1. Product function requirements, such as power switch, mobile phone buttons, keyboard indicator lights, car switches, etc., require that IED part can be light-transmitting.

 

2. Improve feel. Some handheld products require use of Rubber on handheld part, which will make feel more comfortable. For example, walkie-talkie housing, power tool handles, wrenches, screwdriver handles, toothbrush handles, thermos cups, etc.

 

3. Increase beauty, as decoration. For example, if logo of some appearance parts is two-color injection molding, it is beautiful and there is no need to worry about it being rubbed off.
4. Partial areas of product need to be electroplated.
As we all know, in plastic family, only ABS and polysulfone (PSU) can be electroplated. If product requires partial area or one side to be electroplated, electroplated area should be injected as ABS, area that does not need to be electroplated should be injected as other materials such as PC, etc.

 

Structure of two-color mold is divided into:
A: core rotation structure;
B: core (cavity) retreat structure;
C: seesaw two-color mold structure;
D: plate-off rotation mold structure;
E: core sliding structure;
A. Core rotation structure: commonly used structure at present
1. Basic principle:
Double-shot molding mainly uses two material tubes of double-shot molding machine with two sets of molds to form a double-shot product in sequence through two moldings.
Working steps:
1. A raw material is injected into molding mold once through A material tube to form a single-shot product A.
2. After cycle mold is opened, product A is left in public mold, and molding mobile mold plate rotates 180 degrees to B mold.
3. B raw material is injected into molding mold twice through B material tube to form a double-shot finished product, mold is opened and ejected.

 

Core rotating structure
There are two types of core rotation molds:
Two sets of male and female mold cores use two mold bases;
Two sets of male and female mold cores use one mold base;

 

 

 

 

2. Injection molding cycle

 

3. Parallel gun, mainly used for rotary mold, applied to the most common two-color molding machine;

 

 

B Core (cavity) back-moving mold structure
1. Basic principle:
Working principle of core (cavity) back-moving type: During first injection, movable core moves upward under action of cylinder, breaking a hole at boundary of closed area of first product; during second injection, movable core moves downward under action of cylinder, leaving a cavity hole, so that secondary material forms cavity hole. After completion, mold is opened and product is taken out.

 

2. Injection molding cycle

 

B. Core (cavity) back-moving mold structure
3. 45-degree gun, mainly used for core (cavity) back-moving mold structure

 

C Seesaw two-color mold structure
1. Basic principle:
Working principle of seesaw: During first injection molding, breaking needle moves upward under action of seesaw, breaking a hole at boundary of closed area of first product; during second injection molding, breaking needle moves downward under action of seesaw, leaving a circular hole, so that secondary material can drill into closed area from breaking hole.
It is mainly used on numeric keypad, such as closed numbers 0, 4, 6, 8, 9 and closed letters A, B, D, O, P, Q, R. With seesaw structure, secondary material can flow into closed area.

 

2. Injection molding cycle

 

D. Deplate rotary mold structure

Now everyone knows that two male molds of two-color mold are exactly same. However, what should we do if structure of product requires that two male molds are also different? You can apply stripping rotary mold structure.
1. Basic principle:
Working principle of middle plate mold: During injection molding, two male molds do not move. After injection molding machine completes one injection, central rotating axis of molding machine first lifts out stripping plate, then rotates stripping plate 180 degrees, and performs secondary molding. In this way, primary and secondary parts of male mold can be made into different shapes to achieve our expected design purpose.

 

2. Injection molding cycle is same as ordinary male mold rotary structure.

 

E. Core sliding structure
1. Basic principle:
Working principle of core (cavity) sliding type: after one injection, mold is opened, male mold cavity slides under action of motor, and mold is closed to match female mold to a certain distance, then second injection is performed. After that, mold is opened to eject product, and male mold slides again under action of motor to form the first product; it is mainly used in two-color vertical machines.

 

1. Principle of mixed color forming

 

2. Compatibility of material mixtures

 

A Two-color mold: two plastic materials are injected on same injection molding machine, molded twice, but product is only ejected once. Generally, this molding process is also called double-material injection molding, which is usually completed by a set of molds and requires a special two-color injection molding machine.
B Rubber overmolding (secondary molding): two plastic materials are not necessarily injected on same injection molding machine, but molded twice; after product is ejected from one mold, it is placed in another mold for a second injection molding. Therefore, generally this molding process is usually completed by 2 sets of molds, and does not require a special two-color injection molding machine.
VI. Introduction of double shot molding machine
Double-shot molding machines can be divided into vertical machines and horizontal machines according to their appearance. Horizontal machines are commonly used. Horizontal two-color molding machines can be divided into two types:
A: Two parallel injection system molding machines; our company's two-color plugs and mobile phone shells are commonly used machines, commonly used in Taiwan and Japan;
B: One material tube is horizontal and the other is vertical. Commonly used in Europe;
Domestic two-color machines mainly include Haitian and Fuqiangxin;
A: Two parallel injection system molding machines;
1. Movable mold plate is a rotating device mechanism.
2. Movable mold plate can be rotated 180 degrees in both directions

 

 

 

 

B: One material tube horizontal, one material tube vertical forming machine

 

1. Two shapes of cavity are different, forming one product each. Two shapes of core can be exactly same or different; mold structure is different:
2. Front and rear molds of mold must match after rotating 180 degrees around center. This inspection must be done during design.
3. Shrinkage rate: Generally speaking, shrinkage rate of a two-color mold depends on material of molded outer contour. For example, primary material of a two-color plug is ABS or PC1414 (shrinkage rate is usually 0.5%), and secondary material is TPU (shrinkage rate is usually 1.8%). When designing a two-color mold, all 0.5% should be selected, because primary material has already supported product contour, and secondary material will not shrink more.

 

4. Gate location selection;
a: For products with logo, gate should choose the side with logo opening to facilitate filling of secondary materials.

 

b: If primary material is a point gate, it must be rippled to avoid secondary material being penetrated by residue from primary entry point.

 

Figure x-a 1st entry point remains too high and penetrates surface of secondary material
Gate residue
Gate design waveform to avoid excessive gate residue
5. Choice of Gate mode;
The first product should choose latent injection to ensure that product and runner can be automatically cut off. When latent injection cannot be used, three-plate mold or hot runner can be considered. Disadvantage of three-plate mold is large pressure loss and heavy material head
6. Pre-pressing
This is a professional term used in two-color molds. In non-flip molds, because primary product needs to press secondary master mold, if there is a logo on molded appearance surface, this will have a very sensitive effect on shape of logo. Generally speaking, height of logo should be 0.02-0.05 larger than theoretical value. If it is too small, secondary material will run in, making outline of text unclear. If pre-pressing is too large, it will cause pre-pressing deformation of logo.

 

Draft angle selection of primary material of two-color mold is more flexible and should be as large as possible. Draft angle of logo can even be set to 15 degrees, and bottom size is enlarged, so that it is not easily washed away by secondary material.
8. In order to make two plastics "stick" tighter, some ribs need to be made to enhance adhesion, "stickiness" between materials and roughness of mold surface should also be considered. There is a special TPU for two-color injection molding; and the smoother mold surface, the tighter they "stick".

 

9. Pay attention to positioning of front and rear molds; slope difference of all insertions and broken surfaces should be as large as possible, more than 0.1mm.

1. Product image

 

2. Two pictures of male and female molds

 

3. During the first shot molding process, male mold rotates 180 degrees and then closes mold

 

4. Second shot forming process, ejection of finished product after mold opening