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The Benefit of 3-D Printing for Low-Volume Production Parts in Manufacturing

We’ve discussed 3-D printing several times over the last year due to the tremendous importance of this innovative technology for the manufacturing industry. Here we’ll review how 3-D printing is being tested to save money and time for low-volume production parts.

First, just to recap: 3-D printing (aka additive manufacturing) is a process that creates an object by iteratively building two-dimensional layers and joining each to the layer below to ultimately create a 3-D object. Every 3-D printed object begins with a digital design created with computer-aided design (CAD) software or animation modeling software. The design serves as a “virtual blueprint” that is sent to the 3-D printer, which “prints” the object.

Now let’s look at how 3-D printing can benefit plastics manufacturers. The majority of plastic products in the world today are manufactured by injection molding. With affordable desktop 3-D printers and injection molding machines, you can create molds in-house to produce small, functional parts for final products. Low-volume production represents about 10-100 parts, and with 3-D printed molds, you not only can save financial and production time resources, but you also are incorporating a more agile manufacturing approach into your operation. Engineers and designers are able to easily modify molds by adjusting a digital file instead of the equipment to make the mold, and to continue to iterate the design of functional end-use parts.

Technology at Work

Formlabs and Galomb Inc., in a recent white paper, showcased the results of their partnership to produce small injection molded low-density polyethylene (LDPE) parts created with 3-D printed molds produced on a Form 2 printer and then injected using a Galomb Model-B100 Injection Molder. Formlabs designs and manufactures 3-D desktop printers; Galomb provides industrial equipment.

Two mold designs were tested: One of a large butterfly and one that produces four smaller butterflies in one shot. These molds were 3-D printed in Formlabs’ Clear Resin and Galomb produced the injection-molded parts. The partners chose the Clear Resin due to its strength, high detail, and smooth surface finish. Its translucent property facilitates testing and inspecting molds to see if they have filled thoroughly. The molds were printed with a layer height of 100 microns and took about five hours per mold to print. Depending on geometry, multiple molds can be printed at once on a build platform to increase printing efficiency.

The parts and subsequent molds were designed to fit to the dimensions of the Galomb machine’s vise clamp, the 1-in-3-injection capacity of the barrel, and the build volume of the Form 2. After printing, the parts were rinsed in a bath of 90% isopropyl alcohol for 20 minutes each, supports were removed, and support marks were sanded. The parts were then post-cured for one hour under a 405 nm UV bulb in order to reach full mechanical strength and stiffness.

Both the large butterfly logo and four small butterfly logo molds had a cavity, a narrow gate, and a sprue to the injection point, and were designed in Solidworks, 3-D CAD software. The molds were inserted into aluminum frames before injection, eliminating the need to print the entire mold, which reduced both print time and cost. The aluminum frames may also prevent the mold from warping after repeated usage.

Using the benchtop Model-B100 Injection Molder, Galomb tested the printed molds with 25 shots of low-density polyethylene (LDPE). LDPE melts at approximately 400°and was chosen for its low melt temperature.

The results? After 25 shots of LDPE, there were no noticeable chips, cracks, or scratches on the molds. LDPE did not tend to adhere to the resin molds in testing, but it was noted in the white paper that other plastics might require an application of a mold release agent to help with the extraction of the part. Adhesion of the part to the mold can cause deterioration of the mold during extraction. Cycle time for each shot was approximately three minutes. This process was accelerated by applying compressed air to cool the mold. Galomb also improved the mold design by etching in shallow (0.05 mm deep) air vents that led from the edge of the cavity to the edge of the mold so that air did not get trapped inside the cavity during injection.

Some of the shots did exhibit flash at the split line, due to warpage of the resin mold during the cooling phase after multiple shots. Increasing clamping force in the vise can help mitigate flash, as can polishing the mold’s split plane to give it as flat a surface as possible. Galomb proposed including channels in the mold design to embed metal tubes and filling these with aluminum-filled epoxy as a strategy to reinforce the mold, reduce warpage, and improve cooling time.

These tests are just one example underscoring the exciting era the industry is entering with additive manufacturing. Just think about how prototypes and short runs can be made onsite in just hours using 3-D printing. Designers and engineers can test their work more frequently and more accurately, and go to production with greater confidence. Product managers can reduce the time to market and products can turn out better.

At Precision Manufacturing Insurance Services (PMIS), we’re excited about the advanced technologies being used in the manufacturing sector to assist businesses in delivering products more cost effectively and efficiently, and are committed to sharing these developments with you. We also keep abreast of how technology is impacting our manufacturing clients so that we can provide insight and recommendations on any potential emerging and new risks, including liability concerns, which may arise as a result of these advancements. PMIS offers a complete portfolio of manufacturing insurance products and risk management services for firms throughout California. For more information about our manufacturing insurance products, please contact us at 855.910.5788.

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