Serial No. 7 (Friends who are interested can follow Gud Mould to view previous series in historical news)

Usually when moldmakers consider inlay design, their starting points are: ease of processing, lower material costs, reduce tendency of mold core deformation, and improve exhaust. However, few mold designers can proactively consider mold core inlays from perspective of waterway optimization.
Inlay design of mold will affect waterway design and also have a positive impact on exhaust of mold. In general, reasonable and sufficient inlaying is beneficial to exhaust. Inlaying is beneficial to processing and improving steel utilization, and can also improve quality of mold to a certain extent. However, inlaying will make waterway design of mold very complicated and requires comprehensive consideration. If deformation of product and injection molding production cycle of mold are main considerations, then mold core inlay design must accommodate cooling design.

Reasonable and sufficient exhaust design can minimize air resistance in mold cavity, thereby improving filling and reducing internal stress of product. At present, there are common misunderstandings in industry when designing mold exhaust, which is relatively conservative. The first reason is that importance of exhaust to product quality and production efficiency is not fully understood; the second is concern about generation of burrs, so design of exhaust is based on principle of not generating burrs, rather than principle of easiest exhaust. This is a common misunderstanding in design of exhaust in industry. Venting slots and possibility of burring may seem contradictory, as venting slots increase risk of burring. But on the other hand, if exhaust is insufficient, greater pressure will be needed to ensure filling, and increasing pressure will increase risk of burrs. From this aspect, exhaust is conducive to improving burrs. Main cause of burrs is that mold is stretched due to excessive injection pressure, or local deformation of mold causes sealing failure at local sealing locations. Therefore, instead of worrying about depth of exhaust groove, it is better to fully consider strength of mold so that it can withstand higher injection pressure, and increase exhaust, effectively reducing pressure in mold cavity to reduce risk of burrs.
Reasonable exhaust has a positive impact on product quality:
Pressure in mold cavity is reduced, and internal stress of product is reduced.
Fast filling can be achieved, and pressure distribution in mold cavity is more uniform, so shrinkage is more uniform.
Improved bond line quality
Improved appearance defects
Improve ejection
Dimensional stability
other

Mold is subjected to huge injection pressure and clamping force during production process. Mold needs to be balanced in order to withstand long-term production. If mold is unevenly stressed, fatigue damage will occur in areas with excessive stress after long-term production, resulting in mold deformation and even mold damage. However, due to mold placement and product structure, parting surfaces of many molds bear uneven clamping forces. Center of clamping force is not in the center of mold; center of injection pressure is not in the center of mold. Such molds are not conducive to long-term production. It is necessary to increase positioning during design to resist injection pressure; a balance block to disperse clamping force and make mold evenly stressed.
There are two main types of unbalanced stress on mold:
1. Withstand uneven injection pressure
2. To withstand uneven clamping force
During injection molding production process, lateral projection area of product's glue position is too large, resulting in excessive lateral stress, and mold may shift, thereby affecting thickness of product and further affecting deformation.

Mold must be strong enough to withstand these pressures without deforming. If mold is not strong enough to withstand injection pressure and deforms, it will affect shrinkage uniformity of product, thus affecting deformation of product.
During trial touch and injection molding production process, people often blame drag appearance defects on product's insufficient draft angle or poor polishing, without further investigating whether it is caused by insufficient mold structural strength or unreasonable mold positioning design, micro-deformation or micro-deviation produced during injection molding process. This needs to be kept in mind, otherwise solution to problem will go in wrong direction.
Product surface finish grade corresponds to required draft angle requirements, which can be found in various materials. Mold factories and injection molding factories have obtained their own experience data through years of experience summarization. From perspective of mold manufacturing and injection molding production, we hope that the steeper slope, the better. However, from perspective of product design, we do not want to design an excessively large draft angle, because it will affect product's functionality and appearance, and increase difficulty of design. Therefore, as a mold designer, you must not only deeply understand relationship between theoretical draft angle and surface finish, but also consider strength of mold and reliability of mold positioning.

Mold is a shaper, which limits shrinkage of product. Inside mold cavity, shrinkage in free shrinkage direction and restricted direction are different, and this difference is proportional to cooling time. The longer cooling time, the greater difference. Shrinkage in free shrinkage direction is larger, while shrinkage in restricted shrinkage direction is relatively smaller. Product limiting features include raised mold cores, ribs, columns, etc.

Ejection of product needs to be balanced. Ejection force of product is equivalent to external load. Unbalanced ejection may cause excessive local force on product, resulting in large ejection stress and affecting deformation.
Ejection design and cooling design need to be chosen. In many cases, ejection and cooling will interfere, so design choice needs to be carefully considered. Generally speaking, for products with high dimensional deformation requirements, it is recommended that ejection pin layout be adapted to cooling. In terms of impact on deformation, impact of cooling system is far greater than impact of ejection imbalance.

Sometimes, when projected area of product is large and surface finish is very high, vacuum adsorption effect of mold cavity needs to be considered. Another situation is that products with deep cavities, such as trash cans, storage boxes, etc., are prone to vacuum adsorption. Vacuum adsorption is not conducive to product demoulding. Since demoulding has to overcome a large amount of atmospheric pressure, ejection force endured by product is much greater than tightening force generated by its shrinkage, and it is easy to deform.
Air is the best release agent, so design of this case must consider air cap to eliminate vacuum adsorption effect.
(To be continued: Series 8. A paragraph will be published every week. If you are interested, you can follow Gud Mould.)