AN ASPECT OF CURRENT SLA PRACTICES AND FUTURE RESEARCH SCOPE

Satyajeet Udavant sudavant@purdue.edu

Purdue School Of Engineering, Indianapolis

Resources Additive Manufacturing Lab in Science and Engineering department -- Purdue School of Engineering Think It Make It lab -- Herron School of Art and Design, IUPUI Other online resources

Professor Lab Assistance/ Digital Fabrication/Imaging Lab Coordinator Dr. Andreas Tovar Shelley Spicuzza

Keywords Additive manufacturing, SLA printer, alternatives for design and material, insights of problems while printing, maintenance

Objective To discover the limitations and commercial aspect of the SLA printer (formlabs) and an alternative approach so that the highlighted problems can be addressed for a better technology Background When I searched for the recent technology and developments in SLA/ DLP printers, I found limited resources that speaks about the existing problems, but there is ample of resources that talk about the technology and its basics. Very limited open source material is available online related to this topics. A candidate without the firsthand experience of these printers will never be able to understand the limitations. Hence these efforts are made to make the problem statement more open source to the people who cannot actually have the privilege to experience such printers first hand. This paper talks about the normal problems one faces while operating this printer, cautions and maintenance aspects I hope all the information provided in this report shall and will be used for the development of existing technology. Statement 1 Files required for the print are easy to make on any cad software, they are needed to save in stl format. This stl file is now uploaded on the printing software to create slices/ gcodes (in case of FDM). It is only when we upload the file we realize that the peel process1 affects the print, in this case the build process is hinged2 type. This damages the base of the tank which has a coating of the polysilicon material which is seen in the following picture. Pic 1

Damaged base

causes print failure

Satyajeet Udavant This diagrams shows the reasons for above damaged area of resin tank

To avoid this the print needs to be aligned( as in pic 2) at an angel so the peeling is effective without damaging the tank. But this limits the designs that we can print. Pic 2

Scope To overcome this problem few different approaches are advanced like, uniz uses coolant that runs below the tank that helps to remove heat released in exothermic reactions. Form 2 uses a horizontal shift along with it the build platform is raised up. Statement 2 Vatphotopolymerization requires support structures, the problem comes when the design that builds layer by layer, there are layers that even after applying the scaffolding fails to create. This also happen because the prints are way to complex. Pic 3

Alignment of the print is angled as the peeling

process is effect with hinged process. This limits

the design we can print.

This is a layer by layer build

that we can see before

placing the print. This is

useful to analyze where the

support structures might fail

as in this case.

Here, the red part is the

layer that will get print but

the blue part (arrowed) is

being built without support

out of the layer.

Possible cause for failure

Improper peel corrupts polysilicon coating, as shown

above

Satyajeet Udavant Scope Better slicing software that can give more data. Statement 3 Due to limited resin tank life, not much attention is given to the tank. One tank is used for one type of resin. The resin tanks are needed to be changed since same tank cannot be used for different polymers. To store a used resin tank there are lids but the problem is that resin is sticky, while in use it touches all parts of the tank, especially the top cover support. Pic 4

Scope Better design of resin tank / lid. Statement 4 Once we complete the print, we keep the print in Isopropyl Alcohol for some time, later its washed with alcohol again, it washes out the extra resin, that’s glued, if any on the print. Pic 5

Alcohol to clean parts expense

This portion usually gets

sticky after few uses as the

resin is stick, when we

cover this with lid the lid

gets glued, and is left

damaged when we open it

next time

Satyajeet Udavant Statement 5 As stated in stated in statement 1, the peeling process damages the bottom coating of the tank. This peel off also leaves behind small pieces of polymerized resin. The resin after use needs to be filtered once in a while to get rid of small bits and particles. Pic 4

Scope Better cooling alternative and precision laser path will make sure accurate prints there by avoiding these by products. Statement 6 The polysilicon material coated on tank is another issue, it reduces the life expectancy of the tank, increases expenses as new tanks needs to be bought quite frequently. Scope A different type of material is polymer that is used as the base itself rather than the tank coating. Such polymers needs to be developed Statement 7 Solid prints at times fails as the stress and strain developed cannot be withstand by mere supporters. This prints fail with some cracks on surface or within the part. Pic 7

The round half of the print is broken, also internal

cracks developed during the process couldn’t

withstand the stress and as shown in fig a small

portion is fall apart

Satyajeet Udavant Statement 8 The printers got a lot of moving parts. That increases the issue of maintenance. Moreover, increased wear and tear over time. Also the single laser line tracing consumes a lot of time. Pic 11

Scope DLP- Digital light printers are comparatively new among the additive technologies, it uses a layer by layer projection rather than line tracing as in SLA. Statement 9 With the increasing technologies in additive manufacturing the need to compile all simulation and design data is a great challenge. There is a lot of scope for the file formats, old ones that uses .stl file are found to be inadequate in many areas. Scope In the following, I discussed few of the important aspects of .amf file extension over .stl Advantages of AMF over STl.

1. Color: The conventional stl files contains no information related to color, material choice. Coloring of stl file is possible but it

would be limited by the fact that a single triangle can only be one specific color.[1a]

AMF can solve the above issue, materials are defined with particular properties, given an ID and subsequently

associated with AMF volumes by ID. Compositions, colors etc can be specified for various materials. Microstructures, colored

or textured objects can now be defined in CAD programs and then have that information available in a standard AMF file.[1]

2. Metadata: Amf is also better than stl when comes to meta data .The optional metadata element describes additional

information about the object(s) and elements. This can include things like authorship, copyright information, or instructional

data.

3. Mesh: STL files rely on triangle subdivision to account for curvature. As the STL file scales in size, retaining resolution means

introducing significantly more triangles, thereby increasing conversion time and size[2]

In AMF, the internal structure inside a mesh surface is described by defining meta-materials. A primary material is defined as

one of the base solid materials that can be produced by a 3D printer. A meta-material is defined by combining primary

materials (as well as voids) in various combinations. Materials are combined using mixing coefficients: A constant mixing

coefficient makes a simple interpolation of the primary materials.[3]

Example:

A 10cm sphere at 10 micrometer resolution requires 20,000 triangles. Scaling up the 10cm sphere at the same resolution

would significantly increase the amount of triangles, resulting in a much larger file. AMF seeks to address these issues by

redesigning the way a 3D object is digitally stored.

Satyajeet Udavant SUFFIX 1 - peel process- when the light source completes its vat polymerization the part being built is partly/completely sticks to the bottom of tank. Peeling is required so as to carefully lift the build for the polymerizing the next layer. 2 - hinged peel process

Conclusion To conclude, there is a lot to be considered while moving forward with this technology, it is still in its infant stage, yet has a promising future. I hope this work will help open a different aspect of this technology which not many are aware of as the downfalls are not highlighted very much in today’s commercial world

Comparison of STL & AMF - 10cm Sphere (Solid Edge)

STL Format

(Binary)

AMF Format

(Curved Triangles)

PRECISION 10 micron 10 micron

NO. OF MESH TRIANGLES 49,500 320

FILE SIZE 2400k 10k