Heat Treat Todaypublishes twelve print magazines a year and included in each is a letter from the editor. This letter is from the May 2025 Sustainable Heat Treat Technologiesprint edition, and serves as the final message from Jayna McGowan, a dear member of the Heat Treat Today team.
Jayna McGowan 40 Under 40 Coordinator Heat Treat Today
Recognizing a job well done, an individual striving for excellence in their work, and someone who demonstrates leadership potential for years to come is not only a form of integrity in the workplace, but an opportunity to encourage a company and an industry to be the best it can be. A work environment that does not recognize excellence risks undermining it, leaving employees demoralized as they tackle the daily challenges inherent to their work. Those who have worked in both environments — the one that pursues and recognizes excellence and the one that does not — know the value of the former. The individual and the company both benefit from recognizing excellence.
This is why it has been an absolute privilege to coordinate Heat Treat Today’s40 Under 40 initiative. Getting to learn about the accomplishments of rising stars in the heat treat industry and then to share those with our readers speaks to the overall integrity of the people and companies in the industry. My favorite part about communicating with individuals who have been nominated is their tendency to be surprised by their nomination — in their minds, they are simply doing their job the way they know how to do it, which makes it all the more encouraging to hear that someone noticed their effort and wants them to be honored for it.
Another aspect I have enjoyed about supervising 40 Under 40 is seeing how the individuals recognized are contributing to the heat treat industry as a whole. Here at Heat Treat Today, we see firsthand how individuals honored in past years are willing to share their experiences and expertise by authoring articles or being interviewed for a Heat Treat Radio episode. Several highlights of these alumni contributions from the past year include:
“3D Printed Coils Outperform Traditional Coils” in our 2025 April print issue, featuring Josh Tucker from Tucker Induction Systems, 40 Under 40Class of 2024
“CQI-9 vs. AMS2759 for Quench Oil Management” in our 2025 March print issue, featuring Michelle Bennett from Idemitsu Lubricants America, 40 Under 40Class of 2023
“Transformative Takeaways” in our 2025 January print issue, featuring Casey O’Neill from RoMan Manufacturing, Inc., 40 Under 40Class of 2022
The example set by these individuals and so many others has the potential to inspire and inform the entire heat treat industry.
Finally, how can you 1) model the integrity of recognizing a job well done in the industry and 2) encourage young leaders like these to continue pursuing excellence? One way is to nominate a North American heat treater you know for the 40 Under 40 Class of 2025. Nominations officially open May 19 and close June 27.
While I will be stepping away from coordinating this initiative to raise my twin girls due in a couple months (future heat treaters?), please reach out to incoming coordinator, Kelsha Wells (kelsha@heattreatoday.com), with any questions about the nomination process.
In heat treating, the choice of power supply is a critical decision. Whether you’re using an AC transformer or a rectified DC system (AC transformer rectifier), this decision plays a significant role in process efficiency, equipment longevity, and operational costs. While AC transformers have been the industry standard for decades, rectified DC power is becoming more relevant due to its distinct electrical and thermal characteristics. Understanding the differences between these two power sources helps in-house heat treaters optimize furnace performance based on their specific application needs.
This informative piece was first released inHeat Treat Today’sMay 2025 Sustainable Heat Treat Technologies print edition.
Electrical Differences: AC vs. Rectified DC Power
AC Transformer Systems
In a traditional setup, an AC transformer steps down high-voltage grid power to the appropriate level for the heating elements. These elements operate on an alternating current waveform, where voltage and current fluctuate between positive and negative cycles at a standard frequency (typically 50 or 60 Hz).
Rectified DC Systems
In a rectified DC system setup, an AC transformer is combined with a rectifier to convert the stepped-down AC voltage into a pulsating or smoothed DC supply. This provides a continuous electrical current rather than an alternating waveform, changing how heat is delivered to the furnace.
Table 1. Benefits of AC vs. rectified DC power
Heat Distribution and Process Stability
One of the key differences between AC and rectified DC power in furnace heating is how each affects heat distribution within heating elements.
AC Heating
The alternating nature of AC power means the voltage crosses zero multiple times per second, leading to cyclic fluctuations in power delivery. In heat treating, this can create small but notable variations in temperature stability, especially in high-precision applications where uniform heating is critical.
Rectified DC Heating
Because DC power provides a continuous voltage and current, it eliminates these fluctuations. This results in more stable and consistent heating, which can be beneficial in processes that require tight thermal tolerances, such as carburizing, nitriding, and annealing.
Heating Element Performance and Longevity
The type of power supply can also impact the lifespan and efficiency of heating elements.
AC-Powered Heating Elements
Alternating current can cause thermal cycling effects within the heating elements, leading to mechanical stress over time. This may contribute to faster wear, increased oxidation, and potential premature failure of heating elements in some applications. However, for many general heat treating processes, AC remains a cost-effective and widely accepted solution.
Rectified DC-Powered Heating Elements
The stable power flow of rectified DC reduces thermal cycling stress on heating elements, allowing for longer operating life and more efficient heat transfer. This is particularly relevant for graphite and silicon carbide heating elements, which perform better with steady-state power input.
Power System Efficiency and Infrastructure Considerations
When integrating AC vs. rectified DC systems into a heat treating operation, several infrastructure and efficiency factors come into play.
AC Transformer Systems:
Standard in industrial settings and require minimal modification to existing electrical infrastructure
Simpler and often lower cost installation compared to rectified DC systems
More efficient for long-distance power transmission, which can be a factor in large industrial operations with multiple furnaces
Rectified DC Systems:
Require a rectifier in addition to the transformer, adding to equipment costs and complexity
Potentially higher efficiency in localized heating applications by reducing resistive losses in certain furnace designs
Reduced electromagnetic interference (EMI) compared to AC, which can be beneficial in sensitive heat treating processes
Process Suitability: When to Use AC vs. Rectified DC Power
Temperature stability, heating uniformity, and process sensitivity are important factors to consider when choosing between AC and rectified DC power for different heat treatment processes.
Conclusion
Both AC and rectified DC power play important roles in heat treating, and the choice depends on process requirements, equipment lifespan, and infrastructure considerations. AC transformer-powered systems remain the standard due to their low cost, compatibility with existing grids, and simpler installation. They are ideal for general heat treating applications that do not require extreme precision in thermal control. However, rectified DC systems offer more stable heating, reducing wear on heating elements and improving temperature uniformity. While they require additional equipment, they can be beneficial in high-precision applications or when maximizing furnace efficiency is a priority.
Understanding the strengths and limitations of both AC and rectified DC power sources enables heat treaters to select the optimal system for their specific production needs, balancing cost, efficiency, and process performance.
About The Author:
Brian Turner Sales Applications Engineer RoMan Manufacturing, Inc.
For more information: Contact Brian Turner at bturner@romanmfg.com.
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 inHeat Treat Today’sMay 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.”).
Figure 1. Part reduction between Model 3 and Model Y Source: Tesla Q1 2020 Report
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.”).
Figure 2. Tesla Model Y single aluminum die-cast piece Source: Wingens, “H13 Dies”
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
Figure 3. GM Powertrain 16” cube quench test
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
Figure 4. H13 aluminum die casting mold of 5.6 metric tons
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.
Figure 5. Acceptable (left) and unacceptable (right) H11 microstructure (500x)
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.”).
Figure 6. A 6t H13 die, the largest of its time (2004), processed for the German automotive industry
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.
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.
Figure 8. Loading of 5t H13 into a 15 bar Ipsen SuperTurbo Treater
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 & President Wingens Consultants
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.
When an extrusion plant in Ohio began to experience production stoppages and higher temperature variability in their 7 inch press line, they sought out an upgrade with a new induction heating furnace. This article highlights the technical components of the new furnace, revealing its upgrade as an important step in ensuring the efficient production and delivery of high quality aluminum extrusions.
An Excerpt:
The furnace replacement project had several clear objectives—significantly improve process reliability, provide accurate temperature uniformity, and ensure high energy efficiency. In addition, the furnace needed to be installed during GEI’s 2024 Christmas shutdown.
Several furnace concepts were investigated during the course of the project. GEI’s preferred method, from a process control perspective, would have been to retain and modify the induction coil of the original furnace and also add a new induction furnace to apply a temperature taper to the billet. In this scenario, the original coil would be used to apply the base temperature, while the new furnace would be responsible for accurately tapering the billet.
Unfortunately, this concept proved to be impractical for several reasons . . .
Click here to read the entire article byLight Metal Age.
The largest family-owned heat treating company in the United States announced the opening of its seventh U.S. heat treat operation.
Jamie Jones President Solar Atmospheres
Solar Atmospheres will acquire an existing industrial facility located in Berlin, Connecticut. The 28,000-square-foot facility is located in the Spruce Brook Industrial Park and will further expand the company’s capabilities in the Northeast region.
“We are excited to establish a new presence in Connecticut,” said Jamie Jones, president of Solar Atmospheres. “This strategic location allows us to…continue supporting the aerospace, medical, and commercial manufacturing markets throughout New England.”
The company provides vacuum heat treating solutions. This new heat treat operation is slated for completion in 2026.
Press release is available in its original form here.
A site in Oklahoma is the planned future home of a $4-billion dollar smelting operation. The plant would have a capacity of producing 600,000 metric tons of primary aluminum each year that would nearly double current domestic output for the United States.
Governor Kevin Stitt Source: Sengov
Emirates Global Aluminiumplans to build a primary aluminum plant in the Sooner State. If all goes accordingly, the plant will create up to 1,000 new jobs, and 4,000 jobs during its construction.
The plan is currently undergoing a feasibility study, however, Emirates Global Aluminium already has aluminum operations in the United States under EGA Spectro Alloys, the manufacturer of secondary aluminum alloys.
“We want more goods to be manufactured in Oklahoma and EGA is the perfect partner,” said Oklahoma Governor Kevin Stitt. “My administration has worked closely with the company for over a year to clear the way for the first new primary aluminum production plant in the United States for more than four decades.”
“The United States has been an important market for EGA for several decades, and we know there is strong demand for our high-quality metal ‘made in America’,” stated Abdulnasser Bin Kalban, CEO of Emirates Global Aluminium.
Abdulnasser Bin Kalban CEO EGA Source: EGA
Primary aluminum is created by dissolving aluminum oxide in a cryolite solution and applying electrolysis to extract a pure metal. Securing an affordable electric power source will be a major factor in the speed at which this agreement moves forward. Primary aluminum is used in domestic automotive, energy, construction, and aerospace sectors.
If its current deadlines are met, construction would begin next year, and the plant would begin operations by 2029.
Press release is available in its original form here.
Sources
$4B Plan for First US Smelter in 45 Years. American Machinist. Accessed May 20, 2025. https://www.americanmachinist.com/news/article/55291130/4b-proposal-for-first-us-smelter-in-45-years-emirates-global-aluminium.
By Steven Christopher, senior engineer at Super Systems Inc., and Katie Bastine, former quality manager at ThermoFusion.
The three letters, P-I-D, send shivers down most spines; tuning may induce an actual headache. This has proven true for decades, but why is the concept so overwhelming? This article will attempt to answer that difficult question with simple considerations.
This informative piece was first released inHeat Treat Today’sMay 2025 Sustainable Heat Treat Technologies print edition.
PIDs (Proportional-Integral-Derivative) need not be anxiety-producing. Let’s break it down to reduce the stress, but first, let’s credit one of the world’s deepest thinkers. Einstein defined insanity as, “Repeating the same thing over and over and expecting different results.”
Is this happening in our industry? Why does every Proportional-Integral-Derivative (PID) article begin with tuning a new controller? In reality, very few new controllers are installed. Instead, a failing TUS dictates re-tuning an existing controller. Let’s start with an existing controller, and then intentionally RUIN our PIDs.
Katie Bastine, quality manager of Nadcap-certified Thermo-Fusion of Hayward, CA, agreed to help and offered one of the company’s many Endothermic nitriding or batch furnaces. We settled on a vacuum furnace with graphite heating elements, which is a perfect candidate because it was relatively quick to respond and easy to manipulate.
What Are PIDs?
According to Blink author Malcolm Gladwell, we need a basic understanding of PIDs, and perhaps no more. His fantastic book details the brain’s ability to thin-slice situations — meaning the ability to make quick, often correct, decisions. He discusses in great depth the importance of data for experts, but he hypothesizes that too much data for the average person negatively influences the decision-making process. Gladwell claims, “The role of those other factors is so small … that extra information is more than useless. It’s harmful. It confuses the issues.”
This may be our mistake: too much information freezing our ability to act rather than empowering us. The goal of this article is not to train experts but rather to help with that often-paralyzing first step.
Consider the following definitions:
Proportional band (Pb) compares the error at a single moment or the difference between the set-point and control TC. Adjusting the Pb parameter determines how large an error is required to reduce/increase output.
Integral (or reset) compiles this same error over a period of time, appropriately adjusting to the Pb’s output.
Derivative (or rate) monitors the rate of change, estimating future error and “applying the brakes” when necessary. The remainder of this article limits theory and focuses on observations.
TIP: Understand the units. Pb can be expressed as percentage, degrees, or gain. Integral and derivative can be expressed as seconds, minutes, or repeats/minute. This article will use percentage and seconds.
Note: An increase to Pb (percentage) will have the same outcome as an opposite decrease to Pb (gain).
Evaluation Criteria
Before evaluating PIDs, it is important to agree what makes a good one. Th at list could be quite long, so this article will intentionally avoid considerations such as repeatability and recovery time. Instead, we will evaluate:
Aggressiveness — rate at which temperature approaches setpoint
Overshoot — both initial overshoot followed by how quickly it returns
Steady-state — oscillations (both period and amplitude) once settled out Aggressiveness is when the output first reduces as temperature approaches the final setpoint. Reducing too early sacrifices heat-up time while simultaneously improving overshoot. Like many PIDs, a delicate balance exists between any two parameters — a constant set of “give and take.” This consideration is less important when ramping to the final setpoint, because the output typically never reaches its maximum.
Are PIDs the Problem?
Algorithms are stable by nature; input data then calculate output. Thus, changes in behavior are rarely “failing PIDs,” but rather some external factor. If ever there was a time to pause, this is it. Before embarking on the time-consuming effort of tuning, evaluate the furnace holistically. What changed? Are PID changes masking a physical issue? Make sure you are fixing the right problem.
Many confuse PIDs with uniformity. While these concepts coexist, uniformity tends to indicate the health of a furnace, which is influenced by such things as heating system design, element/tube/valve condition, insulation, radiant effects, changes to rheostat/trim settings, and convection turbulence. A negative change in one may result in a failed TUS and prove impossible for PIDs alone to overcome.
Remember, a sudden, exaggerated loss in control suggests PIDs are not at fault.
TIP: Forget the TUS. If the control TC is good, then so are the PIDs.
Uniformity is defined by two characteristics: Delta and balance. Delta is the difference between the coldest and hottest temperature. Balance is the relationship between these temperatures and the control TC. Consider Figures 1 and 2 representing an AMS2750F Class 2 furnace with +/-10°F tolerances.
Figure 1 centers around setpoint. With a delta of 21°F, however, no amount of tuning will pass TUS.
Figure 2 reduces delta to 15°F, but the unbalanced nature results in a failing TUS on the lower limit. PIDs will never improve uniformity.
Poor uniformity (Delta) can be overcome by the aforementioned factors and (balance) by adjusting the control TC position or applying an offset (if allowed). The possible combinations are so wide they are beyond the scope of this article.
Pay Attention to Output
Output is an important (and often overlooked) tuning parameter. PID changes are driven by the control TC, but they have practical limits. These limits are often visible in the output well before they are in the control TC. Tuning efforts should always monitor the output for:
Backing off — temperature when output begins to reduce
Stability — ability of output to converge on an appropriate value
Response — noticeable difference in time for the control TC to respond to an output change
TIP: In addition to setpoint and control TC (PV), record output (CV) to better understand tuning. A lot happens in one minute, so try recording every 1–5 seconds if possible.
Healthy PIDs
Thermo-Fusion’s vacuum furnace ramped to 1000°F at 40°F/min with an aggressive approach, minimal overshoot and continued a “straight line” at soak (using PIDs of 2.0/75/150). As the control TC neared soak, the output backed off 60°F before the soak temperature — neither too early nor too late. The output settled down after a few quick oscillations, suggesting the Pb was not too small.
Figure 3 demonstrates what PIDs should look like. Now let’s disrupt these values, learning from the result. We begin by exploring Pb’s effect because it has the most influence on the trio.
Figure 3. Perfect PIDs
TIP: When adjusting parameters, go big! Start with large (40–60%) changes, then fine-tune with smaller (10–20%) adjustments.
Increase Pb
Figure 4. Increasing Pb
Proportional band influences when output first reduces and how fast it adjusts. The first mostly impacts furnaces experiencing immediate setpoint changes. All furnaces, including those that ramp to final soak, must consider the second — how fast the output adjusts.
A “sweet spot” exists for Pb. Let’s consider the extremes. A Pb of “∞” backs off very early but too slowly. This results in either overshoot followed by slow, rolling oscillations or no overshoot but also failure to reach setpoint. Same cause, but very different outcomes.
Figure 4 demonstrates the first example: reducing early but too slowly to eliminate overshoot.
TIP: Decrease Pb until the output “bounces around”, then slightly increase Pb. This approach offers diminishing returns, with the output eventually becoming unstable.
Decrease Pb
Figure 5. Decreasing Pb
If increasing Pb slows the output, decreasing must offer the opposite effect. A Pb of “0.0” represents on/off control, backing off very late (at setpoint) but quickly (100% to 0% immediately) followed by rapid oscillations. A smaller Pb presents a double-edged sword, which is an advantage to furnaces with an immediate control/output response, but a disadvantage for those with a lagging relationship. This allows the output to wind up or down too much before the control TC responds.
A small Pb minimizes overshoot but sacrifices steady-state control. Pay special attention to the output (specifically the 1/4 Pb line on Figure 5). As the control TC approaches soak, there are tremendous output swings followed by instability — classic signs of too small a Pb.
TIP: Watch the output. If “bouncing around,” increase the Pb, which dampens output.
Increase Integral
Figure 6. Increasing Integral
Integral considers past error, “winding up” as large error exists and adding to the output. Small error conversely “unwinds” the Integral. A larger Integral parameter adds more to the Pb’s output. This may improve aggressiveness, but it sacrifices other aspects of a healthy PID.
Too large an Integral overemphasizes previous error, potentially resulting in overshoot, then quickly unwinding as the error becomes smaller, flattening the control TC. Integral has a second benefit: reducing “droop” as the control TC approaches soak only to prematurely stall. A third benefit compensates for a furnace that heats faster than it cools (or vice versa).
TIP: With similar overshoot to a large Pb, a large Integral differs with less undershoot before stabilizing.
If the control TC stalls before soak without closing, increase the Integral. If the control TC looks more like a saw tooth than a sine curve, increase the Integral.
Decrease Integral
Too small an Integral eliminates the PIDs knowledge of history, leaving all the work to the Pb. Error can change rapidly at any moment, which results in an equally rapid change in output. An appropriately sized Integral offers a smoothing effect on the system. Too small an Integral disregards previous error, possibly making the system unstable.
Figure 7. Decreasing Integral
Changes to Derivative
Derivative is difficult to simplify, but (channeling our inner Malcolm Gladwell) let’s try. Derivative is perhaps most easily thought of as a counterweight to the actions of P-I alone. Derivative evaluates the error’s current rate of change to estimate future error. This forecasting allows Derivative to prematurely reduce or increase output.
Derivative is frequently overused and often not required. Exceptions must be evaluated on a case-by-case basis. A visible indicator suggesting a benefit from Derivative is a delayed response between the control TC and output. As output increases, does the control TC immediately rise? Or does it take a while to respond?
TIP: P-I alone often can’t overcome a significant lag between the control TC and output. Increasing Derivative will counteract the delay.
Summary
We hope this article provides the confidence to take that difficult first step. The beauty of PIDs is they are free to make and easy to undo. Therefore, do not be intimidated in taking that first step. Worst-case scenario, you revert. Pair these tips with the following guidelines, and you will be fine.
Change only one parameter at a time.
Cool the furnace between tests; don’t increase +100°F only to try again.
If you overshoot, don’t abandon ship — observe steady-state. You often learn more from failure than success.
Document, document, document! Simplify your thinking, and don’t simplify your notes.
If stumped, place the controller in manual output, forget the setpoint but watch for stability. If the furnace can’t control, then how can the PIDs?
About The Authors:
Steven Christopher Senior Engineer Super Systems Inc.
Steven Christopher has been involved in countless projects for both captive and commercial heat treaters implementing critical technology applications. He brings a vast knowledge base as it relates to industrial automation, and his experience with heat treat equipment is second to none.
A Chinese partner has purchased two vacuum induction melting (VIM) furnaces for melting and producing castings that will support the aerospace and energy industries.
Sławomir Woźniak CEO SECO/WARWICK Group
SECO/WARWICK Group will be providing the two VIM furnaces, which will be shipped to China. The first of the two furnaces on order is a 50 kg VIM induction furnace for producing castings in an equiaxed structure. The furnace is unique due to its high degree of automation. It is often a chosen solution in the field of vacuum metallurgy. Various metals can be processed in vacuum metallurgy furnaces, such as titanium and its alloys, silicon, nickel, or cobalt alloys. The second furnace is the JetCaster VIM DGCC, used to produce high-quality precision turbine blade castings in the aerospace and energy industries.
Sławomir Woźniak, CEO of SECO/WARWICK Group, stated how the furnace benefited “the field of unidirectional crystallization castings of nickel- and cobalt-based superalloys. Years of work by our R&D engineers on the development of new unidirectional crystallization casting technology has allowed us to create a device equipped with a supersonic argon stream cooling system.”
“The growing popularity of VIM furnaces and the increasing importance of vacuum metallurgy is a consequence of the constantly changing production needs of heavy industries.” said Liu Yedong, managing director of SECO/WARWICK China.
Liu Yedong Managing Director SECO/WARWICK China.
Press release is available in its original form here.
Heat Treat Today has gathered the four heat treat industry-specific economic indicators for May 2025. While April showed a mixed bag of growth and contraction, May sees three out of four areas indicating growth.
May’s industry-specific economic indicators continued to show growth in three of the four indices while one has slipped farther into contraction. The Inquiries and Bookings indices show a sharp turn toward growth, with Inquires rising to 59 (from 49 in April) and Bookings rising to 57.7 (from 52 in April), while the Backlog index hovers at a relatively steady 52.2.
The Health of the Manufacturing Economy index entered contraction in April, and has continued in its decline, dropping from 47.2 in April down to 42.9 in May. Tariffs are now in effect which may begin to impact the economic index.
Despite the decline in the Health of the Manufacturing Economy Index, the graphs overall suggest that the 4-month slowdown in the North American thermal processing industry (that began in roughly December 2024), is beginning to see a turn-around.
The results from this month’s survey (May) are as follows; numbers above 50 indicate growth, numbers below 50 indicate contraction, and the number 50 indicates no change:
Anticipated change in Number of Inquiries from April to May: 59.0
Anticipated change in Value of Bookings from April to May: 57.5
Anticipated change in Size of Backlog from April to May: 52.2
Anticipated change in Health of the Manufacturing Economy from April to May: 42.9
Data for May 2025
The four index numbers are reported monthly by Heat Treat Today and made available on the website.
Heat TreatToday’sEconomic Indicatorsmeasure and report on four heat treat industry indices. Each month, approximately 800 individuals who classify themselves as suppliers to the North American heat treat industry receive the survey. Above are the results. Data started being collected in June 2023. If you would like to participate in the monthly survey, please click here to subscribe.
