Ezy Mechanic

Ezy Mechanic | Machine components and linkages design made easy.

Saturday, July 25, 2015

Stiffness comparison of welded parts - Part 4

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As we can see from previous post that design C is still the best choice since it's light-weight and relatively rigid compared to other designs. Design E is the most stiff design but it's also the most heavy design. Let's continue with the remaining 2 designs with 4 ribs at the mounting base to see whether they're better than design C or not.

FEA result: displacement of welded parts with 4 ribs at the base
Finite Element Analysis result: Displacement of Design G
The weight of this design is in the same level as design D, but it's more rigid. When compared to design A, its weight is 123% and the displacement is 72.8%. Then we increase lengths of those 4 ribs in order to reduce the displacement. This is design H which its mass increases to 133% of design A. Here is the FEA result.

FEA result: displacement of welded tubes with longer ribs at base
Finite Element Analysis result: Displacement of Design H
The displacement is 9.72 mm which is 65.8% of design A. It's comparable to design C, but heavier. So design C is still the best choice. It's simple, not difficult to make, light-weight and stiff. The following is the summary of displacement and mass of all designs. The value in percentages are compared to design A.

Summary of displacement and mass of different designs
Summary of displacement and mass of different welding designs
 The red, yellow and green are used to express what is desirable and what isn't. Red is undesirable and green is desirable.

We hope the experiment about the stiffness using finite element analysis in these 4 posts may provide you the idea of improvement. Sometimes, we add extra materials (more weight, more cost) but gain very little. Sometimes, only minor changes change significantly improve the design with acceptable weight and cost.

The following is the video showing more details of this experiment.


Design C is good when we can't have any parts above the horizontal tube. It may interfere with other parts, for instance. However, if there is no space limitation above the horizontal tube, we could greatly improve the stiffness of the structure and reduce the weight. Let's find out in the next post.

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