Steady State Thermal Analysis - Simulation

[shravanaumesh]

TL;DR

A tool contacts new hot workpiece every 10 sec. What are the factors needed in a simulation to check when the tool reaches steady state temperature?

I am simulating a hot forging process in LS-Dyna. A tool is contacting a hot workpiece for 2 sec every 10 sec (--0 sec--contact--2 sec--no contact---10 sec--) in a factory. Since this is a continuous process, the tool should, at some point, attain steady temperature. I have tried to recreate it in LS-Dyna but I get a continuously increasing curve of temperature at the point of contact at end of 10 sec every time. So I want to clarify my basic understanding of this process.
What factors are needed to be considered for steady-state thermal analysis?
Is having only tool and workpiece resulting in only increase of the tool temperature? OR Will adding the other components of the machine help the tool achieve steady-state?

 

[FEAnalyst]

Make sure that thermal boundary conditions (such as convection) are properly defined. Maybe it will take some time for the tool to reach constant temperature so you may have to increase the simulation time.

 

[shravanaumesh]

Thank you for the reply.

My thermal boundary is limited to the tool having temperature of 20°C and the workpiece with 1050°C. The tool material is defined by MAT_RIGID with THERMAL_ISOTROPIC property. There is Heat Transfer Conductance defined at tool-workpiece contact. Is there any other property that is necessary that I have missed?

I have a reference of the same simulation reaching steady state in 19 cycles so I am trying to validate my model with it.

 

[FEAnalyst]

I don’t use LS-Dyna but it’s probably the same as in other software. When you use rigid bodies defined as isothermal then they have uniform temperature all the time. For this analysis I would use deformable elements with temperature DOFs and apply these temperatures as initial ones so that they can change during the analysis (temperatures prescribed as boundary conditions are kept throughout the simulation).

 

[shravanaumesh]

I checked my model and you are right. The nodes with temperature boundary conditions were not in contact with the tool. Hence there was continuous increase in the tool. I have rectified the problem.
Thank you for your help!