How is the Force Required to Expand Metal Rings Calculated in Forging?

[brewnog]

I am designing a machine called a Ring Expander. Simply put, it's a machine used in metal forging operations to stretch metal rings (15 x 15cm cross section, 30cm inside diameter, 60cm outside diameter) by about 20mm on the diameter. It does this by forcing a cone through a set of jaws, which expand as the cone passes though them, the workpiece having been positioned around the jaws.

What I need to know is how to calculate the force required to expand these rings! Approximate dimensions are given above, materials include stainless steel and titanium, but also 718 alloy (which I believe has a yield stress below 600MPa at the temperatures I'm looking at). I played around with looking at the force required to cause yield at a single cross section, but as these rings are circular I suspect that my assumptions were too simple.

Any help would be appreciated! My engineering knowledge only goes as far as elastic behaviour of rings.

Thanks!

 

[Aaron Barnard]

The force required to expand a metal ring is determined by the material properties of the metal and the level of deformation you are trying to achieve. The force required to cause yield at a single cross section is a good starting point, but you will also need to consider the geometry of the ring and the amount of deformation you are trying to achieve.

To calculate the force required to expand the ring, you will need to take into account the ring’s elastic modulus, which is the ratio of stress to strain, and its ultimate tensile strength, which is the maximum tensile stress a material can withstand before it breaks. You will also need to take into account the angle of the cone that is being used to expand the ring, as well as the rate of expansion and any other factors that might affect the force required.

It is difficult to give an exact answer without knowing more information about the ring, but you can use the formulas for calculating stress and strain to get a general idea of the force required. To simplify the calculations, you can use a finite element analysis software to analyze the ring's behavior under different loads. This will give you more accurate results and provide you with a better understanding of the forces involved.

 

[ravenprp]

The force required to expand the rings will depend on several factors, including the material properties, the dimensions of the rings, and the desired amount of expansion. Plastic deformation of rings involves the permanent change in shape or size of the rings due to the applied force. This deformation is caused by the slip of crystal planes within the material, which leads to dislocations and ultimately results in the permanent change in shape.

To calculate the force required for plastic deformation, the yield strength of the material is a crucial factor. The yield strength is the maximum stress that a material can withstand before it starts to deform permanently. For the materials you mentioned, stainless steel and titanium have higher yield strengths compared to 718 alloy. Therefore, the force required to expand rings made of stainless steel and titanium would be higher than that of 718 alloy.

The dimensions of the rings will also play a role in determining the force required for expansion. A larger cross-section will require more force compared to a smaller one, as the force needs to be distributed over a larger area. Additionally, the thickness of the rings will also affect the required force, as thicker rings will require more force to deform compared to thinner ones.

The desired amount of expansion is another important factor to consider. The more the rings are expanded, the higher the force required. This is because the material will have to undergo more deformation to achieve the desired expansion.

To accurately calculate the force required for plastic deformation, you will need to consider all these factors and use appropriate equations and models. It is recommended to consult a materials engineer or use simulation software to get a more precise estimation of the force required for your specific case. I hope this helps in your design process!