With growth of our country's economy, people's quality of life has improved. Transportation tools cars are becoming more and more popular, but development of cars is also very rapid, models are constantly upgraded and changed, people's pursuit of car appearance and function is getting higher and higher. Plastic products composed of a variety of different plastics are especially important in appearance and function of automobiles. And this process two-color molds or multi-color molds to make product appearance more beautiful and functional.
Now take automobile two-color water channel body as an example. This two-color product is for a good overall appearance. Two-color product of soft and hard rubber has strong adhesion, improves reliability and sealing performance of connection, prevents water leakage in engine room, reduces generation of abnormal noise, does not require glue bonding, finished product processing procedures are reduced and environmentally friendly. Now let's introduce injection mold design of two-color sink for large-scale automobile plastic parts.

 

As shown in Figure 1.1, overall dimensions of plastic products are about 1600mm * 340mm * 200mm, which are produced using two hard and soft plastic materials, PP-TD20 and TPV. Shape of the first color plastic part is complex and has a large slider mechanism. Second color plastic part is distributed in many places and has irregular shapes. It is impossible to adopt a single cavity and double color guillotine structure. Therefore, plastic part adopts a two-cavity and two-color mold design, divided into A and B two-cavity molds. Average wall thickness of product is 2mm, weight of the first color PP-TD20 hard rubber is about 1135g, and second color TPV soft rubber is about 305g.

 

As shown in Figure 1.2, some undercut details of plastic products are displayed. The first color product has a large movable mold slider structure, more than ten movable mold lifter structures, one undercut is forced to demold, and second color product is also forced to demold. Due to large amount of product undercuts at slider structure of first color product, large tightening force, slider needs to be designed with a thimble, so it is necessary to use an inclined guide post + cylinder core. After first color melt injection molding is completed, slider does not move, movable part of mold rotates 180°, and then second color melt injection molding is performed. Mold opening slider first uses inclined guide post to move slider thimble to resist product to separate product from slider, and then cylinder core is pulled .

In the early stage of mold design, Moldflow engineers conduct detailed Moldflow analysis on the most reasonable points of plastic parts layout, obtain the best and reasonable glue feeding position through continuous adjustment.
Moldflow analysis of the first color PP-TD20 material

 

As shown in Figure 2.1.1, the first color hard glue adopts a 10-point needle point sequential valve hot runner system, filling time is 5.7s, maximum injection pressure is 47MPa, which is within injection requirements of PP-TD20 material.
Moldflow analysis of the second color TPV material

 

As shown in Figure 2.1.2, second color soft glue adopts a 12-point needle point sequential valve hot runner system, filling time is 2.4s, maximum injection pressure is 59MPa, which is within required range of TPV material injection.

 

Since overall size of plastic part has reached 1.6m, maximum size of mold has reached 2m, which is a large mold. Because there are two sets of molds A and B, size is too large and too heavy. Traditional clamping wall around horizontal axis 180° parallel nozzles can no longer meet requirements, so front and rear coaxial axis of injection unit is selected: Engel’s two-color 1700T clamping wall rotates double-headed injection molding machine around vertical axis by 180° forward and backward, as shown in Figure 2.2.1. Maximum clamping force is 17000kN, which meets requirements of Moldflow analysis results.

First color A cavity mold structure

 

 

Second color B cavity mold structure

 

 

 

First color material of mold and second color material are designed to be same as movable part of mold. Two-color injection is realized through different structure of fixed mold cavity. Mold structure is shown in Figure 2.3.1 and Figure 2.3.3.
Mold adopts a movable mold slider structure, ten movable mold lifter structures, multiple soft and hard rubber strong release inserts to carry out demolding treatment of product's undercut structure. Tripping structure is shown in Figure 2.3.2 and 2.3.4. Although movable mold slider is driven by an oil cylinder, there is a thimble on the slider as shown in Figure 2.3.5. You must first move slider by inclined guide post to make slider separate from product to prevent product from sticking to slider, and then oil cylinder drives slider to trip. .
Because it is a movable mold slider, the first color cavity does not have an oblique guide post. When second color is injected into mold, oblique guide post enters slider through a special mechanism. When mold is opened, oblique guide post moves slider to exit for a certain distance.

 

 

a. This type of product is also an appearance part, and surface generally needs to be sun-textured. Because surface difference and clearance of front windshield of car are required, deformation requirements of product are also relatively high;
b. Mesh on product needs to calculate amount of air intake and ventilation, and it is not possible to block mesh or increase mesh at will;
c. Pay attention to product size tolerances for important assembly holes such as sealing strip mounting button, nozzle hole, body mounting hole, wiper hole.

 

a. When mold is loaded into injection molding machine, static state is shown in Figure 3.2.1. Simulation of central vertical rotating wall rotating 180° must be performed to prevent interference with front mold parts;
b. Thickness of mold must be calculated with actual data of injection molding machine;
c. Note that floor side of mold base cannot exceed this number to avoid interference with injection molding machine guard plate;
d. All parameters of trial injection molding machine and injection molding machine produced by  customer must be checked.

 

a. Hard rubber at junction of soft and hard rubber appears crushed and indentation is obvious, as shown in Figure 3.3.1, product needs to reserve steel material for design of pressing tape;
b. Soft and hard glue is not firmly bonded, as shown in Figure 3.3.2, product has a step at junction of soft and hard glue, design undercut makes soft and hard glues better bond and bond firmly;
c. Second color of hard rubber is crushing/squeezing deformation, as shown in Figure 3.3.3, positioning ribs need to be added around hard rubber. In non-sealing hard plastic area, increase avoidance, add R angle to sharp corner.