GMW 17920 Heated Laminated Glass Test Procedures

The standard "GMW 17920 Heated Laminated Glass Test Procedures," published by General Motors (GM), describes a test method for evaluating the performance of a heated windshield under environmental conditions. Some tests are performed on the vehicle, while others can be performed at the component level.

This standard applies to passenger cars, multi-purpose passenger vehicles, trucks, and vehicles with a gross vehicle mass (weight) rating of 4536 kg or less.

This standard is the worldwide glass testing standard developed by General Motors. Its purpose is to establish a common testing methodology for heated windshield systems to ensure the continued development and production of a high-quality, world-class system.

In the ever-evolving world of automotive engineering, safety, comfort, and innovation are paramount. One critical component that embodies these principles is heated laminated glass, commonly used in windshields and other vehicle windows to combat fogging, icing, and reduced visibility in adverse weather conditions. The GMW 17920 standard plays a key role in ensuring that such glass meets stringent performance, durability, and safety criteria. By outlining the requirements for heated laminated glass used in automotive applications, this standard helps manufacturers produce reliable components that enhance driver safety.

As vehicles increasingly adopt advanced features like autonomous driver assistance systems and head-up displays, integrating heating elements into laminated glass has become essential. The GMW 17920 standard sets a benchmark for quality, ensuring that these systems not only operate effectively but also withstand the harsh environments encountered on the road.

The GMW 17920 standard specifically addresses the issue of heated laminated glass and focuses on the design, construction and verification of glass assemblies that contain embedded heating elements, such as conductive films or wires, and provide misting and defrosting properties.

Unlike traditional laminated glass, which consists of two or more layers of glass bonded together with an interlayer (usually polyvinyl butyral), heated glass varieties add a conductive layer that generates heat when an electric current is applied. This standard ensures that the glass maintains its optical clarity, structural integrity, and electrical safety under various operating conditions. This is particularly true for vehicles where rapid defrosting is crucial for passenger comfort and compliance with international visibility standards.

This standard was developed in response to the growing demand for energy-efficient heating solutions that outperform traditional defroster grilles at the base of the windshield. By embedding the heating directly into the glass, vehicles can achieve faster warm-up times, typically under a minute, reducing energy consumption from the vehicle's electrical system.

The GMW 17920 standard provides a comprehensive set of specifications to ensure the reliability of heated laminated glass. These requirements cover material selection, manufacturing tolerances, performance criteria, and environmental durability. Key requirements include:

• Material composition:
  • Glass layers: The outer layers should be soda-lime-silica glass of specific thicknesses (usually 2,1-2,6 mm per layer) to balance strength and weight.
  • Interlayer: A thermoplastic interlayer such as polyvinyl butyral or ethylene-vinyl acetate should cover the heating element without compromising acoustic damping or UV resistance.
  • Heating element: Conductive materials such as silver-based printed inks, metallic mesh, or transparent conductive oxide films are specified. The element must provide uniform heating across at least 80 percent of the glass surface and have a resistance range of 2-10 ohms per square meter to ensure efficient power distribution (typically 300-600 watts per square meter).
• Optical and visual features:
  • Clarity is non-negotiable: The glass must maintain at least 70 percent light transmittance (per ISO 9050 standard) to prevent distortion of head-up display projections or camera-based systems.
  • Distortion limits are strict, and allowable wedge angles are below 0,35 milliradians to prevent optical aberrations.
  • The heating grid should be invisible or barely visible and line widths should be below 0,1 mm for aesthetic integrity.
• Electrical and thermal performance:
  • Heating efficiency: The system should reach 40-60 degrees within 180 seconds at an ambient temperature of minus 20 degrees.
  • Power supply compatibility: Designed for 12V or 48V vehicle systems and includes overcurrent protection measures.
  • Thermal uniformity: Temperature gradients across the surface should not exceed 10 degrees to avoid hot spots that could damage the interlayer or cause delamination.
• Mechanical and durability standards:
  • The assembly must withstand stone impact tests (per FMVSS 205 standard) without compromising heating functionality.
  • Vibration and thermal cycling tests simulate real-world conditions and require no more than 5 percent degradation in heating performance after 1.000 cycles between -40 degrees Celsius and +85 degrees Celsius.

These requirements align with broader GM standards, such as the GMW 15760 standard for design verification and the GMW 14872 standard for corrosion testing, ensuring overall product reliability.

Compliance with the GMW 17920 standard is verified through a multi-stage testing process typically conducted by accredited laboratories with advanced facilities for automotive material analysis. The process includes:

• Design validation: Initial prototypes undergo electrical resistivity checks, infrared thermography for heat mapping, and optical distortion analysis using laser interferometry.
• Product validation: Full-scale assemblies are subjected to environmental chambers for humidity (95 percent relative humidity at 85 degrees), salt spray corrosion, and UV aging to simulate five years of exposure.
• Post-verification inspection: Random sampling of production batches ensures consistent quality, and failure rates for key features such as interlayer adhesion are limited to 1 percent.

These tests not only verify performance but also identify potential failure modes, such as electrical shorts due to manufacturing defects or poor heating efficiency due to material fatigue. Using tools such as high-speed cameras for pulse analysis and multimeters for real-time power monitoring, the labs provide data that feeds back into iterative design improvements.

Heated laminated glass, covered by the GMW 17920 standard, is becoming increasingly standard across the GM product line. In addition to defogging, it also supports advanced driver assistance systems (ADAS) by keeping sensors clean. The technology is also extending to side and rear windows, where curved designs make uniform heating difficult. Innovations such as flexible printed circuits ensure seamless integration, meeting the standard's tolerances even in complex geometries.

Ultimately, the GMW 17920 standard stands as a testament to General Motors' commitment to engineering excellence, ensuring that heated laminated glass not only meets but exceeds the demands of modern mobility. By standardizing quality and performance, it paves the way for innovative glass solutions while protecting drivers.

Our organization, which has been serving for many years and meticulously following global developments in science and technology, conducts testing, measurement, and analysis in a wide range of areas for businesses in every sector with a skilled team and extensive infrastructure. In this context, we also provide testing services in accordance with the "GMW 17920 Heated Laminated Glass Test Procedures" standard.