5 Things to Know Before Buying two shot molding

Before diving into the realm of two-shot molding, it's beneficial to grasp the essentials that can guide your purchase decision. Understanding various aspects of this process can enhance the quality and efficiency of your projects. When considering two-shot molding, a few critical elements should come to the forefront. According to several sources, it’s crucial to evaluate equipment specifications, material compatibility, mold design, production capabilities, and supplier experience.

Two-shot molding encompasses several variations such as rotary platen, movable core, and overmolding. Each of these variations has distinct requirements regarding injection units, runner systems, and operational procedures. Typically, the process involves two separate molds dedicated to each material; however, it can also utilize a single mold featuring two runner systems along with manual or robotic part transfer.

Engage with us to explore your two shot molding requirements. Our knowledgeable sales representatives can assist you in identifying suitable options tailored for your needs.

Choosing appropriate materials for two-shot molding is paramount, primarily focusing on their ability to form a strong bond. A mechanical bond is often necessary, especially when the part design includes intricate details or holes. Some materials may exhibit compatibility issues, leading to poor adhesion. In my experience, Thermoplastic Elastomers (TPE) or Thermoplastic Polyurethane (TPU) are frequently employed as the second shot, with Polypropylene (PP), PC/ABS, or ABS serving as the substrate for the first shot. Notably, cases involving the same material in different colors or with various additives are common in two-shot molding.

From my perspective, rotary two-shot molding is one of the more straightforward approaches, but it comes with its challenges. Essential factors to consider include tooling specifications, crush, support, and the processing methodologies required for both shots. This article will primarily focus on the rotary platen process. The tool often features a rotary plate actuated by hydraulic or rack systems, complicating the tooling procedure, particularly for molders who aren't extensively engaged in two-shot molding.

Several interpretations surround the term rotary platen among molders. The basic definition is a vertical platen that rotates on a horizontal axis. Conversely, a more intricate definition applies to what's known as a cube mold or spin stack, which entails a center stack rotating on a vertical axis, generating a multi-daylight stack-mold configuration—this is the most elaborate and expensive type of rotary two-shot mold.

Focusing on the simpler rotary platen, the tooling features a second runner system and dual sets of ejector plates. The rotating half contains the first-shot cavities, while the stationary half features the cavities for both shots. If two parts are produced every cycle, the total number of ejector and cover cavities could reach four.

Click Here for more tooling expertise from Randy Kerkstra. Ensuring proper alignment of the rotary platen mold is critical. Any misalignment can result in severe mechanical failures when the mold rotates, damaging components like leader pins, bushings, or shutoff mechanisms. Furthermore, understanding tonnage in relation to part surface area is vital; often, the cavities will not be centered, affecting the machine's tonnage capacity.

Once the first-shot components are ready, it's crucial to consider crush and support when designing the tool for the second shot. Crush is essentially a mechanism to combat the second-shot material from leaking onto the first-shot plastic, usually achieved through a raised area of cavity steel that effectively seals the connection. Additionally, supporting the first-shot parts adequately within the second-shot cavities is necessary to prevent deformation from the immense pressure exerted during the second-shot injection.

Another variant of two-shot molding is the movable core system, which does not rely on a rotary platen. Molds in this system traditionally behave like standard molds but incorporate internal movable cores that adjust for the second shot. Initially, the first shot is injected; subsequently, the core slides back, configuring the necessary cavity for the second shot. Proper tool design is vital to ensure the first-shot cavity withstands the subsequent pressure exerted during the second shot.

The emphasis on robust process windows is paramount in two-shot molding due to additional variables. It's common to manipulate the processing parameters of one shot to mitigate complications from the other. Issues such as crush, support, deflection, and inadequately sized cylinders can introduce significant risks to quality, leading to scrap products. Maintaining a focus on achieving well-defined process windows is vital for success in two-shot molding.