What Are The Design Standards For Injection Stack Molds?

What is injection stack mold?

Plastic injection stack molds are also called injection stacked molds. There are two ways of mold non-rotation and mold rotation. There are two main types of rotary mold technology: turntable mold technology and mold technology with a built-in rotating mechanism.

Its characteristic is that the two components can be injected at the same time, which greatly shortens the production cycle of the product.

In addition, the use of a hot runner laminated injection mold can give full play to the capabilities of the injection molding machine, save manpower and equipment resources, and greatly improve production efficiency.

What are the injection stack mold characteristics?

  1. The difference from the conventional mold is that the cavity of the laminated injection mold is distributed on two or more levels and is arranged in an overlapping manner, which is equivalent to stacking and combining multiple pairs of plastic injection molds.

The most common two-layer injection mold is usually installed by two single-layer injection molds back-to-back, and the parting surface usually relies on the gear and rack mechanism to keep it open synchronously.

  1. Generally, when the injection molding machine is used in conjunction with a conventional mold, its plastic molding injection volume and injection mold opening stroke only use 20%~40% of the rated value, and the performance of the injection molding machine is not fully utilized.

Compared with the conventional mold, the two-layer mold has a nearly 100% improvement in production efficiency compared to the standard plastic injection mold, and the mold clamping pressure is only about 10% greater than the standard plastic injection mold. Greatly improve equipment utilization and productivity, and reduce plastic molding injection costs.

  1. The laminated injection mold is most suitable for injection molding large flat parts, shallow cavity shell parts, small multi-cavity thin-walled parts, and parts requiring mass production.

Two-layer plastic injection stacked mold

Double-layer plastic injection mold technology can also produce two different products at the same time, for example, the first layer plastic injection mold produces one product, and the second layer plastic injection mold produces another product, these products can be the same or different materials, the same color or different and many other combinations.

For example, a plastic injection stacked mold can be used to realize the first-layer plastic molding injection container cover and the second-layer injection molding container body.

Main points of design of two-layer laminated hot runner injection mold

A maximum plastic molding injection volume of the injection molding machine

The material of the laminated hot runner injection mold in the hot runner plate and the central main nozzle does not affect the plastic molding injection volume required by the injection mold and can be ignored. The plastic molding injection volume required by the injection molding machine is almost twice that of the standard plastic injection mold.

The plastic molding injection pressure of an injection molding machine

The check of plastic molding injection pressure is mainly to check whether the molding injection pressure can meet the needs of molding. The stacked hot runner mold uses hot runner technology, but due to the increase in process flow and projected area, the required plastic molding injection pressure is larger than that of a single layer cold runner injection mold.

When checking the plastic molding injection pressure, the plastic molding injection pressure of various plastics should be combined with the computer simulation flow analysis to determine the molding injection pressure of the plastic molded parts, and then compared with the rated plastic molding injection pressure of the injection molding machine.

Maximum mold clamping force of injection molding machine

The cavity of each layer of the laminated injection mold is set “back-to-back”, theoretically the mold clamping force does not increase. However, because the center main nozzle of the laminated injection mold and the splitter plate increase the flow channel, the projected area of ​​the plastic molded part and the pouring system on the parting surface has increased, and the flow channel is extended due to the lamination.

The pressure loss is greater than that of conventional single-layer injection molds, and the molding injection pressure increases accordingly, resulting in increased cavity pressure. Therefore, the mold clamping force is increased. When checking, the mold clamping force required by the same single-layer injection mold is increased by 10% to 15% It Is relatively safe.

Injection mold opening stroke

The laminated injection mold is divided into two levels to open the mold and eject the plastic molded parts. When checking the injection mold opening stroke, a synchronous injection mold opening mechanism such as a gear rack or a toggle connecting rod injection mold opening device with the same transmission ratio must be used. The injection mold opening stroke is twice that of the layer with the largest injection mold opening stroke in a single-layer injection mold.

Main nozzle length

The center’s main nozzle should not be too long or too short so that when the injection mold is closed, the center’s main nozzle will not exceed the maximum distance that the plastic injection molding machine nozzle retreats or advances on the base. 

Since the center’s main nozzle moves with the middle part of the injection mold during parting, make sure that the center’s main nozzle remains in the fixed mold part after mold opening to prevent the overflow of the center’s main nozzle head from dripping into the fixed model cavity wall on.

Gating system

The lamination type injection mold hot runner pouring system can better transfer the plastic molding injection pressure, which is beneficial to improve the injection molding quality of plastic parts and is easy to realize automated production, but it has certain requirements for plastic varieties, and the hot runner system is expensive.

Mold temperature control system

Mold temperature is one of the important factors that affect the injection molding quality of plastic molded parts. The design of laminated injection molds should ensure that the temperature conditions of each layer cavity are controlled uniformly.

For the laminated hot runner injection mold, in order to reduce the heat loss of the hot runner system due to heat conduction, the contact area between the mold and the hot runner plate should be reduced, and a corresponding heat insulation pad should be provided.

Plastic injection mold opening mechanism

In order to make the plastic molded parts shrink uniformly, the residence time (cooling time) of the plastic molded parts in each cavity should be equal, so the laminated injection mold should ensure that the parting surfaces of the cavity of each layer are opened at the same time.

The rack and pinion transmission mechanism and the mechanical link mechanism are often used as the plastic injection mold opening mechanism of the laminated injection mold. The former has better technical performance and is more economical, but the latter has more flexibility.

Demoulding mechanism

According to the same requirements of cooling time, the laminated injection mold should eject the plastic molded parts in the cavity of each layer at the same time.

Two plastic injections stacked molds plus middle template rotating type

It consists of a two-material injection molding machine, a set of two-layer plastic injection molds, and an intermediate template that can be rotated 180° back and forth.

The injection molding machine completes the first plastic molding injection, opens the injection mold after cooling, and the intermediate template will rotate 180° according to the design requirements, turn the first injection molded part attached to the mold core to the second layer cavity, and then close the mold for injection molding.

In this way, the first injection molding and the second injection molding are also synchronized. Starting from the second injection molding, each time the injection mold is opened, a co-plastic product is formed in the second layer injection mold.

Rotating stacked mold technology is a highly difficult technology in today’s co-injection technology, which is very difficult. It highly integrates the manufacturing technology and system control technology of machines and molds.

It has the advantages of stacking mold co-molding and rotating template co-plasticizing: small mold clamping force can be used to produce larger-sized plastic parts with an injection molding machine with lower clamping force. More accurate, short cycle, and higher production efficiency, it is very suitable for the production of co-plastic injection molded parts with large output or long production cycles.