Post-Forming Mechanical Properties of a Polymer Sheet Processed by Incremental Sheet Forming: Insights into Effects of Plastic Strain, and Orientation and Size of Specimen.

Hongyu Wei,Ghulam Hussain,Behzad Heidarshenas,Mohammed Alkahtani

doi:10.3390/polym12091870

Abstract

The innovative Incremental Sheet Forming (ISF) process affects the post-forming properties of thermoplastic polymers. However, the effects of degree of plastic strain, and the orientation and size of specimen on the mechanical properties are still unknown. In the present study, therefore, the ISF process is performed on a polymer sheet by varying the plastic strain ranging from 6% to 108%. The corresponding effects on the properties and associated polymer structure are quantified by conducting a variety of mechanical and structural tests. The results reveal that the post-ISF tensile properties like yield stress, ultimate stress, drawing stress, elastic modulus and elongation decrease from 26.6 to 10 MPa, 30.5 to 15.4 MPa, 18.9 to 9.9 MPa, 916 to 300 MPa and 1107% to 457%, respectively, as the strain increases in the investigated range. The value of post-ISF relaxation properties, contrary to the tensile properties, increases with increasing strain up to 62%. Particularly, reductions in stress, strain and modulus increase from 41% to 202%, 37% to 51%, and 41% to 202%. As regard the orientation effect, the sheet in the feed direction shows greater strength than the transverse direction (up to 142% in yield stress and 72% in ultimate stress). Moreover, the smaller sample offers greater strength than the larger one (up to 158% in yield stress and 109% in ultimate stress). The analysis of the post-ISF tensile properties and structural results lead us to conclude that the drop in the tensile properties due to increasing strain occurs due to corresponding increase in the voids area fraction (1.25% to 31%) and a reduction in the crystallinity (38% to 31%).

Highlights

The trend of mass customization and rapid manufacturing is consistently rising in the market.On the other hand, the traditional processes mainly relying on the shape dependent tooling cannot meet these compelling demands
The present study addresses these points intending to comprehend knowledge on Incremental Sheet Forming (ISF) of the polymers to provide a guideline to the product designers and process users
−5.6%from to −59%, and ranges from 12%. These results reveal that both important design properties, namely yield stress and elastic results reveal that both important design properties, namely yield stress and elastic modulus, modulus, a drop overrange the entire rangestrain of applied strainthe and further,drop the respective drop received received a drop over the entire of applied and further, respective increases with increases with the plastic strain

Summary

Introduction

The trend of mass customization and rapid manufacturing is consistently rising in the market. The traditional processes mainly relying on the shape dependent tooling cannot meet these compelling demands. New processes, characterized by flexibility, and capable of producing parts without using the dedicated tooling, need to be invented and deployed in the industry. In the 1990s, based upon the idea proposed by Leszak [1], Kitazawa et al [2] invented die-less. Incremental Sheet Forming (ISF) to produce sheet components. Being a die-less process, it reduces the lead time and eliminates the die/punch cost thereby enabling product delivery with short production cycles as compared with the traditional press forming operations.

Methods

Results

Conclusion