How are dual color and multi-color silicone parts made

Color blocking for phone cases, dual color wristbands, dual color handles for kitchen utensils, and contrasting character areas for buttons - multi-color silicone parts are ubiquitous in the consumer market. A product with two colors may sound like adding more colorants, but in reality, they are completely different molds and process systems. This article discusses the implementation methods and cost logic of multi-color silicone components.

Method 1: Split molding+post assembly

The simplest way is to make two sets of molds for each color, shape them separately, and then assemble them (interference fit, snap fit, adhesive).

Advantages: The mold is simple, the colors of each part are independently controlled, and only single color parts are scrapped. Disadvantages: An additional set of molds, an additional assembly process, and assembly seams are the visual boundary (some designs require this effect, while some customers may find it problematic).

This method is widely used for color blocking phone cases - the color blocks themselves are designed in blocks, and the assembly seams and appearance boundaries overlap.

Method 2: Overmolding

First, shape the first color part and place it as an "insert" into the second set of molds, then inject the second color. Between the two molding processes, the use of gentle pressure on the mold causes partial cross-linking at the interface between the two layers of silicone, resulting in a strong bond.

The dual color silicone wristband strap is typical: the hard rubber skeleton is molded in the first color, and then placed in the second mold to package the soft rubber in the second color.

Attention: When the first color parts are inserted into the second mold, they should be accurately positioned (relying on the positioning structure on the mold). If they are placed askew, the second color will be skewed; The interface combination depends on process parameters, and the secondary molding interface with insufficient vulcanization will delaminate as soon as it is peeled off - similar to the adhesive control of the encapsulated parts.

Method 3: Double color machine (multi-color injection molding machine) for one-time molding

Specialized liquid silicone two-color machine: two injection units, one rotating mold (or indexing mold core). After the first color is injected, the mold rotates 180 degrees, and the second color is injected onto the first color. One cycle produces the finished product.

Advantages: No intermediate transfer, highest precision, highest efficiency, and lowest batch cost. Disadvantages: expensive equipment (dual color liquid silicone machine is several times more expensive than single color), complex molds (dual cavity+rotating mechanism), long development cycle. This route is exclusive to products with large quantities - equipment amortization is not cost-effective for quantities below hundreds of thousands.

Method 4: Multi color molding (traditional process of solid silicone)

The multi-color effect of "character+button body" on remote control buttons: First, pre shape the character part (small color block), place it in the button mold cavity, and then press the base color material. Solid state molding has low cost for multi-color production, but its accuracy and automation are not as good as liquid two-color machines.

Cost structure of multi-color components

Compared to monochrome items, what makes multi-color items more expensive

Mold: One set becomes two sets (or one complex set), and the mold cost is nearly doubled; Beat: The cycle time for secondary molding is about twice that of a single piece (except for two-color machines); Yield: One more molding adds an extra layer of defect risk, with the first color defect mixed into the second color scrap, resulting in a higher overall scrap cost; Color matching: The color difference between two colors needs to be controlled, doubling the workload of color matching.

Overall, the unit price of secondary molding multi-color parts is usually 1.5-2.5 times that of single color parts with the same structure.

The money that can be saved during the design phase

1. The color separation surface design is located at the visual natural boundary (edges, curvature changes), and the secondary formed color separation burrs are not prominent; The color separation surface is designed on a large plane, and the unevenness of the dividing line can be seen at a glance.

2. Try to use regular colors for both colors, and adjust the spot color separately. For multi colored items, x2 should be used.

3. If the structure allows, use "monochrome parts+assembly" instead of "two-color integration" - with higher design freedom, mold investment is reduced by half, and small and medium-sized batches are almost always more cost-effective.

4. Clear requirements for combined strength: Decorative dual color (color separation is sufficient) and functional dual color (sealing structure dual hardness) are two different things, with the latter requiring a higher level of process validation.

Multi colored silicone is an important means of differentiating the appearance of consumer goods. The price difference and premium ability between monochrome and multi-color versions of the same product are often greater than the difference in processing costs - this is why this category is attractive and why it is important to calculate the mold and process route before making it.