Aluminum casting & mold design services

Introduction

In the Japanese manufacturing industry, cost reduction and stable quality/delivery are perpetual challenges for management and procurement managers. In particular, the selection of “molds” (dies), which dictates product quality and productivity, is a critical business decision directly linked to the entire supply chain’s TCO (Total Cost of Ownership). When selecting mold materials, many may struggle with whether to choose traditional “steel” or “aluminum (aluminum alloy),” which has garnered attention in recent years.

Are you making judgments based solely on general perceptions like “aluminum is cheap and fast, but lacks durability” or “steel is expensive, but lasts long”? Due to recent technological innovations, the performance of aluminum molds has dramatically improved. This article thoroughly analyzes and compares aluminum molds and steel molds across three main axes: “cost,” “lifespan,” and “precision,” clarifying the advantages and disadvantages of each. We hope this serves as an aid in finding the “optimal solution” for your company’s products and production system.

Why Re-evaluating Mold Materials is Necessary Now

The environment surrounding the manufacturing industry is changing at an unprecedented speed due to the shift to high-mix low-volume production, shorter product cycles, and intensifying global price competition. According to a survey by the Ministry of Economy, Trade and Industry (2022), there are approximately 8,000 mold manufacturing establishments, but about 70% of them are small-scale businesses with 20 or fewer employees, facing challenges in technology succession and cost pressures. Under these circumstances, there is a growing need to review the entire production system, unbound by the conventional wisdom that “large-lot production = steel molds.”

First, let’s compare the characteristics of both in a summary table. The figures may vary depending on the specific materials used, but please consider these as general trends.

Comparison Item	Aluminum Mold (A7075, etc.)	Steel Mold (SKD61, S50C, etc.)	Remarks
Initial Cost	◎ (Low)	△ (High)	Aluminum is approx. **30% to 50%** of steel
Production Lead Time	◎ (Short)	△ (Long)	Can be shortened to approx. 50% of steel
Lifespan (Shot count)	△ (Short)	◎ (Long)	Al: Tens of thousands to 200k / Steel: Over 1 million
Precision (Dimensional stability)	○ (Medium to High)	◎ (Very High)	Steel is advantageous under high temperature/pressure
Thermal Conductivity	◎ (High)	△ (Low)	Aluminum is approx. **5-6 times** that of steel
Machinability	◎ (Very Good)	△ (Poor)	Can be machined at approx. 3-4 times the speed of steel
Weight (Specific gravity)	◎ (Light)	△ (Heavy)	Aluminum is approx. 1/3 that of steel
Suitable Lot Size	Prototype / Small to Medium lot	Medium to Large lot / Mass production
Maintainability	○ (Easy to modify)	△ (Difficult to modify)	Welding and repair are relatively easy for aluminum

In-depth Analysis 1: Cost (Initial Cost vs. TCO)

For procurement managers, cost is one of the most important metrics. However, judging based on simple initial cost alone carries the risk of incurring higher total costs.

The biggest appeal of aluminum molds is that the initial cost can be reduced by **30% to 50%** compared to steel molds. The main factor behind this cost difference is “machining time.”

• Overwhelming Machinability: Aluminum is very soft compared to steel (especially high-hardness tool steels like SKD61) and has properties that make it easy to cut (machinability). This allows machining speeds on equipment like machining centers to be increased to approx. 3-4 times that of steel.

• Reduction in Electrical Discharge Machining (EDM): “EDM” (a method of processing hard metals by melting them using electrodes), which is often essential for steel molds, can be significantly reduced or even eliminated in many cases with aluminum molds.

For these reasons, the man-hours for mold production are dramatically reduced, and processing costs are significantly compressed. As a result, the mold production lead time (period from order to delivery) can also be shortened to approx. 50% of that for steel molds.

What’s important in mold selection is not just the initial cost (Capex), but the Total Cost of Ownership (TCO) after operations begin.

1. Productivity Improvement through High-Cycle Molding: Aluminum’s thermal conductivity (ease of heat transfer) is extremely high, at approx. 5-6 times (A5052: approx. 138 W/m·K) that of steel (S50C: approx. 46 W/m·K). This dramatically improves cooling efficiency inside the mold during injection molding, potentially shortening the molding cycle (time per shot) by **20% to 40%**. High-cycle molding increases production volume per unit of time and directly reduces the operating costs of the molding machine.

2. Operational Benefits from 1/3 Weight: Aluminum’s specific gravity (approx. 2.7 g/cm³) is approx. 1/3 that of steel (approx. 7.8 g/cm³). A lightweight mold provides the following benefits:

   • Faster Changeovers: The burden of mold exchange work (changeover) is reduced, shortening the time required.

   • Compatibility with Smaller Molding Machines: Because the mold weight is lighter, it may be possible to produce using a molding machine with less clamping force (= cheaper).

While steel molds contribute to TCO reduction through lower mold modification/remake costs due to their long lifespan, aluminum molds contribute to TCO reduction through “productivity improvements” and “reduced operational load.”

In-depth Analysis 2: Lifespan (Shot Count and Maintenance)

A mold’s “lifespan” is generally measured by the shot count (the number of times a product has been manufactured with the mold). This is a critical factor directly linked to the required production volume of the product.

Steel molds, especially tool steels like “die steel (SKD61, etc.)” or “pre-hardened steel (NAK80, etc.),” are designed to withstand high temperatures and pressures, boasting extremely high hardness and wear resistance.
With proper maintenance, long-term use exceeding 1 million shots is possible, and steel molds remain the optimal solution for large-lot mass production in units of hundreds of thousands. They also exhibit high durability against the high pressures of injection molding and repeated thermal history (heat shock).
Traditionally, the lifespan of aluminum molds was considered to be several thousand to tens of thousands of shots, with their use limited mainly to prototypes and ultra-small lot items (monthly production levels of a few hundred units).
However, in recent years, materials and processing technologies have evolved significantly.

• Emergence of High-Hardness Aluminum: The use of high-strength aluminum alloys such as A7075, also known as “Extra Super Duralumin.”

• Surface Treatment Technology: Applying treatments like hard anodizing (hard anodic oxidation) or electroless nickel plating to dramatically increase surface hardness (it’s possible to achieve hardness comparable to steel (approx. HRC 50-60)).

Thanks to these technologies, it has become possible to give aluminum molds a durability of 100,000 to 200,000 shots. As a result, there are increasing cases where aluminum molds can cover the “small to medium lot” range (monthly production levels of several thousand to tens of thousands), which was traditionally handled by steel molds.

In-depth Analysis 3: Precision (Dimensional Stability and Surface Quality)

To guarantee product quality, “precision” is a non-negotiable element. The precision required of a mold directly links to the product’s dimensional accuracy and surface beauty (transferability).

During molding, molds are exposed to high-temperature resins or molten metals (like aluminum die-casting) and subjected to high pressure.
Steel has a coefficient of linear expansion (rate of dimensional change due to temperature) that is about 1/2 that of aluminum and is also harder, so it features less deformation (deflection) and wear under high temperature and pressure.
Steel molds have an advantage, especially when using highly abrasive materials like glass fiber (GF) reinforced resins, or in the mass production of products requiring ultra-precise dimensional tolerances in the micron range.
The notion that aluminum molds “struggle with precision” is becoming a thing of the past.
While it’s true that aluminum expands easily with heat and is soft, it’s also possible to use these characteristics to one’s advantage.

1. High-Precision Machining: By leveraging aluminum’s excellent machinability, it’s possible to eliminate the micro-errors often caused by EDM by engraving directly with high precision using the latest 5-axis machining centers.

2. Optimization of Cooling Design: By taking advantage of high thermal conductivity, it’s possible to design the mold to minimize thermal deformation by efficiently placing cooling channels within it.

As a result, an increasing number of aluminum molds can achieve dimensional accuracy and excellent surface transferability (such as texturing or mirror finishing) comparable to steel molds.

Optimal Use: Recommended Scenarios by Application

So, which one should you choose? There is no absolute right answer. The key to TCO reduction is using them appropriately according to the product’s “lifecycle” and “required specifications.”

Scenario 1: Prototype / Development / Ultra-Small Lot (Recommendation: Aluminum)
(Target: Products where shortening development lead time is the top priority)
In the development phase of new products, design changes occur frequently. A lifespan of 1 million shots is not necessary here.
Aluminum’s “speed”—being able to produce a mold in half the time (e.g., 2 weeks instead of 4) and at half the cost of a steel mold—is a powerful weapon in accelerating time-to-market.
Scenario 2: Small to Medium Lot (Thousands to tens of thousands per month) (Consider: Aluminum)
(Target: Products with short lifecycles or high-mix low-volume production)
This is the most challenging zone and the area where aluminum molds are encroaching on the territory of steel molds.
If a product’s total production volume ends at 150,000 units, a steel mold with a durability of 1 million shots is overkill.
A high-hardness aluminum mold, which has a low initial cost and can also reduce production costs through high-cycle molding, becomes a very strong option. In the Small and Medium Enterprise Agency’s “White Paper on Small and Medium Enterprises” (2024 edition simulation), “review of procurement costs” (60%) and “improvement of production process efficiency” (55%) are major TCO reduction measures for manufacturers, and aluminum molds meet this need.
Scenario 3: Large Lot / Mass Production (Hundreds of thousands or more per month) (Recommendation: Steel)
(Target: Products requiring stable supply over a long period, such as automotive parts and home appliances)
For products with long lifecycles of 5 or 10 years, where total production volume exceeds 1 million units, steel molds are indisputably suitable. Although the initial cost is high, the mold depreciation cost per shot becomes the lowest with steel.

Conclusion

In this article, we analyzed and compared aluminum molds and steel molds from the perspective of procurement managers in the manufacturing industry, focusing on the three axes of “cost,” “lifespan,” and “precision.” The once-clear distinction between the two is becoming blurred due to technological advancements.

The important thing is to re-evaluate their characteristics not in terms of “superiority or inferiority,” but as “the right material for the right application.”

• Aluminum molds are no longer “just for prototyping.” In addition to “low cost” and “short lead time,” they wield the weapon of “productivity improvement through high-cycle molding,” evolving into a powerful solution for TCO reduction in small- to medium-lot production.

• Steel molds, with their overwhelming “durability” and “ability to maintain high precision,” remain an indispensable foundation for stable supply in large-lot mass production.

The first step toward TCO reduction is to thoroughly scrutinize your product’s required specifications, production lot sizes, and product lifecycle in your procurement strategy, and ask, “Is a durability of 1 million shots truly necessary?”