Levelling and splitting technology for lighter vehicle components

E-mobility has already fundamentally changed the everyday working lives of many companies and employees in the automotive industry. Planning engineers and production managers as well as assembly workers are confronted with the challenges in levelling and slitting technology in their daily work.

Broadband longitudinal slitting line. Source: Burghardt + Schmidt GmbH

The steady expansion of e-mobility and the legal regulations relating to conventional combustion engines are subjecting the traffic and transport sectors to comprehensive change. To reduce emissions, for example, lighter car bodies and vehicle components are needed. In addition, crash safety also plays a role, because the accommodation of heavy batteries in a vehicle requires appropriately designed body structures that take an accident scenario into account. While fibre composites are sometimes used in small series in this context, materials such as high-strength steel and aluminium are asserting themselves in large series construction with continuous refinement. In addition to the comparatively low costs, the excellent recyclability is a significant advantage of metallic materials. However, their further development often poses new challenges for the processing procedures and the machines used.

In particular, the residual stress state, the flatness and the cutting quality are very important quality characteristics that must be taken into account for the materials in the levelling and slitting technology. Remarkably, these criteria play a decisive role in the quality of the final product even before the final moulding. In production, for reasons of cost and time, the aim is to achieve an ever higher degree of automation, which can only be achieved if the semi-finished products have perfect flatness, a low level of residual stress and a low cut burr. If these requirements are not met, this can have a negative effect on handling and further processing or even make it impossible.

Wide range of applications for aluminium and high-strength steels

Modern and sophisticated materials are used in automotive engineering not only for the outer skin and structure of the actual car bodies, but are also used in vehicle components such as the chassis, drive train, seats or trim parts. Aluminium and steel are used for many components in the form of strips, sheets or plates, which are processed and formed in various manufacturing processes from semi-finished products to finished components. Even during these process steps, special demands are placed on the components. Due to the automated handling, good flatness and the lowest possible degree of cut are very important for a machining process without complications. If these quality criteria do not correspond to the defined specifications, there is no process reliability.

The companies of the b+s group have already supported their customers with appropriate solutions for demanding tasks in the past. Thanks to the experience gained from a large number of different projects in this area, the b+s group continuously optimise their competencies in terms of residual stress state, flatness level and cut quality of strips and sheets to meet the highest requirements. In addition, speed and surface protection play an important role in machining and must be taken into account in all approaches to process improvement.  An important prerequisite for these processes is a perfectly aligned and low-burr starting material. The b+s group has made it its business to react to these challenges and problems with the help of its decades of experience and to offer technologically mature solutions in the field of levelling and slitting technology, strip feeding systems and automation.

Numerical simulation allows for more flexible levelling machines

Aluminium and high-strength steels, for example, place special demands on the individual processing steps. One factor that has a major influence on the quality of the end product is the levelling of the respective metal. In a levelling machine consisting of several staggered levelling rolls, the coil curvature of the starting material is eliminated. In addition, any edge or centre waves in the strip material can be compensated for, using suitable machines. The aim here is to achieve the lowest possible and most homogeneous residual stress state in order to maintain the flatness of the material during subsequent cutting processes. An elementary measure for the efficiency of a levelling process is the degree of plastification of the respective metal, which describes the proportion of the material cross-section that is plastically deformed during levelling. With the same yield strength and material thickness, aluminium requires significantly greater degrees of deformation than steel to achieve comparable plastification.

The reason for this is the significantly lower modulus of elasticity of aluminium compared to steel. However, in order to realise greater degrees of deformation, smaller levelling rolls must be used. With high-strength steels, on the other hand, a conflict of objectives arises. On the one hand, their high yield strengths require enormous forming forces and torques; on the other hand, small levelling roll diameters are also needed here to achieve a sufficient degree of plastification. The levelling of both aluminium and high-strength steels therefore requires a forming geometry adapted to the respective product. This is essentially determined by the number, diameter and spacing of the levelling rolls.

The experts of the b+s group have been dealing with the numerical simulation of forming processes in levelling machines for many years. For this reason, powerful simulation programmes are available today with which optimal configurations can be determined for the respective applications. The software has been validated by means of extensive experimental investigations so that the optimum levelling roll diameters can be determined for a specific area of application. The use of cassettes with different diameters allows a levelling machine to cover a wide range of products. As a pioneer in the field of exchangeable cassettes, Schnutz GmbH developed various solutions that enable efficient work. In the highest expansion stage, a cassette change therefore takes about as much time as a coil change.

Precise adjustment of the slitter shafts enables exact splitting

In addition to levelling, in the field of sheet metal fabrication, attention must also be paid to accuracy and cut quality during slitting in order to avoid failure batches. Although the advanced materials, such as high-strength aluminium in the automotive or aerospace industries, offer completely new possibilities thanks to their great resilience and extraordinary flexibility, they also pose new challenges for slitting technology in their processing. The heart of every modern slitting line is the slitting shear, which can be positioned precisely and stably by means of an extremely precise and preloaded roller bearing and a backlash-free linear guide. However, in order for these shears to meet the high demands of the processing procedure and to cut the strips to the desired width with little burr, tension-free cutting must be guaranteed at all times. For this reason, when manufacturing slitting lines, the specialists at Burghardt + Schmidt attach particular importance to the precise manufacture and adjustment of the slitter shaft. To ensure a perfect cutting pattern, these must run parallel to each other, which is ensured by active repositioning during the cutting process. In this way Burghardt + Schmidt guarantees fast and trouble-free passage of the coils due to precisely manufactured belts.

The b+s group, to which the Schnutz GmbH und Delta Technik GmbH belong, presents itself in the manufacture of cutting and levelling machines as well as automation technology. Under the leadership of Burghardt + Schmidt GmbH, founded in 1945, b+s group is facing the challenges of the constantly changing market. In recent years, the group has developed into one of the world's leading manufacturers of slitting lines, stretch-bend-levelling lines, packaging lines, traverse winders, levelling machines, cut-to-length lines, coil lines and automation solutions and has established itself in the global market. With the help of the experience gained in the process, the requirements for the use of aluminium and high-strength steels in body construction for e-vehicles can be successfully met.