Ezy Mechanic

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Wednesday, July 15, 2015

Stiffness comparison of welded parts - Part 1

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In the machine, we usually make parts to support other machine components from standard steel profiles because they are relatively low cost. In this post, we're going to see how different constructions affect the stiffness of the welded parts. We have 3 different constructions of supports as shown in the picture.
Three welded part designs with mass
Supports with different constructions
The constructions are slightly different.
  • A -- typical welding (mass = 0.9 kg)
  • B -- typical welding with extra tube (mass = 1.3 kg)
  • C -- square tubes welding with thin plate insertion between tubes (mass = 0.92 kg)
All 3 constructions are subjected to the same forces and constraints as shown in the picture. Main parts are square tubes size 25 mm x 25 mm with thickness of 2 mm. The flange on the right is the mounting plate. It is constrained not to move in x, y and z directions. And we assume this is the only mounting plate allowed to use due to the space limitation in the machine.
face loads on the welded parts
Welded square tubes subjected to face loads
There is another flange on the left is subjected to face loads in both x and z directions. So we can expect the displacement of the parts to the left (-x direction) and up (+y direction) directions when loaded.

Let's start with design A -- typical welding with 45 deg angle connection. There is only small area on the perimeter for welding.
typical welding of square tubes with 45 degrees connection
Design A: Cut-away picture of typical welded square tubes with 45 deg. connection
Design B is the extended version of design A. An additional square tube is welded to withstand more forces but we get more weight and required more space. Assume there is nothing above the L-shape welded part and we can put additional square tube as shown in the picture.
additional square tube welded on typical welded tubes
Design B: Typical welded square tubes with extra support
Design C is the modified version of design A where we insert a thin steel plate (thickness = 2 mm) between both square tubes.
insertion of thin plate in between the square tubes
Design C: Cut-away picture of welded parts with a reinforced steel plate
Let's see how we setup the finite element model with constraints and loads in the next post.

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