Complete quality assurance for induction hardening

Production planners in the automotive industry are pursuing zero-defect strategies—as much as possible considering the tremendous increase in the technical complexity of vehicles over the last few years. Consequently, requirements have become even stricter, resulting in even more sources of error in production. The frequent recalls we have seen in recent years have been evidence of this. Therefore, comprehensive quality monitoring is becoming increasingly important for many OEMs and automotive suppliers. This especially true for heat treatment processes, as they have a major influence on the stability of important parts within the automobile. With this in mind, the induction specialists at eldec are intensifying their commitment to the quality monitoring of induction hardening machines: “eldec Quality Control” is proof of that and includes an entire package of new modules designed to optimise process reliability. The components build on and complement one another, and together, they guarantee customers an extensively monitored hardening process.

The numbers keep rising: The Center of Automotive Management (CAM) in Bergisch Gladbach, Germany, has calculated that more than 45 million vehicles were recalled in the USA in the past year alone. According to the CAM, “safety problems” are the cause. That is why over the course of two years, more than 108 million vehicles had to be inspected and repaired, at enormous costs to suppliers. While there are several causes behind this, unreliable production processes definitely play a central role. The machinery industry is therefore committed to raising quality assurance to the highest standards. “eldec Quality Control” (eQC) is an excellent example for this. The induction specialist, based in Dornstetten, Germany, has divided its package of quality assurance tools into two areas: “electrical monitoring” and “mechanical monitoring.” These include three entirely new modules that help to assure the quality of the hardening process: tool identification by RFID chip, continuous measurement of the induct voltage, and monitoring of the quenching medium with a sensor. “Together, these and other eQC measures return a wealth of data, which is all saved and compared against various reference values. When discrepancies are detected, the machine reports the problem and under certain conditions, will stop the process,” says Andreas Endmann, Head of Technology Sales for hardening systems at eldec. “It's hard to imagine better process reliability and quality monitoring than that.”

Is the right tool being used?

Tool identification is a good example of how this actually works in practice. Before production starts, the machine knows if the correct inductor for the selected machining program has been inserted and what condition the tool is in. It gets this information by reading and caching important performance data, such as remaining tool life and impending maintenance intervals, from an RFID chip in the tool. When the process is completed, new information is written to the chip. A new read-write unit is installed in the connection system of the machine for this purpose. In the event of tool defects or errors, the process will not start. “But the possibilities don't end there,” Endmann says. “For example, the machine can be informed about the manufacturing tolerances of the tool and adjust its axis automatically as needed. In this way, the system also improves the machining quality.”

How much electricity is flowing through the workpiece?

Increased quality, fewer process failures—this is also the benefit of the second new module in eQC: The electric voltage can now be measured at the base of the inductor during production. Normally these power values are measured only at the inverter, which sends the electricity to the tool. In other words, the new system tells you for the first time how much electricity actually “arrives” at the tool. Why is this difference so important? “It’s the only way to know how strong the magnetic field is that is generated by the inductor and permeates to the part. This value is directly affected by the shape of the tool and the part, the material, and other factors as well. Measurements at the inverter are not affected by that and are therefore not accurate enough. So we are now collecting the data that is generated right where the work is done and are incorporating it into process monitoring,” Endmann explains. This means the heating of the part is monitored much more accurately, the hardening process is controlled with even greater precision, and the quality of the part increases even further as a result.

How does the quality of the quenching medium change?

Another important factor in the quality and stability of the hardening process is the state of the quenching medium. It changes during the process because the polymer chains in the medium are gradually broken down by light and heat. The quenching medium eventually loses the necessary surface tension. “Checking the quality of the quenching medium regularly is therefore essential. At present, this is still often done by measuring the light refraction index. However, that does not indicate the condition of the polymer chains and is therefore too inaccurate. We now rely on a new sensor that uses ultrasound to continuously monitor the viscosity of the quenching medium and provides very precise information regarding its quality,” says Endmann, explaining the third new module in eQC. This increases reliability especially when producing complex parts with many edges and bore holes, as these parts tend to crack when a quenching medium with deteriorating viscosity is used.

Comprehensive package for greater quality and reliability

All things considered, the German induction company believes that this package puts it in an ideal position. The eQC elements all build on and complement one another: Before production start, the newly inserted tool is checked and its condition recorded. During the process, the electrical power is measured with high accuracy directly on the tool. At the same time, a sensor continuously checks the quality of the quenching medium. Other standard components, such as an energy controller, round out the comprehensive offering. “Industrial production changes very quickly in this day and age,” Endmann observes in conclusion. “The Industry 4.0 concept shows the way forward. Not only does production have to satisfy increasingly high standards of quality. At the same time, the quality and the process that creates it also have to be documented comprehensively. Our eQC concept covers both of these needs.”