- Complex shapes and surfaces: Some products, such as car coverings, aircraft parts, toys, and household appliances, have shapes whose surfaces are composed of a variety of curved surfaces, and some curved surfaces must be processed using mathematical calculation methods.
- High processing accuracy requirements: A mold is generally composed of a concave mold, a punch mold and a mold base, and some may also be multiple modules. The combination of upper and lower molds, the combination of inserts and cavities, and the joining together of modules all require high processing accuracy. The dimensional accuracy of precision molds often reaches μm level.
- There are many processes involved in precision mold processing: Milling, boring, drilling, reaming and tapping are always used in mold processing.
- Repeatable production: the mold has a service life. When a mold exceeds its service life, a new mold must be replaced, so the production of molds is often repetitive.
- Small batch size: The production of molds is not mass production, and in many cases only one is produced.
- Profiling processing: Sometimes there are neither drawings nor data in mold production, and profiling processing must be carried out based on the actual object. This requires high imitation accuracy and no deformation.
- Mold materials are excellent and have high hardness. The main materials of molds are mostly made of high-quality alloy steel. Especially molds with long life are often made of ledeburite steels such as Crl2 and CrWMn. This type of steel has strict requirements from blank forging, processing to heat treatment. Therefore, the preparation of the processing technology cannot be ignored, and heat treatment deformation is also a problem that needs to be taken seriously during processing.
The key dimensions of many precision molds are not allowed to have a slope, but when making the mold, the tolerance zone is generally used to add a small slope, such as gear mounting posts, etc. When building a digital model, you must pay attention to the adjustment of tolerances. Generally, the 3D model provided by the customer is useless because many of its dimensions are the extreme sizes. If the mold is designed according to this, the mold produced will basically be Scrapped.
Ordinary mold processing and manufacturing methods may not have so many specific requirements. Just follow the normal mold design and processing process. If injection mold products are not carefully considered during the design process, many abnormalities will occur. So how to avoid these abnormalities?
- The shape and wall thickness of the product should be considered, the material flow should be smooth, the cavity should be filled, and sharp corners and gaps should be avoided as much as possible.
- The draft of the mold should be as large as possible on the basis of permission.
- The cross-section of the pouring system should be large.
- When setting up the feed port, consideration should be given to preventing insufficient filling and abnormal deformation.
- The mold cavity has sufficient rigidity and strength.
- The mold should be hard polished and wear-resistant steel should be used.
- The ejection mechanism should be uniform and powerful to facilitate replacement.
In addition to the matters that need to be paid attention to in the design of the mold, it is also necessary to select a machine that matches the product, understand the characteristics of the product materials, and create excellent products based on past good experience and the characteristics of the customer’s products. The most common problems in injection molding include batch fronting, excessive glue, encapsulation, shrinkage, cracks, insufficient filling, wrinkles and pitting, overflow, weld marks, warping, deformation and other problems. In addition to some of these problems, some can be found in injection molding. The machine can be improved by adjusting the machine, and can also be controlled through several points in the design of the injection mold:
- The wall thickness should be as uniform as possible, and the demoulding slope should be large enough;
- The transition part should be gradually and smoothly transitioned to avoid sharp corners. Sharp edges are generated, especially PC products must not have gaps;
- The gate runner should be as wide and short as possible. The gate position should be set according to the shrinkage and condensation process. If necessary, a cold well should be added;
- The mold surface should be smooth and clean, with low roughness, preferably less than 0.8MM;
- Vent. The tank must be sufficient to discharge air and gases in the melt in a timely manner;
- Except for PET, the wall thickness should not be too thin, generally not less than lmm.
When designing the mold, in order to prevent the injection mold from poor backflow during molding or uneven cooling, resulting in poor molding, surface defects and deterioration, by doing the above points, you can effectively avoid adverse problems. The scrap is basically the reverse image of the formed hole. In other words, the same direction is the opposite direction. After checking the scrap, you can judge whether the gap between the upper and lower injection molds is correct. If the gap is too large, the scrap will have a rough, bumpy, broken appearance and narrow bright band areas. The larger the gap, the larger the crack point, and the larger the bright band area. If the gap is too small, the scrap will have cracks with small visible spots and wide bright band areas.
The gap between the injection molds is too large, forming a large curved tear edge, which in turn makes the outline slightly protruding and the edge thinner. If the gap between the injection molds is too small, the strip will bend slightly and tear at a large angle, and then the section will be roughly perpendicular to the material surface. The ideal waste should have a reasonable breaking angle and a uniform bright band. This will reduce the drilling pressure to a low level and create a clean, round hole with few burrs. From this perspective, increasing the gap between injection molds to extend the service life of the mold will reduce the quality of the finished hole.
The gap between the injection molds is related to the type and thickness of the stamping data. Unreasonable gaps will cause the following problems: If the gap is too large, the burrs of the stamping parts will be larger and the stamping quality will be poor. If the gap is too small, although the punching quality is excellent, the wear of the mold will be serious, which will greatly reduce the service life of the mold and only cause cracks in the punch. If the gap is too large or too small, it is easy to produce adhesion on the punching data, resulting in strips during the punching process. If the gap is too small, a simple vacuum forms between the bottom of the punch and the sheet, and the scrap rebounds.