SLS Metal Powder: Properties,Applications,and Suppliers

Selective laser sintering (SLS) is an additive manufacturing technique that uses a laser to fuse small particles of plastic, metal, ceramic or glass powders into a 3D object. SLS metal powders with the right characteristics are critical to fabricating high-quality metal parts with complex geometries via this process.

Overview of SLS Metal Powders

SLS metal powders refer to metallic powders that are optimized for use in selective laser sintering 3D printers to produce metal parts and prototypes. The most commonly used SLS metal powders include:

SLS Metal Powder Types

Type	Composition	Key Characteristics
Stainless steel	Fe, Cr, Ni alloys	Corrosion resistance, high strength
Tool steel	Fe, Cr, Mo alloys	High hardness, heat treatable
Alloy steel	Fe, Cr, Ni alloys	Heat treatable, machinable
Cobalt-chrome	Co, Cr alloys	Biocompatible, wear/corrosion resistant
Titanium & alloys	Ti, Al, V alloys	Lightweight, biocompatible, strong
Inconel	Ni, Cr alloys	Heat/corrosion resistant
Aluminum alloys	Al, Cu, Mg alloys	Lightweight, strong

These metal powders must have properties like flowability, particle shape and size distribution tailored to produce high density SLS parts with accuracy, precision and desired mechanical properties.

Key Properties of SLS Metal Powders

Parameter	Description	Requirements
Size range	Powder particle dimensions	10-45 microns common
Size distribution	Range of powder sizes	Mostly spherical with some satellites allowed
Morphology	Powder particle shape	Spherical is optimal, satellites can cause defects
Flow rate	Powder flowability	35-40 s/50g from Hall flowmeter
Apparent density	Powder packing density	Around 60% of true density
True density	Material density	Varies by composition
Surface area	Particle surface area per unit mass	Lower is better to reduce oxidation
Residual gases & moisture	Impurities present with powder	Minimized for high quality parts

SLS Metal Powder Characteristics

Characteristic	Role in SLS Process
Particle shape and surface texture	Affect powder flow into each new layer, laser absorption, reflectivity
Particle size distribution	Impacts packing density, melt pool dynamics, spreadability
Flow characteristics	Allows uniform spreadability, layer consistency
Apparent density	Controls spacing between particles, energy input needed
True density	Determines final maximum attainable part density
Alloying additions	Enables specific material properties like strength, hardness etc.

Applications of SLS Metal Powders

SLS metal powder enables printing of full density functional metal parts serving prototyping, tooling and short run production needs across industries like:

Industry Applications of SLS Printed Metal Parts

Industry	Applications	Common Materials Used
Aerospace	Turbine blades, engine/structural components	Stainless steels, superalloys, titanium alloys
Automotive	Prototype parts, custom tooling	Stainless steels, tool steels, aluminum alloys
Medical implants	Patient-specific implants, guides	Cobalt chrome, titanium alloys, stainless steel
Industrial	Precision tooling, robot grippers	Stainless steels, tool steels
Jewelry	Rings, chains, custom pieces	Precious metals like gold alloys, silver

Some unique benefits versus traditional manufacturing routes:

Advantages of SLS for Metal Part Production

Benefit	Description
Geometry freedom	No part geometry restrictions unlike subtractive/casting methods
Quick turnaround	Rapid printing from CAD data
Light weighting	Lattice structures reduce weight by >30%
Part consolidation	Integrally printed assemblies replace joints
Mass customization	Patient-specific medical devices
Hybrid structures	Metal & polymer multi-material parts possible

Common SLS printed metal part applications across industries:

Typical Applications of SLS Printed Metal Parts

Application	Examples	Materials Used
Functional prototypes	Engine components, implants	Alloy steels, Ti alloys
Tools	Drill guides, fixtures, jigs	Stainless steels
Mold tooling	Injection molding tooling	Tool steels like H13
Series production	Aerospace/medical components	Ti & Ni alloys, CoCr
Lightweight structures	Lattice panels, braces	Al alloys, Ti alloys

SLS Metal Powder Specifications

SLS system manufacturers like EOS, 3D Systems, and Renishaw provide qualified SLS metal powder specifications tailored for their printer models. Some common metal powders and sizes include:

SLS Metal Powder Types and Size Ranges

Material	Powder Types Available	Particle Size Range
Stainless steel	316L, 17-4PH, 303, 410	15-45 microns
Maraging steel	MS1, 18Ni300, 18Ni350	15-45 microns
Cobalt chrome	CoCr, CoCrMo	15-45 microns
Aluminum alloy	AlSi10Mg, AlSi12	15-45 microns
Titanium alloy	Ti6Al4V Grade 5	15-45 microns
Nickel alloy	Inconel 718, Inconel 625	15-45 microns

Standards organizations have defined classifications for different metal powder grades used in AM processes:

Metal Powder Grades per ISO/ASTM Standards

Standard	Grades	Description
ISO 17296-2	PA1 to PA6	Defines increasingly stricter requirements on impurities from P1 to P6
ISO 17296-3	PM1 to PM4	Defines particle shape, size parameters from PM1 to PM4
ASTM F3049	Class 1 to Class 4	Defines allowable limits on composition ranges from 1 to 4
ASTM F3056	Type 1 to Type 3	Defines statistical size distribution parameters from 1 to 3

These grading schemes help set benchmark quality levels and aid buyers in procurement. High purity PA5 grade powder would ensure minimal contamination. Similarly Class 4 tighter chemistry control reduces variability.

SLS Metal Powder Suppliers

A variety of vendors supply ready-to-use SLS powders worldwide. Some leading global suppliers are:

Key SLS Metal Powder Suppliers

Supplier	Materials Offered	Geographies Served
Sandvik	Stainless steel, Ni alloys, CoCr, tool steel, aluminum alloys	Europe, Asia
Praxair	Ti alloys, Ni alloys, stainless, tool steels	North America
LPW Technology	Stainless steel, aluminum alloys, CoCr	UK, Europe
Carpenter Additive	Stainless steels, CoCr, Cu, aluminum alloys	Global
Hoganas	Stainless steels, tool steels	Europe, Asia

Usual supply minimums are around 10 kg per material grade, though large volume contracts also exist for OEM buyers. Packaging options range from vacuum sealed cans to specialized SLS machine cartridges holding 700 g to 1 kg powder each.

SLS Metal Powder Packaging Types

Type	Volume Ranges	Characteristics
Vacuum cans	500g to 20kg batches	Shelf life up to 1 year
Printer cartridges	700 to 1000g batches	Minimized handling exposure
Material towers	700 to 1200g cartridges	Automated feed into printer

Price ranges for common materials in small quantities are:

Metal Powder Cost Ranges for SLS Printing

Material	Small Quantity Price Range*
Stainless steel 316L	$60-$100 per kg
Aluminum AlSi10Mg	$80-$130 per kg
Maraging steel	$90-$140 per kg
Titanium Ti6Al4V	$200-$350 per kg
Cobalt chrome	$300-$500 per kg
Precious metals	$3000+ per kg

Comparing SLS Metal Powder Materials

Various metal alloys are used for SLS printing, each with their own properties and tradeoffs:

SLS Metal Powder Materials Comparison

Parameter	Stainless Steels	Tool Steels	Titanium Alloys	Nickel Alloys	Cobalt Chrome	Aluminum Alloys
Density	Medium	Higher	Lower	High	High	Lowest
Strength	Medium	Highest	Medium-High	Medium-High	Medium	Medium
Hardness	Lower	Very high	Medium	Medium	Higher	Low-Medium
Corrosion Resistance	Excellent	Medium	Excellent	Excellent	Excellent	Medium-Good
Bio-compatibility	Good	Limited	Excellent	Limited	Excellent	Good
Heat Resistance	Medium	Medium-High	Medium	Very High	Very High	Lower
Cost	Lowest	Medium	High	Very High	High	Low

We can see stainless steels offer the best combinational properties when cost is a consideration, while tool steels provide extreme hardness. Titanium brings biocompatibility and strength with low density. Superalloys like Inconel and CoCr offer thermal stability and biocompatibility. Aluminum alloys are the most cost-effective lightweight option.

Pros and Cons of Common SLS Metal Powders

Material	Advantages	Disadvantages
Stainless steels	Cost-effective, readily machinable	Lower hardness and strength
Tool steels	Extremely hard and heat treatable	Less corrosion resistance, biocompatibility
Titanium alloys	Strong, lightweight, bio-friendly	Expensive, can burn in oxygen atmosphere
Nickel alloys	Excellent heat/corrosion resistance	Heavy, toxic, very expensive
Cobalt chrome	Biocompatible, corrosion resistant	Heavy, medium cost
Aluminum alloys	Lightweight, good strength	Lower melting point, hardness

Customer Criteria for Selecting SLS Metal Powder

Selection Criteria	Key Questions
Mechanical properties	Does it meet target application strength, wear resistance and other mechanical specifications?
Material cost	Does desired metal powder type fit application budgets?
Post-processing	Are secondary operations like Hot Isostatic Pressing or heat treatment needed?
Production run size	Is target volume too high for production SLS printing?
Part size dimensions	Is maximum printer build volume sufficient for largest part geometries?
Resolution, surface finish	Can SLS process achieve fine-feature-detail and surface quality requirements?
Delivery lead time	Is supplier lead time acceptable considering production timeline?

The end part application guides optimal material selection balancing performance needs and economics.

SLS Metal Printing Process Overview

Understanding SLS 3D printing helps appreciate how powder properties affect part quality:

SLS 3D Printing Process Stages

Stage	Description
3D Modeling	CAD software creates solid/mesh model of part to print
Slicing	Model is digitally sliced into layers to generate printer file
Powder spreading	Roller or blade spreads thin layer of powder on build platform
Laser scanning	CO2 laser scans over powder bed to melt particles together
Lowering platform	Build platform lowers by 1 layer thickness (~50 microns)
Repeat spreading/melting	Steps repeat until full object is built up layer-by-layer
Post-processing	Excess powder removed, final treatments done to finish part

How Powder Characteristics Impact Print Results

Powder Property	Influence on Print Quality
Powder geometry	Spherical particles with good flow enable uniform layers without defects
Particle size range	Too fine powders have poor flow, too large creates poor resolution
Size distribution	Too wide a distribution can segregate or create variable melting
Apparent density	Higher density yields greater final part density after sintering
True density	Places upper limit on achievable part density
Surface texture	Rougher particles can trap gases or hamper powder flow

We can see several powder physical properties directly impact print results, so tight control by suppliers is crucial.

Post-Processing of SLS Printed Metal Parts

After the SLS printing process, additional finishing steps help improve final part properties:

Common SLS Part Post-Processing Steps

Process	Description	Benefits
Powder removal	Excess powder brushed/blasted off	Reveals printed object
Stress relieving	Heating to remove residual stresses	Improves dimensional accuracy
Surface finishing	Sanding, polishing, bead blasting	Smoothens surface, aids coating adhesion
Infiltration	Liquid fills residual porosity	Further increases density, improves strength
Heat treatment	Hardening and tempering thermal cycles	Enhances hardness in steels

Post-Processing Effects on Part Properties

Property	Post-Processing Influence
Density	Infiltration with epoxy or bronze fills pores increasing density 5-15%
Surface roughness	Manual/automated polishing can achieve under 2 micron roughness
Dimensional accuracy	Stress relieving heat cycle reduces warpage improving precision
Tensile strength	Infiltration improves UTS while heat treatment can double yields strength
Ductility	Tradeoff with strength improvement from post-treatments
Hardness	Precipitation hardenable alloys like 17-4PH respond well to aging treatments

Thus post-processing allows tailoring metal properties further based on application needs.

SLS Metal Printing Quality Control

Consistent high quality powder feedstock coupled with SLS process monitoring ensures reliable parts:

Quality Control for SLS Metal Powder

Parameter	Typical Specification	Test Methods
Particle size distribution	Hall flow rate > 35s/50g	Sieving, laser diffraction
Apparent density	65-80% of true density	Gravimetric measurement
Powder composition	Alloying ranges per ISO 27296	X-Ray fluorescence
Surface morphology	Median circularity > 0.75	Micrographs, image analysis
Contamination	< 50 ppm oxygen, < 150 ppm nitrogen	Inert gas fusion analysis

In-Process Monitoring for SLS Printing

Metric	Sensor Used	Purpose
Laser power	Built-in photodiode	Maintains fusion consistency
Powder bed temp	IR sensor	Ensures part integrity, no warping
Atmosphere	Oxygen analyzer	Avoids powder ignition in build chamber
Layer thickness	Z-axis encoder	Precise reproducible layers

Such stringent control over input powder and process settings results in high quality metal parts from each production run.

SLS Metal Printing Compared to Alternatives

Other metal 3D printing alternatives to SLS include:

Comparison of Metal 3D Printing Methods

Metric	Binder Jetting	DMLS	SLM	EBM
Raw material	Metal/polymer mix powder	Metal powder	Metal powder	Metal wire/powder
Energy source	Liquid binder	Fiber laser	Powerful Yb fiber laser	Electron beam
Build speed	Moderate, faster than laser methods	Slow due to point-by-point scanning	Very fast, full melting occurs	Fastest method
Resolution, surface finish	Poorer due to binder, post-processing helps	Very good due to fine laser spot	Excellent due to full melting	Moderate due to partial melting
Dimensional accuracy	+/- 0.3% with CTQ process	+/- 0.1-0.2%	+/- 0.1-0.2%	+/- 0.2-0.3%
Post-processing	Curing, sintering both needed	Only support removal	Some machining may be needed	Most secondary work needed
Cost per part	Lower material cost helps reduce price	Much higher operating cost	High equipment, material cost	High equipment cost

Among all methods, binder jetting has emerged as most cost-effective for metal part production at lower volumes up to 10,000 units. SLS provides the easiest post-processing combined with good accuracy and surface finish.

FAQs

What industries use SLS metal printing?

SLS metal printing is used in aerospace, automotive, medical, and many other industries where precision metal parts are required.

What is the accuracy and resolution of SLS metal printing?

The accuracy and resolution depend on several factors, including the machine, material, and process parameters, but SLS metal printing can achieve high levels of precision.

Is post-processing required for SLS metal-printed parts?

Yes, post-processing may be required to remove support structures, improve surface finish, and meet specific requirements for the application.

What are the limitations of SLS metal printing?

Some limitations include the cost of equipment, limited size of build chambers, and the need for proper safety measures due to the use of lasers and metal powders.

Can SLS metal printing be used for mass production?

Yes, SLS metal printing can be used for both prototyping and low to medium-volume production of metal parts.

Is SLS metal printing environmentally friendly?

While it can reduce material waste compared to traditional manufacturing methods, the disposal of metal powders and energy consumption are factors to consider regarding its environmental impact.

Are there any safety precautions when working with SLS metal printing?

Yes, safety measures should be taken when handling metal powders, and operators should be trained to work with laser-based systems safely.

What is the cost of SLS metal printing services?

The cost varies depending on factors such as material choice, part complexity, and quantity. It’s best to request quotes from service providers for specific projects.

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