Also called multi-color injection molding process, it refers to injection molding of two or more color materials or different materials through a mold with one or more runners. It was first represented by two-color injection molding, most of our daily contact with two-color products, such as toothbrush we use every morning and evening, handle is made of two-color injection molding, the more commonly used material for handle is PP (hard rubber) +TPE (soft rubber), TPE is the best material that blends with PP encapsulation, and soft encapsulation is to improve grip.

 

 

Combination between two-color injection molding materials

Two-color molds usually have two sets of molds, half of which is installed on fixed mold plate of two-color mold injection molding machine, that is, side with injection gate, and the other half is installed on movable mold rotary plate, that is, side where mold is ejected. Back molds of these two sets of molds are usually exactly same, but front molds are different. When first material is injected in first mold, fixed and movable molds of injection molding machine are opened, movable mold revolving plate takes back mold part of two molds to rotate 180°. At this time, semi-finished product of back mold of first mold is not ejected, then mold is closed, second material is injected (in this process, first material is continued to be injected into second mold into a semi-finished product). After heat preservation and cooling, fixed and movable molds are opened, finished product of movable back mold of first mold is ejected. This is process of a molding cycle, in each molding cycle there will be a semi-product and a finished product.

According to layout of injection unit (secondary injection station), configuration of two-color injection molding machine can be divided into:
1. Two-color injection molding structure is divided into five categories: P type (parallel double injection), L type (right angle double injection), V type (sky-side double injection), W type (oblique back double injection), H type (opposite Double shot).
These two types of two-color injection molding machines have their own characteristics, users need to choose according to their own needs. Among them, V-type and L-type injection molding machines are widely used in Europe, while Japanese and domestic machines mostly use P-type. Based on five forms of two-color machine, definition of injection form of three-color machine and four-color machine can be derived:
2. Three-color injection molding structure is divided into five categories: right-angle three-color-L type, sky-side three-color-V type, back three-color-LW type, back three-color-VW type, independent three-color-LV type.
3. Four-color injection molding structure is divided into two categories: parallel four-color-LV type and back-type four-color-LVW type.

 

P type-parallel bijection

 

L type-right angle double shot

 

V type-double shot from side to sky

 

W type-oblique back double shot

 

H type-double shot
With increase in product complexity, demand for three-color or even four-color has begun to emerge. Generally speaking, there are two types of three-color machines, one is a two-station three-color machine (commonly known as false three-color), and the other is a three-station three-color machine (commonly known as true three-color). In fact, difference between two is not "true and false", but according to product structure design (two molds or three molds) using different turntable control methods.
"Two stations", as name implies, turntable is positioned at two positions, which is equivalent to 180-degree turntable control mode of a two-color machine. In other words, in three groups of injection units of two-station three-color machine, two groups are injected into same mold at the same time. Therefore, if boundaries of two components in product are not adjacent (can be designed to be injected in same mold at the same time) , only two molds are needed to produce a three-component product, a two-station three-color machine is suitable.
"Three-station" is different, turntable can rotate in three positions (120 degrees). In other words, three injection molding units of three-station three-color machine are injected into three molds respectively. Therefore, if boundaries of three components in product are all adjacent, three-station three-color machine is suitable for use.
Similarly, four-color machines can also be divided into "two-station" and "multi-station" four-color machines. From a technical point of view, control accuracy of multi-station turntable is significantly higher than that of two-station, so production cost of machine is relatively high. Therefore, it is necessary to choose the most effective solution according to product structure requirements, such as following three-color U disk case, choosing multi-station seems to have a higher cost performance.

3C consumer electronic products continue to pursue ultimate in appearance: small, simple, beautiful, dust-proof and waterproof, but this demand for materials and craftsmanship often requires "fighting" situations, that is, in traditional design or manufacturing, it is difficult to meet multiple needs at the same time, it is impossible to have both fish and bear paws.
Therefore, how to provide products with different colors and textures in such a small form factor, while taking into account dustproof and waterproof requirements of internal electronic devices, has become a major issue for CMF and structural designers.
In traditional way, above-mentioned functions are made into different plastic parts, which are then assembled together by assembly.
Assembly will bring a series of problems, how to increase fixing structure, how to combine soft and hard glue, how to hide assembly line, how to realize sealing and waterproofing of electronic parts, how to make logo font more permanent, and how to reduce manpower for assembly. . . . .
glue? ---Not environmentally friendly Silk screen? ---Not abrasion resistant, fuel injection? ---Paint off. . . . . .
Can three kinds of plastics be directly molded at one time with an injection molding machine?

 

Traditional horizontal injection molding process has encountered more and more bottlenecks in solving such products.
1. Traditional horizontal two-color machine has a fixed position of injection station, injection station other than second injection can only be arranged on the top and lateral sides (insertion of multi-shot station arrangement). Glue inlet flow channels interfere with each other.
2. Space in clamping area is limited, rotation and rear mold replacement must be completed. Space for mold to arrange cavity and slider is more crowded.
3. Mold is opened horizontally, implant needs to be specially designed with a fixed structure, otherwise it is easy to skew under action of gravity.
For this reason, multi-shot implant injection molding technology (MSIM) came into being.
Multi-shot implantation technology is a comprehensive technology that combines multi-material injection molding and molds, vertical turntable injection molding machines, automatic extraction and implantation, and so on.
In order to solve problem of how to integrate materials with different characteristics and functions through injection molding and implantation in a small space, plastic (soft/hard), silica gel (solid/liquid), hardware (structure/conductor), electronic chips can be completed in one machine cycle to achieve purpose of reducing assembly, enhancing bonding, and improving air tightness.
Take three-color U disk mentioned above as an example to illustrate injection molding process:

 

First, implant U disk chip (electronic device), and then
First shot, white PC, injection molded unilateral white bottom shell and formed bottom font,
Second shot, green PC, injection molded unilateral green bottom shell and formed the other half of bottom font
Third shot, blue TPU, wraps upper and lower bottom surfaces to form a concave-convex effect of font and at the same time produce a soft feel.

 

 

In Multi-shot Implant Injection Molding Technology (MSIM), a three-color six-station vertical turntable injection molding machine will be used, three front and six rear molds, one out of two, manual planting and picking. Full cycle is 30 seconds. After product is out of mold, it is directly packaged and shipped, without other post-assembly processes.
Advantages of multi-shot implant injection molding solution are: to achieve one-piece molding, multi-color modeling, eliminating assembly, and achieving multi-functional integration. It is understood that key to this process technology lies in flexible use of vertical injection molding machines. Common models include single-shot six-station, double-shot four-station, and three-shot six-station. Among them, multi-station cooling can shorten molding time and increase output. At the same time, it is more convenient to implant injection molding and extract products, it can also realize automated production.

With rapid development of smart phones and mobile Internet, more and more smart wearable products have appeared in public's field of vision. More and more of these products require small space and large integration requirements. In production of such products in small spaces For highly integrated products, if traditional injection molding is used, it is difficult to fix horizontal mold opening implants, risk of compression molding exists, space in mold is insufficient, making it more difficult for multi-material injection molding. Multi-shot implant injection molding process (MSIM™), as a new type of production technology, has unique advantages for manufacturers of precision injection molded products that function in small areas.

 

 

Injection molding process: Place pin at No. 1 station, No. 2 station and first shot front mold are combined to inject transparent window parts, No. 3 station is combined with second shot front mold, inject black shading structure, No. 4 station and three-shot front mold are combined to inject a colored shell, No. 5 station is air-cooled, and No. 6 station is used for product taking out. All stations are carried out at the same time.

 

Multi-shot implant injection molding (MSIM™) is very suitable for production of bottom cover of this type of bracelet. Original six processes are combined into one process, which greatly simplifies production process and saves a lot of costs such as material transfer, personnel input and non-performing product consumption, reducing environmental pollution.

 

In original process, a fixed structure or auxiliary materials (sealing ring, viscose) must be designed between parts to meet waterproof requirements. However, aging of sealing ring, strength and stability of dispensing glue have added new variables to waterproof performance. Now, through multi-color implantation injection molding process, key parts are placed in mold to form one piece, which greatly improves waterproof level. However, because this process requires multiple sets of molds, mold cost will naturally increase, so it is more suitable for large-volume, small-scale products.