AS ISO/ASTM 52911.2:2021 pdf free.Additive manufacturing一Design Part 2: Laser-based powder bed fusion of polymers.
5 Characteristics of powder bed fusion (PBF) processes
5.1 General
Consideration shall be given to the specific characteristics ol the manufacturing process used in oraer to optimize the design of a part. Examples of the features of AM processes which need to be taken into consideration during the design and process planning stages are listed in 52 to 5.
5.2 Size of the parts
The size of the parts is limited by the working area/working volume of the PBF-machine. Also, the occurrence of cracks and deformation due to residual stresses limits the maximum part size. Another important practical factor that limits the maximum part size is the cost of production having a direct relation to the size and volume of the part. Cost of production can be minimized by choosing part location and build orientation in a way that allows nesting of as many parts as possible. Also, the cost of powder needed to fill the bed to the required volume (part depth x bed area) may be a consideration. Powder reuse rules impact this cost significantly. If no reuse is allowed, then all powder is scrapped regardless of solidified volume.
5.3 Benefits to be considered in regard to the PBF process
PBF processes can be advantageous for manufacturing parts where the following points are relevant:
— Parts can be manufactured to near-net shape (i.e. close to the finished shape and size), without further post processing tools, in a single process step.
— Degrees of design freedom for parts are typically high. Limitations of conventional manufacturing
processes do not usually exist, e.g. for:
— tool accessibility, and
— undercuts.
— A wide range of complex geometries can be produced, such as:
— free-form geometries, e.g. organic structures[171,
— topologically optimized structures,
— infill structures, e.g. honeycomb, sandwich and mesh structures.
— The degree of part complexity is largely unrelated to production costs.
— Assembly and joining processes can be reduced through single-body construction.
— Overall part characteristics can be selectively configured by adjusting process parameters locally.
— Reduction in lead times until part production.
5.4 Limitations to be considered in regard to the PBF process
Certain disadvantages typically associated with AM processes shall be taken into consideration during product design.
— Shrinkage, residual stress and deformation can occur due to local temperature differences.
— The surface quality of AM parts is typically influenced by the layer-wise build-up technique (stairstep effect). Post-processing can be required, depending on the application.
— Consideration shall be given to deviations from form, dimensional and positional tolerances of parts. A machining allowance shall therefore be provided for post-production finishing. Specified geometric tolerances can be achieved by precision post-processing.
— Anisotropic characteristics typically arise due to the layer-wise build-up and shall be taken into account during process planning.
— Not all materials available for conventional processes are currently suitable for PBF processes.
— Material properties can differ from expected values known from other technologies like injection moulding and casting. Material properties can be influenced significantly by process settings and control.
5.5 Economic and time efficiency
Provided that the geometry permits a part to be placed in the build space in such a way that it can be manufactured as cost-effectively as possible, various different criteria for optimization are available depending on the number of units planned.
— In the case of a one-off production, height is the factor that has the greatest impact on build costs. Parts shall be oriented in such a way that the build height is kept to a minimum, provided that the geometry permits such an orientation.
— If the intention is to manufacture a larger number of units, then the build space shall be used as efficiently as possible. Provided that the part geometry permits such orientation, strategies for reorientation and nesting shall be utilized to maximize the available build space.AS ISO/ASTM 52911.2 pdf download.