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Everything You Need to Know About Plastic Injection Molding

An Overview of the Plastic Injection Molding Process

Plastic injection molding is a manufacturing process in which melted polymer is injected under high pressures into preformed molds. It is used to produce a wide range of solid plastic parts and products, including medical instruments, vehicle components, beverage containers, and consumer goods.

Typical plastic injection molding operations involve the following stages:

  1. Plastic beads and fragments flow through a hopper or cone into the heating barrel. 
  2. The barrel heats the plastic to its melting point, while a rotating screw pushes the melted plastic toward the nozzle.
  3. The melted plastic flows through the nozzle into the mold until all cavities are filled.
  4. The plastic remains under pressure until it has cooled into the desired shape. 
  5. Ejector pins eject the cooled plastic product from the mold. 

Industries Using the Plastic Injection Molding Process

Plastic injection molded parts find application across industry. Some of the sectors that regularly employ them include:

  • Automotive
  • Communications
  • Electronics
  • Manufacturing
  • Medical and Dental
  • Military and Defense
  • Transportation

Material Considerations for Plastic Injection Molding

When choosing a construction material for plastic injection molded parts, it is important to consider the following: 

  • Aesthetic qualities: the color, texture, and transparency desired in the finished product
  • Physical qualities: the strength, flexibility/rigidity, and other physical characteristics desired in the finished product
  • Durability: the resistances to various operating and environmental conditions, such as extreme temperatures, corrosive materials, or UV radiation, the finished product should demonstrate
  • Service life: the length the finished product is expected to last based on standard usage
  • Industry standards and regulations: the industry standards and regulations to which the finished product will be subjected (e.g., FDA, RoHS, REACH, and NSF)

Some of the materials most commonly employed in plastic injection molding operations include:

  • Acetal
  • Acrylic
  • Acrylonitrile butadiene styrene (ABS)
  • High-impact polystyrene (HIPS)
  • Polyamide (Nylon)
  • Polycarbonate
  • Polyethylene
  • Polypropylene
  • Polystyrene
  • Polysulfone

Design Considerations for Plastic Injection Molded Parts

When designing a plastic injection molded part, there are several factors to consider to ensure the finished piece functions as intended. Some of the key design considerations include: 

  • Boss and rib dimensions
  • Corner transitions
  • Gate and vent placement
  • Wall thickness
  • Weld lines

Partnering with an experienced and knowledgeable designer can save both time and money during the development and production stages by preventing part defects and manufacturing delays. 

Factors Influencing the Cost of Plastic Injection Molding Operations

The design and production of the injection mold is the biggest contributor to the total cost of an injection molding operation, as each one is custom-made to suit the part and production specifications of the project. The exact investment amount depends on several factors. For example, parts with simpler geometries require less expensive molds than parts with more complex geometries (e.g., tight tolerances, intricate elements, or multiple cavities). Additionally, more durable mold materials (e.g., steel) have a higher price point than less durable mold materials (e.g., aluminum).

Beyond the mold, some of the other factors that influence the cost of an injection molding operation include:

  • Part material: Materials with special characteristics (e.g., heat resistance, chemical resistance, and UV resistance) or custom formulations are more expensive than standard materials. 
  • Component size: The larger the part design, the more material needed to manufacture both the mold and actual component. 
  • Cycle time: The total time it takes for the injection molding process to finish is the cycle time. This period changes depending on the part material and size. A shorter cycle time translates to lower production costs, while a longer cycle time results in higher production costs. 

Custom Plastic Injection Molding Solutions From Darter Plastics

For more than 30 years, Darter Plastics has provided high-quality plastic products to customers in a broad range of industries, including aerospace, automotive, defense, medical, and product manufacturing. Equipped with extensive industry experience and cutting-edge injection molding technology, our team manufactures injection molded products from all types of thermoplastic material. In addition to our plastic injection molding capabilities, we offer design/engineering, mold making, pad printing, hot stamping, and assembly services. 

To learn more about our injection molding capabilities or partner with us on your next project, contact us or request a quote today.

Injection Molding Costs

How Much Does Injection Molding Cost?

Injection molding is one of the most common processes used for manufacturing plastic parts and components. Injection molding offers a cost-effective manufacturing solution for many applications.

What Is Injection Molding?

Injection molding is a manufacturing process typically used for the mass-production of parts when thousands or even millions are required. The injection molding process accounts for a significant portion of plastic manufacturing and is suitable for the production of products with complicated shapes and designs.

The injection molding process uses heat to melt plastic, which is then injected into a mold where it takes its shape before cooling and solidifying into the final product. The process is used by many industries that require large quantities of parts with the same specifications. Injection molding is used to make automotive parts and components, product packaging, bottle caps, toys, and most other plastic products.

Injection Molding Cost

One of the main considerations with any manufacturing process is the cost. While the mold typically represents the most significant upfront production cost, several variables affect the total cost.

Injection Molding Cost

Material Selection

The material used to create the mold is dependent on the formulation of the plastic used as well as the length of the expected production run. For shorter production runs, many mold makers use aluminum, which has a lower initial cost, but for longer runs, an aluminum mold may be more costly over time. 

Extended production runs and runs that use plastics that cause excessive wear require a mold made from hardened tool steel, which is more expensive but often provides long-term savings. The plastic used is also a factor when determining the best material for the mold. For instance, plastic containing fiberglass material will wear down many mold materials. 

Mold Size and Design

The cost of a mold is dependent on not only the material used to make it but also the size and design of the mold and the amount of tooling required to make it. Intricate parts require more time and skill to create the mold than simple parts. 

Mold Base

The mold base holds the mold cavities, inserts, and components together and is also responsible for directly installing the mold to the plastic injection molding machine. Mold bases are typically available in standard sizes, which are machined to meet the needs of a specific project, with the cost based on the size, material, and any customization required.

Mold Cavities

For short runs, a mold is often designed to make a single piece, but for large runs, it is typically more efficient to create a multi-cavity mold that produces multiple parts at the same time. Multi cavity molds are capable of producing several identical parts simultaneously. While more expensive initially, the ability to increase production capabilities makes it a cost-efficient option for large production runs.

Reducing the Costs of Injection Molding

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How Much Does Injection Molding Cost

The costs of injection molding can be controlled and reduced by carefully analyzing the part produced and ensuring that it precisely meets the desired specifications.

Eliminate Undercuts

Undercuts are complicated features that can disrupt the manufacturing process by preventing molded parts from ejecting correctly. Eliminating undercuts when possible can reduce the tooling costs of the mold, enable production runs to continue uninterrupted, and reduce the overall manufacturing costs of the part.

Eliminate Unnecessary Features

Every feature of the part produced adds to the production costs. Features such as textured surfaces, part numbers, and company logos that are not critical to the part add to the initial cost of the mold and also affect production costs.


There are thousands of different materials that are suitable for injection molding. These materials consist of alloys and blends formulated to have properties that meet nearly any specification.


3D Printing

3D Printing and injection molding are often considered competing technologies, but they each have their advantages. 3D printing is well suited to low volume production runs of 100 parts or less, and relatively small plastic parts or components that require a quick turnaround time. Injection molding has a longer turnaround time but is capable of producing thousands of pieces of any size or complexity.

How long does an injection mold last?

Several factors affect the lifespan of an injection mold, including the type of metal used for the mold and the formulation of the plastic used in production. A plastic injection mold can typically complete anywhere between 100,00 to 1 million or more cycles in its lifetime. 

Contact Darter Plastics

At Darter Plastics, we specialize in manufacturing parts using the injection molding process. Our dedicated team has the skill and knowledge to answer your questions and provide the expertise to help you with your project. To learn more about injection molding or to request a quote for your project, contact us today.

6 Common Plastic Resins for Injection Molding

Common Plastic Resins for Injection Molding

Plastic injection molding is a manufacturing process that enables the production of large volumes of identical parts. It is considered to be one of the fastest, most efficient production methods for plastic parts used in the industrial sector today. It is typically used in projects that require the production of thousands, or even millions of parts through repeatable processes.

Common Plastic Resins for Injection Molding

There are several advantages to utilizing injection molding techniques, such as:

  • A high rate of repeatability. Each produced part will be essentially identical to other parts in the run.
  • Low per-unit costs. While injection molding does require an upfront investment, once the operation is underway it offers a very low per-unit cost, as well as economies of scale for larger orders.
  • Low scrap rates. Injection molding tends to leave very little waste behind, making it one of the most efficient manufacturing processes available today.

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Common Plastic Resins for Injection Molding

Common Plastic Resins

There are multiple plastic resins that manufacturers use within their injection molding operations. Six of the most common plastic resins on the market today include:


Acrylonitrile butadiene styrene (ABS) is a thermoplastic material that merges the strength of acrylonitrile and styrene with the resilience of polybutadiene rubber. ABS can be easily molded at a reasonable cost.

ABS has a reputation as an all-purpose injection molding material. It is strong and sturdy, highly impact-resistant, and easily machinable to achieve a pristine appearance. It is found an expansive range of consumer goods, including but not limited to: 

  • Appliances
  • Electronics
  • Exterior and interior automobile trim
  • Golf clubs
  • Musical instruments
  • Toys


Celcon—also commonly known by variations such as acetal, polyoxymethylene (POM), polyacetal, or polyformaldehyde—is a synthetic thermoplastic formed on a molecular level by the condensation of two alcohol molecules with an aldehyde molecule.

Celcon offers several advantages for manufacturing projects, such as exceptional toughness, good creep resistance, and low moisture absorption. It is often used in parts that are designed to come into contact with other surfaces. Common Celcon applications include: 

  • Toy parts
  • Automotive gears and bearings
  • Food and beverage equipment
  • Electrical components


This exceptionally flexible thermoplastic material encompasses a range of available compounds that vary in quality and cost. Polypropylene has a reputation for offering a high deformation threshold—in other words, it can be twisted, bent, or reshaped without breaking. Due to its flexibility, manufacturers often utilize polypropylene as a living hinge material for products such as bottle caps and container lids.


The nylon commonly used in injection molding operations is reinforced with glass fibers for additional tensile strength. Typically the amount of added glass fibers does not exceed 40%.

Glass-filled nylon boasts higher strength and resistance to heat than both ABS and polycarbonate thermoplastics. Its innate heat resistance makes it a highly suitable material for kitchen applications, such as ovens. It is also highly resistant to electric current, making it a great choice for electrical applications where insulation is a must. 


High-impact polystyrene (HIPS) is a thermoplastic polymer with exceptional machinability and unsurpassed aesthetic attributes. It is popular for use in printed products, such as displays, posters, retail packaging, and graphics arts applications. Manufacturers also use HIPS for TV and audio-visual (A/V) equipment, bicycle trailers, hot and cold Thermos bottles, and electronic components.


Low-density polyethylene is the most flexible kind of polyethylene on the market today. It is highly cost-effective to produce, weather-resistant, and has high impact strength characteristics. It is found in a wide range of everyday consumer goods, as well as specialized equipment. Some common LDPE applications include:

  • Food containers
  • Toys
  • Food service and storage
  • Consumer goods
  • Industrial parts
  • Medical products

What to Consider When Choosing a Material

When selecting a source material for an injection molding project, it is important to consider the following factors:

  • Impact strength. Will your application be subjected to high-impact forces? Which resins are known to be highly impact-resistant?
  • Tensile strength. Will tensile forces be periodically or consistently acting on your final product? Which resins can successfully withstand your expected load without being torn apart?
  • Heat deflection. Will your end product be subjected to high temperatures? Will it require a strong insulating performance? Which options make the most sense for heat deflection/insulation?
  • Water absorption. Will the application be involved in a high-moisture environment, or need to resist water absorption day in and day out? Which resins can provide the best water-resistant properties?
  • Financial considerations. Which resins offer the most cost-effective solution for your particular project? Which ones will ensure that your end products are maximized for durability and functionality?

Material Selection Help From Darter Plastics

There are certainly many options for injection molding source materials on the market today, and many factors to weigh for each project. If you’d like to learn more about the pros and cons of each injection molding material, or want to explore the injection molding process further, reach out to our team of experts at Darter Plastics today.

3 Types of Insert Molding and Encapsulation

Insert Injection Molding

Insert molding is a specialized form of injection molding used to embed a plastic or metal component (the insert) into a final plastic product. Some inserts—such as wood and metal stiffening inserts—may be included solely for structural support, but others will add functionality to a product, such as threaded inserts. 

The exact technique used to embed a component varies based on the component’s size and shape, and it’s important to select the appropriate technique to ensure a stable, durable result. When done properly, insert molding can yield a stronger, longer-lasting component compared to an injection-molded part. It is also a highly cost-effective and efficient process, making it a viable option for customers with a range of budgets.

Whatever your motivation in choosing insert molding, our team at Darter Plastics will guide you toward the optimal choice of insert type, material, and manufacturing method to achieve the best possible result.

The Insert Molding (Encapsulation) Process

While the exact process varies with the type of insert molding, there is a series of general steps common to all encapsulation processes.

  • The first step is to create the tooling that will be used to form the product. This typically requires engineers to design a custom mold that resembles the finished shape while allowing space for the insert. 
  • The insert itself may then need preparation. Even if the insert is already sized and shaped appropriately, hollow ends still need to be sealed before insertion, and the whole insert must be cleaned and sometimes roughened to ensure that it stays in place. 
  • Once all preparation is complete, the injection molding process can begin. This is the part of the process that might differ substantially, depending on the exact technique. 
  • Finally, once the injected plastic has cooled and the insert been embedded, the component is removed from the mold and subjected to any number of secondary services, such as drilling or surface finishing.

Types of Molding

There are three main techniques for encapsulating an insert:

  • Multi-component injection molding, also known as co-molding, involves injecting some combination of multiple plastics and metals into the mold at the same time. These materials then join together, resulting in a stiffer, stronger piece. 
  • Multi-shot injection molding is similar to multi-component molding, but rather than inserting all of the materials at once, the operator layers them into the mold one at a time. As with multi-component molding, the different materials bond strongly to one another, although they do so in ordered layers. 
  • Overmolding is a slightly different approach to encapsulation. Rather than starting with a mold and molten materials, it begins with a pre-molded part onto which the insert is placed. From there, injection molding layers plastic over the insert, sealing it in place.

Benefits of Insert Molding

Insert molding is one of the most cost-effective ways to stiffen a component, making it better able to resist strong forces. Since there are multiple ways to accomplish encapsulation, engineers have significant flexibility in the design process and their mock-ups can be completed with fewer assembly steps

Plastic Insert Molding Materials

Part of insert molding’s flexibility comes from its compatibility with a wide range of materials. Stiffening inserts are usually made from metal, but wood is a low-cost alternative that still provides some gains. The molding material is typically a thermoplastic or elastomer chosen for its physical characteristics. 

Materials compatible with injection molding include:

  • ABS
  • Acetal
  • Acrylic
  • Copolymer and homopolymer polypropylene
  • Flexible PVC
  • Microcellular
  • Nylon
  • PEEK
  • PET
  • Polyaryletheretherketone
  • Polycarbonate
  • Polyester
  • Polypropylene
  • Polystyrene
  • Polyurethane
  • Thermoplastic
  • Thermoset

Darter works with all of these materials and most other compatible plastics except rigid PVC.

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Insert Injection Molding

Darter’s Insert Molding Expertise

At Darter, we’ve developed our insert molding and injection molding services over a period of several decades to ensure that our methods are as affordable and efficient as possible. We work with almost any plastic that is suitable for injection molding, and we craft components of any size and almost any production volume. With our 15 state-of-the-art presses, we can achieve tolerances down to 0.005 inches, and our attention to precision makes us an excellent choice for industries such as aerospace, military, optical, medical, electronics, and more.

To speak with our team about the best insert molding process for your component, contact us or request a quote today.

Benefits of Short-Run Injection Molding

Benefits of Short-Run Injection Molding

Short-run plastic injection molding, also known as low-volume injection molding, is a quick and inexpensive molding process used to manufacture simple plastic components and parts. The process is used to create molds out of high-grade aluminum and lower grade steels, which are less durable than high production molds. 

As a limited volume process, short-run injection molding is ideal for the production of fewer than 10,000 parts. The use of aluminum tooling allows for quicker turnaround times and saves money over more expensive steel tooling. The process is considered a niche market segment which serves highly specialized needs, such as:

  • Prototypes
  • Small marketing production
  • Custom components for specialty automotive applications
  • Custom components for high-end appliances

Advantages of Short-Run Injection Molding

Short-run injection molding offers a number of benefits to suit a variety of customer needs. State of the art automation enhances:

Working Models and Prototypes

With its quick turnaround and low-cost production, short-run injection molding offers an ideal option to bridge the gap between the development of a working prototype component and full production. The short-run production option gives engineers a working first generation model wherein the design can still be affordably adjusted

Fast Turnaround

Short-run injection molding offers quick production at a low cost to get finished components back to the customer and on the market a short period. This allows customers to reduce their in-house inventory while still meeting lead-time demands. 

Low Production Cost

The cost of production for short-run injection molding is quite low due to highly developed automation and the use of less expensive high-quality materials. Aluminum and low-grade steel are the perfect low-cost materials for short-run molding to provide superior parts and components at competitive prices.

Economical and Efficient

When you use short-run injection molding, the parts are ejected from the mold with a finished look, so very little post-production work is required to finish the product. The quick turnaround and low cost of production ensures the frequent delivery of economically priced, small-lot quantities on an as-needed basis. The enables the customer to reasonably stock items in-house, thereby easing cash flow.

The Process

The short-run injection molding process is uncomplicated and typically used in the production of simple parts. Small plastic pellets are gravity fed through a hopper into a heated screw and barrel, where the pellets are melted into a liquid plastic. The liquid plastic is injected into the mold under high pressure, to ensure that the plastic fills every corner and cavity of the mold.

Plastic is then left to cool into the shape of the desired part. Once the plastic has cooled, ejector pins are used to remove the finished part from the mold, and the part is directed down a chute to be inspected, packed, and shipped to the customer. The entire process is automated, which allows for highly efficient and cost-effective production.


Short-run injection molding is used for a variety of applications across numerous industries. 

Low-Volume Production Runs

For applications that require injection molding for fewer than 10,000 parts, such as medical devices, exotic car components, and high-end household tools and appliances, low-volume injection molding is an effective and affordable production option. 

Functional Prototypes

Short-run injection molding is an excellent production method for new product development, including evaluation of product fit and function and life-cycle testing. Since the process is fast and inexpensive, it is ideal for quick production of prototypes to conduct critical tests before design finalization. It also allows for inexpensive adjustments to be made before the parts or components are produced on a larger scale, which saves time and reduces material wastage.

Market Testing and Bridge Tooling

Low volume injection is a useful way to bridge the gap between prototyping or market testing and full production. Once the design is finalized, you can continue production through short-run injection until your full production line is up and running, thereby avoiding any costly lapses in production. This also helps to get products onto the market faster for a faster profit return.

Benefits of Short-Run Injection Molding

Consult a Professional

For more than 30 years, Darter Plastics has been pleased to provide well-crafted, high-quality plastic parts and components to a variety of industries. Our professional and knowledgeable staff are happy to help you find the best plastic injection services for your needs. 

For more information on short-run and low-volume injection molding, contact us today, or request a quote.