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Overview
Our Overmolding Service
What is Overmolding
Overmolding refers to an injection molding process that creates a product that is perfectly combined with two or more materials and colors. Usually, we refer to the first material that we apply in this process as the substrate, which can be a plastic and metal materials. And subsequent materials (usually plastic or rubber materials) are used to completely or partially cover the substrate.
How Does Overmolding Work?

1. Two-color injection molding
The first is two-component molding or two-color injection molding, that is, it is realized on a two-color injection molding machine, and one material is injected into a product, and then the mold is flipped and jumped to the corresponding mold cavity of another injection plastic cylinder on the two-color machine. Among them, this part is used as an insert, and another material is injected on it to form an integrated dual-material product. The injection molding machine has double barrels and double mold cavities. The injection molding process is to produce products of two materials at the same time, but the products of one cavity will enter the next cavity as an insert.

2. Two steps injection molding
The other is two-step injection molding. A part of one material is molded on one injection molding machine, and the part is placed in another mold as an insert, and then injected with the second material.

Features of Overmolding
Advantages
Rapid Turnaround
After the molding is finished, the fastest turnaround can reach 2 days, supports mass production.
Product Quality
To understand your needs and provide feasible solutions for your projects, silicone has good shock and vibration properties, which can prevent products from physical impact and prolong their lifespan.
Cost Saving
Overmolding requires less labor because the process is automated in most steps, and requires no assembly work or other post-production processes, significantly increasing production efficiency.
Custom Materials
It supports the use of multiple materials in different colors. Take TPE as an example, this material is available in a variety of colors and finishes.
Drawbacks
Material Restrictions
Pay attention to material compatibility, and the commonly used material is TPE.
Maximum and minimum part size for Overmolding
Size Metric units Imperial units
Maximum size 800*500*200mm 32*20*8inch
Min thickness 1mm 0.04inch
Minimum part volume 50mm³ 0.03inch³
Available materials for injection molding
Here is a list of our standard injection molding materials available through our online platform.
Injection Molding Plastics
Plastic
ABS POM Nylon Polycarbonate (PC)
PC/ABS PVC Polyethylene (PE) Polypropylene (PP)
Polystyrene (PS) TPU Rubber
Custom Material
The materials available on the online system may not be exhaustive of all materials available on the market. If the materials you need are not listed on the order page, please select "custom" under the material menu, and our engineers will review and purchase.
Injection Molding Design Guidelines
We have summarized recommended and technically feasible values for the most common features encountered in Injection Molding parts.
1. Wall thickness
Wall thickness has a large impact on the performance and cost of plastic injection molded parts. In general, the thinner the wall thickness, the lower the manufacturing cost. The wall thickness of plastic parts is generally in the range of 1-5mm. Injection molded parts should have a uniform wall thickness throughout the part, too much variation in wall thickness can cause the injected material to cool at different rates, leading to sink marks, voids and warpage.
2. Draft angles
Draft angle refers to the gentle taper added to the surface of an injection molded part, aligned with the direction of pull, so that the part can be removed from the mold without damage due to friction or suction. A draft of 1.5-2 degrees is usually a safe minimum for most parts.
3. Avoid sharp edges and inner corners
Sharp edges and inner corners can easily lead to deformation, defects and cracks in plastic injection molded parts. Therefore, sharp edges and inner corners need to be avoided as much as possible in the design.
4. Gates and ejector pins
The material passes through the gate, cools to form the product, and the ejector pins push the part out of the mold, and in most cases, they leave marks. Often these are designed on part surfaces that may not be visible, such as inside housings. The ejector pins needs to be placed on a surface that is perpendicular to the direction of ejector push.
5. Support ribs
Ribs are used to increase the structural integrity of a part and increase its load carrying capacity. Ribs are often used to reinforce a section wall where two section walls meet at a 90 degree angle, or where the length of a particular section is weakened by the section wall thickness. Ribs that are too thick usually cause sink marks. The bottom thickness of the ribs shall be a maximum of two-thirds the thickness of the adjacent wall.
6. Buckle and other structures
Buckles and other structures are commonly used assembly methods for plastic parts, and are formed by lateral core-pulling structures of oblique pins (or sliders) in the mold. The oblique pin (or slider) has a stroke to withdraw from the buckle when the part is demolded. The design of the part needs to provide enough movement space for the withdrawal of the oblique pin (or slider), otherwise the oblique pin (or slider) will appear. slider) cannot withdraw or the oblique pin (or slider) interferes with other features on the part (such as pillars, etc.) during the withdrawal process.
FAQ's
What is injection molding?

Injection molding is a manufacturing process used to create plastic parts in large quantities. Molten plastic material is injected into a mold or cavity, which is then cooled and solidifies into the desired shape. The process involves feeding plastic pellets into a hopper, which are then heated to a molten state and injected into the mold under high pressure. This pressure ensures that the material fills the mold completely and uniformly, resulting in a high-quality finished product. Injection molding is commonly used to create products such as toys, automobile parts, packaging materials, and medical devices.

What materials can be used in injection molding?

A variety of materials can be used in injection molding, including thermoplastics, thermosets, and elastomers.

Thermoplastics: These are the most commonly used materials in injection molding, including polyethylene (PE), polypropylene (PP), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), and polyvinyl chloride (PVC).

1. Thermosets: These materials are harder, more rigid, and more heat-resistant than thermoplastics. Examples include epoxy resins and phenolic resins.

2. Elastomers: These are rubber-like materials with high elasticity and flexibility. Examples include silicone, natural rubber, and styrene-butadiene rubber (SBR).

The choice of material depends on the specific application and requirements for the finished product. Properties such as strength, durability, flexibility, heat resistance, chemical resistance, and color can be tailored by using different materials and additives in the plastic pellets. In addition, recyclable and biodegradable materials are becoming increasingly popular in injection molding as part of a sustainable production process.

What are the different types of injection molding machines?

Single-shot injection molding and multi-shot injection molding are both methods used for producing plastic parts, but they differ in the way that the plastic material is injected into the mold.

Single-shot injection molding: This is the most common method of injection molding. It involves injecting a single material into the mold, which solidifies to form the final part. The mold is typically designed to have a single cavity or multiple cavities, enabling multiple identical parts to be produced simultaneously.

Multi-shot injection molding: This method uses multiple materials to create a single part. It is also known as overmolding. Depending on the design of the mold, two or more materials can be injected into the mold in a single operation. Multi-shot injection molding allows for the creation of parts with multiple colors or materials, or for the creation of parts with rigid and flexible sections.

There are two main types of multi-shot injection molding:

1. Sequential injection molding: This involves injecting one material into the mold cavity and allowing it to partially solidify before injecting the second material. The process can be repeated with additional mold cavities to create more complex parts.

2. Co-injection molding: This involves injecting two materials simultaneously into the mold cavity. This method is typically used for creating parts with a core and skin structure, for example, plastic cups with foam insulation.

The choice of single-shot or multi-shot injection molding largely depends on the specific requirements of the part and the manufacturing process. Multi-shot injection molding is more complex and can be more expensive, but it allows for greater design flexibility and the creation of parts with multiple materials or colors.


What is the maximum injection molding capacity of a machine?

The maximum injection molding capacity of a machine depends on several factors, including the volume of the mold cavity, the shot size, and the material being used. The machine's clamping force and injection pressure also play a role in determining the maximum injection molding capacity.

Injection molding machines can range in size from small benchtop machines with a maximum injection capacity of a few grams to large machines capable of producing parts that weigh several kilograms. High-capacity, industrial-grade machines can have a maximum injection capacity of up to 60,000 grams (or 60 kilograms), depending on the manufacturer and model.

The maximum injection molding capacity of a machine is typically specified in terms of the shot size, which is the maximum volume of material that the machine can inject into the mold with a single injection stroke. The shot size can range from a few grams to several kilograms, depending on the machine's size and capacity.

It's important to note that while a machine may have a high maximum injection molding capacity, the actual production rate will depend on the complexity of the part being produced, the cycle time, and the number of cavities in the mold.