I saw a plastic product in the sample cabinet with two different colors. Engineer Huang explained that this is a classic two-color injection molding process, where two different materials are injected into the same mold to create a product formed from two materials. The two materials may differ in color or hardness, which improves the product's appearance and assembly performance. So, can small appliance casings be made in multiple colors?
First, let's discuss the difference between two-color injection molding and two-color injection molding.
Two-color injection molding involves first creating a colored plastic part on a single-color injection molding machine, then manually placing it into a second mold for final injection molding. It doesn't require a dedicated injection molding machine. Two-color injection molding, on the other hand, is completed using a two-color injection molding machine, involving two injection processes, all within the machine itself. It typically uses a specialized two-color injection molding machine.
II. Advantages of Two-Color Injection Molding
1. Enhanced Performance: Appropriate combination of skin and core materials can reduce residual stress in molded products, increase mechanical strength, or improve surface properties. Skin or core materials with special surface properties can be used, such as those with electromagnetic interference resistance or high electrical conductivity.
2. Increased Efficiency and Reduced Costs: Automated production lines offer high response and repeatability, significantly reducing process and manpower requirements, ensuring stable product output, guaranteeing delivery times, increasing workshop utilization, and reducing management costs.
3. Long Mold Life, Stable Quality, and Reduced Scrap Rate
4. Design Freedom and Exquisite Appearance: Core and skin materials can be freely selected according to different usage characteristics, eliminating the need for assembly, reducing seams, and solving the problem of some products being unable to be mass-produced due to their special structures.
III. Working Principle of Two-Color Injection Molding
Two-color injection molding requires one male mold and two female molds. The first injection is performed in the male mold and the first female mold. After molding, the mold is opened, and without demolding, the product is directly transferred to the second female mold for the second injection. After demolding, the two-color injection molded product is obtained.
In actual production, two sets of male molds are typically used, each responsible for one injection molding cycle. Switching between different female molds is achieved by rotating 180° vertically. This method is relatively simple. Four-disc two-color injection molding machines have emerged, requiring only 90° rotation per cycle, and this horizontal rotation eliminates the influence of gravity compared to ordinary two-color injection molding, resulting in greater stability and efficiency.
IV. Material, Process, and Mold Requirements for Two-Color Injection Molding
1. Material Requirements
The mating materials for two-color injection molding must meet two basic compatibility conditions: adhesive compatibility and processing compatibility.
2. Process Requirements
Dual-injection design for soft and hard plastics
The two materials must have a certain temperature difference in melting points, generally recommended to be 60℃, and suggested to be at least 30℃ or higher. The first injection material has a higher melting point temperature; typically, the first injection is PC or PC/ABS, and the second injection is TPU or TPE. PC thickness is 0.6-0.7mm, and soft plastic is 0.4mm or thicker.
Maximize the contact area by creating grooves or other methods to increase adhesion. Alternatively, use a core-pulling technique for the first injection, with the second injection partially injecting material into the first. Make the surface of the first injection mold as rough as possible.
Transparent and Opaque Two-Injection Design
Small Lens Two-Injection Design: The first injection is opaque, the second is a lens. Use high-melting-point PC for the first injection and PMMA for the second.
Decorative Transparent and Opaque Two-Injection Design: The first injection is opaque, the second is transparent. High-temperature PC is commonly used for opaque materials, while PMMA or PC is used for the transparent second injection. PC requires UV coating for protection, while PMMA can be UV-coated or reinforced. If there are characters on the surface, UV coating is required.
3. Mold Requirements:
1. The two shapes of the female mold must be different, each molding a different product, while the two shapes of the male mold must be identical;
2. The front and rear molds must fit together after rotating 180° around the center;
3. The maximum and minimum mold thickness, KO hole distance, etc., must be carefully checked;
4. The sprue of the three-platen mold should ideally be designed for automatic demolding;
5. When designing the female mold for the second injection molding, to prevent the secondary female mold from scratching the glue area of the first molded product, a clearance can be designed. However, the strength of each sealing area must be carefully considered;
6. During injection molding, the product size of the first injection molded part can be slightly larger so that it can be pressed more tightly against the other mold during the second molding, achieving the sealing effect;
7. Pay attention to whether the flow of plastic during the second injection will impact the product that has already been molded in the first injection, causing deformation of the plastic parts;
8. Before the A and B plates are closed, pay attention to whether the front mold slider or ejector pin will reset first and damage the product;
9. The water channel arrangement of the two female molds and the male mold should be as sufficient and balanced as possible;
10. In 99% of cases, the hard plastic part of the product is injected first, followed by the soft plastic part, because the soft plastic part is easily deformed.
Therefore, small appliance casing injection molded parts can be made in a variety of colors. HUIWEN Plastics is a group enterprise that has been professionally engaged in precision mold design and manufacturing and precision injection molded product production for many years. The company focuses on providing good brands with a complete solution integrating product design, precision mold manufacturing, injection molding and assembly, and after-sales service. The products are widely used in the fields of household appliance casing accessories, medical device injection molded parts, cosmetic packaging injection molded parts, etc. Welcome to call for consultation.
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