Why should the surface of the Injection Mold Cavity be polished?
In most cases, electrical machining techniques like wire cutting and EDM are used to obtain the surface of the Injection Mold Cavity. These processing techniques typically produce surfaces with surface roughness between Ra1.6 and 3.2 m. The plastic product’s surface roughness is determined by the cavity’s surface roughness.
For transparent plastic pieces, the surface of the Injection mold cavity must be as smooth as a mirror because different plastic products have different surface roughnesses—some are thick and some are fine. After machining or electrical machining, the cavity’s surface is typically polished using sandpaper or abrasive paste to meet certain roughness criteria.
The smooth Injection Mold Cavity surface also has the following results.
The item is simpler to demolish
It can lessen the plastic melt’s wear on the mold’s cavity surface.
It can lessen the regional cracking of mold cavities brought on by fatemporarymporarily excessive loads.
Lower the plastic melt’s flow resistance.
How can the surface quality of the Injection Mold Cavity be evaluated?
1.The surface of the Injection Mold Cavity should not have scuffs, wear, or other traces, such as small holes and local peeling left by the carbonized particles being pulled out.
2.The surface of the mold cavity must have a geometrically correct plane or curved surface, free of cracks, blisters, and other defects. If the mold cavity’s surface quality is crucial, an instrument must be used to test and assess the surface roughness. The mirror-polished mold cavity surface is typically assessed with the naked eye.
However, visual judgment frequently results in errors. Considering that a surface that appears smooth to the unaided eye might not be fully smooth mathematically.
Injection Mold Cavity Polishing Standard:
It is necessary to confirm that the polishing fully satisfies the specifications or that it has been completed before the mold test.
If the location of the fire pattern is accurate and if it can be de-molded.
The steel used for mirror-polished parts must be ASSAB136 and have a hardness of 52–54 HRC. Mirror polishing is another option for steel NAK80, which is equally reasonably priced.
*Spark erosion EDM is frequently used to process Injection Mold Cavity. At this moment, it’s important to focus on the following things:
Narrow pulse current machinery. Wide pulse current polishing will leave deep holes because wide pulse current roughing frequently leaves pockets.
The machine tool used for processing EDM is crucial. Poor-quality EDM machine tools have varied fire patterns, and some pieces will have deep holes. Often, these minute deep holes are not noticeable until the diamond paste has been polished. They currently need to be polished with #320 sandpaper, which will waste a lot of labor time.
Injection Mold Cavity Polishing Knowledge and Skills
1. Kerosene should be used to clean the surface of a new light before alcohol is used to remove any oil stains or extraneous material. This will help the Injection Mold Cavity surface make better contact with the oil stone and prevent the oil stone surface from sticking while being polished, dirt, and a decline in cutting ability.
2. Begin with strong depth and dead angle, and then polish the large body and the large plane.
3. For the inlay molded pieces, some areas along the edge must first be polished to remove the rough or fire pattern, and then all of the molded parts must be clamped together and polished to the necessary level.
4. For large flat or deep cavity molds, the rough lines must be thrown away, and then use a flat steel sheet and red to check whether the surface of the cavity is uneven or inverted. If it is uneven or inverted, the molded product will stick to the mold or drag.
5. Some molded items may have a specific plane that is both the molding surface and the surface of the assembly sealant. To safeguard the assembly plane, the sandpaper or saw blade must be fastened to the unpolished plane using double-sided tape.
6. If the core is too high, which makes local polishing difficult, it is best to change the core to an insert.
7. Use the handle that pulls and drags the whetstone to make the cavity plane as flat as possible. The inclination angle shouldn’t be more than 25°. The steep incline makes it simple to create several rough lines inside the cavity.
8. Sandpaper should not be greater than the area of the tool while polishing the surface of a cavity with a copper sheet or a bamboo sheet pressed with sandpaper, otherwise, it will grind into areas that shouldn’t be ground.
9. Avoid using the front and rear guns to clamp the whetstone to polish at 30° or 45° if the cavity area is tiny since this will result in uneven surfaces. It should be ground into fine-grained whetstone, polished with copper-handled front and rear guns or bamboo chips, and then polished with sandpaper once the coarse grains have been eliminated.
10. The tool’s shape should resemble the mold cavity while polishing with copper or bamboo to prevent the deformation of the cavity. For instance, the small or round surface should be polished with a small or round bamboo piece, and the flat surface should be polished with a flat bamboo piece.
11. The sandpaper or whetstone should be inclined 15° to 30° to prevent deep holes when the polishing plane is close to the polisher.
12. Kerosene should not be added when polishing with 150″, 180″, and 220″ rough whetstone, except for polishing sandpaper above 320″. If you use the motor head to pull the sandpaper before and after polishing, you should not add kerosene. Manual use of copper or bamboo depends on the specific situation.
13. The polisher should carefully examine the surface of the mold cavity, look for any fire patterns, and then get rid of them. Cleaning the cavity’s surface and evenly coating it with cupric acid is the first step in determining whether a fire pattern is present. Wash the inserts with water and air-dry them after about 3 to 5 minutes. The surface of the cavity will get dark if there is no fire pattern there, and shiny spots will appear if there is a fire pattern there.
14. Copper electrode polishing. Polishing the rough electrode only needs to polish the protruding things on the surface of the copper electrode, and the concave ones do not have to be polished. The fine electrode should be ground to smooth, and all corners, edges, and planes should be ground to smooth and smooth.
15. The surrounding area should be kept tidy when polishing with sandpaper thicker than 400″. To prevent sudden rough lines while polishing, the sandpaper should be rolled up and rubbed against each other before being cut. Additionally, the slightly coarser grit on the sandpaper should be removed.
16. After the cavity’s surface has been machined by the CNC milling machine, polishing typically begins with 400* paper to remove the coarse grain and continues with 600°800″ and 1000 in that order. It can, if necessary, be further polished with gold sandpaper once the knife grain has been eliminated. You can combine polishing with adding an abrasive paste.
