Types of AM Benchmark Tests

Types of AM Benchmark Tests

Three classes of benchmark test have been defined.  Class 1 and class 2 benchmark tests will likely be included in the first round/conference with class 3 benchmarks added in later years.

Class 1 benchmark test

Intent: Provide rigorous data for the development of quantitative simulation models for the entire AM process, from material feedstock to finished parts.  An extension to full life cycle modeling is provided by the class 3 benchmark tests.

Conduct rigorously defined and executed AM builds using fully characterized feedstock, open architecture machines with in situ process monitoring (as available), and ex situ characterization.  All specifications and characterization plans will be made public, allowing simulation modelers to model any aspect of the problem they like, with detailed knowledge about the starting material, what will be built, how it will be built, what will be measured, and how it will be measured.  Post processing (e.g. annealing, hot isostatic pressing, vapor smoothing, tumbling, machining) of the as-built specimens may also be included. To help coordinate efforts, some specific simulation modeling challenges will be specified. While modelers are attempting to predict the measurement results, the people/organizations that helped design each specific benchmark test (members of the Benchmark Test Committees) will carry out the specified builds and measurements.  If possible, builds using multiple machines with comparable processing characteristics will be used to explore machine-to-machine variability.  Modeling results will be submitted by some deadline before the conference and the measurement results will then be made public.  All results and comparisons will be discussed at the conference in dedicated sessions with discussion periods to discuss what worked, what didn’t work, and how to improve the predictions and measurements.

Example ideas:

• Metals and polymers: Use the laser-based, powder bed fusion method to build a 90° intersection of two vertical walls with different wall thicknesses, build orientations, and locations in the build envelope.  We should specify powder composition, powder size distribution, powder production and conditioning methods, layer spacing, laser power, laser wavelength, laser power distribution at sample position, laser scan speed, complete laser path, coater specifications (geometry, material and speed), ambient gas, humidity, starting temperature of relevant components (baseplate, walls, reservoirs, any IR heaters, build chamber), positions and types of thermocouples, intended part geometry, etc.  Process monitoring and ex situ characterization methods could include in situ thermography, spectroscopy, and co-axial and side-view high-speed imaging, along with ex situ electron microscopies, computed tomography, neutron and synchrotron X-ray diffraction residual stress, part geometry (still on build plate and after removal by EDM), compositional maps, phase maps, texture, grain sizes/shapes, instrumented indentation, etc.  Additional steps could include post-processing including annealing, hot isostatic pressing, sanding, washing and tumbling.
• Metals: Single laser trace on deep metal powder layer (or possibly two crossed laser traces).  Again, we need detailed specifications for all process/powder parameters.  In situ and ex situ measurements can characterize the size, shape, velocity and temperature distributions of ejected particles.  Ex situ 3D methods can be used to characterize the detailed 3D shape of the melt trace and microstructure characterization can provide compositional maps, texture, etc. 
• Polymers: Use the material extrusion method to build a 90° intersection of two vertical walls, with complete specification of materials, geometry, build conditions, in situ process monitoring and ex situ characterization, as described above.

Class 2 benchmark test

Intent: To accelerate development of innovative build strategies for difficult geometries such as overhangs, cantilevers, and other unsupported structures.

Define a specific challenging AM geometry to be built using a specified composition and any AM method.  This may include shapes with overhangs, cantilevers, etc. AM builders will attempt to produce the specified shape and will submit their entries to the benchmark test committee for measurement.  The benchmark test committee may set limits on the number of specimens that can be submitted.  Some of the build geometries may be coordinated with standard test structures under consideration by the joint ASTM F42 + ISO/TC 261 committees.  Although the initial emphasis will probably be just geometrical tolerance, later class 2 benchmark tests may include additional properties such as surface roughness, modulus, directional strength under different loading conditions, creep behavior, etc.

Example ideas:

• Specify geometry and composition of an unsupported bridge or cantilever.  The builder may use any AM methods they choose to build it. 

Class 3 benchmark test

Intent: Part qualification requires assurance that a manufactured part will perform within its design specifications.  The key factor in this benchmark test is functional performance. This may include both performance within a harsh environment (creep, fatigue, corrosion, stress corrosion cracking, impact resistance, etc.) and multifaceted performance metrics (high stiffness with low average density, combination of strength and thermal conductivity, etc.).

Define an overall specimen geometry, material class, and performance metric.  All test procedures used to characterize the submitted specimens will be described.  AM builders will attempt to produce an acceptable test part, usually related to some common functional requirement.  Completed parts will be submitted to the benchmark test committee for evaluation using the announced methods and criteria. 

Example ideas:

• Metals: Specify geometry, material class (say a steel with a minimum UTS), and degree of corrosion resistance.  The builder may use any starting material composition and AM method they choose to build it. 
• Metals and polymers: Specify composition, geometrical boundary conditions, and loads for a specific application.  Design and build a part that minimizes the weight of the part while achieving a minimum specified stiffness.