Ultimate Guide on DLP(Digital Light Processing) 3D Printing – With illustrations

DLP 3d pRinting

DLP 3D Printing also known as Digital Light processing is a type of 3D printing technology (also called as vat polymerization) which creates a 3D Object by solidifying (curing) the Photopolymer liquid resin by projecting a light source from beneath.

How was DLP 3d Printing Invented?

Larry J Hornbeck is an American physicist, who is also known for the creation of Texas instruments, invented the major technique of vat polymerization called DLP(Digital Light Processing) 3D printing in the year 1987.

What is DLP 3D Printing?

DLP  3D Printing is a technique in which the  3d parts are produced by curing or solidifying the photosensitive resin with the help of digital light produced by a projector.

How Does DLP 3D Printing Work?

In this particular article let’s understand in depth about everything to be known about the DLP 3D printing process.

1. DLP 3D printer consists of a tank which can accommodate liquid resin also known as photopolymer. When the build platform is placed into the resin tank in an up-down direction the typical gap between the two would be a layer long. 

DLP 3d printer working
Fig: DLP 3D Printer working (Source:researchgate.net)

2. When the build platform is properly  positioned in the resin tank, a small layer of resin with a height in micrometers is created. This resin layer is exposed to the light rays produced by the digital projector. The produced light is made to fall on a resin in a selective manner and in a pre-fixed path based on the object to be printed. This is achieved by using galvanometers which are placed in a certain fashion to control this light path. This completes the printing or solidification for one layer and the same process is continued for the next layers. 

3. After the creation of one layer, the build platform will safely move upwards meanwhile, the curable surface of the printer is recoated by a sweeper blade.

4. Once the object is printed, post processing can be considered to increase the bondage between the layers and make the object stronger. This also can increase the thermal and mechanical properties of the object.  

Fig: Video of how DLP Printer works

Role Of Galvanometers:

Galvanometer plays a vital role in monitoring the light rays to fall on the resin. When a ray of light from the light source cures or solidifies the photosensitive layers selectively under the guidance of the galvanometer it gets attached to the build platform.The movement of the build platform is kept continuous with safe distance.The monomer chains of carbon gets activated when light rays fall on the resin and thus, the liquid resin is cured or solidified leading to indestructible bond between the layers. This process continues until the complete 3D object is formed.

Characteristics of DLP 3D Printing:

As similar to other vat polymerization technologies, DLP 3D Printing also has its unique characteristics. It is important to know these parameters before printing using this method.  

DLP 3D Printer Parameters:

Most of the parameters are already fixed in DLP 3D Printers and hence they cannot be modified. Only the altitude of the layer and the structure of the part can be given as input by the user.

Layer Height determines the speed of the DLP printing and usually ranges from 25 to 100 microns. When compared to uppermost layers, the downmost layers acquire curved geometries more effectively.

Support Structure in DLP:

DLP and SLA use support structures to hold the object and avoid the floating in the vat resin.

Supporting Structures are the pillar type vertical ribs which have small tips touching only a small portion of an actual object. They are made of the same resin while printing. These will hold the object and to be removed after the printing is done.

Usage of support structures is dependent on the object weight, shape & size (Weight). A software is used to calculate these support structures and also the location at which they touch the object.  

Top – Down DLP printers offer an advantage of printing the support structures in any orientation. In order to reduce the support size and layers, they are printed flat.

How to remove Support Material from DLA printed objects:

First, the accumulated and remaining liquid resin from the finished part is washed off using Isopropyl Alcohol. The pliers are then used to cut the support structure exactly at the touching point of an object. It can also be separated by simply breaking them manually and the remaining spots can be removed by sanding them. 

Curling

As we know that FDM printing is associated with Warping risks, similarly DLP can also create a CURLING effect if adequate measures are not taken during the solidification of the Resin. 

What is Curling?

Curling is the shrinkage of the resin when exposed to UV light rays. The shrinkage happens due to the internal stress build up between the previous solidified layer and the new layer. 

Curling issue in DLP printing

When the operator starts to print the model, he can clearly notice that the initial layers of the model are profitably printed. As he moves ahead, the curling issue appears for sure. This is a pretty natural issue for every 3D printing technology. 

Another major cause for this problem is when the printed part is kept in IPA(Isopropyl Alcohol- agent, used to clean up the remnants of the resin) the post cured part becomes curled.

This common issue which is caused inside the material can’t even be corrected because of the inherent nature of technology. 

Layer Adhesion

The layer adhesion of the DLP printed objects is accelerated by exposing them to rays of light even after the printing completion. This will further solidify the object and make it much harder and resistant to heat.

Types of DLP 3D Printers:

 The DLP 3D printers are of two types namely:

  1. Bottom-Up DLP 3D Printer.
  2. Top-Down DLP 3D Printer.

The major difference between these two printers is the site of the light source and the position of the model on the build platform.

In a Bottom-Up DLP 3D printer, the light source is positioned at the foot of the apparatus and the model normally dangles(hangs)  upside down.

Whereas in a top-down DLP 3D printer, the light source is placed at the tip of the device and the object is formed on the build platform.

The objects created in this DLP 3D printing cannot be brought again to liquid resin and thus the mechanism is unrepairable or irreversible.

The technique of DLP 3D printing is mostly done with the use of thermoset polymer due to its strong nature, by which the part cannot be modified further, after exposure to the light rays. 

Advantages and Disadvantages of DLP 3D Printing:

Pros:

  • The light source remains stagnant and at once solidifies the complete resin layer as opposed to SLA.
  • Parts with detailed structures can be manufactured with crisp edges covering minute details.  
  • Printing speed is relatively higher due to the usage of Digital Projector light when compared to other vat polymerization techniques such as SLA.
  • Intensity of the light source can be controlled by the operator.
  • DLP produces objects that are super accurate with clearly structured geometries.

Cons:

  • Manufactured models should not be exposed to sunlight.
  • Parts are so strong and thus cannot be remoulded or modified.
  • DLP 3D printers run with more cost compared to other digital 3D printers.

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