When did plastic injection molding start?

Machine for manufacturing plastic products

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An injection molding machine (also spelled as injection moulding machine in BrE), also known as an injection press, is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, an injection unit and a clamping unit.[1]

Operation

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Injection molding machine molds can be fastened in either a horizontal or vertical position. Most machines are horizontally oriented, but vertical machines are used in some niche applications such as insert molding, allowing the machine to take advantage of gravity. Some vertical machines also do not require the mold to be fastened. There are many ways to fasten the tools to the platens, the most common are manual clamps (both halves are bolted to the platens); however, hydraulic clamps (chocks are used to hold the tool in place) and magnetic clamps are also used. The magnetic and hydraulic clamps are used where fast tool changes are required.

The person designing the mold chooses whether the mold uses a cold runner system or a hot runner system to carry the plastic and fillers from the injection unit to the cavities. A cold runner is a simple channel carved into the mold. The plastic that fills the cold runner cools as the part cools and is then ejected with the part as a sprue. A hot runner system is more complicated, often using cartridge heaters to keep the plastic in the runners hot as the part cools. After the part is ejected, the plastic remaining in a hot runner is injected into the next part.

Types of injection molding machines

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Machines are classified primarily by the type of driving systems they use: hydraulic, mechanical, electrical, or hybrid

Hydraulic

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Hydraulic machines have historically been the only option available to molders until Nissei Plastic Industrial introduced the first all-electric injection molding machine in 1983.[2] Hydraulic machines, although not nearly as precise, are the predominant type in most of the world, with the exception of Japan.[3]

Mechanical

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Mechanical type machines use the toggle system for building up tonnage on the clamps of the machine. Tonnage is required on all machines so that the clamps of the machine do not open due to the injection pressure. If the mold partially opens up, it will create flashing in the plastic product.

Electric

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The electric press, also known as Electric Machine Technology (EMT), reduces operation costs by cutting energy consumption and also addresses some of the environmental concerns surrounding the hydraulic press. Electric presses have been shown to be quieter, faster, and have a higher accuracy, however the machines are more expensive.

Hybrid injection (sometimes referred to as "Servo-Hydraulic") molding machines claim to take advantage of the best features of both hydraulic and electric systems, but in actuality use almost the same amount of electricity to operate as an electric injection molding machine depending on the manufacturer.[4][5]

A robotic arm is often used to remove the molded components; either by side or top entry, but it is more common for parts to drop out of the mold, through a chute and into a container.

Main components of injection molding machine

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Further reading:
Plastic Injection Moulding Advantages & Disadvantages

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Injection unit

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Consists of three main components:

1. Screw motor drive
2. Reciprocating screw and barrel
3. Heaters, Thermocouple, Ring plunger

Clamping unit

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Consists of three main components:[6]

1. Mold
2. Clamping motor drive
3. Tie bars, the sender is clamped into the edge of a workbench
4. Hydraulic QMC

References

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Further reading

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• Bryce, Douglas M. Plastic Injection Molding: Manufacturing Process Fundamentals. SME, 1996.
• Brydson, J, Plastics Materials, Butterworths 9th Ed (1999).
• Callister, William D, Materials Science and Engineering: An Introduction, John Wiley and Sons
• Lewis, Peter Rhys, Reynolds, K, Gagg, C, Forensic Materials Engineering: Case studies, CRC Press (2004).
• Osswald, Tim, Lih-Sheng Turng, Paul J.Gramann. Injection Molding Handbook 2nd Ed. Hanser Verlag, 2007
• Osswald, E. Schmachtenberg and E. Baur, ”International Plastics Handbook”, Hanser Verlag, (2006). ISBN 978-1569903995
• Rosato, Donald V; Marlene G. Rosato. Concise Encyclopedia of Plastics. Springer, 2000.
• Rosato, Dominick; Rosato Marlene, and Rosato Donald Injection Molding Handbook 3rd Ed. Kluwer Academic Publishers, 2000.
• Todd, Robert H; Dell K. Allen and Leo Alting Manufacturing Processes Reference Guide. Industrial Press Inc., 1994. pgs. 240–245
• Whelan, Tony. Polymer Technology Dictionary Springer, 1994.

Plastic injection molding today works a little differently from before World War II. The opportunities provided by plastic injection molding are applied by essentially every manufacturing sector:

• Electronics
• Automotive
• Home appliances
• Housewares

and more.

In addition, plastic injection molding is an affordable and effective method of producing high-quality parts and products.

Today's technology is quite similar to the technologies used in the past. However, computers have made the whole design and manufacturing injection process more manageable. Injection machines can use computers to make manufactured parts with greater precision. In the present day, plastic components are often the preferred choice for advanced technological and scientific applications.

With the growing concern for the environment, each attempt to make the plastic production process more environmentally friendly and sustainable can significantly contribute to preservation. As a result, many manufacturers have already implemented green practices into their operations.

What Changes Have Happened in Plastic Injection Molding Since It Started?

Ever since the late 1800s, this method of production has been used to manufacture products such as toothbrushes and hair clips. While there have been changes to plastic injection molding methods, the basic techniques are the same. Since the extrusion screw injection machine was invented, other, more automated machines have been created to increase injection speed.

Early plastic was hard to work with and difficult to shape into different items. Inventors worked with the primary material and developed a more durable and easier form with which to work. Shortly after, plastic injection molding was also established.

Although the basic injection molding techniques have remained similar, the materials used have changed. Plastics are now offered in a wider variety than when plastic injection molding methods were first invented. Currently, plastics with different melting points are accessible, and it is also possible to include additives that create specific qualities for the finished product.

Early molds were very simple, with only two parts. Now, very complicated molds are used that may have more than two areas or parts.

Although materials may have changed, the plastic injection molding methods are still the same at their most basic level. The process still calls for heated plastic to be injected into a mold and then chilled. Usually, chilling occurs thanks to coolant passing over and around the molding chamber where the plastic is shaped. The hardened plastic forms are then ejected and cut down to be ready for sale or use.

While early plastic was challenging to work with, a later form of plastic developed soon after was easier to shape into different items. This was the first real step toward modern injection molding processes. As soon as more versatile forms of plastic were invented, plastic injection molding methods similar to those used today were also created.

There changes to the plastic injection molding methods since their invention are minimal, but the more significant changes have been to the plastics themselves. Now, plastics are available in a much wider variety than they were in the late 1800s. In addition, plastic that is being molded can now be colored since dyes and other chemical additives can now be mixed in with the plastic granules themselves. Specific additives can give plastics unique qualities that make them more suitable for use in different industries and products.

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