Hill Engineering Blog

Residual stress in additive manufacturing

In previous blog posts we have discussed various issues related to residual stress in welding. Here, we’ll follow up with a more detailed look at residual stress in additive manufactured parts, which is a form of welding. Additive manufacturing processes, including powder and wire-fed E-beam and laser, produce residual stress as an undesired consequence. Residual stress in additive manufactured parts results from thermal cycles, temperature gradients, and localized plasticity.

The magnitude and distribution of the residual stress from additive manufacturing varies with the process details (e.g., process type, build rate, build sequence, amount of constraint, etc.). Titanium alloys can be thermally stress relieved after manufacture to produce a low residual stress state. Aluminum and nickel based alloys cannot be thermally stress relieved without negative effects on strength, and as a result these materials tend to have high residual stress in finished parts produced from additive manufacturing. Residual stresses can have various negative consequences during manufacturing, including cracking and part distortion (during build and during finish machining). Tensile residual stresses in finished parts can also reduce fatigue and corrosion performance.

To effectively understand and predict residual stress effects on performance, accurate and reliable residual stress measurements are required. In order to characterize and manage manufacturing induced residual stress states and their effects, specialized knowledge, testing methodology, and modeling expertise are essential. When these effects are well understood, minimized, and controlled, significant cost reduction can be derived from increased production rates, reduced manufacturing rework, and better product performance.

Hill Engineering has performed many residual stress measurements on additive manufactured parts and test specimens. The contour method is a very useful technique for evaluating residual stress in welding because it provides a 2D map of the residual stress distribution. Please contact us for more information about residual stress in additive manufacturing and other welding processes.

Results from a contour method measurement on a Ti-6Al-4V plate containing a partial groove electron beam weld deposit.