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ME203: Materials and Materials Processing

Unit 4: Processing of Materials – *How Can We Shape It?*   A material may have the properties we wish, but we still have to shape it for it to be useful as a part. We will consider casting, mechanical forming, sintering, welding, and brazing. These processing techniques will be generally familiar, but we will take a closer look at advantages and disadvantages, and at some specific considerations.

Unit 4 Time Advisory
This unit should take you approximately 18 hours to complete.

☐    Subunit 4.1: 5 hours

☐    Subunit 4.2: 4 hours

☐    Subunit 4.3: 4 hours

☐    Subunit 4.4: 5 hours

Unit4 Learning Outcomes
Upon successful completion of this unit, you will be able to: - identify the principal concerns of common materials processing techniques; and - examine advantages and disadvantages of alternative processing techniques when selecting materials.

4.1 Casting   Advantages

  • Complex shapes can be formed in a single step.
  • Chemically reacting components, such as thermosetting resins and concrete, can be cast.

Limitations - Preparing molds may be time-consuming and expensive. - Not all materials can be cast. Some deteriorate at elevated temperatures before they melt. - The solidification process imparts a grain structure to the interior of the casting that may not be desirable.

  • Reading: The Saylor Foundation’s “Casting” Link: The Saylor Foundation’s “Casting” (PDF)

    Instructions: Please read this short article, which discusses hardening by solidification and chemical reaction.

  • Web Media: YouTube: Getty Museum’s “Adriaen de Vries’s Bronze Casting Technique: Direct Lost-Wax Method” Link: YouTube: Getty Museum’s “Adriaen de Vries’s Bronze Casting Technique: Direct Lost-Wax Method” (YouTube)

    Instructions: Watch this demonstration of an artist’s use of lost-wax casting. This video shows a reconstruction of the speculated technique of Dutch sculptor Adriaen de Vries (ca. 1556–1626).

    Watching this video and pausing to take notes should take approximately 30 minutes.

    Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

4.2 Mechanical Forming   Advantages

  • Cold forming strengthens as well as shapes metals.
  • Long shapes, such as rods and tubes, can be made by extrusion.
  • Hot forming allows almost unlimited change in shape without change in properties.

Limitations
- Cold forming increases the brittleness of a metal. - Like casting, cold forming imparts internal structure to metals. - Brittle materials cannot be mechanically shaped without fracture.

  • Reading: The Saylor Foundation’s “Mechanical Forming” Link: The Saylor Foundation’s “Mechanical Forming” (PDF)

    Instructions: Please read this short article, which discusses cold working, annealing, and hot working.

  • Web Media: YouTube: Learn ChemE’s “Dislocations and Plastic Deformation” Link: YouTube: Learn ChemE’s “Dislocations and Plastic Deformation” (YouTube)

    Instructions: Please click on the link above, and watch this brief video. This is a presentation of how a plane can be shifted by dislocation movement. The dislocation is into the plane of the drawing, so that we are looking at the end of a line. A different definition of dislocation density is mentioned than that given in the next section. The two definitions are equivalent.

    Watching this video and pausing to take notes should take approximately 15 minutes.

    Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

  • Web Media: YouTube: GSEG Media: George Goehl’s “Copper Annealing” Link: YouTube: GSEG Media: George Goehl’s “Copper Annealing” (YouTube)

    Instructions: Please click on the link above and watch this video, which illustrates the annealing of copper. We have to take the narrator’s word that the copper strip is either stiff or soft, but this video emphasizes the purpose of annealing.

    Note: The narrator’s description of work hardening is incorrect. There are no molecules of copper coming closer together; rather, work hardening is caused by the increased density and subsequent entanglement of dislocations discussed in the previous section.

    Watching this video and pausing to take notes should take approximately 15 minutes.

    Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

4.3 Sintering   Advantages

  • High-melting and brittle materials often can be formed no other way.
  • Special properties may be achieved by impregnating the porous sintered product with oil, for example.

Limitations - Specialized equipment involving high temperature and atmosphere control are often necessary. - The variable density and variation in other mechanical properties of sintered materials may be of concern.

  • Reading: The Saylor Foundation’s “Sintering” Link: The Saylor Foundation’s “Sintering” (PDF)

    Instructions: Please read this short article, which discusses sintering.

4.4 Joining   Advantages

  • Welding and brazing are often economical alternatives to machining or casting.
  • In the field, repair by welding or brazing can often prevent replacement of original parts.

Limitations - Welding is a sequence of alloying, casting, and heat treatment. This complex event has many possibilities for less than desired results. - Not all materials can be joined by melting them together.

4.4.1 Welding   - Reading: The Saylor Foundation’s “Welding” Link: The Saylor Foundation’s “Welding” (PDF)

 Instructions: Please read this short article, which discusses
welding.
  • Web Media: YouTube: University of California, Irvine: Teaching, Learning, & Technology Center’s “Basic MIG Welding” Link: YouTube: University of California, Irvine: Teaching, Learning, & Technology Center’s “Basic MIG Welding” (YouTube)

    Instructions: Please click on the link above and watch this video. The video documents a student learning MIG welding for the first time. The instructor refers to the process as Mechanized-Inert-Gas, but Metal-Inert-Gas is the more common label.

    Watching this video and pausing to take notes should take approximately 1 hour.

    Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

  • Web Media: YouTube: Welding Tips and Tricks: “Different Types of Welding” Link: YouTube: Welding Tips and Tricks: “Different Types of Welding” (YouTube)

    Instructions: Please click on the link above and watch this brief video. The video presents an overview of the TIG, MIG, and stick welding methods. The presentation begins with TIG welding, though this is not too clearly identified by the narrator.

    Watching this video and pausing to take notes should take approximately 15 minutes.

    Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

4.4.2 Soldering and Brazing   - Reading: The Saylor Foundation’s “Soldering and Brazing” Link: The Saylor Foundation’s “Soldering and Brazing” (PDF)

 Instructions: Please read this short article, which discusses
soldering and brazing.