Hot Forming Processes require exact Temperature Control

LumaSense non-contact temperature monitoring solutions for press hardening are designed to meet the critical quality assurance standards required by CQI-9

The requirements regarding the adherence to tight temperature limits in hot forming processes become evidently more stringent. Reasons for that are continuously increasing quality requirements on materials, especially on steel parts.

Especially in the automotive industry, highest demands are set on materials and processes due to the constantly increasing safety and quality requirements alongside with material savings for weight reduction, especially in the manufacture of body parts.

For the mentioned weight reduction on vehicle parts, the so-called press hardening is used during body production. This allows a reduction in material thickness while achieving high strength values. A heating range can be precisely defined on dedicated components to form a hardened as well as a non-hardened area.

This implements that a single component with different strength values has to be manufactured, e.g. for crumple zone and passenger compartment. The observance of the tightest temperature tolerances is an essential parameter for quality assurance in order to ensure a graduated, locally defined heating zone.

In industrial hot forming applications (e.g. press forging, bending, press hardening), heat treatment temperatures are instrumental in meeting the specified quality requirements and achieving optimum characteristics of work pieces. In addition to precise temperature measurements, closed-loop process control and documentation of measured data are strongly required.

To minimize systematic measuring errors, which may be caused by external influences (e.g. surface variations, reflections), temperatures on metal surfaces should always be measured at the shortest possible wavelength. This implies that the devices should measure in the near infrared range, depending on the desired process temperature, and on several points of the object.

The use of a thermal camera in the near infrared range enables the determination of an exact temperature distribution. The measured data allow for an exact process control, in addition these measured values are also documented.

The field of view of the thermal imaging camera should cover the entire component, whereby the measurement angle should not be less than 30° to the measurement surface.

 


Pic 1: Typical Thermal Image of a workpiece during press-hardening

The MCS640 thermal imager by LumaSense Technologies offers perfect measuring qualities especially on metallic surfaces offering a temperature range between 600 … 3000 °C. With a resolution of 640 x 480 pixels over 34,000 measuring points on the component surface can be defined. A high accuracy of 0.5% of the measurement temperature guarantees for accurate temperature measurement of each component.

 

Pic. 2: LumaSense MCS640 Short wave Thermal Imager / with protective housing

Thanks to a fast acquisition time in the millisecond range, a thermal image can be recorded when inserting the workpiece into the press and evaluated via the software. Due to the compact design of the MCS640 with air / water cooling housing, the camera can be placed optimally on the side of the press.

Pic. 3: Simplified schematic of a hot forming process set-up

By using the MCS640 Thermal Imaging Camera it is possible to monitor and document the entire pressing process with the required and necessary accuracy.

According to CQI-9 Heat Treat System Assessment especially for vehicle parts, the temperature distribution during curing process must be recorded. This is not provided by a point measurement via a pyrometer.

After the pressing process, it makes perfect sense to monitor the component temperature with a medium wave camera to ensure that the cooling process has reached temperatures below 150 °C
at any point during pressing.

Contact:
LumaSense Technologies GmbH
www.lumasenseinc.com,
info@lumasenseinc.com

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