Application of Incremental Forming process for high customised medical product manufacturing

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Abstract

Incremental Forming processes have been introduced in the recent past as an alternative to the money consuming stamping technology, when small batches have to be manufactured. Anyway, they introduce some advantages in terms of flexibility and material formability but, also, some problems such as the dimensional accuracy decreasing. In this paper, a particular application is carried out taking into account the development of an innovative technique to produce a customised ankle support. In this way Incremental Forming process has been selected for the sheet profiling, exalting the role that this technology may play when single complex product has to be manufactured. The producing procedure finishes with a measure of the dimensional accuracy that shown a good result for the desired application.

Introduction

It is, by now, a widely diffused opinion that Incremental Forming processes are very suitable when high-customised products have to be manufactured. In fact, due to the very low set-up cost, the use of this technology may be strategic when industries require small batch or single products [1], [2].

The basic concept, in fact, is to avoid any traditional die giving to a punch, a set of punches or other deforming agents, the function to progressively form the final shape of the designed component. This fact fully reduces the equipment costs even if the particular process slowness sharply reduces the advantages in terms of cost when a few hundreds of identical products have to be manufactured. Thus, the Incremental Forming processes offer the possibility to implement a powerful alternative if few products (small lot) have to be produced.

And this possibility becomes a need in those applications in which it is clear that the product has to be unique.

The medical field represents, of course, one of these cases. In fact, even if many products may be classified as similar ones, the natural differences in terms of anthropometrical items of each individual move the research interest through a high customisation, in order to guarantee the best allowable performance of the product.

The study here addressed focuses its attention on the manufacturing of an ankle support, which is made starting from what we can roughly name the “patient geometry”. In other words, a reverse engineering approach has been implemented in order to manufacture the support directly starting from the patient's ankle shape, for ensuring the best correspondence between the obtained support and the patient body [3]. In fact, the clearance that is usually present inside the widely diffuse tutors, chosen to compensate the natural differences between individuals of similar characteristics, may generate some problems in terms of ankle stabilization and it is usually reduced using thick layers of compressible foams or polymers. Anyway, the ankle stabilisation function is partially compromised.

The basic idea, that has guided this work, is to avoid the use of thick filling layers, manufacturing a high-customised support that minimizes itself the clearance between the containing structure and the ankle. Of course, this concept requires a special procedure properly developed that has been set-up by the authors and validated in this work.

In detail, a complete reverse engineering cycle has been performed in order to acquire the patient geometry and to use this information for the manufacturing phase. As production technology, Incremental Forming was the natural candidate since the use of customised dies has to be absolutely rejected, taking into account the need of only one product.

Due to the application of Incremental Forming process, a particular strategy for the best positioning of the shape into the forming frame was performed since the technological constraints have been completely observed. The simpler design way has been obtained subdividing the support into two complementary parts that may be separately formed. Subsequently the single shells may be extract from the respective native sheet by using a precise assessed technique (laser, water-jet) and, finally, the two obtained parts can be assembled to compose the final support, by using traditional banding methods.

Anyway some problems exist in the proposed cycle that, up to now, needs further researches efforts for its better assessing. More in detail, in this kind of application but, in general, in all the operations in which Incremental Forming processes are involved, one of the main drawbacks is represented by the discrepancies between the desired shape and the obtained one [4]. For the ankle support this aspect is strategic and, for this reason, a final measure of the manufactured product part has been carried out at the end of the production step.

The results show a good dimensional precision of the component since the discrepancies, measured comparing all the 3D shape, shown a low value. Then, it can be stated that a contribute in the direction of the assessment of Incremental Forming technology, in those areas in which the differentiation degree between the products is a not negligible need, is given by this work.

Section snippets

Incremental Forming: remarks

Among the different typologies of Incremental Forming processes, the Single Point Incremental Forming (SPIF) represents of course the most suitable from an economic point of view (Fig. 1).

Other typologies have been proposed by the researches in the last years. The most diffuse may be classified into two categories: the first includes all the processes in which a support is used under the sheet, to guide the deformation, inhibiting some degree of freedom. Traditionally, wood structures as well

Design process

Nowadays aesthetics aspects, ergonomic quality and the product customisation are assuming an increasing importance in industrial manufacturing; a great variety of products are designed and produced implementing these concepts. In this scenario, the reverse engineering (RE) techniques play a fundamental role since very frequently there is the need to acquire significant data of existing products. RE potentiality permits to carefully re-build, in a short process time, the so-called “free forms”.

Experimental equipment

A Mazak Nexus 410A work-centre machine has been used for Incremental Forming process run. As far as the sheet material is concerned, a DDQ (Deep Drawing Quality) steel 1-mm thick and 290 mm × 210 mm has been used as raw material. The material properties are shown in Table 2. DDQ steel has been chosen due to its particular formability and strength. As alternative material an aluminium alloy can be utilised even if the initial thickness has to be greater then the steel one for avoiding tearing

Conclusions

Even if Incremental Forming is still a new and not fully assessed process, some interesting applications start to appear in the world scenario. In this paper, a particular application has been developed highlighting the point of strength of such a technology. In fact both its simple integration with other RE techniques and its high flexibility, allowed manufacturing a medical device in an easy, fast and effective way.

A high-customised ankle support has been manufactured obtaining a product with

Acknowledgements

This research is funded by Italian Ministry for University and Research (MIUR). The authors would like to thank Mr. F. Pulice and Dr. G. Leggio for their technical contribution to this work.

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