Two-Shot / Multi-Shot

Two-Shot Injection Molding Solutions

If you’re new to two-shot plastic injection molding, you might think it is more complex, more expensive, or more time consuming than other plastic molding processes. Taken alone, those may be true, but two-shot also creates considerable functionality and savings. Maybe you’ve been turned off by a manufacturer’s quality or delivery issues. We’re here to tell you that you deserve better.

Whether you’re new to two-shot or needing a new two-shot supplier, we are here to help.

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When a major automotive OEM failed a side impact crash test, they relied on their Tier 1 supplier and us to develop a two-shot injection molding solution to reinforce the vehicle’s frame. In less than eight weeks, the OEM had their solution and passed the second crash test.

When tolerances and on-time-delivery are important, OEMs choose us for two-shot injection molded parts. We’re more than a manufacturer. We’re problem-solvers, working both with customers and vendors to build functionality, safety, and efficiency into everything we produce. You can rest assured you’re getting the quality you need at a competitive market price when you choose us for your two-shot molding solutions.

Two-Shot Molding Process

Two-shot, also referred to as dual-shot, double-shot, multi-shot and overmolding, is a plastic molding process in which two different plastic resins are molded together in a single machining cycle, as illustrated below.

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There are two phases of the two-shot molding process. The first is similar to traditional injection molding: A shot of resin is injected into a mold and cooled to form a solid part. In the second phase, the just-molded part is transferred to a second mold via a rotating platen or a robotic arm, and receives the second shot of resin – in, through or around certain parts of the first molded part, depending on the design. The two plastic resins then form a molecular bond and the multi-resin molded part is cooled and ejected.


The process isn’t difficult to understand, but it’s highly difficult to master. It requires high levels of technical expertise and attention to detail, and even the smallest mistakes can cost big money, especially in high-volume production scenarios.


That’s why it’s critical to find a highly capable supplier. Look for excellent supplier quality scorecards, defined processes to mitigate against flash, flow lines, and short-shots, and contingency plans to expand capacity as your business and your two-shot molding needs grow.


Once you find a supplier, involve them early on in the design phase of your part. They can identify potential problem areas and engineer value into your product.

To get a jump-start on your two-shot part design, download our free Two-Shot Injection Molding Design Guide today!

Two-Shot Injection Molding Applications

Two-shot injection molding is the ideal plastic molding process for complex, multi-color, and multi-material plastic products, especially in high-volume production scenarios. Thumb Plastics services a variety of industries including lawn and garden, agriculture, and consumer, with significant experience in automotive.


From consumer goods to construction, two-shot molded components are used in nearly every industry, but are most commonly found in applications requiring the following:

  • Movable segments or components
  • Rigid substrates with soft grips
  • Vibration or acoustic dampening
  • Surface descriptions or identifications
  • Multi-color or multi-material components

Benefits of Two-Shot Molding

Compared to other methods of plastic molding, two-shot is ultimately a more cost-efficient way of producing an assembly with multiple components. Here’s why:


Part Consolidation | Two-shot injection molding reduces the number of components in a finished assembly, eliminating an average of $40K in development, engineering, and validation costs associated with each additional part number.


Improved Efficiency │ Two-shot molding allows multiple components to be molded with a single tool, reducing the amount of labor needed to run your parts and eliminating the need to weld or join components after the molding process.


Improved Quality │ Two-shot is carried out within a single tool, allowing for lower tolerances than other molding processes, a high level of accuracy and repeat-ability, and reduced scrap rates.


Complex Moldings │ Two-shot injection molding allows for the creation of complex mold designs that incorporate multiple materials for functionality that cannot be achieved through other molding processes.

Two-Shot Molding Case Study: Active Grill Shutter Guides (AGS)

The front end of a RAM truck with the left side of the grill removed to reveal two-shot molded active grill shutter guides.

The Market:
The customer is a Tier 1 international automotive supplier with an emphasis on innovation and technology. The company’s products include automotive exteriors, closures, roof systems, and seating – to name a few.


The Challenge:
The customer was having issues sealing off an active grille shutter (AGS) system with the air guide seals. The innovative under-the-hood system was designed to help OEMs meet CAFE standards by redirecting air around the vehicle to reduce drag. The sealing components of the system are absolutely critical and the manufacturing process to make them – two-shot injection molding – is difficult to master. The customer was quick to realize this as the incumbent supplier failed to meet stringent quality standards. The customer had to find a supplier experienced enough to manufacture the complex part.


The Solution:
Needless to say, the customer turned to us for design and engineering support and innovation. The key to our success lies within its culture of continuous improvement, it’s adherence to Lean – one piece flow – manufacturing, and its commitment to delivering quality products at a competitive market price. Drawing form over 30 years of experience launching hundreds of two-shot interior, exterior, BIW, and underhood applications, we were able to quote the four-component, multi-million dollar program in less than a week and was awarded the program soon after. The final production design was guided by our internal design support team, optimized for DFM, and is set for production in 2019.


The Result:
The final part design exceeded the customer’s expectations, along with our highest quality and OTD standards. In addition, the efforts of our in-house part and tooling design team reduced the mold expense to our end customer with a savings of nearly $200K in tooling.

Two-Shot Terminology

  • Boss: A raised cavity on the part designed facilitate alignment during assembly or attachment to other parts
  • Cold-runner mold: A mold in which the runners are kept at the same temperature as the mold and must be ejected at the end of each molding cycle
  • Draft: A slight taper built into the mold walls to facilitate removal of the part from the mold
  • Flash: Material that forms in the seams or parting lines of the mold cavity
  • Gate: The channel through which molten plastic resin enters the mold cavity
  • Hot-runner mold: A mold in which the runners are insulated or heated to keep resin in a molten state to facilitate flow control
  • Knockout pin: A pin that ejects the molded part from the mold
  • Living hinge: A thin section of the part along which the part can fold
  • Parting line: A mark on a molded part indicating where the two halves of the mold meet in closing
  • Rib: A thin wall-like feature that increases the bending stiffness of wall sections and bosses
  • Runner: A channel within the mold through which molten resin flows from the machine sprue to the cavity gate
  • Short shot: Failure to fill the mold completely with resin, resulting in missing geometry and melted edges
  • Shrinkage: The contraction of a plastic molded part as it cools
  • Shut-off: An area where the mold seals against the other half of the mold, an insert, or the first-shot substrate formed in the two-shot molding process, to form a slot, hole, or void
  • Sink mark: A surface indentation caused by differential rates of cooling in areas with significant changes in wall thickness
  • Sprue: The channel through which molten plastic resin flows from the machine nozzle to the mold runner
  • Undercut: A protrusion, hole, cavity, or recessed area in the part that impedes ejection from the mold, therefore requiring movable mechanisms within the mold to form the shape

Engineering Success

We’ve spent the past 30 years mastering the art and science of two-shot injection molding. We have the design, engineering, and in-house tooling capabilities you need to streamline your project from conception to production. And as a financially stable company, we’re prepared to expand capacity and scale operations as your company and your two-shot needs grow.


What are you waiting for? Our technical sales team is standing by to give you the information you need to make an informed decision about two-shot.