Custom plastic injection molding 101: Process, Materials, Surface Finishes, Applications

Custom injection molding process

Injection molding is a manufacturing process for producing parts from thermoplastic and thermoset polymers. Injection molding is used to create a wide variety of parts, from small individual components to large complex assemblies.

The process begins with the selection of the appropriate type of plastic resin. The resin is melted and injected into a steel mold cavity. After the part has cooled, the mold is opened, and the part is ejected. This blog post will discuss the various types of resins, surface finishes, and possible applications of custom plastic molding.

What is the Injection Molding Process?

The injection molding process is used to create custom parts from both thermoplastic and thermoset polymers. The steps in the injection molding process include the following:

  • Melting and mixing of the resin
  • Injection into a pre-made steel mold at high pressure
  • Cooling of the heated material
  • Opening of the mold and ejection of the finished part

Custom Plastic Injection Molding Materials

Custom Plastic Injection Molding Materials

The type of raw plastic material used for injection molding is an important consideration when determining the optimal part design. The properties of materials determine their applications.

Acrylonitrile Butadiene Styrene (ABS): 

ABS Injection Molding Parts

Acrylonitrile Butadiene Styrene is a durable, lightweight thermoplastic with high strength and good impact properties. ABS resins produce automotive bumpers, housing shells for consumer electronics, and toys.

Polycarbonate (PC): 

PC Injection Molding

Polycarbonate is an extremely strong material with excellent impact resistance and flexibility. PC resins often produce automotive lenses, medical devices, and protective covers.

Polyamide (PA): 

PA Injection Molding

Polyamide is a strong yet flexible thermoplastic with excellent wear resistance and high impact strength. Nylon resins are commonly used in producing gears, fan blades, automotive parts, and other functional components.

Polyoxymethylene (POM):

Polyoxymethylene is a stiff, strong thermoplastic with excellent chemical resistance and dimensional stability. Acetal resins are often used for precision parts in the automotive, medical device, and electronics industries.

Polypropylene (PE):

Polypropylene is a lightweight, durable material with excellent chemical resistance and thermal stability. Polypropylene resins are often used for parts in the automotive, electronics, appliance, and medical device industries.


High Impact Polystyrene is a strong thermoplastic with good chemical and electrical properties. HIPS resins are often used for food packaging, automotive parts, and other durable components.

What is injection molding mold?

Injection molding can create parts with a wide range of shapes and sizes. Molds are produced from either aluminum or steel, depending on the complexity of the design.

The mold is composed of two parts: moving mold and fixed mold. The moving mould is installed on the moving parts of the injection molding machine, and the fixed mold is installed on the fixed parts of the injection molding machine. 

During injection molding, the moving and fixed mold are closed to form the pouring system and cavity. When the mold opens, the moving and the fixed mold are separated to remove the plastic products.

Custom Injection Molding Moulds

Custom Injection Molding Mould

Custom injection molding design is very important, A set of high-quality molds can reduce the processing cost, reduce the processing difficulty and shorten the processing time to meet customers’ requirements.

Before injection mold design, the designer should fully analyze and study whether the plastic products conform to the principle of injection molding processing. You need to negotiate carefully with the product designer and reach a consensus. Including the geometric shape of the product, dimensional accuracy and appearance requirements, and necessary discussion, as far as possible, to avoid unnecessary complexity in mold manufacturing. 

In the selection of die materials, in addition to the accuracy and quality of the product, you should be combined the actual ability of processing and heat treatment of the mold factory to give a correct choice.

Custom Injection Molding Surface Finishes

PPA Injection Molding

Surface finishes are important for injection molded parts, as they can improve the look and feel of the final product. Injection molds can be machined to achieve different types of surface finishes. Some of the most common include matte finishes, textured surfaces, and glossy finishes.

Matte Finish:

A matte finish is achieved by machining a mold to remove any high spots or imperfections on the part’s surface. This finish gives parts a smooth, uniform look without any sheen or shine.

Textured Surface: 

Textured surfaces are created using a process known as electroplating. This process involves coating the part with a thin layer of metal, typically aluminum or copper. The coated part is then exposed to an electric field which causes the metal particles to adhere to the mold surface, creating a textured finish.

Glossy Finish: 

A glossy finish is achieved by machining the mold to a high level of precision. This type of surface finish gives parts a smooth, shiny look that reflects light.

Secondary Operations Of Injection Molding Parts

Injection molded parts may require additional secondary operations to complete the end product. These operations include Drilling & Tapping, Silk Screening, Painting, Polishing, UV coating, Chrome Plating, and Assembly.

Drilling & Tapping:


Drilling and tapping are used to create holes for bolts or other fasteners on the part. Countersinking allows screws to sit flush with the surface of the part.

Silk Screening:

Silk screening is a process that creates a matte finish on the surface of injection-molded parts. This technique adds logos and other text or graphics to plastic parts.


Painting is often used to give parts a more aesthetically pleasing finish or to protect them from environmental damage.


Polishing is a process that adds shine to the surface of injection-molded parts. This technique can be used to give parts a glossy finish or to create a more uniform look.

UV Coating: 

Custom Injection Molding Surface finishes

UV coating is a process that applies a thin protective layer to the surface of an injection-molded part. This coating can protect the part from environmental damage and add shine.

Chrome Plating:

Chrome plating adds a layer of metal to the surface of an injection-molded part. This process is used to impart strength, durability, and aesthetic appeal.


Assembly processes may be required for certain parts, such as those that require multiple components or intricate shapes. This process can involve assembly by hand or by specialized machines.

Applications Of Injection Molding Services

Custom plastic parts is used in various industries, from automotive to aerospace. It is commonly used for parts that need to be mass-produced quickly and accurately. Some of the most common applications include:

Automotive Parts: 

Custom plastic parts is used in various industries, from automotive to aerospace. It is commonly used for parts that need to be mass-produced quickly and accurately. Some of the most common applications include:

Medical Devices:

This process produces components for various medical devices, including syringes, catheters, prosthetic devices, and implants.

Electronics Parts: 


The durability and accuracy of plastic injection molding make this process well-suited for producing parts for electronics such as computers, phones, and cameras. This process creates components such as housings, connectors, and buttons.

Industrial Parts: 

Plastic injection molding is used to produce a variety of industrial components, including gears, valves, fasteners, and plumbing fixtures. This process often creates parts with complex shapes and tight tolerances.

Aerospace Components:

Custom injection molding s often used to produce components for aircraft and satellites, such as wiring harnesses, fuel tanks, and actuators.

Advantages Of Custom Plastic Injection Molding

It is offers many advantages over other manufacturing processes, including:


Custom molded parts is a cost-efficient process that allows manufacturers to produce large quantities of parts quickly and accurately. This helps to reduce overall production costs.

High Precision:

The accuracy of plastic injection molding makes it well-suited for producing parts with tight tolerances. This ensures that parts are consistently produced to exact specifications.


Injection molding produces extremely durable parts and is resistant to damage. This makes them ideal for applications where strength and reliability are important factors.


Many plastics can be used in the plastic injection molding process, giving designers and manufacturers a wide range of options for creating parts with unique properties.


Custom plastic part is a fast process that can quickly produce large volumes of parts with minimal waste. This helps to reduce lead times and keep production costs low.

How To Choose The Right Injection Molding Suppliers?

plastic injection molding parts

When selecting a plastic injection molding supplier, it is important to consider the company’s experience, capabilities, and reputation. Here are some tips for choosing the right injection molding supplier for your project:


Look for a supplier with considerable experience in producing parts with similar requirements to yours. Ask about the types of materials and processes they use, and review their portfolio for examples of successful projects.


Make sure the supplier you choose has the capabilities to produce your parts promptly. Ask about their production capacity, turnaround times, quality control measures, and delivery services.


Research the suppliers’ reputation and customer reviews. Look for suppliers with a proven track record of producing high-quality parts and providing superior customer service.


Compare prices from different suppliers to get the best deal. Consider not only the cost of materials but also any additional services such as assembly or painting.

Why Choose Aria Manufacturing For Your Injection Molding Project?

At Aria Manufacturing, we specialize in producing custom plastic injection molded parts for a wide range of applications. Our experienced team is committed to providing high-quality products and outstanding customer service. We use the latest technology and advanced production techniques to ensure that each product meets our customers’ requirements.

We offer a variety of services, including:

  • Design assistance to help you create the perfect part for your application
  • Expertise in a wide range of materials and processes, from ABS to PEEK
  • In-house tooling and production capabilities
  • Short lead times with no minimum order requirements
  • Comprehensive quality control measures for consistent results
  • Competitive prices and volume discounts

Contact us today for more information about our custom plastic injection molding services. We look forward to helping you create the perfect part for your project.


Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.