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Which Electric Injection Unit Suits Different Wall Thicknesses: IU, IU-h, or IU-hs?

2026/11/02 By le zhan

Which Electric Injection Unit Suits Different Wall Thicknesses

Selecting the right electric injection unit depends mainly on the product’s wall thickness and the filling speed needed to complete the molding process. The Topstar TEII series electric injection molding machines offer three configurations:

1. The IU model, suitable for thick-walled products (requiring standard injection speeds and longer holding times);

2. The IU-h model, suitable for thin-walled products (requiring moderate injection speeds);

3. The IU-hs model, suitable for ultra-thin-walled products (requiring high injection speeds).

However, you cannot base the final selection solely on wall thickness; you must also consider flow length, gate design, resin viscosity, shot weight, and dimensional accuracy requirements to ensure stable filling and consistent product quality.

Selecting Electric Injection Unit: How Do the IU, IU-h, and IU-hs Models Suit Different Wall Thicknesses?

The three injection unit configurations in the Topstar TEII electric injection molding machine series are designed to meet different molding requirements, not just offer different maximum injection speeds. The key distinctions are the speed required to fill the cavity with melt and the holding-pressure duration required for the product.

Understanding these differences will help you select the most suitable injection unit based on the product’s geometry and material properties.

IU Electric Injection Unit: Suitable for Thick-Wall Products

Compared to thin-wall parts, thick-wall products typically allow for a longer filling window. Due to their larger runner cross-sections and ample space for melt flow, they do not require extremely high injection speeds.

Topstar’s IU injection unit operates at conventional injection speeds and offers extended holding pressure capability, making it ideal for thick-wall products.

During the filling phase, a controlled and moderate injection speed helps distribute the melt more evenly and reduces unnecessary shear forces. Once the cavity fills, the process enters the holding pressure phase to compensate for plastic shrinkage as the material cools and solidifies. Therefore, when the application prioritizes “controlled filling” and “sustained holding pressure” over extreme injection speeds, the IU injection unit is the ideal choice.

IU Electric Injection Unit

IU-h and IU-hs Electric Injection Units: Suitable for Medium- to High-Speed Injection?

Thin-wall and ultra-thin-wall products have special filling requirements because the melt rapidly loses heat as it flows through narrow cavity areas. If the filling time is too long, the flow front may cool prematurely, leading to issues such as short shots, incomplete filling, or insufficient weld line strength.

For such applications, Topstar offers two higher-speed configurations:

IU-h — Medium-Speed Injection for Thin-Wall Products

When the speed required for cavity filling exceeds the range offered by standard configurations, the IU-h is the ideal choice. It ensures that the melt passes smoothly through thinner areas before flow is impeded by excessive cooling.

IU-h — Medium-speed injection for thin-walled products

IU-hs — High-Speed Injection for Ultra-Thin-Wall Products

The IU-hs is designed for applications with more demanding filling conditions. When wall thicknesses are extremely thin or flow paths are particularly challenging, higher injection speeds help fill the cavity within a narrower process window.

However, excessively high speeds may increase shear forces, trigger jet flow, or compress residual air within the cavity, potentially leading to scorch marks. Therefore, when determining injection speed, consider factors such as mold venting, gate size, and melt temperature.

IU-h — Medium-speed injection for thin-walled products

The selection criteria are as follows:

  • IU-h: Suitable for thin-walled parts requiring medium-speed filling.
  • IU-hs: Suitable for ultra-thin-walled parts requiring higher filling speeds.

The key to selection is ensuring that the injection speed is sufficient to reliably complete the filling process.

What Other Factors Should Be Evaluated Before Selecting an Electric Injection Molding Unit?

Wall thickness provides an initial guideline, but it alone is insufficient to determine the final specifications of an injection unit. Two products with the same wall thickness may require different injection performance due to variations in flow length, gate location, material, and shot volume. Therefore, when making the final selection, you must consider speed requirements, injection capacity, pressure capability, and actual molding conditions.

How Do Material, Flow Path Length, and Injection Volume Affect Selection?

Before determining whether to use an IU, IU-h, or IU-hs electric injection unit, the following key factors should also be evaluated.

Material Properties: Different resins have varying melt viscosities and processing windows. For high-viscosity materials, even with thicker wall thicknesses, you may need higher injection pressure to maintain the expected filling speed.

Flow Path and Gate Design: Longer flow paths, smaller gates, or complex cavity geometries all increase filling resistance. Therefore, if the melt must travel a long distance before reaching the end of the cavity, a higher-speed injection unit is required—even for products with moderate wall thickness.

Injection Volume and Screw Diameter: The injection unit must deliver the required material volume within the available injection stroke. If the screw diameter or injection capacity is selected improperly, it may affect filling consistency even if the speed rating is appropriate.

The Topstar TEII Electric Injection Molding Machine Series catalog offers a variety of injection unit sizes and configuration options. The technical specifications table covers parameters such as screw diameter, L/D, injection stroke, injection volume, injection weight, injection pressure, and holding pressure. These technical specifications should be comprehensively reviewed when determining the final configuration.

How Do Material, Flow Path Length, and Injection Volume Affect Selection

How to Determine the Appropriate Electric Injection Unit Configuration?

From an injection molding machine manufacturer’s perspective, we recommend following these four steps when selecting an electric injection unit:

Step 1: Evaluate the product’s wall thickness and flow geometry.

Identify the product’s thinnest sections, longest flow paths, gate locations, and areas prone to premature cooling. This will establish preliminary injection-speed requirements.

Step 2: Determine the required filling performance.

Use mold flow analysis, short-shot (short-material) tests, or actual production tests to determine whether the filling process requires standard, medium, or high speed. Do not blindly select a “high-speed” (IU-hs) model simply because it offers the highest speed.

Step 3: Confirm the injection capacity and pressure requirements.

Verify the required shot weight, injection volume, screw diameter, injection stroke, and pressure requirements. Ensure that the selected electric injection unit can deliver sufficient material within the target filling time.

Step 4: Verify product quality during actual molding.

Assess whether filling is complete, and inspect the part weight, sink marks, dimensional consistency, surface appearance, and molding repeatability. Adjust the injection speed and holding pressure parameters based on the actual molding results.

Final Selection

Ultimately, the appropriate electric injection unit should be selected based on the product’s specific requirements for filling and holding pressure:

For thick-walled products requiring standard speeds and longer holding times, select the IU injection unit; for thin-walled products requiring medium speeds, select the IU-h medium-speed injection unit; and for ultra-thin-walled products requiring high-speed filling, select the IU-hs high-speed injection unit. (For further details, please refer to the TEII electric injection molding machine product catalog.)

 

 

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