Hollow molding is a composite process that combines the high precision of injection molding with the hollow structure characteristics of hollow molding. First, prefabricated parts with specific shapes are manufactured through injection molding, and then hollow parts are formed on the basis of the prefabricated parts through hollow molding technology. This process can be used to manufacture plastic products with complex structures, such as tool housings with hollow handles. In this process, attention should be paid to the connection between injection molding and hollow forming to ensure the compatibility of the two processes and the overall quality of the product.
The hollow forming production line is developing towards intelligence and automation. By introducing sensors, automation control systems, and robot technology, real-time monitoring of the production process, automatic parameter adjustment, and automatic sorting and packaging of products can be achieved. For example, in the extrusion blow molding production line, sensors installed on the extruder and mold can monitor parameters such as temperature and pressure. When the parameters exceed the set range, the control system automatically adjusts to ensure the stability of the production process and the consistency of product quality.
What is the difference between hollow molding and injection molding in Dalian?
1、 Forming principle
blow molding
Mainly used for manufacturing hollow plastic products. Taking extrusion blow molding as an example, plastic particles are first heated and melted in an extruder, and a tubular billet is extruded through the extruder head. After the billet reaches the predetermined length, the mold is closed, the billet is cut and clamped, and then compressed air is blown into the interior of the billet through a blowing needle to expand and fit the mold cavity. After cooling and demolding, the finished product is obtained. Injection blow molding is the process of first obtaining a bottomed billet through injection molding, and then transferring it to a blow molding mold for blow molding. Multi layer co extrusion blow molding is the process of using a special multi-layer extruder head to simultaneously extrude two or more different plastic materials, forming a multi-layer structured preform, which is then blow molded.
injection molding
It is a process of heating plastic raw materials to a molten state and rapidly injecting the plastic melt into a closed mold cavity under high pressure through an injection device. The plastic is cooled and solidified in the mold cavity, and then the mold is opened to remove the formed plastic product. The entire process is based on the injection filling, pressure holding, and cooling shaping of plastic melt.
2、 Equipment structure
Hollow forming equipment
Extrusion blow molding equipment: mainly composed of extruders, blow molds, and blowing devices. The extruder includes a hopper, screw, barrel, heating device, and head, used to plasticize plastic raw materials and extrude preforms. Blow molding molds are used for the blowing and forming of preforms, and their internal structural design takes into account the blowing and cooling of the preforms. The blowing device generally includes an air compressor, a storage tank, and a blowing needle, which are used to provide compressed air for blowing and expanding the billet.
Injection blow molding equipment: including injection machines and blow molding molds. The injection machine consists of an injection device, a mold clamping device, and a hydraulic system. The injection device is responsible for the melting and injection of plastic, the mold closing device controls the opening and closing of the mold, and the hydraulic system provides power for the action. The structure of blow molding molds is relatively complex and needs to meet the requirements of injection molding and subsequent blow molding of preforms.
Injection molding equipment
Mainly composed of injection machines and injection molds. Injection machines include plasticizing devices (screws, barrels, etc.), injection devices (injection cylinders, nozzles, etc.), mold clamping devices (moving templates, fixed templates, locking mechanisms, etc.), and hydraulic or electric control systems. Injection molds include moving molds and fixed molds, which are equipped with cavities, cooling systems, ejection mechanisms, etc. The complexity of the mold depends on the shape and structure of the plastic product.
3、 Product features
Hollow molded products
Structural features: The product is a hollow structure, which makes it lighter in weight and has good thermal and sound insulation properties with the same amount of material used. For example, plastic bottles have a hollow inner part that can serve as a buffer and reduce heat conduction.
Wall thickness characteristics: In extrusion blow molding, wall thickness control is relatively difficult, and the wall thickness of the product may be uneven due to factors such as billet extrusion process and inflation process. However, in injection blow molding and multi-layer co extrusion blow molding, the uniformity of wall thickness can be well controlled.
Application features: Widely used in the manufacturing of various containers, such as plastic bottles, plastic barrels and other packaging containers, as well as products that require hollow structures such as automotive fuel tanks and ventilation ducts.
Injection molded products
Structural characteristics: It can manufacture solid plastic products with various complex shapes, from simple geometric shapes to products with fine structures and complex internal features. For example, plastic products with internal buckles, threads, reinforcing ribs, and other structures.
Wall thickness characteristics: It can accurately control the wall thickness of the product. Through mold design and injection process parameter adjustment, the product can have different wall thicknesses in different parts to meet the performance requirements of the product.
Application characteristics: It has a wide range of applications, including electronic device casings, automotive parts, toys, household items, and many other fields, covering almost all industries that require plastic products.
Optimize the mold structure based on the shape and characteristics of the hollow product. For example, for products with complex shapes, movable inserts or slider structures can be used to facilitate demolding of the product. In multi-layer co extrusion blow molding molds, it is necessary to design the flow channels of each layer of material reasonably to ensure that different plastic materials can be evenly extruded and form multi-layer preforms.
Select mold materials based on the process characteristics of hollow forming and the requirements of the product. For molds with large batch sizes and high precision requirements, high-quality mold steel such as P20 steel should be selected, which has good wear resistance, corrosion resistance, and thermal stability. For some small-scale production or situations with low requirements for mold performance, materials such as aluminum alloy can be chosen, which have the advantages of easy processing and low cost.
