Plastic mold in plastic processing occupies a very important position, mold design level and manufacturing capacity also reflects a country's industrial standard. In recent years, the plastic molding mold production and level of development is very fast, high efficiency, automation, large, precision, long life of the mold accounted for an increasing proportion of the following from the mold design, processing methods, processing equipment, surface treatment and other aspects to summarize the The development status of the mold.
Plastic molding methods and mold design
Gas-assisted molding, gas-assisted molding is not a new technology, but in recent years there has been rapid development and the emergence of some new methods. Liquefied gas assisted injection is a preheated special vaporizable liquid injected into the plastic melt from the spray, the liquid is heated in the mold cavity and expanded by vaporization, making the product 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 by oscillating the product compressed gas to achieve the purpose of controlling the microstructure of the product and improving the performance of the product. Some manufacturers convert the gas used in gas-assisted molding to form thinner products, and also produce large hollow products.
Push-pull molding mold, open two or more channels around the mold cavity, and connected with two or more injection devices or pistons that can move back and forth, before the melt curing after injection, the injection device screw or piston moves back and forth to push and pull the melt in the cavity, this technology is called dynamic pressure-holding technology, its purpose is to avoid the problem of forming thick products with traditional molding methods will have a large shrinkage.
High pressure molding thin shell products, thin shell products are generally long process ratio products, more multi-point gate mold, but multi-point into the pouring will cause melt joints, for some transparent products will affect its visual effect, single point into the pouring and not easy to fill the cavity, so you can use high-pressure molding technology to molding, such as the U.S. Air Force, the cockpit of the F16 fighter aircraft is produced with this technology, has adopted this technology to produce PC Auto windshield, high-pressure molding injection pressure is generally more than 200MPA, so the mold material should also choose a high Young's modulus of high strength just, high-pressure molding is the key to control the mold temperature, in addition to pay attention to the mold cavity exhaust must be smooth. Otherwise, high speed injection leads to poor exhaust will scorch the plastic.
Hot runner mold: in the multi-cavity mold more and more use of hot runner technology, its dynamic into the section technology is a highlight of the mold technology. This means that the flow of plastic is regulated by a needle valve, which can be set separately for each gate for injection time, injection pressure and other parameters, allowing for balanced and optimal quality assurance of the injection. A pressure sensor in the flow channel continuously records the pressure level in the channel, which in turn allows the needle valve position to be controlled and the melt pressure to be adjusted.
Moulds for core injection molding: In this method, a fusible core made of a low melting point alloy is placed in a mould as an insert for injection molding. The fusible core is then removed by heating the product containing the fusible core. This molding method is used for products with complex hollow shapes, such as oil pipes or exhaust pipes for automobiles, and other complex-shaped hollow core plastic parts. Other products molded with this type of mold are: tennis racket handle, automobile water pump, centrifugal hot water pump and spacecraft oil pump, etc.
Injection/compression molding molds: injection/compression molding can produce low stress. Optical properties of good products, the process is: mold closure (but the dynamic fixed mold is not completely closed, leaving a gap for later compression), injection of melt, secondary mold closure (i.e., compression so that the melt is compacted in the mold), cooling, opening the mold, and demolding. In the mold design, it should be noted that since the mold is not completely closed at the beginning of the mold closing, the structure of the mold should be designed to prevent the overflow of material during injection.
Laminated mold: Multiple cavities are arranged overlapping in the closing side instead of multiple cavities in the same plane, which can give full play to the plasticizing ability of the injection machine, and this kind of mold is generally used in hot runner molds, which can greatly improve the efficiency.
Layer products injection mold: layer products injection molding both co-extrusion molding and injection molding characteristics, can achieve any thickness of different materials on the product multi-layer combination, the thickness of each layer can be as small as 0.1 ~ 10mm layer number can reach thousands. This die is actually a combination of an injection die and a multi-stage co-extrusion die.
Mold slip molding (DSI): this method can be molded hollow products, but also molding a variety of materials composite products, the process is: closed mold (for hollow products, the two cavity halves are in different positions), respectively, injection, mold movement to the two cavity halves together, in the middle of the injection combined with the two cavity halves of the resin, this method of molding products compared with blow molding products, have good surface accuracy, high dimensional accuracy, uniform wall thickness, design freedom. wall thickness uniformity, design freedom and other advantages.
Aluminum mold: a prominent point in plastic manufacturing technology is the application of aluminum materials, Corus developed aluminum alloy plastic mold life can reach more than 300,000, PechineyRhenalu company with its MI-600 aluminum manufacturing plastic, life can reach more than 500,000 times
High-speed milling: At present, high-speed cutting has entered the field of precision machining, its positioning accuracy has been improved to {+25UM}, the use of liquid hydrostatic bearing high-speed electric spindle rotary accuracy of 0.2um or less, machine tool spindle speed up to 100.000r/min, the use of air hydrostatic bearing high-speed electric spindle rotary up to 200. 00r/min fast feed rate can reach 30 ~ 60m/min. 60m/min, if the use of large guide and ball screw and high-speed servo motor, linear motor and precision linear guide, feed speed can even reach 60 ~ 120m/min. tool change time reduced to 1 ~ 2s its processing roughness Ra < 1um. combined with new tools (metal ceramic tools, PCBN tools, special hard and gold tools, etc.), can also be processed hardness of 60HRC. materials. The temperature of the machining process only rises about 3 degrees, and the thermal shape is very small, especially suitable for forming materials that are sensitive to thermal deformation of temperature (such as magnesium alloy, etc.). High-speed cutting speed in 5 ~ 100m / s, can fully achieve the mirror surface turning and mirror surface milling of mold parts. In addition cut in cutting force is small, can process thin-walled and rigid poor parts.
Laser welding: laser welding equipment can be used to repair the mold or melt metal layer to increase the wear resistance of the mold, the hardness of the surface layer of the mold can be up to 62 HRC after the laser welding process. microscopic welding time of only 10-9 seconds, thus avoiding heat transfer to the adjacent areas of the weld joint. The general laser welding process is used. This does not cause changes in the metallurgical organization and properties of the material, nor does it cause warping, deformation or cracking, etc.
EDM milling: also known as EDM technology. It is the use of high-speed rotation of a simple tubular electrode for two-dimensional or three-dimensional contour processing, and therefore no longer need to create complex molding electrodes.
Three-dimensional micromachining (DEM) technology: DEM technology overcomes the drawbacks of long and expensive machining cycles of LIGA technology by combining three main processes: deep etching, micro electroforming and micro replication. It is possible to generate molds for micro parts such as gears with a thickness of only 100um.
Precise forming of three-dimensional cavities and mirror electro-fire processing integration only technology: the method of adding solid microfine powder to the ordinary kerosene working fluid is used to increase the inter-pole distance of finishing, reduce the electro-vacancy effect and increase the dispersion of the discharge channel, which can lead to good chip removal, stable discharge, improved processing efficiency and effective reduction of the roughness of the processed surface. At the same time, the use of mixed powder working fluid can also form a high hardness plating layer on the surface of the mold workpiece to improve the hardness and wear resistance of the mold cavity surface.
Mold surface treatment
In order to improve the life of the mold, in addition to the conventional heat treatment methods, the following are some common mold surface treatment and strengthening techniques.
Chemical treatment, its development trend is from infiltration of single element to multi-element, to multi-element co-infiltration, compound infiltration development, from the general expansion, scattered infiltration to chemical vapor deposition (PVD), physical chemical vapor deposition (PCVD that wait for ion vapor deposition).
Ion infiltration
Laser surface treatment: 1 Use the laser beam to obtain extremely high heating speed to achieve surface quenching of metal materials. In the surface to obtain high carbon very fine martensite crystals, hardness than conventional quenching layer 15% ~ 20% higher, while the heart organization will not change, 2, the role of laser surface remelting or surface alloying to obtain high-performance surface hardening 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.
Laser melting treatment is the use of high energy density of the laser beam to melt the surface of the metal cooling treatment organization, so that the metal surface layer to form a layer of liquid metal cooling organization, due to the heating and cooling of the surface layer is very rapid so the organization obtained is very fine, if the cooling rate through the external medium to achieve high enough, it can inhibit the crystallization process, and the formation of amorphous state, so also known as laser melting an Amorphous treatment, also known as laser glazing.
Rare earth elements surface strengthening: This can improve the surface structure, physical, chemical and mechanical properties of the steel, etc. It can increase the penetration rate by 25% to 30% and shorten the processing time by more than 1/3. Commonly, there are rare earth carbon coextrusion, rare earth carbon and nitrogen coextrusion, rare earth boron coextrusion, rare earth boron and aluminum coextrusion, etc.
Chemical plating: It is through the chemical test meter in the solution of Ni P B, such as reduction precipitation on the surface of the metal, so as to obtain the Ni-P, Ni-B, etc. alloy coating on the metal surface. To improve the mechanical properties of the metal, candle resistance and process performance, etc., also known as autocatalytic reduction plating, no electroplating, etc.
Nanosurface treatment: It is a technology based on nanomaterials and other low-dimensional non-equilibrium materials for a period of time, through specific processing techniques, to solid surface materials for a period of time, through specific processing techniques, to strengthen the solid surface or give the surface new functions.
(1) Nanocomposite coating is formed by adding zero-dimensional or one-dimensional nanoplasmonic powder materials to the conventional electrodeposition solution to form a nanocomposite coating. Nanomaterials can also be used for wear-resistant composite coatings, such as n-ZrO2 nanopowder materials added to NI-W-B amorphous composite coatings, can improve the high-temperature oxidation performance of the coating at 550-850C, so that the corrosion resistance of the coating increased by 2 to 3 times, wear-resistant livelihood and hardness are also significantly improved.
(2) Nanostructured coatings have significant improvements in strength, toughness, corrosion resistance, wear resistance, thermal fatigue and other aspects of coating, and a coating can have multiple properties at the same time.
Rapid prototyping and rapid mold making
The process of melt injection molding method is to form a metal melt layer on the surface of the prototype, and then the melt layer is reinforced, and the melt is removed to obtain a metal mold, with high melting point melt material can make the mold surface hardness of 63HRC.
Direct rapid manufacturing metal mold (DRMT) methods are: laser as the heat source of selective laser sintering (SLS) and laser-based melt stacking method (LENS), plasma arc, etc. as the heat source of fusion method (PDM), injection molding three-dimensional printing (3DP) method and metal sheet LOM technology, SLS mold making accuracy has been in for improvement. Shrinkage has been reduced from the original 1% to less than 0.2%, LENS manufacturing parts density and mechanical properties than the SLS method is a great improvement, but there is still about 5% porosity, it is only suitable for the manufacture of simple geometry of the parts or mold.
Shape deposition manufacturing method (SDM), using the welding principle to melt the welding material (wire), and with the thermal spray principle to make ultra-high temperature molten droplets deposited layer by layer forming, to achieve inter-layer cure bonding.
