TIPS WITH TONY: Sorting Out Surface Finishes for Stereolithography

There are a number of factors—resolution, tolerance, material selection, surface finish—to consider when designing for the industrial 3D printing process of stereolithography (SL). For our latest tip, we’ll discuss the four SL finishing options available at Proto Labs, and when it makes sense to use each.

Unfinished
SL technology uses a build platform that requires support structures for all features so they don’t float away or collapse during the build process. These support structures are removed after the build is complete, but they do leave visible markings on the part.

3D-printed parts are moved from the SL chamber after a build finishes. Supports are then removed, parts are UV cured, and a selected finish is applied.

In an unfinished state, after the support structures are removed, dots or nibs are noticeable where structures were attached to the part surfaces. So, when would leaving a part unfinished make the most sense?

  • When a clear part is desired with no custom finishing
  • If you have your own finishing capabilities, or have another shop that can perform post-build finishing
  • To achieve the best accuracy possible

Natural
A natural finish provides a surface finish that absent of dots or nibs, which leaves a more desirable cosmetic appearance. The surface is not as clear on the down-facing surfaces that had supporting structures, but the top surface would remain clear. When should you use a natural finish?

  • On small or delicate features that may be destroyed by additional finishing such as grit blasting
  • On clear parts where down-facing surfaces are not a cosmetic concern

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INDUSTRY SPOTLIGHT: 3D Printing for Production Parts Gains Credibility

Why are some engineers so hesitant to use 3D printing for more than just development?

Engineers are hardwired and trained to make calculated decisions based on facts. Traditional manufacturing processes such as casting and molding have been around a very, very long time—since the Bronze Age—and time has perfected these processes and brought them to what they are today. Both industry experts and novices alike can benefit from hundreds of years of this process evolution. 3D printing processes are relatively new, especially when compared to casting or injection molding.

Motor mounts are among a growing list of automotive parts that are now manufactured using commercial-grade 3D printing.

Modern, commercial-grade printing equipment and processes are capable of predictable results that will ease the mind of the most skeptical engineer. DMLS (direct metal laser sintering) can produce repeatable results for parts that can be manufactured in no other known method. Proto Labs’ 3DP facility is not only ISO 9001:2008, but also AS 9100. This is the supplemental requirement established by the aerospace industry to satisfy DOD, NASA, and FAA quality requirements. This certification should give any engineer a sense of security.

Understanding some basic quality parameters around the processes can help to lay a foundation of credibility. For example, limits are set to the number of times base material can be used, or only virgin powder could be specified. This is no different than controlling the amount of allowable regrind into a plastic injection-molded part.

Rolls-Royce is a notable automaker now using commercial-grade 3D printing for some production parts.

Testing parts to confirm material properties are extremely common in DMLS. Building a standard tensile bar with each build is a great way to confirm batches of production are producing the desired results. This way the first batch can have destructive testing on the tensile bar and parts to confirm the material and process are producing parts with the specified properties. The future batches can test the tensile bar for confirmation the predictable results were achieved.

The aerospace industry has been embracing advanced manufacturing methods for some time now and the automotive industry has also been making great strides in this area. For example, recent articles have been published around the Rolls-Royce Phantom’s printed parts and BMW’s leading spot in adopting printing technologies.

Rapid Manufacturing Webinar Round-Up

In our most recent webinar, we discussed how to optimize part design for direct metal laser sintering (DMLS). The presentation is a great introduction into metal 3D printing as we discussed common applications and many important design considerations. The webinar recording is available on-demand here.

Upcoming Webinars
We have more webinars in the works. On September 22, we’ll be sharing the digital stage with PolyOne as we host an in-depth discussion on selecting the right thermoplastic material for injection-molded parts. Click here to learn more and sign up.

Proto Labs’ On-Demand Webinars 
Interested in learning more about rapid manufacturing? Below you’ll find a complete archive of our past webinars (click the title to view).

How Rapid Prototyping Accelerates Medical Device Development

  • Strategies to accelerate medical device development cycle
  • Prototyping effectively  and reduce design risk with rapid manufacturing

Designing for 3D Printing: Stereolithography

  • Properties of commonly used stereolithography materials
  • The unique benefits of stereolithography and general design tips for overhangs, support structures, finishes, etc.

Improving Manufacturability with ProtoQuote

  • How to get free design for manufacturability feedback for your part
  • Improving manufacturability by adding draft, adjusting wall thickness and incorporating radii

Choosing the Right Rapid Manufacturing Method for Plastic Parts

  • 3D printing, machining and molding processes and specifications
  • Material selection and properties for each process

DESIGN TIP: Choosing Industrial 3D Printing for Production Parts

Using 3D printing for fully functional end-use metal and plastic parts is becoming increasingly common in rapid manufacturing with industrial-grade processes like direct metal laser sintering (DMLS) and selective laser sintering (SLS).

Industrial-grade 3D printing is well suited to produce organic shapes, like this nylon turbine (left) and end-use production parts such as this titanium drill component (right).

With an expanding material selection and improving material properties, designers and engineers have another good option for small quantities of production parts.

Accordingly, our monthly design tip covers this emerging trend.

This month’s tip discusses:

  • Choosing the best 3D printing process for your application
  • Selecting the right thermoplastic and metal materials
  • Designing part geometry for 3D printing
  • Using SL, SLS, and DMLS for end-use production parts

READ FULL DESIGN TIP

WEBINAR: Designing for Direct Metal Laser Sintering

In our next webinar, we’re focusing on direct metal laser sintering—our industrial 3D printing process for metal parts. Join David Bentley, our DMLS expert, to learn why product designers are turning to DMLS for prototyping and end-use parts. The presentation will include:

  • An overview of DMLS including materials and design guidelines
  • A case study on an innovative bike design
  • An open Q&A session 

TITLE: Designing for 3D Printing: Direct Metal Laser Sintering
DATE: Thursday, August 25 at 1 p.m. CDT
REGISTER: Click here to sign up

Busy that day and can’t make it? Not a problem. You can still register and we’ll send a recording that can be watched on-demand. Also, feel free to forward this invite to your colleagues.