Abstract:
Interest in Additive Manufacturing (AM) has grown considerably in the past decades and
industry has gained great benefits from this type of technology. The main advantages are:
geometrical freedom that allows the design of parts with complex shape, which are difficult
or impossible to produce by conventional technology; shortened design-to-product time;
customization and the possibility to use several materials in one process. Direct Metal Laser
Sintering (DMLS) is one of the most promising AM technologies that utilizes metal powders.
Due to the layer-by-layer nature of powder delivery used in DMLS, the drawbacks are:
surface quality and accuracy, high residual stress in as-built parts and porosity – all of which
depend on the powder material, process-parameters, scanning and building strategies. This
can result in a substantial deterioration of the mechanical properties of the products and their
performance characteristics. For this reason, it is very important to identify defective parts
before enrolling into service.
Non-destructive testing (NDT) is effective for detection of internal defects without causing
damage. NDT also covers a wide group of methods of analysis used to evaluate the properties
of a material. NDT techniques like visual, acoustic, ultrasonic, thermal, X-ray and 3Dcomputed
tomography (CT) inspections are now widely used for various industrial
applications. For the analysis of material properties and the detection of defects, each of these
methods uses different physical principles that have their advantages and disadvantages. In this study, some of the NDT techniques are evaluated in terms of their applicability to the
inspection of parts manufactured by DMLS technology: Visual, Ultrasonic, Computed
Tomography and Acoustic Emission inspection.
Artificial defects were used to determine the feasibility of each NDT method. DMLS samples
were produced containing a range of artificial defects. These samples were than subjected to
each method and the results compared. A comparison between the amount of defect
information obtained is made.
It was shown that the nature of the sample; shape, size, material and the type of defects
present plays a vital role in the selection of testing methods. Ultrasonic-Total Focus Method
indicated that some defects are present upon testing relatively big samples with simple
geometry. X-ray Computed Tomography showed some limitations with regard to the
possibilities and the amount of defect detail, the only drawback being the cost and time
involved. Acoustic Emission showed to be a promising method for production parts although
it requires an initial time investment; thereafter it is a simple and easy way of detecting
defective samples.
