As materials are formed or processed into useful products the materials undergo changes in their materials properties. These changes can be beneficial or deleterious. Understanding these changes can enhance the performance of the material or, in some cases, prevent unanticipated materials failure. In this lesson, we discuss the common formation and processing methods for metals, ceramics, and polymers, and how these processes can effect the materials properties of the processed materials.

Learning Objectives

By the end of this lesson, you should be able to:

• Name and describe four forming operations that are used to shape metal alloys.
• Name and describe five casting techniques.
• Name and briefly describe five forming methods that are used to fabricate glass pieces.
• Briefly describe and explain the procedure by which glass pieces are thermally tempered.
• Briefly describe processes that occur during the drying and firing of clay-based ceramic ware.
• Briefly describe/diagram the sintering process of powder particle aggregates.
• Briefly describe addition and condensation polymerization mechanisms.
• Name the five types of polymer additives and, for each, indicate how it modifies polymer properties.
• Name and briefly describe five fabrication techniques used for plastic polymers.

Lesson Roadmap

Lesson 10 will take us one week to complete. Please refer to the Syllabus or course calendar for specific due dates.

Questions?

If you have general questions about the course content or structure, please post them to the General Questions and Discussion forum in Canvas. If your question is of a more personal nature, feel free to send a message to all faculty and TAs through Canvas email. We will check daily to respond.

Things to consider...

As you do the following reading consider the following questions. Remember to keep the learning objectives listed on the overview page in mind as you learn from this reading.

• What are the four forming operations that are used to shape metal alloys?
• What are the five casting techniques?

Now that you have completed the reading assignment regarding the fabrication of metals, let us summarize some of the important points.

For the last process, drawing, please proceed to the next section.

The last of the four mechanical forming processes, drawing, is one of the processes discussed in the following video (4:45) on How are Aluminum Cans Made? While you are watching this video, please think back, way back, to Lesson 1 of this course and the reading in the textbook about different materials used for carbonated beverage containers. And remember to look for the drawing operation (hint: it is the operation that gives the can its height).

Now that we have reviewed the four mechanical forming processes for metals: forging, rolling, extruding, and drawing, hopefully, you also understand why I refer to them as pounding, rolling, pushing, and pulling. In the next section, we will look at how metals that cannot be mechanically formed are typically formed.

Not all metals are amenable to the mechanical deformation which occurs with mechanical forming processes discussed in the previous sections. Those metals that can undergo mechanical forming are referred to as wrought metals. For those metals that are not amenable to mechanical deformation, they are typically cast.

Casting is the process in which molten metal is poured (or cast) into molds. In the reading, you were introduced to five different casting techniques: sand, die, investment, lost foam, and continuous. Typically, it is more economical to use mechanical forming processes, since it requires more energy to heat metals until molten in the casting process. However, there are times when casting makes more sense, in addition to the obvious case of a metal not being amenable to mechanical deformation. Some of those cases include when making complicated shapes or when prototyping a part. When prototyping, the cost of making a forging die might be much more expensive than the cost of molds.

Now, please go to the second reading (2 of 3) of this lesson and read about how ceramics are fabricated.

Things to consider...

While doing the next reading, use the following questions to guide your reading. Remember to keep the learning objectives listed on the overview page of this lesson in mind as you learn from this text.

• What are five forming methods that are used to fabricate glass pieces?
• How are glass pieces thermally tempered?
• What are the processes that occur during the drying and firing of clay-based ceramic ware?
• What is the sintering process of powder particle aggregates?

The fabrication methods of ceramics are classified in three categories: glass-forming, particulate forming, and cementation. In glass-forming processes, the raw materials are heated until they melt. There are five glass-forming processes: blowing, pressing, drawing, fiber-forming, and sheet-forming. The following five-minute video highlights automated glass blowing for the production of glass bottles. Again, while you are watching this video, please think back to Lesson 1 of this course and the reading in the textbook that covered different materials used for carbonated beverage containers.

In the next section, we will discuss the important subject of heat treating glass to control stress.

When fabricating glass, it is usually vitally important to control the cooling of the fabricated pieces. Due to the brittle nature of ceramics, failure to remove internal stress in the glass either introduced during fabrication or due to uneven cooling will likely result in catastrophic structural failure of the piece. There are two basic types of heat treatments applied to glasses. In annealing, cooling is controlled in an effort to remove (or minimize) the internal stress in the glass. This is in contrast with tempering. In tempering, compressive stress is intentionally introduced into the surface of the piece as shown in the figure below. This compressive stress can prevent surface scratches and cracks from growing, which would likely fracture the glass.

Tempering: Compressive stress is intentionally introduced into the surface of the piece.

Click for a text description of image.

Compressive stress process: Before cooling the surface is very hot but once initial cooling begins the outside of the surface is cooler than the inner core. Once the material reaches room temperature there is compression on the outside surfaces and tension on the inner core. As a result surface crack growth is suppressed.

Credit: Callister

In the next section, we will discuss sintering, which is very important for particulate forming of ceramics.

During powder press processes for the formation of ceramics, heat and pressure are used to densify and bind ceramics together as illustrated in the figure below in a process called sintering. Unlike melting, during sintering, materials are not liquefied, but instead, rely on reducing surface area effects between particles to drive the process. Ceramic materials usually have a very high melting temperature, so sintering (which is done at temperatures well below bulk melting temperatures) offers significant savings in terms of energy.

During powder press processes, heat and pressure are used to densify and bind ceramics together.

Credit: Callister & Rethwisch 5e

Now, please go to the third reading (3 of 3) of this lesson and read about how plastics are fabricated.

Things to consider...

While you do the following reading let the following questions guide your reading. Remember to keep the learning objectives listed on the overview page for this lesson in mind as you learn from this text.

• What are the addition and condensation polymerization mechanisms?
• What are the five types of polymer additives and, how do they modify polymer properties?
• What are the five fabrication techniques used for plastic polymers?

As we discussed in the polymer lesson, there are two types of polymerization: addition (or chain) polymerization and condensation (or step) polymerization. In addition, in polymerization, a free radical attaches to a monomer. This results in an unsatisfied bond on the monomer, which is free to attach to another monomer. This process repeats over and over again, building a polymer chain. In condensation, two chemical groups react together. Typically, one of the groups has an exposed hydrogen, while the other has an exposed oxygen-hydrogen. When the two compounds join, a monomer is formed with an exposed oxygen-hydrogen or hydrogen and releases a water molecule, H₂O.

Polymers are synthesis by polymerization and the polymer properties are modified by the usage of additives. These additives are used to improve mechanical properties, processability, durability, etc. The five additive types discussed in the e-book are fillers, plasticizers, stabilizers, colorants, and flame retardants. Fillers are added to improve tensile strength, abrasive resistance, and toughness, as well as to reduce cost. Plasticizers are added to transform brittle polymers to ductile ones. Stabilizers are added to protect from degradation due to exposure to ultraviolet light. Colorants are added to provide color to the polymer. Flame retardants are added to eliminate or reduce the flammability of polymers.

Fabrication of plastic polymers can utilize one of several molding techniques: blowing, compression, injection, and transfer, or by extrusion or casting. Fibers can be spun or drawn. Films can be formed by extruding, blowing, or calendaring. The following video [9] (4:50) highlights blow molding for the production of plastic bottles. Again, while you are watching this video, please think back to Lesson 1 of this course and the reading in the textbook about different materials used for carbonated beverage containers.

You have now finished the reading for Lesson 10. Please proceed to the next page and watch the video for Lesson 10.

Now that you have read the text and thought about the questions I posed, go to Canvas and watch this 53-minute video about how glass, titanium, fiberglass, lacquer, and aluminum alloy become a jet. In "Raw to Ready: Bombardier," we see how various components are painstakingly fabricated beginning with the raw materials to the final assembly into the regional jet aircraft.

Summary

Materials are formed or manufactured into components that are incorporated into useful products. During these processes, the properties of the materials can be enhanced or adversely affected. Knowledge of these effects and the economic costs are many times needed to successfully bring a product to market. In this lesson, we looked at the most widely used fabrication and synthesis techniques for metals, ceramics, and polymers, as well as, discussed how these processes impact materials properties.

Reminder - Complete all of the Lesson 10 tasks!

You have reached the end of Lesson 10! Double-check the to-do list on the Overview page to make sure you have completed all of the activities listed there before you begin Lesson 11.