Semirolling

Semirolling is a metal forming technique characterized by partial plastic deformation introduced through rolling, with the total deformation accumulated over multiple passes rather than in a single pass. It occupies a midpoint between traditional rolling, which applies substantial thinning in each pass, and incremental forming, which deforms small regions with localized tooling. In semirolling, each pass uses rollers set to a bite smaller than in full rolling, delivering a defined thickness reduction while leaving portions of the cross-section less deformed. The process is typically guided by automation that synchronizes bite, speed, and temperature to control the evolving microstructure and residual stress state. Back-up rollers and precise alignment are often used to maintain flatness and surface quality.

Process and materials: The workflow begins with a prepared billet or sheet; the workpiece passes through rolling stands configured for controlled deformation. Lubrication and possibly temperature control are used to optimize flow. Typical materials include aluminum alloys, low- to medium-strength steels, and titanium alloys. Reduction per pass is commonly in the single-digit to low double-digit percent range, with total reductions tailored to final thickness and geometry. The partially deformed layers experience altered strain profiles, enabling targeted microstructural refinement through subsequent passes or controlled cooling.

Applications, advantages, and limitations: Semirolling is used where tight thickness control and surface integrity are important, such as in aerospace skins, automotive panels, and specialized enclosures, and where residual stress management is desired. Advantages include smoother surfaces, lower work-hardening per pass, and greater control of microstructure. Limitations include reduced throughput relative to conventional rolling, higher equipment and control needs, and sensitivity to material properties such as flow stress and friction. The technique remains less widespread than conventional rolling and may be more common in research or specialized production contexts. See also: rolling, incremental forming.