5 Must-Have Features in a plastic mold design company

Originally published on fastradius.com on February 18,

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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).

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.

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.

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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.

When it comes to manufacturing high-performance plastic parts, several things have an impact on quality and functionality ' think things like process parameters, material selection, and industry expertise. But one of the most essential things to get right is the mold design. With an expertly engineered injection mold design, manufacturers are better able to meet strict tolerances, maintain dimensional accuracy, and ensure part performance. How, exactly? Let's take a look at five essential tips for injection mold design that will help you create parts that not only meet but exceed performance expectations.

Tip 1: Prioritize Material Compatibility in Injection Mold Design

When conceptualizing and designing high-performance components, material selection is one of the most important factors that manufacturers must consider. The same can be said for injection mold design. High-performance polymers like PEEK are known for their exceptional thermal and mechanical properties. But the flipside of this advantage is that they require higher processing temperatures and pressures than standard plastics ' which means the material of the injection mold design itself must also be able to perform under these conditions.

And on top of that, the mold material must be able to withstand those conditions without degrading over time. If a manufacturer makes a poor choice for the material of the injection mold design, it could result in premature wear, corrosion, or even permanent damage, all of which can lead to unplanned downtime and higher production costs. To further combat this, high-temperature alloys, hardened steel, and specialized coatings are often required to maintain the mold's durability and ensure a smooth surface finish for the molded parts. Additionally, selecting the right surface finish helps optimize material flow and prevents issues like sticking or warping.

Tip 2: Optimize Gate and Runner Design for High-Performance Parts

During injection molding, how the molten polymer flows into the mold cavity directly influences part consistency, structural integrity, and defect minimization. That's why gates and runners are pivotal to the injection mold design. Proper gate and runner design help ensure that the polymer fills the mold evenly and efficiently, which is particularly important for complex, high-tolerance parts.

The choice between hot runners and cold runners is also essential when working with high-performance polymers like PEEK. Hot runners, for instance, allow for more precise control over material flow, reducing waste and enabling faster cycle times. Cold runners, on the other hand, may be better suited for simpler part designs.

And when it comes to the gates, location and size are everything; well-placed gates can help manufacturers avoid issues like sink marks, voids, and incomplete fills.  By optimizing both gate and runner design, manufacturers can enhance part quality, reduce defects, and improve material flow for more efficient and reliable production outcomes.

Tip 3: Precision Cooling Channel Placement for High-Tolerance Parts

Another essential element of injection mold design is the cooling system, which plays a critical role in determining both the quality of the components and the efficiency of the production process. Especially in the case of high-tolerance parts made from advanced polymers, precise control over the cooling phase is essential to avoid issues like warping, shrinkage, or internal stresses. If cooling is uneven or too rapid, it can result in dimensional inaccuracies or parts with compromised mechanical properties.

One way that manufacturers ensure uniform cooling is by using conformal cooling channels. These differ from traditional straight channels in that they follow the complex contours of the mold; this results in more consistent temperature regulation across the entire part. This element of injection mold design is particularly beneficial for high-performance thermoplastics like PEEK, which require high heat during molding but gradual and controlled cooling to maintain dimensional accuracy.

Effective placement of cooling channels not only reduces the risk of defects but also shortens cycle times and enables faster production without sacrificing precision.

Tip 4: Optimize Injection Mold Design Features to Handle Shrinkage and Warpage

Shrinkage and warping are common concerns when working with high-performance polymers. To address these issues, the injection mold design must incorporate specific design features that anticipate and manage shrinkage during the cooling phase.

Ribbing, for example, is a feature that helps reinforce areas prone to warpage which can reduce the chances of deformation. Similarly, incorporating draft angles and ejector pins can help ensure an easy ejection of the completed part, reducing the risk of damage. All of these features work together to allow for more predictable shrinkage behavior to ensure the final part meets specifications.

Tip 5: Ensure Mold Durability and Longevity for High-Performance Materials

And finally, it's vital that the injection mold design accounts for the stresses that will be placed on it throughout the injection molding process. As we've established, these pressures can be significantly greater when working with high-performance plastics.

In order to achieve the necessary durability, manufacturers sometimes turn to hardened steel for mold cavities, which can withstand the wear and tear associated with processing high-performance polymers. Specialized coatings can further enhance the mold's resistance to high temperatures and reduce friction, extending the lifespan of the mold.

Investing in robust injection mold design doesn't just ensure longevity ' it also maintains consistent part quality throughout high-volume production. By prioritizing mold durability, manufacturers can minimize downtime, reduce costs associated with repairs and replacements, and provide a more efficient and reliable production process.

Ensinger Specializes in High-Performance Plastic Part Production

At Ensinger, our speciality lies in high-performance injection molding and we're well-versed in the science of an optimized injection mold design. In business since , we provide plastic manufacturing services to a wide range of critical industries. Alongside our extensive injection molding capabilities, we also offer CNC plastic machining, post-molding services, and design and engineering assistance, amongst others.

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