Recommended General Motors Steel Reparability Matrix
The Recommended GM Steel Reparability Matrix is a chart that identifies GM’s repair recommendations according to the type of steel that the part is made from. The matrix contains information on the steel identification stamping symbols, steel grade, GM specifications, recommended welding methods, cold repairability, use of heat for repairs, the temperature range that should be used, and the maximum heat allotment. The second page of the matrix is a chart of Descriptions of GM Steel.
The Recommended GM Steel Reparability Matrix can be found free of charge at genuinegmparts.com. Adobe® Acrobat Reader® is required to view the information on this site. On the Collision Repair tab on top of the home page, select the Technical Documents link. Then select the Steel Reparability Matrix file from the list on the Technical Documents page.
There are eight main columns in this matrix. The first three columns are used to explain the type of steel that is being referenced. The first column identifies the steel ID stamping symbol or International Organization for Standardization (ISO) symbol for the steel. The second column identifies the grade of steel, such as mild, laminated, dual phase, or boron steel. The third column is used by the steel companies to identify the GM specification for the type of steel.
The fourth column identifies whether or not certain types of welding are recommended including GMA (MIG) welding, squeeze-type resistance spot welding (RSW), and MIG brazing. It is stated in footnote number one that when MIG brazing is recommended, slotted holes 8 x 16 mm should be used. For some steels, like DP>800, UHSS, martensitic, boron, and TRIP, it is noted that GMA (MIG) plug welds are the only type of GMA (MIG) welding that is recommended. The footnote stresses that these steels should not be stitch welded during repairs, nor used as a backer for stitch welding. It is noted that “Deviation from this chart is only allowed if there has been a crash analysis completed by the Design Engineer and a service procedure has been written.”
The last four columns address straightening and the use of heat. The fifth column addresses if a steel part may be repaired without the use of heat. If cold repairs are allowed, footnote number two states that it should only be done if the damaged area is not kinked. The sixth column identifies if heat may be used for repairs. When heat is allowed, the last two columns show a maximum temperature of 1200°F (650°C) with heat being applied for no more than 90 seconds and no more than two heat applications.
Additional information in the footnotes includes number three which references sectioning being allowed on DP<800 using a sleeve or backer plate. It is also noted that GM does not endorse door impact beam repairs.
Descriptions of GM Steel, found on the second page of the matrix, includes information on the steel grades, alloy content, heat treatment process that are used when making the steel, typical applications of the types of steel, and additional comments.
The Recommended GM Steel Reparability Matrix is a good source for general information on repairing the steels that are found on GM vehicles. Keep in mind that vehicle-specific repair procedures may vary from the general recommendations listed in the matrix based on specific application and design intent. Always reference the repair procedures for the specific vehicle model and year during repairs. The second page of this GM document gives additional information on GM steels including a column that gives typical applications for the types of steel to help make the technician aware of areas where they may encounter these types of steels.
This article first appeared in the September 11, 2007 edition of the I-CAR Advantage Online.
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