Post-Processing & Quality Assurance Flashcards

What is the primary purpose of post-processing in additive manufacturing?

Answer: To improve part functionality, appearance, and dimensional accuracy

Parts produced directly from additive manufacturing often have rough surfaces, visible layer lines, and require removal of support structures. Post-processing encompasses various techniques like surface finishing, heat treatments, or machining to refine the part. These steps are crucial to improve its aesthetic appearance, achieve the required dimensional accuracy, and enhance its mechanical properties for optimal functionality in its intended application.

Which post-processing method is commonly used to improve surface finish on metal AM parts?

Answer: Sandblasting

Metal AM parts typically emerge from the printer with a rough surface finish due to the layer-by-layer deposition process and residual powder particles. Sandblasting, or abrasive blasting, is a common post-processing method that uses a high-pressure stream of abrasive media to remove loose powder and smooth out surface irregularities. This process improves the part's aesthetic appearance and can also enhance its fatigue life by reducing surface stress concentrators.

What is the purpose of Hot Isostatic Pressing (HIP) in metal AM post-processing?

Answer: To eliminate porosity and increase density

Hot Isostatic Pressing (HIP) is a post-processing technique that subjects metal AM parts to high temperature and uniform gas pressure. This process causes internal voids, micro-porosity, and un-melted powder pockets within the material to collapse and bond. By eliminating these defects, HIP significantly increases the part's density and improves its mechanical properties, such as fatigue strength, ductility, and overall structural integrity.

Which quality assurance technique uses X-rays to detect internal defects?

Answer: Computed Tomography (CT) scanning

Computed Tomography (CT) scanning is a non-destructive testing method that uses X-rays to generate detailed 3D images of an object's internal structure. This technique is invaluable for quality assurance in AM because it can detect internal defects such as porosity, cracks, or un-melted powder that are hidden from surface inspection. Identifying these internal flaws is critical as they can significantly impact the part's mechanical performance and reliability.

Why is support structure removal considered a critical post-processing step?

Answer: To prevent surface imperfections and stress concentrations

Support structures are essential for successful additive manufacturing builds, but their removal is a critical post-processing step. Improper or careless removal can leave behind rough surfaces, gouges, or remnants that act as stress concentrators, weakening the part and potentially leading to premature failure. Careful support removal ensures a smooth, aesthetically pleasing surface and maintains the part's structural integrity, which is vital for its intended performance.

What does a Coordinate Measuring Machine (CMM) typically measure?

Answer: Part dimensions and geometric tolerances

A Coordinate Measuring Machine (CMM) is a precision inspection device used to accurately measure the physical geometric characteristics of an object. It employs a probe to touch multiple points on a part's surface, precisely determining its dimensions, form, and geometric tolerances such as flatness, perpendicularity, or concentricity. This capability is essential for quality control in manufacturing, including additive manufacturing, to ensure parts meet design specifications.

Which post-processing method is used to relieve internal stresses in metal AM parts?

Answer: Stress relief annealing

Metal additive manufacturing processes involve rapid heating and cooling cycles, which can induce significant internal stresses within the printed part. Stress relief annealing is a heat treatment process designed to mitigate these stresses. By heating the part to a specific temperature below its critical point and then slowly cooling it, the material's microstructure can rearrange, reducing internal stresses and preventing distortion, cracking, or premature failure.

What is the purpose of dye penetrant inspection in QA?

Answer: To reveal surface cracks or porosity

Dye penetrant inspection (DPI) is a non-destructive testing method used to detect surface-breaking defects in non-porous materials. A liquid penetrant is applied to the surface, allowed to seep into any cracks or porosity, and then a developer draws the penetrant out, making these defects visible. This technique is crucial for identifying surface flaws that could compromise the integrity or performance of AM parts.

Which parameter is typically verified during mechanical testing of AM parts?

Answer: Tensile strength and elongation

Mechanical testing is fundamental for validating the structural integrity and performance of additive manufactured parts. Tensile strength measures the maximum stress a material can withstand before fracturing, while elongation quantifies its ductility or ability to stretch before breaking. These parameters are critical indicators of a part's mechanical properties, ensuring it meets the necessary strength and flexibility requirements for its intended application.