Advanced hot-runner technology Miniaturisation is rewriting the rules of injection moulding

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Micro-moulding demands more than simply making everything smaller. Precise thermal control, short residence times and stable melt delivery are becoming critical as medical and technical components shrink while their functionality increases.

The trend toward miniaturisation continues to reshape the plastics industry. Across medical, diagnostics, electronics, drug delivery and high-precision consumer applications, manufacturers are increasingly challenged to produce smaller components with greater functionality, tighter tolerances and more demanding material requirements.

What was once a simple moulded component is now frequently part of a sophisticated subassembly designed to integrate multiple functions into a smaller footprint. At the same time, pressure to reduce material consumption, improve sustainability and lower manufacturing costs has never been greater.

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For mould makers and processors, these market forces are creating a fundamental question: does it still make sense to mould small components with cold runner systems?

For decades, cold runners have been widely accepted as the preferred solution for many micro and small-part applications. However, advances in hot runner technology are changing that perception. Advanced high-performance manifold designs that support significantly smaller melt channels are enabling applications previously considered impractical for hot runner systems.

The challenges created by miniaturisation

The push toward miniaturisation presents several technical challenges for both mould makers and processors.

OEMs are continually seeking opportunities to reduce device size while adding functionality. Components must often incorporate intricate geometries, thin wall sections and increasingly complex resin formulations. Lightweighting initiatives further reduce shot weights, often resulting in moulded part weights measured in tenths or even hundredths of a gram.

At the same time, many of the engineering and medical-grade polymers used in these applications have relatively narrow processing windows. Maintaining material integrity throughout the moulding process becomes increasingly critical as part size decreases.

Historically, these factors have led many designers to favour cold runner systems. Yet the disadvantages of cold runners become increasingly difficult to justify in modern manufacturing environments.

Why cold runners are losing acceptance

The changing economics of manufacturing are causing many companies to reconsider traditional cold runner approaches.

In many small-part applications, the runner can weigh significantly more than the finished component itself. This creates an ongoing material cost penalty and generates waste that is difficult or impossible to regrind when processing medical-grade materials.

Sustainability initiatives have become a key driver. Medical manufacturers are under increasing pressure to reduce waste streams throughout production. As manufacturers pursue aggressive sustainability targets and tighter margins, these inefficiencies are attracting greater scrutiny.

Material costs also continue to rise for many specialty engineering resins. When expensive polymers are being converted into runner scrap rather than saleable components, the financial impact can be significant.

Perhaps most importantly, cold runners inherently impose a cycle-time penalty. Every production cycle requires the cold runner to cool sufficiently for ejection. The additional cooling requirements reduce machine productivity and increase manufacturing costs. The result is longer cycle times, reduced productivity and higher cost per part.

As a result, many processors are searching for alternatives that eliminate waste while maintaining the process stability required for high precision applications.

Speaking of real-world scrap savings, an eight cavity cold-runner application that involved moulding a 0.15 g part produced about 4 g of scrap with each cycle. Transitioning to a hot runner system allowed them to double the mould capacity (16-cavity) and lowered cycle times by about 40 percent. Hot runner production eliminated cold runner scrap amounting to about 250,000 euros per year. The conversion to hot runner system for this specific application paid off within only four months.

The combination of increased output and reduced material consumption provides a powerful return-on-investment case for transitioning away from cold runner technology wherever possible. However, mould designers often face the reality that conventional hot runner systems have their limitations.

The limitation of conventional hot runner technology

Despite the obvious advantages of hot runner systems, adoption in very small-part moulding has historically been limited. The primary challenge lies within the manifold itself. Conventional hot runner manifolds are typically manufactured using gun-drilling processes. While effective, this method imposes practical limits on how small the internal runner channels can be made. Larger flow channels result in greater melt volume within the manifold and increased residence time. For applications involving extremely low shot weights, this can create processing concerns, particularly when moulding heat-sensitive or highly engineered materials. As a result, many moulders continued to view cold runners as the safer option for micro and small-part production.