The precautions for Plastic mold different type polishing

- Apr 01, 2019-

The precautions for Plastic mold different type polishing


(1) Matters needing attention in mold sanding and oilstone grinding


1) For harder mold surfaces, only clean and soft oilstone sanding tools should be used.


2) When changing the sand level in the grinding, the work piece and the operator's hands must be cleaned to avoid carrying the coarse sand to the next fine grinding operation.


3) When performing each grinding process, the sandpaper should be sanded from different 45° direction until the upper sand grain is removed. When the upper sand grain is removed, the sanding time must be extended by 25%. The next finer sand number can be converted.


4) Change the different directions during grinding to avoid the waves and other unevenness of the work piece.


(2) Matters needing attention in diamond polishing


Diamond grinding and polishing must be carried out under lighter pressures, especially when polishing pre-hardened steel parts and polishing with fine abrasive pastes. When polishing with 8 000# abrasive paste, the common load is 100-200 g/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 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. When using diamond grinding and polishing, not only the working surface is required to be clean, but the workers' hands must also be very clean.


(3) Matters needing attention in plastic mold polishing


The polishing of plastic molds is very different from the surface polishing required in other industries. Strictly speaking, the polishing of plastic molds 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.


The standard for mirror polishing is divided into 4 levels:


A0=Ra0.008 μm

A1=Ra0.016 μm

A3=Ra0.032 μm

A4=Ra0.063 μm


Because electro-polishing, fluid polishing and other methods are difficult to precisely control the geometric accuracy of the part, and the surface quality of chemical polishing, ultrasonic polishing, magnetic polishing and other methods can‘t meet the requirements, so the mirror processing of precision mold is still mechanical polishing the Lord.


The precautions in polishing are as follows:


1) When a new cavity begins to be machined, the surface of the work piece should be inspected first, and the surface should be cleaned with kerosene so that the surface of the oilstone does not stick to dirt and the function of cutting is lost.


2) When roughing the grain, it should be carried out in the order of difficulty and easyness. Especially some dead corners that are difficult to study, the deep bottom must be studied first, and finally the side and the big plane.


3) Some work pieces may have multiple pieces assembled together for grinding. It is necessary to separately study the rough or fire pattern of a single work piece, and then all the work pieces are ground and smoothed.


4) For work pieces with large planes or side planes, use oil stone to grind rough lines and then use straight steel sheets for light transmission inspection to check whether there are any uneven or inverted buckles. If there is a reverse buckle, the work piece will be caused. Difficulty in demoulding or strained parts.


5) In order to prevent the mold work piece from being inverted or to have some bonding surfaces to be protected, it can be pasted with a saw blade or sanded on the edge to obtain the ideal protection effect.


6) The plane of the grinding mold is pulled back and forth. Drag the handle of the oil stone as far as possible, not to exceed 25°. Because the slope is too large, the force is pressed from top to bottom, which may lead to the development of many rough lines on the work piece.


7) If the plane of the work piece is polished with copper or bamboo pressed sandpaper, the sandpaper should not be larger than the tool area, otherwise it will be researched where it should not be studied.


8) Try not to use the sander to repair the mold surface. Because the parting surface of the grinding wheel head is rough and the waves are uneven, if necessary, the grinding wheel head must be repaired to the concentricity balance.


9) The shape of the tool to be ground should be close to the surface shape of the mold to ensure that the work piece is not deformed by grinding.

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