Aluminum castings (metal products manufactured by melting aluminum and pouring it into a mold), with their light weight and high corrosion resistance, are used in many fields such as automotive, aviation, industrial machinery, and housing equipment. Among them, in the automotive field, their application to parts that require reliability under severe durability conditions, such as engine parts and wheels, is expanding, and the demand for aluminum castings in the overall market is on a steady rise.

In this trend of expanding applications and increasing performance, the “quality challenges of aluminum castings” are unavoidable. Aluminum casting is easily affected by many variables such as mold filling, solidification, alloy component management, and the influence of temperature and humidity, and the challenge of achieving “zero defects” is not straightforward. On the other hand, defects such as dimensional defects, porosity (gas holes), cracks, and inclusions are directly linked to the risk of impairing the safety and performance of the product, and ultimately the brand value.

Conventional quality control was centered on “pre-shipment inspection,” but that is no longer sufficient. Modern quality control requires the perspectives of “prevention” and “optimization.” Specifically, integrated management across the entire process is required, from stabilizing melting and casting conditions, improving equipment and mold design, developing inspector skills and work environments, to operating traceability records.

This article systematically explains the particularly important aspects of “quality control in aluminum casting.” We will introduce practical knowledge and abundant examples, covering the types of defects and their causes, control points in each process, inspection technology, development of skills and factory environments, and even quality control case studies at overseas bases (Vietnam).

Quality is not built in a day. Daily efforts and company-wide awareness reform are the foundation that supports the creation of high-quality, high-reliability castings. Please use this for your company’s quality improvement and for evaluating outsourcing partners.

In the manufacturing of aluminum castings, the three most frequent and serious quality problems are “porosity,” “cracks,” and “inclusions.” These are directly related to the functionality and safety of the product and can become a cause for claims and returns, so it is important to understand the mechanism of their occurrence and to take countermeasures at an early stage.

“Porosity” refers to bubble-like cavities formed inside or on the surface of a casting, which significantly impairs the strength and airtightness of the product. Pinhole (micro-cavities) are difficult to confirm with the naked eye, and their discovery through non-destructive inspection (X-ray, CT, etc.) is mainstream. Blowholes are relatively large and may be discovered during post-machining inspection.

“Cracks” that occur during the cooling process after casting or during machining are defects that cause fatal damage to the durability and functionality of the casting. Hot tears are caused by stress concentration at high temperatures, and cold cracks occur due to shrinkage and external forces after solidification.

“Inclusions” are oxides or non-metallic foreign substances mixed into the aluminum casting, which cause a decrease in casting strength and machining problems. In particular, oxide films (non-metallic inclusions) are easily generated by agitation of the molten metal or contact with the atmosphere, and if they are trapped inside the casting, the risk of quality degradation increases.

The quality of aluminum casting is greatly influenced by the skillfulness of management at each stage of the manufacturing process. Here, we will explain the management perspectives in the three main phases: “Melting and Casting,” “Solidification,” and “Post-processing.” Since each process is closely related, a perspective of overall optimization is essential.

It is often said that much of the casting quality is determined “at the time of melting.” If the management of molten aluminum, especially temperature and atmosphere, is lax, it can cause porosity and inclusions, and the flow into the mold will also become unstable.

In the solidification process, the temperature gradient and cooling rate are directly linked to the occurrence of defects. Excessive speed differences or deviations become a hotbed for shrinkage porosity and cracks.

In the post-processing stage, important treatments are performed that affect the final accuracy and durability of the product.

To stably supply high-quality aluminum casting products, a high level of maintenance is also required in the post-manufacturing inspection process. It is essential to build a system that goes beyond mere “detection of defective products” to early detection of abnormal trends and feedback for improving manufacturing conditions.

Since defects such as porosity, cracks, and inclusions inside aluminum castings cannot be judged from the outside, Non-Destructive Testing (NDT) is essential.

Manual visual inspection is still an important process, but the challenge is the subjectivity and fatigue effect that comes with relying on the “human eye.” Therefore, it is required to clarify visual inspection standards and to maintain the inspection environment.

Ensuring the accuracy of various measuring instruments used for product dimension and strength evaluation is a core requirement in certification standards such as ISO9001.

No matter how precise the equipment or how strict the inspection system, what ultimately determines the “difference in quality” is the “people” working on-site and the “environment” in which they work. The impact of education level, work consciousness, and factory 5S activities on quality is greater than you can imagine.

There is a big difference in the ability to detect abnormalities and the ability to propose improvements between workers who have a systematic understanding of quality control basic knowledge and improvement methods and those who do not.

In the casting workplace, invisible environmental factors (temperature, humidity, dust, salt) are directly linked to the quality of the product. In particular, aluminum is prone to white rust (corrosion), which is a risk factor in terms of both appearance and function.

Tidiness and orderliness on-site (5S) may seem unrelated to quality at first glance, but it is the first step in preventing causes of defects such as foreign object contamination, tool failures, and procedural errors.

As cost competition intensifies, the selection of Southeast Asian regions such as Vietnam and Thailand as procurement sources for aluminum castings is progressing. However, overseas production is also accompanied by concerns about “quality uncertainty.” What is required is the management ability to reproduce “Japan Quality” globally.

At Daiwa Light Alloy Industry Vietnam (our Vietnam factory), we operate with the same quality standards as our Japan headquarters, based on ISO9001. Even in aluminum casting in Vietnam, we thoroughly implement Japanese-style QC methods.

As a result, the following results have been obtained at our Vietnam site:

What is particularly emphasized in the ISO standard is “record maintenance and traceability.” At our company, we systematically store all records, from calibration records of various inspection equipment, work logs, to improvement proposals, and have a system in place that can immediately respond to external audits.

In global procurement, to prevent quality problems, it is important to clarify the “criteria for selecting overseas suppliers“ before starting a transaction. The following are the quality-related checklist items recommended by our company:

There is no perfection in quality control. No matter how carefully you design and manufacture, the “unexpected” can always happen on-site. However, what is important is the attitude of “what to learn from failure and how to prevent recurrence.” Here are two real-life examples.

In a switch case for power equipment, a serious problem occurred during the initial mass production where the defect rate due to a mix of porosity and shrinkage porosity exceeded 80%. The cause was that the casting plan was not suitable for the product shape, and cooling delay was concentrated in the central part. Gas and metal were unevenly distributed inside the casting, causing a chain of defects.

The following three countermeasures were taken:

As a result, the defect rate of the product was improved to 20% or less at once, and subsequent mass production was also stabilized. This became a case that made us re-recognize the importance of “design for manufacturability (DFM)” in the preliminary stage.

On the other hand, in a prototype project for an automotive exhaust cooling part, achieving both development speed and quality was a challenge. High pressure resistance was required in the harsh operating environment around the engine, while the development period was a tight condition of only 3 weeks.

Our company handled all processes from wooden pattern design → casting → machining → pressure resistance inspection in-house, and built the following system:

As a result, we received high praise from the customer, who said, “quality, speed, and cost were all in place,” which also led to an order for mass production development.

As these cases show, the flow of not neglecting failures, but visualizing the causes and connecting them to improvements is the foundation of “strong quality.”

Quality control of aluminum castings is not just about “inspection” to reject defective products. It requires “cross-functional improvement of casting quality” through all processes from design, casting, machining, inspection, to shipping.

This article has explained from multiple perspectives the types and causes of defects, control points for each process, inspection systems, on-site environment, and international quality対応 at our Vietnam base. Here, we will once again summarize the three key points in quality control.

To improve casting quality, it is necessary to understand that each process, from managing melting temperature, controlling solidification, post-processing, to clarifying inspection standards, influences each other. Fragmented measures have their limits, and the PDCA cycle that connects all processes holds the key.

True quality cannot be created with non-destructive testing and high-performance measuring instruments alone. Investment in “people and the environment,” such as the skills of on-site workers (QC education), a tidy and orderly environment (5S), and attention to white rust and dust, is also a major pillar that supports the essence of quality.

The ability to capture “what is happening on-site” with numbers, such as traceability, calibration management, inspection logs, and temperature/humidity data collection, leads to recurrence prevention, predictive maintenance, and ultimately to the reduction of the defect rate. Visualization is the starting point for quality improvement and a testament to customer trust.

Quality is not built in a day. However, with the right perspective and a system for improvement, any workplace can definitely change. We hope this will be of help to your company’s quality reform.