The Ice Cream Spoon, Part 3

I’ve previously blogged about the ice cream spoon, but when I wrote those articles the weather was more suited for eating ice cream!  Personally, I like ice cream year-round, but some people choose warmer desserts when the winter months set in.  The first ice cream spoon blog discussed Surface Modeling techniques to create the spoon design.  The second ice cream spoon blog discussed using SOLIDWORKS Plastics to analyze the injection molding of the ice cream spoon.  In this installment, I will use SOLIDWORKS Simulation Premium to solve Finite Element Analysis studies and compare the spoon design with and without the underside rib.

In the SOLIDWORKS Plastics blog, I showed that the thick rib on the underside of the spoon handle played a significant role in reducing the maximum injection pressure required to mold the spoon.  But what role does the rib have for structural performance?  Is the rib necessary when I consider the loading conditions that the spoon will encounter?  With SOLIDWORKS Simulation Premium, I can answer those questions!

There are several items to be addressed before I begin the Finite Element Analysis setup.  I need to determine what a serving size of ice cream is so I know how much force to apply.  I also need to look at how the spoon is held which will determine required fixtures and find a material data sheet that includes a stress-strain curve.  Finally, I want to get to my FEA “answers” as quickly and efficiently as possible, so I need to consider how to simplify the model.

Based upon several internet searches, a recommended serving size of ice cream is three ounces.  On a hot summer day, I can imagine some people eating a single scoop in six bites, maybe less if the person can handle brain freeze!  That determines the force I will apply to the spoon.  In considering how the spoon is held, most of the handle would be clasped in a persons’ hand or between their fingers.  In the Finite Element Models, I will add a fixture to last two inches of the spoon handle.  In the Plastics analysis blog I used a Polystyrene resin for the injection material.  For the FEA studies, I obtained a material model for a Polypropylene resin with a stress-strain curve, another of the commonly used materials for plastic utensils.  As for simplifying the analysis, I chose to use symmetry and analyze one half of the spoon, split along the length, to reduce the size of the problem and speed up the solve time.

Now that I have answered the preliminary questions, I proceed to set up the analysis.  For the initial Linear Static analysis of the spoon without the underside rib, I apply a fixed boundary condition at the handle end.  I also applied a symmetry restrain on the long, cut face of the spoon and the corresponding block being used to push down on the spoon.  Finally, I apply a downward force equal to half of the ice cream bite size.

After solving the Linear Static study of the spoon without the underside rib, I create a new Nonlinear Static study using most of the previously discussed setup and boundary conditions.  The one change I do need to make is modify the material model, Linear Elastic Isotropic in the original study, to a Von Mises Plasticity material model for the Nonlinear study.  I need to repeat all the setup steps for the Linear Static and Nonlinear Static studies on the spoon with the underside rib, as well.  If you’re still following all of the setup and project details, great!  Let’s cut to the chase and discuss the results.

Based upon the Linear Static studies, the spoon with the underside rib deflects less than the spoon without the underside rib and has slightly lower calculated stress.  To be honest, though, the values from these Linear Static studies can only be used to provide a preliminary indication that the underside rib improves the design.  Looking at the comparison from the Nonlinear Static results, it is clear that the underside rib reduces deflection, which is what I’m primarily interested in.  If the end of the spoon deflects too much, you will drop the delicious bite of ice cream on your lap!

The underside rib provides two significant benefits for the spoon – reduced injection pressure for molding and reduced deflection for holding ice cream.  Using tools such as SOLIDWORKS Plastics and SOLIDWORKS Simulation Premium will give you the advantage of knowing that structural design changes improve your design performance.  I think it’s time to go get a double scoop of some delicious ice cream again!  Now go make your products better with SOLIDWORKS Simulation!