Joni Reijonen: Sources of Variability in Metal Additive Manufacturing

Sources of Variability in Metal Additive Manufacturing

By Joni Reijonen

Overview

I conducted my doctoral research in the field of metal additive manufacturing (3D printing). Compared to traditional metal manufacturing methods, 3D printing enables nearly unlimited geometric freedom, shorter lead times from design to production, and cost-effective, decentralized small-batch manufacturing.

Research Focus

However, the technology still faces challenges. In my doctoral thesis, I investigated the significant variability observed in the quality of additively manufactured metal components, particularly in their mechanical properties.

I focused especially on differences between powder bed fusion machines and on how fundamental parameters determined by machine architecture—such as shielding gas flow, powder spreading, and laser focal point—affect the quality of the final product and how these factors should be addressed in process qualification procedures.

Key Findings

I identified the underlying phenomena behind quality variation in the process and quantified their impact on the performance of the final product.

Understanding the root causes of variability and stabilizing the process to make it consistent and repeatable are essential steps for enabling metal additive manufacturing to fully deliver on its potential as a transformative technology for Finnish manufacturing—truly digital, decentralized, and customizable on-demand production.

The findings of my doctoral thesis, along with the practical guidelines derived from them, contribute to reducing quality variation in the field.

Impact

I am grateful for the incentive grant from the Walter Ahlström Foundation, which supported the completion of my doctoral thesis.

In addition to financial support, receiving the grant for three consecutive years provided significant encouragement. External recognition reinforced that my research was meaningful, progressing well, and worth supporting.

With this support, I was able to complete my doctoral thesis alongside other project work and earned my Doctor of Science degree at the University of Turku in January 2025.

Current Work

I now continue research and development in metal 3D printing as a Senior Research Scientist at VTT Technical Research Centre of Finland, where my doctoral research was also carried out.