Custom Plastic Injection Molding FAQs

Blog, Monday, August 1, 2022

Custom Plastic Injection Molding FAQs

Developing a part or product is a daunting task that can be made even more complicated when selecting and implementing the manufacturing process. With so much manufacturing going overseas, problems with quality, freight costs, and timely delivery are becoming more and more commonplace.

If you want to improve your manufacturing lead times, stay on top of product quality, and help bring manufacturing back to the US, then choosing local plastic injection molding companies like CBM Plastics, Inc. is the perfect solution.

CBM Plastics has been family-owned and operated in the Midwest for more than 25 years. Our years of experience have provided us with in-depth knowledge and experience working with custom injection molding, profile extrusion, and thermoforming to provide the best solutions for your plastics manufacturing needs.

We provide manufacturing services to a wide range of industries, and our state-of-the-art technology allows us to maintain the highest quality standards while efficiently producing your product. Our Midwest location also means less of a headache when it comes to lead times, shipping delays, and high freight prices, allowing you to get your products when you need them.

Ready to get your next plastic project started? Contact the specialist at CBM Plastics today to get your project quote.

What is the plastic injection molding process?

Injection molding is a manufacturing process that uses heated plastics to form finished parts or products. Once the plastic is heated, it is injected into the mold to cool and form the desired shape. The product is taken out of the mold and finished. This manufacturing process is ideal for large runs and projects with complex shapes.

What is custom plastic injection molding suitable for?

Injection molding is the ideal plastic manufacturing process when you are looking at producing a large volume of products and are looking for the lowest per piece cost after tooling. Injection molding can be used to produce thousands or even millions of products in one run. It can be used in any type of mass production of plastic products from small items such as bottle caps to large parts such as bumpers in the automotive industry.

Are there different types of plastic injection molding?

There are multiple types of injection molding processes that can turn molten plastic into a high-quality finished plastic part or product. The process you ultimately use will depend on if you have high volumes of products to produce and what type of aesthetics you wish to achieve with your final product.

What are the advantages and disadvantages of injection molding?

As with any manufacturing process, there are pros and cons to injection molding, which may make injection molding the perfect option or one that is less than ideal.


From low per piece costs, to less waste, to efficiency, there are many benefits to choosing plastic injection molding. Some of the best advantages of this process include:

  • Low scrap rates: Injection molding results in low scrap rates similar to other traditional processes, such as CNC machining. Thermoplastic materials can be recycled, re-melted, and used again, meaning less waste.
  • It allows for tight tolerances and more complex designs: With injection molding, it is easy to create a high volume of uniform complex parts. In most cases, the ability to achieve tight tolerances makes it comparable to highly accurate applications such as 3D printed parts.
  • It allows for a wide variety of colors and materials: You can choose from more than 25,000 types of materials for injection molding, enabling you to find one with the best chemical properties, colors, and physical attributes.
  • It’s hugely efficient: Faster cycle times result in more parts per hour, which means a lower per piece cost.
  • It provides for high repeatability: The ability to repeat the molding process thousands of times before re-tooling allows consistent uniformity through longer runs.


Even though injection molding can be great for high volume and uniformity, the process also has some drawbacks.

  • Initial costs can be high: The tooling costs for the injection mold part is the most expensive part of the process and can make the process more costly per piece for low-volume production runs.
  • Lead times can be long: While the actual injection molding process can move rapidly and efficiently, the lead time for the tooling is often several months, which can make the lead time for the first run much longer than other plastic manufacturing options.
  • Design changes can be costly: Some manufacturing options, such as 3D printing, can allow you to easily make design changes as you perfect your part or product. With injection molding, any design changes will result in mold modifications which can be expensive. You can reduce the cost of changes by avoiding undercuts and sharp edges and ensuring consistent wall thickness in your design.

What types of materials are used for injection molding?

There are tens of thousands of different types of plastic materials and polymers that can work for the injection molding process. While the material used for your injection molding project will be determined by the properties needed to support the end use and look, below are some of the more commonly used polymers.

  • HDPE: High-density polyethylene has a high ductility level, strong impact resistance, and is resistant to moisture.
  • ABS: Acrylonitrile butadiene styrene is impact-resistant, has low shrinkage rates, and is resistant to acid.
  • PC: Polycarbonate is a transparent plastic often chosen for its heat resistance and a high-end cosmetic finish.
  • POM: Polyoxymethylene is hard, stiff, and tough. It has good elasticity and is resistant to organic solvents and hydrocarbons.
  • PMMA: Polymethyl methacrylate is scratch-resistant acrylic with a high gloss finish. It is ideal for thin wall designs.
  • PBT: Polybutylene terephthalate is ideal for electrical and automotive parts as it has good electrical properties and is tough but flexible.
  • PEI: Polyetherimide is resistant to high temperature, flame retardant, chemical resistant, and strong.
  • PP: Polypropylene is impact and wear-resistant, and resistant to both acids and bases.


What are the five steps to injection molding?

Understanding the five steps in the injection molding process can help you determine the best way to design your product to maximize efficiency and quality. While many details go into the injection mold process, injection molding can ultimately be broken down into five primary steps.

  1. The mold closes: The injection mold process begins when the injection molding cycle is set, and the mold closes.
  2. Mold injection: The heated polymer will inject into the closed mold. As the liquid fills, displaced air will escape through vents along a parting line.
  3. The cool-down process: After the mold has filled, it will sit for a specific amount of time, depending on how long the chosen material will take to cool. The thickness of the part and the material used will affect the time the cooling process takes.
  4. Resin plasticizing: During the cooling process, new plastic will be drawn into the barrel of the injection mold and brought to temperature for the next mold.
  5. Part ejection: The final step in the mold injection machine is the ejection. The model will open, and ejector pins will push forward, expelling the part to a tray or bin below.

What are the three main parts of the injection molding machine?

Three primary parts make up an injection mold machine.

  1. The injection unit inserts the plastic material into the mold.
  2. The mold is the tooling that forms the product or part.
  3. The clamp holds the mold closed until the formation is complete.

How many people are needed to operate an injection molding machine?

Only one operator is needed to run an injection molding machine, and in most cases, the operator can operate two to three machines at one time. This system helps to keep products produced efficiently and helps us to keep true to our lead times.

What is the purpose of the runner system?

Plastic injection molding processes may utilize either a hot or a cold runner system as part of the process. The chosen option will depend on the needs of the final product and the material used.

  • Hot runner: A hot runner system uses molds with a hot runner manifold designed to keep the material heated throughout the entire process. Typically, the runners are separate from the mold and will pass the heated resin into the mold cavity. These runners can be heated either internally or externally. This option is most often utilized with larger-scale runs.
  • Cold runner: The material in a cold runner system is delivered by a runner and sprue into the mold. The runner and mold are kept at the same temperature. The material will cool and harden in the runner the same as the mold. This process works best with shorter runs and runs where colors may change during the run.

How much does it cost for an injection molding project?

A large part of the cost of injection molding is the cost of the mold. More cavities in a mold mean higher costs for tooling. Another significant component in the project’s cost is the tolerance requirements, surface finishing, detailing, and the number of undercuts.

While smaller less complex molds will run on the lower side and large, complex molds on the higher side, most molds will fall somewhere in the range of $10,000 to $250,000.

What is the lead time for an injection molding project?

Lead time for plastic injection molding varies greatly, depending on the complexity of the mold and the length of time it takes for fabrication. Molds are typically produced within 8 to 14 weeks of the final design approval. Once the mold is complete, the time frame will be determined by the length of your run and whether or not assembly is required after.

Can I do custom colors with injection molding?

There are various options when it comes to choosing a color for your injection mold-produced product. Pre-colored resins, colorants, blends, and other additives can be used to help create the customized color you are looking for for your project.

Can CBM assemble my parts/products?

CBM Plastics, Inc. is here to help you with your plastic product concept through completion. Our knowledgeable staff can help you with the particulars of your tool design, help you choose the best process, and even complete the final assembly of your parts or products.

Which process should I use for my plastic part production needs?

Whether you are looking for low-volume runs or high production of your plastic part or product, choosing the proper manufacturing process is critical to getting the right price for your product and the final look you had envisioned.

Injection molding is a great option when you have a high-volume run of uniform parts or products and have enough lead time for mold creation and tooling. The process works well with large and small designs and designs with more intricate details.

If your product or part consists of a continuous profile, such as those with blinds or weather stripping, plastic profile extrusion can be a cost-effective solution for any size of run. Profile extrusion has a shorter lead time than other options and does not require high tooling costs at the outset.

Thermoforming is another option, especially if you have a larger part or one that you want more detailed or textured. By molding heated sheets of plastic over the mold, you can regulate the thickness and detail of the part or product.

What are the latest technologies in plastic injection molding?

Among the recent innovations in plastic injection molding, Additive Technology and Digital Manufacturing, particularly Direct Metal Laser Sintering (DMLS), stand out. This advanced technology employs metal 3D printing to fabricate molds that traditional methods find difficult or impossible to create.

CBM Plastics, Inc. Can Help With Your Plastic Production Project

Whether you want to learn more about injection molding or find a U.S.-based plastic injection molding company, CBM is here to help. We will help determine your project goals and specific needs and assist you with choosing the best type of production to achieve your desired result. From design help to final assembly, we are here to make your plastic project a success. Contact us today to determine your product needs.