Exploring Resin Injection Molding: Unleashing Possibilities

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The application of resins in plastic manufacturing has paved the way for various tools and materials one of which is resin injection molding. These tools have been crucial to several industries, if not all industries in satisfying human needs. In any case, resin injection molding being employed by plastic manufacturers has unlocked endless possibilities in the plastic manufacturing world. 

resin injection molding

And with that, engineers and designers are allowed to create and manufacture complex parts with quality features such as durability, longevity, and optimal functionality. Resin injection molding also comes with design flexibility, amazing part consistency, and efficient production as part of the package. So, fasten your seatbelts as we take a ride into the endless possibilities resin injection molding offers using injection molding machines. 

1. Understanding Resin Injection Molding

Knowing what is entailed in a technical production process like resin injection molding is the first step in understanding the entire process. Let’s begin with an overview of the resin injection molding process.

1.1 Overview of Resin Injection Molding Process

Don’t be surprised at the kind of questions that an enthusiastic mind often asks. Questions like Can plastic make strong hard parts? 

The answer lies within the context of our subject matter for this piece. Resin injection molding harnesses the ability to make such hard and complex parts. It entails the injection of melted resins with adequate pressure into mold cavities that solidifies and voila, there goes your hard, intricate, high-quality part. 

But before this enormous success can be achieved, there are steps crucial to it. First a suitable resin with qualities suited for the required project such as material properties and volume of the part to be produced determined. Then the resin is cleaned and dried of every moisture present, and kept at a temperature suitable for melting, before melting in the barrel. 

Once these steps are completed and the resin melted, it is injected with controlled pressure into the mold cavity where it takes the form of the desired part. Curing takes over from there and the mold is solidified. Ejecting the part from the mold prepares it for post-processing such as surface finish and trimming wherever necessary if at all, then shipment to their respective applications.

1.2 Advantages of Resin Injection Molding

The benefits resin injection molding offers are the best part of this method of plastic production. Remember when we said resin injection molding unleashes a world of possibilities, that’s the first benefit right there. It unleashes a world of creative and imaginative designs to engineers and part designers alike. Complex dimensions that seem impossible to other methods of production are made possible with resin injection molding. Concepts that may have been thought unimaginable and unachievable. 

To further buttress the first advantage, resin injection molding creates parts with an impressive surface finish. This eliminates any need for post-process activities and makes the parts attractive and appealing to the eyes. For parts that require excellent fit and functionality that boosts the part’s performance, look no further than resin injection molding. It’s no wonder many industry professionals seek parts produced by resin injection molding. 

As part of its benefits, resin injection molding is budget-friendly, faster in production cycles, and reduces the wastage of materials used in production, unlike other conventional methods. Its ability to produce small to medium quantities makes it the best option for prototyping, part customization, and low-quantity productions.

resin injection mold

2. Applications of Resin Injection Molding

Where resin injection molding is applied gives another level of understanding especially regarding its limitation and the level of possibilities it offers the high-quality mold manufacturing industry. Here are the most popular applications of this innovative plastic production material. 

2.1 Automotive and Transportation

It is not surprising to find resin injection molded parts in this industry. The interior parts and some of its structural parts are parts that require less weight yet strong parts. Interior parts such as the dashboard panels, door handles, and arm and head rests, are all made with resin injection molded parts. All thanks to the ability of resin injection molding to produce durable, versatile, weightless, and strong parts. This, in turn, assists in assembling fuel-efficient, excellent-performance, and less heavy automobiles that offer convenience to their users. Some structural parts such as brackets that help with the functionality of automobiles are manufactured by resin injection molding. 

On top of that, aesthetics, and functionality, which is the focal point of this industry, is enhanced. Resin injection molding permits engineers and designers to open their minds to imaginative ways of creating beautifully crafted and assembled automobiles. With features that increase the user experience of consumers yet are appealing and eye-catching to them. Yet you wonder why car lovers can boast of their car’s performance capacities, safety, and aesthetics. The next time you are in an automotive and transportation assembling facility, you can check out resin injection molded parts and feast with your eyes.

2.2 Consumer Electronics and Appliances

The records have it that over eighty percent of parts manufactured in the consumer electronics and appliances industry are made with resin injection molding. That alone tells of the importance of resin injection molding to this industry. Precision and functionality are the names of the games in this industry and especially in high-quality mold manufacturing which are crucial tools for this sector. With precise dimensions and functional components, resin injection molding has made its mark in this sector. With resin injection molding, designers and manufacturers are able to build and produce electronics such as casings, covers, and other appliances used domestically. In addition, resin injection molding empowers professional designers to incorporate seemingly difficult interlocking-like designs in electronic products. These designs can be complex, but their degree of functionality is spectacular. Even so, the capacity to incorporate these designs simplifies product assembling and optimal performance. 

A noteworthy contribution of resin injection molding to consumer electronics and appliances is in aesthetics. The ability to produce exceptionally smooth and top-quality products is outstanding and appealing. It screams professionalism and authenticity. The accuracy in detailing electrical parts such as smartphones, and household electrical appliances is captivating enough to make consumers acquire them at the mere sight of them. The outstanding innovative and flawless craftsmanship can only be matched by advanced methods like high-quality CNC Machining which are more expensive and slower than injection molding.  

2.3 Medical and Healthcare Devices

The medical and healthcare industries aren’t taking a backseat either. Resin injection molding meets the three most important benchmarks for producing medical devices. Precision, biocompatibility, and reliability of medical equipment, and these are all parameters duly served by resin injection molding. Medical tools such as drug delivery instruments, surgical tools, and medical device casings are some of the products resin injection molding methods have been deployed in making. The precision devoted to creating medical tools using the right resins makes medical products exceptional with super meticulously crafted dimensions. Not just that, the textured surfaces precisely fashioned enhance their capacity to function optimally. 

Biocompatibility fosters the completely safe interaction of the resin injection molding component with the human body. The level of safety of the human body is not taken lightly, hence the strict compliance to use industry-certified medical tools. Resin injection molding has consistently delivered top-standard medical and healthcare devices amongst other medical tools. All medically approved tools manufactured with resin injection molding are produced at the lowest cost. And for that reason, its cost-effectiveness did not diminish its value.

3. Material Selection for Resin Injection Molding

The failure or success of a production procedure such as resin injection molding often starts with the material selection process and criteria. Here are the most important considerations for selecting resin material for injection molding. 

3.1 Thermosetting and Thermoplastic Resins

In the adoption of resin injection molding in plastic production of various materials, one of the most crucial stages of this method is where we are now. That is the selection of the appropriate material for this process. There are two commonly deployed types of resins, each with their particular properties. Thermosetting and thermoplastic resins are the two categories of resins utilized in resin injection molding. Epoxy and phenolic resins are perfect examples of thermosetting resins. 

They offer strength, and high chemical and heat-resistant features. This is because they undergo a chemical reaction phase during solidification that permanently makes them tough and long-lasting in harsh conditions. These types of resins, when subjected to severe temperature, thrive, and even ensure the stability of their intricate parts. For instance, applications that require stealth and stability, are your best choice for getting these high-quality results. 

Thermoplastic resins, on the other hand, provide a high moldability rate as they are easily softened under intense heat temperatures, and solidify when in a cool temperature. These features enable easier and faster processing, flexibility, and impact-resistant results. Examples of such resins include polycarbonate (PC), polyethylene (PE), polypropylene (PP), and many other types. Its ability to be easily melted and solidified through cooling promotes recyclability. 

3.2 Material Compatibility and Processing Parameters

Material compatibility comes with understanding what material to use for different projects and what material can accomplish certain process parameters. It also determines if other manufacturing technologies like 3D printing technology might be suitable. Although both factors are essential to creating functional and quality products, the compatibility of a material to its mold must be considered. Consequently, improper material compatibility makes room for part defects, mold degradation, or deformation, which in turn impacts the quality and functioning of the part.

Additionally, process parameters entail the steps that directly affect the outcome of the parts produced. They include injection speed, temperature, and pressure. The processing parameters for each resin differ, this is why the strict compliance with directives and guidelines on the application of each resin must be duly complied with to avoid complications such as inadequate flow or incomplete cavity filling. Should there be any need for post-curing processes, this must be meticulously executed for resins to reach their maximum efficiency and capacity. Post-curing steps may include thermal subjection to required conditions to enhance the structural integrity, chemical resistance, and geometrical accuracy of the part. These are prerequisites to selecting the best resin for your project requirement, and with such knowledge, there isn’t going to be a wrong selection. 

resin injection diagram
Source: https://upload.wikimedia.org/wikipedia/commons/f/f3/Schnitt_dosierkopf.png

4. Design Considerations for Resin Injection Molding

Getting the best result from resin injection molding is hinged on specific design considerations. These design considerations will serve their best purposes if carefully considered and adhered to. 

4.1 Part Design Guidelines

  1. Wall thickness: it is crucial to maintain consistent wall thickness to achieve steady filling of the mold. Consistent wall thickness results in proper material flow and enhanced part integrity. Uneven wall thickness leads to warping and sink marks.
  2. Draft angles: The inclusion of draft angles in part designing permits easy and safe removal of the part from the mold without damage to either. Draft angles required per part produced are 1-3 degrees, although this is dependent on the complexity of the part and the material used.
  3. Undercuts: to eliminate or reduce undercuts, integrating side actions or sliders would be appropriate. Undercuts make part ejection arduous and can increase production costs because secondary operation might be necessitated. However, minimizing undercuts streamlines mold design, and increases part uniformity.
  4. Gating locations: the point of entry for the resin needs to be strategically placed, this is so that issues such as irregular flow of the resin into the mold are prevented, such occurrence can result in irregular filling and air traps.

Designing for moldability also entails considering the resin’s flow characteristics. This includes ensuring regular wall thickness, reducing sharp angles, and the complexity in design. With all these factors observed, flow characteristics and moldability will be optimized.

4.2 Mold Design and Tooling

When it comes to mold design and tooling, specific considerations should be examined. These factors ensure the efficiency of resin injection molding if observed. These considerations include.

  1. Mold materials: The selection of mold material should typically be based on material features, temperature differences, and injection pressure. Common mold materials remain aluminum and steel alloys, and it is usually picked based on the complexity of the part, the volume of the part, and the quantities to be manufactured. 
  2. Cooling systems: The mold’s cooling system can either increase or shorten cycle times. Manufacturers will mostly prefer shorter cycle times, and with an effective cooling system that regulates the temperature of the mold, cycle times are likely to be less, consistency in part is guaranteed, and production efficiency is boosted.
  3. Venting: Integrating a functional venting system in the mold allows the escape of air or gas that may likely be trapped during resin injection molding. If air gets trapped in the mold, it will cause defects in the part. And that is possibly going to impair the performance and functionality of the part. 

Mold makers and designers can combine collaborative efforts in ensuring the mold as a tool is efficient to enhance resin injection molding and also reduce cycle times thereby improving production efficiency.


In a nutshell, exploring the world of resin injection molding has been insightful, examining the design possibilities it offers while being cost-effective. Resin injection molding permits designers to tap into their imaginative ideas to bring to life nearly impossible feats. With applications ranging from the automotive industry to medical and electrical industries, it has become a viable option for manufacturers and users of parts produced by resin injection molding being the biggest beneficiaries. Furthermore, thermosetting, and thermoplastic resins are the most suitable materials for resin injection molding, not forgetting the compatibility and processing parameters that make them the best option for this process. Conclusively, complying with part design guidelines and the collaboration between mold makers and designers, resin injection molding will leave you wowed with the kinds of products it can manufacture. 


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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