How Does Injection Molding Work | From Concept to Product

Table of Contents

How does injection molding work it machine
How does injection molding work – its machine

1. Introduction

Products with Intricate and complex geometries have immensely benefited from the possibilities that injection molding offers. However, if you ask many individuals “How does injection molding work?” you’ll probably get a blank facial expression. 

The truth is that many of these people have never even seen where plastics are manufactured and it really doesn’t matter so long as the products work perfectly for them. But whether you know it or not, plastic injection molding is the manufacturing method that turns raw plastic materials into intricate products that have been very useful to our everyday existence.

Fortunately, this article is written for you if you are curious enough to want to find out what really makes the injection molding method tick. We’ll explore its pivotal role in shaping everything from everyday plastic parts to critical components for medical devices. So, if you’re ready, then let’s dive in.

2. Understanding Injection Molding

Now let’s get to the meat of the matter which is getting an overview of how injection molding does really work. While it has impacted several industries positively, injection molding is often associated with mass production among several benefits that it offers manufacturers. These benefits are highlighted below.

  • Precision at Scale: Despite being able to manufacture several thousands of plastic parts at a go, injection molding still ensures the precision of all of the parts making it highly sought after in many sectors.
  • Cost-Effectiveness: While the initial tooling cost can be significant, the long-term cost of manufacturing several components makes it a very cost-effective manufacturing method. This is especially true considering that it eliminates the cost of rework often associated with other methods.
  • From Concept to Reality: It is also an end-to-end manufacturing method allowing manufacturers to integrate it into their process right from conception through design to production.

So, there you have it. the modern wonder of the manufacturing world.

3. The Injection Molding Process

From conception to production, plastic injection molding encompasses several steps that are key to experiencing high-quality production and a precision-centered product. The components of this process are highlighted below with a breakdown of how they fit into the overall process.

  • Concept to Mold: The obvious starting point in the injection molding process is the conception stage where the blueprint is laid out considering the desired use of the product. Mold design and production using a high-quality mold manufacturing method follows the conception stage.
  • Material Selection: This stage is where the characteristics and functionality of the end product are considered along with choosing a suitable material that ensures the desired product emerges. Material properties such as strength, durability, and chemical resistance along with their cost implications are put into consideration.
  • Injection: Next is the release of the molten plastic resin into the mold through the use of pressure. These pressures along with the temperature of the molten plastic are essential to get a consistency that allows for appropriate flow speed and adequate infilling of the mold. Monitoring at this point is critical to ensuring a quality finish.
  • Cooling: The molten plastic injected into the mold has to cool to produce the desired product. Effective cooling is often crucial to achieve a high quality for the product which is why specific cooling-enhancing features like vents are strategically installed in the molds.
  • Ejection: Typically, the removal of the product from the mold needs careful consideration right from the mold design where ejector pins are designed to aid easy removal of the molded part. Sometimes, you may require the use of a release agent to ensure easy ejection of the product from the mold and to avoid any harm to the molded parts.
  • Quality Control and Testing: Ensuring the quality of the end product is often a deliberate act rather than luck. Specific quality management systems that include inspection and testing plans are put in place.
the mold
The mold

4. Step 1: Mold Design

Designing a suitable mold with thoughtful and quality-enhancing features is the first stage in the injection molding process. It is comparable to having an architectural blueprint of how the final production will look like. For this reason, the production of suitable molds for plastic parts is often dependent on the high-quality mold manufacturing industry. Below is a highlight of the specific factors that are critical to a perfectly designed mold.

  • Tailoring to Perfection: Attention to detail is a fundamental skill for mold designers considering that molds require a high level of detail and precision to deliver quality products.
  • Efficiency and Cost-Effectiveness: These factors are the hallmarks of the injection molding process as all production must be done efficiently without incurring unnecessary heavy costs. 
  • Iterative Process: The design is one aspect of the injection molding process that is often not achieved on the first attempt. It often requires some forms of iteration and repetition to arrive at a suitable design that fully captures the desire of the designer.
Plastic material for injection molding
Plastic material for injection molding

5. Step 2: Material Selection

Now is a good time to expand on the material selection stage of injection molding given that we’ve already hinted at its importance for the end product’s quality. Consequently, we’ve highlighted critical considerations to evaluate when choosing the best material for your injection molding project.

  • Versatility of Plastics: There are different types of plastics, each with its unique set of properties. Thankfully, injection molding works well with all these plastic materials based on their versatility. Nevertheless, consider each option carefully to select the one with the best set of properties that suits your project.
  • Application-Specific Choices: You also need to consider the specific needs of your project to ascertain the best plastic with a fitting characteristic. Each project will have its own unique specifications and these should determine your choice of material.
  • Cost-Effectiveness: Budget is often a critical consideration in any project including injection molding. Your choice of material should not break the bank despite having the best properties for your injection molding project.
  • Material Compatibility: Ensuring that the mold designs perform optimally requires a significant contribution from the materials used in the production. 
injection molding process
The Injection stage

6. Step 3: Injection

Just like other manufacturing methods like high-quality CNC machining, several factors are responsible for achieving the required precision specified in the design. The injection stage occupies a pivotal position in the achievement of this precision and crucial factors to consider at this stage are shared here.

  • Precision Injection: Melting the raw materials at the injection stage goes beyond just heating the pellets. Specific materials behave differently at different temperatures. Hence, you should understand the optimum temperature required by the plastic material to decide on the best temperature that will help you achieve precision during its injection.
  • Controlled Flow: The flow of the molten plastic in the mold is also critical to the accuracy of the whole injection molding process. You need to understand the flow of the specific plastic material employed and be able to control it appropriately to achieve the required quality.
  • Injection Speed: For the liquid plastic to achieve complete infilling of the mold the injection speed has to be adequate. This injection speed will eliminate the formation of certain defects in the product including air bubbles, flash, and discontinuities.  
  • Consistency and Repeatability: Lastly, you want to ensure that you achieve the right consistency with your mix and also be able to repeat the cycle with the same accuracy.

7. Step 4: Cooling

Melting the plastic material is the only way to get it into the mold. However, the mold’s retention of the molten plastic only lasts until it solidifies. This is where cooling comes in as it is the stage in the injection molding phase where the temperature subsides to reveal the injection molded parts. Some critical considerations for this cooling are also highlighted below.

  • Temperature Control: Regulating the temperature is actually the most crucial activity in the stage as the pliable material regains its solid state as the temperature reduces. Hence, the temperature control has to be systematic in line with the properties of the plastic material employed for the project.
  • Solidification: While the temperature control ensures a strategic reduction in the heat generated in the material the solidification also needs to be monitored to ensure the integrity of the product.
  • Cycle Time Optimization: With a balance of temperature control and cooling efficiency, ensuring the optimization of cycle times in production becomes easy. This optimized cycle time helps to save time and increases the volume of production per time.
  • Consistency Matters: Yes, it matters. Ensuring a high-quality product is not a one-time thing, it should be consistent and repeated notwithstanding the volume of production.

8. Step 5: Ejection

Struggling to remove the molded part from the mold after its solidification shouldn’t be the standard practice. This can cause unnecessary damage to the product and introduce certain defects that are avoidable. Here are specific considerations to aid the easy ejection of product from the mold to achieve a flawless molded part.

  • Mold Release Agents: Certain compounds and lubricants are often added to the mold’s body to ease the removal of the product from the mold. These release agents ensure that there are no damages done to the part during the ejection process.
  • Ejector Pins: Another feature of the mold that is strategically positioned for easy part ejection is ejector pins. These devices help to avoid distortion of the parts during ejection.
  • Preventing Damage: Handling ejection with care and precision is a requirement that every operator and demolding personnel should observe to ensure there are no product defects.
  • Repeatable Performance: Getting the ejection process correct every time is a conscious effort that should be done without fail. Putting measures in place to ensure repeatable accuracy is essential.

9. Quality Control and Testing

Installing and effecting a good quality management system is necessary to ensure that there is effective monitoring and testing at every stage of the injection molding process. Here are essential steps to activate an effective quality control plan for the project.

  • Stringent Inspections: It’s a popular saying that people do what you inspect and not what you inspect. In essence, you cannot leave the quality of your product in the hands of any individual without close and adequate inspection. This will help to catch any inconsistencies caused by negligence or oversight on the part of the production personnel.
  • Measurement and Precision: Part of the inspection criteria is the check for precision and measurement. These parameters are one of the causes of significant defects occurring in a molded component.
  • Defect Identification: An inspector must be duly trained to identify all forms of defects that can occur in an injection molding project. This will help them to quickly spot them and ascertain the root cause to find a lasting solution to these anomalies.
  • Statistical Process Control: SPC for short gives insights to the production analysts and manufacturers using real-time data generated in the course of the injection molding. It also helps to monitor and regulate critical parameters that have grave consequences for the project if not attended to in time.
Interior panel for automotive using plastic injection molding
Interior panel for automotive using plastic injection molding

10. Applications and Industries

At this stage, it should be quite obvious that injection molding can be found in almost every manufacturing sector seeing that it has permeated virtually every part of our lives. We have highlighted the most popular industries that have found extensive applications for injection molded products.

  • Automotive Precision: Every automaker from the very recent to the established household names uses plastic molding in one form or shape in their manufacturing. The precision for making components like dashboards, interior panels, and bumpers all come from using injection molding.
  • Medical Devices: The biocompatibility of the plastic materials used for medical appendages and the precision required for making medical tools and devices are all attributed to injection molding. Saving lives in the health sector hugely depends on this manufacturing method known as injection molding.
  • Consumer Goods: Toys, kitchen appliances, and other consumer goods that we’ve grown to love all take their ergonomic possibilities from injection molding manufacturing. It combines aesthetics and functionality to satisfy the end users of these products.
  • Mass Production: When compared to other innovative methods like 3D printing technology, injection molding can be called the king of mass production. This is because high-volume manufacturing is its forte as it can produce thousands of similar parts quickly and with ease.
  • Complexity with Simplicity: The ability to make complex parts with ease is one of the reasons injection molding is highly sought after in the manufacturing industry. It makes intricate designs possible in the simplest of ways.

11. Challenges and Innovations

With all the benefits and pros that injection molding has going for it including its versatility and precision, yet, it isn’t totally flawless. But with its challenges, advances in manufacturing technology continue to proffer solutions and increase the efficient options to get things done.

  • Complex Molds: Certain items require complicated and intricate molds. These can be expensive to make and difficult to design. Complexity has become easier to manage thanks to developments in mold design tools, including the incorporation of 3D printing.
  • Cycle Time Optimization: It’s difficult to cut cycle times without sacrificing quality. This problem has been considerably solved by innovations including high-speed injection molding machines, enhanced mold cooling methods, and automation.
  • Variability in Materials: Because each material has different qualities, it might behave differently when it is molded. To combat this, material suppliers are constantly creating materials that are easier to process and more predictable.
  • Sustainability: Concern has been raised about how injection molding affects the environment. The adoption of more energy-efficient machinery and material innovations like bioplastics are steps in the direction of a more sustainable future.
  • Intelligent Manufacturing: Real-time monitoring, preventive maintenance, and data-driven process optimization have all entered the injection molding industry thanks to Industry 4.0. It’s like adding intelligence to a method that is already accurate.


In a nutshell, from injection to ejection, and from mold design to the choice of material, each step contributes its own quota to the achievement of quality injection molded product

The mechanism that links imagination to reality is injection molding. It’s how ideas, plans, and inventions are translated into concrete forms.

Take some time to recognize the skillful design that went into each injection-molded product as you come across them in daily life, from the complex parts of your smartphone to the comfortable inside of your car. It serves as a monument to the skilled injection molding craftsmen who transform basic materials into pieces of art.


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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