• 2024-01-04

What are the materials of the mold?

The most important factors for mold materials are thermal strength and thermal stability. Common mold materials include working temperature, forming materials, and mold materials

<300 ℃ Zinc alloys Cr12, Cr12MoV, S-136, SLD, NAK80, GCr15, T8, T10.

300-500 ℃ aluminum alloy, copper alloy 5CrMnMo, 3Cr2W8, 9CrSi, W18Cr4V, 5CrNiMo, W6Mo5Cr4V2, M2.

500~800 ℃ aluminum alloy, copper alloy, steel titanium GH130, GH33, GH37.

800~1000 ℃ titanium alloy, steel, stainless steel, nickel alloy K3, K5, K17, K19, GH99, IN100 Ж C-6NX88, MAR-M200, TRW-NASA, WA.

>1000 ℃ nickel alloy copper based alloy mold, hard alloy mold.

Classification of pouring systems

Plastic molds can be divided into three categories based on the type of pouring system:

(1) Large water outlet mold: The runner and gate are on the parting line and demolded together with the product during mold opening. The design is the simplest, easy to process, and the cost is lower, so many people use the large water outlet system for operation. The structure of plastic molds is divided into two parts: moving molds and fixed molds. The movable part of the injection machine is a moving mold (mostly on the ejection side), and the non movable part at the ejection end of the injection machine is generally referred to as a fixed mold. Due to the fact that the fixed mold part of the large water outlet mold is generally composed of two steel plates, this type of structural mold is also called a two plate mold. The two plate mold is the simplest structure in the large water mouth mold.

(2) Fine nozzle mold: The runner and gate are not on the parting line, usually directly on the product. Therefore, it is necessary to design an additional set of nozzle parting lines, which is more complex in design and difficult to process. Generally, the selection of fine nozzle system depends on the product requirements. The fixed mold part of the fine nozzle mold is generally composed of three steel plates, so this type of structural mold is also called a "three plate mold". The three plate mold is the simplest structure in the fine nozzle mold.

(3) Hot runner mold: This type of mold has a similar structure to a fine nozzle, with the biggest difference being that the runner is located in one or more hot runner plates and hot pump mouths with constant temperature, without cold material demolding. The runner and gate are directly on the product, so the runner does not need demolding. This system is also known as a non nozzle system, which can save raw materials and is suitable for situations where raw materials are expensive and product requirements are high. Design and processing are difficult, and mold costs are high. Hot runner system, also known as hot runner system, mainly consists of hot runner sleeve, hot runner plate, and temperature control electrical box. Our common hot runner systems come in two forms: single point hot gate and multi-point hot gate. Single point hot gate is a plastic mold that uses a single hot gate sleeve to directly inject molten plastic into the mold cavity. It is suitable for single cavity and single gate plastic molds; Multi point hot runner is a method of branching molten material into various sub hot runner sleeves through a hot runner plate and then entering the mold cavity. It is suitable for single cavity multi-point feeding or multi cavity molds.

Forming classification

(1) Injection molding

Plastic is first added to the heating cylinder of the injection machine, which is heated and melted. Under the push of the injection machine screw or plunger, it enters the mold cavity through the nozzle and mold pouring system. Due to physical and chemical effects, it hardens and forms an injection molded product. Injection molding is characterized by periodicity, as it consists of a cycle consisting of injection, pressure holding (cooling), and demolding processes. Thermoplastic injection molding has a short molding cycle, high production efficiency, and minimal wear on the mold caused by molten materials. It can form complex shaped, clear surface patterns and markings, and high dimensional accuracy plastic parts in large quantities; However, for plastic parts with significant changes in wall thickness, it is difficult to avoid forming defects. Anisotropy of plastic parts is also one of the quality issues, and all possible measures should be taken to minimize it.

(2) Compression molding

Commonly known as compression molding, it is one of the earliest methods for forming plastic parts. Compression molding is the process of directly adding plastic into an open mold cavity with a certain temperature, then closing the mold, and under the action of heat and pressure, the plastic melts into a flowing state. Due to physical and chemical reactions, plastic hardens into plastic parts with a certain shape and size that remain unchanged at room temperature. Compression molding is mainly used for molding thermosetting plastics, such as phenolic molding powder, urea formaldehyde and melamine formaldehyde molding powder, glass fiber reinforced phenolic plastics, epoxy resin, DAP resin, silicone resin, polyimide and other molding materials. It can also be used for molding and processing unsaturated polyester pellets (DMC), sheet-like molding materials (SMC), prefabricated integral molding materials (BMC), and so on. In general, compression molds are often classified into three types based on the matching structure of the upper and lower molds of the compression film: overflow type, non overflow type, and semi overflow type.

(3) Extrusion molding

It is a molding method that allows plastic in a viscous flow state to pass through a die with a specific cross-sectional shape under high temperature and certain pressure, and then shape it into a continuous profile with the desired cross-sectional shape at a lower temperature. The production process of extrusion molding involves preparing molding materials, extrusion molding, cooling and shaping, traction and cutting, and post-processing (quenching or heat treatment) of extruded products. During the extrusion molding process, pay attention to adjusting the temperature, screw rotation, traction speed, and other process parameters of the heating section of the extruder barrel and the die of the machine head in order to obtain qualified extruded profiles. Special attention should be paid to adjusting the extrusion rate of polymer melt from the die of the machine head. Because when the extrusion rate of the molten material is low, the extruded material has a smooth surface and a uniform cross-sectional shape; However, when the extrusion rate of the molten material reaches a certain limit, the surface of the extruded material will become rough, lose its luster, and exhibit phenomena such as shark skin, orange peel patterns, and shape distortion. As the extrusion rate further increases, the surface of the extruded material exhibits distortion, even detachment and fracture into melt fragments or cylinders. Therefore, the control of extrusion rate is crucial.

(4) Pressure injection molding

Also known as casting and pressing. It is to add plastic raw materials into the preheated feeding chamber, and then place the pressure column into the feeding chamber to lock the mold. The pressure is applied to the plastic through the pressure column, and the plastic melts into a flowing state under high temperature and pressure. It gradually solidifies into the mold cavity through the pouring system. This molding method, also known as transfer molding. Pressure injection molding is suitable for plastics that are lower than solid plastics and can be compressed in principle. It can also be formed by pressure injection method. But it is required that the formed material has good fluidity in the molten state when it is below the curing temperature, and has a large curing rate when it is above the curing temperature.

(5) Hollow forming

It is the process of solidifying tubular or sheet-like billets produced by extrusion or injection, which are still in a plasticizing state