Metal Cutting and Manufacturing Economics Project for Freshmen

This paper describes a practical student experience consisting of a manufacturing laboratory experiment and a team project designed to teach manufacturing concepts to freshmen engineering and engineering technology students at the Old Dominion University. Students learn engineering concepts and skills they will need later. First, students organize into randomly assigned teams with specialized responsibilities for the purpose of calculating the total production time and cost of manufactured parts using turning, drilling, and milling operations. Then, students learn or improve their spreadsheet skills while performing data entry and necessary machining calculations. While these first-year students do not perform any metal cutting themselves, they observe a machine shop technician who performs the operations. Students collect data and take pictures of the operations as they are exposed to rather messy realities of metal cutting. Then, they calculate manufacturing cost of the part. Each team wrote a technical team report to document the manufacturing experience they had. The experiment and the team project are described in sufficient detail to allow easy adoption. Students reflections and informal interviews show that the students are satisfied with the experience and that they highly value gained insights and skills. Introduction Experiential learning1-3 is a well recognized part of Kolb’s experiential learning cycle/spiral4-6 that is used as a powerfull pedagogical strategy in many engineering programs. Creating products is the essense of manufacturing, thus the product realization-based learning seems a natural model for learning manufacturing engineering7. Project-based learning (PBL) pedagogy is well accepted in education8, 9. It is also emphasized as one of the high priority education methods/pedagogies required in manufacturing engineering education10. PBL pedagogy is successfully implemented in a manufacturing processes course11. The practical experience described in this paper is product realization centered. Also, it uses PBL pedagogy and teamwork. Curricular Context ENGN 110 is an introduction to engineering and technology course designed to “introduce a variety of engineering and technology disciplines” through a series of engineering projects. The course emphasizes team work, design, manufacturing, testing, communication and presentation skills, as well as discovery, creativity, and innovation12. The course is a one-semester, 2 credit course required for all engineering and engineering technology programs. The described practical manufacturing-related engineering experience presents one of the major learning modules in this course. The practical experience encompasses all four pillars of manufacturing engineering: “1) Materials and manufacturing processes; 2) Product, tooling, and assembly engineering; 3) Manufacturing systems and operations; and 4) Manufacturing competitiveness13.” Student work in teams of three to four with about 100 students per semester. Educational Goals, Activities, and Outcomes Educational goals of this project include increased excitement for engineering resulting in increased retention, motivational preparation for further studies in engineering, and gaining an insight into what engineers do. The practical experience consists of several activities: observation of real metal cutting operations, realizing overhead costs, calculating realistic manufacturing costs, applications of learning curves, and development of spreadsheet skills. There are several project learning outcomes that stem from project educational goals that are reinforced/implemented through project activities. They include 1) development of teamwork skills, 2) increased appreciation for future coursework in physics, statics, dynamics, and thermodynamics, 3) an early understanding of the role of experimental and analytical approaches to engineering problem solving, 4) development of written communication skills through writing technical team reports, 5) increased appreciation for engineering by experiencing a “real life” like hands-on engineering project from start to finish, and 6) learning about manufacturing in general. These outcomes are closely related to ABET-EAC Criterion 3, a-k student learning outcomes14, specifically outcome a an ability to apply knowledge of mathematics, science and engineering, outcome b an ability ... to analyze and interpret data, outcome g an ability to communicate effectively, and outcome k an ability to use the techniques, skills, and modern engineering tools necessary for engineering practice. Practical Experience Manufacturing Task A steel coupler is machined. The intended use of the coupler is to connect two other metal parts. A 1018 mild steel with a diameter of 3” and a length of 10” is turned down to a diameter of 2.25” in three passes for a length of 7” on a manual engine lathe. Then, a 2” deep and 1.75” diameter hole is drilled on the uncut side of the part on the same lathe. The part is then moved to a HASS CNC mill that removes, 3” from the end lengthwise, top 0.84” section of the turned 7” long cylindrical section and drills a 1.5” diameter hole in the middle of milled area. Finally, a 3/8” diameter pin hole is drilled on the side with 2” deep blind hole at the end. Figure 1 shows 3-D view of the finished part. Each student team was also required to envision a potential application and sketch it freehand. Appendix B shows some sample sketches that depict potential uses for the coupler. Figure 1. 3-D Rendition of the Finished Product (Coupler) Figure 2 shows the side view engineering drawing of the coupler. The dimensions and the tolerances were adhered to. Figure 2. Engineering Drawing of the Coupler Showing Basic Dimensions and Tolerances Each cut is timed and the part is weighed before and after each cut to calculate experimental metal removal rate (in3/min.) for each cut. All experimental observations are compared against analytical results for each machining parameter set (spindle speed, feed, and depth of cut). Calculated energy for each cut is compared against the maximum power the motor can deliver at the cutting point with an assumed machine efficiency of 80%. Necessary set up times and other unavoidable time losses are also noted and used in final calculation of total production time per part. Actual tool, energy, raw material, and hypothetical labor and overhead costs are used in calculation of total production cost per part under various cost and annual demand scenarios. Learning curve effect is included for non-machining activities such as handling and minor setup times. It is also assumed that raw material cost decreases as the quantities increase. This is a complex project with multiple educational goals. One of the goals is to educate students on the circle of manufacturing in which the final product of one company becomes the input of another company. In this case, raw material shown in Figure 3 was used to manufacture the coupler shown in Figures 1 and 4. Figure 4 shows painted finished couplers as well as the raw material to illustate how manufacturing, by applying energy to raw material, has transformed it into a finished product. Students were able to withness how value was added to raw material through series of machining operations. Appendix C contains pictures of these operations. Figure 3. Incoming Raw Material (1018 Cold Rolled Steel) at $22.25/piece Figure 4. Finished and Raw Coupler Parts. Another objective of this project was to expose the first year students to the process of using collected data to write a report from an engineering perspective. Manufacturing is the process of fabricating a raw material into a predetermined functioning final product. During this project the students were able to see the manufacturing process firsthand and experience it albeit without actually making the cuts. Discussion of Project Calculations Each team calculated coupler cost under the assumption that learning curve applies in two ways: 1) Raw material cost per coupler decreases as quantities purchased double. A 95% learning curve was applied. This means a reduction of 5% will be realized in raw material cost. This assumption is supported by literature and the quotes obtained from the supplier for increased order quantities. According to a textbook on cost estimation15 the learning curve is 93% – 96% for raw materials, 85% – 88% for purchased parts, and 85% for operations that are half hand assembly and half machining. 2) Indirect labor time will decrease with a learning curve of 85% as the quantities double. Initially, it was assumed that the indirect time per part (handling, positioning, measuring, etc.) is equal to 100% of the direct time. This seemed reasonable as each part took about twice as long as the sum of all operations of the direct times. The total direct cutting time of about 31 minutes is a constant, but the indirect times improve with repetition. 3) No cost reduction is assumed for tool, energy, and paint usage with increasing quantities. Some cutting tool costs (drills and milling cutters) were assumed to be a part of the overhead cost charge as a percent of the labor cost shown in Table 1. In case of turning operations, disposable carbide insert cost was available ($10.25 for a 3 pack with a total of 9 cutting edges). This cost is distributed to each coupler as a direct cost. Table 1 shows six likely cost scenarios the company may face in manufacturing of couplers. It is assumed that the maximum of 5000 parts/year can be manufactured. Table 1. Scenarios Considered in Manufacturing Cost Calculations Overhead Rate Direct Labor: $18.25/hr Direct Labor: $25.00/hr Direct Labor: $34/hr. 60% Scenario 1 Scenario 2 Scenario 3 40% Scenario 4 Scenario 5 Scenario 6 It is also assumed that the overhead rate fully covers all indirect costs of the company. In scenario 2 for example, direct labor rate of $25/hr is inflated to 25*(1+0.6) = $40/hr. and t