The Difference Between Precision Injection Molding and Ordinary Injection Molding

Injection molding is one of the most widely used plastic manufacturing processes, offering efficiency, repeatability, and flexibility for producing parts of various complexities. However, not all injection molding is the same. Depending on the part’s performance requirements and tolerances, manufacturers typically choose between ordinary injection molding and precision injection molding.

This article explores the key differences between these two techniques, their applications, and how to choose the right one for your project.

What Is Ordinary Injection Molding?

Definition and General Characteristics:
Ordinary injection molding (also called standard injection molding) is a process used to produce general-purpose plastic components in large quantities. It involves melting plastic resin and injecting it into a metal mold under pressure, where it cools and solidifies into the desired shape.

This method is ideal for non-critical parts—where dimensional precision, tight tolerances, or complex surface finishes are not the top priority.

Typical Process Flow:

1. Material feeding: Plastic granules are fed into the machine’s hopper.

2. Melting: The material is heated and melted in the barrel.

3. 
   

4. Injection: The molten plastic is injected into the mold cavity.

5. Cooling: The part cools and solidifies inside the mold.

6. Ejection: The mold opens, and the finished part is ejected.

Advantages:

• Cost-effective: Tooling and machine costs are relatively low.

• High efficiency: Suitable for mass production of large volumes.

• Material flexibility: Compatible with a wide range of thermoplastics.

• Fast cycle times: Short molding cycles make it ideal for consumer products.

Limitations:

• Limited precision: Dimensional tolerance is typically around ±0.05–0.1 mm or higher.

• Inconsistent repeatability: Environmental factors and machine wear can affect quality.

• Not suitable for micro-scale or high-accuracy parts.

• May require post-processing for finishing or fitting precision assemblies.

Ordinary injection molding works well for products such as containers, caps, toys, automotive interiors, and other general consumer goods.

What Is Precision Injection Molding?

Definition and Purpose:
Precision injection molding is an advanced manufacturing technique designed to produce plastic parts with extremely tight dimensional tolerances, high repeatability, and exceptional surface quality. It is typically used for components that must meet exact specifications—often within microns of accuracy.

Industries Requiring Precision Molding:

• Electronics: connectors, micro housings

• Medical devices: syringe tips, diagnostic components

• Automotive: sensor housings, engine components

• Optics: lenses and light guides

• Telecommunications: fiber optic connectors

Characteristics of Precision Injection Molding:

• Tolerance levels as tight as ±0.005 mm or less

• Uniform wall thickness and weight consistency

• Advanced process monitoring and closed-loop control systems

• Use of high-performance materials such as PEEK, LCP, or PC/ABS      blends

• Controlled environment (temperature and humidity)

Advantages:

• High dimensional accuracy: Suitable for critical or mating parts.

• Superior surface finish: Reduces or eliminates post-processing.

• Consistent quality: Maintains identical parts across large production runs.

• Reduced assembly errors: Ideal for  multi-component or automated assemblies.

Key Differences Between Precision and Ordinary Injection Molding

Aspect	Ordinary Injection Molding	Precision Injection Molding
Tolerance Level	±0.05–0.1 mm	±0.005–0.02 mm
Part Consistency	Moderate	Very high
Surface Finish	Standard	Excellent
Material Type	General-purpose plastics	High-performance engineering plastics
Machine Requirements	Conventional machines	High-precision, closed-loop systems
Mold Quality	Standard steel molds	High-grade steel with micro-polishing
Production Environment	Normal conditions	Controlled cleanroom environment
Applications	Consumer goods, toys, packaging	Medical, electronics, optics, automotive   precision parts

In essence, precision injection molding focuses on achieving the highest possible accuracy, while ordinary injection molding prioritizes cost efficiency and speed for less demanding parts.

Applications of Precision Injection Molding

Precision injection molding is used in sectors where performance, fit, and reliability are non-negotiable. Typical examples include:

• Medical industry: Syringe components, microfluidic chips, surgical instrument housings.

• Electronics: Connectors, sockets, smartphone housings, and micro gears.

• Automotive: Fuel system parts, sensor housings, and interior precision clips.

• Optics: LED lenses, light guides, and camera modules.

• Aerospace: Lightweight components with strict performance requirements.

These industries rely on tight tolerances, micron-level accuracy, and consistent mechanical performance—all hallmarks of precision molding.

Applications of Ordinary Injection Molding

Ordinary injection molding is perfect for high-volume, low-cost production of parts where extreme precision is unnecessary. Common applications include:

• Household products: Containers, lids, handles, kitchenware.

• Packaging: Bottle caps, closures, cosmetic containers.

• Toys and consumer goods: Figures, casings, and simple enclosures.

• Automotive interiors: Dashboards, trim panels, clips, brackets.

• Industrial components: Spacers, covers, and non-critical housings.

The focus is on efficiency and durability, rather than micron-level tolerances.

Factors Affecting Precision in Injection Molding

Achieving precision in injection molding depends on multiple interrelated factors. Here are the main ones:

1. Mold Design Accuracy and Steel Quality:
The mold determines the final part’s geometry and tolerance. Precision molds use high-grade tool steel (e.g., S136, H13) and undergo meticulous polishing and finishing. Dimensional errors in mold design directly translate into part inaccuracies.

2. Machine Performance:
High-precision machines offer:

• Stable clamping force to prevent flash or deformation.

• Accurate shot control with servo-driven injection units.

• Real-time feedback systems to ensure repeatability.

3. Material Characteristics and Moisture Content:
Moisture or contamination can cause warping or dimensional shrinkage. Using dried and certified-grade materials helps maintain consistency.

4. Environmental Stability:
Temperature and humidity variations can cause thermal expansion or contraction in both the mold and parts. Precision molding often takes place in temperature-controlled cleanrooms.

5. Skilled Operator and Process Monitoring:
A qualified technician continuously monitors parameters like injection pressure, melt temperature, and cooling time. Precision molding relies heavily on automated process control systems combined with human expertise.

Choosing Between Precision and Ordinary Injection Molding

When deciding which method suits your product, consider:

Criteria	Choose Precision Injection Molding    If…	Choose Ordinary Injection Molding If…
Part Tolerances	You require micron-level accuracy	Minor deviations are acceptable
Production Volume	Moderate to high	High-volume, low-cost production
Part Function	Critical functional or mating parts	Non-critical parts
Budget	You can invest in high tooling and   equipment	You need low-cost tooling
Industry	Medical, automotive, electronics	Consumer goods, packaging, toys

If your product’s success depends on fit, performance, or regulatory compliance, precision injection molding is the right choice. But if speed and affordability matter most, ordinary injection molding offers better economics.

Cost and Efficiency Comparison

Tooling Cost:

• Precision molds require high-grade materials, fine machining, and tight tolerances, making them significantly more expensive—often 2–5 times higher than ordinary molds.

Production Cost per Part:

• For large production runs, the per-unit cost difference narrows, as precision molding delivers lower rejection rates and consistent quality.

• Ordinary molding remains cheaper for simple, high-volume parts where defects are tolerable.

Efficiency:

• Precision injection molding involves longer setup and calibration time, but once optimized, it delivers superior repeatability.

• Ordinary molding achieves faster cycle times but may require more frequent adjustments.

Conclusion

Both precision injection molding and ordinary injection molding serve essential roles in modern manufacturing.

• Ordinary injection molding is the backbone of mass production for everyday plastic components—fast, economical, and efficient.

• Precision injection molding, on the other hand, caters to industries that demand accuracy, reliability, and high-performance parts.

In short:

• Choose ordinary molding for simplicity and cost savings.

• Choose precision molding for quality-critical, high-value components.

As manufacturing technology advances—with smarter machines, improved materials, and tighter process control—the line between these two methods continues to blur. Still, understanding their differences remains key to achieving the best balance of cost, performance, and product quality for your specific application.