In product development within the manufacturing industry, it is no exaggeration to say that “design” dictates all subsequent processes. Particularly in aluminum casting, careful consideration is required because decisions at the design stage directly impact the product’s strength, precision, productivity, and cost.

For example, a single setting for the casting’s wall thickness or draft angle can change the risk of defects that occur during casting (such as shrinkage cavities, blowholes, and dimensional inaccuracies). Furthermore, in mass production using molds, even a minor design mistake can lead to rework costs, such as the mass production of defective parts or mold modifications.

The first reason is that optimization at the design stage has become indispensable as the trend towards high-mix, low-volume production progresses. The conventional approach of “making the mold first and figuring it out later” only leads to an increase in the number of prototypes, ballooning both costs and delivery times.

The second point is the need for technology to determine the balance between strength, precision, and cost at the design stage. For instance, simply “reducing wall thickness for weight reduction” can lead to insufficient fluidity during casting and a deterioration in structural strength. Conversely, prioritizing strength by making walls thicker can lead to the formation of cavities due to uneven cooling and higher costs.

The third point is that the spread of simulation technologies such as structural analysis (CAE) and solidification analysis has made it possible to improve design accuracy. This is shifting the paradigm from an era of “covering design mistakes on the shop floor” to a design-led era of “eliminating defects at the design stage.”

For example, at Daiwa Light Alloy Vietnam, by utilizing solidification analysis for designing casting plans and cooling balance, they have reduced the defect rate by over 30% at the mold design stage. However, to fully reap the benefits of such analysis technologies, designers themselves must be well-versed in the casting process and its challenges.

Thus, it is crucial to recognize that “design is the process that determines the product’s fate.”

This article focuses on the three key elements in aluminum casting design—”strength,” “precision,” and “cost”—and introduces design know-how and practical examples for optimizing each. It is packed with checklists and tips for avoiding failures that can be applied on-site. Please use it to review your company’s design processes.

One of the attractions of aluminum castings is that they are “light and strong,” but consideration of strength at the design stage is essential to achieve this. Especially for parts subjected to loads, such as automotive components and housings, cracking or fracture due to insufficient strength is a major cause of product defects.

For this reason, it is important not just to “simply increase the wall thickness,” but to design a structurally strong shape.

The basis of strength design is the optimization of “wall thickness” (nikuatsu). Generally, increasing thickness also increases strength, but there is a casting risk in that thick sections have longer solidification times, making them more prone to defects such as shrinkage cavities (internal voids) and blowholes (gas bubbles).

Therefore, in recent years, the mainstream method has been to increase rigidity using “ribs” (reinforcing fins) instead of making the walls thicker. Ribs are a technique to enhance structural bending and torsional rigidity while keeping the wall thickness down. They are particularly effective in plate-like or cylindrical structures and also contribute to weight reduction.

Additionally, it is recommended to keep the wall thickness as uniform as possible. This is called “uniform wall thickness.” This is because abrupt changes in thickness cause uneven solidification, leading to cracks. For example, in large parts, a design that uses a core (nakago) to create a hollow structure is also adopted to achieve a substantially uniform wall thickness.

Strength is greatly influenced not only by the design shape but also by the alloy material used. Representative aluminum casting materials have the following characteristics.

In particular, while ADC12 has high strength, it also has a high risk of shrinkage cavities and cracks, making optimization of the casting plan through solidification simulation essential.

Nowadays, many foundries utilize “solidification analysis” and “structural analysis (FEM: Finite Element Method).” This makes it possible to visualize uneven cooling and stress concentrations, thereby avoiding defect risks in advance at the design stage.

At Daiwa Light Alloy Vietnam, a case has been reported where, by fully utilizing these analysis technologies, they reduced cracking defects originating from design by 40%.

In summary, the key to strength design is the shift from “making it thicker” to “making it structurally stronger.” Understanding material and casting characteristics, and approaching design, analysis, and casting in an integrated manner is the shortcut to achieving light and strong castings.

In the design of aluminum castings, “dimensional precision” is a fundamental element of product functionality. No matter how excellent the strength or appearance, a product is not viable if its dimensional tolerances are not suitable for assembly or machining.

Furthermore, designing tolerances is not simply a matter of setting them strictly; “realistic optimization” that includes the casting method, mass production conditions, and machinability is required. Here, we will explain the basics of tolerance design and the techniques for securing precision.

The first thing to understand in dimensional precision design is JIS B 0403 “Castings—System of dimensional tolerances and machining allowances.” This standard defines dimensional tolerances for castings as “FCT (Foundry dimensional Casting Tolerances)” and specifies tolerance grades for each casting method.

For example, for sand casting (FCT G), a tolerance of about ±1.5 to ±5.0 mm is common, whereas for permanent mold casting (FCT M), it is highly precise at ±0.5 to ±1.5 mm.

On the other hand, in actual casting, the following factors affect dimensional variation:

In particular, local dimensional deviations are likely to occur in parts with complex shapes, making uniform wall thickness and ingenious gate design essential.

For mass-produced products requiring high precision, permanent mold casting (gravity casting, low-pressure casting, die casting) is the mainstream method. Since the mold is used repeatedly, it is important to consider not only the initial dimensions but also the dimensional changes (secular changes) with each cycle.

The following two points require special attention:

At Daiwa Light Alloy Vietnam, there is a case where they optimized the gate position and cooling lines through 3D analysis, improving the NG (No Good) rate from the initial stage of mass production by 20%.

Furthermore, by implementing “machining-friendly tolerancing” at the design stage—such as designing intentionally offset machining reference surfaces or layouts that balance draft angles and dimensional tolerances—it is also possible to boost the overall yield.

Dimensional precision is not just a “matter of millimeters,” but can be described as a “design lever that simultaneously affects both quality and cost.”

From dimension assurance left to the shop floor, to design-led dimensional management—this is the new standard in precision design.

In the product development of aluminum castings, the cost is almost entirely determined at the design stage. This is because “design dictates the process, and the process dictates the cost.”

Especially in recent years, not only suppressing initial investment but also cost optimization over the entire lifecycle is required. Here, we introduce the cost structure of molds and machining, and cost avoidance measures that can be taken at the design stage.

The core costs in casting are “molds” and “machining.”

Mold costs vary greatly depending on the product size, complexity, and casting method (sand casting / permanent mold / die casting). The approximate market rates are as follows.

In addition to this, it is necessary to account for mold modification costs (due to aging or design changes) and initial setup adjustment costs.

Factors that affect machining costs include “machining allowance” and “draft angle.”

Therefore, an optimal balance of the seemingly contradictory elements—”minimal machining allowance and sufficient draft angle”—is required.

While castings offer high design freedom, unreasonable integrated designs or extremely thin-walled structures can be counterproductive.

Such “designer intentions” are typical examples that ultimately drive up costs.

By conducting a design review with the foundry before finalizing the product specifications, the following cost avoidances become possible:

In fact, at Daiwa Light Alloy Vietnam, there is a case where they reduced machining costs by 30% by “optimizing intermediate wall thickness” during the review stage.

The reason it is said that “80% of the cost is determined by the design” is none other than that the designer holds the trigger.

Pursuing optimal cost design through the trinity of design, casting, and machining is the source of competitiveness.

Automotive parts manufacturer A, headquartered in the Kansai region, was experiencing higher-than-expected machining costs for its mass-produced aluminum casting products. A high incidence of burrs occurred when removing the product from the casting, significantly increasing the finishing work in the machining process.

The cause was an insufficient draft angle at the design stage. The initial design prioritized appearance and dimensions, applying only a minimal draft angle. As a result, the phenomenon of the casting seizing in the mold during ejection occurred frequently. It took over 15 minutes per piece for burr removal and finishing.

Therefore, after consulting with the foundry, they implemented a redesign that added +1.0 degree to the draft angle. As a result, ejectability improved, and burr formation was significantly reduced, halving the labor in the post-processing stage. After the process review, they achieved a machining cost reduction of over ¥500,000 per month.

This case illustrates the importance of linking design and manufacturing.

Company B had adopted aluminum castings for the housing of its communication equipment. Although the parts required high appearance precision and heat dissipation, casting porosity (internal cavities) occurred at a high rate in the initial mass production lot. Multiple fatal defects were detected by CT scan inspection, and product shipments were temporarily halted.

The cause was the existence of localized, structurally thick sections. In particular, metal flow stagnated at the intersection with the ribs, and porosity formed due to delayed solidification.

At the design stage, “uniform wall thickness” and “cooling balance” were not considered, and solidification simulation was not performed. As a result, recasting the entire initial lot and mold modification became necessary, leading to a triple whammy of delivery delays, increased costs, and loss of customer trust.

This case is a typical example of how insufficient consideration of strength in casting design can lead to such serious risks.

Design can be the key to success or the root of failure. Dialogue between design and the shop floor is the decisive factor in optimizing casting quality and cost.

A. At a minimum, clearly specify the dimensions, tolerances, material, finishing instructions, and the direction of the draft angle.

Especially for castings, it is important to specify casting-specific elements (shrinkage allowance, machining allowance, pouring direction, draft angle, etc.). Submitting a general mechanical drawing as-is can lead to the mold being made without considering casting characteristics, causing dimensional defects and ejection problems.

In addition to the drawings, it is advisable to attach a separate casting specification sheet (or a memo of requirements). Specifying the following content, for example, can prevent misunderstandings with the foundry:

A. Intermediate file formats (STEP, IGES) are the most versatile and are highly recommended.

Since 3D data is used for mold design and simulation, it is ideal to submit it in an intermediate format with the highest possible surface precision.

As a supplement, it is safest to provide the 2D drawings and 3D data as a set. With 3D data alone, tolerances and finishing instructions can be ambiguous, increasing the risk of problems in subsequent processes.

A. The golden rule is to transition only after all items—”tolerance, strength, appearance, and castability”—have been fully evaluated.

“Potential NG factors” like the following are often overlooked during the prototyping stage:

To identify these, it is effective to replicate the actual environment with a small pilot production run (10–50 pieces) and perform CT scans and destructive testing.

Furthermore, sharing a “production transition judgment table” or a “startup checklist” with the foundry can enable a smooth handover to mass production.

“A little extra effort before ordering” leads to the avoidance of major losses after manufacturing. Increasing the precision of drawings, data, and specifications dramatically improves the success rate of casting design.

In aluminum casting design, the three elements of “strength,” “precision,” and “cost” are always intertwined, and the designer must find the optimal solution by balancing them.

How to resolve these trade-offs at the design stage determines the success or failure of the cast product.

For this, not just creating drawings, but “design based on an understanding of the casting process” is essential. True design capability lies in deriving the most rational shape, tolerances, and specifications by foreseeing all aspects: molten metal flow, cooling, solidification, ejection, machining, and surface treatment.

We hope the know-how and examples introduced in this article will be helpful in improving your company’s product design. If you have concerns about a specific product design, please collaborate with foundries and expert designers from an early stage to build a design process that leverages “shop-floor wisdom.”

Design is not only the “blueprint” of a product but also the company’s competitiveness itself. The evolution required of the manufacturing industry from now on is the optimization of casting quality and cost, led by design.