Injection molding high gloss seamless

Injection molding high gloss seamless 

First, the principle of high-gloss seamless injection molding:
1. The mold molding has higher temperature requirements (generally 80°~130°). After the injection molding is transferred to the pressure holding, the cooling water is used to cool the mold to 60°~70°. The pressure-holding molding at a higher mold temperature is advantageous for eliminating defects such as weld lines, flow marks, and internal stress of the product. Therefore, the mold needs to be heated during operation. In order to prevent heat loss, a resin heat insulation board is usually added on the fixed mold side.

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2. The surface of the cavity is extremely bright (generally mirror level 2 or higher). The products produced by Gaoguang Mould can be used directly for installation without any surface treatment. Therefore, it has high requirements for mold steel and plastic materials.

3. There are more hot nozzles in the hot runner system. Each hot nozzle must be equipped with a sealing needle and a separate air passage. It can be individually controlled by a solenoid valve and a time relay to achieve time-sharing, thereby achieving the purpose of controlling or even eliminating weld lines.

4, the mold heating method is usually heated by water vapor (see Figure 1) and heating rod heating (see Figure 2). The steam heating method is to pass the steam through the mold in the injection molding process through a specific mold temperature machine, so that the mold is rapidly heated; after the injection molding, the normal warm water (or ice water) is changed to quickly cool the mold. The heating rod heating method is to rapidly heat the mold by adding a heating rod inside the inner molding material during the injection molding process; after the injection molding is completed, the water inside the inner molding material (normal temperature water or ice water) or the aluminum at the bottom of the laminated molding material is used. The material (the water inside the aluminum material) cools the mold temperature quickly.

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Second, the mold material
(1) The mold material for the general requirements of the product surface can be used NK80 (Japan Datong)

(2) Products required by Gaoguang use S136H (Sweden) and CEANA1 (Hitachi)

(3) NK80 can be quenched without treatment; S136 should be quenched to 52 degrees after roughing; CEANA1 itself has 42 degrees and no quenching is required (this material is recommended because it does not affect subsequent processing or modification)

(4) There is also a good choice in the German Gritz brand: CPM40\GEST80

 

Third, the mold waterway design
(1) The water channel adopts a hole of 5mm-6mm size; the faucet uses 1\8 or 3\8 teeth (mold side), the other side uses 3\4 inch thread; the pipe material is made of stainless steel pipe

(2) The side of the waterway is not less than 5mm-6mm from the product surface; the waterway is parallel to the product surface and evenly arranged (the center of the principle is 15mm,); the thermocouple should be designed in the middle of the two waterways, with a depth of about 50mm; The PT100 of the mold set is one-fitted, keeping its precision, buried in the mold, like the thermocouple of the hot runner, connected to the outside of the mold by wires, and the adapter socket, the PT100 must have a corresponding plug to dock with it. .

(3) The mold waterway joints must be designed on the upper and lower sides or the rear side of the mold; the water supply outlets or water pipes are not allowed to be arranged on the operation side to burn and personnel.

(4) The mold inlet and outlet nozzles adopt the design of the manifold. The water-heat mold temperature control system has only one inlet and one outlet pipe to reduce the excessive water pipe connection and reduce the unnecessary loss of heat energy; and achieve the purpose of safety and energy saving. And the outer surface of the bellows is wrapped with heat-insulating tape, which plays a role of heat preservation and safety.

(5) Plugging In order to ensure no leakage and leakage, it is necessary to first block the copper and then use the taper throat to add high temperature resistant rubber seal; the high light mold is more important for the arrangement of the cooling water channel, and the good water channel arrangement can not only greatly improve the injection molding. Efficiency, but also plays an important role in improving product quality. The water channel of the high-gloss mold should not only be uniform but also must be sufficient, so that the required temperature can be easily reached by the mold temperature machine; at the same time, the long water pipe is used to directly transport the mold core water without using a sealing ring, thus preventing the mold from being long-term. Working at high temperatures can cause the seals to age and also reduce the cost of repairing many molds. It is worth mentioning that the water pipe of Gaoguang Mould must use a tubing that can withstand high temperature of 250 degrees and high pressure of 16 kg/MPa to prevent the water pipe from bursting under high temperature and high pressure. For round products, ring-type water transport is used; for long-type products, parallel water transport is used; for high-altitude products, water wells are used; for shaped products, three-dimensional water transport is used.

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Fourth, mold insulation system
(1) Mold fixed mold core or dynamic mold insert core to be hollowed out: the mold frame and the insert core must have a certain gap (depending on the thermal expansion coefficient of the mold material, 1mm on one side) to prevent the mold frame from expanding to reduce The core of the mold is effectively used for the contact surface of the mold frame; the lock of the mold core on the mold frame adopts a slanting manner or the like, and the front end adopts a dust resin or other material with obvious heat insulation effect.

(2) The detailed structure of the mold frame and the insert core is shown in Figure 1 and Figure 2; the cooling water of the mold frame is very important. In order to prevent the heat energy in the mold core from being transmitted to the mold frame, it is arranged close to the guide column position. A circle of water.

(3) As far as possible, the moving part of the guide sleeve should be made of graphite material or the front end of the guide post should be avoided. It is sufficient to ensure the length of the joint is 25mm;

Five, mold gate design
The mold gate design is to reduce the weld line as much as possible, and to facilitate the exhaust and reduce the shear. For the mold using the water heating mold temperature machine, the size of the gate should be relatively large, and the glue should be used as much as possible or the hot runner should be used. Without affecting product function and molding efficiency, the gate should be as short as possible, and the width should be as large as possible. If the gate is too small, it is likely to cause defects such as insufficient filling (short shot), shrinkage depression, and weld line, and the molding shrinkage will increase. If the gate is too large, excessive residual stress is generated around the gate, which causes deformation or cracking of the product, and the removal of the gate is difficult. It is best to use a gate unless the flow ratio exceeds the actual limit. The flow length plot of the resin will provide the flow length of the material under a defined molding condition. Multiple gates often produce sutures and fusion lines. In addition to long, narrow finished products, the use of a single gate will ensure a more consistent material, temperature, pressure distribution, and better alignment.
The exhaust material of the rubber port should be fully excluded and the cross-sectional area of ​​the main channel and the branch channel should be enlarged.

Six, mold exhaust
As far as possible, the product is separated by 10mm for a section, and the exhaust groove is evenly distributed, and the depth is 0.02mm; the product is also required to be exhausted in the middle of the product; the high-gloss mold must be welded to the sample plate after T1. The position of the gas is added to the exhaust.

Seven, the mold parting surface matching
Because the temperature of the high-gloss mold has a large drop, so the matching requirements of the face are high, and at the same time, the area of ​​the touch-face is reduced. It is enough to have a 10mm fit around the parting surface. Others should be avoided as much as possible.

Eight, heating rod high optical mode design
(1) There should be electric heating rods on the upper and lower sides of the feeding inlet, the water conveying hole is generally ∅6; the distance between the center of the two conveying water holes is 15mm-20mm; the distance between the heating rod wall and the surface of the product is 5mm, between the two heating rods The center distance is 20mm; the water wall is 6-8mm away from the heating rod wall.

(2) The inner mold cavity water can be sealed with high temperature sealing ring or hard sealed;

(3) The diameter of the heating rod is ∅4.92, and the mold is designed to be ∅5. Before assembling the heating rod, the burr of the heating rod hole is removed by the thimble grinding edge of ∅5;

(4) The mold inlet and outlet nozzles adopt the same manifold design as the steam heating mold, because the electric heating mold temperature control system has only one inlet and one outlet water pipeline.

Nine, Gaoguang's requirements for products
The high-light mold has strict requirements on the product structure. The brighter the product is more sensitive to the light refraction effect, the surface is slightly defective and will be discovered soon. Therefore, how to solve the shrinkage problem is the primary problem of high-gloss products. The thickness of the general product ribs does not exceed 0.6 times the thickness of the main body glue position, so it will not shrink, or the shrinkage is less likely to be found, which can be ignored. However, for high-gloss products, such requirements are far from enough. The thickness of the product ribs should be reduced to not more than 1 times the thickness of the main body glue. For the screw column, a crater-type sloping roof structure must also be used.

The most important thing is that the draft angle of the product should be pulled to more than 3 degrees. Because it is a mirror product, it is easy to adsorb and has an effect on the mold.

Ten, high-gloss mold selection of plastic materials
At present, commonly used high-gloss plastic materials are generally ABS+PMMA and ABS+PC. As a common two-shell material, although the cost of ABS+PC is larger, the molded product is better than HIPS in terms of impact resistance, surface gloss and hardness, so it is usually used in the production of high-gloss products. It is a high-gloss ABS material. ABS is an amorphous polymer with no significant melting point. Due to the wide variety of grades, appropriate process parameters should be formulated according to the grades in the injection molding process, generally above 160 °C, below 270 °C. In the molding process, ABS has good thermal stability, and the range of options is large, and it is not easy to degrade or decompose. And ABS has a moderate melt viscosity, and its fluidity is better than that of polyethylene (PS), polycarbonate, etc., and the melt cooling and solidification speed is relatively fast, and generally it can be cooled in 5 to 15 seconds. The fluidity of ABS is related to both the injection temperature and the injection pressure, with the injection pressure being slightly more sensitive. For this reason, it is possible to start from the injection pressure during the molding process to lower the melt viscosity and improve the filling performance. ABS has different properties of water absorption and adhesion to water due to different components. The surface adhesion water and water absorption rate are between 0.2% and 0.5%, and sometimes between 0.3% and 0.8%. In order to obtain a more ideal product, Drying is carried out before molding to reduce the water content to less than 0.1%. Otherwise, bubbles, silver, etc. will appear on the surface of the part. Usually plastic materials need to add 1% metal powder to improve the effect of high-gloss metal.

11. Polishing and maintenance of the mold
The polishing described in plastic mold processing is very different from the surface polishing required in other industries. Strictly speaking, the polishing of the mold should be called mirror processing. Not only does it have high requirements for polishing itself, but it also has a high standard for surface flatness, smoothness and geometric accuracy. Surface polishing generally requires only a shiny surface.

The standard of mirror processing is divided into four levels: AO=Ra0.008μm, A1=Ra0.016μm, A3=Ra0.032μm, A4=Ra0.063μm. It is difficult to accurately control the geometric accuracy of parts due to electropolishing, fluid polishing and other methods. However, the surface quality of chemical polishing, ultrasonic polishing, magnetic polishing and other methods does not meet the requirements, so the mirror processing of precision molds is mainly based on hand polishing.

(I) Basic procedures for manual polishing To achieve high-quality polishing, the most important thing is to have high-quality polishing tools and accessories such as oilstone, sandpaper and diamond paste. The most important thing is the polished working environment, which requires a clean room. The choice of polishing procedure depends on the surface condition of the previous processing, such as machining, EDM, grinding and so on.

The general process of hand polishing is as follows: (1) manual oil stone grinding, strip oil stone plus kerosene as a lubricant or coolant. The general order of use is #180~#240~#320~#400~#600~#800~#1000. Many mold makers choose to start with #400 in order to save time.

(2) Semi-finishing Semi-finishing mainly uses sandpaper and kerosene. The number of sandpaper is: #400~#600~#800~#1000~#1200~#1500. In fact, #1500 sandpaper is only used for hardened die steel (above 52HRC), not for pre-hardened steel, as this may cause burns on the surface of pre-hardened steel.

(3) Fine polishing Fine polishing mainly uses diamond polishing paste. If the polishing powder is mixed with a diamond abrasive powder or a polishing paste, the usual polishing order is 9 μm (#1800) to 6 μm (#3000) to 3 μm (#8000). The 9μm diamond paste and polishing cloth wheel can be used to remove the hair marks left by #1200 and #1500 sandpaper. The polishing is then carried out using a felt and a diamond paste in the order of 1 μm (#14000) ~ 1/2 μm (#60000) ~ 1/4 μm (#100000). A polishing process with an accuracy of more than 1 μm (including 1 μm) can be performed in a clean polishing chamber in the mold shop. For more precise polishing, an absolutely clean space is required. Dust, smoke, dandruff and saliva can all leave high-precision polished surfaces that are obtained after hours of work.

(2) Problems to be paid attention to in manual polishing The following points should be noted when polishing with sandpaper:
(1) Polishing with sandpaper requires the use of soft wood sticks or bamboo sticks. When polishing a round or spherical surface, use a cork stick to better match the curvature of the round and spherical surfaces. The harder wood strips are like cherry wood, which is more suitable for the polishing of flat surfaces. The end of the trim strip is adjusted to match the shape of the steel surface so that the acute angle of the strip (or bamboo strip) is prevented from contacting the surface of the steel and causing deep scratches.

(2) When changing to different types of sandpaper, the polishing direction should be changed from 45° to 90°, and the streak shadow left after polishing the former type of sandpaper can be distinguished. Before changing the different types of sandpaper, the polished surface must be carefully wiped with 100% pure cotton and a cleaning solution such as alcohol, because a small gravel left on the surface will destroy the entire polishing work. This cleaning process is equally important when polishing from sandpaper to diamond polishing. All pellets and kerosene must be completely cleaned before polishing continues.

(3) In order to avoid scratching and burning the surface of the workpiece, special care must be taken when polishing with #1200 and #1500 sandpaper. It is therefore necessary to load a light load and polish the surface using a two-step polishing method. When polishing with each type of sandpaper, it should be polished twice in two different directions, with each rotation between 45° and 90°.

(3) Diamond grinding and polishing should pay attention to the following points:
(1) This polishing must be carried out under light pressure as much as possible, especially when polishing pre-hardened steel parts and polishing with fine abrasive paste. When polishing with #8000 abrasive paste, the common load is 100~200g/cm2, but it is difficult to maintain the accuracy of this load. To make this easier, you can make a thin and narrow handle on the strip, such as adding a piece of copper; or cut a part of the strip to make it softer. This helps control the polishing pressure to ensure that the mold surface pressure is not too high.

(2) When using diamond grinding and polishing, not only the working surface is required to be clean, but also the hands of the worker must be carefully cleaned.

(3) The polishing time should not be too long, the shorter the time, the better the effect. If the polishing process is carried out too long, it will cause "orange peel" and "pitting".

(4) In order to obtain a high-quality polishing effect, polishing methods and tools that are prone to heat should be avoided. For example: polishing wheel polishing, the heat generated by the polishing wheel can easily cause "orange peel".

(5) When the polishing process is stopped, it is very important to ensure that the surface of the workpiece is clean and carefully remove all abrasives and lubricants. Then, a layer of mold anti-rust coating should be sprayed on the surface.

(4) Factors affecting the quality of mold polishing
Since manual polishing is mainly done manually, polishing technology is still the main reason for the quality of polishing. In addition to this, it also works with mold materials.
These are Injection molding high gloss seamless 

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