through the material, the sound waves travel and then bounce back to the transducer, where they are picked up and turned into an electrical signal. After then, the signal is examined by a skilled technician or inspector to look for any alterations that would point to a flaw (39). The technician can assess all kinds of problems using a variety of ultrasonic testing methods. For instance, in pulse-echo testing, sound waves are pulsed into the casting, and the time it takes for the wave to return to the transducer is recorded. The location and size of casting faults can be found using this technique. Utilizing two transducers to transmit sound waves through the casting from opposing sides is another method known as through-transmission testing. This technique can find flaws such as voids or fissures that go all the way through the casting (40). Ultrasonic testing requires careful preparation and safety precautions to ensure accurate results and protect personnel from exposure to high-frequency sound waves. The casting must be cleaned and prepared, and the ultrasonic equipment must be calibrated and maintained to ensure accurate results (41). The technician must be trained and qualified to perform ultrasonic testing and analyze the results.

Ultrasonic testing is a valuable method for detecting internal defects in castings. It is an essential part of the casting quality control process and should be performed by trained and qualified personnel with adequate knowledge of ultrasonic testing principles and safety procedures (42). The results of ultrasonic testing should be properly documented and analyzed to ensure that the casting meets the required standards and specifications.

3.4. Magnetic particle testing

Casting flaws including fractures and porosity are found using magnetic particle testing on the surface and close to the surface. This technique includes coating the casting’s surface with iron particles before applying a magnetic field to it. Any magnetic leakage fields created by flaws will draw the particles to them. Casting surface and near-surface imperfections can be found using the non-destructive testing technique known as magnetic particle testing. To find flaws including cracks, laps, seams, and porosity, it uses magnetic fields and iron oxide particles.

The casting is magnetized during the magnetic particle testing process utilizing a magnetic field. After that, the casting’s surface is covered with a ferromagnetic powder, typically made up of iron oxide particles. Any magnetic flux leakage brought on by surface or near-surface flaws attracts the particles, which makes the flaw obvious. Depending on the casting material and the sort of flaw being found, the particles can be applied either dry or wet. Dry particles are applied to non-porous surfaces, while wet particles are used to detect defects in porous materials such as cast iron (43).

Depending on the size and shape of the casting, other methods, such as yokes, prods, or coils, can be used for the magnetic particle testing process. To carry out magnetic particle testing and correctly interpret the data, the technician or inspector needs to be trained and competent. Magnetic particle testing requires careful preparation and safety precautions to ensure accurate results and protect personnel from exposure to magnetic fields and iron oxide particles. The casting must be cleaned and prepared, and the magnetic particle equipment must be calibrated and maintained to ensure accurate results. Casting surface and near-surface flaws can be found via magnetic particle testing (44). It is an essential part of the casting quality control process and should be performed by trained and qualified personnel with adequate knowledge of magnetic particle testing principles and safety procedures. The results of magnetic particle testing should be properly documented and analyzed to ensure the casting meets the required standards and specifications.

3.5. Dye penetrant testing

In non-magnetic materials, surface fractures and porosity are found via dye penetrant testing. In this technique, a fluorescent or colored dye is applied to the casting’s surface, and then a developer is used to remove any dye that has seeped into surface pores or fractures. A non-destructive testing technique called dye penetrant testing is used to find surface flaws in castings. It entails the application of a penetrating liquid to the casting’s surface, typically a colored dye (45). Any surface flaws are penetrated by the dye, which is then dragged out with the help of a developer to produce a visual indication of the flaw.

There are various steps in the dye penetrant testing procedure. Cleaning the casting’s surface in order to get rid of any impurities or dirt is the first step. After applying the penetrant to the surface, any surface flaws are given time to absorb it. Following the removal of the extra penetrant, a developer is used to pull the penetrant from any surface flaws. Depending on the type of fault being found and the lighting in the testing area, visible or fluorescent dyes can be used for dye penetrant testing (46). While fluorescent dyes require the use of UV light to identify the signal of the defect, visible dyes are employed in well-lit areas.

The technician or inspector must be trained and qualified to perform dye penetrant testing and interpret the results accurately. The testing environment must be properly controlled to ensure accurate results and protect personnel from exposure to the penetrating liquid. In conclusion, dye penetrant testing is a valuable method for detecting surface defects in castings. It is an essential part of the casting quality control process and should be performed by trained and qualified personnel with adequate knowledge of dye penetrant testing principles and safety procedures. The results of dye penetrant testing should be properly documented and analyzed to ensure that the casting meets the required standards and specifications.

3.6. Tensile testing

The mechanical characteristics of casting, including strength, ductility, and elongation, are assessed through tensile testing. This technique entails measuring the force necessary to cause the failure after subjecting a sample of the casting to a controlled load until it fails. In order to ascertain the mechanical characteristics of castings, such as their ultimate tensile strength, yield strength, and elongation, tensile testing is a destructive testing technique. It entails putting a test specimen under tension until it breaks, which is often a small portion of the casting.

The tensile testing process involves several steps. The first step is to prepare the test specimen by cutting it from the casting and removing any surface defects or irregularities. The test specimen is then placed in the jaws of a tensile testing machine, which applies a uniaxial tensile load to the specimen (47). The machine measures the force needed to stretch the specimen and its corresponding elongation when the load is applied. The casting’s mechanical characteristics are computed using the load and elongation data.

Depending on the application and the casting’s needs, tensile testing can be carried out at ambient temperature or at high temperatures. The testing environment must be properly controlled to ensure accurate results and protect personnel from any hazards associated with the testing process. Tensile testing is an important part of the casting quality control process, as it provides valuable information about the casting’s mechanical properties and performance under load. The results of tensile testing should be properly documented and analyzed to ensure that the casting meets the required standards and specifications.

In conclusion, tensile testing is a valuable method for determining the mechanical properties of castings. It is a destructive testing method and should be performed on a representative sample of the casting. The testing should be performed by trained and qualified personnel with adequate knowledge of tensile testing principles and safety procedures. The results of tensile testing should be properly documented and analyzed to ensure that the casting meets the required standards and specifications.

3.7. Hardness testing

Testing for hardness is used to determine a casting’s hardness, which can reveal the material’s strength and durability. This technique entails pressing a diamond-tipped indenter into the casting’s surface and determining its depth. A casting’s hardness can be assessed using a non-destructive testing technique called hardness testing. It requires measuring the casting’s resistance to indentation, which is usually accomplished with the aid of a hardness tester. There are various steps in the hardness testing procedure. The first step is to prepare the surface of the casting by cleaning and smoothing it to remove any surface irregularities that may affect the hardness measurement. A small area of the surface is then indented using a hardness tester, which applies a known load to the surface and measures the resulting indentation depth.

The hardness tester can use different scales, such as the Rockwell or Brinell scales, depending on the casting material and the requirements of the application. The test’s hardness result can reveal details about the casting’s characteristics, including its durability and resistance to wear. A representative sample of the casting, or the complete casting, depending on the situation, can be subjected to hardness testing. The testing environment must be properly controlled to ensure accurate results and protect personnel from any hazards associated with the testing process.

Hardness testing is an important part of the casting quality control process, as it provides valuable information about the casting’s properties and suitability for its intended application. The results of hardness testing should be properly documented and analyzed to ensure that the casting meets the required standards and specifications. In conclusion, hardness testing is a useful technique for figuring out how hard castings are. It is a non-destructive testing technique that, if necessary, can be used on both the entire casting and a representative sample. The testing should be performed by trained and qualified personnel with adequate knowledge of hardness testing principles and safety procedures. The results of hardness testing should be properly documented and analyzed to ensure the casting meets the required standards and specifications.

In conclusion, there are various methods for testing and evaluating casting defects, and the choice of method will depend on the type and severity of the defect. A combination of methods may be required to fully evaluate the quality of a casting.

4. Remedies for common casting defects

Casting is a popular manufacturing process used in various industries for producing complex metal components. However, it is not uncommon to encounter defects during casting that can affect the quality and functionality of the final product. Here are some common casting defects and their remedies outlined in Table 1.

In conclusion, casting flaws can materially affect the finished product’s functionality and quality. The use of alloys and additives, temperature management, correct design, gating and riser design, and stress-relieving procedures are some remedies for these flaws. The specific remedy used will depend on the type and cause of the defect.

4.1. Process Optimization

Process optimization is a crucial component of casting that strives to raise the casted product’s caliber and effectiveness. Here are some suggestions for improving the casting procedure:

● Design optimization: Proper design of the casting geometry can improve the quality and efficiency of the casting process. This includes factors such as gating and riser design, parting line location, and fillets and radii.

● Material selection: The selection of the appropriate material for casting can improve the quality and efficiency of the casting process. This includes factors such as material properties, cost, and availability.

● Process parameter optimization: The quality and effectiveness of the casting process can be increased by optimizing process variables such as pouring temperature, mold temperature, cooling rate, and solidification time.

● Simulation and modeling: By forecasting the behavior of the molten metal and spotting potential flaws, simulation and modeling tools can aid in casting process optimization.

● Quality control: By identifying and preventing flaws, quality control procedures including inspection, testing, and analysis can raise the standard and effectiveness of the casting process.

● Process automation: By lowering variability and raising precision, casting process automation can enhance the quality and effectiveness of the casting process.

● Equipment and tooling optimization: The selection of appropriate equipment and tooling can improve the quality and efficiency of the casting process. This includes factors such as the type of furnace, casting machine, and mold materials.

● Lean manufacturing: The implementation of lean manufacturing principles can improve the efficiency of the casting process by reducing waste, improving throughput, and increasing productivity.

● Continuous improvement: Continuous improvement of the casting process involves ongoing monitoring, analysis, and optimization of the process to identify and eliminate inefficiencies and defects.

● Employee training and development: Proper training and development of employees can improve the quality and efficiency of the casting process by increasing their skills and knowledge.

● Environmental impact reduction: Optimization of the casting process can also involve reducing its environmental impact by minimizing waste and emissions, and reducing energy consumption.

● Collaboration and communication: By lowering errors and enhancing coordination, effective collaboration and communication among all parties involved in the casting process can enhance quality and efficiency.

Optimizing the casting process involves a range of factors, including design, material selection, process parameter optimization, simulation and modeling, quality control, process automation, equipment and tooling optimization, lean manufacturing, continuous improvement, employee training and development, environmental impact reduction, and collaboration and communication. By optimizing these factors, the casting process can be improved in terms of quality, efficiency, and sustainability.

4.2. Alloy modification

Alloy modification is an important aspect of casting that involves changing the composition of the alloy to improve its properties and performance. Here are some ways that alloy modification can be used to optimize the casting process:

● Improved mechanical properties: The mechanical characteristics of the casting, such as strength, hardness, and ductility, can be enhanced through alloy change. This can be accomplished by altering the alloy’s composition to improve its microstructure and grain size.

● Improved corrosion resistance: Alloy modification can also be used to improve the corrosion resistance of the casting. This can be achieved by adding elements such as chromium, nickel, or molybdenum to the alloy to enhance its corrosion resistance.

● Improved machinability: Alloy modification can also be used to improve the machinability of the casting. This can be achieved by adding elements such as sulfur or lead to the alloy to make it easier to machine.

● Reduced casting defects: Additionally, alloy modification can be utilized to lessen the prevalence of casting flaws such as porosity, hot ripping, and shrinkage. This can be accomplished by changing the alloy’s composition to enhance its fluidity, rate of solidification, or shrinkage properties.

● Environmental benefits: Additionally, alloy alteration can be employed to lessen the negative environmental effects of the casting process. This can be accomplished by substituting more ecologically friendly elements for poisonous or dangerous ones in the alloy.

● Improved thermal properties: Alloy modification can be used to improve the thermal properties of the casting, such as thermal conductivity and heat resistance. This can be achieved by adding elements such as copper or tungsten to the alloy to enhance its thermal properties.

● Improved wear resistance: Alloy modification can also be used to improve the wear resistance of the casting. This can be achieved by adding elements such as silicon or manganese to the alloy to enhance its wear resistance.

● Reduced cost: Alloy modification can be used to reduce the cost of the casting process by replacing expensive elements with less expensive ones. This can be achieved by adjusting the composition of the alloy to use more abundant or cost-effective elements.

● Improved casting process: Additionally, alloy alteration can be employed to enhance the casting procedure. For instance, the refinement of the alloy’s grain structure with the addition of modest amounts of specific elements can aid to improve its casting qualities.

● Customization: Custom alloys made for particular casting applications can be created through alloy modification. This can be accomplished by modifying the alloy’s composition to satisfy the casting’s particular performance needs.

A versatile tool, alloy modification can be utilized in a number of ways to optimize the casting process. The qualities and performance of the casting can be enhanced, the casting process can be optimized, and the cost of the process can be decreased by changing the alloy’s composition. Alloy modification also allows for customization of the alloy to meet specific casting requirements, making it a valuable tool for manufacturers.

4.3. Use of coatings and additives

Coatings and additives are commonly used in casting to improve the surface finish, prevent oxidation and corrosion, enhance mechanical properties, and reduce casting defects. Here are some ways coatings and additives are used in casting:

● Coatings for mold surfaces: To increase the surface finish of the casting, prevent the casting from sticking to the mold, and lengthen the life of the mold, coatings are added to the surfaces. Graphite, zircon, ceramic, and refractory coatings are common coating materials.

● Coatings for parts: Additionally, coatings are placed on the casting surface to enhance the surface finish and stop corrosion and oxidation. Nickel, chromium, and zinc are frequently used as coating components.

● Release agents: Release agents are used to prevent the casting from sticking to the mold during solidification. Common release agents include silicone-based sprays and powders.

● Additives for improved mechanical properties: The molten metal can be supplemented with silicon, magnesium, and copper to enhance the casting’s mechanical qualities. For instance, silicon can be added to a casting to increase its strength and resistance to wear.

● Additives for reduced casting defects: Casting flaws such as porosity, shrinkage, and hot ripping can be avoided by adding additives such as strontium, titanium, and zirconium to the molten metal.

● Additives for reduced environmental impact: To lessen the casting process’ negative effects on the environment, additives such as bismuth and tin can be added to the molten metal. These substances can take the place of harmful substances such as lead and cadmium.

Coatings and additives are crucial casting process tools. While additives are intended to increase mechanical characteristics, decrease casting flaws, and lessen the casting process’ negative environmental effects, coatings are used to improve the surface quality of the casting and keep it from sticking to the mold. Manufacturers can optimize the casting process to obtain greater quality, efficiency, and sustainability by employing coatings and additives.

5. Conclusion

Porosity is a typical casting flaw that can seriously affect the effectiveness and quality of castings. This review has investigated the causes and remedies for porosity defects in the casting process. The causes of porosity can be attributed to a variety of factors such as gas entrainment, shrinkage, and improper gating and venting. The remedies for porosity defects can be broadly categorized into process control measures, design optimization, and material modification. Process control measures include proper gating and venting, optimized casting parameters, and the use of vacuum or pressure casting techniques. Design optimization includes the use of fillets, chamfers, and uniform wall thickness. Material modification involves the addition of elements such as strontium, beryllium, and titanium to reduce the occurrence of porosity defects.

It is important to note that the effectiveness of each remedy may vary depending on the specific casting process and the type of porosity defect. Thus, a combination of these remedies may be required to achieve optimal results. Identifying the causes of porosity defects and implementing the appropriate remedies is essential for achieving high-quality castings. Through proper process control, design optimization, and material modification, porosity defects can be minimized or eliminated, leading to improved casting quality and performance.

5.1. Practical implications

The investigation of the causes and remedies for porosity defects in the casting process has practical implications for manufacturers in the casting industry. Here are some practical implications:

● Improved quality control: By identifying the causes of porosity defects and implementing the appropriate remedies, manufacturers can improve their quality control processes. This can lead to better product performance, reduced waste, and increased customer satisfaction.

● Increased efficiency: The efficiency of the casting process can be improved by implementing efficient solutions for porosity flaws. This may result in shorter manufacturing times, lower expenses, and greater profitability.

● Enhanced design capabilities: Manufacturing companies can improve their design capabilities by better understanding the causes of porosity flaws. Manufacturers can lower the incidence of porosity problems and enhance the quality of their goods by creating castings with homogeneous wall thicknesses, fillets, and chamfers.

● Sustainable manufacturing: Manufacturers can lessen their influence on the environment by implementing methods for material modification to eliminate porosity defects. Toxic substances such as lead and cadmium, for instance, can be replaced by bismuth and tin to lessen the casting process’ impact on the environment.

● Industry competitiveness: By implementing effective remedies for porosity defects, manufacturers can improve the quality and performance of their castings, making them more competitive in the industry. This can help to increase market share and profitability.

The investigation of the causes and remedies for porosity defects in the casting process has practical implications for manufacturers in the casting industry. By implementing effective remedies, manufacturers can improve their quality control processes, increase efficiency, enhance design capabilities, promote sustainable manufacturing, and improve industry competitiveness.

5.2. Limitation

Despite the important findings on the causes and remedies for porosity defects in the casting process, there are some limitations to the investigation. Here are some limitations:

● Limited scope: This investigation may not have covered all possible causes and remedies for porosity defects in the casting process. Further research may be required to fully understand the complexities of the issue.

● Generalization: The causes and remedies for porosity defects may vary depending on the specific casting process and the type of metal being used. Therefore, the findings of this investigation may not be applicable to all casting processes.

● Experimental validation: While the remedies suggested in this investigation have been reported to be effective in reducing porosity defects, further experimental validation is required to confirm their effectiveness in different casting processes.

● Cost: Implementing some of the remedies suggested in this investigation may increase the cost of the casting process. This may be a limitation for manufacturers who are looking to reduce their production costs.

● Training: Implementing process control measures and design optimization techniques requires skilled labor. Manufacturers may need to invest in training their workforce to effectively implement these remedies.

While the investigation of the causes and remedies for porosity defects in the casting process has provided important insights, there are some limitations to the study. Further research may be required to fully understand the complexities of the issue and to validate the effectiveness of the suggested remedies in different casting processes. Additionally, the cost and training requirements associated with implementing some of the remedies may be a limitation for manufacturers looking to reduce production costs.

5.3. Future scope

The investigation of the causes and remedies for porosity defects in the casting process has opened up several future research avenues. Here are some potential areas for future research:

● Advanced modeling techniques: The investigation of the causes and remedies for porosity defects in the casting process has mainly focused on empirical observations. The use of advanced modeling techniques such as computer simulations can help to better understand the underlying physical phenomena.

● Novel materials: While the investigation has suggested the addition of elements such as strontium, beryllium, and titanium to reduce the occurrence of porosity defects, further research is required to explore the use of novel materials that can improve casting quality and performance.

● Automated process control: Porosity faults can be minimized and the casting process can be made more efficient by implementing automated process control systems. To investigate the possibilities of these approaches in other casting processes, more study is needed.

● 3D printing and additive manufacturing: The casting business could be greatly impacted by the quickly developing technologies of 3D printing and additive manufacturing. The potential of these solutions to lower porosity flaws and enhance casting quality needs more investigation.

● Environmentally friendly remedies: Although the study recommended using material modification techniques to lessen porosity problems, more research is needed to examine the usage of ecologically friendly solutions that can lessen the casting process’s negative environmental effects.

Several new directions for future research have been made possible by the investigation of the causes and treatments for porosity flaws in the casting process. Advanced modeling techniques, novel materials, automated process control, 3D printing and additive manufacturing, and environmentally friendly remedies are potential areas for future research that can significantly impact the casting industry.

Author contributions

SS and SG equally contributed to the ongoing research. SS contributed to the collection, processing, and writing of the manuscript. SG helps in editing and proofreading the manuscript. Both authors contributed to the manuscript and approved the submitted version.

Acknowledgments

We would like to extend our sincere gratitude to everyone who helped with this study endeavor. We would like to start by expressing our gratitude to the people with disabilities who so kindly donated their time and wisdom to share their thoughts on the wheelchair’s layout and functionality. We also acknowledge the assistance and knowledge of our collaborators from IGIT, Sarang, and BPUT, Rourkela in creating the wheelchair prototype. Finally, we would like to thank our research supervisor and colleagues for their crucial advice and assistance throughout the project. This research would not have been achieved without their guidance and experience.

References