Fundamental research of wide panel roll forming

Abstract

The problems in wide-panel roll forming become more serious when higher strength, thinner materials are used. The occurrence of edge wave, oil-canning and splitting degrades the quality of products and affects the application of such materials. In this thesis, research is performed in three areas: 1) an investigation of mechanical behaviour of coated steel; 2) a new method of generating the sheet surface between stands in roll forming and of investigating this using differential geometry; and 3) a novel approach to the design of a roll forming system for wide corrugated sheet products. Through comparison of several test methods - tensile, bend, springback, holeexpansion, Olsen and edge wave tests - it is concluded that the tensile test is limited in the information it gives, particularly for harder sheet. For the coated materials, G300 and G55O, the paint-baking process ages the material and reduces the elongation; this can be observed from different test methods such as tensile, hole-expansion and Olsen tests. Especially for G550 material, the hole-expansion and Olsen tests could be useful test methods for routine testing. A springback parameter is proposed to identify strength and ageing effects in the material. Also, the springback property of material under bending and tension is investigated. A new spline model based on a reciprocal equation is developed and used to create a new software package. The generated surface satisfies the geometrical boundary conditions including the roll radius. Based on the spline model, the application of differential geometry in roll forming is discussed. This provides a new perspective of the characteristics of roll forming processes. A novel method of forming corrugated sheet is proposed and a prototype model built. As all CoiTUgations in the profile are formed simultaneously and follow an identical geometric path on a conical reference surface, the difference between corrugations is eliminated. The advantages of small transverse strain, no strain path difference and the small longitudinal strain within the corrugation given by this method are expected to reduce the problems of oil-canning, splitting and edge-wave.