Alexei Volkov
Injection molding is a manufacturing process used to make plastic parts. The process involves injecting molten plastic into a mold, which is then cooled and hardened to form the desired shape. Injection molding can be performed with a variety of materials, including metals, glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers. The number of cavities and the complexity of the part's design play a vital role in molding costs. The process can be used to create anything from small components to entire car body panels.
| Characteristics | Values |
|---|---|
| Process | Injecting molten material into a mould |
| Materials | Thermoplastic, thermosetting polymers, metals, glasses, elastomers, confections |
| Moulds | Made from hardened steel, pre-hardened steel, aluminium, beryllium-copper alloy |
| Mould Design | Cavities, surface finishing, tolerance requirements, internal/external threads, fine detailing, undercuts |
| Injection Moulding Cycle | Mould closes, injection of polymer, holding pressure maintained, screw turns, mould opens and part ejected |
| Cooling | Well-designed cooling system reduces costs and increases productivity |
| Post-Processing | Surface defect removal, decoration, component joining |
| Sustainability | Use of bioplastics, recycling scrap plastic, energy-efficient machines |
| Safety | Respirator, leather apron, closed shoes, welding gloves, face mask, fire extinguisher |
| Volume | Low-moderate capacity (<10,000 units) to high-volume (up to 750,000 units) |
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What You'll Learn
Choosing the right injection moulding company
Injection moulding is a manufacturing process used to make plastic parts. The process involves injecting molten plastic into a mould, which is then cooled and hardened to form the desired shape. The success of your business is dependent on the injection moulding company you choose, so it is important to select the right one. Here are some key considerations to keep in mind when choosing an injection moulding company:
Firstly, determine your volume needs and size requirements. If you require a small volume order, typically under 10,000 units, opt for a low to moderate-capacity moulder. These companies specialise in low-volume production and can quickly create prototypes for part testing. Conversely, if you need a large number of units, a high-volume injection moulder can deliver up to 750,000 units.
Secondly, choose a company with expertise in material selection. There are thousands of injection moulding plastic materials, each with unique properties. A knowledgeable company will be able to guide you in choosing the right material for your specific requirements, ensuring the final product meets your expectations. Consider factors such as strength, heat resistance, and chemical resistance, and cost when selecting a material.
Additionally, select a company with a strong track record of delivering projects on time and within budget. Missed deadlines can cause significant setbacks for your business, so it is crucial to choose a reliable partner.
Furthermore, look for a company that can provide end-to-end services, from design to finishing. Working with a single team throughout the process improves communication and streamlines feedback, and reduces the potential for errors. This integrated approach can save both time and money while increasing the likelihood of achieving the desired results.
Finally, consider the technical capabilities of the injection moulding company. Evaluate their equipment and ensure it meets your specific needs. For instance, if you require complex shapes or specific weight parameters, confirm that the company has the necessary technology and expertise to deliver consistent results.
By carefully considering these factors, you can make an informed decision when choosing the right injection moulding company for your business.
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Understanding the thermophysical properties of plastics
Plastic injection molding is a manufacturing process used to make plastic parts. The process involves injecting molten plastic into a mold, which is then cooled and hardened to form the desired shape. The thermophysical properties of plastics play a crucial role in this process.
One of the key thermophysical properties to consider is the melting point of the plastic. Different plastics have varying melting points, and it is important to select a plastic with a suitable melting point for the specific application. For example, ABS plastic has a relatively low melting point, while polypropylene (PP) is a cost-effective option that offers rigidity.
Another important consideration is the thermal degradation of the plastic. Residence time, or the duration the plastic material stays in a heated state, should be minimized to prevent thermal degradation. This is crucial for maintaining the mechanical properties of the thermoplastic material. Proper nozzle temperature is also essential to maintain the flow and consistency of the plastic as it enters the mold.
The clamp force required to keep the mold closed during injection is influenced by the thermophysical properties of the plastic. The clamp force typically ranges from a few tons to several thousand tons and is necessary to counteract the high injection pressure and prevent mold flash. Additionally, the shot size, or the amount of plastic injected into the mold, must be accurately calibrated based on the plastic's properties to completely fill the mold without causing excess material.
Understanding the cooling behaviour of the plastic is also critical in injection molding. The cooling time and system design impact the integrity of the final part. The molded plastic products must be cooled and cured to a certain rigidity to avoid deformation due to external forces after demolding.
By comprehending the thermophysical properties of plastics, manufacturers can effectively select suitable materials, optimize processing parameters, and ensure the quality and integrity of the final plastic parts produced through injection molding.
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The importance of cooling systems
The cooling system is a crucial aspect of plastic injection molding, significantly impacting the overall process's efficiency, productivity, cycle time, and the quality of the final product.
The cooling stage accounts for about 70% to 80% of the entire molding cycle. It is the stage where the molten plastic injected into the mold cavities solidifies, taking on the permanent shape of the mold. A well-designed cooling system can significantly reduce molding time, increase productivity, and reduce costs. Conversely, an improperly designed cooling system will lead to longer molding times and increased costs.
The cooling time must be accurately calculated to avoid defects in the final product. This calculation is a complex equation that considers wall thickness, thermal diffusivity, and the type of thermoplastic used, as each has different melting and molding temperatures. If the cooling time is improperly calculated or executed, it can result in defects such as warping, deformation, sinking, discoloration, and delamination.
Conformal cooling is a method that introduces cooling channels that closely follow the geometry of more complex parts, allowing for consistent cooling, even in difficult-to-reach areas. Proper cooling system design ensures homogeneous cooling, which is necessary for the quality of the product. Additionally, cooling channels implemented into the mold's design aid in heat dispersal and lower the cavity wall's temperature, promoting even cooling.
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Overmoulding and insert injection moulding
Overmoulding and insert moulding are both types of injection moulding used to create structurally similar parts. However, they differ in the process and the number of materials used.
Overmoulding
Overmoulding is a multi-step injection moulding process where two or more components are moulded on top of one another. Unlike conventional moulding, where a finished product is made in one cycle, overmoulding requires at least one additional injection cycle using a different material. This process is also known as 2K overmoulding, two-shot moulding, or multiple material moulding. The process can theoretically be expanded to include an indefinite number of additional overmoulds, but in practice, more than two becomes increasingly complex and expensive. Overmoulding is often used for large production runs and products with colourful and multi-layered designs. It is also useful for manufacturing complicated components that are too uneconomical to produce using a single moulding process.
Insert Moulding
Insert moulding is a form of injection moulding where a secondary part is formed over a substrate or pre-existing base component. This process involves placing a pre-manufactured component, such as a threaded fitting or electrical contact, onto a mounting pin or fixture in a plastic injection moulding tool. Insert moulding is typically done by heating a thermoplastic resin to a molten state and injecting it into a steel mould. This technique lowers assembly and labour expenses while granting manufacturers greater design flexibility without sacrificing structural integrity.
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Post-processing operations
There are six common types of post-processing activities, which include corrective actions to remove surface defects and secondary processes for decorative or functional purposes. Post-processing operations can remove excess material, also known as flash, which can interfere with sealing and assembly. This excess material is created when plastic is forced from a mould cavity at the parting line or ejector pin locations.
Painting is a pivotal post-processing technique, adding vibrant coloured coatings to enhance moulded parts. In-mould painting is an option, but it may not be as cost-effective as painting after the moulding process. Coatings that offer protection against electromagnetic interference (EMI) also fall under the category of post-process painting.
Other post-processing operations include texturing, which can be applied to the injection mould in various ways, from etching in a chemical bath to engraving by hand or with a laser. Heat treatment can also be used to improve strength, durability, and other mechanical properties.
Ultrasonic welding is another post-processing technique, useful for bonding two plastics together or working with other dissimilar objects that have trouble bonding. This process involves holding the two components together in a fixture under pressure and then applying high-frequency ultrasonic acoustic vibrations through a vibrating tool called a horn.
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