Induction hardening has played a critical role for decades in heat treating. In this Heat Treat Today Technical Tuesday feature, Kyle Hummel, Professional Engineer at Contour Hardening, shares his engineering insights on the necessity of induction-hardened components for automotive powertrains. As a manufacturer with in-house induction hardening or a commercial heat treater, learn about viable considerations in moving forward with your induction hardening process.
This article appeared in the edition June 2020 edition of Heat Treat Today's Automotive Heat Treating magazine.
Induction hardening has played a crucial role in the automotive industry for many decades and is poised to continue that role into the future as the industry prepares for the inevitable shift to electric vehicles. Over the past 15 years, the emphasis on fuel economy, increased quality standards, and the emergence of other heat treat methods have drastically altered the design and necessity of induction-hardened components for automotive powertrains.
Transformation of Component Design
Increased residual compressive stress, minimal distortion, and the ability to selectively harden portions of a component are some of the main characteristics that have made induction hardening a popular choice for gears and shafts in the automotive industry. From the early 1980s to the 2000s the number of gears being hardened via induction was tremendous. The strength requirements for gears in four- and six-speed transmissions demanded the added compressive stress coupled with low distortion for noise reduction that induction hardening provides. As transmissions have increased to eight, nine, and 10 speeds over the past 10 years, the peak loading conditions of the gears has decreased, opening up the availability of other heat treat options. Low distortion processes such as nitriding and ferritic nitrocarburizing have now been successfully utilized in these gear applications because the gears do not require the high amounts of residual compressive stress. As the volume of these gears has decreased, other highly complex and high-volume components still remain great candidates for induction hardening.
Constant velocity joints (CVJ) rely on induction hardening and should remain relatively unaffected by the transition to electric vehicles. CVJs are typically designed for individual vehicle platforms rather than transmission platforms which can encompass a number of different vehicles. This leads to a greater variety of different part numbers to be hardened, and most CVJs typically require hardening in more than one region. These aspects require the need for specialized equipment to harden the CVJs that are difficult to adapt to other types of components.
In addition to CVJs, the advancements in powder metal (PM) capabilities in the past decade have also created a surge in the number of PM components that require induction. PM sprockets and other uniquely shaped components that require high wear resistance are paired with induction hardening to replace traditionally machined components.
As the technology in PM has improved, the ability to achieve full density at varying depths below the surface has recently led to the production of internal gears that can be induction hardened for added strength and wear properties. Other technically complex components such as sliding panels, stator shafts, and input shafts continue to utilize induction to increase strength and wear resistance in specific areas. As engineers continue to push the design limits of components, specialized induction hardening equipment with precision control, higher power, and shorter heat times is required to successfully develop a robust process.
Unique Technical Challenges
The technical challenges for induction heat treaters have increased with the added complexity of these components and the emphasis on several quality standards. It requires an entire team of engineers to provide input with coil design, process development, and adherence to quality standards. The days of having a print specification simply list a visual case depth and a surface hardness are a distant memory. Specifications now commonly require effective case depths at multiple locations, microstructure evaluations, and hardness and dimensional inspections. CVJs in particular can have over 35 metallurgical inspection points and over 25-dimensional inspection points. The component complexity has also led to the need for increased crack inspection. Sharp corners, thin walls, lubrication holes, and the use of higher carbon steels have led many parts to require nearly 100 percent inspection for cracks.
Along with the print specifications, heat treaters must also comply with the growing number of technical standards required to be an approved automotive supplier. IATF 16949 Quality Management System, AIAG’s Heat Treat Assessment (CQI-9), ASTM standards, and customer specific requirements can create a vast network of conditions that must be examined and constantly monitored to ensure compliance. Although these added requirements can be an inconvenience, the quality of parts being produced has significantly improved and that ultimately leads to safer and more reliable vehicles for the customer.
Adapting to the Future
Unfortunately, the technical challenges and increased quality requirements of automotive parts do not always come with higher margins. With the competition in Mexico and Asia, U.S. manufacturers with their own in-house heat treating and commercial heat treaters must continue to find ways to remain competitive. The volatility of OEM volume predictions and platform start and end dates requires manufacturers and heat treaters to be dynamic in capacity considerations. With induction hardening, having excess capacity at a variety of different frequencies and power capabilities can be crucial to landing the next job. Automotive work can frequently come in due to unplanned downtime at a competitor, or on a customer’s own heat treat line. If your organization does not have the ability to produce test samples almost immediately, that opportunity for valuable work will be missed. Having the knowledge and equipment to understand and provide testing for dimensions is another key to offering value to automotive customers. The ability to test parts green and immediately after hardening can drastically reduce scrap and rework and can be a crucial selling point to customers.
The piece by piece processing of induction hardening is suited well for automation and the benefits reach beyond simply reducing labor costs. The reduction in tooling changeovers not only reduces wasted time, it also improves the quality and consistency of the product. With tight dimensional tolerances on final parts, slight variations in heat treat patterns can be eliminated by dedicating and automating a heat treat line. The ROI for automating a cell, including temper and rust preventative application can be as little as six months with the added bonus of supplying a more consistent part to the customer.
The modern induction hardening facility should be moving to automate not only the production itself, but also the inspections, factory information systems, and ERP systems. Inspections such as eddy current can be automated to reliably inspect 100 percent for proper hardening and even crack detection. Automated microhardness equipment can save lab technicians hours of valuable time they would have spent waiting at the tester. These technologies, when used appropriately, can result in more efficient processes that produce higher quality parts at competitive prices.
Although the landscape of the automotive industry in the next 15 years is as exciting as it is uncertain, induction hardening will continue to be a vital process that is utilized into the future. The changes over the past 15 years have produced more complex components with stricter requirements that must be processed with greater efficiency. Induction hardening suppliers must remain focused on keeping pace with the developments in technology that continue to improve the heat treat industry as a whole in order to remain relevant and be a value-added process for automotive customers.
About the author: Kyle Hummel is a licensed Professional Engineer who has worked for Contour Hardening for 14 years as a metallurgical engineer focusing on process development and quality improvement.
For more information, contact Kyle at khummel@contourhardening.com or (317) 876-1530 ext. 333.
