In recent years, China's domestic mold technology has made rapid progress, mainly manifested in: extension of commercial Internet to molds and their industrial chain, widespread application of 3D printing in mold manufacturing, intelligentization of molds and development trend of high-volume production of molds. UPG has been committed to application of new technologies in mold field, for example, through intelligent detection and control of mold production by cavity pressure sensors, development and research of multi-cavity molds. Here I will introduce to you stacking mold technology that is widely used in consumer electronics and home appliance industries.

 

Stacking mold structure consists of multiple systems such as stacking mold hot runner system, special mold frame system, load-bearing guide system, two-way ejection system, opening and closing mold linkage system.

 

Stacked mold technology has following characteristics:
Production efficiency of stacked molds is one or more times higher than that of ordinary single-layer molds, which greatly reduces cost of injection molding production. From perspective of structural characteristics, stacked molds combine multiple cavities in one mold, and can fully utilize ordinary injection molding equipment to meet production needs. Filling, holding and cooling time of mold are same as those of single-layer molds, which determines that production efficiency of stacked molds will be one or even more times higher than that of ordinary single-layer molds, greatly improving output of products per unit time. (Stacked mold designs are famous for their production efficiency far exceeding that of ordinary single-sided molds)

 

Stacked molds can be installed on same injection molding machine as single-layer molds, without need to invest in additional machines and equipment, thus saving cost of machines, equipment, plant buildings and additional labor. Manufacturing requirements of stacked molds are basically same as those of ordinary molds. According to statistics, manufacturing cycle of a double-layer stacked mold is 5% to 10% shorter than that of two single-layer molds. According to production verification, stacked injection mold has a reasonable and reliable structural design, good product size consistency, 30% reduction in mold costs, and double or multiple times higher molding efficiency. Stacked mold is suitable for mass production of large products with flat shapes, small multi-cavity thin-walled products, and medical products. The larger batch, the lower product production cost.

 

Unlike conventional molds, cavities of stacked injection molds are distributed on two or more levels and are arranged in an overlapping manner, which is equivalent to stacking multiple molds together. The most common two-layer stack mold is usually composed of two single-layer molds installed back to back, parting surface usually relies on gear and rack mechanism to keep opening synchronously.

 

Usually, when injection molding machine is used in conjunction with a conventional mold, its own injection volume and mold opening stroke only use 20%~40% of rated value, and performance of injection molding machine is not fully utilized. Compared with conventional molds, two-layer stack mold has a nearly 100% improvement in production efficiency compared to standard mold, and clamping pressure is only about 10% greater than that of standard mold. It greatly improves equipment utilization and productivity, and reduces injection molding costs.
Stacked injection molds are most suitable for molding large flat parts, shallow cavity shell parts, small multi-cavity thin-walled parts and parts that need to be produced in large quantities.
What are advantages of stacked molds?
⊙ Production efficiency of stacked molds is one or more times that of ordinary single-layer molds, which greatly reduces cost of injection molding production.
⊙ Compared with conventional molds, clamping force of stacked injection molds is only increased by 5%~10%, but output can be increased by 90%~95%, which greatly improves equipment utilization and productivity.
⊙ Stacked molds can be installed on same injection molding machine as single-layer molds, without investing in additional machines and equipment, thus saving cost of machines, equipment, plant and additional labor.
⊙Production verification shows that structure design of stacked injection mold is reasonable and reliable, product size consistency is good, mold cost is reduced by 30%, and molding efficiency is doubled or more.
⊙According to statistics, manufacturing cycle of a double-layer stacked mold is 5% to 10% shorter than that of two single-layer molds.

 

As a new type of mold technology, stacked injection mold has been continuously developed, especially in combination with hot runner technology, making it a cutting-edge technology in development of plastic molds today. Traditional conventional mold design theory is no longer applicable to design of stacked injection molds, so it is urgent to develop a new set of mold design theories to guide design of stacked injection molds. Following will explain design points of stacked injection molds. Stacked injection molds can use cold runners or hot runners. When using cold runners, it is necessary to consider amount of plastic used for casting system condensate; when using hot runners, it is necessary to achieve non-return condensate production, materials in hot runner plate and central main nozzle do not affect injection volume required by mold, can be ignored. Therefore, when checking maximum injection volume of injection molding machine, it depends on specific situation.

 

Middle area of stack mold is not fixed to injection molding machine because it is very heavy. When stack mold is opened, mold guide pin will bear weight of the entire mold. After mold is opened and closed many times, guide pin will wear and affect positioning effect. In severe cases, guide pin will bend and deform, making it impossible to close mold or even damage mold. Therefore, when designing a stack mold, it is necessary to add a mold middle support system to allow middle part of stack mold to be positioned with Green column of injection molding machine to avoid above problems.

 

Cavities of each layer of stacked injection mold are set "back to back". In theory, any number of stacks can be achieved on same injection molding machine without increasing clamping force. However, since central main nozzle and manifold of stacked injection mold increase flow channel, projected area of plastic part plus pouring system on parting surface is increased:; and because stacking extends flow channel, pressure loss is greater than that of conventional single-layer mold, and injection pressure increases accordingly, resulting in an increase in cavity pressure, so clamping force increases. When checking, it is safer to increase clamping force required by same single-layer mold by 10%~15%.

 

Injection pressure check is mainly to check whether injection pressure can meet needs of molding. For laminated injection molds, most of plastic parts with thin walls, large projection areas and long processes require higher injection pressure and injection speed during filling process. Laminated hot runner mold uses hot runner technology, which can better transmit injection pressure compared to laminated cold runner mold. Therefore, required injection pressure is smaller than that of laminated cold runner mold; but due to increase in process and projection area, required injection pressure is greater than that of single-layer cold runner mold. When checking injection pressure, injection pressure of plastic part should be determined according to injection molding process of various plastics and combined with computer simulation flow analysis, then compared with rated injection pressure of injection molding machine.

 

Cavities of each layer of stacked injection mold are set "back to back". In theory, any number of stacks can be achieved on same injection molding machine without increasing clamping force. However, since central main nozzle and manifold of stacked injection mold increase flow channel, projected area of plastic part plus pouring system on parting surface is increased; because stacking extends flow channel, pressure loss is greater than that of conventional single-layer mold, and injection pressure increases accordingly, resulting in an increase in cavity pressure, so clamping force increases. It is safer to increase clamping force required by same single-layer mold by 10%~15% during verification.

 

Stacked injection mold opens mold and ejects plastic parts on two layers or multiple layers of parting surfaces. When checking opening stroke, for injection molding machines using hydraulic-mechanical clamping mechanisms, mold thickness does not need to be considered. When stacked injection mold has a core pulling mechanism for lateral parting, influence of core pulling distance needs to be considered. If a synchronous mold opening mechanism such as a gear rack or toggle connecting rod mold opening device with same transmission ratio is used, stroke of each layer of stacked injection mold is not limited by product height, and its mold opening stroke is n times maximum mold opening stroke of layer in multi-layer mold (n is number of layers of stacked injection mold).

 

 

 

If this type of mobile phone housing product uses a high-tech hot runner system combined with a new type of stacked mold design and use, it will effectively increase output by 80-90% on a certain amount of equipment.

 

 

 

Summary: Use of stack injection molds, especially hot runner stack injection molds, can give full play to capabilities of injection molding machine, save manpower and equipment resources, and greatly improve production efficiency. Although design and processing costs of stacked injection molds are relatively high, if following aspects can be improved, mold costs can be greatly reduced and its application range can be expanded:
(1) Improve design theory of stacked injection molds and shorten R&D cycle;
(2) Extend service life of some core components (such as heating components, temperature control components, etc.);
(3) Make stacked injection mold compatible with ordinary injection molding equipment;
(4) Use CAD/CAE/CAM technology to design, analyze and process to optimize mold structure;
(5) Standardize and commercialize common parts of stacked injection molds;
(6) Improve pressure transmission capacity to make it suitable for production of thick-walled plastic parts;
(7) Optimize process parameters of stacked injection molding;
(8) Fully automate stacked injection molding.

 

With continuous improvement of related technologies, application of stacked injection molds in plastic products processing industry will continue to expand, especially economic efficiency of hot runner stacked injection molds can better meet needs of market, create huge economic benefits, and meet requirements of development of my country's equipment manufacturing industry. There will be broad market prospects in the future.