Latest News

Complex Molded Parts: When to Integrate and When to Assemble

Today’s complex injection molded parts and assemblies for critical applications are asked to do more than simple one-shot components. They must meet stringent functional demands, operating environment specifications, and often meet aesthetic requirements as well.

For instance, a single housing may need threaded bosses, sealed internal channels, snap features and a clean surface that hides every line. This is rarely achievable with a single, simple tool.

In these situations, design teams are faced with a big question: how do we tackle this? Can it be done as one complex integrated part? Should it be broken into simpler components that can later be joined? Can the whole process be automated, or will it require manual labor? Ultimately, the answer usually depends on the complexity and geometry of the end product. In this post, we’ll look closer at what it takes to produce complex parts. We’ll look specifically at the role of secondaries, strategic assembly, and integrated design.

What Is Integrated Design in Plastic Injection Molding?

Integrated design in injection molding is a method that combines multiple materials, functions, or separate components into a single finished part during the molding process. The most common integrated approaches are:

Insert molding – where preformed components are precisely placed inside the mold cavity before the plastic is injected. These typically include metal thread inserts, pins, sensors and other functional parts.

Overmolding – when a second material is molded over or onto a preformed substrate.

Two-Shot Molding – also known as dual-shot or multi-material molding. This molding process relies on two-stage injection. Each stage molds a different plastic within a single machine.

What Are the Benefits of Integrated Design?

There are several advantages to this approach. First, there are fewer parts and lower costs. The process reduces secondary assembly labor, fasteners and manual alignment steps. Further, finished components have higher strength and durability. Especially when compared to gluing, snapping or other joining methods. Better sealing is another benefit, making the components resistant to leaks, vibration issues and dust ingress.

There are some drawbacks as well. The biggest is that tooling typically gets more expensive than simple ones. Creating undercuts and certain internal features may require side actions, lifters, or collapsible cores. These all add to the tooling’s complexity and also complicate maintenance. Though generally speaking, if the part or assembly requires features such as living hinges, integrated snaps, and molded-in threads, integration often wins on overall price. This is especially true for higher volume runs. Material compatibility can also be an issue, particularly for overmolding, and should be considered carefully.

Secondary Operations

Certain complex parts along with their overall job requirements such as run volume may not be practical or profitable to produce with integrated methods. Instead, employing secondary operations might be the better route. For instance, joining certain parts of dissimilar materials or finishes is often easier through secondary operations. Sometimes, parts have internal geometry that can’t be molded as one piece. For these cases, each part can be molded simply, to its required spec and material, then joined afterward. Approaches include:

• Ultrasonic Welding – creates strong hermetic bonds along with clean cosmetic results.
• Snap Fits – flexible features, such as hooks or cantilever beams, molded into one part. They deflect and lock into a mating feature on another part, allowing for fast, fastener-free assembly.
• Post-Mold Inserts – add threads and wear surfaces via ultrasonic or heat-staking instead of complicated tooling.

The Role of Automation

Let’s not assume integrated parts mean fully automated ones. Automation is a separate consideration that can apply to either integrated parts or secondary operations. For example, robots can load inserts for insert molding. Also, automated ultrasonic welding and insert placement can run alongside molding as secondaries. Automation can shift the cost balance of either approach.

Design the Part and Process Together

The biggest mistake we see clients and prospects make is designing parts without thinking much about what it takes to produce them. Both aspects must be considered in the early phases. As for the process itself, the best place to start is with part geometry. If multiple tool actions are required to produce it, then determine if a split eliminates them. Once geometry is out of the way, weigh performance requirements, materials, cosmetics, volume and the likelihood of design changes. Then assess if automation can be a benefit, depending on complexity and run size versus manual labor costs. Make sure to include tooling costs as part of your calculations, not just piece price alone.

Bottom line is to make these calls before tooling is cut. Consider molding and the potential role of secondaries and automation together. Doing so will help ensure a successful program that delivers predictable parts and performance over time.