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1. ​​Clamping Force Calculation and Selection​​

Clamping force is a core parameter of injection molding machines, used to counteract the mold-opening force exerted by molten material. It is calculated based on the projected area of the part (cm²), the number of cavities, and the internal mold pressure (kg/cm²). The formula is: Clamping force = Projected area × Number of cavities × Internal mold pressure. For general materials, the internal mold pressure is typically 350–400 kg/cm², and the machine’s clamping force should exceed the calculated value by at least 1.17 times for safety. For example, thin-walled or high-precision parts may require higher clamping forces (600–1000 kg/cm²). Insufficient clamping force can cause flash, while excessive force wastes energy and accelerates mechanical wear

2. ​​Injection Volume and Screw Diameter Matching​​

The injection volume must meet the part weight and cavity count, usually requiring the injection volume to be ≥1.35 times the part weight (i.e., the part weight should not exceed 75% of the injection volume). Screw diameter selection balances injection pressure and speed: smaller screws provide higher pressure but lower speed, suitable for high-viscosity plastics (e.g., PC); larger screws offer higher speed but lower pressure, ideal for low-viscosity plastics (e.g., PET). Special cases may require “large mold with small screw” configurations to optimize performance

3. ​​Mold Dimensions and Machine Compatibility​​

The machine must accommodate the mold’s width, height, thickness, and opening stroke. The mold width/height should be less than the tie-bar spacing, and the thickness must fit within the machine’s mold height range. The opening stroke should be ≥2.5 times the part height (or 4–5 times for in-mold labeling). Additionally, the mold’s minimum size must meet machine requirements to avoid instability. Ejector stroke and platen size must also align with mold design for smooth demolding

4. ​​Material Properties and Screw Design​​

Different plastics require specialized screws:

• ​​PC​​: Low-shear, high-compression-ratio screws.
• ​​PVC​​: Chrome-plated, corrosion-resistant screws.
• ​​PET​​: Anti-drool design.
  The compression ratio (typically 16–25) and length-to-diameter ratio (standard: 16–25; high-speed: 20–28) affect plasticization. For example, amorphous materials (e.g., PMMA) use gradual-compression screws, while crystalline materials (e.g., PA) use abrupt-compression screws. Color-mixing or glass-filled plastics require mixing-type screws

5. ​​Injection Speed and Pressure Requirements​​

Injection speed impacts filling efficiency: thin-walled parts need high speed (200–500 mm/s) with accumulators to reduce pressure loss. Injection pressure varies with material flowability: easy-flow materials (e.g., PE) require 70–100 MPa, while difficult-flow materials (e.g., PC) need 120–150 MPa. High pressure demands smaller screws but risks energy waste and thermal degradation. Multi-circuit systems enable synchronized actions to shorten cycles

6. ​​Plasticizing Capacity and Production Efficiency​​

Plasticizing capacity (kg/h) depends on screw diameter, speed, and metering depth, and must match the production cycle. Material residence time should be 2–12 minutes to avoid overheating. High-speed machines improve efficiency via larger motors/pumps or multi-circuit designs, but cost trade-offs exist. For example, PET preform production requires uniform plasticizing, while standard parts tolerate lower requirements

7. ​​Clamping Mechanism Selection​​

Hydraulic direct-pressure systems offer stable clamping for precision molds; toggle-type systems save energy but require complex maintenance. Direct-pressure suits special processes (e.g., injection-compression), while toggle-type suits rapid cycles. Large machines favor hydraulic systems; small/medium machines may use toggle-type for cost savings

8. ​​Safety and Electrical Systems​​

Machines must comply with safety standards (e.g., GB12265.1), including guards, emergency stops, and insulation. Poor grounding or heater failure poses risks. Reputable brands (e.g., Haitian, Engel) ensure reliability and after-sales support. Regular checks of lubrication and hydraulic oil cleanliness prevent failures

9. ​​Special Functions and Add-Ons​​

Optional features include:

• ​​Accumulators​​: Boost injection speed.
• ​​Gas-assisted injection​​: Reduces warpage.
• ​​Mold pressure sensors​​: Enhance repeatability.
  High-speed machines may use closed-loop control; multi-color machines need separate screws. These add costs but solve specific challenges

10. ​​Energy Efficiency and Cost Analysis​​

Motor power and pump type (fixed/variable) affect energy use. Servo motors save power but cost more upfront, ideal for long-term production. Evaluate total cost (purchase, maintenance, output): e.g., high-speed machines cut cycle times but raise energy use by 20%. Used machines require checks for hydraulic leaks and screw wear