With a wide range of plastic products, excess applications such as cosmetic products and beverage packaging containers, often require the appearance of the surface of the plastic mold cavity requirements to the extent mirror-polished. The production of optical lenses, CD and other mold surface roughness demanding, thus polishing requirements are extremely high. Polishing the workpiece not only increase the aesthetic, but also improve the corrosion resistance of the material surface, wear resistance, the mold can also have other advantages, such as easy to make the plastic mold release, to reduce the production of injection molding cycle. Thus polishing plastic mold making process is a very important step.

Currently used polishing methods are the following:

1.1 mechanical polishing
        * Mechanical polishing is cutting, plastic deformation of the material surface is polished to remove the convex portions obtained smooth surface polishing method generally used Whetstone, wool wheel, sandpaper, mainly manual, special parts such as rotor surface, may use the turntable and other aids, surface quality
        Demanding Superfinishing throwing method can be used. Superfinishing is cast using a special abrasive in polishing liquid containing abrasive, and pressed against the surface of the workpiece to be machined, high speed rotary motion. Using this technology can achieve surface roughness Ra0.008μm of various polishing methods in the highest. The optical lens mold often use this method.

1.2 chemical polishing
        Chemical polishing is to make the material in the chemical medium surface micro-convex portion of the depression part of the preferential dissolution, resulting in a smooth surface. The main advantage of this approach is that without complex equipment, can polishing the complex shape of the workpiece can be polished at the same time a lot of artifacts, and high efficiency. The core issue is to formulate a polishing chemical polishing liquid. Chemical polishing to obtain a surface roughness of the general number of 10μm.

1.3 Electropolishing
        Electrolytic polishing and chemical polishing the same basic principle, namely * selective dissolution of surface minor projecting portion, to smooth the surface. Compared with chemical polishing, it can eliminate the influence of the cathodic reaction, the better. Electrochemical polishing process is divided into two steps:
(1) macroscopic leveling dissolution product diffusion to the electrolyte, the material surface geometry rough drop, Ra> 1μm.
(2) shimmer formation of anodic polarization, the surface brightness increase, Ra <1μm.

1.4 ultrasonic polishing
        The workpiece into the abrasive suspension and placed in an ultrasonic field together, rely on ultrasonic oscillation effect, the abrasive surface of the workpiece grinding and polishing. Ultrasonic machining macroscopic force is small, it does not cause deformation of the workpiece, but the tooling fabrication and installation more difficult. Ultrasonic machining can be combined with chemical or electrochemical methods. Solution corrosion, electrolysis, based on the ultrasonic vibration is applied and then stirring the solution, so that the surface lysate from near the surface corrosion or electrolyte evenly; ultrasonic cavitation in liquids is also capable of inhibiting the corrosion process, in favor of the bright surface

1.5 hydrofinish
        Polishing fluid is a liquid and carry rely abrasive scouring workpiece surface high-speed flow to achieve the purpose of polishing. Common methods are: abrasive jet machining, liquid jet machining, grinding fluid power. Fluid energy mill is driven by a hydraulic fluid medium carrying the abrasive high-speed reciprocating flow through the workpiece surface. Mainly in the lower pressure medium flowing through good special compound (polymer-like substance) and mixed with abrasive made of abrasive silicon carbide powder can be used.

1.6 Magnetic polishing
        Magnetic abrasive polishing abrasive is formed by a magnetic abrasive brush in the magnetic field on the workpiece grinding. This method of high efficiency, good quality, easy to control processing conditions, good working conditions. Using abrasives suitable surface roughness can be achieved Ra0.1μm.
        Plastic mold processing and polishing the surface of said polishing required by other industries are very different, strictly speaking, should be called the mold polishing a mirror finish. It is not only polishing their own high demands and the surface roughness, smoothness and geometric accuracy also has a high standard. Surface finish is generally only required to obtain a bright surface. Standard mirror finish is divided into four: AO = Ra0.008μm, A1 = Ra0.016μm, A3 = Ra0.032μm, A4 = Ra0.063μm, since the electrolytic polishing, polishing fluid is very difficult to precisely control the geometric accuracy and the surface quality chemical polishing, ultrasonic polishing, magnetic grinding and polishing methods and meet the requirements, so the mirror processing precision molds or mechanical polishing based.

2.1 Basic mechanical polishing procedures
        To obtain high-quality polishing effect, the most important thing is to have a high-quality stone, sandpaper and diamond paste abrasive polishing tools and aids. Polishing procedures selected depend on the surface condition after the pre-processing, such as machining, electrical discharge machining, grinding and so on. General mechanical polishing process is as follows:

(1) rough polishing
        The surface process after milling, EDM, grinding, etc. can be selected in the 35 000-40 000 rpm rotation speed of the rotating surface polishing machine or ultrasonic grinding machine polishing. Commonly used methods use diameter Φ3mm, WA # 400 white spark wheel removal layer. Whetstone is then hand-grinding, strip Whetstone add kerosene as a lubricant or coolant. The general order of use of # 180 to # 240 - # 320 - # 400 - # 600 - # 800 to # 1000. Many mold manufacturers in order to save time and choose from # 400 begins.

(2) semi-fine polishing
        Semi-fine sandpaper and polishing the main use of kerosene. Number of sandpaper were: # 400 to # 600 to # 800 to # 1000 to # 1200 to # 1500. # 1500 sandpaper actually only suitable for hardened tool steel (52HRC above) does not apply to pre-hard steel, as this may lead to pre-hard steel surface burns.

(3) fine polishing
        The main use of fine polishing diamond polishing paste. If mixing diamond abrasive grinding paste or powder with a polishing cloth polishing wheel, then the usual grinding order is 9μm (# 1800) ~ 6μm (# 3000) ~ 3μm (# 8000). 9μm diamond polishing paste and polishing cloth wheel can be used to remove the # 1200 and # 1500 sandpaper grinding marks left hairy. Followed by sticky carpets and diamond polishing paste for polishing, the order of 1μm (# 14000) ~ 1 / 2μm (# 60000) ~ 1 / 4μm (# 100000).
        Accuracy in 1μm or more (including 1μm) polishing process in the mold shop in a clean indoor polishing can be carried out. If a more precise polishing is absolutely necessary for a clean space. Dust, smoke, dandruff and saliva foam are likely to be scrapped after a few hours to obtain a high precision polishing surface.

2.2 mechanical polishing should be mindful

Polished with sandpaper should note the following:

(1) polished with sandpaper need to use soft sticks or bamboo sticks. Polishing spherical or round face, use a soft stick can better cope with a round face and a spherical curvature. The harder wood like cherry, are more suitable for flat surface polishing. End of wood trim to keep it consistent with the shape of the steel surface, to avoid wood (or bamboo) acute contact with the steel surface and cause deep scratches.

(2) When switching to different types of sandpaper, polishing direction should transform 45 ° ~ 90 °, so that the former model sandpaper polished shadow stripes left to tell the difference. Before changing different types of sandpaper, you must use a cleaning solution 100% pure cotton dampened with alcohol or the like on the polished surface carefully wipe, because a small gravel left on the surface will destroy the entire polishing work goes on. Sandpaper polished diamond polishing paste polishing replaced from the cleaning process is equally important. Before polishing continues, all the particles and kerosene have to be completely clean.

(3) In order to avoid abrasions and burns the surface, when using the # 1200 and # 1500 sandpaper polishing must be particularly careful. It is necessary to load a light load as well as a two-step polishing method for polishing the surface. When using each model sandpaper polishing should be performed twice in two different directions polishing, each between two directions rotated 45 ° ~ 90 °.

Diamond polishing should note the following:

(1) must be kept at such a polishing lighter pressure especially pre-hardened steel and polished with fine abrasive paste polishing. When using # 8000 abrasive paste polishing, the commonly used load is 100 ~ 200g / cm2, but to maintain this load accuracy difficult to achieve. To make it easier to do this can be done on a thin and narrow wooden handle, such as adding a copper; or on bamboo cutting part to make it more flexible. This helps control the polishing pressure to ensure that the mold surface pressure is not too high.

(2) When using diamond grinding and polishing, it is not only the requirements of the work surface clean hands of workers must also be carefully cleaned.

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

(4) In order to obtain high-quality polishing effect, easy to heat polishing methods and tools should be avoided. For example: polishing buff, buff the heat generated can easily lead to "orange peel."

(5) is stopped when the polishing process to ensure a clean surface and carefully remove all abrasive and lubricant is very important, followed by a layer of mold should be rust-proof coating on the surface of the shower.

* Due to mechanical polishing mainly done manually, so polishing technology is now mainly affect the quality of the polishing. In addition, also the mold material, surface condition before polishing, heat treatment and so on. Quality steel is polished to obtain a good quality prerequisite, if the steel surface hardness or uneven difference in characteristics, tend to produce polishing difficult. Steel in a variety of inclusions and pores are not conducive to polishing.

3.1 Effect of different hardness of the polishing process

Hardness increased so difficult ground increases, but the roughness after polishing is reduced. Because of increased hardness, the polishing time to reach the required low roughness corresponding increase. Meanwhile hardness increased, a corresponding reduction in the likelihood of over-polishing.

3.2 Effect of the surface condition of the polishing process

Steel cutting machining process in the crushing of the surface layer due to heat, stress or other factors damage, improper cutting parameters will affect the polishing effect. EDM surface after surface than ordinary machining or grinding after heat treatment more difficult, so the process should be adopted before the end of EDM precision gage EDM dressing, otherwise the surface will form a hardened layer. If EDM finishing gage inappropriate choice of heat-affected layer depth of up to 0.4mm. Hardening thin layer hardness higher than the hardness of the matrix, it must be removed. Therefore, the best increase in a coarse grinding process, the elimination of damage to the surface layer to form an average rough metal surfaces, providing a good basis for Lapping