Abstract: Based on the practical courses for undergraduates, this paper explores product development through the integration of handmade clay (oil) modeling, advanced reverse scanning technology, and 3D gypsum precision casting. It first discusses the necessity of curriculum reform, then delves into the curriculum reform and the implementation of the teaching plan, and finally summarizes the importance and significance of the platform construction process in practical courses.
1. Introduction
The gypsum precision casting course introduced in this paper is primarily applied in teaching modules such as metalworking practice, manufacturing engineering experience, personalized 3D printing and realization, engineering literacy and humanistic practice, engineering cognition and innovation, and other courses for undergraduates at Tsinghua University. Using project-based jewelry design as the teaching carrier, students learn about the entire lifecycle of jewelry production through stages such as wax model making, wax tree assembly, gypsum pouring, gypsum baking, vacuum pouring, and post-processing. This paper provides a comprehensive exploration of the innovative teaching methods and practical applications of this course.
2. Necessity of Curriculum Reform
The Forming and Manufacturing Laboratory of the Training Center has already established a practical teaching platform for investment casting with gypsum molds and conducted interdisciplinary and cross-trade teaching reform attempts on this basis. Aiming at the previous experimental teaching characterized by small modules, single trades, and single equipment, it explores integration with the existing precision engraving teaching system to build an interdisciplinary inquiry-based experimental teaching platform. Based on this experimental platform, a brand-new practical teaching mode is developed for the first time to help students systematically learn experimental techniques that combine precision casting with subtractive material processing and forming. The main content is to organically integrate precision casting with precision engraving, completing CAD/CAM modeling and wax mold processing through the precision engraving system, and realizing processes such as wax mold tree assembly, gypsum pouring, high-temperature baking, gypsum mold hardening, melting, pouring, and post-processing through the gypsum precision casting system to ultimately obtain metal castings. Based on this innovative teaching platform, students can independently complete the entire process of product design, model processing, and manufacturing, which is conducive to establishing students’ systematic cognition of industrial production processes. Developing practical teaching programs and systems that integrate multiple trades and disciplines can effectively achieve the “three-in-one” teaching goal of knowledge imparting, ability cultivation, and value shaping with students as the main body.
Due to the popularity of the investment casting with gypsum molds teaching module in the practical teaching of this course and its application in nine practical courses for undergraduates, each course serves different professional students, and the design and hands-on abilities of students from different majors vary. This results in repetition of this module in many courses and a lack of clear teaching objectives for students from different majors. Therefore, in order to better integrate existing practical teaching resources and effectively demonstrate the systematic concept of engineering practice, the training mode focused on learning technical skills and transforming students’ ideological style is transformed into a training mode integrating knowledge, ability, quality, and innovative practice to cultivate students’ sense of innovation and meet the talent needs in the era of mass entrepreneurship and innovation, further optimizing the practical teaching module. Customized teaching modes are developed for students from different courses and majors, organically integrating advanced 3D printing, reverse scanning, clay modeling, pottery, and gypsum precision casting to further promote the cross-integration of multiple trades.
3. Curriculum Reform Combining Hand Modeling, Reverse Scanning, and 3D Gypsum Precision Casting
3.1 Cultural and Creative Ornament Design with Festival Cats as an Example
This case combines the characteristics of different festivals (sending blessings during the Spring Festival, eating zongzi during the Dragon Boat Festival, the Magpie Bridge on Qixi Festival, mooncakes during the Mid-Autumn Festival, etc.), ultimately selecting seven festivals: the Spring Festival, Lantern Festival, Qingming Festival, Dragon Boat Festival, Qixi Festival, Mid-Autumn Festival, and Double Ninth Festival. To create a consistent element throughout the ornaments corresponding to each festival, after comparing various alternative elements, cats that conform to popular aesthetics were selected as the main body of the ornaments. Then, the easily made and interesting elements and corresponding cat actions from each festival were selected, and finally determined as follows: for the New Year’s Eve, a cat holding a Fu character; for the Lantern Festival, a cat with a bowl of lanterns in its wide-open mouth; for the Dragon Boat Festival, a cat sticking out of a zongzi; for the Qingming Festival, a ghost-like cat; for the Qixi Festival, cats meeting on the Magpie Bridge; for the Mid-Autumn Festival, a cat lying on a mooncake; and for the Double Ninth Festival, a cat sitting on the top of a mountain.
3.1.1 Hand Modeling Technique
In this case, for some models with complex curved surfaces, especially when there is no foundation in three-dimensional design, the three craft techniques are organically combined. Firstly, the method of hand modeling is utilized to present the clay or oil clay models. Modeling in ceramics involves two aspects: molding and shaping. It is the earliest molding method among the basic forming techniques in ceramics, where clay is molded into various object shapes by hand. The moisture content of the clay is generally between 20% and 26%. Among the hand-shaping methods in sculptural pottery, molding is the most concise and flexible one. Therefore, this case selects the molding method to realize the prototype production of the festival cat ornaments.
3.1.2 Reverse Scanning
In manufacturing, a 3D scanner serves as a rapid three-dimensional measurement device. Scanning samples or models with a 3D scanner can obtain their three-dimensional dimensional data, which can be directly interfaced with CAD/CAM software. Within the CAD system, the data can be adjusted, repaired, and then sent to a machining center or rapid prototyping equipment for manufacturing, significantly shortening the product manufacturing cycle. The portable handheld laser scanner used in this case boasts a maximum accuracy of 0.02mm and a maximum scanning speed of 2,100,000 points per second, capable of scanning complex curved surfaces. The three-dimensional optical scanner adopts photographic three-dimensional scanning technology, which is a combination of phase and stereo vision technologies. It projects a grating or laser line onto the object’s surface, captures distorted grating images using two cameras, and calculates the three-dimensional spatial coordinates of points to achieve the measurement of the object’s surface three-dimensional contour. The clay greenware obtained through hand modeling undergoes reverse scanning to obtain an STL file recognizable by a 3D printer, with the detailed process.
3.1.3 3D Gypsum Precision Casting
3D gypsum precision casting is a technology that combines 3D printing with gypsum precision casting. The process involves acquiring a data model using reverse scanning technology or three-dimensional modeling, using 3D printing to create a wax mold, and ultimately obtaining a metal casting through gypsum pouring, burnout, dewaxing, and pouring. This technology effectively shortens the product development cycle, reduces production costs, and holds broad application prospects. This project leverages the discrete/additive manufacturing principle of 3D printing, adopting contour scanning and jet solidification processes to achieve rapid direct forming of wax molds in gypsum precision casting without the need for patterns. The materials used in the printing process are UV-curable plastics, with support material being Visijet M2 SUP hands-free soluble wax, and the detailed process.
This case selects the STL model obtained through reverse scanning for wax mold printing, obtaining metal castings through gypsum precision casting, and completing the final product through subsequent processes such as mold execution, buffing with cloth wheels, ultrasonic cleaning, polishing stick grinding, and electroplating.
3.1.4 Main Roles of Curriculum Reform in Laboratory Construction and Talent Cultivation
This curriculum reform is primarily applied within the precision casting courses offered in the casting section of the Forming and Manufacturing Laboratory. It is most frequently utilized in the course on personalized jewelry design and creation within the Manufacturing Engineering Experience. It attempts to integrate traditional hand modeling, advanced reverse scanning, and 3D gypsum precision casting, reflecting the characteristics of multidisciplinary integration, which aligns with the laboratory’s practical teaching objectives. Bold integration and innovation have been introduced in curriculum setting, transforming the original single-module practical teaching. Meanwhile, the curriculum content leaves some flexibility for students, stimulating their creative desires and potential, which helps to:
- Enhance students’ abilities to independently design, analyze, and solve problems.
- Enable students to diversely master practical operational skills, encourage innovation, and exert autonomy and enthusiasm in practical learning.
The integration of practical teaching resources combines advanced technology with exquisite art, breaking professional barriers and better serving practical teaching. This effectively achieves the “three-in-one” teaching objective of knowledge imparting, ability cultivation, and value shaping with students as the main body.
Since the majority of enrolled students are liberal arts majors, some may be less proficient in using software for three-dimensional modeling. Therefore, the integration of these three technological processes effectively addresses the disadvantage of liberal arts students’ weaker ability to use software for three-dimensional modeling, solving the problem of complex model design at the source and effectively improving classroom efficiency. Moreover, hand modeling is low in cost and flexible in process, making it convenient for experimental teaching.
The reform outcomes constitute an important part of the precision casting practical teaching module construction in the laboratory. Besides being used for undergraduate practical teaching, it is also applied in exchange experience activities, open day experiences, and some external scientific research services. It combines tradition with advancement, art with technology, and aesthetics with science.
Through theoretical instruction, hands-on practice, and project guidance, teaching is organized in a step-by-step manner. During implementation, the approach of “theory + practice + school + enterprise” is adopted to jointly cultivate undergraduates’ perspective on grand engineering and their engineering innovation and comprehensive practical abilities. It combines extracurricular practical ability cultivation, school-enterprise collaborative cultivation, and humanities and craftsmanship spirit cultivation, constructing a new engineering practical teaching system with “four levels and three combinations” that spans the main line of multidisciplinary integration.
In summary, through the innovative exploration of the practical teaching mode that integrates hand clay (oil) modeling, reverse scanning technology, and 3D gypsum precision casting, a further realization of combining traditional handcrafts with advanced manufacturing technology in practical courses has been achieved. It also combines art with technology and aesthetics with science, embodying the characteristics of multidisciplinary integration. Additionally, it effectively addresses the disadvantage of liberal arts students’ weaker ability to use software for three-dimensional modeling, solving the problem of complex model design at the source. This significantly improves classroom efficiency, and hand modeling is low in cost and flexible in process, making it convenient for experimental teaching.