AWS D8.9M

This document contains several standardized test methods thatare designed to evaluate the resistance spot welding behavior ofcoated and uncoated sheet steels in a laboratory environment. Thetest methods allow for uniform testing of automotive sheet steelsto determine the following:

(1) The effect of the interaction between a sheet steel’scoating (metallic, nonmetallic, or both) and the welding electrodeson electrode deterioration and weld size/quality behavior over anextended number of welds

(2) Current levels and current range

(3) Mechanical properties of welds at different weld sizes andhold times

(4) Metallurgical and hardness properties of welds

(5) The effects of sheet lubricants, conductive paints, or othersurface treatment on current break-through

(6) The robustness of a grade of steel to variations in keywelding process variables

The test methods are intended for application in a laboratoryenvironment to characterize certain aspects of the welding behaviorof sheet steel products under controlled experimental conditions.They are not intended to simulate production weldingpractices or to predict welding performance of a given grade ofsteel in production operations. The test methods andparameters are designed to be used for sheet steels ranging inthickness from 0.6 mm to 3.0 mm. The tests may be used for sheetsteel materials of all yield strengths typically used in automotiveapplications. In the endurance test, a minimum of two tests permaterial is recommended to obtain an accurate assessment. Theendurance test was developed for low strength (tensile strengthless than or equal to 300 MPa) coated steels of lighter gauges.This test is normally used for coated steels with tensile strengthless than or equal to 500 MPa and gauges less than 1.2 mm. The weldproperty tests are designed primarily for gauges of 1.2 mm andheavier.

The specific type and number of tests that are required shall beat the discretion of the specifying party. While the test methodswere developed to compare the welding behavior of different steelgrades, they can be judiciously applied to evaluate other aspectsof welding behavior. Not all of the above mentioned tests arerequired to establish the resistance spot welding behavior of agiven grade of steel. The current level/current range testing andweld property testing together generally provide a good indicationof the resistance spot welding behavior, whereas the DoE testing isintended to examine the robustness of a given grade of highstrength steel to variations in key process variables.

The specific tests required to establish the resistance spotwelding behavior of a given grade of steel should be agreed upon bythe steel supplier (or test laboratory) and the automotive company(or buyer of the steel).

A commentary is provided in Annex D on alternative test methodsand is intended to serve as a guide should the users of thisdocument desire to utilize alternative test methods for the weldcharacterization of sheet steels. Because the weldabilityevaluation procedures in alternative methods deviate from theprocedure described in this document, the use of the alternativetest methods may add to the complexity and cost of the materialevaluation. The type of evaluations required, and any deviationsrequired to perform them, should be agreed upon between the partyfor whom the testing is to be performed and the testinglaboratory.

Resistance spot welding behavior is dependent upon a widevariety of interacting material and weld process factors. To obtainrepeatable and reproducible performance data, it is imperative thatall experimental variables and the way a test is conducted beclosely controlled. Therefore, the instructions for the varioussampling and testing procedures in this manual are stated inmandatory language and should be followed as closely as possible.Deviations from the prescribed procedures or test methods,permissible with the consent of the party for whom the testing isperformed, have to be noted and reported.

For the purpose of determining appropriate welding parametersand tests required, steel grades have been classified into fourgroups based on their minimum tensile strength. These groups arelisted in Table 1. Also provided in Table 1 are examples of typicalsteel grades that fall into each of these four groups.

Edition:

3

Published:

01/01/2012

ANSI:

ANSI Approved

Number of Pages:

126

File Size:

1 file , 1.8 MB