3D-Printed Molds vs. Aluminum Tooling

Industrial 3D printing has made a tremendous impact on the manufacturing world. Rapid prototypes are possible within a day, material selection continues to grow stronger and parts with un-manufacturable designs have found their happy place. Recently, some companies have begun using this important technology to produce injection molds.

Molds made with thermoplastics-based 3D printing are kind of like the plastic storage sheds some of us put in our back yards. They’re a little cheaper than metal sheds. They go up quickly and are fine under light loads. Pile too much snow on them, however, and they’ll collapse like a house of cards.

A 3D-printed Digital ABS mold built in an Objet Connex machine.

Still, printed molds have their place, and some shops have had good success with them. Proponents argue that 3D printing produces molds up to 90 percent faster and 70 percent cheaper than using traditional moldmaking processes. And while this may be true in some circumstances, it’s important to understand the pros and cons of printed plastic molds compared to those machined from metal.

Quality is king. 3D printing builds parts in layers. Because of this, printed parts can exhibit a stair-step effect on any angled surface or wall. Printed molds are no different, and require machining or sanding to remove these small, jagged edges. Holes smaller than 0.039 in. (1mm) must be drilled, larger holes reamed or bored, and threaded features tapped or milled. All of these secondary operations eliminate much of the “print-to-press” speed advantage associated with printed molds.

Size matters. Part volumes are limited to 10 cubic inches (164 cm3), roughly the size of a grapefruit. And although modern additive machines have impressive accuracy, they cannot compete with the machining centers and EDM equipment at Proto Labs, which routinely machine mold cavities to +/- 0.003 in. (0.076mm) and part volumes up to approximately 59 cubic inches, about six times larger than parts made with 3D printing.

The heat is on. To make material flow properly, injection molding requires very high temperatures. Aluminum and steel molds are routinely subjected to temperatures 500°F (260°C) or greater, especially when processing high-temperature plastics such as PEEK and PEI (Ultem). Aluminum tools can easily produce many thousands of parts, and can also serve as bridge tooling until a production mold is available. Molds produced with SL and similar 3D printing technologies use either photoreactive or thermoset resin, which is cured by ultraviolet or laser light respectively. These plastic molds, though relatively hard, break down fairly quickly when subjected to the demanding thermal cycles of injection molding. In fact, printed molds typically become ineffective within 100 shots of soft, hot plastic such as polyethylene or styrene, and may produce only a handful of parts from glass-filled polycarbonate and other tough thermoplastics.

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TIPS WITH TONY: Shedding Light on Clear Materials

Designing luminaires or lenses with clear materials? Our tip this week looks at the material selection and surface finishes available for prototyping and low-volume production of lighting applications.

Prototype built in clear WaterShed XC 11122 material with stereolithography.

Additive Manufacturing
If you haven’t considered using additive manufacturing (3D printing) for your lens design, you may want to check it out. Proto Labs offers stereolithography (SL) with three options for clear parts.

  • Somos WaterShed XC 11122 — ideal for lens and high-humidity applications
  • 3D Systems Accura 60 (10 percent glass-filled) — creates a clear part with slight blue tint and high stiffness
  • 3D Systems Accura 5530 — high temperature resistance, suitable for under-the-hood applications

TIPS WITH TONY: Additive Manufacturing for Microfluidics

Prototyping small volumes of microfluidic parts has traditionally been difficult using CNC machining or injection molding, but Proto Labs offers microfluidic fabrication through additive manufacturing (3D printing) for just this purpose.

Microfluidics typically requires very flat surfaces, and clear and thin/shallow features that are difficult to produce in a mold that is milled and hand polished. These tiny features are not easily distinguishable, requiring careful polishing and injection molding pressures can sometimes role the edges even further, not to mention the effect that the ejector pins have on the part surface. Ejector pins play a huge factor in removing the part from the mold and can cosmetically impact microfluidic parts that are molded. We will continue to injection mold microfluidics, but please first discuss these projects with a customer service engineer at Proto Labs.

Additive Approach
Additive microfluidics changes all of this as ejector pins are a non-factor. We use stereolithography (SL) to produce parts using an ultraviolet laser drawing on the surface of a thermoset resin, primarily our Somos WaterShed XC 11122 material. High-resolution SL is able to produce features as thin as 0.002 in. layers to provide the fine detail that microfluidics require. We recommend channel sizes of 0.025 in. square cross sections with a minimum wall thickness of 0.004 in. for X and Y dimensions and 0.016 in. for the Z dimension. Of course, we can produce features smaller than this, but it would need to be carefully reviewed by our engineers before the build begins.

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Proto Labs Extends Additive Manufacturing Reach in Europe

Proto Labs’ corporate headquarters are in Maple Plain, Minn. (above). With the Alphaform acquisition, Proto Labs now has manufacturing plants in the United States, United Kingdom, Germany, Finland and Japan.

Proto Labs closed this week on the purchase of select assets and operations of German-based manufacturer Alphaform AG, which significantly extends its additive manufacturing (3D printing) capabilities across Europe.

Alphaform is a leading service bureau headquartered in Feldkirchen (Munich), Germany. The purchase includes Alphaform divisions operating in Germany, Finland and the United Kingdom. This acquisition will significantly expand Proto Labs’ recently launched additive manufacturing capabilities in Europe by adding selective laser sintering, direct metal laser sintering and additional stereolithography capabilities. The acquisition also includes the injection molding service currently offered by Alphaform Claho, in Eschenlohe, Germany. MediMet Precision Casting and Implants Technology GmbH, a 100 percent subsidiary of Alphaform AG, is not part of the transaction.

Proto Labs entered the additive manufacturing market last year with the purchase of Fineline in Raleigh, N.C. Proto Labs is spending $25 million to expand that plant, which is set to open in 2016.

You can read the full press release here.

TIPS WITH TONY: Fine-Tuning Your Additive Resolution

When you’re watching an epic movie filled with sweeping cinematography, you probably want the highest on-screen resolution possible with, say, a Blu-ray disc or high-definition stream. But if your children are watching old Disney movies in the playroom while arguing with each other over Legos, a standard picture from a classic DVD will probably suffice. The point: Don’t overpay for something that isn’t really necessary.

Normal resolution.

Normal Res
The same thought can be applied during 3D printing when you’re prototyping with stereolithography (SL). Proto Labs uses three resolutions that range in cosmetics and functionality. Normal resolution (NR) provides the lowest cost, but lacks fine detail. With NR you get a layer thickness of 0.004 in. with a minimum feature size of 0.010 in. — but that might be all you need in early prototyping.

High resolution.

High Res
If your part requires an elevated level of precision, there’s high resolution (HR). Here, you get a layer thickness (0.002 in.) and minimum feature size (0.004 in.) half of NR. It costs more, but the boosting the part quality may be well worth it depending on your intended application.

Micro resolution.

 

Micro Res
You can even step up to a higher level of precision, which most manufacturers are unable to provide. Micro resolution (MR) — the Blu-ray of additive resolutions, if you will — can provide optimal part detail on the smallest of part features. With MR, you get a layer thickness of 0.001 in. and minimum feature size of 0.002 in. Yes, that is an actual life-sized ant (not an evil oversized ant) atop a microscopic chess board. You can even see the staircase inside the rook!

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