3D Printing (3DP) and Selective Laser Melting (SLM), a comprehensive comparison

1. Working Process

3D printing is an additive manufacturing process that creates physical objects from digital design. In 3DP layer of powder is deposited automatically in the tray. Then print head applies resin to power layer and it dries almost immediately. When the layer dried another layer will be added to finish the model. The working principle of SLM differs from 3DP and it works on the principle of melting. Powder heated and melted and forms pool of liquid where its phase changes from liquid to solid by reforming and hardening. The final part wont porous, thereby it can be used for wide range of applications.

2. Process Variations

3DP is available with single-head as well as multi head printing devices. A sintering stage can also be added in the system to further bond the powders. Jetted Photopolymer System (JPS) and Thermal phase change Inkjet printers also a part of 3DP method. Printing head selected based on the requirement. SLM doesn’t offer process variations like other traditional printing methods. However lot of research institutes are doing research on alternative materials such as gold and its alloy. Many industries are trying variety of materials. Due to the non flowing character of gold powder, the usages are limited in this application.

3. Processing materials

Generally 3DP use wide range of materials. The materials used in 3DP are powder form of stainless steel, plaster, starch, bronze, ceramics, moulding sand and starch. Liquid form of resins / binder is used such as wax, epoxy resin, elastomer and polyurethane. However higher end printers may support different materials. SLM offers variety of material flexibility when compared to 3DP. The processing materials used here are stainless steel and aluminium / titanium alloys which have good strength and ductility. Titanium also offers bio compatibility, this helps to use this material in bio-medical application. Titanium also offers good mechanical properties and corrosion resistance.  

4. Design aspects

Separate support structures not required for 3DP; the power material can act as support. 3DP prefer smaller dimension parts in order to reduce the number of layers. It is good in X-Y axis however there are limitations in the Y axis. The tensile strength and product quality depends on the type of material used. SLM offers very completed design when compare to 3DP. Very thinner details also can be made in SLM; this allows engineers to design complex features and undercuts in a single part. When compare to 3DP it don’t requires huge raw material since SLM eliminates the usage of fasteners and mounting components.

5. Quality aspects

3DP finished part is grainy and requires additional finishing. It offers multiple colour products. 3DP has poor tolerance and strength. It is not suitable for the application where accurate fit required. Resins are used to improve the finish, durability and strength; wax also used instead and strength will be poor. SLM commonly known technology and it can provide good relative density products, than other printing methods. It offers good mechanical properties than 3DP. The tolerance limits vary machine to machine and typically varies from ±0.05-0.2mm. It also requires post processing like finishing; however this is limited when compared to 3DP.

6. Economical aspects

3DP has fast build speed which is the main advantage of 3DP method. The materials are low cost and material utilization also high. Excess powder is also reusable. It is an automated system and requires highly skilled labours. The initial investment for this system also less when compare to other. SLM offers minimal material usage compared to 3DP and usage of 100% laser is not possible practical. SLM is a known technology for compact and any thickness of layer can be used. This is completed in many ways such as getting approval for installation and development of the same. This offers minimal material usage when compared to 3DP.