Advantages and Disadvantages of Injection Moulding

Advantages and Disadvantages of Injection Moulding

Injection moulding has a number of advantages. It minimises moulding costs and is a highly repeatable way of producing plastic or elastomeric parts with high precision. Once set up, it can manufacture a large volume of parts per hour, from a wide range of different plastics plus other materials such as liquid silicone rubber.

Like any manufacturing process, it does have some disadvantages, and if these prove important then you may be better off exploring alternative technologies such as 3D printing or CNC machining.

Here we will take you through the main advantages of Injection Moulding and explore when it may be better for you to consider an alternative option.

6 Major Advantages of Plastic Injection Molding

Plastic injection molding is an extremely versatile method of producing plastic parts and has multiple advantages over other methods of plastic molding. Not only is the process simpler and more reliable than others methods, but it is also extremely efficient.

Let's take a look at the top six advantages of this process:  

1. High Efficiency- Fast Production

There are several good reasons that plastic injection molding is known as the most common and most efficient form of molding. The process itself is extremely fast compared to other methods, and the high production output rate makes it even more efficient and cost-effective. Speed depends on the complexity and size of the mold but only about 15-120 seconds pass between each cycle time.

With the short period between cycles, a greater quantity of molds can be produced in a limited amount of time, thus increasing possible revenue and profit margins. At Rodon, we run parts 24/7 using an MRP system (Material Requirement Planning System). While the MRP system can’t replace the input and experience of manufacturing managers, it does help improve efficiencies within the factory and this, in turn, creates savings for the customer. 

2. Complex Part Design

Injection molding can handle extremely complex parts, and uniformity, as well as the ability to make millions of virtually identical parts. To optimize the effectiveness of high-volume injection molding and maximize the precision and quality of your parts, key design elements should be taken into account. The part design must be developed to maximize the efficiency inherent in high-volume molding.  With the right design, parts can be made consistently and with quality.  Without a good design, costly processing mistakes can be made.

Around the industry, most molding professionals agree that there are fundamental design elements that must occur during the injection process to work correctly. They include wall thickness, rib design, boss design, corner transitions and weld lines and gate placement, and properly placed vents. You can learn more about all of these elements here.
 

3. Enhanced Strength

Strength is one of the key factors that need to be determined when designing a plastic injection molded part. The designer will need to know if the part needs to be flexible or rigid so that he/she can adjust the integrating ribs or gussets. Understanding how the customer will be using the part and what type of environment the part will be exposed to is also important.  

Finding the proper balance of design considerations will help address your part’s need for strength and stability. Material selection plays another key role in the strength of the part.  See below for more information on the types of resins used in the process. 
 

4. Flexibility- Material and Color

Choosing the right material and color for a project are two of the essential factors in creating plastic parts. Due to the wide variety of both, the possibilities are almost endless.  The advances in polymers over the years have contributed to the development of a large selection of resins from which to choose.  It is important to work with an injection molder that has experience with a variety of resins and applications including resins that are compliant with FDA, RoHS, REACH and NSF. To ensure you select the right resin for your project, keep in mind the following variables: impact strength, tensile strength, a flexural modulus of elasticity, heat deflection and water absorption.

Plastics can be colored using various coloring systems, each of which offers its own unique properties, benefits, and drawbacks. Masterbatches,”salt and pepper” blends, Liquid Color, and precolored resins are four of the most common coloring techniques.  To learn more, check out our recent article on how plastic resins get their color. 
 

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5. Reduced Waste

When looking for a high-volume injection molding partner, it’s important to consider companies’ green manufacturing initiatives, as these signify a commitment to quality, sustainability, and optimal safety. During the molding process, excess plastic is generated. You want to look for a company that has a system in place to recycle its excess plastic. The most eco-friendly plastic injection molding companies employ state-of-the-art machinery to assist them in minimizing waste, transportation, and packaging. 

6. Low Labor Costs

Labor costs are typically relatively low in plastic injection molding, in comparison with other types of molding. The ability to produce the parts at a very high level with a high output rate helps with its cost efficiency and effectiveness. 

The molding equipment typically runs with a self-gating, automatic tool to keep operations streamlined and production ongoing, requiring minimal supervision. 

Automation abounds at Rodon, from our 3D computerized design capability and automated tool fabrication processes to our computerized and automated plastic injection molding machines and robots. The entire Rodon facility is setup to produce the highest quality most economical plastic injection molded components in the industry.
 

Advantages and Disadvantages of Injection Molding

Injection molding involves injecting molten plastic into carefully designed molds before cooling and ejecting the final part. It’s a highly repeatable process that enables companies to create high volumes of identical plastic parts with good tolerances at a low cost per part.

Injection molding has numerous applications in a wide variety of industries — from the automotive industry to the medical industry — but it isn’t the best choice for every project. Before you decide whether or not to injection mold your part, carefully consider the injection molding pros and cons.

The Advantages of Injection Molding

Many manufacturers turn to injection molding because:

1. It allows for complex geometries with tight tolerances.

Injection molding allows for large volumes of uniform, complex parts. However, you must pay attention to vent and gate placements, weld lines, corner transitions, wall thickness, rib and boss design, and more to ease ejection and achieve precise parts.

With injection molding, you can easily achieve repeatable part tolerances of ± 0.500 mm (0.020’’). In some cases, you can even produce parts with tolerances of ± 0.125 mm (0.005’’), giving you parts that are accurate enough for most applications and comparable to 3D-printed or CNC machined parts.

2. It’s compatible with a wide range of materials and colors.

Today, there are over 25,000 engineered materials that are compatible with injection molding, including thermoplastics, thermosets, resins, and silicones. With all of these options, you’ll be able to find one that offers the right balance of physical, mechanical, and chemical properties. Commonly used materials include acrylonitrile butadiene styrene (ABS), polyethylene (PE), polystyrene (PS), and polypropylene (PP). You can also use a mixture of materials to produce a part with the strength, impact resistance, or stiffness you need. For example, you might add glass fibers to your thermoplastic to create a strength-enhancing composite.

You also have a variety of options when it comes to colors. Consider using masterbatches, pre-colored resins, liquid colorants, or salt and pepper blends to achieve your desired color.

3. It’s very efficient.

While it can take several minutes — or even hours — to 3D print or CNC machine a single part, most injection molding cycles only last 10 to 60 seconds. Even if you have a complex geometry that takes around 120 seconds to mold, you can include several smaller parts in one larger mold. This helps maximize efficiency and gets the most out of each mold, allowing you to create hundreds of identical parts an hour at a low cost.

4. It offers high repeatability and reliability.

One of the main benefits of plastic injection molding is its high repeatability. Once you’ve created your mold, you can produce thousands of parts before needing to maintain your tooling. An aluminum mold will generally last between 5,000 and 10,000 cycles, and a full-scale steel production mold can last for over 100,000 cycles. Plus, since injection molding uses the same mold for each part, you’ll have identical products.

5. You can reuse material.

Though injection molding generates less post-production material waste than many other manufacturing processes, it still creates excess scraps. However, you can easily regrind, melt, and reuse any sprues, runners, or other leftover plastic parts to save on material and reduce material waste.

The Disadvantages of Injection Molding

There are plenty of advantages of plastic injection molding, but it’s not without its drawbacks. Some disadvantages include:

1. Start-up costs are high.

Since custom tooling must be created for each injection molded part, initial start-up costs are high and this isn’t economical for low-volume production runs. Tooling for a simple design and a small production run can cost between $2,000 and $5,000, but tooling for large, complex molds ready for full-scale production can cost several times that. Although you can reuse these molds again and again and save on tooling costs down the line, it’s worth considering how much molds cost upfront. An injection molding manufacturing partner can help you maximize your budget and refine your mold design so you can produce the best possible part for the best price.

2. Initial lead times are long.

A CNC machined part can be delivered within 5-10 days, and industrially 3D printed parts often have lead times of 3-5 days. However, injection molding has a longer lead time. It often takes 5-7 weeks to manufacture tooling and 2-4 weeks to produce and ship parts.

In part, this long lead time can be attributed to the complexity of the molds themselves. In addition to containing the negative of the part, these molds have complex runner and water cooling systems to facilitate material flow and faster cooling. It can take months of design and testing before the final mold is ready for production, and any design changes can further increase turnaround times.

With the help of a manufacturing partner’s expertise, you can avoid falling into common mold pitfalls that might set you back weeks and thousands of dollars. They can also help accelerate the design, testing, and production phases.

3. Design changes are expensive.

With 3D printing, you can simply upload a file and print a new part whenever you make a design change, but that’s not the case with injection molding. If you make a design change, you’ll likely need to create a new mold from scratch, which means pouring more time and money into your project.

To avoid costly design changes and ease the demolding process, avoid undercuts and sharp edges, ensure wall thicknesses are uniform, and add draft angles. If you need some guidance, an experienced manufacturing partner can offer expert design advice.