Differences Between Precision Injection Molding and Standard Injection Molding Precision in

Precision injection molding and standard injection molding represent two distinct manufacturing systems within the plastics industry. The core difference lies in the ability to control dimensional accuracy, the stringency of process management, and the hardware requirements for molds and machinery. Precision molding focuses on extreme dimensional stability and surface quality, while standard molding prioritizes production efficiency and cost control. Below is a detailed comparison across six key dimensions.

1. Part Precision and Quality Requirements

This is the fundamental distinction that dictates all subsequent standards.

Precision Injection Molding

Part tolerances must be held to the micron level, typically within ±0.005mm to ±0.02mm, meeting ISO 2768 standards f to h. Surface quality requirements are extremely high, often demanding a mirror finish (Ra ≤ 0.05μm), with zero sink marks, weld lines, or flash. Strict mechanical properties and dimensional stability are required. Applications include medical devices, optical lenses, and electronic connectors.

Standard Injection Molding

Part tolerances are in the millimeter range, usually ±0.1mm or more, meeting ISO 2768 standards m to c. Surface quality requirements are lenient; minor weld lines or sinks are acceptable, and flash can be removed via post-processing. This method is suitable for toys, daily necessities, and general appliance housings where precision is not critical.

2. Mold Precision and Design

The mold is the foundation of precision molding; precision molds are far more difficult and costly to manufacture than standard molds.

Precision Molds

Cavity and core machining accuracy must reach ±0.002mm, requiring 5-axis machining centers and mirror EDM machines. Materials are typically high-hardness, wear-resistant steels like S136 or H13, often treated with mirror polishing or nitriding. Designs are complex, featuring precision hot runner systems, conformal cooling channels, and ball-bearing guide pillars to ensure minimal clamping clearance and uniform temperature distribution.

Standard Molds

Machining accuracy is generally ±0.01mm, achievable with standard milling or EDM machines. Materials are often P20 pre-hardened steel or 45# steel, with lower polishing requirements. Structures are simpler, often using cold runners and straight cooling lines. Standard guide pillars are used, and precise temperature control is not a priority.

3. Injection Molding Machine Performance

Precision molding places extreme demands on the machine's control system and mechanical rigidity.

Precision Injection Molding Machines

These use closed-loop control systems for extremely accurate regulation of injection pressure, speed, holding pressure, and temperature, with repeatability within 1%. The clamping unit has high rigidity to prevent mold deformation under high pressure. Servo motors and high-precision metering devices ensure minimal shot volume error. Advanced models offer multi-stage holding pressure and position control.

Standard Injection Molding Machines

Most use open-loop control systems, resulting in larger parameter fluctuations and lower repeatability. The clamping unit has moderate rigidity, and the equipment cost is only one-third to one-half that of a precision machine. They are suitable for regular production with low precision requirements, featuring simple operation and maintenance.

4. Process Parameter Control

The production process for precision molding requires meticulous management.

Precision Injection Molding

Parameters must be set with pinpoint accuracy. Often, segmented holding pressures are set for different cavity positions, and mold temperatures are controlled in zones. Even minor parameter fluctuations can cause part failure. Therefore, real-time monitoring and in-line inspection equipment are necessary for constant measurement and adjustment.

Standard Injection Molding

Process adjustment is relatively broad; uniform injection and holding parameters are usually applied to the entire mold. The process is insensitive to minor environmental or equipment fluctuations. Production typically requires only periodic spot checks of part dimensions, and the technical skill level required for operators is relatively low.

5. Raw Material Selection

Material stability directly determines the success of precision molding.

Precision Injection Molding

Requires high-purity, low-shrinkage materials with stable flow properties, such as optical-grade PC or reinforced PA. Raw materials must undergo strict drying to remove moisture. Some products require modified materials to further reduce shrinkage and ensure dimensional stability.

Standard Injection Molding

Uses general-purpose plastics like standard PP, PE, or ABS. There are no strict requirements for material purity or batch stability. Drying is relatively simple, and some non-hygroscopic materials can be used directly, resulting in low material costs.

6. Production Cost and Efficiency

Precision Injection Molding

Due to the high cost of molds, equipment, and materials, combined with long debugging cycles, initial investment and unit costs are high. However, because the products have high added value and require no post-processing, the overall economic benefits are still substantial.

Standard Injection Molding

All costs are low, and production efficiency is high, making it suitable for large-scale mass production. Although some products require post-processing, the overall cost advantage is obvious, making it the most widely used injection molding method in the market.

Summary

Precision injection molding is a high-accuracy, high-investment, and high-control production model aimed at manufacturing high-end products with minimal tolerances and stable quality. Standard injection molding is a low-cost, high-efficiency, and widely applicable production model that mainly meets the needs of consumer goods. In actual production, the appropriate injection molding process should be selected based on the specific application and precision requirements of the product to avoid unnecessary cost waste from over-specifying precision.