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Terminology 101

Terminology 101 Every Industry uses key terminology to express their ideas. At Mckees Rocks Forgings, we use a variety of terms in our daily vocabulary that may not be part of most peoples' knowledge base. This series of articles is designed to help spread our common terms out to our customers so that we all can better communicate. For this first article, I want to reference the Forging Industry Association's "Glossary fo Forging Terms" link. This link is used with their permission as well as the following article: FIA - FORGING TERMS

While the FIA represents all types of forgers, at McKees Rocks we forge using a single hydraulic press. The following sentences represent our typical forging process explanation using terms that are standard to us but may be new to the end consumer. 

“Our 10,000ton water powered hydraulic press provides the required force to re-form cast ingots through plastic deformation into a new form using our impression dies. These hot forgings provide a near net shape that benefits machining by limiting "hogout" to a minimum and produce beneficial directional properties within the part that relate to the grain flow, forging reduction, and microstructure.”

From the sentence above and the linked FIA document you can see that there are many terms used daily by MRF that might confuse or lose some value without additional clarification. Through this first Terminology blog post, I would like to begin shedding some light and de-mystifying our terms to help our customers understand the value of our products. Below you will find each term used above and a definition to help provide insight.  

Impression die forging: one formed to shape and size in die cavities or impressions; also commonly referred to as closed die forging.
    Hot forging: same as hot working - plastically deforming an alloy at a temperature above its recrystallization point, i.e. high enough to avoid strain hardening.
    Plastic deformation: permanent distortion of a material without fracturing it.
  • A typical example using our WC-243 crane wheel starts as a 13" cylindrical blank and after two press operations yields a near-net-shape. The hot working process of heating the steel close to its melting point ensures that the material will smoothly flow in the mold like wet clay rather than tearing the surface apart or forming seams if you tried to move dry clay. 
Near-net-shape forging: forging components as close as possible to the required dimensions of the finished part. While some forging operations produce a finished part, our process always requires some machining due to our finish allowance. This allowance also aides other phases of processing (such as heat treatment) and will be examined in further Terminology posts. 
    Finish allowance: amount of stock left on the surface of a forging to be removed by subsequent machining.
    Hogout: product machined from bar, plate, slab, or other material. The hogout process increases machining time which then increases the price of the finished good. It is also cause for a significant waste of removed material which again can increase cost.
  •  Again using the WC-243, near-net forgings can save hundreds of pounds of material upfront rather than a forged disk of material. 
  • For industrial wheels, the forging process can even form the angled or curved contours of the web area. 
Directional properties: refers to the inherent directionality within a forging such that properties are optimally oriented to do the most good under in-service conditions. Typically, maximum strength is oriented along the axis that will experience the highest loads. For the rolling product we produce, this relates to the rolling surface or tread that is contacting the ground, rail, and other surface. 
    Grain flow: fiber-like lines that show (via macroscopic etching) the orientation of the microstructural grain pattern of forgings achieved by working during forging processes. Optimizing grain flow orientation maximizes mechanical properties.
    Forging reduction: ratio of the cross sectional area before and after forging; sometimes refers to percentage reduction in thickness. This compression of the material adds to the longevity of the part and prevents defects (like pits or voids) from forming. 
    Microstructure: the microscopic structure of metals/alloys as seen on a mounted, ground, polished, and etched specimen to reveal grain size, constituent phases, etc.
  • Again using the WC-243, having the grain flow radially expand from the center out to the tread surface improves loading, and the microstructure of the material should be homogenous throughout which will add to life of the part. 

To recap this post, this is the first in a series of posts that will help to identify key terms that will help MRF and our customers to communicate more effectively. In following post to this series there will be a more indepth look at each factor in our process. This first post and the 100 series of post will relate to forging, each additional factor will start it's own series of numbering. Future topics will Products, Machining, Materals, and more.