How to Select an Injection Molding Machine

Table of Contents

selecting an Injection molding machine
selecting an Injection molding machine


Injection molding relies on an injection molding machine to guarantee that procedures and finished products meet the required level of excellence. And, these machines have different configurations, each designed for specific applications with unique benefits.

However, if you’re thinking of using injection molding to create innovative custom-made items then it’s important that you understand the basics of this equipment especially when in the market for one. Still, handing everything over to your injection molding manufacturers to handle the matter independently is yet another option.

So, if you are ready to explore the different types of injection molding machines then come along.

Section 1: Understanding Injection Molding Machine Types

Injection molding machines come in different classes based on their performance methods, and each class utilizes specific parts, resulting in varied performances and outcomes. So, let’s help you understand these machines and their parts for maximizing their potential.

  • Hydraulic Plastic Injection Machine: We start with the hydraulic injection molding machine which relies on hydraulic power for injection force. But here is the thing about this machine, you’ll need to closely monitor the machine’s temperature during production to avoid defects in plastic components. Also, continuous operation is necessary to prevent damage from inactivity. However, the hydraulic injection machine has many benefits that make it rock solid. They include lower cost, inexpensive parts, stronger components, and exceptional clamping force. Interestingly, this machine will suit your needs if your molded parts have fewer complex features but require a strong clamping force to achieve flawless results.
  • Fully Electric Injection Molding Machine: Next is the fully electric injection molding machine which comes at a higher price tag than its hydraulic counterpart. However, it offers stability without standby or temperature changes. Interestingly, it’s more efficient, eliminating liquid leaks common in hydraulic machines. But the best part is its benefits. This includes energy efficiency, less downtime, a faster and repeatable process with minimal supervision, and clean operation without oil. It all boils down to its application which involves parts with more complexity, requiring minimal clamping force for excellent results.
  • Hybrid Injection Molding Machine: Here is the best of both worlds – the hybrid machine, combining high efficiency and cost benefits. It incorporates the advantages of both hydraulic and all-electric processes, offering median costs compared to other types. This energy-efficient machine provides design flexibility and diverse benefits, outperforming its counterparts.

Moreover, hybrid molding machines combine the precision of electric molders with hydraulic power, reducing downtime and maintenance needs. The efficiency is enhanced with a pump that operates only when needed, making it an affordable option, especially for medical device manufacturers.

selecting a hydraulic Injection molding machine
selecting a hydraulic Injection molding machine

Section 2: Assessing Your Project Requirements

A mistake in choosing an injection machine can cause operational problems, waste resources, and, ultimately, lead to customer dissatisfaction. Here are important factors to consider when selecting a suitable injection molding machine:

Firstly, the size and complexity of the parts you want to produce are crucial because it determines the machine’s capacity required to meet your production requirements. If the machine doesn’t have enough tonnage and sophistication to meet the required precision, making quality parts will be hard. This can lead to issues like inconsistent weights, burrs, incomplete parts, variations in wall sections, poor surface finishes, and differences in part dimensions.

Secondly, choosing the right material may seem obvious, but different types and grades of plastics and polymers have various uses and properties. Make sure the material you select is compatible and appropriate for the final product’s use. As an example, the plastic requirements for a medical part can be significantly different from those for a subassembly component for an automotive application. Considerations such as temperature, biological and chemical interactions, contact with food or animals, and more must be considered.

Again, considering the volume of your production when choosing an injection molding machine can be critical because different machines perform differently in terms of efficiency. Durability becomes a question when machines exceed their volume capacity, leading to high maintenance costs and downtimes.

Clamping force of an Injection molding machine
Clamping force of an Injection molding machine

Section 3: Key Specifications to Consider

Regardless of the type of machine you eventually choose, key specifications that support your injection molding project remain true during your selection and they are highlighted below.

  • Clamping force: When it comes to clamping force, it’s all about how big your product is and what it’s made of. The required clamping force depends on the projected area of the item, the number of cavities, and the pressure needed to inject. Other factors like the material being injected and the type of casting also play a role. As a general guideline, you’ll need 2 to 3 US tons of force for every inch of the projected area. But for tough-to-flow resins like PC, you might need 4 or more tons per square inch.
  • Injection capacity: Injection capacity is the maximum amount of material a machine can inject, and it’s calculated by multiplying the injection volume by the density of the molten material. Usually, this value is given in grams of PS, which has a density of 0.9 grams per cubic centimeter. That’s why the injection capacity is typically 10% less than the injection volume. For example, if you want to inject 100 grams of Polypropylene, you’ll need an injector with a capacity of 137 cubic centimeters or 125 grams of PS.
  • Platen size, Tie-bar spacing, and Ejector Stroke: Essentially, the mold opening distance should be such that the space between the fixed template and the injection plate is adequate, especially for three-plate or double-wall injection molds. Most importantly, when designing the mold for the injection molding process, make sure the tie-bar distance is not exceeded. This ensures the proper functioning of the mold and the machine. Additionally, since the ejection stroke of the machine is fixed, it’s important to select a machine with an ejection stroke that matches the mold structure and the product design. A longer ejection stroke is often better for a variety of parts.
Injection molding Manufacturers Automation
Injection molding Manufacturers Automation

Section 4: Evaluating Machine Features and Technology

With the advancement in the technological space swiftly creeping into many industries including the injection molding sector, manufacturers now have ample options to enhance their production.

  • Advanced control systems: The use of modern injection molding machines avails the manufacturer the option of advanced control systems to fine-tune the process. Fine-tuning the overall injection molding process, including optimizing parameters such as filling time, packaging time, and cooling time, can help shorten cycle time. And with advanced systems and controls these optimizations can be done on the fly and in real-time. Process optimization involves finding the right balance between part quality, cycle time and overall productivity. By carefully analyzing and optimizing these factors, manufacturers can achieve shorter cycle times, higher productivity and greater efficiency in the injection molding process. Reducing cycle time not only benefits production performance but also improves competitiveness in meeting customer demands and achieving profitable operations.
  • Energy efficiency: When thinking of buying an injection molding machine, an important understanding is the differences between the options available: hydraulic, electric, and hybrid especially their energy consumption. Hydraulic machines are used a lot in the industry. They’re great because they have really strong clamping force, which is perfect for making big parts. But they do use up more energy and work at slower injection speeds compared to electric machines. On the flip side, electric machines are becoming more popular because they’re much better with energy and they inject things faster. They also give you more control when you’re injecting, so you end up with better quality stuff at the end. But they can’t clamp as much as hydraulic machines, so they’re better for making smaller pieces. Then there are hybrid machines, which take the best of both worlds. They’re super energy-efficient and inject really fast, and still have good clamping force. Even though they cost more upfront, they’re really versatile and work great, which might make spending more worth it.
  • Software and Automation: Modern injection molding machines often come with advanced software that enables semi-automatic and fully automatic operation. With a well-designed mold, a modern injection machine can operate fully automatically from injection to molding and product ejection. Additionally, if equipped with robots, it can even run unmanned. Automated functions, such as core extraction, plugging, hydraulic nozzle control, and rapid channel probe heating, can all be programmed into the injection molding cycle for automatic operation.
Injection molding cost
Injection molding cost

Section 5: Cost Considerations and Budgeting

Buying an injection molding machine can be seen as an investment rather than just an expenditure. This perspective arises from the high initial cost of purchasing this machine. However, when you consider the long-term benefits, it all starts to make sense. These benefits include the repeatability of molded parts and the ability to produce a high volume of parts. In the long run, this production comes at a reduced cost per unit compared to other forms of manufacturing.

Additionally, if you ever consider buying a used machine especially when budget becomes a critical factor, ensure that you critically consider the pros and cons before finalizing your decision. For instance, ensure that the used machine is well-tested and trusted before picking it up from the seller. Issues like leaking oils, incessant maintenance, and unavailability of parts can render a used machine less productive and costlier on the long run.

Although maintenance and repair costs are still part of the lifetime cost of owning a molding machine, you should understand that equipment depreciates over three years due to fast changes in technology. This is because every 4 or 5 years, there are significant changes in technology, making it challenging to get spare parts. This can also render existing equipment partly or entirely obsolete.

Plastic injection molding partner
Plastic injection molding partner

Section 6: Vendor Selection and After-Sales Support

Choosing a reputable injection molding machine vendor is both critical to the success of your projects and the reputation of your company.  The truth is your vendor is also your partner in this matter and selecting one that does not enhance your productivity can be disastrous. However, you consider the following points when choosing a suitable injection molding machine manufacturer,

Firstly, check the reviews and customer feedback. Most injection molding machine suppliers provide consumer feedback on their websites. It’s an effective way to ascertain their reliability.

Secondly, check the website for the “About Us” section. If you can’t find what you’re looking for, try contacting them and starting a conversation from which you can determine if they are reliable or not. 

Thirdly, it’s crucial to contact the maker of the injection molding machine. Unless you reach out to them, you won’t know much about the supplier. Pay attention to how quickly they respond to messages and inquiries. This will give you an idea of their eagerness and what it’s like to deal with them.

Lastly, you should ask critical questions of your vendor including their warranty policies if they give product warranties. Also, find out if they offer personnel training to enable your employees to operate the machines correctly and effectively. In all, confirm their aftersales support policy and their response rate when called upon for technical support. All these secondary features and services will aid your informed decision in arriving at a suitable injection molding vendor as a partner.


In all, selecting a suitable injection molding machine for your project is not that hard. It only becomes daunting when you don’t have the necessary information required to make an informed decision like we’ve presented in this post. The most important thing is to select a reliable vendor who understands your peculiar needs and has the experience and track record to pull it off.

Ensure you engage this vendor with critical questions regarding your project requirements, suitable machine types, material compatibility, and customer feedback. Also, enquire about their warranty policies, aftersales technical supports, and personnel training as these are the bedrock of a successful injection molding project. So, now that you’ve been equipped with this information, go out there and get for yourself a fitting injection molding machine.


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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