How to Choose the Right Injection Mold Machine -

introduction

Injection molding is a widely-used manufacturing process in the plastics industry. To ensure optimal production efficiency, product quality, and cost efficiency when selecting a plastic injection molding machine, we will cover key factors to consider when making this choice. Furthermore, we’ll answer common questions such as “How do I know what size injection molding machine I need?” or “What are the three basic types of injection molding machines?” with keywords like “injection molding machine,” “plastic injection molding,” and more to get you on your way.

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What to Consider When Selecting an Injection Mold Machine

A. Dimension of the Machine

The size of plastic injection molding machine plays a significant role in determining production efficiency and product quality. Here are some factors to take into account when deciding on the ideal machine size:

Product Requirements: The size, weight, and complexity of a product dictate its optimal machine size. Generally speaking, larger items require larger machines.

Mold Size: The size of a mold used for injection molding determines the machine required. Larger molds necessitate larger machines.

Shot Size: The amount of plastic material required for each shot of injection molding determines the machine size. Larger shots necessitate larger machines.

Clamping Force: The clamping force required to hold a mold closed during injection molding determines its size. A stronger clamping unit requires larger machines.

To calculate the required machine tonnage and injection volume, consider the following:

Tonnage: Calculate the tonnage required by multiplying the projected area of the part being molded by the pressure required to inject the plastic material into the mold. This calculation determines the force needed to hold the mold closed during the injection.

Injection volume: Calculate the injection volume by multiplying the part volume by a factor of 1.5 to account for material shrinkage during the molding process.

Overall, choosing the right machine size is critical to ensure efficient and effective injection molding production

B. Type of Injection Molding Machine

1. An overview of various injection molding machine available on the market today

Injection molding machines come in three basic varieties: hydraulic, electric, and hybrid. Each has its advantages and drawbacks; ultimately, which type best meets your production requirements depends on what works best for you.

Hydraulic injection molding machine are the oldest and most widely used type of machine. Their high clamping force makes them perfect for producing large parts, though they use more energy and have slower injection speeds compared to electric machines.

Electric injection molding machines have become more and more popular due to their energy efficiency and faster injection speeds. Furthermore, these machines provide precise control of the injection process which ultimately results in higher product quality. On the downside, electric machines have lower clamping forces compared to hydraulic ones, making them better suited for smaller parts.

Hybrid injection molding machine bring together the benefits of both hydraulic and electric machines, offering faster injection speeds with greater energy efficiency compared to hydraulic machines while having greater clamping force compared to electric ones. Unfortunately, they tend to be pricier than either type of machine.

When selecting the type of machine to use, take into account factors like production efficiency, energy consumption, and product quality. Electric machines may be cost-effective in the long run due to their lower energy usage but may not be suitable for large parts requiring high clamping force. Ultimately, selecting the correct type of machine depends on your specific production needs.

C. Injection Molding Process Parameters

When selecting an injection mold machine, parameters like injection pressure, speed, and screw diameter When selecting an injection mold machine, parameters like injection pressure, speed, and clamp tonnage must be taken into account. Here are a few things to keep in mind when making your selection: clamp tonnage must be taken into account. Here are a few things to keep in mind when making your selection:

Injection Pressure: This refers to the force required to inject melted plastic into a mold cavity. It depends on both the viscosity of the plastic material and the size and shape of the cavity. Higher injection pressure may lead to better product quality but also increases defects.

Injection Speed: This refers to the rate at which plastic material is injected into a mold cavity. It depends on the size of the injection unit and desired filling time. A higher injection speed can result in improved production efficiency, but may also increase defects.

Clamp Tonnage: Clamp tonnage refers to the force necessary to hold a mold closed during injection molding. It depends on the size and shape of the mold as well as the material being used. Adequate clamp tonnage is essential for maintaining consistent product quality by avoiding defects.  

When setting parameter values for your product, take into account both technical specifications and raw materials used. For instance, certain plastic materials may need higher injection pressure to achieve the desired quality.

Maintaining accurate parameter values throughout the production process is essential for achieving optimal product quality and production efficiency. Regular upkeep and monitoring can help prevent deviations in parameter values, thus minimizing the risk of defects.

D. Other Factors to Consider

Physical fit and technical requirements of the machine

The injection machine should be physically suitable for the workspace and production needs

Technical requirements should be considered, such as compatibility with the plastic material being used

Power consumption and energy efficiency

Electric injection molding machine generally have lower power consumption than hydraulic machines

Hybrid machines offer a balance between energy consumption and performance

Availability of parts and technical support

Choose the right injection molding machine manufacturer that offers reliable technical support

Availability of parts and maintenance services should also be considered.

Production cost and return on investment

Consider the production cost and potential return on investment when choosing an injection molding machine

The right machine can lead to increased production efficiency and cost savings in the long run.

Conclusion

Selecting the ideal injection mold machine is critical for the success of plastic injection molding. By taking into account factors like machine size, type, process parameters, and other important details, manufacturers can guarantee optimal production efficiency and high-quality finished products. When selecting a machine it must meet both product-specific needs as well as plastics industry requirements while considering factors like power consumption, parts availability, and production cost. Doing this allows manufacturers to achieve the balance between performance and cost efficiency which then leads to more profitable operations overall.

It is important to select suitable models of plastic machinery for your plastic products. You will learn 7 proved procedures to choose right models of injection molding machines. Meanwhile, you will grasp 4 ways to calculate locking force of clamping units. You will be an expert in selection of models after minutes-reading.

In general, most customers who have been in plastic industry for many years have the ability to select suitable model of plastic injection machines for their own projects. But sometimes, customers will require support from us, the manufacturers of plastic injection moulding machines to give suggestion on correct models of machines. Sometimes, customers only have samples in hand or just idea of new item in their brains, and then they need to be sure if our machines can make their new products or which model is best. And customer maybe require complete solution for efficient production. For example, for some special plastic parts, the production line will require accumulator, close loop, injection compress, etc. So, it is very critical to select right model of plastic injection machines. We prepared below information for your reference.

Preparation before selecting suitable models of machines

Usually, there are important factors like injection molds, products, plastics, shape, output, etc. So, before our choice, we need to collect all information as below:

7. Procedures to choose correct machines

When we have the above information, we can choose suitable plastic machines by following procedures:

1.Choose correct series by plastics and finished products
As you know, there are so many series or types of plastic injection machines. So at the beginning, we need to make sure which series or which type of plastic machines are suitable for you. For example, material or products has different property like thermosetting or thermoplastic, single color, double colors or multi-colors, interlayer or color mixing, etc. And some products require higher production conditions like close loop, high accuracy, ultra-high injection speed, high injection pressure, quick production, etc. By analyzing plastics and finished products, we can decide the series of plastic injection machines.

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2.Choose big enough clamping force of machines according to your mold
We can decide the required tie-bar distance, mold thickness, minimum mold sizes, platen size, etc. as per mold sizes.

The height and width of molds should be smaller or at least one-side smaller than tie-bar distance.

It will be better if the height and width of molds are among the sizes of platen.

The thickness and the height of mold is within the range of mold thickness of plastic injection machines.

The thickness and the height of mold is bigger than minimum mold sizes. Too small molds are also not suitable.

3.Enough stoke to take out the products
As per mold and product size, we will judge if the open stroke and eject stoke is enough to take out the products. Mold open stroke should be at least twice of products sizes in the direction of mold open and mold close. And Mold open stroke should be larger than the length of vertical sprue.

Ejection stroke should be enough space to eject out the products.

4.Enough locking force
When plastic material in melting status is shot into the mold cavities by high pressure, it will bring high pressure inside of the mold. So, if without the enough locking force, the mold will be open and raw material will leak, even cause accident to molds and operators. It is very critical to have enough locking force.

There is ways to calculate the locking force:

-as per product sizes, we can get projected area in the direction of mold open and mold close.

-high pressure inside of the mold=projected area (cm2) *number of cavities*cavity pressure(kg/cm2)

Mold cavity pressure is different with different material. Usually, we can take 350-400kg/cm2.

Only when locking force is larger than mold-inside pressure which is trying to open the mold, the injection process can be successful. For safety’s sake, the clamping force should be over 1.17 times of mold-inside pressure.

Till here, we can be roughly sure which specification and locking tonnage for clamping unit. In next procedures, we will decide which screw in injection unit is suitable.

5. Full injection or full shot
As per finished products weight and number of cavities, we can check suitable shot weight and suitable screw diameter.

For better stability, the shot weight of machines should be 1.35 times at least of products weight. In another word, the products weight should be 75% lower than shot weight of molding machines

6. Well shot
We can get rough idea of screw L/D ratio and injection pressure, etc. Some engineering plastics require high injection pressure and suitable screw L/D compress ratio. To get better finished products, we need to consider injection pressure and L/D ration during selection of screw.

Generally speaking，screw with small diameter can produce high injection pressure.

7.Faster injection
Some plastic parts require high injection speed to get stable shape like thin-wall products. In this situation, we need to check if injection speed is enough, check if the machines need to equip with accumulator, close loop controller, etc. Generally speaking, under same condition, screw having higher injection pressure has lower injection speed, reversely, screw having lower injection pressure has faster injection speed. In a word, during choosing screw, we need to consider injection rate, shot volume, shot pressure.

With above 7 procedures, we will have the skills to choose suitable models of plastic injection machines for common situation. But we still need to consider some other factors when customers need some special injection molding machines:

1.In some special situation, customers’ plastic products or plastic molds are smaller in sizes but require bigger shot volume or mold is big in sizes but require small shot volume. Thus, our standard specification of machines cannot meet with the requirement. So, we need to consider new combination like using standard mold platen with smaller screw or using standard mold platen with bigger screw.

2.Don’t use big injection molding machine to make small plastic items. Big machines have big platen, but small items have small molds. During injection, there is risk for the mold platen to be bended which will cause lower product’s quality even platen broken. Furthermore, using big machine will lead to longer stay time for plastics. The melted plastic will be decomposed in the screw barrel.

3.High speed plastic injection molding machines. Currently, more and more customers will want to buy “high-speed machines” or “fast speed machines” partly because of products requirement, mainly in order to shorten forming cycle, increase output, reduce production cost, improve the competitiveness, Usually, to achieve these, there are several ways:

-increase injection speed by using bigger electric motor or oil pump, or adding accumulator

-increase feeding speed by using bigger electric motor or pump, or reducing hydraulic motor to increase screw revolving speed.

-adopting multi-loop system to shorten forming time

-increase cooling water runner to improve molds cooling efficiency

There is no such thing as a free lunch. The improvement of machinery performance and modification do increase productivity but it will also lead to more investment and operation cost. Therefore, It will be better to carry out benefit analysis in order to choose most suitable plastic injection machines for biggest benefit.

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