Two-color/multi-color soft and hard rubber products are more and more common in our lives. Their products have stronger functional purposes, generally have good sealing performance, outstanding impact resistance and cushioning performance, strong soft touch texture, strong soft, hard glue bonding and environmental protection. Hard rubbers commonly used in injection molds are ABS, PA6, PP, PP+TD20, etc., and soft rubber materials: TPE, TPV, TPU, etc. Aiming at this type of two-color/multi-color soft and hard rubber products, let's share experience of designing two-color product soft and hard rubber exterior molds.

 

Question 1: Soft rubber of second color product is covered with burrs, as shown in Figures 1.1.1 and 1.1.2 below.
 
Figure 1.1.1
 
Figure 1.1.2
Problem two: the first color hard rubber embossing deformation/crushing, as shown in Figure 1.1.3 and 1.1.4 below.

 

Figure 1.1.3

 

Figure 1.1.4

1. Mould strength: insufficient mould strength, which causes deformation of mold plate during injection molding, which will cause burrs;
2. Product shrinkage: Shrinkage creates a gap, which is prone to problem of soft rubber drape, and warpage of hard rubber product after mold is opened is easy to crush when second color product is injected;
3. Injection pressure: when soft rubber is injected, injection pressure will squeeze hard rubber product;
4. Fixed mold packing force: it is possible that product sticks to fixed mold, deforms product or causes product shell to separate;
5. Insufficient avoidance: Second color fixed mold and hard rubber part are insufficiently avoided, and avoidance height is not enough to cause crushing;
6. Temperature problems: uneven cooling of hard rubber products causes product deformation;
7. Product structure: Product itself has design defects, and designer cannot find problem in the early stage with insufficient experience.

If thickness of the mold is not enough, pressure deformation of mold during injection will be greater, and cracking will easily appear. Analyze mold deformation, as shown in Figure 2.2.1 below.

 

Figure 2.2.1

Hard rubber product of the first color will cool and shrink after injection, and it is easy to cause problems such as glue overflow and cracking when injecting soft rubber product of second color, as shown in Figure 2.2.2 below.

 

Figure 2.2.2

Hard rubber product of the first color will cool and shrink after injection molding, problems such as overflow of glue and cracking may easily occur when soft rubber product of second color is injected, as shown in Figure 2.2.3 below.

 

Figure 2.2.3

When first-color hard rubber product is opened, product is partially pulled loose and a gap is created with movable mold core. When second-color soft rubber product is molded, problems such as overflow of glue and product crushing are likely to occur, as shown in Figure 2.2.4 .

 

Figure 2.2.4

Due to insufficient clearance, hard rubber product of first color is likely to be crushed when second color soft rubber product is molded, as shown in Figure 2.2.5 below. .

 

Figure 2.2.5

Uneven cooling of hard rubber product of first color results in large product deformation. When soft rubber product of second color is injected, hard rubber product of first color is prone to imprint deformation, as shown in Figure 2.2.6 below.
Cooling analysis schematic

 

Figure 2.2.6

Product R-angle sealing or sharp-angle joints are likely to cause product cracking, problems such as overflowing and cracking may occur when second color soft rubber product is injected, as shown in Figure 2.2.7 below.

 

Figure 2.2.7

Countermeasures: Stress analysis function of 3D design software CAE module can be used to directly analyze strength of mold accurately.
Based on system platform, setting of analysis conditions and calculation instructions required for analysis are set in a wizard manner, helping designers to obtain deformation of mold under stress more accurately and quickly, analyze whether mold strength is reasonable in the early stage of mold design, prevent risk of deformation and cracking in the later stage of mold, and improve economic benefits.
(1) Fast: directly analyze 3D model, calculation speed is extremely fast;
(2) Intuitive: analysis results can be colored rendering, data display, section preview;
(3) Accurate: Built-in patented algorithm, combined with a large number of example analysis and verification.
As shown in Figure 3.1.1 below.

 

Figure 3.1.1

Countermeasures: (1) In order to prevent shrinkage and deformation of product, offset injection pressure, prevent soft rubber fixed mold from damaging product, hard rubber movable mold side is reinforced around soft rubber, as shown in Figure 3.1.2 below.

 

Figure 3.1.2

(2) Design pressure tape at intersection of soft and hard rubber on A side of product, as shown in Figure 3.1.3 below.

 

Figure 3.1.3

(3) Sealing position of hard rubber and soft rubber side. Hard rubber side should be divided into fixed mold, as shown in Figure 3.1.4 below.

 

Figure 3.1.4

Countermeasures: Product movable mold part or side wall is made of inverted buckle ribs or thimble tube is made of inverted buckle ribs, as shown in Figure 3.1.5 below.
 
Figure 3.1.5

Countermeasures: (1) For second color fixed mold and first color hard rubber products, we generally divide it into avoidance zone, transition zone, zero collision zone and interference caulking zone. For different products, we need to analyze detailed design of these areas, as shown in Figure 3.1.6 below.

 

Figure 3.1.6

(2) The smaller R angle, the greater probability of crushing product, and R angle of second color fixed mold transition zone needs to be larger, as shown in Figure 3.1.7 below.

 

Figure 3.1.7

Countermeasure: Mold cooling analysis function of 3D design software CAE module can be used to directly analyze mold cooling accurately, as shown in Figure 3.1.8 below.
(Analyze 3D model of mold directly, without need for waterway drawing and data conversion.)

 

Figure 3.1.8

Countermeasures: 1. Check and analyze whether there is any problem with customer's product. For unreasonable part of customer's product structure design, product DFM data should be proposed and revised in the early stage.

1. Design of art groove at the joint of soft and hard glue is given priority as possible, as shown in Figure 3.1.9 below.

 

Figure 3.1.9

In view of mold design problem of soft and hard rubber appearance surface of two-color product, we mainly shared and discussed causes of soft and hard rubber parting surface, imprinting and crushing, determined improvement measures. Through implementation of measures, mold design can be further optimized.

Soft and hard rubber two-color products have more details to be considered than single-color products, difficulty of mold design is greatly increased. It is important to grasp details of design, otherwise various problems will easily occur in mold trial.