Plastic moulding is a key process within injection moulding that makes the method one of the most popular within the manufacturing industries. It brings precision and versatility that older methods do not offer, and it continues to be adopted by businesses looking to up their output, something that we at Sinoscan have done. There are, however, a lot of questions surrounding plastic injection moulding, especially from those looking to make the jump into this manufacturing type.

In this article, we will explain what plastic moulding is, how it is implemented and why this method needs to be in your business’s manufacturing processes to ensure the continued growth of your business.

What is the Plastic Moulding Process?

In simple terms, the plastic moulding process (mainly called plastic injection moulding) is the method of taking raw plastic material and feeding it into a hopper at a high temperature to be injected into a mould. The process operates at precise technical parameters: melt temperatures typically range from 200-280°C, depending on the material, while injection pressures reach 500-1500 bar to ensure proper cavity filling. Complete cycle times typically range from 15-30 seconds, with cooling accounting for approximately 50% of this time.

It is able to be moulded into many shapes and sizes, and can be done very quickly, meaning you can have an efficient turnover of parts to keep up with demand. It is a process that works in synergy with other manufacturing processes, like 3D printing, to open up plastic moulding’s potential for more intricate designs.

How Does Plastic Injection Moulding Work?

The plastic injection moulding process follows a precise sequence of four main stages that work together to transform raw plastic material into finished components. Understanding plastic part manufacturing steps is essential for manufacturers looking to optimise their production efficiency and part quality.

Stage 1: Clamping: The two halves of the mould tool are tightly closed and held together by the clamping unit. This creates a secure, sealed environment that can withstand the substantial pressures generated during injection. The clamping unit applies sufficient force to keep the mould securely closed while the liquid resin material gets injected into the mould cavities, with larger machines requiring longer clamping times due to their size.

Stage 2: Injection: Raw plastic material in the form of granules or tiny pellets is fed through a hopper and melted at high heat. The injection unit takes the molten plastic using built-up pressure and packs the material into the cavities of the mould. The injection process requires careful control of multiple variables:

• Pressure
• Temperature settings for optimal flow
• Injection speed to ensure complete cavity filling without defects

Stage 3: Cooling: This stage is often the most time-consuming part of the cycle. The cooling time can vary depending on several factors:

• Type of plastic used
• Wall thickness of the moulded part
• Presence of cooling channels within the mould tool

During this phase, the molten plastic solidifies into the exact shape of the mould cavity, with wall thickness playing a crucial role in determining the duration of the cooling phase.

Stage 4: Ejection: Once the part has cooled sufficiently, there are several methods for ejecting the part, including pins, blades, bars, sleeves, or lifters, with ejector pins being the most common approach. The mould then opens, the finished part is removed and the cycle begins again. This entire sequence, from mould closure to the beginning of the next cycle, defines the injection moulding cycle time, which directly impacts production efficiency and manufacturing costs.

Types of Plastic Moulding Techniques

While plastic injection moulding dominates high-volume manufacturing, several different plastic moulding types serve specific applications and production requirements. Understanding the various moulding types is crucial for manufacturers looking to optimise their production strategy and costs.

Plastic Injection Moulding: Plastic injection moulding remains the cornerstone of high-volume polymer processing, offering unmatched precision, speed and material versatility. Key characteristics include:

• Cycle times: 10 seconds to 2 minutes
• Tolerances: As tight as ±0.001 millimetres
• Material efficiency: 95% utilisation rates
• Best for: 10,000+ annual parts with complex geometries
• Applications: Automotive dashboards, medical syringes, electronics housings

Blow Moulding: Blow moulding transforms thermoplastic materials into hollow parts through controlled inflation. This plastic moulding technique offers superior economics for container production:

• Three main variants: Extrusion (75%), injection (24%), injection stretch blow moulding
• Primary materials: Polyolefins, with HDPE representing 40% of applications
• Tooling costs: Significantly lower than injection moulding
• Ideal volume range: 1,000-500,000 parts annually
• Applications: Bottles, containers, automotive fuel tanks, hollow components

Compression Moulding: Compression moulding excels where superior mechanical properties and large part capability are required:

• Process: Controlled heat and pressure (7-130 bar at 120-200°C)
• Materials: Advanced composites, thermosets, highly filled compounds
• Cycle times: 2-10 minutes
• Volume range: 1,000-100,000 parts annually
• Applications: Automotive panels, aerospace panels, industrial enclosures

Rotational Moulding: Rotational moulding delivers unmatched design flexibility through low-pressure forming:

• Process: Powder loaded into moulds, heated and rotated biaxially under 20 RPM
• Primary material: Polyethylene (84% market share)
• Tooling costs: Exceptionally low
• Volume range: 50-20,000 parts annually
• Applications: Chemical storage tanks, kayaks, agricultural equipment

Choosing the Right Moulding Types: Production volume represents the primary selection criterion when comparing different moulding types:

• High volume (10,000+): Plastic injection moulding for precision and complex features
• Medium-high volume (1,000-500,000): Blow moulding for hollow parts
• Medium volume (1,000-100,000): Compression moulding for strength and large size
• Low-medium volume (50-20,000): Rotational moulding for design flexibility

Part geometry also determines feasibility, with hollow parts requiring blow moulding or rotational moulding, while complex solid parts favour plastic injection moulding’s precision capabilities.

Materials Used in Plastic Moulding

The choice of material in plastic forming directly impacts part performance, cost and manufacturability. Understanding the fundamental differences between material types and their properties enables manufacturers to select the optimal plastic for their specific applications. The two primary categories of plastic moulding materials serve different requirements and processing methods.

Thermoplastics vs Thermosets 

Thermoplastics can be reheated and reformed multiple times, while thermoset plastics cannot be remelted and remain in a permanent solid state once set. Thermosetting plastics solidify irreversibly when heated through a process called curing, which involves chemical reactions that create strong cross-links between polymer chains.

Thermoplastics dominate plastic injection moulding due to their recyclability and processing advantages. They come in resin pellet form and excess material from runners can be recycled back into production, making them both economically and environmentally attractive. However, thermoplastics have lower heat resistance and chemical resistance compared to thermosets.

Common Thermoplastic Materials 

The most widely used plastic moulding materials include several versatile thermoplastics:

• ABS (Acrylonitrile Butadiene Styrene): One of the most popular and versatile materials, combining strength and rigidity with toughness and excellent stress, impact, creep and heat resistance
• Polypropylene (PP): Offers excellent chemical resistance and elastic properties, making it ideal for food applications
• Nylon (Polyamide): Available in various types including Nylon 6, 6/6, and 66, offering high strength, temperature resistance and excellent wear properties
• Polycarbonate (PC): Offers higher strength and heat resistance than ABS, making it suitable for impact-resistant applications.

Material Selection Considerations 

Several factors influence plastic moulding material selection. Heat resistance is the primary function of thermoset materials, while thermoplastics can only withstand heat to a certain degree. For applications requiring chemical resistance, thermosets provide superior performance due to their cross-linked molecular structure.

At SinoScan, our material expertise enables us to guide clients through the selection process, considering factors such as operating temperature, chemical exposure, mechanical requirements and cost targets. Our experience with both commodity plastics and high-performance engineering materials ensures optimal material selection for each application, whether it requires the cost-effectiveness of polypropylene or the precision properties of advanced nylon grades.

Advantages of Plastic Moulding for Manufacturing

Plastic moulding offers compelling advantages that make it the preferred manufacturing method across industries ranging from automotive to medical devices. Understanding these benefits enables manufacturers to make informed decisions about their production strategies and leverage plastic moulding’s capabilities for competitive advantage.

Cost Effectiveness and Efficiency 

Once established, plastic moulding delivers exceptional cost efficiency through high-volume production capabilities. Cycle times range from 15 to 120 seconds, depending on complexity. Key economic benefits include:

• Per-unit costs decrease dramatically with volume through economies of scale
• Labour costs remain relatively low due to automated production
• Minimal waste production with recyclable unused plastic

Speed and Volume Capabilities 

Modern plastic moulding machines deliver impressive production rates, producing tens or hundreds of parts per hour once optimised. Multi-cavity moulds enable the production of hundreds of thousands of identical parts, allowing companies to respond quickly to market demands and reduce time-to-market for new products.

Design Flexibility and Precision 

Plastic injection moulding accommodates complex requirements with tolerances as tight as ±0.001 millimetres  for precision applications. The process handles intricate geometries with multiple integrated features in single components that would be impractical with other manufacturing methods. Design advantages include:

• Hundreds of different plastic resins for specific performance needs
• Surface finishes from smooth to textured with integrated colours and logos
• Complex geometries which may be impossible with traditional manufacturing methods

Quality, Consistency and Reliability 

The process delivers exceptional repeatability, producing virtually identical parts across production runs through tightly controlled parameters and comprehensive data collection. This consistency ensures dimensional accuracy and material properties remain constant, providing the quality assurance necessary for critical components in automotive and medical applications where reliability is crucial.

At SinoScan, our commitment to quality consistency has enabled us to maintain long-term partnerships with clients requiring precise, repeatable results. Our investment in modern equipment and process control systems ensures that every part meets specification, whether producing thousands or millions of components. This reliability, combined with our technical expertise, allows us to deliver the competitive advantages that plastic moulding offers to manufacturers across diverse industries.

Conclusion

Plastic injection moulding is a reliable, scalable, and highly efficient way to produce plastic parts with precision. Whether you need a short production run or mass manufacturing, it allows for excellent repeatability and material versatility, with tight control over tooling and part tolerances.

At SinoScan, we work closely with clients to deliver fully customised, injection-moulded plastic components, supporting everything from prototyping to full-scale production. Get in touch to find out how we can help with your next plastic moulding project.