What is Injection Molding? Everything You Need to Know

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Everything You Need To Know About Injection Molding

Injection molding is a manufacturing process used to produce plastic parts. Molten plastic is injected at high pressure into a mold cavity, where it cools and hardens. The mold is then opened, and the finished molded part is ejected. Injection molding is known for its ability to produce complex parts with high repeatability and efficiency.

The heart of the injection molding process is a specialized machine. It’s meticulously designed to transform plastic feedstock into final products.

What is Injection Molding Machinery? 

The injection molding machine consists of three main parts that work together. The injection unit melts the plastic, the clamping unit holds the mold tightly closed, and the control system makes sure everything happens at the right time.

What is Injection Molding Machinery?
Injection Molding Machine and its Components
  • Injection Unit: This is where the plastic material begins its journey. The hopper feeds plastic pellets into the heated barrel. Here, a rotating screw melts and mixes the plastic. The screw also acts as a plunger, pushing the molten plastic forward. 
  • Clamping Unit: This component securely holds the mold during the production process. It consists of platens (large metal plates) and tie bars. The mold is attached to the platens. The clamping unit uses hydraulic or mechanical systems to generate tremendous force, keeping the mold closed during the injection phase. 
  • Control System: The control system oversees temperatures, injection pressure, injection speeds, and timings. Modern control systems offer precise regulation, ensuring consistency in production.

The Mold 

Molds for injection molding are custom-built. They’re typically created from hardened steel or aluminum. These molds are precision engineered with cavities that match the shape of the desired product. Due to the pressure and temperatures of injection molding, mold creation is a meticulous and skilled process. 

Basic Mold Types

Basic Injection Mold Types
Different Mold Types for Injection Molding
  • Two-Plate Mold: The most common type, consisting of two halves—a cavity-side and a core-side. This type is generally the most cost-effective to produce.
  • Three-Plate Mold: This design includes an extra plate. It allows for more complex part designs and auto-removal of any plastic left over. 
  • Hot Runner Mold: Use heated channels to keep the plastic in a molten state within the mold, reducing waste and cycle times. 
  • Cold Runner Mold: The plastic within the runners and sprues solidifies. It’s typically reground for reuse in future molding cycles.

How They Work Together 

The injection unit, clamping unit, and control system work in a synchronized sequence. Together, they complete each injection molding cycle, delivering consistent and high-quality plastic parts. 

Material Preparation 

The primary material used in the plastic injection molding process is thermoplastic pellets. Thermoplastics soften when heated and harden when cooled. This is perfect for repeated use in the molding process. These pellets are fed into the injection molding machine through a hopper.


The plastic pellets are fed into a heated barrel where they’re melted. A rotating screw mixes the molten plastic and forces it into the mold cavity at high pressure. The pressure helps the plastic to fill every detail of the mold before cooling. 


Coolant circulates through channels in the mold. The cooling process causes the plastic to harden in the mold cavity, in the desired shape. Efficient cooling is crucial! It maintains short cycle times and ensures consistent quality.


Once the plastic part has cooled, the mold opens. Ejector pins push the hardened part out, allowing it to be removed. The mold then closes, ready to begin the cycle again. 

Materials Used for Injection Molding 

Injection molding offers compatibility with a wide range of materials. This adds to its versatility across industries.


Thermoplastics are the cornerstone of injection molding. Their ability to melt, solidify, and be re-melted makes them ideal for high-volume production. Common thermoplastics include:

  • ABS (Acrylonitrile Butadiene Styrene): Known for toughness and impact resistance. 
  • Polypropylene (PP): Balanced properties, including chemical resistance and low cost. 
  • Polyethylene (PE): HDPE (High-Density) and LDPE (Low-Density) for a range of applications. 
  • Nylon (PA): Strong, with good wear resistance. 
  • Polycarbonate (PC): Excellent transparency and high impact strength. 

Other Injection Molding Materials Used

  • Thermosets: These plastics undergo a chemical reaction that permanently sets them. This makes them ideal for parts needing heat or chemical resistance.
  • Elastomers: Rubbery materials used to create flexible components like seals and gaskets. 
  • Metals and Glass: These may be used in specialized injection molding techniques. However, they’re less common. 

What Are the Benefits of Injection Molding? 

  • Complex Designs: Injection molding is used to produce parts with complex shapes and fine details. These might be difficult or impossible to achieve with other manufacturing processes.
  • High Repeatability and Consistency: One mold can be used to manufacture thousands of parts, virtually identical. This ensures quality and uniformity across large production runs. 
  • Efficiency and Speed: The injection process itself is fast, with short cycle times. This means high-volume production capabilities and lower time-to-market.
  • Cost-Effectiveness: Cost per part decreases with higher production volumes. This makes it cost-effective for large-scale manufacturing.
  • Wide Material Selection: Injection molding supports a vast range of materials. This offers flexibility with things like strength, flexibility, heat resistance, and color. 
  • Reduced Waste: Other manufacturing methods that cut away material. Injection molding leaves minimal scrap, which means less waste. 
  • Durability and Strength: Modern plastics have impressive strength-to-weight ratios. They’re suitable for demanding applications and sometimes even replace metal parts. 
  • Enhanced Finishing Options: Parts come out of the mold with surface textures and finishes. This saves time and money on extra finishing processes. 
Enhanced Finishing Options

What Are the Different Types of Injection Molding? 

Standard Plastic Injection Molding 

This is the most common injection molding form. Thermoplastic polymers are melted and then injected into a steel or aluminum mold. The plastic cools and hardens into the final shape. 

Insert Molding 

In this method, a pre-placed insert (often metal or another material) is placed into the mold before injection. The plastic flows around it and creates a part with added functionality or strength. A good example of this would be a plastic screwdriver handle with a metal shaft.


This involves injecting multiple layers of plastic over an existing part. It’s often used to add soft-touch surfaces to tools, create two-color parts, or mix different materials for enhanced properties.

Micro Injection Molding 

Designed for making very small precision parts. Micro injection molding uses extremely high pressure and accuracy to produce tiny components. These are often used in medical devices and electronics. 

Gas Assist Injection Molding 

Some of the injected plastic is replaced by a pressurized gas, typically nitrogen. The gas creates hollow sections, reducing weight. It’s used for large parts where weight reduction is handy, like automotive panels or structural components.

Structural Foam Molding 

Plastic is injected with a chemical blowing agent. This creates a part with a solid outer skin and a foamed core, with a high strength-to-weight ratio. It’s used in structural parts like pallets, crates, and housings.

Reaction Injection Molding (RIM) 

The materials undergo a chemical reaction when mixed (like polyurethanes). It often produces larger, thicker-walled parts. As a result, they have excellent thermal and acoustic insulation. Body panels or appliance enclosures may use this type. 

Thermoset Injection Molding 

Unlike thermoplastics, thermosets permanently cure after heating. This method creates parts that can withstand very high temperatures and chemical exposure. It’s used in automotive, electrical, and aerospace applications.

Design Considerations for Injection Molding 

Successful injection molding is all about careful part design. Overlooking things can lead to production trouble, part defects, or extra costs. 

Draft Angles

The surfaces of a part should be slightly angled for easy ejection from the mold. Not enough draft can cause parts to stick in the mold, causing damage, molding defects, or delays. 

Wall Thickness

Wall thickness affects how the plastic flows, cools, and hardens. Consistent wall thickness is important to prevent sink marks and warping. Changes in wall thickness should be gradual for smooth transitions.


Undercuts are features like side holes or recessed areas that prevent a straight pull from the mold. They often need complex mold designs or side-actions, increasing cost. When possible, it’s best to reduce or get rid of undercuts.

Ribs and Gussets

These are reinforcing structures added to parts. They increase strength and prevent warping. Proper design and placement of ribs and gussets optimize how well a part performs.

Gate Types and Location

Gates are the points where molten plastic enters the mold cavity. Their type and location impact how the plastic flows, influencing aesthetics and strength.

Parting Lines

This is the line where the two halves of the mold meet. Give careful consideration to its placement on the part to reduce visibility.

Is Injection Molding the Right Option for Your Project? 

Consider the volume of parts needed and the material requirements. It also offers a wide range of material options and finishes. Injection molding is a popular and versatile choice for various applications. 


Injection molding has a higher initial cost due to mold creation. It’s best suited when production volumes are large enough to justify the tooling investment by spreading the cost over many parts.

Production Quantity

Check the total number of parts you’ll need. For very small quantities, other methods, like 3D printing, might be more cost-effective.

Design Factors

Simpler part designs need less complex molds, reducing cost and potential design issues. Wall thickness, draft angles, and radii should be carefully considered during design. 

Production Considerations

Optimize your production line for assembly, do quality checks, and streamline the molding process. Whether through automation or cycle time reductions, these help reduce labor and per-part costs.

Time Constraints

Creating high-quality injection molds takes time. If you have a tight deadline, factor in mold design and manufacturing time. It’s crucial for aligning expectations with your production schedule. 

Injection Molding for Your Project 

Do you have a plastic product in mind that needs to be manufactured? Injection molding might be the perfect solution to bring it to life. At Kemal Precision Manufacturing Ltd, we specialize in turning your designs into high-quality, cost-effective plastic components. 

Here’s how we can help:

  • Design Guidance: Our experts work with you to ensure your part design is optimized for injection molding. Our goal is to save you time and money in the long run.
  • Material Selection: We’ll help you choose the right plastics or other materials. Each one is selected to match your product’s performance and aesthetic requirements.
  • Precision Mold Manufacturing: Our state-of-the-art equipment and skilled team creates high-quality molds built for longevity and consistent part production. 
  • High-Volume or Small Batch Production: We can handle production runs of various sizes. Whatever you need, we’ve got the flexibility to meet your needs.

Injection Molding Frequently Asked Questions (FAQs)

What Industries Can You Use Injection Molding In?

What is injection molding good for? It’ a highly versatile manufacturing process used across various industries, including:

  • Automotive Parts: Interior and exterior components, engine parts, housings.
  • Consumer Electronics: Housings, internal parts, packaging.
  • Medical and Pharmaceutical: Syringes, vials, devices, packaging.
  • Food and Beverage: Containers, lids, packaging.
  • Household Products: Storage solutions, toys, furniture components.
  • Agriculture: Irrigation systems, feeders, tool components.

How Long Does It Take to Make an Injection Mold?

Creating an injection mold typically takes 2 to 18 weeks. It depends on the complexity and size of the mold, as well as the precision required for the part. 

Smaller, simpler molds can be completed in as little as 2 to 3 weeks. Larger or highly precise molds may need up to 18 weeks or more.

Is Injection Molding Environmentally Friendly?

Injection molding is becoming more eco-friendly due to its efficiency. It only uses the necessary amount of plastic, reducing waste material. 

The plastics used are recyclable, lowering the need for new materials. The durability of molded parts means they rarely require replacing, which minimizes manufacturing impacts. Modern machines for injection molding are also more energy-efficient, reducing their environmental footprint.

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