The previous section presents a general method to develop tutorials for educating undergraduate engineering students with the knowledge and skills of 3D printing. This section implements the method by eliciting a tutorial. In particular, the tutorial deals with 3D printing of a spur gear. Thus, it is suitable for senior-level undergraduate students enrolled in mechanical, industrial, and manufacturing degree programs. The descriptions of the tutorial are as follows.
4.2. Administering the Tutorial
To administer A, the instructor can assign students to determine the governing equations of a tooth of a spur gear. The instructor can assign students to formulate a tooth model consisting of six segments (a
, …, f
as shown in Figure 4
) within the realm of the four circles known as pitch, base, outer, and root circles. Out of these segments, the segments b
are the involute curves [52
]. Others are the lines connecting b
to the abovementioned circles. If the students can perform the above assignment, they fulfill the primary outcome (Outcome 1).
Afterward, the students can consider the engineering design aspect, which refers to a secondary outcome (Outcome 2). As such, the students can apply a system approach—input processing–output approach. In the input module, the students can ask a gear designer to input the values of velocity ratio, number of teeth of the gear, number of teeth of the pinion, pressure angle, and diametric pitch. In the processing module, all sorts of calculations can be performed to determine the distance between the centers of gear and pinion; dimensions of the addendum and dedendum; values of clearance and contact ratio; dimensions of the pitch, base, outer, and root circles of gear/pinion; values of working depth; tooth thickness; and rotation angle of gear/pinion [52
]. In the output module, the designed gear–pinion pair can be visualized.
shows the screen-print of a spreadsheet-based gear design tool. If the students can build a similar design tool, they fulfill both primary and secondary outcomes (Outcomes 1 and 2). Therefore, the instructor can evaluate students based on whether they can build a design tool similar to the one shown in Figure 5
In B, the instructor can assign students to extract the design information of gear/pinion in terms of some points because most of the off-the-shelf CAD packages nowadays have a function to input coordinates of points collected from an external source. Thus, the students must go through the manual of the given CAD package and make sure of the underlying data format. This means that the students’ self-learn how the coordinate data input function works for the given CAD package. As a result, Outcome 7 becomes the primary outcome of B. On the other hand, Outcome 1 becomes the secondary outcome because the students must apply the knowledge of parametric curves to parameterize the equations of gear/pinion segments (a
, …, f
) for representing the segments using some points. At the same time, the students must apply basic geometric modeling techniques (e.g., rotation of point/curve centering a point/axis). Therefore, the instructor monitors and evaluates the students’ performance based on Outcome 7 (primary outcome) and Outcome 1 (secondary outcome). If successful, the students produce documentation similar to the one shown in Figure 6
. As seen in Figure 6
, the students plot the coordinates of the gear and pinion’s outer boundaries and store them in text files (ASCII) so that the information becomes meaningful to the tasks underlying C.
In C (object visualization and digitization domain), the gear/pinion coordinate information generated in B (the text files are shown in Figure 6
) is used to create a solid model of gear/pinion. In this respect, the students need to know how a set of points stored in an ASCII text file can be input into the given CAD package. The students also find out the required operations to perform constructive solid modeling [53
]. The students self-learn how the CAD package converts points to a curve, and then a solid model. Therefore, Outcome 7 becomes the primary outcome of C. At the same time, the students must apply the knowledge of geometric modeling to triangulate all faces in the solid model of the gear/pinion. The triangulation process stores the gear/pinion in terms of facets where a facet means three vertices of a triangle and a normal vector defining the orientation of the triangle. Thus, Outcome 1 becomes a secondary outcome of C. If successful, the students produce documentation similar to the one shown in Figure 7
. As seen in Figure 7
, the students produce the solid models and triangulate models of the gear and pinion, respectively using the output of B. Thus, the instructor assesses the students’ performance based on the contents shown in Figure 7
, keeping in mind that Outcomes 7 and 1 are the primary and secondary outcomes, respectively.
In D (STL data domain), the students are required to create the STL [49
] datasets of gear and pinion. Most of the off-the-shelf CAD packages have the function to generate STL data from a solid model. Thus, the students need to know how to create an ASCII text file that stores the STL data using a given CAD package. This means that the students self-learn how the CAD package converts a triangulated model into STL data format. Therefore, Outcome 7 becomes the primary outcome of D. At the same time, the students must know the construction of an STL data block. An STL data block consists of three vertices and a normal vector, and the information of these four elements must be stored in a specific format [49
]. This requires the knowledge of calculating the normal vector from three vertices of a triangle [54
]. Thus, Outcome 1 becomes a secondary outcome of D. If successful, the students produce documentation similar to the one shown in Figure 8
. As seen in Figure 8
, the students produce two text files (ASCII format) storing the STL datasets of the designed gear and pinion. Thus, the instructor assesses the students’ performance based on the contents shown in Figure 8
(only the segment marked D), keeping in mind that Outcomes 7 and 1 are the primary and secondary outcomes, respectively.
In E (3D printing domain), the students are required to print the gear and pinion using a given (most likely a commercially available) 3D printer. Thus, the instructor assesses the students’ performance based on the contents shown in Figure 8
(only the segment marked E). In this case, the instructor uses Outcome 6 as the primary outcome and Outcome 1 as the secondary outcome. As a result, the instructor must instruct the students to print the same object (in this case, a gear–pinion pair) several times by changing the printing conditions (filling rate, printing head feed rate, layer thickness, and alike) and to measure the printing performance (e.g., printing time, the material used, energy consumption, accuracy/precision of the gear and pinion, shape error, surface roughness, and alike). The students can interpret in terms of quality, sustainability [55
], and alike using relevant analytical knowledge (Outcome 1). Figure 9
shows some of the examples of gear and pinion pairs that the students printed. Based on the students’ preferences, the size and shapes of the gears and pinions are different. A group of students has taken a video clip demonstrating that the gear–pinion pair has been printed according to the design because they rotate very smoothly. Refer to the Supplementary materials
to run the video clip.
The students can form teams to perform the tasks underlying Figure 5
, Figure 6
, Figure 7
, Figure 8
and Figure 9
and keep the teamwork and leadership documentation. Finally, the students can present their work and submit a term-report, as elaborately as possible. This way, the students demonstrate their ability regarding the tertiary outcomes, that is, Outcomes 3, …, 5.
It is worth mentioning that while offering the tutorial, it can be divided into two parts. In the first part, the students are exposed to the tutorial. In this case, the course materials (Figure 5
, Figure 6
, Figure 7
and Figure 8
) can be distributed using a course content management system. The student can participate in the first half, either being at home or visiting a laboratory facility equipped with 3D printers and other relevant facilities. A report showing that they have understood the underlying processes and have built an attitude toward engineering design can be used to evaluate individual student performance. The picture shown on the left-hand side in Figure 9
shows students’ activities in the first half. In the last half, the students can form teams and choose shapes (may not necessarily be a gear) and print the selected shapes following the instructions they received in the first half. A detailed presentation of the work done can be used for evaluating the performance of the teams. The picture shown on the right-hand side in Figure 9
shows some of the results of students’ activities in the last half.
4.3. Effectiveness of the Tutorial
Apart from the outcomes assessments based on the outcomes shown in Table 1
, the tutorial’s effectiveness can be evaluated by studying the comments and the reports and presentation documents submitted by the students who took part in the first half and second half, respectively. Appendix A
presents Table A1
listing the comments of fifteen students (from seventy-six students) who took part in the first half of the tutorial this year.
As seen in Table A1
, regarding the first half of the tutorial, the students discuss various aspects of the tutorials, their expectations, and what they have learned, what they could not learn, positive aspects about 3D printing, negative aspects of 3D printing, and alike. The authors briefly describe fifteen randomly selected comments from the seventy-six students who took part in the tutorial this year. In particular, the students understood the processes underlying engineering design, CAD modeling, and 3D printing. They appreciated the role of 3D printing in materializing different shapes very quickly. They also became aware of the limitations of 3D printing (e.g., printing time, accuracy, and metallic part making). The students also extended their learning process regarding manufacturing through the tutorial. For example, some students wanted to apply 3D printing in other areas such as reverse engineering (rebuilding of broken objects), the materialization of natural objects (leaf-shape), and alike. They also grasped the contents they learned in other courses through the tutorial more effectively.
Regarding the second half of the tutorial, the students formed small teams and applied the knowledge they learned in the first half and performed the tasks underlying the five processes (A, …, E). Each group produced a detailed presentation, including video clips and other necessary evidence showcasing their learning performances. For example, one of the gear trains shown in the picture on the right-hand side in Figure 9
was 3D printed by the students, where they used different gear-profiling equations. The students then assembled the gears and tested the backlash of the train, as prescribed in https://www.nmri.go.jp/oldpages/eng/khirata/design/ch06/ch06_02.html
. This way, the students showed the accuracy of the 3D printed gears and their enhanced understanding of precision mechanisms. This kind of self-motivated learning attitude of the students can prepare them for the agile job market more effectively.