Laser Sintering (SLS) of plastic parts

Highlights

Laser Sintering is the second most commonly used process after Stereolithography. Whilst accuracy and surface finish are not as good, the real benefit is the functionality that can be achieved. Working with nylon, (or a filled nylon) parts demonstrate a level of toughness that even permits on board usage in today's Formula 1 cars. This functionality is also behind the success that Laser Sintering has achieved in Rapid Manufacturing.

There are two machine manufacturers serving this market, EOS and 3D Systems, both with standard and large format machines. Most materials originate from one manufacturer or the other, although third party materials are starting to make inroads.

Whilst the process is faster than Stereolithography, there is a requirement for an appreciable cooldown period post build. This is due to the process operating close to 180 degrees Centigrade, and it is vitally important that parts are allowed to cool naturally. Trying to improve delivery times by short cutting the cooldown process inevitably results in component distortion.

Smartprototype regularly accesses a full range of materials and process platforms, offering the latest technology, the largest platforms and the highest levels of resolution.

Whilst deliveries are always tailored to customer requirements, a typical turnaround would be 5 - 7 days, small projects can be faster.

In evaluating Laser Sintering also consider CNC machining, especially for large parts as the overall accuracy and material choices can be attractive.

Process Features

Accuracy

Tolerances vary depending on material and supplier, however as a general rule using ± 0.3mm to 100mm and ± 0.3% thereafter will provide a 'safe' estimate.

Minimum Feature Size

This is machine dependent but anything under 1mm should be evaluated carefully. It is possible to build down to 0.5mm but not without discussions with the Plunkett Associates.

Layer thickness

Typically 0.1 or 0.15mm.

Bed sizes

Vary from circa 300 x 280 mm (usable) up to 700 x 380 mm allowing the single piece manufacture of a wide range of part sizes.

Post processing

Parts can be dressed to a high cosmetic finish for display purposes. Laser Sintered parts may also be electroformed, ie plated with a thin layer of metal, to significantly increase their strength and hermetically seal the substrate inside a metal shell. This can be used just to provide EMI/RFI shielding, but offers serious strength and stiffness benefits as well.

Description

Like most RP processes Laser Sintering relies on the 3D CAD data of the component being resolved (sliced) into a series of layers that can then be sequentially recreated. A laser drawing on the surface of a bed of powder sinters the powder together to form each layer.

Parts are built without support structures as the loose powder supports and anchors the developing part.

The additive nature of the process permits almost any geometry to be created without concerns about 'access' that would be applicable to machining.

Flexible Parts using Laser Sintering

Laser sintering is capable of producing flexible parts.

Lightweight Structures

For thick walled parts and very large parts there can be process advantages to hollowing out the inside.

Benefits range from basic process advantages to being able to create lightweight structures that utilise the full potential of additive manufacture

For more information, please contact:  stefan@smartprototype.net