Advanced ISF Variants
To minimise geometric inaccuracies, improve the surface quality of parts and overcome limitations in manufacturing hard-to-form materials, advanced process variants have been developed by investigators worldwide. This page covers some of the researched variants.
Heat Assistance
The use of heat improves the ductility of the sheet material being formed, and many ISF variants (some of which are highlighted below) focus on increasing temperatures during the forming process. This is because a key aim of research is to improve formability — for example, by increasing the maximum strain on the sheet material before it fractures.
Formability improvements improve the viability of ISF in industrial applications, allow for the production of more complex geometries, and enable a wider range of materials to be formed. A limitation is that surface finishing generally becomes poorer, which may make a workpiece unsuitable in some applications.
Laser Heating Assisted ISF
Laser heating assisted ISF provides a wide forming temperature range and excellent temperature control, which makes it suitable for forming most materials. The laser's movement is synchronised with the forming tool on the same or opposite side of the workpiece, which generates localised heating in the sheet.
Drawbacks include that the laser heating equipment is expensive, which compromises the cost-effectiveness of ISF, and that high-temperature forming results in lower surface quality. The selection of lubrication is an important consideration to reduce surface roughness.
The process is considered effective at improving formability and geometric accuracy.
As proposed by Duflou et al. in 2007: Laser Assisted Incremental Forming: Formability and Accuracy Improvement.
Electrical Heating Assisted ISF
Electrical heating assisted ISF uses the Joule heat from the metal sheet's own electrical resistance to generate localised heating in the sheet. The first electrical heating setup used a DC current circuit between the clamping system and forming tools.
Like laser heating assisted forming, the drawbacks of this variant are the additional equipment required and the reduced surface quality of parts, which is a critical issue for its use in real-world applications.
The process is considered effective at improving formability and geometric accuracy.
Friction Stir ISF
Friction stir incremental forming employs a forming tool which rotates at a high speed, generating localised frictional heating at its contact point with the sheet metal.
The forming temperature obtained by the method is generally limited. Surface quality is compromised by the abrasion at elevated temperatures caused by friction, which makes it even more important to select appropriate process parameters. With an ideal forming temperature, the sacrifice to workpiece surface quality can be minimised.
The process has been shown to have a limited effect on formability owing to its limited forming temperature and the significant wear to the sheet's surface.
Ultrasonic Vibration Assisted ISF
Incorporating ultrasonic vibration into forming can reduce required forming forces and improve the geometric accuracy and surface finishing of ISF parts.
The variant employs an ultrasonic generator attached to the forming tool. During the forming process, an ultrasonic vibration field with a frequency between 20 kHz and 100 kHz is applied to the sheet.
The process is currently in its infancy, and its effectiveness at enhancing material formability has not yet been fully demonstrated.
As proposed by Vahdati et al. in 2015: Investigation of the ultrasonic vibration effect in incremental sheet metal forming process
Hybrid ISF with Stretch Forming
Current ISF processes can be time-consuming for large products and complex geometries.
Hybrid ISF with stretch forming can shorten forming time by pre-stretching the sheet metal into an approximate shape based on the desired geometry containing its global geometric features. A supporting die is required to stretch the sheet to the approximate geometry, and a conventional ISF process follows to form local geometric features.
The process is a feasible method of reducing forming time for large parts, but it requires additional investment for the support die and a longer development cycle.
As proposed by Lu et al. in 2014: A Hybrid Flexible Sheet Forming Approach towards Uniform Thickness Distribution