Comparing Two 3D Printing Processes

Abstract

In this paper two additive manufacturing technologies will be compared. The analysis will dig deeper into two specific companies that use these technologies. Then even further with two specific machines from these companies will be analysed. After reading this paper you will have a good understanding of each technology and which one you would prefer in your application. A conclusion will be made in the paper, but it will also be possible to come to your own conclusion from the information provided.

1 Introduction

Additive manufacturing (AM) or three-dimensional (3D) printing is also referred to rapid prototyping which is not always the only use for it. Initially it was for rapid prototyping but as the technology advanced there is more application of it being used for production parts. It is now commonly being used for biomedical, fashion, science and even food industries [5]. Two methods commonly used is Stereolithography (SLA) and Continuous Digital Light Processing (CDLP). Both of these technologies are Vat Photopolymerization Processes (VP). This is the process of curing a liquid resin inside a vat with ultraviolet (UV) light to create a solid structure. They have some similarities but also some contrast differences. One major similarity between them is they are commonly used in a higher-level application rather than a hobbyist which is more using Fused Deposition Modeling (FDM) extrusion method. There are desktop versions of the SLA with Formlabs, but they are still a higher quality. Anyone can buy a Form 3 and get it set up in their home shop, but it takes a bit more work and research than a FDM machine; which is a plastic filament extrusion method commonly used among hobbyists.

In this paper we will look at SLA and CDLP technologies. SLA is stereolithography which is the grandfather of 3D printing. It was first invented by Chuck Hall in the 80’s [1]. After the patent Hall founded 3D Systems which is an industrial additive manufacturing company.

The SLA technology uses UV light in a laser to cure a resin in a bath to create a 3D shape [7] [4]. It is done layer by layer to render a 3D object in the real world. This creates a highresolution model compared to the FDM extrusion method. This method of printing is commonly used to enhance other forms of manufacturing. By creating custom complicated molds from the SLA method, it can be used along the process of other manufacturing process [9][6]. It can also be used in 3D bioprinting where it can print in biomaterial to create complex tissue structures [8].

SLA products can be used in production as well outside of prototypes. Since SLA resolution is high it can be used in different applications like molds or in production. Just depends on the strength of the resin after it is cured. Formlabs can change the resin to get different properties, but with limitations.

CDLP is a process that uses a UV light projector to cure the resin. The outline of the desired shape is displayed on the projector and then projected into the resin bath from the bottom with a layer of glass in between. In DLP a non continuous method of this technology it is done layer by layer [4]. The CDLP is a continuous method to take out the layer wise method of printing. This continuous technology decreased the printing time as well which has great benefits for production.

In this paper the two technologies will be discussed then two companies that use these technologies will be compared. Finally, a specific machine from each company will be analysed. After reading this paper you will have a better understanding of which one you prefer. There will be a suggested technology, company, and machine but the reader will be able to conclude too

2 Material & Method

2.1 Methods

2.1.1 Stereolithography

Stereolithography (SLA) was invented in in 1986 by Chuck Hall [1]. His machine in the patent was a bit different than what is used today especially in the Formlabs technology. Hall founded 3D Systems on with this patent and that was the original 3D printing company and technology in the world. They specialize on commercial uses and manufacturing. It was the first one and created the initial marketplace for the AM industry. It works by curing a resin using a UV laser, in traditional SLA the laser is above the resin bed indicated in figure 1.

Figure 1 Stereolithography patent [1]

2.1.2 Continuous Digital Light Processing

One of the biggest differences between SLA and CDLP is that SLA cures layer by layer. While CDLP is a continuous print where the part emerges from the resin smoothly. To be able to continuously print without layers the CDLP machines ensure there is an uncured layer of resin between the basement plate and the build piece before the next UV projection is made. This creates a buffer of uncured resin to allow for a smooth and continuous print [3]. This creates for a really fast print time. Another difference that makes CDLP work is the UV light to cure the resin is with a projector instead of a laser. This creates the entire design per layer to project onto the resin to be cured.

Figure 2 CDLP projection system [3]

This method allows for a very quick print time. This print time allows for a higher flexibility of uses that is not constrained by time. Parts could be printed with this method for production a lot more practically than SLA because of the print times.

2.2 Materials

Comparing the two technologies there are a few similarities. They both use a resin and cure it with UV light. The resin being used cures into the final material the part will be. It is important to know the material properties of the cured resin to be able to design the part in a specific application. If the printed part is going to be a prototype, then it does not have to be as strong. But for a mold for further manufacturing process, it is important to know the material properties being worked with. Also, it is important to have desired materials if the part is going to be used in production.

2.2.1 Formlabs

Formlabs have a few different resins that they can print with. They have a prototype resin that has the quickest print time. Formlabs also has engineering material resins too. In Table 1 you can see the different resin materials available from Formlabs.

Table 1 Formlabs 3 Material List [16]

Formlabs have green and post cured strengths for its materials. The post cured is cured for 60 minutes with temperature and light. For standard resins and draft resins, not cured will be assumed. In a quick printing application with standard resin or draft resin one would not typically cure it. But for an engineering material one would typically cure it to get its highest strength. For engineering materials, the post cured was assumed but not the post cured plus 5 thermal treatment. For Speciality materials the post cured plus thermal treatment to get the highest capability was assumed.

2.2.2 Carbon3D

Carbon3D printers are able to print in engineering materials to be used in a wide range of applications. They have high temperature capable resins that can be used in certain applications where competing printed parts would not work. The materials that Carbon3D use is in table 2.

Table 2 Carbon3D Material List[15]

3 Comparison of Machines

Now that the VP technology and the two types being showcased have been explained and two specific companies and their machines that use these technologies; the advantages and disadvantages for each one will be looked at. There might be an obvious one that is better or maybe a not so obvious one. Once they are looked at it will be clearer. There will definitely be differences in the application where one is better, and the other isn’t as strong and vise versa. But the over all picture of which one is preferred will be considered.

3.1 General Methods

3.1.1 Formlabs

SLA works by using a UV laser to cure a resin in a bed layer by layer. This will create a solid part. In traditional SLA the laser is above the resin bed and in Formlabs the laser apparatus is below the resin bed [12]. The Formlabs technique of having the UV laser below the resin bed creates for a highly compact unit. 6 In the early 2000’s the patents were expiring and Formlabs wanted to create a desktop version of the SLA method to bring to the everyday user [15]. They then created the Form 1. They got funding from a crowd sourcing method where people had pre-orders. The first machine they were making had a lot of delays in their design and manufacturing that the pre-order customers were growing dissatisfied with their order. After a few months of delay, they finally launched their first product, and it was a success [10].

3.1.2 Carbon3D

Digital Light Processing is a form of additive manufacturing that using the VP technology, where a resin is cured using UV light in a layer wise fashion. The UV light source is a projector with the shape of the outline projected onto the resin. In Continuous Digital Light Processing it is not done layer by layer it is done continuous. It is a smooth transition from liquid resin into the working part. It is also a quick process therefore has lots of benefits in production. The way this is able to do this is by having the glass that is under the resin where the projector shines the UV light be oxygen permeable and there is a layer between the glass and the part that doesn’t cure so the part continuously moves upwards as it prints [2]. This method allows for a wide range of applications since it is fast and has a high resolution. Not having layers helps with create a smooth one-part piece ready for production.

3.2 Specific Machines

3.2.1 Formlabs Machine

Each specific machines in each of the company we will compared. For Formlabs the Form 3 will be the machine being case studied. It is their desktop version. First, they had the Form 1 which was their very first machine they made using SLA for desktop applications. They have progressed it into the third version the Form 3. Since this is the desktop version it is the one that will be used by hobbyist or companies wanting to make prototypes. It is not as much of a commercial manufacturing use. But typically, if a company wants to have a rapid prototyping process, they can conceptualize it in real life. And if they want it to be a high resolution then the SLA and Form 3 is a good choice.

Formlabs technique for SLA is to have the laser underneath the resin bed and use a series of mirrors to create the shape that is desired. Where in traditional SLA printing the UV, laser is 7 above the resin bed. Having the laser system underneath really reduces the size of the entire machine.

Figure 3 Form 3 3D printer from Formlabs [13]

Taking a look at some specifications of the Form 3 we can see the resolution and layer thickness and other specifications. The resolution is quite high for the Form 3. The XY resolution is where it really differs from other technologies. The Z resolution (layer height) can get really fine but having layer thickness of 25 µm typically isn’t practical.

Table 3 Formlabs Form 3 Printer Specifications [12]

3.1.1 Carbon3D Machine

The machine that will be looked at for Carbon3D is the M1 Printer. It is their smaller model that could be used as a desktop version as well. It creates smaller printed parts and is easily 8 accessible. This machine is ideal for same sort of customer persona. A company that wants to have the capability to bring designs into real life quickly. This can have many benefits in the design process. This printer uses the CDLP technology described. Allowing to print without layers continuously which is very fast. They can print with engineering materials for in use production.

Figure 4 Carbon3 M1 3D printer [12]
Table 4 Carbon3D M1 Printer [11]

4 Discussion

After looking at each machine a final conclusion can be made which one is better for a certain use. Both machines are quite good and print in a high resolution. Where Carbon3D M1 is continuous and is a very fast print, it does not have as high of a resolution than the Form 3. With a similar build plate, they can be compared but the big difference is that the Form 3 could be used by pretty much anyone whereas the M1 is more for industrial or commercial settings. The price difference is way too big to compare them for everyday people users. With this information the Form 3 is the superior model since it has higher resolution, more affordable price and engineering materials. The print time is slow but that is not a problem when that amount is being saved. It is a good trade off to wait a bit longer for the part. In some applications where the quick print is necessary then the Carbon3D M1 makes perfect sense. The speed would have to be a big factor to make up for that price.

5 Conclusion

First, the VP technologies were looked at and what they are used for. Two different types of VAT technology were looked at. Both of these technologies cure a liquid resin with UV light. They both have different variations to them. SLA from the company Formlabs which allows for a more useful and widely used products. And CDLP a continuous printing method using a projector to cure the resin by the company Carbon3D. After looking at the different advantages and disadvantages from a specific machine from each company it was concluded that the Form 3 was the superior model.

References

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Cory Hisey

Cory Hisey

I am a Mechanical Engineer graduate and I am currently studying masters of Mechatronics Engineering.