- Complex forms and surfaces: Certain products, i.e., car covering, aircraft components, toys, and household appliances, see their shape described by the surfaces composed of a variety of curved surfaces and part of the curved surfaces are needed to be processed by calculative methods of mathematics.
- High accuracy needed in processing: A mold is typically a combination of concave mold, punch mold and a mold base and some of them could also be modules. Both upper and lower mold combination, Insert/cavity combination, and module combination all need good processing accuracy. The accuracy on the dimension of precision molds is frequently in 0-5 and can be up to 0-1.
- Precision mold processing has a lot of processes: In the processing of a mold, the processes of milling, boring, drilling, reaming and tapping are always applicable.
- Identical venture: production in the mold is repeatable. When a mold has expired its service life, a new mold just has to be changed thus manufacturing of molds tends to be routine.
- Small batch size: Molds are not mass-produced and in most cases only a mold is produced.
- Profiling processing: In other cases, no drawings and data are provided when you are performing mold production and you have to perform profiling in real based objects. This necessitates perfect imitation and without deformation.
- Mold materials are magnificent and are highly hard. The high-quality alloy steel is mainly the materials of molds. Long life especially molds are frequently produced of ledeburite steels, i.e. steels Crl2 and CrWMn. There are high demands of blank forging processing and heat treatment on this type of steel. Thus, it cannot be overlooked that (the technology of the processing technology) is an important problem that should be considered in the processing
The main dimensions of most precision molds won t permit a slope, but during manufacturing often the margin of tolerance is employed to provide a slight slant, e.g. gear mounting posts, etc. The most important thing to notice when constructing a digital model is to consider the tolerance. As a rule, the 3D model given by the customer seems to be useless as most of the dimensions of it are extreme. In the event that the mold is generated as per this, the molded will effectively be Scrapped.
Simple procedures of processing and manufacturing mold may not require such specifications. The mold design and processing is usually followed. It is true that with lack of consideration of injection mold products in the design process, a lot of abnormalities will arise. How then to prevent these abnormalities
- The product shape and wall thickness are to be taken into consideration, the material flow has to be as smooth as possible, it has to be filled in cavity, and sharp corners and gaps are to be avoided, as far as possible.
- Resting on the permission, the draft of the mold should be as big as possible.
- The pouring system at the cross-section must be big.
- In the installation of the feed port, one should consider whether the inadequate filling and the deformation abnormalities could occur.
- The mold cavity is rigid and very strong.
- The mold must be hard polished and wear resistant steel must be applied.
- The spare strength of ejection mechanism should be constant with high power to easily replace.
Besides the issues that should be taken note of during the design of the mold, a match between the machine and products also has to be chosen as well as the recognition of the nature of the product material that should also be created based on good experiences in the past and also based on the nature of the products of the customer. Batch fronting, too much glue, encapsulation, shrinkage, and cracks as well as an incomplete fill, wrinkles and pitting, overflow, weld marks, warping and deformation and other issues are the most usual issues in injection molding. Besides some of these issues, there are those, which can be observed in injection molding. The machine is correctable by correction of the machine, but it is also controllable in a number of places in injection mold design:
- The demoulding slope must be sufficiently great; and the thickness of the wall must be as nearly uniform as possible;
- Sharp corners should be avoided by gradual and smooth transition to the part. There is creation of sharp edges and especially PC products should not have gaps;
- The point runner of the gate must be broad and short as can be possible. The gate setting position is to be set in relation to shrinkage and condensation process. In case required a cold well is to be attached;
- The surface of the mold must be smooth, and the roughness of the surface is low, which is ideal to be lower than 0.8MM;
- Vent. The tank should be adequate to remove the air and gasses in the melt in good time;
- The thickness of the walls must not be too small with the exception of PET, this has to be not less than lmm.
In designing the mold, to avoid the molding problems caused by poor backflow of the injection mold, or poor cooling of the mold, thus producing poor molding and defective surfaces and decay of mold, by the foregoing, you can avoid adverse results effectively. The scrap is simply the mirror picture of the hole shaped. That is to say, opposite direction is the identical direction. Once you examine the scrap, you will be in a position to determine whether there is a correct gap between the upper and the lower injection molds or not. When the gap is too big, the scrap will look irregular, rugged, scratched, with small and thin areas of bright bands. The bigger the gap the bigger the crack point and the bigger the area of the bright band. When the gap is small the scrap will be having cracks with small visible spots and broad bright band areas.
Injection molding spacing is quite large and the tear edge is large and curved that results in an outline that is a bit protuberant and the edge is slimmer. In case of excessive closeness of the injection molds, the strip will curl partially and rip at a wide angle, and the fragment will be not quite right, along the material surface. A good waste possesses a decent breaking angle with even bright band. This will lessen the drilling stress to near all time low and leave the hole clear, round and there are rare larger numbers of burrs. In this light, the service life of the injection molds has to be extended by widening the gap between the injection molds and this will cause deterioration in the quality of finished hole
The spacing of injection molds is dependent on the information in the stamping data (type and thickness). Unreasonable gaps will distribute the following problems: A too big gap leads to that the burrs of the stamping parts will be bigger and the stamping quality will be poor. When the gap is narrow, even though the quality of the punching will be of high standarts, then the wear of the mold will be very severe, significantly decreasing the service life of the mold, and only the cracks will appear on the punch. When the gap is excessively small or huge, it is simple to come up with adhesion of the data punched and this leads to strips during the punching. When the gap is too small a mere vacuum arises between the bottom of the punch and the sheet and the scrap bounces back.