New Technology of Plastic Mold Design and Manufacture

New Technology of Plastic Mold Design and Manufacture

Plastic moulds play a very important role in plastic processing. The design level and manufacturing capacity of moulds also reflect the industrial level of a country. In recent years, the output and level of plastic forming moulds have developed rapidly, and the proportion of moulds with high efficiency, automation, large scale, precision and long life has become larger and larger. Next, from mould design, processing methods and processing equipment, Surface treatment and other aspects to summarize the development status of the mold.Household Plastic Mold.

Plastic molding method and mold design

Gas-assisted molding, gas-assisted molding is not a new technology, but it has developed rapidly in recent years and some new methods have emerged. Liquefied gas assisted injection is to inject a preheat special gasified liquid into the plastic melt from the injection. The liquid is vaporized and expanded in the mold cavity when heated, making it hollow, and pushing the melt to the surface of the mold cavity. This method can be used for any thermoplastic. Vibration gas assisted injection is to apply vibration energy to the plastic melt through the compressed gas of the oscillating product, so as to control the microstructure of the product and improve the performance of the product. Some manufacturers convert the gas used in gas-assisted molding into thinner products, and can also produce large hollow products with higher quality and lower cost, but the key point is the leakage of water,

Push-pull molding mold, which opens two or more channels around the mold cavity and is connected with two or more injection devices or reciprocating pistons, after the injection is completed and before the melt is solidified, the screw or piston of the injection device moves back and forth to push and pull the melt in the cavity. This technology is called dynamic pressure retaining technology, which aims to avoid the problem of large shrinkage when using traditional molding methods to form thick products, High-pressure molding thin shell products are generally products with a long process ratio, and most of them use molds with multi-point gates. However, multi-point pouring will cause fusion joints, and some transparent products will affect their visual effect. Single-point pouring is not easy to fill the mold cavity, so it can be formed by high-pressure molding technology, such as the cockpit of the F16 fighter plane of the United States Air Force, At present, this technology has been used to produce PC automobile windshield. The injection pressure of high-pressure molding is generally more than 200MPA. Therefore, the mold material should also choose high-strength steel with high Young's modulus. The key of high-pressure molding is the control of mold temperature. In addition, it is necessary to pay attention to the smooth exhaust of mold cavity. Otherwise, the high speed injection will cause poor exhaust and burn the plastic.Servo Type Injection Molding Machine

Hot runner mold: hot runner technology is increasingly used in multi-cavity mold, and its dynamic entry technology is a highlight of mold technology. That is, the flow of plastic can be adjusted by a needle valve. The injection time, injection pressure and other parameters can be set for each gate respectively to achieve balance and injection and the best quality assurance. The needle valve can move dynamically and steplessly by hydraulically driving the piston. The position of the needle valve determines the injection flow and pressure. There is a pressure sensor in the channel, which can continuously record the pressure in the channel, and then control the position of the needle valve and adjust the melt pressure.

Molds for fusible core injection molding: This method is to put the fusible core made of low melting point alloy into the mold as an insert for injection molding. Then heat the product containing fusible core to remove the fusible core. This molding method is used for products with complex and hollow shapes, such as hollow plastic parts with complex shapes such as oil delivery pipes or exhaust pipes of automobiles. Products molded with this type of mold include: tennis racket handle, automobile water pump, centrifugal hot water pump and spacecraft oil pump, etc. Injection/compression molding mold: injection/compression molding can produce low stress. For products with good optical performance, the technological process is: mold closing (but the moving and fixed mold are not completely closed, leaving a gap for later compression), melt injection, secondary mold closing (that is, compression makes the melt compacted in the mold), cooling, mold opening, and mold release. In mold design, it should be noted that the mold is not completely closed at the beginning of mold closing, so in order to prevent overflow during injection, a structure to prevent overflow should be designed in the mold. Laminated mold: multiple cavities are overlapped at the side of mold closing, instead of multiple cavities on the same plane, which can give full play to the plasticizing ability of the injection machine. This mold is generally used in hot runner mold, which can greatly improve efficiency, Injection mold for layered products: The injection mold for layered products has the characteristics of co-extrusion molding and injection molding. It can realize multi-layer combination of materials with different thickness on the products, and the thickness of each layer can be as small as 0.1~10mm, and the number of layers can reach thousands. This mold is actually a combination of an injection mold and a multi-stage co-extrusion mold.

Mold slip molding (DSI): This method can form hollow products and composite products of multiple materials. The process is: close the mold (for hollow products, the two halves of the cavity are at different positions), inject the mold separately, move the mold to the two halves of the cavity to match, and inject the resin that combines the two halves of the cavity in the middle. Compared with blow molded products, the products formed by this method have good surface accuracy, high dimensional accuracy, and uniform wall thickness, Large design freedom and other advantages.

Aluminum mold: A prominent point in plastic manufacturing technology is the application of aluminum alloy materials. The service life of aluminum alloy plastic mold developed by Corus Company can reach more than 300000, and the service life of PechineyRhenalu Company can reach more than 500000 times using its MI-600 aluminum material to manufacture plastic

Mold manufacturing

High-speed milling: At present, high-speed cutting has entered the field of precision machining, and its positioning accuracy has been improved to {+25UM}. The rotation accuracy of high-speed electric spindle with hydrostatic bearing is below 0.2um, the rotation speed of machine tool spindle can reach 100.000r/min, and the rotation speed of high-speed electric spindle with hydrostatic bearing can reach 200. The rapid feed speed of 00r/min can reach 30~60m/min. If the large guide and ball screw, high-speed servo motor, linear motor and precision linear guide are used, the feed speed can even reach 60~120m/min. The tool change time is reduced to 1~2s, and the machining roughness Ra is less than 1um. Combined with new tools (cermet tools, PCBN tools, special hard and metal tools, etc.), it can also process materials with hardness up to 60HRC. The temperature of its processing process is only increased by about 3 degrees, and the thermal shape is very small, which is especially suitable for forming materials with complex thermal deformation to temperature (such as magnesium alloy, etc.). The high-speed cutting speed is 5~100 m/s, which can completely achieve the mirror turning and mirror milling of mold parts. In addition, the cutting force is small, and it can process thin-walled and rigid parts

Laser welding: laser welding equipment can be used to repair the mold or cladding the metal layer to increase the wear resistance of the mold. The hardness of the mold surface layer after laser cladding can reach 62HRC. The micro-welding time is only 10-9 seconds, so heat transfer to the adjacent area of the welding point can be avoided. General laser welding process is adopted. The temperature at 15mm from the welding point can reach 150~200C while the temperature is only 36C when micro-welding technology is used. This will not cause changes in the metallographic structure and properties of the material, nor will it cause problems such as warpage, deformation or cracking

EDM milling: also known as EDM generation processing technology. It uses a simple tubular electrode with high speed rotation for two-dimensional or three-dimensional contour processing, so it is no longer necessary to manufacture complex shaped electrodes.

Three-dimensional micromachining (DEM) technology: DEM technology overcomes the disadvantages of long processing cycle and high price of LIGA technology, and integrates three main processes: deep etching, micro-electroforming and micro-replication. It can generate molds for micro-parts such as gears with a thickness of only 100um,

The integrated technology of precision forming of three-dimensional cavity and mirror surface electrothermal machining: the method of adding solid fine powder into the common kerosene working fluid is adopted to increase the distance between the electrodes of finishing, reduce the electropneumatic effect, and increase the dispersion of the discharge channel, so that the chip removal is good, the discharge is stable, the processing efficiency is improved, and the roughness of the machined surface is effectively reduced. At the same time, the powder mixing working fluid can also form a higher hardness coating on the surface of the mold workpiece, improving the hardness and wear resistance of the mold cavity surface

Mold surface treatment and strengthening

In order to improve the life of the mold, in addition to conventional heat treatment methods, the following are some commonly used mold surface treatment and strengthening technologies, chemical treatment, and its development trend is from infiltration of single element to multi-element, to multi-element co-infiltration, and to compound infiltration, from general expansion, diffusion to chemical vapor deposition (PVD), physical chemical vapor deposition (PCVD).

Ion implantation

Laser surface treatment:

1. Use laser beam to obtain extremely high heating speed to realize surface quenching of metal materials. High-carbon and ultra-fine martensite crystals are obtained on the surface, and the hardness is 15%~20% higher than that of the conventional quenching layer, while the core structure will not change,

2. Use laser for surface remelting or surface alloying to obtain high performance surface hardness layer. For example, after unalloyed with CrWMn composite powder, its volume wear is 1/10 of that of quenched CrWMn, and its service life is increased by 14 times.

3. Laser melting treatment is a kind of quenching treatment organization that uses high energy density laser beam to melt the metal surface, making the metal surface layer form a layer of liquid metal quenching organization. Because the heating and cooling of the surface layer are very fast, the obtained organization is very fine. If the cooling rate is high enough through the external medium, the crystallization process can be inhibited and the amorphous state can be formed, Therefore, it is also called laser melting - amorphous processing, also called laser glazing.

Surface strengthening of rare earth elements: This can improve the surface structure, physical, chemical and mechanical properties of steel. It can increase the penetration rate by 25%~30%, and shorten the treatment time by more than 1/3. Commonly, there are rare earth carbonitriding, rare earth carbonitriding, rare earth boronizing, rare earth boronizing, and rare earth boroaluminizing. Chemical plating: It is to reduce and precipitate Ni P B in solution on the metal surface through chemical test, so as to obtain Ni-P, Ni-B and other alloy coatings on the metal surface. In order to improve the mechanical properties, candle resistance and technological properties of metals, it is also called autocatalytic reduction plating, electroless plating, etc.

Nano-surface treatment: It is a technology based on nano-materials and other low-dimensional non-equilibrium materials, based on solid surface materials through specific processing technology, to strengthen or endow solid surface with new functions through specific processing technology. (1) Nano-composite coating is formed by adding zero-dimensional or one-dimensional nano-particle powder materials into the traditional electrolyte. Nano-materials can also be used for wear-resistant composite coatings. For example, adding n-ZrO2 nano-powder material into the NI-W-B amorphous composite coating can improve the oxidation performance of the coating at 550-850C, improve the corrosion resistance of the coating by 2-3 times, and significantly improve the wear resistance and hardness. (2) Nano-structure coating has significantly improved in strength, toughness, corrosion resistance, wear resistance, thermal fatigue resistance and other aspects, and one coating can simultaneously have the above properties, rapid prototyping and rapid molding

Rapid prototype manufacturing and rapid tooling are important technologies in new product development. In the past, people have always believed that rapid mold making is limited to small batch trial production, but in recent years, rapid mold making has also made great efforts in medium batch, even large batch. The process of manufacturing quasi-durable metal mold is to form a metal spray layer on the surface of the prototype, and then strengthen the spray layer, and then remove the molten layer to obtain the metal mold. The surface hardness of the mold can reach 63HRC by using the high melting point molten material.

The direct rapid manufacturing metal mold (DRMT) methods mainly include: selective laser sintering (SLS) with laser as the heat source, laser melt deposition (LENS) with plasma arc as the heat source, deposition (PDM) with plasma arc as the heat source, 3D printing (3DP) with spray forming and metal sheet LOM technology, etc. The mold manufacturing accuracy of SLS has been improved. The shrinkage rate has decreased from 1% to below 0.2%. Although the density and mechanical properties of the parts manufactured by LENS are greatly improved compared with SLS method, there is still about 5% porosity. It is only applicable to manufacturing parts or molds with simple geometric shapes. Due to the adhesion of unmelted particles, the surface quality is not too high.

The shape deposition manufacturing method (SDM) uses the welding principle to melt the welding material (wire), and uses the thermal spraying principle to make the ultra-high temperature droplet deposit and form layer by layer to realize the combination of layer metal treatment, which can avoid the side step effect caused by the RT technology based on the principle of lamination method, resulting in low precision, poor surface quality, and low comprehensive mechanical properties.

Rapid die making technology is produced and developed in the competition with traditional machining technology, but the milling speed is as high as 100.000r/min, and the high-speed milling technology with excellent surface accuracy has become the biggest competition of DRMT technology

BY ELEVEN