A 101 Guide to Understanding Plastic Injection Molding Machines for Industrial Manufacturing


Plastic injection molding is one of the most reliable and cost-effective plastics manufacturing processes, producing mass quantities of diverse plastic components for virtually every industry. The injection molding process delivers high-quality plastic components at high volumes thanks to the design of plastic injection molding machines. While other plastics manufacturing processes exist, like 3D printing, none have the versatile and high-production capabilities of plastic injection molding.

What is Plastic Injection Molding?

Plastic injection molding is a manufacturing method where molten plastic is injected into a mold, then cooled and solidified to create a product. The plastic injection process is particularly adept at producing complex-shaped items in large quantities, playing a pivotal role in plastic processing.

The process’s popularity stems from its flexibility, allowing manufacturers to choose mold designs and thermoplastics tailored to each component’s needs. Moreover, the plastic injection molding process’s efficiency leads to high-volume production once set up, especially when using energy-efficient electric machines.

Consistency is critical in plastic injection molding. Tight control over process parameters ensures the rapid, uniform production of thousands of high-quality plastic components. The cost-effectiveness of the method becomes evident after the initial investment in the mold, making per-component production costs relatively low, especially in large-scale mass-production scenarios. With plastic injection molding, quality remains constant, repeatedly delivering solid and finely detailed plastic components.

The History of Plastic Injection Molding

The history of plastic injection molding traces back to 1846 when British inventor Charles Hancock patented an early version of the injection molding machine. However, significant progress came in 1872 when American inventor John Wesley Hyatt and his brother Isaiah patented one of the first injection molding machines, resembling a large hypodermic needle.

The industry advanced slowly, producing collar stays, buttons, and hair combs. In 1903, German chemists Arthur Eichengrün and Theodore Becker invented soluble forms of cellulose acetate, a less flammable alternative to cellulose nitrate. Years later, Eichengrün developed the first injection molding press in 1919, with a patent for plasticized cellulose acetate injection molding in 1939.

The injection molding industry experienced rapid expansion during World War II due to the demand for inexpensive, mass-produced products. In 1946, American inventor James Watson Hendry revolutionized the field with the first screw injection machine, providing precise control over injection speed and material mixing. Hendry later pioneered gas-assisted injection molding in the 1970s, improving design flexibility, strength, and production efficiency.

Today, screw injection machines dominate the industry, evolving from producing combs and buttons to manufacturing endless plastic products across various sectors, including aerospace, automotive, construction, consumer goods, medical, packaging, plumping, and toys.

What is a Plastic Injection Molding Machine (IMM)?

Plastic injection molding machines (IMM) facilitate the transformation of plastic materials into new products to meet customer and commercial demands. A plastic injection molding machine has various parts such as a material hopper, barrel, injection ram or rotating screw, heating device, movable pattern, ejectors, and a mold within the mold cavity.

The Importance of IMM Components

Injection molding machine (IMM) components, including controllers, servo systems, auxiliary equipment, and robots, play crucial roles in the injection molding process. The two main units aside from the mold are the clamping and injection units.

What is the clamping unit of an IMM?

Clamping units open and close molds and eject the finished products. There are two primary types of clamping methods: toggle and straight-hydraulic. The injection unit focuses on melting plastic through heat and injecting the molten material into the mold.

Plastic Injection Molds

Plastic injection molds consist of high-strength metal components machined into two halves. The molten plastic flows through sprues, runners, and gates, filling cavities. After cooling, the mold opens, and the ejector rod pushes the ejector plate to release the moldings. To enhance efficiency, molds are designed with multiple cavities connected by a runner.

Cycle Time

The entire plastic injection molding process cycle is relatively short. However, each stage requires precise control and consideration of material properties, part geometry, and cooling requirements. These variables are highly dependent on the cycle time, clamping force, and input material to the machines.

Molding Conditions

Molding conditions, including cylinder temperature, injection speed, and mold temperature, greatly influence molded products’ appearance, dimensions, and mechanical properties. Selection of suitable molding conditions requires expertise and experience, and standard conditions are provided for various materials.

Reprocessed Materials

Reprocessed materials, obtained from discarded sprues and runners, are blended with virgin pellets for reuse. The ratio of reprocessed materials is limited to about 30 percent to avoid compromising plastic properties.

The Advantages of Plastic Injection Molding

Plastic injection molding has numerous advantages. Firstly, the process is highly automated and efficient, translating to swift production at reduced costs. Beyond speed and cost-effectiveness, the lightweight nature of plastic, compared to metal, ensures superior quality, consistently delivering precise and uniform products.

The compatibility of plastic injection molding machines with design software like CAD, CAM, and SolidWorks enables the seamless production of simple and intricate components, adhering to exact specifications.

Furthermore, the potential for recycling excess material adds another layer to the plastic injection molding process’s eco-friendly profile. These advantages make plastic injection molding the versatile and preferred manufacturing method.

The Cost of a Plastic Injection Molding Machine

The cost of plastic injection molding machines varies depending on size, features, and manufacturer. Smaller machines may cost a few thousand dollars, while larger ones can range from $50,000 to $100,000.

Understanding the press size required is vital for selecting the right plastic injection molding machine. Plastic injection molding machines are classified based on tonnage or clamping pressure, ranging from less than 5 tons to over 4000 tons. The press ton rating indicates the clamping force during the plastic injection process.

Ongoing operational costs, including electricity, maintenance, and materials, add to the overall investment. However, the quality of the machine can contribute to increased production efficiency and reduced waste. Additionally, taking advantage of energy-efficiency incentives and rebates from utilities further offsets operating costs and energy consumption.

Energy-Efficient Solutions for a Plastic Injection Molding Machine

Manufacturers seeking energy efficiency in their plastic injection molding facilities can explore various opportunities utility companies provide. Prioritizing the whole-life cost over the initial purchase cost when investing in plastic injection molding machines can lead to significant energy savings, with new-generation machines offering improved efficiency.

Choosing the correct-sized machine is crucial, as efficiency peaks near a machine’s design load. All-electric plastic injection molding machines, powered directly by electricity, eliminate the need for hydraulic oil, perform operations through electric servos, and contribute to reduced cycle times and increased energy savings.

Installing Insulation jackets for machine barrels minimizes heat loss, while variable speed drives (VSDs) and variable frequency drives (VFDs) control electric motor speed, saving energy. Smart manufacturing, leveraging automation and IoT technologies, optimizes processes, schedules maintenance cycles, and reduces energy consumption by turning off components when unnecessary.

Contact APenergy, the Energy Efficiency Experts of Plastic Injection Molding, Today

APenergy has over 35 years of experience working with industrial plastics manufacturers to identify areas of inefficiency and make data-driven decisions to reduce energy consumption and costs.

We utilize utility incentives and rebate programs for plastic injection molding machines on projects like thermal insulation jackets, VSDs, VFDs, and, most importantly, productivity improvement applications to specific machines. The energy savings and monetary incentive potential of plastic injection molding machines are bountiful. These are energy-intensive applications with a broad application that facilities should be considering to reduce operational costs.

Through our incentive management service, APenergy can help companies set energy-saving goals, track progress, and achieve favorable ROIs. Our expert team is ready to assist companies with energy-efficient solutions. For more information, contact the APenergy team, the leading energy efficiency consultants, at 740-862-4112 or message us today and find out how we can help.