GMW15356 Sheet Metal Grading Scale

The purpose of the rating scale, whose requirements are outlined in the "GMW15356 Sheet Metal Rating Scale" standard developed by General Motors, is to ensure comparison between vehicles and consistency among personnel. Corrosion rating involves the detection of an objectionable surface, and judgment is largely subjective. In developing corrosion scales, an effort has been made to provide objective criteria to guide subjective judgment. Essentially, nothing in this standard supersedes applicable laws and regulations.

The corrosion rating scale guides (Appendix A) included in this standard appendix contain corrosion rating scales, rating guides, and photographs for determining corrosion severity on all vehicle components, including body and sheet metal, underbody and underhood components, and fasteners. The scales are intended for use in both institutional corrosion inspections and field investigations.

This sheet metal guide includes body panels, flanges, and door hinges.

When rating components on a vehicle, the type of part being rated must be considered. For a customer, objectionable corrosion on a panel differs from that on a component or fastener in terms of the total area of ​​corrosion. A panel is more likely to be punctured or to experience significant metal loss long before 100 percent of its area is corroded. Consequently, when rating a panel, one should locate and rate the worst area on the panel. For components and fasteners, it makes sense to rate by estimating the percentage of visible corrosion area. If the correct rating truly falls between two rating values, the lower of the two rating values ​​should be used.

The guides are organized into four independent documents. The first three guides consist of a cosmetic corrosion rating scale and photographs for red rust. The fourth guide provides the same type of rating scale and photographs for white corrosion. The red rust guides consist of the "GMW15356 Sheet Metal," "GMW15357 Components," and "GMW15358 Fasteners" standards. The "GMW15359 White Corrosion Guide" standard covers coated components. The use of the white corrosion rating scale is not limited to this material and can be used on any coating or material exhibiting white corrosion. When rating a part, determine the type of part being rated and use the appropriate section of the guide. In all cases, using a pictorial reference ensures consistent ratings and is easier than a rigid written description. Rating guides can be helpful in determining the range of photographs to use for comparison.

The corrosion rating scale reflects the various degrees of corrosion and ranks them as shown in the rating guidelines. On a scale of 1 to 10, 1 indicates perforation, 2 indicates significant metal loss, and 10 indicates no visible corrosion. Ratings 3 to 9 reflect degrees of corrosion ranging from very slight to extensive. The photo guidelines for this scale focus on showing examples of ratings 3 to 10. These ratings are inherently cosmetic in nature. Ratings 2 and 1 indicate significant metal loss or actual substrate perforation, respectively, and are not included.

Regarding the sheet metal,

• Body panel rating scale: This section is used to rate red rust corrosion on body panels. The worst area of ​​the panel or panel section being evaluated is located. When rating panel corrosion, the customer's perception of corrosion is evaluated rather than assessing a specific area of ​​corrosion. The area is compared to the series of panel photographs in Appendix B, and the comparable level is selected for rating.
• Hem flange rating scale: Only corrosion originating from the curved areas of the panel should be rated. The worst area of ​​the hem flange where corrosion is occurring (approximately 15 cm) is located. Instead of assessing a specific area of ​​corrosion, the severity of the corrosive attack is assessed. The area is compared to the series of hem flange photographs in the figure, and the comparable level is selected for rating.
• Door hinge grading scale: Compare the area of ​​the hinge with the door hinge photo series in Appendix D and select the comparable level for grading.

In the table titled “Corrosion rating scale” given in the standard, the rating is as follows:

• 10 = No visible corrosion
• 9 = Corrosion trace
• 8 = Light corrosion
• 7 = Light corrosion
• 6 = Moderate corrosion
• 5 = Moderate corrosion
• 4 = Mostly corroded
• 3 = Completely corroded
• 2 = Severe corrosion (corrosion causing significant metal loss)
• 1 = Puncture

The GMW15356 standard is important because it outlines the specifications and requirements for labels used on General Motors vehicles and parts, with a particular focus on durability, readability, and adhesion. This standard is critical to ensuring that labels meet quality expectations throughout the life of the vehicle or component. This standard is considered important for the following reasons:

• Ensures long-term label durability: This standard specifies how labels must withstand harsh environmental conditions, such as heat and cold, humidity and moisture, UV exposure, and chemical exposure (oils, fuels, cleaners). This standard is crucial for labels containing safety warnings, service instructions, and regulatory information, which must remain legible for years.
• Standardizes label requirements globally: General Motors operates globally, and this standard helps ensure consistent quality and performance of labels across all suppliers, manufacturing sites, and markets. This standard simplifies communication and reduces variability in product labeling.
• Supports regulatory compliance: Many vehicle labels are required by law (e.g., emissions labels, tire pressure, airbag warnings). This standard ensures that General Motors and its suppliers comply with regulations such as those of the U.S. Department of Transportation), the Environmental Protection Agency (EPA), and international regulations (UNECE).
• Minimizes warranty and safety issues: Unreadable or faulty labels can lead to maintenance errors, safety hazards and increased warranty claims: following the GMW15356 standard minimizes these risks by ensuring labels remain intact and legible throughout the life of the vehicle.
• Supplier quality assurance: This standard is often included in supplier contracts and helps to:
  • Evaluate and qualify label suppliers
  • Inspecting materials and performance
  • Establishing clear test protocols (e.g. abrasion, adhesion, fade resistance)

In short, the GMW15356 standard is vital to ensuring quality, compliance, safety, and consistency across General Motors' global supply chain. This standard is an essential document for companies involved in automotive labeling.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, has a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the "GMW15356 Sheet Metal Rating Scale" standard.