When you purchase induction equipment, the perishable tooling (i.e., induction coils) will become a point of reoccurring cost over the life of the program. The loss of production that occurs when an induction coil fails and the equipment is idled, is more costly. It is important to note that some coils have a short usable life while others will last for months or years. Some of the notable factors include the coil type, equipment process parameters, the quality of the coil design, and specific coil features employed. All these influence coil life, some profoundly. Due to the number of factors that influence coil life, no induction equipment supplier can closely approximate the expected coil life. A proper understanding of these factors will enable the program manager to execute proper planning for the annual cost of induction coil tooling, number of coils on hand, coil changeover schedule, and possible downtime of induction equipment. It is important that your induction coil supplier has the expertise to provide you with good coil designs and is committed to continuous improvement by resolving early failure modes to maximize coil life.

This presentation will discuss the most common types of induction tooling failures and the best practices to improve the performance and longevity of inductor coils, bus bars quenches and related tooling. We will discuss the harsh environment of a typical induction machine installation and what can be done to reduce contamination, which is the leading cause of tooling failure. Robust tooling designs and how water cooling is essential to longevity shall be discussed. Cooling water temperature and how the water is presented and routed through the tooling components and the impact this has on performance and longevity shall be discussed. We will discuss the use of proper materials, fittings and hoses which are often overlooked and can be detrimental to a process if not correctly selected. We will cover the induction machine and how it is essential to have a proper earth ground and the importance of proper machine fixturing and alignment. We shall discuss the importance of scheduled machine maintenance, scheduled service and calibration. The presentation will summarize the most common types of failures, how maintenance is essential for longevity and the importance of high-quality robust tooling.

Carburizing and induction hardening are two commonly used surface heat treatments that increase fatigue life and surface wear resistance of steels without sacrificing toughness. It is hypothesized that induction hardening following carburizing could yield further increased torsional fatigue performance through reducing the magnitude of the tensile residual stresses at the carburizing case-core interface. If successful, manufacturers could see gains in part performance by combining both established approaches. A carburizing heat treatment with a case depth of 1.0 or 1.5 mm and an induction hardening heat treatment with a case depth of 0, 2.0, or 3.0 mm were applied to torsional fatigue specimens of 4121 steel modified with 0.84 wt pct Cr. The carburized samples without further induction processing, the 0 mm induction case depth, served as a baseline for comparison. The as-received microstructure of the alloy was a combination of polygonal ferrite and upper bainite with area fractions of approximately 27% and 73% respectively. The case microstructure of the heat-treated conditions was primarily tempered martensite and transitioned to a bainitic microstructure around the deepest overall case depth. Material property characterization consisted of radial cross-sectional hardness testing and torsional fatigue testing. The hardness profiles confirmed that the designed case depths were achieved for all conditions. Torsional fatigue testing was conducted using a Satec SF-1U Universal Fatigue Tester. Of the six tested conditions, the condition with the deepest case depths, i.e. carburized to 1.5 mm and induction hardened to 3.0 mm, was expected to have the greatest increase in fatigue performance. However, initial fatigue results potentially indicate the opposite effect as the non-induction hardened samples exhibited longer fatigue lives on average.

Induction hardening is used to harden small cylinders of SAE 1074 steel. Parts were quenched with a high concentration of a polyalkylene glycol (PAG) type quenchant. Soft spots were found on a small percentage of the parts. These soft spots were consistently at one location about 2/3 from the bottom of the part. These soft spots were circular, and consistent in size. The product was examined and determined to be adequate and to specification. Using a lower concentration of quenchant, the quench speed was increased. While this reduced the number of soft spots, it did not eliminate the soft spots. Faster quenches were tried with similar results. Using Transvalor SIMHEAT, we were able to duplicate the results, and eliminate the source of soft spots.

The Ultra Large Bearing (ULB) industry can increase the production performances by using induction heating on a full range of thermal processes. The paper presents the technological, economical, and process optimizations that can be achieved using induction heating technology in both hardening and tempering. Two different solutions are available for (seamless) race hardening: a high-power induction single shot process for small to medium size rings and induction seamless scan hardening for large sized bearings. The ultra-low frequency induction tempering process is described and compared with a traditional furnace. These technologies are presented and compared to show application ranges, specific features, metallurgical results, and efficiencies in processing and cost.

Commercially, carbon steels are induction heated at heating rates on the order of 100 to 1,000 °C·s -1 for surface hardening. The high precision DIL 805L dilatometer employs induction heating and is often used to study transformation characteristics and prepare test specimens for metallurgical analysis. However, heating the commonly used 4 mm diameter by 10 mm long specimens at rates above 50 °C·s -1 results in non-linear heating rates during transformation to austenite and large transient temperature variations along the specimen length. These limitations in heating rate and variances from ideal uniform heating can lead to inaccurate characterization of the transformation behavior compared to commercial induction hardening practices. In this study it is shown that changing the specimen design to a thin wall tube allows faster heating rates up to 600 °C·s -1 and modifies the pattern of temperature variations within the test sample. The response of selected specimen geometries to induction heating in the dilatometer is characterized by modelling and tests using multiple thermocouples are used to verify the models. It is demonstrated that the use of properly designed tubular test specimens can aid in more accurately establishing transformation characteristics during commercial induction hardening.

This paper revisits a case study presented at Heat Treat 2009, investigating the failure of induction coils used for heat treating automotive wheel hubs. At the time, computer simulation was beginning to allow for virtual prototyping of heat treat applications as an alternative to experimental testing. As explained in the original paper on p. 86 of the 2009 HTS conference proceedings, although simulation helped in the development of a more robust coil, it was not used to pinpoint the cause of failure. In this current work, the authors tackle the same problem aided by more than a decade of improvements in compute power and finite element analysis techniques. To highlight the leaps made in virtual prototyping, the induction hardening coil previously analyzed using an axisymmetric 2D model is now examined using more precise 3D electromagnetic and thermal models while accounting for the rotation of the part.

Induction hardening, although a safe repeatable process, can require a lot of tuning whenever an input parameter or inductor is changed. This paper discusses the nature of the problem and how it can be alleviated using 3D technology. It explains that long setup times and tedious adjustments after tooling changes are due to inaccuracies in the inductors and their positioning relative to the workpiece. It then describes how these inaccuracies are removed using 3D construction, production, measurement, and positioning technology, including FEA and CFD software, laser powder bed fusion, and optical scanning. To verify the approach, two inductors were additively manufactured and tested in a hardening system. The first inductor was used to harden a bearing seat on a shaft. The inductors were then swapped and another part was hardened without any adjustment to the process. The hardening depth and surface hardness of the two parts are identical within the scope of measurement accuracy.

This paper investigates the effect of various types of errors on the accuracy of finite-element models used to simulate electromagnetic induction heat treating processes. By comparing simulation outputs, it shows how FEA calculations are affected by incorrect material specifications, incorrectly entered data, imprecise data, misassigned elements, unsuitable mesh sizing, inadequate current or power, and failure to properly account for skin effect depth. The paper includes relevant data and equations in addition to computer generated plots.

This study demonstrates the use of simulation in the design of induction hardening coils. It compares three coil geometries, two of which leverage the flexibility of 3D printing. The paper explains how to set up and run the simulations in order to predict temperature fields, hardness profiles, and microstructure distributions in the workpiece. Based on the simulations, the conventionally manufactured coil and one of the two 3D-printed coils do not achieve the desired martensitic microstructure everywhere along the surface of the workpiece. In the case of the 3D-printed coil, the simulations show that the workpiece overheats in an area where its diameter abruptly changes. To fix the problem, the coil was adapted with an additional winding that carries current in the opposite direction. Simulations show that the redesign reduces hot spot temperature by more than 200 °C, producing the desired microstructure in that area of the workpiece and a more uniform hardness profile.

Large slewing bearings are employed in wind turbines and other energy industry applications where they are subjected to harsh working conditions. In order to bear heavy dynamic loads, slewing ring tracks can be surface hardened by induction heating with a seamless process which allows for a uniform heat treatment without soft zones. In comparison with the traditional furnace carburizing, seamless induction hardening is faster, consumes less energy, and has been developed to achieve the same results utilizing medium carbon steel. The presence of a pre-heating coil, with an independent power source, allows for the adjustment of the heat input rate in order to tune the heating process according to the steel characteristics. The pre-heating operation allows for case depths up to 10 mm to be reached without a reduction in scanning speed or productivity. A mechanical tracking system adjusts the coils to compensate for ring deformation and thus assure a uniform heating pattern. Surface hardness tests and metallography have been performed in different process stages to verify the process consistency. A fine grain microstructure in the end zone has been obtained thanks to the pre-heating coil, which avoids surface overheating.

In this contribution, we attempt to optimize the heat process of a gear. The goal is to evaluate the best use of two frequencies to complete the heating phase in the least amount of time achieving a uniform distribution of temperature in the treated area of the gear. Assuming the application of the appropriate cooling, this temperature distribution will lead to the appropriate hardness along and between the teeth of the gear. A 3D model of part of the gear wheel is modelled in a multiphysics magneto-thermal analysis. The two frequencies used for the heating are first evaluated. In the optimization process, the duration of the application for each frequency is a parameter. Temperatures are evaluated through the heating process at selected locations as constraints of the optimization process.

This paper describes some of the ways manufacturing data are being used to reduce variations in heat treat processes and achieve higher levels of conformance in treated parts. It also includes a review of quality management practices and demonstrates the use of Six Sigma statistical analysis in an induction heat treating application.

Rapid induction hardening of martensitic steel can attain the very high strength levels needed for light-weighting components subjected to high operating stresses. Specimens of martensitic 0.6% C steels were heat treated using a dilatometer to investigate the effects of heating rates of 5 to 500 °C/s to temperatures of 850 to 1050 °C on the transformation to austenite and subsequent transformation to martensite during quenching. Selected specimens were quenched after partial transformation to austenite to assess the initial cementite precipitate size formed in ferrite during heating. Other specimens were isothermally held at the austenitizing temperature to assess cementite dissolution rates. Higher heating rates increased the Ac1 and Ac3 temperatures, and lowered the Ms temperature. Alloy content and prior microstructure also influenced the transformation temperatures.

Quenching is a process of cooling a metal at a rapid rate. This is most often done to produce a martensite transformation. In ferrous alloys, this will often product a harder metal, while non-ferrous alloys will usually become softer than normal. Quenching is a very important part of the induction process in order to get the desired hardness of a metal, and improper quenching may lead to a variety of problems. Various type of aqueous quenchants for induction hardening will be reviewed along with the three stages of the quenching process. Basic information on care and maintenance of those quenchants will also be reviewed.

Although great strides are being made in the simulation of induction patterns, most of today’s inductor design and validation activities are still done through experience and experimentation. This paper provides a brief overview of how an inductor is designed, fabricated, and prepared for integration into manufacturing. Each aspect of its manufacture is critical to deliver a hardening inductor capable of meeting engineering drawing requirements and to be ready for production. The paper covers determination of requirements, inductor design, fabrication and assembly, process development, inductor characterization, metallurgical validation, and delivery of a production-ready inductor. Each step is described, and important considerations for each are presented.

Vanadium microalloying additions are common in medium carbon ferrite-pearlite steel shafts. The increased load capacity provided by vanadium carbonitride precipitation is beneficial in many applications. Induction hardening can further increase the surface strength of a component; however, the implications of the vanadium carbonitride precipitates on microstructural evolution during induction hardening are unclear. Evidence that vanadium microalloying influences the microstructural evolution of the induction hardened case as well as the case/core transition regions are presented in the current study. Vanadium increases the amount of non-martensitic transformation products in the case while decreasing austenite formation kinetics in the case/core transition region. Observations in induction-hardened shafts were supported by Gleeble physical simulations of computer simulated thermal profiles. Characterization was conducted using scanning electron microscopy, dilatometry, and microhardness testing.

Historically, steels with carbon contents above about 0.45% C that are quenched to attain hardness above about 53 HRC (560 HV) are prone to premature brittle fracture when stressed in uniaxial or cyclic tension. In this study, five laboratory melted steels containing nominally 0.56% C and no grain refining additions (Ti, Al, V, or Nb) were heat treated on a Gleeble 3500 simulator to emulate thermal heating and quenching cycles for induction hardening. Limiting the peak heating temperatures and times produced very fine grained austenite with final hardness above 60HRC (700HV). Fracture resistance measured by the peak breaking load in notched bend tests increased by up to 3 fold for the short low temperature heating cycles as compared to longer higher temperature cycles. Fracture surfaces showed trans-granular crack propagation for the short low temperature cycles as compared to inter-granular propagation for the longer higher temperature cycles.

Application of 3D finite element method (FEM) simulation for induction hardening of gears is still a time-consuming and expensive task. The significant cost of a simulation remains in the manual preparation of the 3D description of geometry. In the current work, we propose to complement the numeric simulations with automatic geometry generation based on a parametric representation of a gear and an induction coil. The parameters used to describe a gear are module, pitch diameter, and pressure angle. The circular coil is described by the height, external and internal diameters. FEM computations are implemented to solve magneto-quasi-static Maxwell’s equations. A demonstration of the possibilities of the proposed approach via a parametric study is presented by varying the module of a gear while keeping a constant number of teeth. A heuristic tuning of heating power frequency- time is presented here and compared to the classical semi-analytical equations and 2D simulations.

In single-shot hardening applications, heat treated components often feature a variety of geometric complexities including variable wall thicknesses, sharp diameter transitions, lightening holes, slots, etc. Due to the inherent 3D electromagnetic nature of single-shot coils and the complex geometry components which they must accommodate, the design and optimization of single-shot hardening coils is typically a demanding and intricate task. This paper presents combined electromagnetic-thermal and thermal-mechanical FEA simulation results for the single-shot induction hardening of a power transmission shaft. The simulation results, including electromagnetic, thermal, metallurgical, and mechanical data demonstrate the value of computer simulation in the design and development of single-shot induction hardening systems.