Technical_Specifications.docx

Technical Specifications Powder Rheometer National Institute of Standards and Technology

Background Information

The National Institute of Standards and Technology’s (NIST) Production Systems Group (PSG) conducts research regarding the effects of varying characteristics of metal powders used in Additive Manufacturing (AM). The study of the manner in which the powder particulates interact with one another and how the material flows as a whole (rheology) must be conducted to understand how the final AM part is affected. Currently, only crude powder characterization techniques are used (i.e. funnel flow tests, angle of repose).

A Powder Rheometer allows data to be collected on various processes that aim to characterize the powders mechanical behavior. Depending on the machine these tests include shear cell, permeability, aeration, consolidation, and dynamic flow tests. These test procedures provide insight as to how the powder will behave in various conditions. The goal is to imitate the spreading and pneumatic flow present in the Direct Metal Laser Sintering (DMLS) and Direct Metal Deposition (DMD) processes and to provide insight as to how the powder will behave in the processes.

Minimum Requirements

NIST requires one (1) powder rheometer that meets all of the following requirements:

1. Powder Rheometer

· Ability to characterize metal powders used in additive manufacturing with sizes in the range of 1 µm to 150 µm

2. Capable of Various Testing Methods. The following is a list of suitable test methods:

· Shear Cell Testing: a consolidated, conditioned powder is subjected to a shear stress along with a normal stress using an apparatus consisting of multiple blades held in a vertical orientation. The loads are applied until the powder yields. The relationship between the shear stress and the normal stress provide insight into how the powder will behave when confided and/or when subjected to sporadic flow.

· Wall Friction Testing: similar operation as Shear Cell Testing, but instead of using a Shear Cell head with multiple blades, an insert of a specified material allows the interaction between various materials and the powder to be characterized.

· Dynamic Testing: a twin-blade impeller is rotated while moving axially through powder. The torque and normal load are recorded.

· Permeability Testing: the pressure drop across the sample is measured while a constant volumetric air flow is maintained and a normal force is applied.

3. Measurement Specifications:

· Torque resolution of 2E-6 Nm or better

· Maximum torque: +/- 900mNm

· Normal force resolution of 1E-4 N or better

· Maximum normal force: +/- 50N

· Vertical range of motion of 200mm with +/-.1% accuracy

· Ability to measure particulates with sizes from 1 µm to 150 µm

· Ability to test specimens as small as 1ml

· Maximum axial speed of 30mm/sec

4. Aeration Unit Specifications

· The powder rheometer must have an aeration control unit capable of controlling the volumetric flow rate of air

· Accuracy of .1% or better

· Repeatability of .05% or better

· Output range of 2-5000 ml/min