Stereolithography: Sorting Out Surface Finishes

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 stereolithography finishing options available at Proto Labs, and when it makes sense to use each.

Unfinished

Stereolithography (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.

stereolithography proto labs

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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Injection Molding: Aluminum vs. Steel Tooling

Aluminum molds are milled in rapid CNC machines.

Conventional injection molding typically uses steel tooling capable of producing millions of parts, however, it often takes months to manufacture a mold and a capital investment of $50,000 or more. But what if production demands call for smaller quantities? That’s where aluminum tooling is ideal. Here’s a quick look at the differences between steel and aluminum tooling.

Low-Volume Production with Aluminum Tooling

  • Mold production AND parts within 15 days or less
  • Low manufacturing costs with molds beginning around $1,500
  • Production quantities of up to 10,000 parts or more; depending on material type and geometry, some molds are capable of producing hundreds of thousands of parts
  • Simplified mold designs decrease manufacturing time and cost
  • Single and multi-cavity tooling: 1-, 2-, 4- and 8-cavity molds are possible depending on part size and complexity
  • Thermoplastic and thermoset materials identical to that of high-volume production materials; more than 100 different materials can be used including ABS, PC, PP, LCP, POM, and liquid silicone rubber
  • No maintenance fees and lifetime replacement of mold if damaged
  • Improved heat dissipation and without the need for messy cooling lines
  • Inexpensive mold-safe tooling modifications

High-Volume Production with Steel Tooling

  • Lower part cost when quantities increase
  • Part production in the millions
  • Multi-cavity tooling greater than 8 cavities
  • Part complexity can be increased
  • More finishing options

If you part volumes don’t stretch into the millions, if you need on-demand production parts within days, and if you’re looking to avoid risky tooling investments before your part design is truly validated, low-volume injection molding with an aluminum tool might be good option.

Once an aluminum mold is ready, part production begins almost immediately. This allows manufacturing to finish every order in three weeks or less.

At Proto Labs, we include a free interactive design for manufacturability (DFM) review within a few hours in every injection molding quote. In the time it takes to get the initial quote from a high-volume production molder, you can have several design reviews and a mold already in production.

If you have any further questions about rapid manufacturing at Proto Labs, check out protolabs.com or contact one of our application engineers at 877.479.3680 or customerservice@protolabs.com.

TIPS WITH TONY: New Silicone Rubber Materials

We’ve expanded our selection of liquid silicone rubber (LSR) materials, which have some distinct elastic and optical advantages over certain thermoplastics. In addition to three durometers of general-use Elastosil LSR, and medical- and optical-grade Dow Corning materials, we now have two new durometers of Elastosil and a fuel-resistant flourosilicone material at Proto Labs.

Elastosil LSR
Elastosil LSR is a great general-use material that has good moldability characteristics, a good overall appearance and is transparent until colorant is added. Shore A durometers of 40 and 60 have been added our current offering of 30, 50, and 70 durometers.

Technical specs:

  • 40 durometer Elastosil has a tensile strength of 10.0 N/mm² with a tear strength of 33 N/mm and an elongation break of 610%.
  • 60 durometer Elastosil has a tensile strength of 9.40 N/mm² with a tear strength of 27 N/mm and an elongation break of 340%.

TIPS WITH TONY: Machining Capabilities for High Performance Parts

Do you know how machining a part from titanium can improve its functionality and performance? How about using key inserts for improved durability to your part. Here are few capabilities and design options to keep in mind for your next machined part.

Titanium machined parts.

Titanium
Let’s start off with some big news. Previously, we only offered titanium for 3D-printed parts, but it’s now available to customers for machined parts. And, if that wasn’t enough to catch your attention, how does titanium machined parts in as fast as three days sound?

Titanium is extremely strong and boasts a high strength-to-weight ratio. It also has excellent corrosion resistance, high operating temperatures (up to 1,000°F) and is nontoxic.

Titanium has range of applications due to its advanced material properties. Frequently, you’ll find titanium parts in the aerospace, medical, military and marine industries. More specifically, it’s used for parts like rotors, compressor blades, hydraulic systems, surgical equipment, dental and orthopedic implants as well as in military aircrafts due to excellent ballistic characteristics.

The only drawback is the cost of the raw material. It’s more expensive than steel. For this reason, most manufacturers don’t hold a lot of inventory, but that isn’t the case at Proto Labs. We maintain a level of inventory that allows for on-demand milling and turning of titanium parts

Visit our machining materials page for more information.

Key insert for added durability.

Key Inserts
Key inserts are steel threaded inserts commonly used in aluminum parts for added durability. Note that these are different from standard coil inserts as they have an added keyway with a tab inserted to prevent twisting under extreme load.

Key inserts are primarily used by the aerospace and military industries following the military standard of MS51835B. We offer eight thread sizes ranging from #8-32 to ½-13. For a full list, visit our threading page and click the key inserts tab.

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TIPS WITH TONY: Flame-Retardant Thermoplastics and UL Classifications

UL 94 is a plastics flammability standard released by the Underwriters Laboratories (USA). The standard classifies plastics according to how they burn in various orientations and part thicknesses from the lowest flame-retardant to most flame-retardant in six different classifications.

UL 94 Rating

Definition of Rating

HB

                                          Slow burning on a horizontal part.

V-2

                                          Burning stops within 30 seconds on a vertical                                             part allowing for drops of flammable plastic.

V-1

                                          Burning stops within 30 seconds on a vertical                                             part allowing for drops of plastic that are not                                               inflames.

V-0

                                          Burning stops within 10 seconds on a vertical                                             part allowing for drops of plastic that are not                                               inflames.

5VB

                                          Burning stops within 60 seconds on a vertical                                             part with no drops of plastic allowed but may                                               burn through the part.

5VA

                                          Burning stops within 60 seconds on a vertical                                             part with no drops of plastic allowed and                                                     cannot burn through the part.

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