SLM

Question 1

What are alternative names for the SLM process?

Answer 1

LPBF (Laser Powder Bed Fusion) or PBF-LB/M (ASTM standard names).

DMLS (Direct Metal Laser Sintering)

Question 2

Name the four main components found inside an SLM Build Chamber.

Answer 2

Build cylinder (with base plate).

Feed cylinder (holding the powder).

Elevator systems.

Coating system (recoater blade/roller).

Question 3

What is the primary function of a Galvano Scanner in an SLM machine?

Answer 3

En Galvano scanner (eller galvanometer-scanner) är “styrmekanismen” för lasern i processer som SLM, SLS och SLA. Du kan tänka på den som maskinens sikte som bestämmer exakt var lasern ska träffa pulverbädden.

It uses two electromechanical actuators to rotate mirrors, which steer/deflect the laser beam in the X and Y directions

Question 4

Why is Gas Circulation necessary during the SLM process?

Answer 4

To provide an inert atmosphere (using Argon or Nitrogen) to keep oxygen levels low (typically <100 ppm).

To remove spatters and smoke to keep the laser window clean.§

Question 5

What are the common types of Porosity in SLM?

Answer 5

Lack of fusion: Large irregular pores from insufficient melting.
Gas pores: Spherical pores caused by trapped gas (e.g., Hydrogen).
Keyhole pores: Caused by excessive energy density

Question 6

What is “Balling” and how is it prevented?

Answer 6

Balling uppstår när den smälta metallen inte vill fästa i lagret under. Istället drar ytspänningen ihop metallen till små runda kulor (som liknar små pärlor på ett snöre).

Balling occurs when molten material fails to wet the underlying substrate, creating sphere-like beads.

Prevention: Avoid oxidation/contamination and ensure proper processing variables

Question 7

What causes Residual Stresses in SLM parts?

Answer 7

En termisk gradient är en “temperaturbacke”.

Large thermal gradients caused by rapid heating/melting and subsequent cooling/shrinkage of layers.

Question 8

List three ways to mitigate Residual Stresses.

Answer 8

Scanning strategies: Use “island” or “chessboard” scanning (smaller sections).
Preheating: Heating the substrate/base plate.
Post-processing: Stress-relieving heat treatments

Question 9

What are the four main Processing Parameters that define Energy Density (E_p)?

Answer 9

Laser Power ($P$).
Scanning Speed ($v$).
Hatch Spacing ($s$ or $h$) (line spacing).
Layer Thickness ($t$)

Question 10

Why is Spherical Powder preferred over irregular powder in SLM?

Answer 10

Spherical powder flows better and allows for a more uniform/smooth layer deposition. Irregular powder can get stuck.

Question 11

What are the microstructural advantages of Rapid Solidification in SLM?

Answer 11

Refined microstructure: Very small grain sizes.

Extension of solid solubility.

Increased chemical homogeneity (reduced segregation).

Question 12

What is the “rule of thumb” for Self-Supporting Angles in SLM?

Answer 12

Supports are generally required for overhang angles less than 45°.

Question 13

Where does the minimum surface roughness typically occur on an SLM part?

Answer 13

On the top surface (0° sloping angle). Down-facing surfaces are typically the roughest.

Question 14

What causes the “Stair-step effect” in AM?

Answer 14

The layer-by-layer nature of the process, which creates visible “steps” on sloped or curved surfaces

Question 15

Råmaterial SLM

Answer 15

SLM är den mest mångsidiga metoden och kan hantera ett brett spektrum av metaller i pulverform. Pulvret bör helst vara sfäriskt för att flyta jämnt i maskinen.
Vanligaste materialen:
Titanlegeringar: Särskilt $Ti$-$6Al$-$4V$, som är mycket tacksamt att printa med SLM.
Aluminiumlegeringar: Exempelvis $AlSi_{10}Mg$.
Rostfritt stål: Exempelvis 316L.
Kobolt-krom (CoCr): Används mycket inom dental- och medicinteknik.
Specialmaterial:
Verktygsstål: Såsom M2 HSS (snabbstål).Nickel-titan (NiTi): En formminneslegering.

Question 16

Consequence of excessive energy density in SLM

Answer 16

Keyhole porosity and material vaporization

Question 17

Rapid cooling in SLM affect microstructure of Ti-6Al-4V?

Answer 17

Du måste förstå varför man nästan alltid värmebehandlar Ti-6Al-4V efter SLM-processen:För att bryta ner den spröda martensiten ($\alpha’$) till den stabila och segare $\alpha + \beta$-strukturen.För att få bort de inre spänningarna så att delen inte spricker eller slår sig när man sågar loss den från byggplattan.Sammanfattning: Titan är “känsligt” för snabb kylning eftersom det ändrar sin atomstruktur helt (fasomvandling), medan andra metaller oftast bara får mindre kornstorlek.

Causes formation of a martensitic alfa phase, increasing hardness but reducing ductility