The industrial advent of automated manufacturing practices offers new and more efficient ways of making parts and components for products and machines of all kinds. Plastic injection molding and injection molding machines have become more and more popular. Today, there are hundreds of thousands of designs and consumers use injection molded plastic or rubber with different wall thicknesses to fill a single cavity in a wide variety of products and tools that are found commonly in the home, garden, and workshop. This comprehensive guide to molded parts and the injection process will give you an overview to all you need to know about injection molding, injection pressures, custom plastic and rubber design guidelines, the mold cycle and die casting, and how it is of benefit to consumers and manufacturers alike.

Introduction to Molded Parts

Why Molded Parts Matter for You

Why should you (the reader) care about injection molded plastic or rubber and the injection process itself? Well, simply because you use them every day. One of the hallmark components produced through injection molding are O-rings and other parts used to create a liquid seal for machinery, plumbing, and more. They are common to everyday products, such as garden sprinklers, kitchen sinks, carpet cleaners, and many other things found around the house, which necessitate the sequestration of a liquid.

For the average person, when the sprinkler can’t make a watertight seal with the garden hose or the kitchen sink won’t stop drip-dropping in the middle of the night it is likely due to a worn or damaged O-ring. Beyond the home, injection molded components are essential for submarines, spacecraft, engines of all kinds and so much more. Without these precision-made rubber sealing components, our boats would sink, cars would blow up, nuclear reactors would go into meltdown and chaos would reign over the world. So, though you perhaps never knew it, everyone has plenty of reason to care about the parts made through the process of injection molding.

What are molded parts, exactly?

A molded part is a component which has been formed from a cast mold. For example, imagine making a paper mache cast of your own face. Once the cast is made, you can fill it with cement as many times as you want—creating hundreds or thousands of casts the exact same statue of your face. The cement copy, which comes out of the face cast, is the molded part. It has been molded to the specifications of its cast. However, molded parts, in an industrial context, do not consist of cement or paper mache. They are often made of rubber, plastic, metal, or another material that can be formed from a liquid state.

Molded parts are made through the manufacturing process of injection molding. Injection molding produces a specified part or component on a mass scale, using a cast mold repeatedly. The cast is filled with the injection medium, where it dries in the physical form specified by the mold and is meant to produce copies quickly at scale. Injection molding can be implemented for a wide variety of parts and products—from O-rings to electric drill bodies, car parts, and more.


 Precision-Molding Process Types

Several processes may be used for the molding of precision parts. Any one of these processes might be the most appropriate for a precision manufacturing job, depending on the volume, materials, and usage requirements of the specific part in question. The cornerstone of precision-molding technology rests on the ability to produce a constant output of identical molded parts in a short duration of time.

Precision-molded parts are often used for critical jobs and necessitate the highest standard of accuracy and reliability in their manufacturing. That being the case, each type of molding process is likely bookended by a human quality control associate, who performs an in-depth final preparation of each molded piece. The types of molding processes are as follows:

●       Blow Molding

This process is used to create parts with a hollow core. Similar to glass blowing, blow molding is the process of injecting a hollow pocket into a heated rubber, plastic, or metal material. The material is heated to a malleable state and placed into a slightly larger cast mold. Then it is blown through with air until the material expands to the dimensions of its mold—at which point it is left to cool. Blow molding is used to manufacture rubber toilet diaphragms, plastic soda bottles, glass jars, exercise balls, and more.

●       Compression Molding

The process of compression molding involves a pre-formed rubber piece being forced into a mold, which consists of two plates. This process uses high pressure to rid the finished piece of all extraneous air pockets and bubbles. Compression molding often leaves an amount of excess rubber to be cut off after the piece is extracted from the mold.

This molding process is well suited to the manufacturing of precision parts, such as O-rings, gaskets, and other automotive parts as compression molding culminate in a vulcanization process, which creates a strong, resilient finished product. Often, compression molding is used for larger parts and small volume manufacturing.

●       Extrusion Molding

The extrusion molding process is similar to that of blow molding in that it produces a molded piece that is hollow. However, extrusion molding is used for manufacturing long, cylindrically shaped pieces such as straws, pipes, and tubes. This process implements a dye cast, which determines the final form taken by the molded piece. The dimensions of a piece can be uniquely designed and accurately produced many times over through extrusion molding.

●       Injection Molding (Hot and Cold)

For large volume manufacturing of small to medium-sized components, which require a strictly uniform finished product, injection molding is the most efficient and reliable process. Injection molding is responsible for manufacturing some of the most crucial components used in industrial machinery, home appliances and more. This process caterers itself towards intricate, small dimensional designs and complex, insertable components and pieces.

The injection molding process comes in two forms: Hot runner injection molding and cold runner injection molding. The latter is used mainly with thermoplastics and involves heating the material to a liquid state, at which point it is pumped into a mold, where it cools before being released from the system. Cold runner injection molding is the standard process for molding rubber components. The rubber is only heated to the point of malleability before it is pumped into a heated mold cast. However, before the rubber is injected into the mold, it is combined with a curing agent: Platinum. The platinum causes a chemical reaction inside the mold, which significantly reduces the curing time for each manufactured piece.

Cold runner injection molding is the ideal process for making high volume, strictly uniform component parts at high speed. Due to its quality reliability and negligible human contact throughout the process, cold runner injection molding is the preferred method of manufacturing for the medical industry and other high-priority industries, such as military, aerospace, and more. Additionally, this process produces the lowest scrap rate of any molding process and scraps can be recycled for later use.

Injection-Molded Precision Parts

Injection molding is used to make a huge variety of products, parts, and components for just about every industry in the world. The possibilities are almost endless as to the shapes that can be manufactured at scale through this process. For those with a need for custom-made components and parts, a precision-injection molding service will offer the knowledge and knowhow to take your project’s requirements from conception to completion. A few of the commonly-manufactured injection-molded parts are as follows:

  • O-Rings
  • Custom Metal and Rubber Shapes
  • Backup Seals
  • Oil Seals
  • Quad Rings
  • U-Cups
  • Diaphragms
  • Cord Stock
  • Gaskets



Thanks for reading. Feel free to leave comments or questions at the bottom of the page. If you are in need of more comprehensive guidance or services for your precision-molded parts, be sure to contact ROTHKOPF, for a professional consultation.