AUTOMOTIVE HEAT TREAT

Thomas Wingens, Founder & President, WINGENS CONSULTANTS 

The increasing adoption of large-scale aluminum die casting, often termed Giga casting, in the automotive industry presents significant challenges in the manufacturing and maintenance of the massive dies required. Learn how heat treatment plays a critical role in ensuring the performance and lifespan of these Giga dies, primarily made from H13 tool steel or its derivatives. 

This informative piece was first released in Heat Treat Today’s May 2025 Sustainable Heat Treat Technologies print edition.

Introduction

In an article from 2005 on vacuum heat treating of large dies, I concluded, “The use of very large die cast tooling in the automotive industry with part weight over 3 metric tons will increase as aluminum cast parts are increasingly used to lower the manufacturing cost to produce lighter weight automobiles” (Wingens, “H13 Dies.”). Now, 20 years later, a couple hundred “Mega” dies have been heat treated. Six years ago, Tesla decided to take on Giga casting, gaining global attention and taking aluminum die casting to its next level.  

Tesla is working on an upgrade to its Giga casting technology to die cast almost all vehicle underbody parts in one piece. They pioneered the use of presses with 6,000 to9,000 tons of clamping pressure to mold the front and rear structures of Model Y during the Giga casting process. 

For Tesla, the use of a single component in the rear of the Model Y allowed it to cut related costs by 40%. In the Model 3, Tesla was able to remove 600 robots from assembly by using a single piece from the front and rear of the vehicle (Greco, “Weekly Gigacasting News.”).  

They have 14 Giga presses already installed, including two presses with 9,000 tons of clamping pressure for Tesla’s large Cybertruck production at its plant in Austin, Texas, with more to come.  

Tesla strategically incorporates inserts in the dies for high-heat zones. These metal elements are specifically placed in areas prone to higher corrosion. Inserts serve a crucial purpose, as they can be replaced individually, mitigating the need to discard an entire costly tool. The dies last hundreds of thousands of shots while individual inserts may only have a lifespan ranging between 30,000 and 80,000 shots (Greco, “Weekly Gigacasting News.”). 

Tesla currently employs two sets of dies per machine. While one set is actively mounted on the Giga Press, the other set undergoes routine maintenance. These sets are periodically rotated to ensure continuous and efficient production (Greco, “Weekly Gigacasting News.”). 

Ford, Toyota, Volkswagen, Volvo, and most Chinese electric car manufacturers have Giga Presses on order. The first North American Giga casting machine, aside from Tesla’s, will be installed at Linamar in Ontario (Greco, “Weekly Gigacasting News.”). This highlights the transformation occurring within the automotive industry with the increasing demand for lighter vehicles and reduced manufacturing costs, which in turn is driving the adoption of large aluminum structural castings produced through Giga casting (Greco, “Weekly Gigacasting News.”). This revolutionary technique necessitates the use of exceptionally large die-casting dies, often weighing several metric tons.  

These Giga dies, typically manufactured from hot-work tool steels, such as H13, are subjected to extreme thermal and mechanical stresses during the high-pressure injection of molten aluminum. Consequently, heat treatment plays a pivotal role in achieving the desired mechanical properties, maximizing die life and minimizing the risks of distortion and cracking. This article delves into the complexities of heat treating Giga dies, highlighting the evolution of techniques, current challenges, and emerging solutions. 

Historical Perspective

The heat treatment of large aluminum die-casting dies has evolved significantly over the last few decades. In the early days of vacuum heat treating for die-casting dies (1980s and 1990s), the primary focus was on minimizing distortion and achieving a clean surface finish. This was often accomplished using slow gas quenching rates (<30°F or 17°C/min), which, while reducing distortion, led to the precipitation of grain boundary carbides and consequently, shorter die life due to reduced impact toughness (Wingens, “H13 Dies.”). 

Recognizing the need for improved die performance, the North American Die Casting Association (NADCA), along with leading companies in the die casting industry, issued recommendations for a minimum surface quench speed of 50°F/min (28°C/min). This shift, coupled with the selection of higher quality die materials and the development of heat treatment specifications, such as GM Powertrain DC-9999-1 (1995) and Ford AMTD DC2010 (1999), resulted in significant cost savings and improved die life within the North American automotive industry. These specifications emphasized the importance of both material quality and heat treatment procedures (Wingens und Edenhofer, “Bauweise und Funktion.”). 

Challenges in Heat Treating Giga Dies

Heat treating large H13 aluminum die-casting dies has traditionally balanced the need for sufficient quench rates to achieve robust mechanical properties against the risk of distortion and cracking. As modern automotive and industrial applications demand ever-larger die-cast components, metallurgists and equipment suppliers have focused on several key developments: faster quenching methods in high-pressure vacuum furnaces; process strategies, such as interrupted quenching, to stabilize temperature gradients; and increasingly powerful auxiliary systems capable of handling extremely heavy loads and high thermal loads (Wingens, “H13 Dies.”). 

Achieving Adequate Quench Rates to Avoid Grain Boundary Precipitation

H13 (or similar hot-work tool steels) benefits from a sufficiently rapid quench to bypass detrimental grain boundary precipitation, which compromises toughness and die longevity. Many die-casting specifications — including those from NADCA — recommend a minimum quench speed of 50°F/min (28°C/min) measured near the die surface to maintain a uniformly fine microstructure (Wingens, “H13 Dies.”). Without such fast cooling, large dies can exhibit unwanted carbides at prior austenite grain boundaries and reduced impact strength. 

For dies weighing several metric tons, however, achieving even 50°F/min (28°C/min) at the die surface is nontrivial. Heat must be extracted swiftly from thick cross-sections, yet the bulk thermal conductivity of H13 places inherent limits on how quickly the die core can be cooled. The result has been widespread adoption of high-pressure gas quenching (HPGQ) in single- or multi-chamber vacuum furnaces, with nitrogen pressures often exceeding 10 or 15 bar (Wingens, Maximizing Quenching and Cooling in Vacuum Heat Treating 2015). 

The advent of Giga casting, with its significantly larger dies (weighing > 3 metric tons), introduces a new set of challenges for heat treatment processes. Achieving the required metallurgical properties and minimizing defects in such massive components demands sophisticated techniques and equipment.  

Key challenges include: 

• Uniform heating and cooling: Ensuring uniform temperature distribution throughout the large die volume during heating to the austenitizing temperature and subsequent quenching is critical to avoid uneven phase transformations and the development of internal stresses that can lead to distortion or cracking. 
• Achieving adequate quench rates: Extracting heat swiftly from the thick cross-sections of Giga dies to achieve the recommended quench rate of at least 50°F/min (28°C/min) at the surface thermocouple (Ts), as mandated by NADCA #207, is nontrivial due to the inherent limitations of the thermal conductivity of H13 steel.  
• Minimizing distortion and cracking: The substantial temperature difference between the surface and the core during rapid quenching increases the risk of both distortion and cracking in these large components. 
• Applying existing specifications: Current specifications, like NADCA #207, were primarily designed for die inserts estimated at up to 1 ton. The applicability and adequacy of these specifications for Giga dies, which weigh several tons, are being questioned. Issues, such as the number and location of test coupons needed to accurately represent the properties of the entire block, need to be addressed. 
• Equipment capacity: Heat treating Giga dies necessitates vacuum furnaces with adequate weight and cooling capacity, capable of handling the large dimensions and masses involved. 

Modern Heat Treatment Techniques for Giga Dies 

Advanced vacuum heat treatment technologies and process strategies have been developed and implemented to address the challenges associated with heat treating Giga dies. 

High-Pressure Gas Quenching (HPGQ)

The widespread adoption of HPGQ in single- or multi-chamber vacuum furnaces, with nitrogen pressures often exceeding 10 or 15 bar, is crucial for achieving the necessary rapid cooling rates for large H13 dies. Systems with radial gas nozzle systems and powerful fans (up to 800 kW) ensure effective gas flow through the large load volume (Wingens, “Maximizing.”). 

Directional Cooling  

Some advanced vacuum furnaces incorporate directional controlled cooling capabilities, allowing for the manipulation of gas flow patterns to promote more uniform heat extraction from complex die geometries, thus minimizing distortion (Wingens, “Maximizing.”). 

Interrupted Quenching (Isothermal Hold) 

Interrupted quenching techniques are employed to mitigate the risk of distortion and cracking caused by extreme temperature gradients. By pausing the quench at an intermediate temperature (sometimes referred to as a “warm bath” effect), the internal heat of the die has time to diff use outwards, equalizing temperatures and reducing residual stresses before the quenching process resumes (Wingens, “Maximizing.”).

Large Vacuum Furnaces 

Furnace manufacturers have developed Giga vacuum furnaces specifically designed to handle the size and weight of these large dies, with load capacities up to 5,000 kg or even 8 tons (Wingens, “H13 Dies.”). 

Adherence to NADCA Recommendations 

Despite size difference, the fundamental principles of heat treating H13 steel for die casting, as outlined in NADCA #207-2003, remain relevant. Achieving a minimum surface cooling rate of 50°F (28°C) per minute in the critical temperature range is still a key objective. Furnaces with high backfill capabilities (minimum 2 bar for premium, 5 bar for superior quality) are preferred.  

Precise Temperature Control 

Modern furnaces are equipped with sophisticated digital controls and multiple thermocouples to monitor and adjust temperature profiles in real time, ensuring uniform heating to the austenitizing temperature — typically around 1885°F (1030°C) for H13 — and precise control during the quenching and tempering stages. 

Tempering 

Following the rapid quench, a minimum of two tempering cycles is required, with cooling to ambient temperature between each cycle. A final stress temper is often performed to relieve residual stresses. 

Impact of Material Science 

While the heat treatment process is critical, the selection of high-quality die steel is equally important. Typically, Giga dies are made from premium or superior grade H13 steel, which, according to NADCA #207-2003, should meet stringent requirements for cleanliness, micro-banding, and impact toughness.  

Ongoing research also explores the use of improved die steels like Dievar and QRO-90, which exhibit enhanced thermal fatigue resistance. Proper heat treatment is essential to unlock the full potential of these advanced alloys. 

Future Trends and Outlook 

The field of heat treating Giga dies is continuously evolving to meet the increasing demands of the automotive industry. Future trends and considerations include: 

• Revision of specifications: The NADCA organization recognizes that the current NADCA #207 specification may need to be revisited to better address the unique challenges posed by Giga dies in terms of testing, quality assurance, and acceptable property variations across the large die volume. 
• Advanced process control: The increasing use of heat treatment simulation and finite element method (FEM) analysis allows for the prediction and optimization of hardening processes, including the estimation and compensation of thermal gradients. 
• Innovative heat treatment processes: Emerging techniques like long martempering, which offer a balance of high hardness and toughness in less time, are being explored as potential alternatives to traditional quenching and tempering for hot-work tool steels (Duarte, “Improving Hardening.”). 
• Energy efficiency: Efforts to reduce the energy consumption associated with HPGQ are ongoing, focusing on optimizing furnace design and control systems. 
• Integration with Industry 4.0/5.0: Digitalization and automation are expected to drive advancements in heat treatment processes, leading to improved efficiency, higher quality, and simplified task execution. 

Conclusion 

The efficient and effective heat treatment of Giga dies is paramount to the success of large-scale aluminum die casting in the automotive industry. While the fundamental principles of heat treating H13 steel remain relevant, the sheer size and weight of these dies necessitate the use of advanced vacuum furnace technologies, including HPGQ, directional cooling, and interrupted quenching strategies. Adherence to industry recommendations, such as the minimum quench rates specified by NADCA, is crucial for achieving the desired metallurgical properties and maximizing die lifespan. As the Giga casting market continues to expand, ongoing research and development in heat treatment processes, equipment, and specifications will be essential to meet the evolving demands for these critical manufacturing tools. 

References 

Chrysler Corporation, Hot Work Tool Steel Manufacturing Standard, Auburn Hills, MI, 1983. 

Duarte, Paulo. “Improving Hardening and Introducing Innovation for In-House Heat Treat.” Heat Treat Today, March 2025, https://www.heattreattoday.com/improving-hardening-and-introducing-innovation-for-in-house-heat-treat.  

Greco, Luca. “Weekly Gigacasting News.” 2024. 

Wingens, Thomas and Bernd Edenhofer. “Bauweise und Funktion eines neuartigen Großkammer-Vakuumofens zum Härten von Schweren Formen und Gesenken.” 60thHeat Treat Colloquium (2005).  

Wingens, Thomas. “Maximizing Quenching and Cooling in Vacuum Heat Treating.” 28th ASM Heat Treating Society Conference (2015).  

Wingens, Thomas. “Vacuum Furnace Hardening of Very Large H13 Dies.” Industrial Heating, January 2005. 

About The Author:

Thomas Wingens, founder and president of WINGENS CONSULTANTS, boasts over 35 years of experience in the heat treat industry, more than 15 of which are in strategic and executive positions. With his masters in Material Science and Business Administration as well as having served as a heat treater and metallurgist, Thomas holds a unique combination of academic knowledge and industry skills. He has worked in executive positions at Ipsen, Bodycote, SECO/WARWICK, and Tenova. Thomas has also contributed his knowledge and experience as a co-presenter with Doug Glenn at Heat Treat Boot Camp for the last five years. 

For more information: Contact Thomas Wingens at wingens@gmail.com. 

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