Key knowledge to learn about plastic molds

Mold: A process equipment or tool that uses a specific shape to shape plastic products in a certain way.
Molding methods for plastic parts: molding, lamination, rolling, pasting, and other molding,
Molding includes injection molding, compression molding, transfer molding, extrusion molding, blow molding, vacuum forming, casting molding, rotational molding, plastic lining molding, and foam molding.
Plastic: A mixture composed mainly of high molecular polymers and a certain amount of additives. The main performance depends on the performance of the polymer.
Resins, i.e. polymers, play a role in determining the type and basic properties of plastics; Adhesion.
The function of plasticizers is to improve their plasticity, fluidity, and softness, reduce their stiffness and brittleness, and improve their processing performance.
The function of a heat stabilizer is to inhibit or prevent the degradation of resin during processing due to heat.
Effect of light stabilizer: Prevent resin from degrading and discoloring under sunlight, and reduce mechanical properties.
Antioxidant effect: prevents plastic oxidation and degradation.
Classification of plastics: Thermoplastics and thermosetting plastics are classified according to their structure. According to performance and purpose, it is divided into general plastics, engineering plastics, and special functional plastics.
ABS acrylonitrile butadiene styrene copolymer PA polyamide (nylon) PC polycarbonate PE polyethylene
POM formaldehyde PP polypropylene PPC chlorinated polypropylene PS polystyrene PVC polyvinyl chloride PF phenolic resin
Glass state: When T<Tg, all the inter chain and segment movements of the polymer molecules are "frozen", and the energy possessed by the molecules is less than the energy required for segment rotation. The molecular cohesion is high, the elastic modulus is high, and the entire substance appears as an amorphous solid, like glass, called a glass state.
Factors that affect viscosity: temperature and pressure.
Determination of plastic flowability: Melt flow index, spiral test method.
Good fluidity: polyethylene, polypropylene, polystyrene, acetate fiber
In terms of fluidity: modified polystyrene, ABS, AS, organic glass, polyoxymethylene, chlorinated polyether.
Poor fluidity: polycarbonate, polyvinyl chloride, polyphenylene ether, fluoroplastics.
Factors that affect the change in shrinkage rate: plastic variety, plastic part characteristics, mold structure, and molding process parameters.
Generally speaking, crystalline plastics are opaque or semi transparent, while non crystalline plastics are transparent. However, ionic polymer poly (4-methylpentene-1) belongs to crystalline plastics but is highly transparent, while ABS belongs to non crystalline plastics but is opaque.
Principles of plastic products:
On the premise of ensuring the usability, physical and mechanical properties, electrical properties, chemical corrosion resistance, and heat resistance of the product, it is recommended to choose plastics with low cost and good molding performance as much as possible.
When designing plastic products, consideration should be given to the overall structure of the mold, making the mold cavity easy to manufacture, and the core pulling and pushing mechanisms of the mold simple.
When designing products, the molding process of plastic raw materials, such as flowability and shrinkage, should be considered, and the shape should be conducive to mold parting, exhaust, feeding, and cooling.
When the appearance requirements of the product are high, the sample should be gradually drawn after shaping.
The size of the demolding slope on the product is related to its properties, shrinkage rate, friction coefficient, wall thickness, and geometric shape.
Classification of injection machines: according to appearance: horizontal, vertical, and right angle. According to the transmission mode: mechanical, hydraulic, and mechanical, hydraulic combination. By purpose: universal and specialized.
The composition of the injection machine includes injection device, mold closing device, hydraulic transmission, and electrical control system.
Preparation before forming: 1. Inspection and pre-treatment of raw materials. 2. Cleaning of the material barrel. 3. Preheating of inserts. Selection of release agent.
Injection process: feeding, plasticizing, injection, pressure maintaining, cooling, and demolding.
Post processing of plastic parts: annealing and humidity adjustment treatment.
Injection molding process conditions: temperature, pressure, time.
Classification of injection molds: single parting surface, double parting surface, with movable inserts, with side core pulling, automatic thread removal, ejection mechanism on the fixed mold side, and hot runner injection molds.
Principles for selecting parting surfaces: 1. Easy demolding 2. Consider and ensure that the appearance of the plastic parts is not damaged 3. Make every effort to ensure the accuracy requirements of the plastic parts size 4. It is conducive to exhaust 5. Try to make the mold processing convenient as much as possible
The pouring system of an injection mold refers to the melt flow channel from the beginning and end of the boiling channel to the mold cavity. The function is to smoothly and orderly fill the plastic melt into the mold cavity, achieving a dense structure and clear contour of the plastic part.
Classification of gating systems: ordinary gating systems and runner free gating systems
The composition of the pouring system: main flow channel, diversion channel, gate, and cold material cavity.
The form of cold material hole: 1. Cold material hole matched with push rod 2. Cold material hole matched with pull rod 3. Cold material hole without pull rod
The cross-sectional shape of the diversion channel: circular, rectangular, trapezoidal, U-shaped, and hexagonal
Cavity: The space used to fill plastic melt during the molding process to form products is called a cavity. The parts that make up this cavity are called forming parts, including: concave molds, convex molds, small cores, threaded cores, and molded rings.
Composite concave molds can be divided into: overall embedded, partial embedded, and modular combination.
The punch includes: integral type and combination type.
The function of a guiding mechanism is to guide, locate, and withstand a certain amount of lateral pressure.
When designing guide pillars and guide sleeves, attention should be paid to: 1. The guide pillars should be reasonably and evenly distributed around the mold parting surface, and there should be sufficient distance from the center of the guide pillar to the outer edge of the mold to ensure the strength of the mold. The length of the guide pillar should be 6-8mm higher than the height of the end face of the core to avoid damage caused by the core colliding with the concave mold when it enters.
According to the parts pushed out of the mold, it is divided into: 1. Push rod type demolding, 2. Push tube type demolding, 3. Template type demolding, 4. Push block type demolding, 5. Demolding of products using formed parts, 6. Multiple joint demolding
The inclined guide pillar core pulling mechanism is the most commonly used side core pulling mechanism, which has the characteristics of simple structure, convenient manufacturing, safety and reliability.
For the side core pulling mechanism of the inclined guide pillar in the fixed mold and the slider in the moving mold, the reset of the slider is achieved during the mold closing process, and the reset of the ejection mechanism is generally also achieved during the mold closing process. If the slider is reset first and the push rod is reset later, there may be a phenomenon of collision between the side core and the push rod, which is called interference phenomenon.
The inclination angle of the inclined guide pillar is generally taken as 15-20 degrees. Maximum not exceeding 25 degrees.
Compression molding, also known as compression or compression molding, is the main molding and processing method for thermosetting plastics. Compression molding is the process of directly adding plastic from powdered or pre pressed ingots to a heated mold feeding chamber, then closing and pressing at a certain speed to form and solidify the desired plastic parts.
Classification of compression molds: by connection: mobile, semi fixed, fixed, by parting surface: horizontal parting surface, vertical parting surface, by the form of the feeding chamber: overflow (open) compression mold, non overflow (closed) compression mold,