Experimental work on Single Point Incremental Forming of Sheet Metals

New methods of forming sheet metal are now at a stage where it is possible to make either custom manufactured parts or to manufacture small batch production quantities, with very short turnaround times. Current developments have been focused on forming symmetric parts using CNC technology, without the need for costly dies. Incremental forming uses the same principle that of rapid prototyping i.e. forming a model step-by-step. Single Point Incremental Sheet Forming has the potential to revolutionize sheet metal forming, making it accessible to all levels of manufacturing.

The most commonly used test for predicting metal formability is the uniaxial tension test. Specimens were prepared and test is conducted as per the standard of ASTM standard B-557-M which is Standard Test Methods for Tension Testing Wrought and Cast Aluminium- and Magnesium-Alloy Products. Sheet metals possess anisotropy i.e. their properties are dependent of the direction. Hence to find anisotropy; tensile tests were conducted along three different directions, with the tensile axis being parallel (0), diagonal (45) and perpendicular (90) to the rolling direction of sheet. The strain hardening coefficient (n) and strength coefficient (k) of material were determined from the slope of true stress-true strain curve when plotted on logarithmic coordinates.

Theoretical Prediction of Forming Limit Diagram

Forming limit diagram is needed to predict the behaviour of sheet during forming and to compare the strain development in cup. Theoretical prediction of FLD is made using Levy- Mises flow rule for limiting strain. The limiting strains are calculated using Levy-Mises flow rule for plastic deformation

Finite Element Analysis & Experiment

In this work FEA of incremental sheet metal forming was carried out using ABAQUS/Explicit. Formability of sheet material was predicted from a tension test. Theoretical forming limit diagrams which were constructed using Levy-Mises flow rule for plastic deformation. Rotational parts i.e. frustum of cone were formed by incremental method using 3axis CNC machine. L9 model was selected using design of experiment by Taguchi method which gave 9 experimental runs to be conducted. Three process parameters considered were tool diameter, vertical step size and feed rate.

Results

To analyse the design of an experiment; observed response of final thickness and signal to noise ratio are calculated. Responses measured were fracture depth and thickness distribution. To analyse the design of an experiment; observed response of final thickness and signal to noise ratio are calculated and represented using graph.

Results show tool diameter, steps size and feed rate have percentage contributions of 84.86, 9.09 and 3.04 on the final thickness of sheet blank respectively. the tool diameter, step size and feed rate had a percentage contribution of 0.63, 97.49 and 0.19% on the fracture depth of frustum of a cup respectively.

The most influencing parameters and their percent contribution to response is calculated using ANAOVA statistical models.

CONCLUSION

From Taguchi analysis and ANOVA we can conclude that

1. Vertical step size has a major influence on fracture depth

2. Tool diameter influences the surface finish of the part

3. In conventional forming sheet is under both simple tension and biaxial stretching

4. In SPIF Wall surfaces are under Plane stretching condition and

5. Corner surfaces are under biaxial stretching condition

Note: The complete article is available on International Journal of Engineering Research & Technology (IJERT) - ISSN: 2278-0181, Vol. 3 Issue12, December-2014