Plastic products have deeply penetrated modern industry, and their applications are almost everywhere, from home appliances, medical devices to automotive parts. As the mainstream process of plastic manufacturing, injection molding has become the preferred solution for large-scale production due to its high efficiency and precision.
If you are looking for the answer to "What is injection molding?", here we will systematically analyze the technical essence and industry value of this key process for you.
This article will deeply analyze the core elements of the injection molding process. As one of the most reliable and efficient plastic processing methods in modern manufacturing, injection molding requires precise process control to ensure stable product quality. We will systematically disassemble the entire production process, from raw material preparation to finished product demolding, and share optimization techniques for key process parameters to help you comprehensively improve production efficiency and product yield.
How is plastic injection molded?
Plastic injection molding is a large-scale production process that injects molten plastic into the mold cavity under high pressure and obtains a specific shape product after cooling and solidification. It has the characteristics of high efficiency, high precision and batch replication, and low cost. It is widely used in product manufacturing in the fields of electronics, medical care, and automobiles.
Importance of injection molding in manufacturing
The widespread application of plastic injection molding in the manufacturing industry is inevitable: first, plastic materials are economical, durable and versatile, and can meet the stringent requirements of various industries; especially engineering plastics, whose strength, toughness and aesthetics are comparable to traditional metal materials. Secondly, modern injection molding technology has significantly improved environmental friendliness through the use of closed production systems and recyclable materials (such as PCR plastics) - the waste rate can be controlled within 5%, and the material recycling rate is more than 90%. More importantly, the process combines three major advantages: 1) The cost of a single piece can be as low as 0.1 yuan (million pieces); 2) The tolerance accuracy is ±0.05mm; 3) A molding cycle can be completed in as fast as 15 seconds, perfectly balancing mass production efficiency and quality requirements.
History of injection molding
Injection molding technology originated in the celluloid material era in the mid-19th century. The development of the first plunger injection molding machine in Germany in the early 20th century marked the beginning of industrialization. With the emergence of new materials such as polystyrene in the 1930s, the technology gained initial development. The invention of the screw injection molding machine (replacing the plunger type) and the application of engineering plastics in the mid-20th century brought the first revolutionary breakthrough. After the 1980s, the introduction of all-electric injection molding machines, micro-injection molding technology and computer control pushed the industry into the era of precision. Entering the 21st century, injection molding technology has developed rapidly in the direction of intelligence, energy saving and environmental protection. The production accuracy has been improved from the early ±1mm to ±0.01mm, and the molding cycle has been shortened from several minutes to the fastest 3 seconds. At the same time, the application of biodegradable materials has also given this traditional process a new sustainable development connotation.
Plastic Injection Molding Process
Now that you have understood the development history of injection molding and its important value in the manufacturing industry, understanding the step-by-step process of injection molding can help you reap the greatest benefits.
As the core equipment of the injection molding process, the design and manufacturing quality of the mold directly affects the product molding accuracy and production stability. Professional engineers use CAD 3D modeling combined with CAE mold flow analysis to design molds, and complete processing through high-precision CNC machine tools to ensure that the mold size tolerance is controlled within ±0.01mm and the surface roughness reaches Ra0.8μm or less.
Mold structure composition
The standard injection mold adopts a modular design, mainly including:
Molding system: It consists of a fixed mold core (cavity) and a movable mold core (core), which accurately reproduces the geometric features of the product
Gating system: Including main runners, branch runners, gates and other components, the use of hot runner technology can increase the plastic utilization rate to 95%
Ejector system: Including ejector pins, push plates and other components to achieve automatic demolding
Temperature control system: Accurate temperature control is achieved through water channel design
Mold material selection
Select different materials according to production needs:
Mass production mold: Use pre-hardened steel (such as P20) or quenched steel ( Such as H13), the service life can reach millions of molds
Trial production mold: choose 7075 aviation aluminum alloy, reduce costs while ensuring 10,000-50,000 mold life
Quick prototype: use metal 3D printing technology to complete mold manufacturing within 72 hours
Mold verification process
After the mold is manufactured, it needs to be strictly verified:
Conduct mold flow analysis (Moldflow) simulation test
Implement trial mold production and optimize process parameters
Complete dimensional inspection and functional testing
The mold development cycle usually accounts for 40-60% of the total project cycle, but high-quality molds can reduce the production cost of a single piece by more than 30%.
Common mold types Includes:
1：Two-plate mold (standard mold): the most basic structural form, consisting of a fixed mold and a movable mold, suitable for the production of simple structural parts.
2：Three-plate mold: adding a runner plate structure, which can realize automatic gate cutting, suitable for multi-cavity production
3：Hot runner mold: equipped with a heating system to keep the runner molten, with a material utilization rate of more than 95%, suitable for mass production
4：Laminar mold: multi-layer structure design, production efficiency can be increased by 100%, suitable for mass production of thin-walled parts
5：Multi-color injection mold: can realize double/multi-material co-injection, one-time molding of complex structures, used for double-color Product production
6：High-speed precision mold: special cooling system design, molding cycle shortened by 30%, suitable for electronic precision parts
7：Gas-assisted mold: combined with gas injection technology, reduce shrinkage marks, improve strength, suitable for thick-walled parts production
8：Insert molding mold: can achieve metal/plastic composite, complete assembly in one go, used for electronic connectors, etc.
Each mold type has its specific application scenarios and advantages. When choosing, you need to consider product requirements, production batch and cost factors
What are the most common plastic materials for injection molding:
Here's a professional table summarizing the most common injection molding materials, their advantages, and primary application fields:
| Material (Abbr.) | Full Name | Key Advantages | Primary Applications |
|---|---|---|---|
| ABS | Acrylonitrile Butadiene Styrene | Good impact resistance, machinability, surface finish | Automotive parts, electronics housings, toys |
| PP | Polypropylene | Chemical resistance, fatigue resistance, low cost | Food containers, living hinges, medical devices |
| PC | Polycarbonate | High strength, transparency, heat resistance | Optical lenses, bullet-proof glass, electronic displays |
| PA | Polyamide (Nylon) | Wear resistance, mechanical strength, temperature resistance | Gears, bearings, automotive components |
| POM | Polyoxymethylene (Acetal) | High stiffness, low friction, dimensional stability | Precision parts, zippers, fasteners |
| PMMA | Polymethyl Methacrylate (Acrylic) | Optical clarity, UV resistance, weather ability | Light guides, signs, transparent covers |
| PE | Polyethylene | Chemical resistance, flexibility, low cost | Bottles, pipes, packaging films |
| PS | Polystyrene | Rigidity, clarity, easy processing | Disposable cutlery, CD cases, test tubes |
| TPE | Thermoplastic Elastomer | Rubber-like elasticity, recyclability | Seals, grips, soft-touch components |
| PBT | Polybutylene Terephthalate | Electrical properties, chemical resistance | Electrical connectors, switches, housings |
| LCP | Liquid Crystal Polymer | High flow, thin-wall capability, heat resistance | Miniature connectors, surgical devices |
| PPS | Polyphenylene Sulfide | Flame resistance, chemical inertness | Aerospace components, industrial parts |
Material Selection Notes:
Engineering Plastics (PC, PA, POM) are typically 3-5x more expensive than commodity resins (PP, ABS)
High-performance polymers (LCP, PPS) can cost $15-50/kg but offer exceptional properties
Material hybridization (e.g., glass-filled PP) can enhance properties while maintaining cost efficiency
This table covers approximately 85% of industrial injection molding applications. For specialized requirements (e.g., FDA compliance, V0 flammability), material formulations may require additives or custom compounding.
Is injection molding suitable for your project?
Although injection molding has many advantages, there are also some disadvantages that need to be noted before starting a project. For example, the product only needs a small number of prototypes (<500 pieces), the product design is still being optimized, the budget is limited and the mold cost cannot be borne, the material is special or the demand is unstable, etc. These situations are not suitable for injection molding.
1. Initial investment cost
Injection molding requires customized special molds, which constitute the main initial investment: the cost of simple molds starts at about US$5,000, and complex mass production molds can reach more than US$100,000. The mold cost increases exponentially with complexity
Return on investment analysis: Suitable: When the annual output is >5,000 pieces, the unit cost advantage is significant. Unsuitable: Small batch production (<500 pieces) is not economical
2. Design flexibility, compared with digital manufacturing processes. CNC processing, support for modifying CAD files at any time
3D printing, zero cost for design changes
Injection molding: high mold modification cost (US$500-10,000)
Main modification methods: mold cavity expansion (additive) metal welding (reduced material is limited) new mold manufacturing (major changes)
Production Lead Time Comparison
| Process | Lead Time | Ideal Application |
|---|---|---|
| CNC Machining | 5-10 days | Prototyping / Small batch |
| 3D Printing | 3-5 days | Rapid validation |
| Injection Molding | 7-11 weeks | Mass production |
Includes 5-7 weeks for mold making + 2-4 weeks for production & shipping
4. Material utilization optimization
Main waste sources and improvement plans:
Gating system waste (accounting for 15-30%) Hot runner technology can reduce it to less than 5%
Process waste (3-8%) is optimized through mold flow analysis parameters
Overfilling (2-5%) accurately controls injection volume
5. Environmental sustainability
Environmental impact and improvement measures: Energy consumption: New all-electric injection molding machine saves 40% energy, waste heat recovery system
Material recycling: waste crushing and reuse rate reaches 90%, and the application of bio-based plastics increases by 35% per year
Comprehensive suggestions:
Injection molding is a typical "high investment-high return" process:
Initial investment: mold cost + time cost
Long-term benefits: ultra-low unit cost + stable quality
Best application: large-scale production after design finalization
