Modeling, Rapid Prototyping, Casting, Cnc Producing, And Comparing The Mechanical Properties

Junior level mechanical engineering students’ have designed, rapid prototyped, cast, and tested a link in the laboratory portion of a materials and manufacturing course. A portion of this activity was described originally in a 2005 ASEE Conference paper. The activity has been used for several years in the laboratory portion of the course and it has been very successful. However, one question that comes to mind is May we compare cast mechanical properties with those of wrought properties for similar alloys. During lecture, comparisons of wrought and cast properties are frequently made, and it is shown that ratio of wrought to cast properties is frequently greater than one. To date, the direct comparison has not been done in this course. Using the student designed solid models, it is possible to directly make a rapid prototype part that can be used for the mold in a casting process, and that same model may be used in a CNC machine to make a similar part. Alloy 6061 was used to make the cast links and a section from the five inch diameter ingot will be used to make the CNC produced link. Mechanical properties will be measured using a universal testing machine. The results will be compared, and student interpretation of the results will be evaluated. Introduction In fall 2003, Texas A&M University at Qatar (TAMUQ) started an engineering program in Doha, Qatar under the auspices of Texas A&M University College Station and funded through the Qatar Foundation. The University has four engineering programs, which are Chemical, Electrical, Mechanical, and Petroleum Engineering. The initial group of engineers graduated in 2008. In steady state Texas A&M at Qatar is expected to have between 400 to 500 students enrolled in the four programs. Currently Mechanical Engineering has 67 students enrolled. TAMUQ follows the mechanical engineering curriculum at the College Station campus. Currently, the program has nine faculty members, and plans are to hire several more within the next couple of years. Currently, our upper division classes have only been taught two or three times. The laboratory facilities were completed and available for use in fall 2007. The initial ABET review took place during fall 2008. P ge 14882.2 Within mechanical engineering, two required materials course are taught one is a three credit sophomore material science course and the second is a four credit junior materials and manufacturing course, which has been reported on before at ASEE meetings. 1,2,3 The course, MEEN 360, has three lectures per week and one three hour laboratory. The objective of this paper is to compare mechanical properties of cast versus wrought components for links that students’ have designed, rapid prototyped, cast, and tested. The objective for the students was to maximize the ratio of the failure load to the mass of the link, which were made from aluminum alloy 6061. Procedure The activity extends over several weeks during the semester. Initially, the students design a link within the design space of 100 mm long, 5 to 7 mm thick and 30 mm wide. The design is done in solid works and the files are exported as STL files. Student’s often use Cosmos, which is part of Solid Works to help them minimize the weight. Unfortunately, their method of operation is to remove material where blue shows up and add material where red appears. The laboratory is divided into three or four person groups. Each person designs a link, but the links for one group are all cast in the same flask and are attached to the same runner. Students are in completion to develop a link that can carry the maximum load with the minimum mass (failure load divided by mass of link). A prize is given to the group with the highest ratio. Once the link is designed and rapid prototyped, the students have time to prepare their links before casting. The links are used as the pattern in a green sand mold casting. The aluminum alloy was 6061. Examples of the rapid prototyped (RP) links on the pattern board are shown in Figure 1 Before testing, the students are given a second homework assignment where each of them has to predict where failure will occur, what the failure load will be and what it will cost to design, test, and manufacture the links. This activity requires them to use mechanics of materials formulations to solve for the failure loads. Design Figure 1 shows four of the designed links. One mistake that we made was to remind the students to put a draft angle on the edges of their designed link. This mistake will result in a problem later during the casting process.