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Internship Self-Summary

The four-day comprehensive metalworking internship at the Engineering Teaching Center (June 15th to June 18th) was completed strictly in accordance with the rotation schedule of the center, covering all training modules including material chemistry experiments, traditional hot and cold processing, digital numerical control machining, 3D printing, as well as special machining such as laser cutting and wire electrical discharge machining (WEDM). The intensive practical training mode with alternating operations across multiple trades allowed me to step out of textbook theories completely, and experience the entire mechanical manufacturing process from raw material forming, cutting machining, special manufacturing to material property testing. It also enabled me to gain a comprehensive and in-depth understanding of the rigor and practicality of the engineering manufacturing industry.

On the first day of the internship when I first entered the training workshop, I was unfamiliar with most of the equipment and processes. In the morning, group-based material chemistry experiments were carried out simultaneously with rotational training in casting, laser processing, 3D printing and CNC lathe operation. During my first attempt at sand casting molding, I failed to control the ramming force properly and handled the parting surface roughly, resulting in repeated problems such as mold collapse during pattern drawing and cavity defects. When operating the CNC lathe, I was not familiar with the tool setting logic and messed up the setting of tool compensation parameters, leading to severe dimensional errors of parts during trial operation. When grinding metallographic specimens for material testing, I skipped grit grades of abrasive paper, leaving deep scratches on the specimen surface, which made it impossible to distinguish metal microstructures under a microscope. I felt overwhelmed at first when confronted with successive operational mistakes. Fortunately, the supervising instructors broke down the operating standards step by step. Meanwhile, I recorded key operating points and error-prone details of each trade on the schedule every day, reviewed the causes of mistakes during breaks, and corrected my operating habits bit by bit.

As the rotation proceeded, I successively got involved in welding, forging, wire electrical discharge machining and other trades, each of which brought new difficulties to tackle. In the manual arc welding training, I frequently encountered improper current matching and erratic travel speed of the welding rod, causing defects including excessive spatter, slag inclusion and incomplete penetration on welding seams. During forging practice, I could not accurately judge the heating temperature of forgings, and my movements for drawing out and upsetting were uncoordinated, so the size and shape of forgings failed to meet drawing requirements. When conducting wire electrical discharge machining, I had no clear understanding of the adjustment logic for molybdenum wire tension and discharge gap compensation, resulting in obvious taper and rough surface on the machined part contours. At the end of practical training every afternoon, I sorted out problems based on the daily rotation content, took the initiative to consult teachers about process optimization schemes, and repeated practical drills. Gradually, I mastered the core skills of each working procedure: ramming sand evenly in layers and designing reasonable vent grooves to reduce blowholes and sand holes in casting; matching current according to plate thickness, adopting a uniform zigzag travel speed and thoroughly cleaning welding slag after each welding pass; tensioning molybdenum wire tightly before wire cutting and setting discharge compensation precisely according to workpiece thickness to greatly improve machining accuracy.

The full-day training on Wednesday covered forging, wire cutting, group-wide 3D printing and cyclic practice on CNC lathes, where I also encountered various technical difficulties in 3D printing operation. Initially, unreasonable slicing parameters caused problems such as warping at the bottom of printed models, large interlayer gaps and loose filling. By adjusting hot bed temperature, reducing the printing speed of the first layer and optimizing filling density, together with standardizing the post-printing polishing and support removal procedures, I finally obtained well-formed models with accurate dimensions and smooth surfaces. Material chemistry experiments ran through the four-day internship. After repeated practice of the whole workflow including specimen cutting, rough and fine grinding, polishing, etching, metallographic microscopic observation and hardness testing, I truly understood the correlation between the composition and internal metallographic structure of metal materials and processing technologies such as casting, forging and welding. I realized that different hot working processes would change grain morphology and directly affect service properties including hardness and strength of parts. An integrated engineering thinking that "material properties determine processing technologies, and processing technologies modify material performances" was established in my mind, freeing me from viewing material experiments and mechanical processing in isolation.

Thursday was designated for comprehensive rotation training across all trades, where students from Material Class One and Material Two took full training projects covering benchwork, turning, milling, grinding, casting, forging, welding, numerical control machining, 3D printing, laser cutting and wire cutting. It also served as a comprehensive assessment of what I had learned in the previous three days. In traditional cold working training, filing, drilling and assembly in benchwork demanded great patience and precise control of hand strength. My arms ached after long hours of manual operation, yet only repeated filing and polishing could guarantee accurate flatness of parts. When operating milling machines and grinders, feed rate and cutting speed had to be strictly controlled; slight carelessness would lead to scrapped workpieces due to overcutting. In the programming session for CNC turning and milling, I attempted to write complete machining programs for stepped shafts and grooved parts. I independently finished the whole process from program input and single-block trial run to continuous automatic machining, and truly experienced the advantages of high precision and high efficiency brought by digital manufacturing. Laser cutting is suitable for rapid b