Injection Molding Plastic

The Complete Guide to Injection Molding Plastic Parts

When it comes to large batch production of plastic parts with intricate designs, nothing beats the injection molding process. Every industry, whether it manufactures auto parts or kitchen utensils chooses injection molding methods for large-scale production of plastic parts. With more than 15 years of service, Rally Precision is recognized as one of the most trusted manufacturers for injection molding plastic parts. We provide injection molding services not only for local clients but also to our valuable customers around the globe. The fundamental principle of the injection molding method is to achieve flexible designs, at a reduced cost.

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This article focuses on every aspect you need to know about injection molding of plastic parts. By the end of this article, you will have a better understanding of the basic mechanism of the injection molding process. Moreover, enhance your injection molding knowledge by learning about its applications, materials, benefits, and limitations.

What is Injection Molding?

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Injection molding is a manufacturing method that produces large batches of complex design products by injecting molten plastic into a mold. The injection molding produces huge amounts of identical plastic parts with good strength and high accuracy. The plastic parts manufactured using the injection molding process can be colored using different additives and pigments.

With a flourishing plastic industry, injection molding is becoming widespread with each passing day. The typical working principle of injection molding is based on melting the polymer granules, injecting them into molds, and taking them out when cooled. However, the complete process of injection molding plastic parts is not as simple as this. There are several steps involved in injection molding, including:

  • Mold Closing

The timer for the injection molding process starts when the mold is positioned into the injection molding machine (IMM). The clamping tools of the machine close the mold.

  • Injection

The melted granulated polymers are injected into the closed mold, with the help of an injecting cylinder. Before the injection process, the granules are mixed with pigments.

  • Pressure

As soon as the melted granules are injected into the mold, a constant holding pressure is applied to them. This phase allows the liquid granules to become denser in volume.

  • Cooling

The resin in the mold is left for cooling so that it completely solidifies. The cooling time for each type of polymer varies on several factors.

  • Mold Opening

When the resin cools down completely, the clamping tools allow the mold to be opened. The final plastic product is then pushed out of the mold by ejectors.

Designing mold for injection molding

Designing the suitable mold for your injection molding products depends on a number of factors. The first thing to consider is the characteristics of your desired plastic-type. Commonly there are two types of plastics; one is called thermosets and the other type is thermoplastics. The thermosets undergo reversible chemical changes when processed in the injection molding, so the design of the mold needs more attention. Whereas, thermoplastics do not go through any chemical change and are easier to injection mold.

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The second crucial factor for designing the mold in injection molding is the choice of the gate for the injection process. There are plenty of designs available for molds used in plastic injection molding, ranging from simplest to highly complex shapes. For each kind of mold design, some basic requirements remain the same, such as the gate of the design. A gate is an opening in the mold design that permits the molten granules to be injected into the mold. The location, design, and the type of gate used in a mold design can have an impact on the final product. Manufacturers generally use two types of gates for designing molds; automatically trimmed and manually trimmed gates.

Materials selection for Plastic Injection Molding

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Figure: Materials for plastic injection molding

Choosing the right material for the injection molding plastic parts plays a vital role in the quality and accuracy of the final products. There are unlimited material options for injection molding plastic parts. To select the suitable material for your plastic molding, the first thing is to consider the application of your final product. Each material has a unique set of properties that work best in a certain industry. Apart from that the strength, color, flexibility, price, and durability of the injection molding material should also be considered. Nylon, Polycarbonate, PVC, Acrylic, POM, PA6, PA66, TPEE, and ABS are some of the commonly used materials for injection molding.

Why use Injection Molding?

The main reason why you should choose injection molding for manufacturing your desired plastic parts is the cost. When compared to the other manufacturing methods, injection molding is extremely cheap. The major expense of injection molding is the initial setup, after which the cost for individual pieces of plastic becomes relatively lower. The cost of the injection molding process reduces with the increase in the number of plastic parts to be manufactured.

Many industries prefer injection molding for their desired order because it can manufacture plastic parts on a massive scale, within no time. The injection molding process has a unique ability to multiply the production of hundreds of identical parts. This proves to be extremely beneficial for the industries that require the mass production of plastic products. When they can get their batch order at a practical cost and lesser time, injection molding seems the most feasible manufacturing process.

Benefits of Plastic Injection molding

Plastic injection molding is one of the versatile methods of manufacturing high-quality plastic parts at a massive level. There are plenty of benefits of injection molding, such as:

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  • Efficient Production

Injection molding is best known for its high-efficiency production of plastic parts. It can produce even the most complex designs of plastic parts at a high speed. The time cycle for the production of each batch of plastic parts is lower than many other production methods with the same results.

  • Versatile products

Injection molding can produce plastic parts with extremely complex designs and higher strength. Injection molding offers great flexibility in terms of colors, shapes, and designs of the final products, which is hard to achieve with any other process.

  • Lower waste

In this era, companies are keen on investing in manufacturing processes that preserve the environment, such as injection molding. This method produces a minimal amount of waste materials, allowing an eco-friendly production of plastic parts.

  • Cost-efficient

The cost of injection molding plastic parts is extremely low, as compared to any other manufacturing method. Being an automated process, the labor cost is nearly eliminated in this method. Similarly, the cheap raw material used for injection molding makes its production prices lower.

Applications of plastic Injection molding

Figure : Applications of plastic injection molding

The production of a large variety of complex plastic parts is made possible by the injection molding process. Plastic parts produced using this method are being used in all sorts of industries. Here are some applications of plastic injection molding:

  • Food Factories

Injection molding for plastic parts is used in the food and beverage factories for the manufacturing of safe food materials. The production of BPA-free components and non-toxic plastic items, like bottle caps, and food containers is a typical application.

  • Construction Materials

Injection molding is done for the production of numerous construction materials such as locks, plugs, handles, and stoppers, etc. The use of this method for the manufacturing of windows and door covers is fairly common due to excellent insulation.

  • Medical and Pharma Industries

As the injection molding process can create plastic parts with high quality and eco-friendly properties, it is prevalent in the medical and pharma industries. Goods like X-ray tools, testing kits, surgical preparation gadgets, and pill holders are produced.

  • Electronics

A never-ending list of everyday used materials is being produced by the process of injection molding, such as CDs, switches, and hooks, etc. The electrical industry invests a lot in the production of plastic electronic tools by the injection molding process.

Injection molding quality assurance

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To ensure the highest quality of the plastic parts produced by the injection molding process, there is a credible structure maintained by the ISO. A well-maintained system provides certifications authorized by ISO for the quality assurance of the end products. All the manufacturers of injection molding like Rally have to go through a quality control audit to secure ISO certifications. Maintenance of strict quality standards is mandatory for meeting the safety guidelines assigned by the ISO. We own the following certifications:

  • FDA registration: ISO 7, cleanroom
  • ISO certification 9001 for manufacture, and testing for industry
  • ISO certification 13485 for the medical industry products

Inspection equipment

For the quality assurance of the injection molding parts, specialized equipment is used that not only identifies the defects but also matches the customers’ requirements to the final products. Rally Precision is equipped with the latest inspection equipment for delivering the best products to our customers. We use OGP Smartscope 500 to measure the accuracy of the plastic parts. For the inspection of the color standards, a Spectrophotometer is used. During the manufacturing process of plastic parts, a Moisture Analyzer measures the level of moisture in the resin.

Surface finishing solutions of injection molding plastic parts

One of the noteworthy benefits of injection molding is the natural surface finishing its offers for its molded parts. However, some companies prefer to have much glossier finishing for their molded parts, for which there are plenty of surface finishing solutions. Here are some of them:

  • Grade A

This type of surface finishing is achieved by surface finishing solutions like diamond buff polishing. The end results are extremely smooth and glossy finishings.

  • Grade B

Grade B surface finishing produces a mildly glossy appearance, and it is suitable for a wide range of molding materials. This type of surface finishing takes place by grit sanding.

  • Grade C

For a matte finishing of the plastic molding parts, gritstone sanding works the best. This finishing grade can be accomplished for almost all plastic materials.

  • Grade D

Grade D offers the roughest and textured finishing for injection molding plastic parts. For this type of finishing sandblasting process proves most efficient.

What are some of the considerations and limitations of injection molding?

Despite its innumerable benefits for manufacturers and customers alike, there are some considerations and limitations of this process that need to be addressed.


Before initiating the manufacturing of injection molding plastic parts, consider the following aspects:

  • Start-up Costs

Even though the cost of the injection molding plastic parts is very low for mass production, and raw materials, the initial expense for setup is a lot.

  • Mold Designing

Injection molding with utmost accuracy requires expertise and knowledge of mold designing. Some design tools are also required for flawless products.

  • Cycle Time

For the mass production of injection molding plastic parts, the cycle time has to be as minimum as possible.


These are some limitations listed by the experts for the injection molding process:

  • Expensive Tooling

The cost and time for the initial design and prototype that can produce multiple identical copies is a lot. Before starting the mass production of any design of molding plastic, there has to be a testing phase, which is fairly expensive and time-taking.

  • Less Room for Errors

Unlike other manufacturing procedures, there is little room for errors in this process, as the changes are extremely difficult to make. In most cases, to amend the product, you have to start over.

Does Rally Precision offer injection molding services for plastic parts?

Yes, Rally Precision does offer injection molding services globally under the guidelines allocated by the ISO. Our 15 years of experience in injection molding enables us to provide flawless plastic parts with intricate designs. We produce premium-quality and versatile plastic parts by injection molding and ship them to our customers after doing a thorough quality inspection. Rally Precision is laden with more than 30 advanced injection molding machines that range from 50-500 tons. We have a hefty list of versatile plastic materials for the injection molding operations including, HDPE, PVC, ABS, PA66, POM, and PMMA, etc.


Injection molding is a high-tech manufacturing process for the large-scale yield of various complex and simple plastic parts. The process of injection molding is very simple yet it is difficult to make any amendments to the product during the process. Injection molding plastic parts can be surface finished using polishing and sandblasting methods. Along with producing low-cost molding plastic parts for vast industrial applications, injection molding is also suitable for prototype making.

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