• Skip to main content
  • Skip to header right navigation
  • Skip to site footer
SyBridge Technologies

SyBridge Technologies

Bridging the gap between innovation and mass production

  • Capabilities
    • Design & Engineering
    • Rapid Prototyping
    • Tooling
    • Advanced Manufacturing
    • Supportive Injection Molding
    • Reliability Services
  • Technologies
    • 3D Printing
    • Urethane Casting
    • CNC Machining
    • Injection Molding
    • Manufacturing Intelligence
    • SyBridge Connect
  • Industries
    • Life Sciences
    • Health & Beauty
    • Consumer Products
    • Aerospace
    • Mobility & Industrial
  • Resources
    • Material Selector
    • Press Room
    • Knowledge Center
    • Events
  • About Us
    • Evolution
    • Sustainability
    • Careers
  • Contact
    • Locations
Home / Resources / 5 Design Tips for Injection-Molded Parts With Complex Features

5 Design Tips for Injection-Molded Parts With Complex Features

February 18, 2021 by SyBridge Technologies
Injection molded part

Originally published on fastradius.com on February 18, 2021

Design for manufacturability (DFM) is the general practice of designing parts so that they are also efficient to produce. While specific best practices vary by manufacturing technology, the ultimate goal of DFM in general is to optimize part design so as to minimize the manufacturing costs — without sacrificing on performance or function. DFM also helps you identify potential issues or defects early and avoid disruptive re-designs down the line, which is why assessing possible manufacturing methods is crucial during the initial design and prototyping phases.

Intentional, method-focused design is especially important when attempting to produce parts with complex geometries or intricate features. And while there are many viable manufacturing methods for producing parts with complex geometries, injection molding is among the most common.

DFM is especially important for injection-molded parts, as the hard tooling and molds used to create injection-molded parts introduce a number of variables that may impact design — including mold temperature, material temperature, and air pressure. What’s more, injection molds are expensive and time-consuming to tool, and the process typically only becomes cost effective when producing parts in high volumes, so consistency and repeatability are critical when designing parts with complex geometries or intricate features.

Here are 5 key tips for how to design plastic injection molded parts with complex features.

1. Take advantage of sliding shutoffs for clips and snap fits

Clips and snap fits are two forms of fastening mechanisms that can be incorporated directly into the injection mold design — a few common examples being tool set lids and electronics housings. Both operate similarly: on one side of the mechanism, a flexible tab of material catches on a slot or pocket in the mating part, thereby securing the two.

Sliding or telescoping shutoffs are components machined into one side of the mold that extend into the other half, sliding into place when the mold is closed. This prevents material from flowing into particular areas, which makes it possible to easily incorporate features like hooks and holes (including long through-holes) without the need for expensive side actions, bumpoffs, inserts, and other features that increase the cost and complexity of the mold design.

Sliding shutoffs can be designed to have the same tab and slot to match the part’s clips and snap fits, creating features that fit together securely and retain enough flexibility to pull apart without breaking. Shutoffs can reduce mold design and operating costs and also generally be used as a workaround for undercuts and recessed features.

In general, both the part and mold should have a minimum of 3 degrees of draft to prevent metal from rubbing against metal, which can create flash and damage the shutoff.

2. Choose the right material for living hinges

Living hinges, another flexible lid feature, are an excellent way to attach the two halves of injection molded plastic components (think of the lids on the individual containers of a weekly vitamin dispenser, for instance).

While material consideration is always a critical consideration in design and product development, it should be your primary concern when designing living hinges. Polypropylene, for instance, is better-suited for this feature than polycarbonate (which can be an excellent material for clips and snap fits). Depending on the range of motion that’s expected of the lid, you may need to incorporate a radius at the hinge’s midpoint to allow the two parts to close more easily.

3. Keep an eye on wall thickness

Wall thickness should remain uniform whenever possible, as variations in thickness can introduce serious complications. Parts with non-consistent wall thickness are at risk of warping (caused by different sections of the part cooling at different rates, which creates internal stress that bends the part permanently).

Variations in wall thickness
 Variations in wall thickness, like this example, can lead to sink marks, voids, and warping.

Furthermore, if the walls of a part are overly thick or thin, further issues may arise. For example, thin walls and poorly designed support ribs can impede flowability, causing short shorts (or incomplete mold fills). On the other hand, parts with thick walls and poorly designed ribs are prone to developing sink marks, or impressions on the surface of the part caused by the interior resin cooling faster than the exterior material. If you see signs of either flaw, it might be time to reexamine your mold design.

4. Add draft and reduce the height of tall features

Tall features like bosses, ribs, and standoffs may require you to incorporate greater draft angles (generally up to 3°) to ensure the part leaves the mold without drag lines or other ejection issues. Bosses and tall features allow for threaded inserts and additional part strength, but they increase the risk of developing sink marks.

Furthermore, increasing the height of ribs and other features likewise increases the depth of the mold, increasing the need for longer end mills, more venting, and slower cutting rates during the machining process. One way to work around this is to support bosses with peripheral vertical ribs, which have thinner walls, reducing the chance of sinks.

safe minimum draft
1.5-2 degrees of draft is typically a safe minimum for most parts.

Angled bosses and other features increase the complexity of production, as the axis of the boss no longer aligns with the parting line or the line of pull — which all but necessitates that an insert will need to be manually loaded into the mold before each shot.

5. Be strategic about text and logos

Text (such a product or company name) or logos are commonly added to injection molded products. The good news is that small font sizes are actually fairly easy to achieve through injection molding — so long as you follow a few key guidelines.

First, text should be a sans-serif font and the shortest stroke length (the crossbar of a T or a A, for example) must be at least 0.020” in length. Raised text is easier to read and to produce than text sunk into a part’s surface. Unless the text is inordinately large, it should not be more than 0.015” tall.

Finally, unless you’re working with flexible materials like silicone rubber or thermoplastic elastomer (TPE), text should face the direction of pull if possible — otherwise, manually loaded inserts or side actions might be necessary in order to ensure smooth ejection.

Start refining your injection molding design today

Complex geometry and a high degree of feature complexity aren’t the end of the world for injection-molded parts. By paying attention to key design factors like mold design, material selection, boss orientation, and text style and size, you’ll be able to improve your part’s manufacturability (and therefore cost-effectiveness) and quality at the same time.

Of course, partnering with an experienced manufacturer is another surefire way to streamline the design and production phases of product development. SyBridge brings decades of engineering and design experience to the table, and we work diligently alongside every customer to ensure that your parts are not only made well — but that they’re made in the most efficient and cost-effective way possible. Contact us today to find out how we can make your designs a reality.

Category: Knowledge CenterTag: Injection Molding

Related Articles

How SyBridge Expertise Optimizes Your Process and Lowers Costs

Polyoxymethylene (POM), more commonly known as acetal or its branded name Delrin®, is an engineering plastic offering low friction, high stiffness, and excellent dimensional stability. Polyoxymethylene is a category of thermoplastics and includes many different formulations of the material, all of which vary slightly. As such, it’s important to learn as much as you can about each type before choosing one for your next project. Delrin® is a semi-crystalline engineering-grade thermoplastic widely used to create highly precise parts. In general, Delrin® provides impressive dimensional stability and sliding properties. It’s known for its high strength, wide operating temperature range (-40°C to 120°C), and excellent mechanical properties. Here’s everything you need to know about this material, from how it’s made to its best-fit applications. Inside the polyoxymethylene production process Acetal was first discovered by German chemist Hermann Staudinger in 1920 before it was commercially synthesized by research chemists at DuPont, the original manufacturers of Delrin® plastic, in 1956. Like all other plastics, acetal is created by distilling hydrocarbon fuels down into lighter groups called “fractions,” which can then be combined with other catalysts via polymerization or polycondensation to produce a finished plastic. To make an acetal homopolymer like Delrin®, anhydrous formaldehyde must be generated by causing a reaction between aqueous formaldehyde and alcohol to form a hemiformal. The hemiformal is then heated to release the formaldehyde, and the formaldehyde is polymerized by anionic catalysis. The resulting polymer is stabilized when it reacts with acetic anhydride, which creates polyoxymethylene homopolymer. Acetal comes in many different commercial varieties and formulations, each with its own advantages and disadvantages. For example, Delrin® 500 is medium-viscosity, all-purpose polyoxymethylene that has a good balance of flow and physical properties. It can be used to produce parts via CNC machining and injection molding and is frequently used to manufacture mechanical parts, fuel systems, and fasteners. Delrin® 1700P, on the other hand, is a very low- viscosity, fast-molding resin that is best suited for parts with complex shapes, thin walls, long flow paths, or multi-cavity tools. It also offers the best molding thermal stability for deposit-free molding in demanding conditions. Since there are dozens of different formulations of acetal, it’s important to do your research and make sure your prospective plastic offers all of the properties you need for your application. Delrin® plastic properties and mechanical specifications small black Delrin pieces Delrin® can also be found in all-purpose industrial equipment like bearings, gears, pumps, and meters. Acetal’s excellent mechanical properties make it extremely versatile, offering a unique blend of properties that you won’t find in most metals or other plastics. Delrin® plastic is strong, rigid, and resistant to impact, creep, abrasion, friction, and fatigue. It’s also well known for its excellent dimensional stability during high-precision machining. Acetal can also stand up to moisture, gasoline, solvents, and a wide range of other neutral chemicals at room temperature. From a design standpoint, parts made with extruded POM naturally have a glossy surface finish. Since acetal is compatible with CNC machining, injection molding, extrusion, compression molding, rotational casting, and more, product teams are free to choose the manufacturing process that works best for their budget and their needs. However, it’s worth noting that Delrin® plastic is typically very challenging to bond. Acetal material properties vary by formulation, but the mechanical properties for Delrin® 100 NC010, one of the most popular formulations, include: Tensile modulus: 2900 MPa Yield stress: 71 MPa Yield strain: 26% Density: 1420 kg/m3 Charpy notched impact strength, +23°C: 15 kJ/m2 Coefficient of linear thermal expansion, normal: 110 E-6/K Water absorption: 0.9% Delrin® does have a few limitations. For instance, even though Delrin® is resistant to many chemicals and solvents, it’s not very resistant to strong acids, oxidizing agents, or UV radiation. Prolonged exposure to radiation can warp the color and cause the part to lose its strength. Also, this material isn’t readily available in a flame-retardant grade, which limits its utility for certain high-temperature applications. Why choose Delrin® plastic? These limitations notwithstanding, there are many reasons to choose acetal over other materials. When compared to other plastics, acetal offers better creep, impact, and chemical resistance, better dimensional stability, and higher strength. It also has a lower coefficient of friction. Acetal outpaces certain metals as well. Parts built with this material have a higher strength-to-weight ratio, better corrosion resistance, and offer more opportunities for part consolidation. You can build thinner and lighter parts faster and at a lower price point with acetal than with a comparable metal. Delrin® plastic can be found in almost every major manufacturing sector. In the automotive industry, common applications include heavy load-bearing gears, fuel system components, loudspeaker grilles, and safety system components like seatbelt hardware. Delrin® can also be found in all-purpose industrial equipment like bearings, gears, pumps, and meters. In the consumer goods and appliances space, this material can be used to make anything from zippers and pens to knife handles and lawn sprinklers. Getting started with Delrin® There’s a lot for product teams to love about Delrin®. It’s strong, stable, versatile, and its excellent mechanical properties make it a good choice for a wide variety of applications in a number of industries. However, with dozens of different formulations of acetal on the market, it can be very challenging to determine which one might be the best fit for your unique project. A seasoned manufacturing partner can help demystify the material selection process. When you partner with Fast Radius, you partner with a team of on-demand manufacturing experts who have years of experience helping product teams navigate material selection. We’re well-versed in the wide range of materials that can be used for both traditional and additive manufacturing — including Delrin®. Once you’ve selected the Delrin® formulation that’s the right fit for your application, our team of experts can help facilitate the entire manufacturing process — from design and prototyping to production and fulfillment. With a full suite of manufacturing services including CNC machining and injection molding, Fast Radius can bring your vision to life quickly and easily. Contact us today to get started.

Know Your Materials: Delrin (Polyoxymethylene)

Injection molding

What You Need To Know About Material Compatibility For Multi-Material Injection Molding

Injection molding

Is Multi-Cavity Injection Molding Right for Your Project?

Top 5 Impact-Resistant Plastics

Polystyrene

Know Your Materials: Polystyrene (PS)

Ready to discuss your next project?

Connect with an expert

We Bring Ideas to Life

  • LinkedIn
  • Facebook
  • Instagram
  • YouTube

Global Headquarters

265 Spring Lake Drive
Itasca, IL 60143 USA

info@sybridge.com

+1 (833) 824-1116

Copyright © 2025 · Return To Top

  • Legal Information
  • EULA
  • Terms and Conditions​
  • Accessibility​
  • Privacy Policy
  • Sustainable Purchases Policy