Feeling the heat
The ability to produce complex geometries and internal features has led many to believe that additive manufacturing will change the nature of advanced manufacturing. But as the industry moves from solely prototype manufacturing to production of ready-to-use parts, quite a few challenges need to be addressed.
Additive manufacturing (AM) dates back to the 1980s when the first computer graphics software came on the market and made it possible to create 3D models on the computer. Scientists and inventors found a way to convert the models into reality, and 3D printing was born. The solution has remained the same for almost 40 years: An object is built up layer by layer, using a molten material.
For many years, 3D printing was mainly a rapid way to produce polymer prototypes. Over the past two decades, however, several metal-based additive manufacturing processes have been developed and become widely available for larger-volume component production.
Additive manufacturing offers many unique advantages, such as unrivaled design freedom, short lead times from design to finished part and the possibility to minimize material waste. Components that would not have even been possible a few years ago can now be made to high standards using a wide range of metal powders.
Increased demand for quality
However, the move into producing ready-to-use metal parts presents new challenges for the additive manufacturing industry, says Todd Palmer, a professor of engineering science and mechanics and materials science and engineering at Pennsylvania State University in the United States.
“Moving from prototyping to production increases the demand for quality and the requirements on parts production by orders of magnitude,” Palmer says. “It’s a challenge to do something in the same way time and again. With the AM process and the complexity of the layer-by-layer build methodology, the processing windows will become much smaller than those used in more traditional wrought processes. These smaller windows and more rapid thermal cycling conditions will create significant issues for quality, especially as volumes of products continue to increase.”
To obtain the same part quality as in traditional, subtractive manufacturing processes, post-process heat treatment is necessary, regardless of the additive manufacturing method.
“The need for heat treatment is primarily materials-related, and the alloys used in metal AM require some type of post-process heat treatment,” Palmer says. “If not used, there is no way for the material to achieve the desired microstructure and properties.”
Repeatability possible with heat treatment
“In terms of quality, the role of heat treatment can be tied to repeatability of the process and lower scatter in data,” Palmer says. “Tight property ranges are attractive to designers, since their level of certainty is increased, and safety factors needed for material properties can be reduced with greater confidence.”
Repeatability of high-quality parts is essential if AM is ever going to be used to produce larger-volume and larger-sized components, he says. “AM was initially developed as a prototyping tool and for low-volume and customized parts. Mass production is still somewhat new. It will be a challenge to maintain a high quality level.”
Palmer says a good deal of work is being dedicated to process sensing and monitoring and the development of tools to attempt to detect defects that form in the builds. However, for AM to see more widespread use, he says more attention has to be put on material research.
“The materials should be more in the forefront than what they are,” he says. “Today we are using the same alloys for AM as for wrought processes. The problem is that we melt these alloys with lasers and expect them to behave in the same way. They don’t. In the additive process you simultaneously produce the material and the component. This creates a more symbiotic relationship between the design, processing, structure and resultant material properties than in more traditional wrought systems.”
Palmer says the way forward is to establish integrated design approaches that enable designers to consider both materials and processing parameters as variables that can be adjusted for optimum component design.