SCIED855:

Lesson 3 Introduction

This two-week lesson will look at some basic manufacturing processes and how solid-object modeling software is used by engineers to design, test, and fabricate useful technologies. One reason that this lesson spans two weeks is that you are likely to need some time to identify and install (or make arrangements to access elsewhere) the software that you'll need to complete this lesson's primary assignment. You're also probably going to need to carve out a good chunk of time to learn how to use that software. It's time worth spending, however, because you're likely to use your modeling software again later in the course.

The first week focuses on choosing and installing a solid-object modeler, viewing a series of videos about modeling, and learning the basics of the modeling software that you've selected. The second week focuses on building a model of your own.

Learning Objectives

After completing this lesson, you should be able to do the following things:

• Define solid-object modelers and why they are important in engineering.
• Distinguish between subtractive and additive manufacturing processes, and give examples of each.
• Describe how solid-object modeling is used in your workplace. If your workplace is a school, you should be able to identify the modelers that are used by students and the classroom settings in which they are used (if any).
• Compare a couple of modelers and evaluate their utility in a specific educational setting.
• Demonstrate facility in using numerical coordinate systems by designing an object with a modeler.
• Exhibit and describe the model of a novel technology that you have designed on a computer.

Lesson Readings and Activities

By the end of this lesson, make sure you have completed the readings and activities found in the course schedule.

3.1. Solid-Object Modelers

In this lesson, you'll be using solid-object modeling software to design a model of some physically tangible technology; that is, something you can touch: an engine part, a printed circuit, a truss beam. We leave until Lesson 4 models of systems, which may be made up of exclusively intangible components (such as the operating system for a computer), or complex assemblies of tangible and intangible components (such as an automotive entertainment system or an air traffic control system).

Solid modeling programs help people build computer models of physical objects, such as gears, buildings, or integrated circuits. They are indispensable in modern engineering. To reduce the problem space here somewhat, in this course, you're going to focus on building models of things that are basketball-sized or smaller. Among "makers," these are popular objects for 3-D printing. Amateur engineers use 3-D printers to create technologies as varied as orthodontic appliances, animal-limb prosthetics, and Star Wars action figures. But the general principles that we will explore are applicable to the design of skyscrapers or aircraft.

You are free to use whatever software you like. The good news is that, if you are a teacher, you can get free access to sophisticated programs that would cost a professional engineer many thousands of dollars. Alternatively, you might prefer to use software that's free to everyone (e.g., through the GNU Project). The specific tool is up to you. Here's what we suggest:

1. Use your favorite search engine to do an initial search for "solid modeling programs" (with no quotation marks). Spend a few minutes looking through the first three or four links. You may also want to check the Wikipedia entry "List of 3D Modeling Software," which is continually updated. Obviously, you'll want to use a program that will run on your computer. 
2. Find out whether your students have used solid modeling software in prior coursework or if they will use such software in a subsequent course. Whether you teach third grade or AP physics, it's usually sensible to check with your school district's middle school technology teachers; they're very likely to have students use this type of tool. Obviously, there's merit in building on students' prior experience or helping develop their expertise for future work; that may tip your decision in one direction. (Hint: If you do Step 1 before Step 2, you're more likely to understand what your colleagues have to say.)
3. Choose a program. If Steps 1 and 2 don't yield an obvious winner, here are some suggestions (but read through the rest of this numbered list before installing anything): 
   • If you're not currently working as a teacher and you're new to solid-object modeling, download and install SketchUp Make, which is free to everyone.
   • If you're employed as a teacher of children age 13 or under, download and install SketchUp Pro, which is free to teachers.
   • If you teach middle school technology or at the secondary level (ages 15+), download and install Autodesk Inventor, which is free to teachers.
   • If you're an experienced CAD user, choose the tool you like. 
   • If you're unable to install any software, locate a computer that you can use that already has solid modeling software installed (public library, school technology room, etc.). You can also access SolidWorks and other programs virtually via a browser, but that can be slow and frustrating, so other options may be preferable. 
4. Now, if you're following the instructions in Step 3 ("read through the rest of this list"), you haven't downloaded anything yet; you're still considering your options. Good. Two more things to consider:
   • If you're learning to drive, it doesn't matter all that much what kind of car you use. It's just a tool. You're not making a lifelong commitment. (It applies here as well.)
   • Choose a tool that challenges you, not necessarily one that will "fit" your students' abilities. Today's Cadillac software is tomorrow's freeware. Why take the time to learn skills that will soon be obsolete?

Now pick a program, download it, and install. Allow yourself at least 24 hours for this step if you choose software for which you must verify your status as a teacher.

3.2. Solid Objects and Basic Manufacturing Processes

Figure 3.2.1 is an image from Wikimedia Commons of a wooden cogwheel. The wheel was used as a model to manufacture an iron version of the same object. A mold like this might be pressed into wet sand and carefully removed, after which molten iron would be poured into the mold impression in the sand. After this "cast-iron" wheel cooled, it would be removed from the sand and finished through a combination of machining and manual processes.

Many other metals are used in casting. In Figure 3.2.2, gold is poured into a cast to create a bar of bullion.

Subtractive Versus Additive Manufacturing

Mentally consider the wooden and iron cogwheels. The former was created by starting with a piece of wood and removing material; the latter was created by starting with an empty mold and adding material. Therein lies the difference between subtractive manufacturing and additive manufacturing. There are many fundamental processes of subtracting or adding materials in different fields of engineering. But they always begin with a model of some kind, either a physically tangible one like the wheel above or a computer representation.

Subtractive Manufacturing

The white cabinets of the Taylor Guitar Factory (Figure 3.2.3) contain computerized numerical control (CNC) milling machines. From blocks of wood, material is milled off automatically to produce components like guitar necks. The instructions for this precision cutting are generated from a computerized solid-object model of the guitar assembly. A mill operates by holding the stock material in place and moving a cutting head through three-dimensional space.

A CNC lathe (Figure 3.2.4) also uses subtractive processes to shape metal, plastic, or other stock material. It differs from a mill in that its cutting tools are locked into position and the stock moves. Because the stock rotates, a lathe is used when the part being made is symmetrical around an axis. Lathes perform functions like cutting, sanding, drilling, and threading. You might think that, being limited to machining axially symmetrical parts, lathes would be of very limited utility. Not so. It turns out that a surprising percentage of the components used in manufacturing the things we use are axially symmetrical: lamp parts, screws, brake drums, bicycle tubes, plumbing components, and so on.

Note how many of the parts in the device pictured in Figure 3.2.5 are axially symmetrical.

Additive Manufacturing

Now very popular in school technology programs and in makerspaces, 3-D printers like this Airwolf (Figure 3.2.5) can be used to create complex shapes. Inexpensive models typically extrude small beads of plastic in layers, and the three-dimensional movement of the extrusion nozzle is computer controlled. This type of printing is also being done using metals, ceramics, and even food!

With 3-D printing and other additive technologies, it's possible to create remarkably shaped objects. If two materials with different properties are deposited in the same process, it's even possible to add subtractive features to 3-D printed parts. MakerBot Industries sells a water-soluble polymer filament that can be used in conjunction with an insoluble polymer. When the part is put in water, the soluble parts of the component will dissolve away, leaving specified voids.

These modern computerized processes use instructions called G-code, generated by computerized solid models. Note that not all solid models can actually be manufactured from any possible material. For example, you could cut a solid cylinder from quartz using a CNC lathe, but a hollow, intact quartz cylinder isn't possible (unless you happen to find a piece of quartz that has a cylinder-shaped cavity in it!).

 

Pause to Reflect

Before you proceed, put on your mathematical thinking cap and try to answer a question about how an object could be specified mathematically. Consider this model, a solid plastic cylinder that is 10 centimeters long (about four inches) and one centimeter in diameter.

What are some ways that you might mathematically describe the shape of this cylinder to a manufacturing robot (using subtractive and/or additive processes)? Think about this a minute before you proceed to the next page.

3.4. Video Introduction to Solid-Object Modeling (Part 1)

Let's explore some basics of solid-object modeling without restricting ourselves to modeling only, say, machine parts. You'll use a Penn State license to access and view some Lynda tutorials on modeling. (There are actually a gazillion Lynda clips on all kinds of subjects, so if you want to learn about music editing or video production, go for it. But first, finish your SCIED 855 work!)

3.5. Video Introduction to Solid-Object Modelers (Part 2)

Before continuing, let's recap:

• Solid-object modelers ("modelers") use one or more 3-D (X, Y, Z) coordinate systems to define and manipulate objects.
• Modelers can display objects in a number of ways, including 2-D projections, rotatable 3-D views, and wireframes.
• Basic manipulations of objects (or object components) include moving, rotating, and scaling. Using relative coordinates allows these operations to be performed on selected components relative to other components.
• Objects have properties and can be organized in hierarchies. The previous video showed how hierarchies can be used to group and move a car, its roof rack, and a suitcase. Extending that idea here, note that each of these objects has properties that can be either inherited or specified individually. If you want the color of your car and its roof rack to match, for example, you could specify that the rack's "color" property should be inherited from the car. If you later decide to change the color of the car, the rack color would be updated automatically.

3.6. Moving On to Your Own Modeler

Let's recap Part 2 of the video tutorial and, while we're at it, expand a little on the subject of modelers:

• The surface geometry of objects can be defined using polygons. Most surfaces can be resolved into triangles, which have the virtue of being flat—always.
• Solid-object models often begin with primitives, basic 3-D objects like cubes or spheres. A user tells his or her modeling software, "Make me a cube." Presto: That virtual cube is created as a set of eight square surfaces (polygons) at right angles to each other. The user might later ask for each of those eight surfaces to be further subdivided into two triangles each, or into nine smaller squares each. Often, the software will do this automatically when the user initiates some other operation.
• The surfaces of models can be manipulated in different ways depending on the specifications that were used to define those surfaces, such as vertices (points), edges (lines), and faces (polygons).
• Why this emphasis on surfaces? In modeling, objects are typically defined as "what's contained within the surfaces." That tends to be different from how we think in the non-modeling world. In the morning, do you think of a glass of orange juice as "a substance contained within a tapered cylinder?" If you do, you're an engineer. (Okay, sorry, hoary engineer joke here: An optimist sees a glass half full. A pessimist sees the same glass half empty. An engineer sees a glass that is twice as large as it needs to be.)
• Modeling often entails pushing, pulling, resizing, or otherwise manipulating parts of the surface of an object. Sometimes those manipulations correspond to real operations that will actually take place in manufacturing. For example, pushing a circular surface into a metal object might correspond to drilling a hole (a subtractive process) in a manufacturing step. Designing solid objects using a modeler involves more than simply making shapes; it also draws upon knowledge of materials, machining processes, human capabilities, and economics. There's little value in specifying that a hole should be drilled in a place that no real drill bit could actually access.

Roll Up Your Sleeves and Model!

It's time to roll up your sleeves. You could spend the rest of your career learning about modeling by watching videos. Right now, there are over 200 Lynda videos on just the subject of CAD (computer-aided design) using modelers like Autodesk Inventor, AutoCAD, SketchUp, SOLIDWORKS, Rhino, and the like. But we'd rather have you actually model, not just watch videos.

If you followed the instructions at the beginning of this lesson, you've already selected a modeler and installed it, and can now run it on a computer. So do that—spend five to 10 hours familiarizing yourself with your modeler. Most modelers come with free user-friendly tutorials. If those tutorials don't launch automatically when you install your software, do a little research on the company's website, YouTube, or Lynda. Stretch yourself. You're an educator: Create an informal individualized educational plan that is tailored to your interests, current expertise with modeling software, and job responsibilities. Then complete the assignments on each of the next two pages. The assignment on page 3.7 is due this week, while the assignment on page 3.8 is due next week. Have fun!

3.8. Solid-Object Modeling: Week 2 Assignment Description

Your assignment for the second week of Lesson 3 is to use your new skills with solid-object modeling to create and share a computer model of a new technology—something of your own design.

The assignment does not require you to actually fabricate your new technology, but, because you will be engineering, you are required to design within specific constraints:

• Your technology must solve a real problem in your actual life (professional or personal).
• It must be something that can be realistically defined with a solid-object model (which should rule out "technologies" like a pan of brownies).
• The technology must be something that could realistically be fabricated on a teacher's salary (not necessarily by you, though—if your technology includes a turned machine part, you need not factor in the cost of purchasing a CNC lathe, or the time required to learn to operate it).
• It should be no larger than a refrigerator.
• It should be ethical to fabricate and use. No clever student-restraint devices or smartphone jammers.

Submit your solution on page 3.9. Like last week, we'll use a discussion board to collect your work and allow for comments by members of our class community. Here's what you'll need to provide: 

• a concise one-paragraph description of the problem and your solution: Indicate what modeling software you used.
• a single image of your technology: Use an appropriate representation generated from your modeling software (2-D projection, 3-D screenshot, wireframe, etc.), and embed that in your reply. (Use the "Embed Image" tool in Canvas, which looks like a little mountain with a giant comet bearing down on it. Or maybe that's the sun?)
• one or more file attachments: These should provide the actual model.

You'll see an example on page 3.9. Have fun!

3.10. Lesson 3 Conclusion