Induction Heating Process Simulation for Forging
One goal of every forger is to get the best heating process possible for their application with respect to temperature uniformity, efficient energy consumption, welding rates and scaling rates. When setting up a new line or making changes for a new part run, one of the biggest challenges is to determine the optimum settings for the billet heating system to ensure the proper temperature profile as the hot billet enters the forming process (Figure 1).
Manual Setup and ConfigurationIn the past, the only way to achieve this delicate balance was through the time-consuming and costly processing of billets to determine the right recipe. This manual trial-and-error process renders a significant amount of loss in production time and scrapped billets. In some cases, such as when evaluating the possibility of adding a new part to the line, the manual testing process may not even be an option if the forge shop does not have the proper induction coil for the new part. New simulation technology allows quick part-to-coil size analysis versus rule of thumb or costly trial and error analysis (Figure 6).
Induction Heating SimulationFor many years, induction equipment manufacturers have utilized complex in-house coil calculation programs and process-simulation software for forging-system conception and design. The simulation of induction heating is very complex because of the selectable frequency and adjustable power levels available. Furthermore, the effect of frequency on the depth of current penetration varies by a factor of four during the heating process as the part transitions from below the Curie magnetic point to above the Curie point to non-magnetic conditions. Additional influences include the resistivity of the material, coil coupling range, current cancellation, scaling and rejection rates.
End-User Software Package AvailableAs computing technology has progressed, the computing power contained in a commercial PC is sufficient to run the complex algorithms necessary to simulate all of the variables that go into a heating process simulation. To this end, ABP Induction developed THERMPROF, a heating process-simulation software package that offers the power of an induction manufacturer’s complex in-house programs in a user-friendly program. This Windows-based program is offered to end-users in conjunction with the ABP Zone Control forge heating concept. This multi-converter heating approach enables the energy input to be regulated zone by zone, providing great flexibility to economically cope with different workpiece dimensions.
The simulation software is used to find the correct settings for individually actuating the converter modules without time-consuming and costly trials. This allows the expected temperature profile to be computed and the heating optimized according to the individual aspects of the job. Together with the physical billet dimensions, required throughput or tact cycle, the target average and admissible deviation of the billet’s temperature in each separately controlled zone can be stipulated. The software functions extend to displaying the thermal history of the forged part from its initial heating and up to its first deformation.
Dynamic Visualization of Heating ProcessThe result is a dynamic process-curve chart that displays the core, surface and average temperature of the billet through its entire heating cycle (Figure 2). To obtain more details about billet temperature, another window can be opened in which the temperature distribution within the billet is shown in a colored 3-D visualization (Figure 3). This visualization can be viewed for any position within the heating zone by moving a slider, which represents the billet along the heater’s length. The temperature once the billet has left the heater can also be analyzed, as it is possible to define the number of seconds from the exit of the last coil to the first forming operation. This provides the user with total control of the billet temperature throughout the heating process to the first forming.
Additionally, the energy consumption, material cost and scale losses are analyzed, enabling the user to minimize the unit cost for any forging operation. Converter load and temperature are monitored in order to avoid converter overload or prevent localized billet overheating, where the admissible maximum local temperature for each separately controlled zone section can be defined by the user (Figure 4).
Another feature is a cost-estimation calculator. It considers the energy consumption, the material costs with respect to scale losses and die wear against the uniformity of the temperature distribution within the billets at first forming. This allows for unit heating cost to be accurately calculated for a specific part simulation (Figure 5).
Forging Simulation Software IntegrationThe output from the THERMPROF software, used in combination with ABP’s Prodapt-FX heating-system main processor, can control and optimize performance under all operating conditions. The Prodapt-FX hardware incorporates a PLC controller and has a user-friendly HMI control panel with visual touch screen and function keys. This allows the forge operator to visually analyze the main system components, as well as the heating process, to quickly make any desired changes in process parameters if needed.
Importing Heating Simulation DataHot-forging designers who perform metal-flow simulation often start with an invalid assumption on the initial billet temperature. The assumption is made that the initial temperature of the billet is uniform throughout. In reality, however, the billet temperature is not uniform, and this will affect the material flow.
The flow stress varies as a function of temperature, and if the initial temperature is not correctly defined it can lead to unexpected material flow problems. The only solution so far is to make assumptions based on experience and actual measurements, and then initialize the billet temperature with this approximated data.
However, during the Hannover Fair 2009, a better solution was proposed for customers who use the Simufact.forming metal-forming software of Simufact Engineering GmbH. The idea was to couple the ABP THERMPROF heat-profile simulation software with the Simufact.forming software package, allowing hot-forging designers to fully take into account the results of ABP’s modular Zone Control induction heating process during metal-flow simulations (Figure 7).
The Simufact.forming package offers a fully integrated 3-D and 2-D solution using two well-known solution models: the Finite Element Method and the Finite Volume Method. Typical examples of simulations are hot and cold forging, tool and die stress anal-ysis, ring rolling and reduction. One benefit gained from these simulations is the early detection of flaws in the process, such as die underfill and creation of cracks, folds and laps. It also enables the evaluation of internal die loads and stresses and the determination of residual stresses in the part after forming.
ConclusionContinued advances in simulation technology allow forgers to be more flexible in their production planning and analysis of complex cycles, alternative part geometries and specialty alloy compositions. Simulation of the induction heating process for forging can assist in the optimization of the heating profile to maximize throughput while minimizing energy consumption. The partnering of induction thermal simulation with forming simulation software benchmarks a new level of sophistication not previously available.
Author Stephen Klostermeyer is VP Sales & Marketing – Heating, Brookfield,Wis. He may be reached at firstname.lastname@example.org. Author Don Gibeaut is Forging Leader. He may be reached at email@example.com. Author Arjaan Buijk is Managing Director, Simufact-Americas, Plymouth, Mich. He may be reached at 734-238-2173 or firstname.lastname@example.org. For more details on THERMPROF visit www.ABPinduction.com/heating. For more details on Simufact.forming, visit www.simufact-americas.com.