Living proof: Mouldmaking brings innovation to medical manufacture

Schöttli explains how clever mouldmaking solutions help meet the growing demands of medical manufacturers.

The growth of the world's population, increasing urbanisation, aging societies, growth of emerging market accessibility to healthcare service and increasing self-medication mean the demand for medical consumables continues to rise.

As a result, the productivity requirements that must be met by manufacturers of medical consumables are also rising. Manufacturers are caught between the conflicting priorities of ever-increasing demands from customers in terms of quality and reliability, and the constant pressure to reduce costs.

Manufacturers have limited production space, the costs of which is increasing. This has become an important factor in growth markets such as China and has created a demand for increased productivity per square metre of production space, coupled with higher demands in terms of production volumes and output.

In recent years, medical manufacturers have countered this trend by increasing demand for compact solutions that yield higher productivity. At Schöttli, a Swiss mould manufacturer acquired by Husky Injection Molding Systems in 2013, those requirements are met with innovative designs such as compact side gate solutions and stack mould technology.

Integrated side-gate solutions meet the need for high quality

In the field of medical engineering, many components are required in increasingly large quantities, including syringe barrels, syringe plungers, IV set components, connection adapters, insulin pen components and more. There is also increased demand for higher productivity per square metre of production space and growing requirements on production volumes and output, as well as the need for greater efficiency or profitability.

Due to its compact size and sprue quality, a side-gating variant is generally used for the high-cavitation injection moulds that are required to produce these components. Gating systems of this kind are now supplied by a variety of manufacturers. There is no such thing as an all-round, multi-purpose side-gating solution. In the past, a range of concepts were therefore developed and optimised for specific application areas or even for individual applications.

Schöttli has also developed various side-gating systems to its range, enabling the mould manufacturer to cover many different medical applications with its own systems.

Schöttli side-gating moulds use different drop concepts for each application. As a result, the number of drops varies between one and six for the production of injection cylinders, needle holders, needle holders for insulin pens, connection adapters, etc, depending on size, number of cavities and installation situation.

In the manufacture of injection pistons, there is generally no space for a two-arm or multi-arm star drop in the compact mould. Schöttli therefore offers a "hot edge" drop. This side-gating concept is designed for the specific mould concept and is more compact and therefore more suitable for applications such as injection pistons.

According to customer requirements, injection moulds without side gating can also be equipped with a valve gate as a gating variant for a variety of medical applications, such as petri dishes. Valve gates are also particularly suited for a range of materials such as TPE or low-viscosity plastics. This allows for a particularly clean gate, but is not always possible for reasons of space.

One further application example that does not use side gating is needle protection caps that are directly injection moulded. In this case, compact drop holders with up to ten drops are used, ensuring excellent heat transfer.

These side-gating concepts have their limitations, such as when more challenging plastic materials like PC, PA or PET are used. The processing temperature window for PA is very small, for example, and the total thermal capacity of PC and PET sets tight constraints.

Precision stack moulds double output

With this gating technology, Schöttli’s compact mould design opens up potential to optimise and increase production. With the aim of increasing the output rate of a production unit and in addition to the use of multi-cavity moulds, the capacity of an injection moulding machine can be doubled by using stack moulds with two separating layers within a single mould. These systems, which use two mould parting surfaces within a single mould, achieve this with the same mould mounting surface and almost the same clamping force. As a result, production efficiency is greatly increased – at Schöttli, the proportion of stack moulds manufactured is now more than 30%.

As with conventional moulds with very deep mould halves, the alignment of the individual mould segments in stack moulds is crucial to the quality of the injection-moulded parts and the lifespan of the mould. At the commissioning stage, the manufacturer shows customers how they can align moulds to achieve an optimum production flow. The moulds include systems that support the customer, helping them to precisely configure and check the moulds, and to continually monitor the production process and make adjustments: monitoring systems with sensors, for example, helps ensure that mould halves are optimally aligned during the injection moulding process. The sensors record and evaluate data to detect possible deviations at an early stage.

Increasing electrification in the injection moulding process

The trend towards electrification in the injection moulding process is noticeable in the medical market, with an increasing proportion of fully electrical machines. The use of electrical drive concepts is also increasing for moulds. Clearly defined pathways within moulds allow for quick, efficient and repeatable sequences. The advantages are clear — in the sensitive medical market, many systems operate in clean rooms where oil-free moulds contribute to a reliable, particle-free production process. Furthermore, electrical drives require less energy and can be integrated into existing control systems. Programmable control devices allow movements to be triggered independently and in parallel. Using the shortest possible reach and stroke distances within the moulds leads to a reduced cycle time. The possibility to limit the load and monitor torque reduces wear and tear and increases the service life of the mould.

Complex system with ease of maintenance

Although you may consider stack moulds, unscrewing technology or side-gating technology as complex, it does not mean that manufacturers require a complex, demanding set of maintenance requirements.

In applications involving complex cylindrical or conical connection pieces, such as a needle holder for an insulin pen, the pin protection system allows for reliable and accurate centering of the extremely thin core and optimises system reliability. As this solution also offers the ability to retract the entire core after the mould opening and to only move the core into the injection position field once clamping force has been built up, it prevents any risk of damage that might be caused by bending or even breakage. The benefit of making these cores, as well as drop-side threaded cores, accessible for simple handling and improved availability from the rear of the injection mould directly to the injection moulding machine, is made possible by the individual hot runner distributor design. Schöttli hot runner systems are individually designed for specific applications.