The Fundamentals of Injection Molding Design


Whenever molding plastic parts comes up in any conversation, injection molding is also bound to be mentioned in the same conversation. That begs the question of what is injection molding, especially for newbies and enthusiasts. Simply put, injection molding is the plastic part production technique you employ when you seek to manufacture high-volume quality plastic parts. If you’re wondering how it does that, this can be accomplished merely by utilizing a multi-cavity injection mold which allows it to manufacture multiple identical plastic parts in every production cycle. This gets even more interesting, but we’d like to show you how it is so if you’ll journey with us on this exploratory course.

Custom Injection Mold

Section 1: Understanding Injection Molding

Injection molding machine manufacturers

Continuing our discourse on injection molding, it is imperative to understand the mechanics of injection molding which eventually leads us to its applications. Many industries that are the end-users of plastic parts are usually concerned with specific aspects. A little hint into such concerns includes the form and function of what their desired part should offer, and with that in mind, it is the reason why injection molding thrives. The quality plastic parts injection molding provides is why industries such as automotive, medical, consumer goods, packaging, and even electronics trust it both in form and performance. Take a quick survey of your environment and you’ll notice a whole lot of plastic products that are the result of the success of injection molding. From plastic containers to door handles on your cars, injection molding has served dutifully these industries in their application of plastic parts.

What’s even more intriguing is the injection molding process. These steps are a carefully curated demonstration that ends with the brilliant engineering of some outstanding plastic parts. Although it may seem a little complex, with dead-set compliance to certain conditions it becomes seamless. The injection molding process is preceded by carefully preparing the plastic pellets to meet melting conditions. Once prepped, these plastic pellets are transferred from the hopper straight into a barrel where it heated and melted. When melting is completed at the right temperature, the resulting molten plastic is pushed through into the mold where the formation of the desired part begins. Since the mold carries the template for the intended design of the plastic part, the injected molten material begins to take form once the material enters the mold. In addition, maintaining a regulated temperature ensures the efficient cooling and solidification of the molded part within the mold. Ejecting the part completes the process.

Section 2: Guidelines for Material Considerations

Mould Cost 3

Injection molding materials are like ingredients in a chef’s spectacular recipe, with each adding its unique quality according to the flavor it possesses. The same can be said of the materials employed in injection molding. In light of this reality, each material’s individual quality must be examined for its unique qualities before selection is made. Nonetheless, let’s consider the uniqueness of these materials.

Polyethylene: is a durable plastic material that is very convenient to choose for the manufacturing of plastic containers and pipes. This unique plastic material is highly chemical resistant. That makes it able to endure harsh environments that deal with chemicals.

Acrylonitrile Butadiene Styrene: this material, popularly known as ABS finds its purpose in manufacturing components like electronics and automotive parts production. this material is very rigid yet soft to handle. What distinguishes ABS from other materials is its impact resistance and chemical resistance qualities.

Polypropylene: This material, commonly referred to as PP joins the league of extraordinary plastic materials by offering an impressive melting point, and like its other counterpart an outstanding chemical resistant quality. Its versatility is witnessed in numerous industries.

Polyethylene Terephthalate: Manufacturers looking to produce packaging materials, bottles, and containers often use a strong but lightweight material. This is what PET as a plastic material offers.

Polycarbonate: The biggest beneficiaries of these materials are manufacturers of medical and electronic devices. That is because polycarbonate (PC) possesses transparent qualities that are efficient in the manufacturing of eyewear and electronic gadgets.

These highlighted materials all offer similar or variant properties, all requirements for manufacturers to select from for various projects. From tensile strength to flexibility and finesse, these materials ensure that the concerns of their various applications from end users are adequately answered.

Section 3: Design Principles for Injection Molding

Mold Manufacturing Computer Aided Design

Injection molding projects are heavily reliant on design principles. Manufacturers design components applying efficient and budget-friendly ways. For that reason, a Design For Manufacturability analysis is conducted to effectively analyze the part’s components that may increase the costs of production. The DFM analysis also helps to find ways of optimizing the process to guarantee efficiency and part quality, that way the need for post-processing is eliminated. Some of the part qualities to consider under DFM include the part’s dimensions, draft angles, chosen material, and wall thickness.

For instance, the existence of undercuts can undermine the quality of the part by making ejection difficult and in turn create post-processing practices. To combat this issue, the adequate application of draft angles will ensure ejection is seamless, the quality of the part is maintained, the cost of post-processing is no longer needed, and the production process is efficiently simplified. In addition to applying precise draft angles under DFM, another noteworthy design principle is a consistent wall thickness. Inconsistent wall thickness impairs the performance of the component by allowing warping in the component’s structures. However, maintaining equal wall thickness is paramount as it ensures the mold filling is perfect and the performance of the molded part, is excellent.

Section 4: Mold Design Essentials

Metal Injection Molding Design 2

Designing the mold is the most essential aspect of injection molding. The mold itself is responsible for forming the shape of the desired part. Consequently, designing the mold must be a meticulous process that encompasses all necessary features that account for part quality and part efficiency. The mold’s features that require detailed attention include

Gate Placement: The proper placement of the gate, that is, the gate design ensures that the injection of the molten material flows evenly. The gate design not only ensures the uniform distribution of materials but also maintains perfect part formation void of flaws and defects.

Mold Cavities: The mold’s cavities account for the number of parts that can be molded per injection molding cycle. The more cavities in the mold, the more complex it becomes, and likewise the higher the cost.

Cooling System: The function of the cooling system in mold design cannot be understated. This is because the cooling system plays a crucial part in the solidification of the injection molded part. With proper regulation of temperature, the component is allowed to solidify and cool efficiently.

Ejection System: As earlier mentioned, the presence of undercuts hinders the easy ejection of the molded part, hence the inclusion of draft angles. This does not only remove the part easily, it avoids damage to the molded part as well.

Section 5: Avoiding Common Design Mistakes

Plastic Product Design

In a bid to attain perfection, there can be a few hiccups on the way. These hiccups do not undervalue the bonuses injection molding proffers as there are solutions to these setbacks that help put them right back on track to perfection. With that said, let’s examine a few common errors that are bound to show up in injection molding, either self-inflicted or due to natural occurrences.

Material Selection: There’s a reason selecting the right material takes the topmost spot. This is because choosing the wrong material leads to defects and higher production costs. It is a common mistake that proves a nightmare to manufacturers, thus, they avoid making such errors at all costs. Material selection going wrong also veers into chemical resistance, brittleness, and abysmal surface finish. Selecting the right material on the other hand ensures the injection molded component meets industry standards and customer satisfaction.

Wall Thickness: Thin-walled molded parts can result in deficiencies such as warping weak structures, and sink marks. This is why designers and engineers are required to maintain thick walls all around for durability and sturdiness, while judiciously applying the materials.

Draft Angles: Injection molded parts without infusing draft angles always end up with sink marks, damage to the part, or being stuck in the mold. These possibilities only lead to two outcomes, the first is the production time increases and secondly, the cost of production is increased. It is no surprise why designers integrate draft angles into the mold design.

Ribs and Bosses: A common mistake that tends to affect injection molding is the improper design of ribs and bosses. The ribs cannot be too thick and the bosses cannot be too large. Placing both ribs and bosses at the right location and in the right size will guarantee your injection molded part is phenomenal.

Section 6: Advanced Design Techniques

Mold DesignInjection molding has undergone some advancement courses and the culmination of these advancements presents us with additional modes of molding, Insert molding, and Over-molding. Both advanced injection molding methods have similar yet different techniques. But both provide us with an improved and aesthetically pleasing molded part. Then what are insert molding and over-molding techniques?

Insert molding: For insert molding, its name already gives it away. Insert molding entails the placement of an insert, typically a pre-molded part in a mold before injection molding molds around the insert. Usually, the inserts are metallic, and it envisions the combination of both rigid and flexible materials to form a wholesome component. Imagine the marriage between a metal insert and a flexible plastic material molded together. That’s how some of your electrical connectors, medical gadgets, and automotive parts are molded.

Over-molding: Over-molding on the other hand, merges two or more materials to form a softer, stronger, and more durable component. Most times over-molding is adopted in creating power tools or consumer products that encourage user-friendly components. Over-molding apart from creating aesthetically pleasing parts also ensures improved functionality.

Injection molding gives birth to a twin more advanced method of molding that improves product quality, provides excellent performance, and eye-catching components. isn’t that brilliant?


As we draw the curtains, it is essential to give injection molding a huge shout-out for its immense contributions to the plastic manufacturing world. Injection molding finds its applications across several industries with reliable and impressive performing components, employing innumerable types of quality plastics in achieving this engineering feat. On that account, several design considerations must be adhered to if we’re to get the best of the phenomenal plastic part manufacturing technique. What’s more, it blesses us with a set of twins in insert molding and over-molding.

Conclusively, there can be mistakes such as neglect of draft angles, wrong choice of material, and inconsistent wall thickness, but they are adjustable errors that offer unimaginable results. So, trust the process.