ISO 20928:2018

Overview

ISO 20928:2018 specifies design and application information for spring plungers used in press tools - covering both plungers with helicoidal compression steel springs and those with gas (nitrogen) springs. The standard sets out required dimensions, stroke and forces, provides calculation basics, cautions and installation examples for separation of tools and sheet‑metal parts after stamping or forming operations.

Key Topics and Requirements

• Dimensions and tables: Dimensioning rules and example tables for steel‑spring and gas‑spring plungers (see Figures and Tables in the standard) to ensure interchangeability in press tooling.
• Stroke and force limits: Specifies working stroke recommendations (maximum recommended stroke is 90% of L) and force values for initial/final stroke states; includes limits on impact velocity (maximum 0.8 m/s for gas‑spring plungers, aligned with ISO 11901 calculation basics).
• Design details and cautions:
  • For gas springs, the filler opening is located vertically in the cylinder bottom and filling pressure is measured at 20 °C.
  • Lateral forces must be minimized for both types; gas‑spring plungers must not be subjected to lateral loads.
  • Safety note: removal of forward sealing set on gas springs is prohibited.
• Installation guidance: Includes fitting tool dimensions and installation examples (e.g., snipping applications), plus recommendations such as the use of a maintenance‑free guide bush to absorb axial forces and bending compressive stress and the need for an air hole in pocketed holes.

Practical Applications

• Separation of die and stamped/forming parts (preventing part sticking during ejection)
• Snipping and cutting bar applications in press tooling
• Locating, supporting or cushioning components in progressive dies and press tools
• Use where compact, repeatable spring force is required inside tool assemblies

Keywords: ISO 20928, spring plungers, gas spring plunger, steel spring plunger, press tools, stamping, sheet‑metal forming, dimensions, stroke, forces.

Who Should Use This Standard

• Tool designers and die makers creating or specifying press plungers
• Press tool manufacturers and maintenance engineers
• Purchasing and quality teams verifying component conformity
• Application engineers working on stamping, forming and snipping operations

Related Standards

• ISO 11901 (Tools for pressing - Gas springs): calculation basics referenced
• ISO 272 (Hexagon widths across flats): referenced for wrench flats
• Derived from VDI Guideline 3004 (background development)

ISO 20928:2018 is a practical reference for ensuring safe, standardized selection and installation of spring plungers in press tooling, improving reliability and interchangeability in sheet‑metal manufacturing.