SAMPE Journal - November/December 2019 - 16

FEATURE / ADDITIVE MANUFACTURED TOOLSET PARTS

Figure 1. AM parts may exhibit printing local defects.

process models can be validated for use in defining
process parameters for target part thermal
response, and thus, the ICME tool can be utilized to
determine the defects in the microstructure from
the monitored variables. Continuum-based models
for heat diffusion and residual stress formation will
be used and complemented with ICME approaches
in order to determine defects in printed parts. In
addition, powder bed thermal conductivity will be
tailored to ensure specific heat flux directionality
and support reaction forces throughout the AM
process in order to enable the fabrication of
complex (contorted, twisted, distorted) structures
with no defects.
Problem: AM parts may exhibit printing local
defects such as balling, keyhole, humping, unfused
powder, and delamination (Figure 1), which
are related to thermal processes, i.e. Heating,
Melting, Melt-Superheated, Superheat-Cooling,
Solidification, and Cooling. The resulting micro
defects, which take the form of intergranular
cracks, surface cracks "dendrite', surface roughness,

micro/macro voids, distortion, warpage, wrinkles,
shrinkage and residual stress have a profound effect
on part qualification and performance. In the case
of surface roughness, post heat treatment and/
or surface removal may be used as a remedy, but
such a solution may cause additional grain growth,
loss of material plasticity, more intergranular
cracks, and sometimes collapse of specimen.
Fortunately, ICME tools and methodologies are
available to utilize material data, machine data and
thermal history to identify optimal build solutions
that minimize and/or eliminate manufacturing
anomalies. However, these solutions tend to be
machine specific and require the duplication of the
ICME methodology on each and every platform for
each and every part.
Problems with qualification of AM trial and
error part fabrication may be addressed by
in-situ monitoring, big data processing, data
discovery, and ICME calculations. The key steps
in qualification of AM parts are 1) optimization of
the machine parameters (i.e., laser power, speed,

Table 1. AM machines primary printing parameters.

16

|

Item

Parameter

Description

Controlled or Predefined

1

Average Power, P

Total Energy Output of Laser

Controlled

2

Scan Velocity, v

Velocity of laser across surface

Controlled

3

Scan Spacing, Ss

Distance between neighboring
passes

Controlled

4

Scan Strategy

Pattern of laser scanning
(spirals, zig zag)

Controlled

5

Deposition System Parameters

Recoater vel, pressure, recoater
type, closing

Controlled

6

Layer Thickness, L

Height of single powder layer

Controlled

7

Powder Bed Temperature, Tp

Build temperature of powder bed
Controlled

Controlled

8

Oxygen Level, %O2

Likely most important environment
parameter

Controlled

9

Gas Flow Velocity, vg

Influences convective cooling

Controlled

10

Ambient Temperatures, Tinf

Affecting cooling, reheat, and
residual stress

Controlled

SAMPE JOURNAL

|

N OV E M B E R / D E C E M B E R 2 0 1 9

w w w. s a m p e . o r g
http://www.sampe.org
SAMPE Journal - November/December 2019

Table of Contents for the Digital Edition of SAMPE Journal - November/December 2019
