Inner Surface Morphology and Roughness Evolution of Pilgering Thick-Walled Tubes

Area of Science:

• Materials Science
• Manufacturing Engineering
• Tribology

Background:

• The Pilger rolling process is crucial for manufacturing seamless tubes, particularly from high-strength materials like hot-working die steel.
• Controlling inner surface roughness is essential for the performance and longevity of tubes in demanding applications.
• Understanding the evolution of surface topography during Pilger rolling is key to process optimization.

Purpose of the Study:

• To investigate the formation and evolution of inner surface micro-wrinkles during the Pilger rolling of hot-working die steel tubes.
• To analyze the relationship between process parameters, strain states, and inner surface roughness (Sa).
• To identify the critical factors influencing the reduction of inner surface roughness.

Main Methods:

• Hot-working die steel thick-walled tubes were subjected to Pilger rolling using an LG40 Pilger mill.
• Inner surface morphology and roughness were quantitatively analyzed using white-light interferometry.
• Three-dimensional strain was calculated, and finite element simulations were employed to analyze the strain state during deformation.

Main Results:

• Micro-wrinkles formed in the diameter reduction zone, increasing surface roughness parameters (Sz and Sa).
• In the wall thickness reduction zone, micro-wrinkles flattened, significantly decreasing Sz and Sa.
• The ratio of radial to circumferential strain was identified as the critical factor for flattening micro-wrinkles and reducing Sa to 0.174 μm.

Conclusions:

• Inner surface roughness evolution during Pilger rolling is governed by the interplay of compressive strains and mandrel support.
• Circumferential compressive strain promotes micro-wrinkle formation, while radial compressive strain aids in their flattening.
• Optimizing the radial-to-circumferential strain ratio is crucial for achieving a smooth inner surface in the final product.