This article analyzes a patented T-section blank-to-ring stamping apparatus that eliminates fold marks, offering practical insights for mold makers working on thin-walled circular components.

In precision stamping of thin-walled rings from T-section blanks, one persistent challenge is the formation of fold marks at the joint where the blank’s ends meet during the bending process. A recently disclosed patent (CN-based utility model) addresses this by integrating a pre-forming step with a segmented die structure. The device uses a lower die with a circular cavity and an upper punch that features a tapered lead-in section, allowing the T-shaped blank to be progressively curled into a full circle without localized compression. Key data from the patent indicates a blank thickness range of 0.3–1.2 mm and a diameter tolerance of ±0.05 mm, which is achieved by controlling the punch’s entry speed at 15–20 mm/s and maintaining a die clearance of 1.1 times the material thickness. This design significantly reduces stress concentration at the T-junction, which is where conventional dies typically crack or leave visible creases.

From a mold engineering perspective, the innovation lies in the split-core construction: the lower die is composed of four radially movable segments, each spring-loaded and synchronized via a cam driver. During the downstroke, the segments close radially to form a complete ring cavity, while the punch’s internal core expands slightly to support the inner wall, preventing buckling. The patent specifies the use of Cr12MoV steel for the punch, hardened to 58–62 HRC, and a D2-grade die insert with a TiN coating to reduce friction. Real-world trials cited in the document show a fold-free rate of 99.2% over 10,000 continuous strokes, with tool wear measured at just 0.008 mm on the critical radius. For die setters, the key adjustment is the segment closing force, which must be set to 2.5–3.0 kN per segment to ensure consistent ring closure without over-squeezing the material edge.

For shops currently producing similar parts using multi-step bending or welding, this single-station device offers a 40% cycle time reduction and eliminates secondary deburring. However, the patent notes that the blank’s grain direction must be aligned parallel to the rolling direction to avoid edge tearing, and a lubrication film of 0.02 mm (e.g., low-viscosity stamping oil) is recommended on the T-section’s vertical leg. While the design is optimized for low-carbon steel and stainless steel 304, adapting it to aluminum alloys requires reducing the punch speed to 10 mm/s and increasing die clearance to 1.3× thickness. For more detailed die drawings and parameter tables, visiting MoldWorld (www.moldw.com) provides access to a database of patented stamping solutions and sourcing contacts for custom die components.