Next, we'll focus on the design of the support ribs. The ideal way to design ribs is by using a rib-to-wall thickness ratio of 40 to 60 percent the thickness of adjacent surfaces. The main body of the part should be designed thick enough so any adjacent rib extruded from it is about half of the thickness. This helps you avoid thick sections that may cool at different rates than the thin sections. It also helps in reducing sink and stresses that can create warp in your part.

Our helpful design aid demonstrates part features that are too thin or too thick, bad bosses, right and wrong ribs, and other considerations to be mindful of while designing parts for injection molding.

This guide walks you through everything from quoting, design analysis, and shipment to best practices that ensure your model is optimized for molding.

As a thermoplastic that has a high melting point and viscosity, Polyethylene is best suited for high-strength applications that require thin walls. Because of its high viscosity level, polyethylene is also suited for complex molds although setup and cooling times may be longer than other materials. PET is commonly used in applications where recycling is recommended, making it a common plastic material choice for commercial water bottles.

Ramps and gussets are yet another design element to strengthen and cosmetically improve your part. Again, plastic prefers smooth transitions between geometries and a small ramp helps the material flow between levels. Gussets help supporting walls or features while reducing molding stresses.

Most used in consumer-packaged goods and household items, polypropylene can be used in a variety of applications from scientific lab supplies to common items like flatware or garbage cans. Since it has a low overall cost and high flexibility, polypropylene is a great plastic material choice for high-volume production runs and still provides great results for complex molds. Other common products that are made from polypropylene include water bottles and medical applications.

Rapid injection molding requires that your part design should be as simple as possible, right? This is another false assumption as we support complex part designs that requires undercuts, through holes and other features.

Proto Labs, Inc. 5540 Pioneer Creek Dr. Maple Plain, MN 55359 United States P: 877-479-3680 F: 763-479-2679 E: [email protected]

A good rule of thumb is to apply 1 degree of draft per 1 inch of cavity depth, but that still may not be sufficient depending on the material selected and the mold's capabilities. Protolabs uses CNC milling to manufacture the majority of the features in the mold. The result of our manufacturing process drives a unique wall thickness and draft angle based on the end mill that we are using for each feature. This is where our design for manufacturability (DFM) analysis becomes particularly helpful as our software looks at each part feature separately and compares it to our toolset. The design analysis highlights the part geometry where increased draft and thickness may be required.

Our digital factories create prototypes and low-volume parts fast, while our manufacturing network, offers advanced capabilities and volume pricing.

The resin filling the mold cavity flows better around soft corners much like the flow of a river. Rivers don't have 90 degree corners as the water flow creates inside and outside corners so it moves easily towards its final destination. Similarly, plastic resin wants to take a path of least resistance to minimize the amount of stress on the material and mold. Radii, like draft, also aid in part ejection as rounded corners reduce the chance that the part will stick in the mold causing it to warp or even break.

As a thermoplastic suited for a wide variety of products, ABS is not only inexpensive but also remains strong to resist shattering or breakage. One industry in which ABS is not recommended is food applications because it is often flammable and has poor UV resistance; however, it is a great choice for electronic casing or automotive components due to its shock-resistance capabilities. One common product that is known worldwide that is created from ABS is LEGO® blocks.

The core and cavity are often referenced as the A and B sides or top and bottom halves of a mold. A core-cavity approach to part design can save manufacturing time and money and improve the overall part cosmetics.

Choosing the right material is critical for nearly every step of the injection molding process. For this reason, it is often one of the most vital steps that a manufacturer and their client will have to make throughout the entirety of the production run. Although there is sometimes secrecy about why specific plastic material types and brands are chosen, several common plastic injection molding materials may be used due to their different qualities and functions. When considering the right material for a project, some key material properties should be considered during the planning and development process.  Don’t’ forget about biodegradable material options as well.

Applying draft and radii to a part is vital to a properly designed injection-molded part. Draft helps a part release from a mold with less drag on the part's surface since the material shrinks onto the mold core. Limited draft requires an excessive amount of pressure on the ejection system that may damage parts and possibly the mold.

Parts arrive at injection molding in different ways. Some are first prototyped through 3D printing where moldability considerations are of limited concern. Others take a more traditional machining route that allows for iterative testing in engineering-grade materials similar to that of molding. And many simply jump right to injection molding.

Along with employing proper wall thickness, additional considerations should be looked at to ensure a part's design integrity remains intact. One may assume that the thicker the part, the stronger the part—this is a false assumption. A properly designed part that is intended to be structural should contain ribs and supporting gussets, which increase strength and can help eliminate cosmetic defects like warp, sink, and voids.

With a solid grasp of the techniques to improve part moldability, it is much easier to move into low-volume, and eventually high-volume injection molding. The next step is to upload your 3D CAD model online where you'll receive an interactive quote with free DFM analysis within hours. As we said earlier, the DFM analysis will highlight any moldabilty issues and even suggest solutions. We recommend pairing that design feedback with a conversation with one of our experienced applications engineers who will help with any further guidance you might need before production begins. They can be reached at 877-479-3680 or [email protected].

As another thermoplastic, epoxy also offers a high level of strength while adding heat and chemical resistance after curing. Although, caution is required, as the qualities of epoxy can vary widely depending on the curing agent used. It is important for manufacturers and their clients to thoroughly understand the end requirements of a product before using epoxy materials for their products. Common applications for epoxy include transistors and electronic circuit components, as well as marine components and plugs.

PFA, Inc. is the perfect partner for plastic injection molders that are looking for ways to improve their processes and focus on cost-effective production runs. The enhanced processing window available when using high preload KOR-LOK Hydraulic Locking Cylinders and high-speed SMED Quick Mold Change options available with PFA’s Hydra-Jaws™ QMC systems for aluminum and steel molds, can greatly improve productivity. If you have questions, we would be happy to explain how our unique products can enhance your process and cut overall costs. To get started, please contact us and our friendly and knowledgeable staff will happily assist you.

External undercuts are the easiest and most cost effective as we accommodate through pin-actuated side-actions. These side-actions move in tandem with the mold when it is opened and closed while the cam rides along an angled pin. When opened, the cam is fully retracted so the part can be easily ejected without mold damage and closes again till the cam is in position to create the next part.

We've learned from experience that, before production begins, there are important design elements to consider. These may improve the moldability of the parts, and ultimately, may reduce the chance of production hiccups, cosmetic defects and other issues.

One of the strongest thermoplastic materials, polycarbonate is one of the most shatter-resistant plastic materials available for use in injection molding. While commonly used for eyeglass lenses and bulletproof glass, polycarbonate will often need additional treatments to be scratch resistant. Unfortunately, polycarbonate is not resistant to repeated stress or vibration, so it is not a great fit for many aerospace or automotive components.

Gating and ejector pins are a necessity for plastic resin to strategically enter the mold and plastic parts to effectively be ejected from the mold. We've learned from experience that there are several ways to gate or eject your part, and the locations should be considered before you are ready to proceed with tooling.

Sharp corners have high-stress concentration and plastic flow is hindered. Rounded corners have reduced-stress concentrations and plastic flow is enhanced.

You can minimize all of these concerns through a core-cavity approach. This design technique requires the outside and inside walls to be drafted so they are parallel to one another. This method keeps a consistent wall thickness, maintains the part integrity, improves the strength and moldability, and decreases the overall manufacturing cost.

When budget is a primary concern, polystyrene is often the most recommended plastic material; however, it is not ideal for products that require strength. For this reason, it is often used to create Petri dishes and food packaging products that are designed for single use. Unlike other materials, polystyrene also provides limited heat resistance and breaks relatively easily compared to other plastic materials that are available at a higher price.

Direct sprue gates are the least appealing and are used with specific materials that have a high glass content or where the middle of the part requires secondary machining. Direct sprue gates have a large diameter that is difficult to manually remove and often times require a fixture that is removed by milling.

Sub gates are generally used by incorporating a tunnel gate into the side of the part or into an ejector pin (post gate). Both gate styles generally can decrease the size of the vestige left on the exterior of the part. Tunnel gates still enter the part externally, but are mid-way down a parts surface, so they typically leave less of a gate vestige. Post gates leave no visible vestige on the exterior of the part as the part fills through one of the ejector pins close to the perimeter of the part. The risk is the cosmetic shadow left on the opposite side of the part due to heat and part thickness. So, be cautious when using this for highly cosmetic parts that have texture or a high polish.

Tab gates are most commonly used as they offer a mold technician the optimal processing capabilities and have the ability to be increased in size if the process requires it. A tab gate is tapered down in size from the runner, so the smallest point is at the part's surface. This allows a freeze point between the part and runner removing the heat from the surface of the part. You want the heat removed from this surface to minimize any risk of sink in the part. After molding, the tab gate needs to be manually removed leaving a gate vestige within 0.005 in.

Tough Black (Loctite Henkel 3843) and Ceramic-Filled (BASF 3280) are two new advanced photopolymer materials now available for 3D printing.

Radii on the other hand isn't a necessity for injection molding, but should be applied to your part for a few reasons—eliminating sharp corners on your part will improve material flow as well as part integrity.

Controlling wall thickness during part design helps manage cosmetics, weight and strength of your part. Parts that are too thick result in unsightly sink, warp and internal voids (pockets of air). To avoid this, materials have recommended wall thickness guidelines—remember this is only a general rule as not all parts may have wall thicknesses at the high and low ends indicated on the chart.

Let's begin by coring out your thick part, which will still retain the overall height and diameter of your part without necessarily sacrificing performance. There's a good chance you'll increase the part's performance and cosmetic appearance, too.

In cases that are not adaptable for side-actions, we can use manually removed inserts. These are mold components that are greater than a half-inch cube and are loaded by an operator into the press before it closes. After the part has been molded, the part is ejected along with the insert. The operator then takes the part and manually removes the insert and places it back into the mold for the next part.

One of the most striking characteristics of acrylic is the ability to closely mimic glass. As you might imagine, this makes it an excellent plastic material choice for applications such as display cases or sunglasses. Since acrylic has a high hardness rating, it also retains scratch-resistant properties and is typically highly resistant to breakage. Other applications in which acrylic may be a suitable choice include medical devices, security barriers, or LCD screens.

Get machined parts anodized and chromate plated with our quick-turn finishing option. Eligible materials include aluminum 6061/6082 and 7075.

Hot tip gates work well as they have minimal part waste from sprue and runner systems. A hot tip is best for parts that require a balanced fill from the center to the outside edges. This minimizes any mold shift as tab gates can create an unbalanced pressure in a mold. Hot tip gates are often the most cosmetically appealing gate (about 0.050 in. diameter) and often times can be hidden in a dimple or around a logo or text.

Let's say you're designing a simple box. When draft is applied to the outside and inside surfaces in the same mold half, you create a very deep rib that is difficult to manufacture and increases tooling costs. It also increases the chance of mold damage due to difficult ejection and short shots due to lack of mold venting in the deep rib.