Guide to Plastic Injection Molds: Construction and Design Considerations
Guide to Plastic Injection Molds: Construction and Design Considerations
- What is a Plastic Injection Mold?
- Types of Plastic Injection Molds
- Designing and Manufacturing Process of Plastic Injection Molds
- Considerations for Plastic Mold Design
- Common Materials for Plastic Injection Molds
- Advantages of Plastic Injection Molds
- Applications of Plastic Injection Molds
- Your Trusted Plastic Injection Mold Maker: Pass Card
In plastic injection molding, the mold is a critical factor for success. Whether you are a product designer, a mold manufacturer, or a plastic injection production facility, a deep understanding of plastic injection molds' structure and design considerations is essential. In this article, Pass Card aims to provide valuable insights to assist readers in designing and manufacturing injection molds.
What is a Plastic Injection Mold?
A plastic injection mold is a specialized tool used in the plastic injection molding process, a manufacturing technique for producing plastic parts in large volumes. The mold is a precision-made, typically metal, tool that shapes and forms molten plastic material into a specific design or shape.
Structure of Plastic injection mold
The mold consists of several critical parts, including the injection mold (A plate), the ejector mold (B plate), molded parts (core, die, insert), the gating system (main runner, branch runner gate, cold well), guiding mechanisms, release mechanisms, lateral parting and core-pulling mechanisms, heating and cooling systems, exhaust systems, and additional parts for fixation and support. This structure ensures precise shaping and efficient production of plastic components for various applications, such as food packaging, automotive parts, medical devices,
construction materials, and electronic components.
During injection molding, hydraulic pressure, and guide columns facilitate the closing and alignment of these molds. The plastic melt is injected into the cavity via the gating system. After cooling, the molds are separated, leaving the plastic parts on the movable mold. The ejection mechanism then expels the plastic components.
▲Simplified diagram of the process
Photo Source: ariel cornejo, CC BY-SA 4.0, via Wikimedia Commons
Photo Source: User:Brockey, CC BY 3.0, via Wikimedia Commons
Hot Runner System vs. Cold Runner System
Plastic injection molding is commonly carried out through two distinct methods, namely, hot runner systems and cold runner systems. Let’s take a look at both methods:
A hot runner system is a collection of heated elements used in plastic injection molds that inject molten plastic directly into the mold's cavities. This system is advantageous for reducing waste and is commonly used for complex or large parts where maintaining a consistent temperature is crucial.
In a cold runner system, molten plastic is injected into a mold through a cooler runner. Once the part is formed, the runners solidify and need to be ejected, resulting in more material waste. While cold runner systems are simpler and useful for smaller production runs, they can be less efficient for large-scale production due to the material waste.
Hot runner systems are preferred for large-scale production of complex parts. In contrast, cold runner systems are more suitable for smaller runs or situations where material waste is not a primary concern. At Pass Card, molds primarily use a hot runner system, categorized into open gate pin and valve systems. Hot runner systems eliminate channels guiding molten plastic, reducing cooling time and increasing efficiency. They maintain plastic temperature, reducing sink marks and under-filled parts. Hot runners offer flexibility in gate placement. Additionally, our unique waterway design enhances cooling efficiency and reduces pressure loss, extending mold life.
Types of Plastic Injection Molds
Plastic injection molds come in various types based on different classification methods:
- By structural features: Two-plate molds, three-plate molds, etc.
- By molding characteristics: Thermosetting plastic molds, thermoplastic plastic molds.
- By injection system: Cold runner molds, hot runner molds.
- By molding process: Injection molds, extrusion molds, blow molds, thermoforming molds, etc.
Designing and Manufacturing Process of Plastic Injection Molds
The manufacturing process of plastic injection molds includes several crucial steps to ensure precision and quality. Here's a clear overview of a typical manufacturing process:
Evaluation and Analysis:
The process begins with an evaluation and analysis of samples and requirements provided by the customer. This step is crucial to understanding the specific needs and characteristics of the medical component to be produced.
Design Confirmation:
Once the customer confirms the design details of the finished product, the mold design phase commences. This includes creating detailed mold drawings and considering the intricacies and specifications required for final products.
Mold Flow Analysis:
Mold flow analysis is conducted to simulate the flow of molten plastic within the mold. This analysis helps identify potential issues and ensures the mold design produces a high-quality and precise product.
Cross-Departmental Discussion:
Before manufacturing the mold, professionals of the mold-making company come together to discuss and finalize the product and mold design. This collaborative approach ensures that all design aspects, including production feasibility, are thoroughly examined.
Material Procurement and Processing:
The next step is purchasing the required materials. Materials with high corrosion resistance and durability are chosen. The mold goes through rough and finished machining processes. The production of molds entails using several processing machines, such as CNC milling machines, lathes, and grinding machines, among others. These machines process the mold base and produce the core components of the mold core.
Mold Assembly:
The mold components are assembled, considering the specific requirements of the application. This phase ensures that the final mold will produce accurate and consistent medical components.
Trial Molding:
Before full-scale production, the assembled mold undergoes a trial molding phase. This step identifies potential issues and ensures the final product meets the required standards and specifications.
Quality Inspection:
The molded products are thoroughly inspected to meet established quality standards and specifications. This inspection includes checking dimensions, tolerances, and product integrity. This ensures the products are ready for customer delivery and comply with regulatory requirements.
Considerations for Plastic Mold Design
When it comes to designing a plastic mold, several important factors must be considered to ensure a high-quality, efficient production process. The following aspects should be given careful attention to achieve the best possible results:
1. Simplifying the structure:
A simple mold structure is generally easier to manufacture, maintain, and repair. Minimizing the number of components and features also helps to reduce production costs and improve the reliability of the mold.
2. Ensuring uniform thickness:
Variations in wall thickness can lead to defects in the final product, such as warping or cracking. Therefore, it is essential to design the mold with a uniform wall thickness. This can be achieved through careful material selection, proper mold design, and machining techniques.
3. Using rounded corners:
Sharp corners in a mold can increase stress concentrations and promote material flow issues. By incorporating rounded corners in the mold design, stresses can be minimized, and material flow can be improved, resulting in a higher-quality finished product.
4. Allowing for draft angles:
Draft angles are essential to facilitate the easy removal of the finished part from the mold. Without proper draft angles, the part may become stuck in the mold or suffer from surface defects. Incorporating appropriate draft angles into the mold design can significantly improve production efficiency and reduce the likelihood of defects.
5. Estimating production and disassembly cycles:
Considering the expected production volume and disassembly frequency when designing the mold is important. By estimating these factors, the designer can ensure that the mold is designed to withstand the expected wear and tear and that it can be easily and safely disassembled for maintenance and repair.
6. Matching production machine dimensions and parameters:
The mold should be specifically designed to match the dimensions and parameters of the production machine. By doing so, the mold can be more easily integrated into the production process, and the finished product can be produced more efficiently and with greater consistency.
Common Materials for Plastic Injection Molds
Materials for mold cores and cavities primarily use stainless steel to prevent corrosion.
The material choice for a plastic injection mold depends on cost and product life cycle. High-quality materials are preferred for established and mass-produced products to increase mold lifespan and reduce overall costs. Cost-effective materials like aluminum alloy are preferred for new products intended for small-scale market tests. Pass Card chooses Swedish ASSAB or German Buderus as preferred materials. Mold bases commonly use plastic mold steels P-5 or P-20.
Advantages of Plastic Injection Molds
- Mass Production Capability
- High Customization
- Lightweight
- Lower Raw Material Costs
- High Product Size Consistency & Accuracy
- High Automation Level
- Minimal Waste and Recyclability
Applications of Plastic Injection Molds
Plastic injection molds find applications across various fields and products, including:
- Food packaging: PET bottles, food containers, caps, utensils
- Automotive: Bumpers, dashboards, side mirror casings, internal parts
- Medical: Blood collection tubes, Petri dishes, microtubes
- Construction: Tools, fasteners
- Electronic products: Gears, pulleys, pumps, and other components
Your Trusted Plastic Injection Mold Maker: Pass Card
Today, we discussed the basic knowledge and design considerations of plastic injection molds. Plastic injection molds play a crucial role in the manufacturing industry, allowing for the creation of precise and complex plastic parts at large volumes. Pass Card believes this article has provided you with the necessary knowledge to consider mold design and manufacturing.
If you are seeking a plastic injection mold maker, Pass Card is a leading provider of plastic injection mold making and design. With years of experience and advanced technology, we offer a wide range of services, from mold design and prototyping to production and quality control, ensuring a seamless and efficient plastic injection molding experience for our clients.
By choosing Pass Card, you can rest assured that your plastic injection molding needs will be met with the highest expertise, reliability, and customer service. Should you require more information about plastic injection mold, please do not hesitate to contact us.