Apprentice Training: Metallurgy

Metallurgy for mold materials for tool and die apprentices should cover mining, furnaces, properties, testing, alloying, processing, classification and heat treatment.

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Metallurgy is an important differentiator between a person with average skills and a person with exceptional skills. I have experienced this firsthand while training hundreds of machinists and tool and die makers throughout the last 15 years.

When a person in a metalworking trade truly understands metals, there is a noticeable difference in his or her ability to problem-solve and innovate. I have witnessed projects that were either over-engineered or under-engineered due to a lack of knowledge in metals, alloying, processing and heat-treatment, which cost companies thousands of dollars. Many of the most skilled and talented tradespeople that I know directly attribute their success to a solid understanding of metals and their proper applications.

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This obvious difference in skill levels across various metalworking job functions is the reason I strongly recommend that every apprenticeship program include a practical metallurgy class. I do not mean a class that dives into the science of alloying, metal cell structure and testing but one that discusses the metallurgical applications that are relevant to every tradesperson. I recommend these topics:

Mining and furnaces. Moldmaking is a heavily process-oriented industry, so it seems appropriate to teach metallurgy from the perspective of the process through which the metals will go. This approach has helped my students to understand the applications of metals better. 

The most logical starting point is to explain which metals are mined and to explain where and how the primary metals are mined. The key focus should be iron ore and its various types, including magnetite, hematite and taconite. Then provide a brief overview of bauxite and its relevance to producing aluminum, which is a common material used for molds these days. 
Next, review the various furnaces used in the steel-making process, beginning with the blast furnace and its pig-iron or hot-metal byproduct and how the byproduct is used in steel-making furnaces. The Basic Oxygen Furnace (BOF) and the Electric Arc Furnace (EAF) are two primary steel-making furnaces to discuss. It is important for students to understand that the vast majority of steel is made in a BOF. However, the bulk of tool steel that moldmakers use today is produced in an EAF because an EAF more effectively  controls the heat. 

Finally, explain the role of scrap and recycling in the  steel-making process to help illustrate the importance of capturing chips produced during machining. 

Properties and testing. Material properties and proper measurement techniques are next. If students do not understand the material’s properties, they cannot understand how to apply the materials properly. 

Spend the majority of this section discussing the mechanical properties of metals, including material hardness, brittleness and ductility. Cover the various types of mechanical strengths that a metal might exhibit, such as tensile, flexural, torsional, compressive, shear or impact strength. Review how steel exhibits these strengths when they are machined and how mold blocks should be engineered to perform to these strengths.

Coverage of material properties leads to a discussion on strength versus strain and how to measure material performance under load. A true metallurgist who teaches may dive too deeply into the science of the testing process and in doing so runs the risk of losing student engagement. Try to keep this portion focused on the stress and strain diagram with its various stages. Then tie this back to the way that a chip is made in the machining process. It is important that the students understand a material’s measurable reaction to force or load and to learn how to use that information. Lastly, cover other material, electrical, chemical and thermal properties.

Alloying and processing. Once the students understand the basics of material properties, move on to alloy usage and the processing that is needed to achieve these properties in the finished product. Understanding the difference between iron and steel is also key. 

Students must know that the base alloy used in manufacturing is steel, a mixture of iron and carbon. They should also understand that adding other elements can change material properties. For example, adding carbon to iron creates a hard and strong alloy, adding lead increases machinability, adding chromium increases hardness and corrosion resistance and adding nickel increases toughness and strength. 

Understanding the difference between iron and steel is also key. Students must know that the base alloy used in manufacturing is steel, a mixture of iron and carbon.

The steps to steel processing are next. These include casting slabs, blooms and billets, sending material down a continuous casting line, cold-rolling, hot-rolling and forging.
Classification. Material classification is essential. Students need to understand who classifies the materials and how and why it is done. They also need to be able to read and understand a material processing and alloy data sheet. These skills will be vital if the apprentice becomes an engineer who is expected to make material application decisions. 

Heat treatment. Close the class with an in-depth overview of heat treatment, which includes how processing and heat treatment impact steel’s atomic structure and grain size. This is another area into which a metallurgist would be tempted to take an unnecessarily deep dive. I believe an awareness of atomic structure and grain size is sufficient for tool and die apprentices. It is more important that they understand the practical applications involved in material heat treating. Examples include heating, furnace types, quenching and its various mediums, annealing, normalizing, tempering, surface hardening, and an overview of the iron-carbon phase diagram. 

About the Contributor

Ryan Pohl

Ryan Pohl is founder of Praeco Skills LLC. He is also on the 2017 Editorial Advisory Board for MoldMaking Technology.

 

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