Quick Answer

Selecting an injection molding machine based on product weight requires evaluating several factors, including shot size, clamping force, mold dimensions, material type, cavity quantity, and production requirements.

In most cases, the total injection weight should use approximately:

30% to 80%

of the machine’s maximum injection capacity for stable production performance.

Choosing the wrong machine may cause flashing, short shots, unstable quality, excessive energy consumption, or material degradation.

Why Product Weight Is Important in Machine Selection

Product weight directly affects:

• Injection shot capacity
• Screw diameter selection
• Plasticizing performance
• Cycle stability
• Production efficiency

If the machine injection capacity is too small, the machine may not fill the mold completely.

If the machine is too large, material residence time may increase, causing degradation and unnecessary energy consumption.

What Is Injection Shot Size?

Shot size refers to the maximum amount of molten plastic an injection molding machine can inject into the mold during one cycle.

Shot size is commonly measured in:

• grams
• ounces
• cubic centimeters (cm³)

The machine must provide sufficient injection volume for:

• Product weight
• Runner system
• Sprue weight
• Cushion material

General Rule for Machine Selection

Most manufacturers recommend using:

30% to 80%

of the machine’s maximum shot capacity.

This helps ensure:

• Stable plasticizing
• Consistent injection pressure
• Better product quality
• Reduced material degradation

Basic Machine Selection Formula

Total Injection Weight Calculation

The total shot weight includes:

Product Weight + Runner Weight + Sprue Weight

Example

In this case, the machine shot capacity should exceed 160g.

For stable production, a larger safety margin is recommended.

Recommended Machine Size by Product Weight

Actual machine selection also depends on mold structure and material type.

Product Weight Alone Is Not Enough

Many buyers incorrectly assume machine selection depends only on product weight.

However, buyers must also consider:

• Projected area
• Mold dimensions
• Material type
• Number of cavities
• Injection pressure
• Product wall thickness

All factors affect final machine selection.

Projected Area and Clamping Force

Even lightweight products may require high clamping force if the projected area is large.

General formula:

$F=A\times P\times S$

Where:

• $F$ = Required clamping force
• $A$ = Projected area
• $P$ = Injection pressure
• $S$ = Safety factor

Large projected areas increase mold opening force during injection.

Material Type Affects Machine Selection

Different plastic materials require different injection pressures.

Engineering plastics often require larger machines because of higher injection pressure requirements.

Multi-Cavity Mold Considerations

Multi-cavity molds increase total shot weight significantly.

Example:

Higher cavity molds usually require:

• Larger shot capacity
• Higher clamping force
• Faster plasticizing systems

Thin-Wall Product Considerations

Thin-wall products require:

• High injection speed
• High injection pressure
• Fast response systems

Even lightweight products may require larger machines for stable production.

Typical applications include:

• Food containers
• Packaging products
• Thin-wall cups

PET Preform Production Considerations

PET preforms require:

• High-speed injection
• Specialized screw design
• Precise temperature control
• Stable plasticizing

Machine selection depends heavily on:

• Preform weight
• Mold cavity quantity
• Production target

Servo injection molding machines are generally preferred for PET applications.

Servo vs Hydraulic Machines

Servo Injection Machines

Advantages:

• Energy saving
• Better precision
• Stable injection control
• Lower oil temperature

Recommended for:

• Precision products
• PET production
• High-volume production

Hydraulic Injection Machines

Advantages:

• Lower initial investment
• Strong power output
• Heavy-duty production capability

Suitable for:

• General plastic products
• Large industrial parts
• Thick-wall products

Common Problems from Incorrect Machine Selection

Machine Too Small

Possible issues:

• Short shots
• Flash defects
• Unstable injection
• Mold opening
• Poor product consistency

Machine Too Large

Possible issues:

• Excessive energy consumption
• Material degradation
• Higher operating cost
• Longer material residence time

How Overseas Buyers Should Prepare

Before selecting a machine, buyers should provide:

• Product drawing
• Product weight
• Material type
• Mold dimensions
• Number of cavities
• Production target
• Factory voltage standard

This helps suppliers recommend accurate machine configurations.

Common Questions

Can I select a machine using only product weight?

No. Product weight is important, but buyers must also consider mold size, projected area, material type, and cavity quantity.

What percentage of shot size should be used?

Most manufacturers recommend using 30% to 80% of machine shot capacity.

Why is oversized machine selection bad?

Oversized machines increase electricity consumption and may cause material degradation.

Which machine is best for lightweight thin-wall products?

High-speed servo injection molding machines are generally preferred.

How does runner weight affect machine selection?

Runner systems increase total shot weight and must be included in machine selection calculations.

How DAYA MACHINERY Supports Machine Selection

DAYA MACHINERY helps industrial customers choose suitable injection molding machines based on:

• Product weight
• Mold structure
• Material characteristics
• Production volume
• Energy-saving targets
• Factory conditions

We provide:

• Servo injection molding machines
• Hydraulic injection molding machines
• PET production solutions
• Technical consultation
• Spare parts support
• Industrial sourcing services

Conclusion

Selecting an injection molding machine based on product weight requires more than simply matching shot capacity.

Factors such as clamping force, projected area, material type, mold structure, and production requirements must all be evaluated carefully.

Professional machine selection helps improve production stability, reduce operating cost, and increase factory profitability.

Contact DAYA MACHINERY

Need help selecting the right injection molding machine?

DAYA MACHINERY provides professional machine selection support for industrial customers worldwide.

Contact us for:

• Technical consultation
• Machine recommendations
• PET production systems
• Energy-saving solutions
• Spare parts support
• Industrial sourcing services