With the wide application of plastic products, the requirements of mold polishing is also higher and higher, and even to achieve the degree of mirror surface, our common polishing needs are as follows:
1. Polishing for the sake of optical skills and the appearance of the workpiece, you can increase the beauty of the workpiece.
2. Polishing can improve the material surface corrosion resistance, wear resistance.
3. Polishing can reduce the resistance of plastic flow.
4. Polishing can improve the precision of the molded surface, preventing phi.
5. Polishing can make plastic products easy to demold, reduce the production of injection molding cycle.
II. Problems caused by insufficient polishing of the mold
1. Insufficient polishing, the mold will be left on the processing lines, foreign objects, polishing marks, the formation of bump.
2. When the product is demolded, it will cause abrasion and pull rubber powder.
3. The glue threads are attached to the PL surface of the male and female molds due to static electricity, and the PL surface will be swollen when the mold is closed in this state.
4. The swollen and broken surface will not be able to close and produce a sharp edge.
5. Although it can be repaired, the real reason is that the polishing is not enough, so no matter how to repair it, it can't be completely solved, wasting labor time.
6. Repairing the mold many times in mass production reduces the machine's operating rate and causes a waste of raw materials.
III. Grade classification of mold polishing
IV. Polishing tools and machinery
Polishing tools are commonly used: sandpaper, oil stone, fluff wheel, diamond plaster, diamond table file, flint, diamond grinding needles, various types of copper, various types of bamboo, fiber oil stone, emery cloth, ultrasonic, sanding machine and so on.
V. Steps and methods of polishing Steps and methods of polishing
To get high quality polishing effect, the most important thing is to have high quality oil stone,
sandpaper and diamond abrasive paste and other polishing tools and auxiliary products. The choice of polishing program depends on the surface condition after the previous
stage of processing, such as machining, EDM, grinding machine processing and so on.
The general process of mechanical polishing is as follows:
1. Rough polishing:
The surface after milling, EDM, grinding and other processes can be selected to rotate the surface polishing machine or ultrasonic grinding machine with a rotational speed of 35,000-40,000 rpm for polishing. Commonly used methods include removing the white EDM layer by utilizing a wheel with a diameter of Φ3mm and # 400. This is followed by manual oil stone grinding with a strip oil stone with kerosene as a lubricant or coolant. The general order of use is #180 ~ #240 ~ #320 ~ #400 ~ #600 ~ #800 ~ #1000. In order to save time, it is chosen to start from #400 to flatten the discharge pattern.
2. Semi-finish polishing:
Semi-finish polishing mainly uses sandpaper and kerosene. The number of sandpaper in order: #400 ~ #600 ~ #800 ~ #1000 ~ #1200 ~ #1500.
3. Fine Polishing:
Fine polishing mainly uses diamond grinding paste. If the polishing wheel is mixed with diamond grinding powder or paste, the usual polishing sequence is 9μm (#1800) ~ 6μm (#3000) ~ 3μm (#8000). 9μm diamond grinding paste and the polishing wheel can be used to remove hairline abrasions left by #1200 and #1500 sandpaper. Next, polish with sticky felt and diamond abrasive paste in the order of 1μm (#14000) ~ 1/2μm (#60000) ~ 1/4μm (#100000).
Note:
Polishing with an accuracy of 1μm or more must be done in an absolutely clean space. Dust, smoke, dandruff, and spit foam can ruin a high precision polished surface after hours of work.
VI. Precautions for mold polishing
(1) Polishing with sandpaper requires the use of soft wooden or bamboo rods. When polishing round or spherical surfaces, the use of soft wooden sticks can better match the curvature of the round and spherical surfaces. Harder wood sticks like cherry wood, on the other hand, are better suited for polishing flat surfaces. Trimming the end of the wood stick so that it can match the shape of the steel surface will prevent the sharp corners of the wood (or bamboo) stick from touching the steel surface and causing deeper scratches.
(2) When changing to a different type of sandpaper, the polishing direction should be changed 45 ° ~ 90 °, so that the previous type of sandpaper polished after the stripe shadow can be distinguished. In the change of different types of sandpaper before, must use 100% pure cotton dipped in alcohol and other cleaning fluid on the polished surface carefully wiped, because a very small grit left on the surface will destroy the next whole polishing work. This cleaning process is equally important when switching from sandpaper polishing to diamond abrasive paste polishing. All particles and kerosene must be completely cleaned before polishing can continue.
(3) In order to avoid scratching and burning the surface of the workpiece, special care must be taken when polishing with #1200 and #1500 grit sandpaper. It is therefore necessary to apply a light load and polish the surface using the two-step polishing method. Polishing with each type of sandpaper should be done twice in two different directions, with a 45° to 90° turn each time between the two directions.
■Precautions for sandpaper polishing:
■Precautions for diamond grinding and polishing:
(1) Polishing must be carried out under as light a pressure as possible, especially when polishing pre-hardened steel and when polishing with a 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, a thin and narrow handle can be made on a strip of wood, for example by adding a brass piece; or a bamboo strip can be made softer by cutting away part of it. This can help 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 work surface requires clean, the worker's hands must also be carefully cleaned.
(3) Each polishing time should not be too long, the shorter the time, the better the results. If the polishing process is too long will cause "orange peel" and "pitting".
(4) in order to obtain high-quality polishing results, easy to heat the polishing methods and tools should be avoided. For example: polishing wheel polishing, the heat generated by the polishing wheel will easily cause "orange peel".
(5) When the polishing process stops, to ensure that the surface of the workpiece is clean and carefully remove all abrasives and lubricants is very important, and then should be sprayed on the surface of a layer of mold rust coating.
? VII. Factors affecting the quality of polishing
1. As mechanical polishing is still mainly done by hand, so the polishing technology is still the main reason affecting the quality of polishing.
2. Related to the mold material, surface condition before polishing, heat treatment process. High-quality steel is a prerequisite for obtaining good polishing quality, if the steel surface hardness is uneven or differences in characteristics, often resulting in polishing difficulties. Various inclusions and porosity in the steel are not conducive to polishing.