Design essentials of multi-color / multi material injection molded products

Design essentials of multi-color / multi material injection molded products

The structure of multi-color injection molded products is very different from that of ordinary plastic products. The design of product structure and shape first needs to be considered from the purpose and purpose of the product. It is necessary to carry out a detailed structural design of injection molded products and fully consider the compatible characteristics of several materials.

Generally, it is necessary to increase the contact area of raw materials to enhance the firmness. Many small grooves and convex grooves can be designed inside the products for inlay and stitching, so as to increase the contact area of materials, improve the service strength and service life of products, and enhance practicality.

1. Multi color material joint mode

Generally, in the design of multi-color / multi material injection molded products, the combination of adjacent components is realized by two methods, and the following two methods are usually used at the same time:

(1) Mechanical fixation method

The mechanical fixation method does not include the physical bonding between adjacent substances. Generally, it has connection points, and the collapse or hole on the semi-finished product is obtained by injection molding, or the structural interconnection between the two materials is used.

(2) Combination method

The joint of multi-color / multi material injection molded products usually refers to the physical joint of two adjacent substances. This kind of joint is sometimes considered as chemical connection. In fact, there is no obvious chemical reaction between thermoplastics, Binding is caused by the interaction between molecules (van der Waals forces) and molecular entanglement (driven by heat energy, macromolecules are prone to mechanical entanglement and intermolecular entanglement, and the adjacent parts of macromolecules are interspersed to form mechanical connections).

2. Sealing position design

Glue sealing position refers to the combination position and boundary line position of hard glue and soft glue; Generally, the "feather" design of the sealing position must be avoided (that is, the sealing position cannot be gradually thinned), because poor bonding and reverse edges are easy to occur on the too thin edges, as shown in figure 4-17a;

The design of the ideal sealing position must be able to make an obvious step and depression to ensure that the wall thickness of the glue position is consistent, as shown in figure 4-17b and C; In some products, when the process is very long or the area needs to be worn frequently, some mechanical connections can be designed between soft glue and hard glue to make the two materials penetrate each other in the product structure and ensure the connection strength of the product.

3. Reasonable selection of wall thickness and surface etch

Taking TPE coating as an example, because the price of TPE material is very expensive, designers must consider reducing the cost in the process of product design, and use a smaller TPE wall thickness. The excellent hand feel and touch of TPE are directly related to the wall thickness and hardness of TPE; When the thickness of TPE is less than 1.5mm, the feeling of softness and hardness mainly depends on the hardness of the hard glue under TPE, and the cushioning and shockproof from the functionality of TPE will also be affected by the hardness of the hard glue under TPE. The decrease of TPE thickness will seriously affect the bonding strength between TPE and hard glue, mainly because too thin TPE will make TPE cool too early in the mold, resulting in the decrease of bonding strength.

After the surface of PE products is etched, it can give people the feeling of leather, produce a better feel, and cover up many surface defects; Some etchings can also adjust the surface hardness of TPE products to make them softer or harder than when TPE materials are made into a smooth surface. If the designer polishes the surface of TPE into a mirror, many material lines and color lines will appear on the mirror, or whiten in the process of use, resulting in poor surface quality.

3、 Key points of mold design for multi-color / multi material injection molding

1. The cavity shape of the front mold of the multicolor mold is different, and the cavity of the rear mold needs to be exactly the same.

2. It must be ensured that after the rear mold of the mold rotates with the center, it must coincide with the front mold. This must be paid attention to in the design.

3. Before mold design, you must understand the parameter data of the multi-color injection molding machine used in mass production. (maximum / minimum modulus of capacitance or thickness of modulus of capacitance, distance of ejector pin hole, etc.)

4. The nozzle of the three plate mold should be designed to automatically demould. Pay special attention to whether the demoulding action of the soft rubber nozzle is reliable.

5. Special attention should be paid to the selection of materials, including the viscosity of materials, deformation during injection and the risk of melting.

6. When designing the cavity of the second injection molding, in order to avoid inserting (or rubbing) the cavity into the rubber position of the product that has been molded for the first time, a part of void avoidance can be designed. However, we must carefully consider the strength of each sealing position, that is, whether there will be large injection pressure in the injection molding, which will deform the plastic, resulting in the possibility of batch front in the second injection molding.

7. During injection molding, the product size of the first injection molding can be slightly larger, so that it can be pressed more tightly with another cavity during the second molding, so as to achieve the function of sealing glue. 8. Pay attention to whether the flow of plastic will impulse the product that has been molded for the first time and deform its glue position during the second injection? If this is possible, we must find ways to improve.

9. The water transportation arrangement of the cavity and core shall be as full as possible, balanced and the same.

10. 99% of the cases are that the hard rubber part of the product is injected first, and then the soft rubber part of the product is injected. Because the soft glue is easy to deform.

11. In order to make the plastic "stick" tighter, we should consider the "viscosity" between materials and the roughness of the mold surface.

12. In the process of primary injection, secondary injection and multiple injection, the reservation and disposal of exhaust gas need to be considered in advance.