RKT Editorial Team in collaboration with
Technical Management
One of the strongest arguments for choosing plastic over metal is weight reduction. In many applications, lighter components contribute to improved efficiency, reduced energy consumption, and more compact product designs.
Plastics also hold a clear advantage from a manufacturing perspective. High-volume production using high-cavity injection molding tools is generally far more economical than metal processing via machining or other methods, making plastics particularly appealing.
It’s true that when maximum strength or inherent electrical conductivity is essential, metals generally maintain a clear advantage. However, whether those properties are actually required depends on the specific application, and in many cases, plastics can be engineered to deliver comparable performance.
To enhance the mechanical strength of plastics, reinforcing fillers such as glass fibers or glass beads can be incorporated to improve rigidity and dimensional stability. For applications requiring even greater strength and stiffness, carbon fibers are used, enabling plastic components to meet the demands of high-performance environments.
Another advanced solution for conductivity is two-component injection molding. In this process, metal pins are inserted into the mold to act as electrical connectors and are encapsulated with a conductive plastic to establish current-carrying capability. A second injection step then adds a layer of insulating plastic around the conductive core. This technique allows for the integration of electrical conductivity within lightweight plastic components, eliminating the need for heavy metal parts. In summary, while plastics may not replace metals in every scenario, modern material technologies offer numerous ways to close the gap, allowing designers to take advantage of plastics’ lower weight, versatility, and cost-efficiency without sacrificing performance.
RKT successfully supported a client in replacing a metal component with a plastic alternative in an insulin pen used for diabetes treatment. Originally, the pen featured a brass threaded rod—an essential mechanical part responsible for accurate dosage delivery.
Despite its strength, the pen failed a critical drop test during the product licensing phase. When dropped from a height of two meters, the metal rod’s weight caused excessive impact force, rendering the pen unusable. At the client’s request, the metal component was replaced with a specially engineered plastic version. RKT advised on the design layout and recommended a customized plastic granulate tailored to meet the strength and performance requirements of the threaded rod. The result was a lightweight, durable plastic component that maintained high precision while improving impact resistance—ensuring the pen passed drop testing and met regulatory standards.
One of the key benefits of plastics in medical and laboratory applications lies in their surface structure and adaptability. While metals are durable, they lack transparency and have overly smooth surfaces and high thermal conductivity—factors that make them less suitable for laboratory analysis or cell culture environments. Glass, although transparent, is brittle and limited in terms of the complexity of shapes it can accommodate.
Plastics offer a number of advantages:
Surface functionality: The microstructure of plastic surfaces can be tailored to improve cell adhesion, a crucial feature for cultivating a wide variety of cell types. Unlike glass, plastic surfaces can be easily customized or coated to support specific cell cultures.
Design flexibility: Complex geometries, such as microchannels for cell migration studies, are much easier and more cost-effective to produce in plastic than in glass.
Cost efficiency: Items like microscope slides, cell culture bottles, and Petri dishes can be manufactured more economically in plastic, which is why plastic has become the standard material in many laboratories.
Safety and durability: Unlike glass, plastic does not shatter or form sharp edges when broken, significantly reducing the risk of injury in the lab.
One minor limitation of plastic is its lower optical transparency compared to glass. However, for most microscopy and analysis applications, modern plastic materials provide adequate clarity by ensuring high-quality raw granulate and precise melt preparation in injection molding to avoid bubbles, streaks, or inclusions that could affect transparency and usability.
The variety of shapes that can be produced using plastics, which is advantageous for laboratory products, can offer significant advantages in many industries traditionally dominated by metal components. While plastics don’t allow completely unrestricted shapes due to the need for demolding (part ejection from the mold), they still enable a remarkable range of complex and flexible geometries.
In a recent project, due to limited design flexibility with metal magnets, RKT was tasked with producing plastic magnets of a specific shape. By incorporating magnetic metal fillers into the plastic granulate and using strong permanent magnets in the mold to orient the magnetic domains during injection, RKT successfully created plastic magnets in a variety of shapes. Although these plastic magnets have a lower holding force compared to their steel counterparts, their customizability opened new design opportunities.
Another innovative technique that leverages plastic’s shaping freedom is MID (Molded Interconnect Devices) technology. Unlike traditional flat, 2D printed circuit boards, MID enables the production of three-dimensional circuits through two-component injection molding. This process combines coatable and non-coatable plastics, which are then coated with metallic conductor tracks via electroplating. The result is a 3D printed circuit board molded directly into the plastic part, offering enhanced design freedom and superior performance in applications such as ESP brake control systems, where these 3D components outperform their metallic 2D counterparts.
Incorporating fillers such as carbon fibers or glass fibers into plastic injection molding demands extensive expertise from skilled plastics and mechanical engineers, as these materials introduce unique challenges in processing and tooling. For example, these abrasive fillers affect shrink rates and also accelerate mold wear which increases maintenance requirements and costs. To mitigate this, inserts within the injection molds must be manufactured from specially selected high-alloy tool steels that offer enhanced wear resistance. This proactive approach helps preserve mold longevity even under demanding conditions.
Similarly, when using additives like flame retardants common in components for the electrical industry, the additive’s chemical aggressiveness can rapidly corrode or degrade standard mold materials. To address this, RKT designs and fabricates mold inserts from specialized high-chrome steels within its in-house tool and mold-making department, ensuring durability and consistent production quality despite the harsh conditions.
Across the diverse range of industries and applications, each with its own unique requirements, both metals and plastics offer distinct advantages. However, the prevailing trend is clear: wherever feasible, metal components are increasingly being replaced by lighter, more cost-effective plastics. This shift is driven primarily by plastics’ lower weight and the greater economic efficiency of their production processes.
