Automatic Multi-Stage Cold Forging of an SUS304 Ball-Stud with a Hexagonal Hole at One End

• Published in: Materials Vol. 13; no. 22; p. 5300
• Main Authors: Byun, Jong Bok, Razali, Mohd Kaswandee, Lee, Chang Ju, Seo, Il Dong, Chung, Wan Jin, Joun, Man Soo
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 23.11.2020; MDPI
• Subjects: Aluminum; Austenitic stainless steels; Behavior; Cold; Cold flow; Cold forging; Compression tests; Dies; Finite element method; flow stress characterization; Heat treating; high-strength material; non-isothermal analysis; Plastic deformation; Predictions; Room temperature; Stainless steel; Strain hardening; Strain rate; Temperature; Temperature effects; Yield strength
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma13225300

SUS304 stainless steel is characterized by combined tensile and compression testing, with an emphasis on flow stress at higher strain and temperature. The plastic deformation behavior of SUS304 from room temperature to 400 °C is examined and a general approach is used to express flow stress as a closed-form function of strain, strain rate, and temperature; this is optimal when the strain is high, especially during automatic multi-stage cold forging. The fitted flow stress is subjected to elastothermoviscoplastic finite element analysis (FEA) of an automatic multi-stage cold forging process for an SUS304 ball-stud. The importance of the thermal effect during cold forging, in terms of high material strength and good strain-hardening, is revealed by comparing the forming load, die wear and die stress predictions of non-isothermal and isothermal FEAs. The experiments have shown that the predictions of isothermal FEA are not feasible because of the high predicted effective stress on the weakest part of the die.