Breaking the mold: ultrasonic molding & product design

Enric Sirera, Ultrasion, explains how ultrasonic forming has come of age as the technology of choice for OEMs looking to innovate and push the boundaries of product design.

Medical device OEMs face numerous challenges, not least in the development of ever smaller products and components with greater functionality. The miniaturization of medical devices is being driven by the demand for less invasive interventions and the cross-industry advance towards cheaper and lighter products.

There are certain areas where demands continue to exist for effective parts that are as small as possible, for example in various in vivo diagnostic applications such as embedded sensors, in the development of intravascular ultrasound catheters, and in numerous microinvasive technologies to treat a variety of chronic conditions Diseases.

Regardless of whether product designers focus on such innovative developments or seek miniaturization in other areas of medical device development, product design parameters are often limited due to the nature (and availability) of inexpensive manufacturing alternatives.

In the field of plastic medical device manufacture, until recently, OEMs have faced manufacturing processes that are iterations of technologies that have been used in the manufacture of plastic products on a larger scale for decades. There are now plastic micro-injection molding technologies that enable the production of smaller, more precise plastic parts. However, they are still based on traditional screw, cylinder and heating tape technology that has been around for decades. The basic process of putting plastic pellets in a hopper, melting them in a heated cylinder, and then injecting them into the mold (often through a cold runner system) has remained the same.

Injection molding at any level has inherent disadvantages in terms of waste of materials, energy consumption, and expensive tooling – disadvantages that are exacerbated as the mold size decreases.

In recent years, ultrasonic molding technology has become commercially available that overcomes these drawbacks, but is critical to medical device OEMs. It also opens up areas for innovation as it adds beneficial properties to the molten plastic and allows OEMs to design and manufacture longer. flatter, thinner, more functional and increasingly complex micro-parts than previously possible. If you look at “Design for Manufacturing” (a phrase often heard when discussing small plastic parts), ultrasonic forming makes it possible to write a new chapter as the boundaries of what is possible have changed.

The unique properties of ultrasonic forming

Four years ago, Ultrasion introduced the industry’s first ultrasonic precision molding machine. Since then, this ultrasonic forming has been the “go to” technology for medical OEMs (and indeed OEMs in all areas where precision and repeatability are critical) when the required parts cannot be made with traditional precision molding machines.

In the precision forming field, material degradation is possibly the primary concern for plastic part manufacturers. Material degradation is a product of the dwell time, and the dwell time itself is a product of the screw barrel and heater band configurations found in all conventional molding technologies. Ultrasion’s ultrasonic precision molding technology was developed primarily to overcome the problems associated with material deterioration by eliminating dwell time.

To achieve this, the technology was built from the ground up without screw barrels and heating tapes, and instead of heating the material before injecting it into the mold, it was melted in situ in the mold right on the gate, and only the amount of material needed per shot has been processed. This reduces the thermal history of the plastics to milliseconds, drastically reduces waste (since only the amount of material required per shot is processed) and makes rinsing the material superfluous.

After addressing the issues of degradation, it was also found that ultrasonic processing of polymers led to other benefits.

The key to this was that ultrasonic melting dramatically reduced the viscosity of the polymer being processed. In most cases, ultrasonically fused polymer is almost the consistency of water and this allows for much better flow through the mold using dramatically reduced mold pressures.

Today, as technology has advanced, the advantages of low pressure forming are key to the success of ultrasonic precision forming. Ultrasion’s technology uses molding pressures between 250 and 400 bar compared to the typical 2000-2500 bar used in conventional precision injection molding machines.

The possibilities that this offers manufacturers of precision plastic parts are obvious. A variety of overmolding and insert molding applications can be accommodated using ultrasonic molds that would be impossible with conventional molding machines. In addition, by using greatly reduced molding pressures, manufacturers can shape extremely delicate core pins or tricky core pin configurations that would deflect or break under normal molding pressures.

The advantages inherent in ultrasonic forming are best recognized in the precision forming space, rather than on a large scale, and the company is in the process of expanding its ability to accommodate larger shot sizes, but the process above is unlikely to be anywhere near beneficial 20g shot sizes. It was never designed to be made to make bumpers!

The first commercially manufactured machine on the ultrasonic forming platform was the Sonorus 1G, which could take a maximum shot weight of 2 g. This machine has been successfully sold to numerous OEMs in the USA, Europe and the Far East. However, there was demand from the industry for a machine that could accommodate slightly larger shot sizes. Therefore, at the K Show 2016, the company presented the second version (the Sonorus S210 machine) with a maximum shot weight of 5 g.

Ultrasion offers its customers a unique offer. Any machine purchased can be designed to order, customizing the basic ultrasonic forming platform to accommodate different shot sizes, different sonotrode sizes, different amplitudes, different frequencies, etc. It is also process optimized to suit specific materials used in specific applications when this information is shared by the customer. This ensures that the delivered machine is manufactured so precisely according to customer specifications.

By increasing the processing weight that can be processed, ultrasound can be used in a significantly larger number of applications across all industries. Coupled with the fact that the technology can process all materials with equal ease, including the tricky and high temperature melt grades of PEEK that are widely used in medical applications, it’s easy to see why ultrasonic forming has made a name for itself and a valued one Alternative to traditional molding technologies.

Summary

Ultrasion’s precision molding technology represents a new and innovative approach to the manufacture of microplastic parts and, as an alternative to traditional precision injection molding technologies, offers significant advantages in terms of stimulating innovation as it creates parts that are not possible with conventional molding machines.

The type of process and, in particular, the reduced viscosity properties that ultrasound can achieve as a flux, open up the possibility of part construction and part properties that were previously unattainable. This is where the interest Ultrasion is drawing from OEMs across the industry, particularly in the medical device and microfluidics sectors, is focused.

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