Spring fabrication and plastic deformation

Abstract

This is a workshop introducing the participants to spring fabrication and plastic deformation processes involved in making and using springs including the use of software packages like Microsoft Excel for data analysis. The first part explains elastic and plastic deformation followed by some demonstrations involving plastic deformation and the accompanying strain-hardening effect in coiling copper wires to make springs. The participants then make a spring and evaluate its elastic and plastic deformation with the help of Excel. Copper wire is chosen because it is commercially available in a wide range of sizes, easy and safe to deform, and inexpensive. The fact that copper springs are easily deformable provides us with an opportunity to study plastic deformation processes and the accompanying strain-hardening effect. Once these processes are understood. Hooke's law and elastic limit experiments using springs are better understood and appreciated.
The second part involves actual spring fabrication and design where the participants will make their own springs, evaluate their spring constants using a Hooke's law apparatus for springs, and investigate the dependence of the spring constant with the spring geometry: the number of coils in the spring, its coil diameter, and the diameter of the wire used for the spring. Aspects of spring stretching during the Hooke's law experiment are discussed. Logarithmic graphs are used to evaluate the dependence of the spring constant on its geometry. An empirical equation is then formulated to summarize the dependence of the spring constant on spring geometry. Microsoft Excel is used to facilitate data analysis: data tabulation, calculation of values, graphing data points, making logarithmic graphs and curve-fitting. Participants with little or no exposure to Excel will be given a tutorial kit that will allow them to do the required analysis.
The insights gained on plastic deformation and the spring constant will help teachers and students appreciate their value as they are discussed in class and will lead to a better appreciation of Hooke's law experiments involving springs and springs in general. The spring fabrication facility used in the workshop can be made from locally available materials at a cost of around PHP 150 per set (materials only). With the ability to fabricate springs with the desired spring constant, other classroom activities are suggested involving springs made from copper or other materials.