Wilo SE is a worldwide manufacturer of pumps and pump systems for building services, the entire water management chain and industry. They have a long history of successful innovations based on their strong knowledge foundation and sense for future technology and market requirements. This requires a strong focus on R&D as well as the best equipment to get the job done.
It comes as no surprise that Wilo is working with cutting-edge technologies such as Additive Manufacturing, also called 3D printing, to develop the products of tomorrow. In one project, they use Selective Laser Sintering (SLS), which is known to produce high- quality structural polymer parts with complex geometries, internal structures and thin walls. Tool-less production without loss of material, the shortening of development processes as well as mechanical properties comparable to injection molded parts make SLS a suitable alternative for many workpieces and even whole assemblies. What is more, some hollow geometries are actually only feasible with a powder-based additive manufacturing process.
The SLS process uses a laser to locally melt small particles of polymer powder to form a homogeneous layer and this is repeated layer by layer until the whole part is melted. The surrounding build chamber is keeping the material at elevated temperatures to hinder crystallization until the whole part is finished. Only then is the part cooled down. Thus, the precise melting and crystallization behavior of the polymer powder needs to be known to define the process settings for a given material.
In order to develop new materials that possess all the required properties for a new product, this thermal behavior needs to be understood.
The NETZSCH DSC 214 Polyma provided the solution
All the new material choices with and without fiber reinforcement were characterized using a NETZSCH DSC 214 Polyma by performing dynamic measurements from room temperature to 70 K above melt temperature using a heating and cooling rate of 20 K/min. The resulting graph and the process window are depicted in Figure 1. The hysteresis between the onset of melting and the onset of crystallization is smaller than for the typically used PA12. This means the process window is only about 20 K compared to about 30 K for PA12.
Figure 2 shows the effect of glass and carbon fibers on the onset of crystallization. Both fibers (blue: CF, green: GF) act as nucleating sites and shift the start of crystallization to higher temperatures making the process window even narrower. This is important to identify the most suitable build temperature and requires lots of expertise in optimizing the process. For temperatures close to the onset of melting, the surrounding solid powders starts to sinter onto the hot, molten part. This effect is called lateral growth. For temperatures close to the onset of crystallization, warpage can be a problem. This is often called curling. One explanation for the difference in crystallization onset between glass and carbon fibers could be the surface-to-volume ratio of the two different fibers. Given that the diameter of carbon fibers is in the range of 7 µm and of the used glass fiber at about 11 µm, the carbon fibers provide slightly more surface area to act as nucleating sites for the same volume content in the mixture.
If the hysteresis between melting temperature and crystallization temperature of a material of interest is very small, isothermal crystallization studies can be performed to analyze the crystallization rate in more detail or compare different mixtures with otherwise similar properties to select the best one.
“The DSC 214 Polyma is easy to use and provided us with all the relevant data to successfully produce parts using the new powders. Together with the knowledge we gained in discussions with NETZSCH’s application specialists, we were able to select the most suitable materials for continuing our development work.”Dennis Glinski, Project Engineer, Wilo SE
Are you keen to learn more about the characterization of SLS powders?
In previous articles, we covered the following topics:
- How does Selective Laser Sintering (SLS) work?
- How to Determine the Process Window for SLS Powders Using DSC
- How to Study the Isothermal Crystallization Behavior of SLS Powder Using DSC
About Wilo Group
The Wilo Group is one of the world’s leading premium providers of pumps and pump systems for the building services, water management and industrial sectors. The company’s innovative solutions, smart products and individual services move water in an intelligent, efficient and climate-friendly manner. It is also making an important contribution to climate protection with a sustainability strategy and in conjunction with partners (Source).