Thermoforming is a key manufacturing process used across industries such as packaging, automotive, construction, and consumer goods. The process relies on heating thermoplastic materials to a specific temperature — typically near the glass transition point — where the material becomes pliable and can be formed into the desired shape.
Precise temperature control at this stage is critical. Even minor deviations can lead to defects such as uneven thickness, weak structural zones, or surface imperfections. As a result, reliable and accurate temperature monitoring becomes a fundamental requirement for stable and efficient thermoforming operations.
Process Characteristics and Measurement Challenges
In thermoforming, plastic sheets are heated using infrared radiators and then shaped through vacuum, pressure, or mechanical forming. After forming, controlled cooling ensures that the product retains its geometry and mechanical properties.
However, accurate temperature measurement in this process is particularly challenging due to several factors:
• thin plastic films (often < 400 µm) that can be partially transparent
• interference from infrared heaters operating in similar spectral ranges
• varying emissivity depending on material, surface, and wavelength
• rapid heating cycles and dynamic production environments
These conditions make conventional contact measurement methods unsuitable and require advanced non-contact infrared solutions.
Importance of Glass Transition Temperature Control
A critical parameter in thermoforming is the glass transition temperature (Tg) — the point at which the material becomes soft enough to be formed. Maintaining uniform temperature across the entire plastic sheet ensures consistent material behavior.
Insufficient or uneven heating can result in:
• incomplete forming or deformation
• internal stresses and weak spots
• reduced product quality and repeatability
Achieving homogeneous temperature distribution is therefore essential for ensuring reliable production outcomes.
Infrared Measurement and Spectral Considerations
Infrared pyrometers provide the fastest and most direct method for measuring surface temperature in thermoforming processes. However, correct sensor selection is crucial.
A key challenge is spectral interference. Infrared heaters typically operate in:
• Near infrared (NIR): 0.75 – 1.5 µm
• Mid infrared (MIR): 1.5 – 5.0 µm
To avoid measurement errors caused by reflected radiation, temperature sensors should operate in a different spectral range, typically:
• Long-wave infrared (8 – 14 µm) for standard applications
For thin or semi-transparent plastics, measurement must be performed in material-specific absorption bands, such as:
• 3.43 µm (C-H band) – suitable for PE, PP, PS
• 7.95 µm (C-F band) – suitable for fluoroplastics and polyimides
Selecting the correct spectral range ensures accurate temperature detection without interference from heaters or background radiation.
Optris Infrared Solutions for Thermoforming
Optris offers a range of infrared pyrometers designed specifically for challenging industrial environments such as thermoforming.
CT LT Pyrometers
For many thermoforming applications — especially with thicker plastic films (> 400 µm) — long-wave infrared sensors such as the Optris CT LT provide a reliable and cost-effective solution.
Key advantages:
• operation in long-wave IR range (8–14 µm)
• stable measurement unaffected by heater radiation
• thermoshock-resistant design for harsh environments
• suitability for continuous industrial operation
These sensors can be installed directly near infrared heaters, where the material reaches peak temperature, enabling precise process monitoring.
Integration into Industrial Processes
Infrared sensors can be easily integrated into thermoforming lines and connected to control systems such as PLCs. This enables real-time process control and automatic adjustment of heating parameters.
Typical implementation includes:
• installation of multiple sensors along the production line
• continuous monitoring of temperature distribution
• automatic adjustment of heater output based on sensor feedback
This approach ensures stable temperature conditions and minimizes process variability.
Advantages of Real-Time Temperature Monitoring
The implementation of infrared measurement systems in thermoforming provides several key benefits:
• uniform heating of plastic sheets for consistent product quality
• reduction of material waste caused by overheating or underheating
• improved process stability and repeatability
• real-time process control through PLC integration
• optimized energy consumption by adjusting heater performance
Additionally, Optris sensors are designed for easy installation and maintenance. Features such as separable sensor heads, mounting accessories, and protective housings simplify integration into existing equipment and reduce downtime.
Application Value in Industrial Production
Accurate temperature control transforms thermoforming from a sensitive process into a stable and optimized production system.
By using infrared measurement solutions, manufacturers can:
• maintain consistent glass transition conditions
• improve product quality and dimensional accuracy
• reduce defects and production losses
• increase overall efficiency and energy savings
As a result, thermoforming processes become more reliable, cost-effective, and aligned with modern industrial requirements, including automation and Industry 4.0 integration.
