Constraint-Based Modeling in the Engineering Graphics ... - CiteSeer

Constraint-Based Modeling in the Engineering Graphics Curriculum: Laboratory Activities and Evaluation Strategies Theodore J. Branoff Department of Mathematics, Science and Technology Education North Carolina State University, Raleigh, North Carolina 27695-7801

ABSTRACT – Three-dimensional solid modeling,

engineering design graphics faculty reflect a concern

especially constraint-based modeling, has significantly

for how to integrate current technology into the

changed the way engineering graphics programs are

curriculum, while deciding what traditional topics need

structured. Although traditional concepts such as

to remain.

orthographic projection, sectional views, auxiliary

In a recent study, Barr, Krueger, and Aanstoos

views, and dimensioning are still covered in many

(2004) surveyed engineering and technical graphics

programs, they are couched within the context of a 3D

faculty and asked them to rate the importance of

database centered engineering design process. The

traditional and modern engineering design graphics

Graphic Communications Program at North Carolina

topics. They reported that the modern engineering

State University has made course and programmatic

design graphics curriculum should include a trichotomy

changes over the last 10 years to adapt to changes in

of instruction. Instead of only focusing on engineering

how 3D modeling is used in industry. After completing

drawings, faculty should focus on three areas of

a 3 course sequence in engineering graphics, students

instruction: computer graphics modeling fundamentals;

should be able to complete a wide variety of activities

engineering graphics fundamentals; and computer

related to constraint-based modeling. To meet these

graphics modeling applications. The items related to

objectives, students complete tutorial-based laboratory

computer modeling were ranked the highest in their

assignments, reverse engineering activities, and

survey,

structured design activities. The way student work is

engineering graphics concepts related to drawing and

evaluated has also changed. This paper presents the

sketching

objectives for each course, gives examples of

curriculum.

however, were

faculty a

valuable

still

felt

component

traditional of

the

The change to a curriculum focused more on 3D

constraint-based CAD activities in each course, and discusses evaluation techniques for the activities and

modeling has forced faculty to examine how students

projects.

are assessed. Because constraint-based modelers allow I. Introduction

the user to build intelligence into a 3D model,

Constraint-based solid modeling has significantly

evaluating only print-outs of CAD assignments is no

changed the types of activities in engineering and

longer sufficient to assess student work. Assessment of

technical graphics courses and the way those activities

constraint-based models must be done by examining

are evaluated. Presentations and publications by

each student’s electronic file. This can be one of the

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most difficult things for faculty to incorporate into their

introductory courses is placed on the decision-making

instructional routines, especially with classes having

process

large numbers of students. Evaluating models can be

geometry and the development of solid modeling

done by the faculty member (Branoff, Wiebe, &

strategies that incorporate the intentions of the

Hartman, 2003), by trained teaching assistants or

designer. Students participate in activities that involve

graduate students (Elrod & Stewart, 2004), or by an

their analysis of geometry at a fundamental level, the

automatic grading system (Baxter, 2003; Baxter &

relationships between geometric elements, and the new

Guerci, 2003). The challenge can be providing valuable

mentality of “modify and re-define” rather than “delete

feedback to the students in a timely manner. In addition

and re-create”.

involved

with

creating

constraint-based

At the end of the introductory course, students

to evaluating CAD assignments, faculty have been traditional

should be able to perform the following related to

engineering graphics topics (Demel, Meyers & Harper,

constraint-based modeling: select and create sketch

2004) as well as how students work within teams

planes; create and constrain sketches; define sweep

(Elrod & Stewart, 2004; Kelley, 2001).

parameters (extrudes & revolves, one or two sided,

exploring

strategies

for

assessing

Graphic

etc.); revise sketches and features; create repetitive

Communications faculty at North Carolina State

features such as circular and linear patterns; create

University has been revising the content and evaluation

features such as fillets, chamfers, sweeps, lofts, and

methods in their courses to provide better learning

shells; create assemblies of parts and apply appropriate

experiences for students. What follows is a description

3D constraints; render the assembly by applying

of 3 courses in engineering and technical graphics and a

materials to each part and define an appropriate scene

summary of the activities and evaluation strategies used

or environment; and create detail drawings of parts

in each course.

(including sectional views, dimensions, and other

Over

the

last

several

years,

the

notations) by extracting information from the 3D II. Introductory Courses

models. Students are asked to complete a range of

Three introductory courses in engineering and

assignments during the semester to develop their

technical graphics are offered within the Graphic

knowledge and skills in constraint-based CAD. Figures

Communications Program – one is open to any student

1 through 4 show some of the assignments that are used

at the university (GC120), one is for mechanical and

to develop and assess students in the introductory

aerospace engineering majors (GC211), and one is

courses.

designed for industrial engineering majors (GC210). The main goal of the introductory courses is to provide an orientation to the language of technical graphics. The courses help students develop and refine their ability to use this universal technical language within the context of the concurrent engineering design process as well as gain an understanding of how computer-aided design is used to create objects that

Figure 1. STOP BASE.

students use on a daily basis. Emphasis in the

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report of the project. Figures 5 & 6 are examples of student projects.

Figure 2. DRYER CLIP.

Figure 5. Bicycle Axle.

Figure 3. PISTON CAP.

Figure 6. Dividers. III. Applied CAD & Geometric Controls The second course in the engineering and technical graphics series (GC350) was designed to give students direct exposure to and interaction with the evolving industrial use of computer-aided design and modeling. Students produce mid-level computer models of

Figure 4. TAILSTOCK CLAMP Detail Drawing.

individual parts and assemblies of parts that encompass For the final project, students are asked to select a

the full range of current CAD software capabilities

design that contains 3-5 parts that they must reverse

from 3-Dimensional feature-based solid modeling to an

engineer. Along with planning and documenting the

exploration of design for manufacture. Students apply

modeling strategies for each part through freehand

conventional tolerancing, geometric dimensioning and

sketching, students must model each part, create a

tolerancing, and technical documentation to a variety of

rendered assembly of the design, create a detail

standard and non-standard parts in the course.

drawing of one of the parts, and submit a technical

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At the end of the course students should be able to perform all modeling activities included in the introductory course as well as the following activities: build design intent into a model based on specific parameters;

apply

conventional

tolerances

(limit

dimensions) and geometric tolerances to 3D models and

engineering

drawings;

create

multiple

configurations of a 3D model using design tables;

Figure 9. Design Table of Woodruff Key.

model objects that require sweeps and lofts; create a rapid prototype of a model using a 3D printer; and

The final project in the GC350 course involves

create an assembly drawing of a design which includes

creating a complete set of working drawings for a

a bill of materials. Figures 7 through 9 show examples

design. Students model all individual parts, create detail

of assignments used to develop and assess students in

drawings of non-standard parts (including applying

the GC350 course.

conventional tolerances to all mating parts and geometric dimensions to one part in the design), create an assembly drawing (which includes a bill of materials), and create a rendered assembly of the design. Figures 10 and 11 illustrate examples of final projects in this course.

Figure 10. CLAMP FIXTURE Assembly. Figure 7. TRIP LEVER Drawing and Model.

Figure 11. TOOL REST Assembly.

Figure 8. SLIDING DOOR GUIDE.

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IV. Advanced CAD The capstone course in the engineering and technical graphics series (GC450) was designed to provide students with a culminating experience where they could apply their knowledge of computer-aided design. Students explore the theory and application of manufacturing databases developed with 3-D modeling tools. They also examine the development and management downstream

of

3-D

geometry

applications

such

and

investigate

as

analysis,

Figure 13. Carbide Lattern Design.

documentation, and prototyping. In addition to readings in the areas of modeler types and databases, curves and

The second large project in the course is a group

surfaces, constraint-based and parametric modeling,

project. As a class, students reverse engineer a small

mass properties, kinematic and dynamic analysis, finite

lawn mower engine (see Figures 14 and 15). The

element

control,

students determine logical divisions for groups (eg.

documentation, and modeling for manufacturing,

drive train, engine block, sheet metal parts, etc.) and

students complete two large projects. The first is a

then divide the modeling tasks equitably among group

flashlight design project where students research

members.

analysis,

computer-numerical

flashlights for a particular application, sketch multiple iterations of their designs, narrow the design down to one, model all parts using solid and surface modeling tools, render the design, and present their design to the class. Examples of designs from the course are shown in Figures 12 and 13.

Figure 14. Small Engine Assembly.

Figure 12. Handlebar Mounted Light.

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An example of feedback to a student for the TRIP LEVER might be: “3/5 points. Sketches for CutExtrude2, Cut-Extrude3, & Cut-Extrude4 are missing dimensions.

Please

make corrections per these

comments and show the modified part to me in class Wednesday. There is no need to resubmit the part to the homework directory.” Some instructors will allow students to correct their models and resubmit them. Although this can make managing homework grades Figure 15. Drive Train Sub-Assembly.

and classroom activities more difficult, correcting existing models appears to be more valuable to students

V. Assessment Strategies

than just receiving comments and a grade.

A variety of assessment strategies are used

For the final projects in each course, students are

throughout the courses. Approximately 20 sections of

given a detailed rubric for how each part of the project

the introductory courses are taught each semester by at

will be evaluated. An example grading rubric for the

least 9 different instructors. Each has their own

final project in the introductory course is shown in

preference for how to evaluate assignments. Constraint-

Figure 16.

based modeling activities are evaluated electronically by the instructors. This may be done in a couple of different ways. Instructors may grade assignments in the lab with the students present or they may ask the student to submit their files to a server so the file can be graded in a remote location (in the office or at home). For most assignments, instructors will focus on a handful of items. Table 1 shows the items that the instructor examines for the TRIP LEVER (Figure 7). Table 1. Grading Rubric for the TRIP LEVER. Description Part dimensions are correct Part orientation is correct Spotfaced hole remains centered when depth of part is changed Slot remains centered size is changed 9.5 diameter hole remains centered on tab when tab depth is changed Total

Points 1 point 1 point 1 point 1 point 1 point 5 points Figure 16. Project Grading Rubric.

Feedback to a student might come in the form of an email or a print-out handed to the student in class.

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VI. Discussion and Reflections

Baxter, D.H. (2003). Evaluating an automatic grading system for an introductory computer aided design course. Proceedings of the 58th Annual Midyear Conference of the Engineering Design Graphics Division of the American Society for Engineering Education, Scottsdale, Arizona, November 16-19, 2003.

Two of the biggest challenges to this point have been faculty training and instructional materials development. With new releases of the software coming out every year, faculty development must be a priority. Instructors have to understand the power of the

Baxter, D.H. & Guerci, M. J. (2003). Automating an introductory computer aided design course to improve student evaluation. Proceedings of the 2003 Annual Conference of the American Society for Engineering Education, Nashville, Tennessee, June 22-25, 2003.

constraint-based modeling tool to be able to make connections between it and the engineering graphics topics covered in the course. They also must be able to troubleshoot a wide range of problems that students run

Branoff, T. J., Wiebe, E. N, & Hartman, N. W. (2003). Integrating constraint-based CAD into an introductory engineering graphics course: Activities and grading strategies. Proceedings of the 2003 Annual Conference of the American Society for Engineering Education, Nashville, Tennessee, June 22-25, 2003.

into while creating models. The development of supporting instructional materials has also been a challenge. Revising materials for new releases can be time consuming, and creating materials that are acceptable to every instructor is

Demel, J. T., Meyers, F. D. & Harper, K. A. (2004). Developing a nationally normed test for engineering graphics-First pilot tests and results. Proceedings of the 2004 Annual Conference of the American Society for Engineering Education, Salt Lake City, Utah, June 2023, 2004.

almost impossible. The integration of constraint-based modeling into the Graphic Communications curriculum appears to be going well. Students taking the three course sequence

Elrod, D. & Stewart, M. D. (2004). Assessing student work in engineering graphics and visualization course. Proceedings of the 2004 Annual Conference of the American Society for Engineering Education, Salt Lake City, Utah, June 20-23, 2004.

in engineering and technical graphics typically major in mechanical and aerospace engineering or technology education. They are securing employment throughout the country in a variety of careers. Some recent

Kelley, D. (2001). Cooperative learning as a teaching methodology with engineering graphics. Proceedings of the 2001 Annual Conference of the American Society for Engineering Education, Albuquerque, New Mexico, June 24-27, 2001.

graduates are working for engineering firms where they use their knowledge of constraint-based CAD along with their engineering degree for firms such as Integrated

Industrial

Information,

Inc.,

FineLine

Prototyping, Inc., Boeing, and Raytheon Missile Systems. Others are using their degree in education to teach technology education and drafting courses in public schools in North Carolina.

VII. References Barr, R. E., Krueger, T. J. & Aanstoos, T. A. (2004). Results of an EDG student outcomes survey. Proceedings of the 2004 Annual Conference of the American Society for Engineering Education, Salt Lake City, Utah, June 20-23, 2004.

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