vital role in the process. More specifically, removal of the material can be characterized in two ways: Positive feature removal (Fig. 1) or negative feature removal (Fig. 2). Positive features are those that exist in space and are not surrounded by other material. Negative features exist in space but are surrounded by other material. Following are some common applications that illustrate the difference. Typical positive feature removal applications include • Casting sprue removal • Seized bolt or nut removal • Removal of other protruding surface features, such as a fillet weld. Typical negative feature removal applications include • Backgouging • Excavation of weld defect • Spot weld removal. Positive feature removal is fairly straightforward. In most cases, the results are directly related to the highest speed at which one can remove the feature while protecting the workpiece from collateral damage. In positive feature removal, there is no requirement for a profile shape. Negative feature removal can be more complex depending on the application. In many cases, the gouge profile is more important than the rate at which one can remove material. The profile (cross-sectional shape of the gouge) must reveal enough access for the subsequent weld. Of course, this can be highly situational depending on the orientation of the workpiece, thereby making it difficult to define an ideal gouge without a context. However, a few general assumptions can be made regarding characterization of a gouge profile: • The width of a gouge should always be greater than its depth. • The profile should be as close to symmetric as possible. • The width-to-depth ratio can be expressed as a unitless ratio. Furthermore, there are other features of the gouging process that are of importance: • Slag buildup should not affect the base material and should be easily removed. • The surface texture of the gouge should be relatively smooth such that it does not present adverse conditions to the subsequent welding process. • If the gouging process results in surface hardening, then removal of the hard surface material will be required. Additionally, note that cutting tools can be used to gouge and gouging tools can be used to cut. Therefore, a distinction should be made between a cut and a gouge. A gouging process removes any amount of material from a body or bodies regardless of shape or rate such that piercing or severing of that body does not occur. Conversely, a cutting process is defined by piercing and/or severing a body or bodies. Last, Fig. 3 details the anatomy of a negative feature gouge. This would be a typical gouge used for weld preparation or removal. The suitability of the geometric condition of a gouge is highly situational and can vary depending on the application. Nominal dimensions and other specifications can be found in a variety of welding specifications, such as those published by the DECEMBER 2016 / WELDING JOURNAL 39 Fig. 1 — Example of positive feature removal. Fig. 2 — Example of negative feature removal. Fig. 3 — Anatomy of a typical negative feature gouge.
Welding Journal | December 2016
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