[Complete Guide] Selective Laser Melting – SLM 3D Printing

In this guide, we break down the selective laser melting 3D printing method to help you understand it better even if you’re not too technical.

What Is Selective Laser Metling?

Selective laser melting (SLM) is one of the powder bed fusion additive manufacturing technology for metal. Its other name is direct metal laser sintering (DMLS), and they are often mentioned interchangeably.

However, SLM melts a single metal while DMLS fuses/sinter metal alloys. On a molecular level, the laser melts the powder together layer by layer until the model is complete.

SLM technology is very useful for rapid prototyping and mass production for complex metal parts.

Pros:

• Wide selection of metal alloy applications
• Fast prototyping by reducing lead time than traditional subtractive manufacturing methods
• Print multiple parts at the same time if printer volume allows
• Build very complex metal parts with integrated structures that’s impossible to build before
• Reuseable metal powder, less waste

Cons:

• Expensive
• Can’t build super tiny parts that have high complexity
• High learning curve
• Tons of post processing required
• Rough surface finish

Material Selections

The most common SLM materials are pure materials such as

• Titanium – Corrosion resistance, low thermal expansion, great strength to weight ratio
• Nickel based alloys – Excellent mechanical properties
• Aluminum – Low density, good electrical conductivity
• Stainless steel – Great hardnes and ductility, high wear resistance
• Tool steel –
• Cobalt chrome – Excellent wear, corrison & temperature resistance
• Tungsten
• Copper

SLM 3D Printer Core Components

Most powder bed fusion machines are SLM printers, and most metal additive manufacturing companies use SLM.

A basic SLM printer consists of the following:

• Laser
• Laser beam
• Laser lenes
• Metal powder supply bay
• Build platform
• Recoater arm

The build volume is based on the size of the printer, just like a regular paper printer. The larger object needs a larger printer that fits the print.

Basic SLS 3D Printing Process

3D Model Design

A talented 3D drafter will CAD the model, process it, and make sure it’s in STL or OBJ files that are compatible for the 3D printer to print.

The dimensional accuracy of a 3D part design can be as close as +/- 0.1 mm.

Print

1. Metal powder is spread across the build plate in very thin layers by the coater blade
2. High power laser fuses a 2D slice of the part by melting the powder material via the 3D printer’s topology optimization algorithms
3. Build plat drops down to the next height of layer and repeats the process and spread another layer of powder material
4. While the entire process is going, the printing chamber is atmosphere controlled to a specific temperature

Support Material

Minimizing support structures greatly reduce the cost of metal printing

For parts that overhang, the support material is required. For the most part, support structures are always needed for metal printing

• Support anchor the part to prevent warping as its being build
• Draws heat away from the part at a controlled cooling rate
• Support the next layer to be built upon

Most SLM parts have some isotropic mechanical and thermal properties, so are hardened with very little porosity, which means there is less hollow (empty void) inside the part.

Unlike the SLS process, large hollow sections are not commonly used because they are difficult to remove later.

Skin and cores are very useful when manufacturing parts with large solid sections, as they significantly reduce the print time and the likelihood of warping.

The lattice structure is common way metal parts are printed in order to reduce weight and the topology optimization algorithms can help aid the design of organic light-weight form.

Post Process

Once the part is complete, all parts requires the following steps:

1. Remove part from the powder bed
2. Cut away from the build plate
3. Trim off support

When To Use SLM Method To Print 3D Metal Parts?

Use SLS 3D printing method for:

• Fast prototyping
• Build complex metal part that’s literally impossible with traditional methods
• Complex patient specific implants
• High value medical device components
• Aerospace ducts
• Turbine chambers
• Tooling