Journal of Engineering and Technology

: 2015  |  Volume : 5  |  Issue : 1  |  Page : 14--18

A Paradigm to Produce Customized Ankle Support Using Incremental Sheet Forming

Vishal Gulati, Sumit Kathuria, Puneet Katyal 
 Department of Mechanical Engineering, GJ University of Science and Technology, Haryana, India

Correspondence Address:
Vishal Gulati
Department of Mechanical Engineering, GJ University of Science and Technology, Haryana


This paper presents a paradigm to produce customized ankle support through the use of reverse engineering (RE) process, which uses the patient«SQ»s scan data to an optimal form using a computer-aided design (CAD) system and then transferring the three-dimensional CAD model to Incremental Sheet Forming (ISF) technique for the production of tangible prosthesis product. This work is in the direction of forming of such a customized ankle support that minimizes the gap between the implanting prosthesis and the ankle. Such type of products may be prefabricated or customized. Prefabricated products are manufactured according to the standard sizes of different persons and customized are fitted after observing the patient«SQ»s computed tomography scan. Prefabricated products do not guaranteed that the product will fit or not to the geometry of patient. On the other side, customized products provide more comfort and satisfaction than prefabricated products. RE design process has been implemented in order to acquire CAD model from the patient«SQ»s scan data and to use this information for computer controlled layered manufacturing technique like ISF.

How to cite this article:
Gulati V, Kathuria S, Katyal P. A Paradigm to Produce Customized Ankle Support Using Incremental Sheet Forming.J Eng Technol 2015;5:14-18

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Gulati V, Kathuria S, Katyal P. A Paradigm to Produce Customized Ankle Support Using Incremental Sheet Forming. J Eng Technol [serial online] 2015 [cited 2019 Jan 24 ];5:14-18
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 1. Introduction

Injuries in the lower limb parts are common and generally seen in the knees and ankles. Due to injuries, these parts get damaged and cannot work properly, so permanent replacement of these body parts with artificial parts becomes necessary. These artificial parts are called prostheses in the medical field [Figure 1]. There are two options available in the market for having such prostheses products: Prefabricated and Customized. Prefabricated products available in the market are developed according to the ordinary sizes of body parts. On contrary, customized products are patient specific and developed from computed tomography scan of patient's anatomy. However, customized products are more pleasurable and comfortable as compared to prefabricated products. Moreover, due to the anthropometrical differences between each person, prefabricated products sometimes do not suit the patient's anatomy and may not fit the geometry of the patient. Hence, the need of customization in the medical field is necessary, particularly in the development of prostheses products. Mavroidis et al. [6] also described in his work that custom-fit products are superior to prefabricated devices.{Figure 1}

Although, a lot of work have already been carried out to produce customized prostheses using three-dimensional scanning in conjunction with Rapid Prototyping (RP), but this work is towards the development of customized freeform surface like the surface anatomy of human ankle that combines three-dimensional scanning with incremental sheet forming as it is more advantageous over RP in terms of time, cost, and life, particularly in bio-medical field. Jeswiet et al. [5] and Schaeffer et al. [1] have shown some of the medical applications of the ISF process. ISF is more strategic for small batch or single product while RP is mainly a mass production technique which uses the punch and dies system. ISF denies the deforming tools (punch and die system) and hence it is a time-saving technique. It offers the possibility to implement with low set-up cost as it produces a single customized product by avoiding conventional deforming tools. It also offers the possibility to produce longer life of the products as these are mostly made up of metals like stainless steel, titanium, aluminum alloy, etc. However, it may lack in terms of surface smoothness, but this disadvantage has been minimized when forming the metal with the use of proper lubrication [8] .

This paper presents a paradigm to produce customized ankle support through the use of Reverse Engineering (RE) process which uses the patient's scan data to an optimal form using a Computer-Aided Design (CAD) system and then transferring the three-dimensional CAD model to ISF technique for the production of tangible prosthesis product [2],[3] . This work is in the direction of forming of such a customized ankle support that minimizes the gap between the implanting prosthesis and the ankle. The basic idea here is to avoid the use of thick filling layers between the containing structure and the ankle [4] . Although, Ambrogio et al. [4] has already developed a customized ankle support using three-dimensional scanning with ISF, in which the ankle CAD model is divided into two separate symmetrical parts and then joined by using simple welding technique. Hence, there is a chance of occurrence of residual stresses and change in the properties of the sophisticated biomedical product. Therefore, for negotiating the existing method, a modification has been carried out in the present work during CAD modeling of ankle part to further produce a complete prosthesis product rather than in two parts with the help of ISF process.

The existing work used a deep drawing quality stainless steel as a forming material. In this work, another deep drawing quality material Aluminum alloy with the grade AA6063 [composition and properties shown in [Table 1] and [Table 2] has been used. It has a high ductility, malleability and also has the biocompatible properties. In 2012, P.D. Eksteen et al. and Van der Merwe [7] discussed the manufacturing of customized product of knee implantation with the use of titanium sheet.{Table 1}{Table 2}

 2. Design Process

Reverse engineering design process has been implemented in order to acquire CAD model from the patient's scan data and to use this information for ISF. Firstly, a three-dimensional laser scanning method is carried out to scan the ankle part [Figure 2]a. Three to five scans are to be taken for complete scanning of the ankle. Millions of point clouds are generated in the irregular shape of ankle geometry. Then after deleting some unwanted data of point clouds, remaining point clouds come in the form of ankle [Figure 2]b. As it is necessary to generate surfaces from the point clouds for converting the point cloud format into a three-dimensional CAD model, therefore in the next step, the surfacing is done on CATIA V5 CAD system. This is achieved after generating three-dimensional curves by joining points through each other and then merging all the curves. Actually, the surfaced model [Figure 2]c is CAD model, but this model doesn't have any thickness. In order to create tool path generation and perform force analysis of the ankle, some thickness is required. Therefore, a specified thickness is provided to the ankle model, and this thick surfaced model [Figure 2]d is the complete three-dimensional CAD model of the ankle. Finally, in this work, a modification in the CAD model is conceded to take away the disadvantage of occurrence of residual stresses in the material of the ankle due to type of the production process implemented earlier [4] .{Figure 2}

As in computer numerical control (CNC) milling operation, tool cannot be operated on angle more than 90°, so in earlier work the CAD model was separated into two halves and then manufactured. In this work, a modification is carried out on the lower back portion of the ankle (removed some portion) and forward portion (increased near the toes) in order to just produce a complete prosthesis product using ISF process. This production process takes less time and involves low cost as compared to the production in two parts then joining into the complete piece.

 3. Production Process

The CAD model of ankle support is further used to create information like tool path for computer controlled fabrication. MASTERCAM software has been used to create a tool path for feeding it to the three axis CNC vertical milling machine (DMC70V) for employing ISF. The spiral toolpath is considered as it is an optimized form of the tool path among other techniques [9],[10] . The manufacturing parameters are considered as: Tool radius = 12 mm, step size = 0.25 mm, spindle speed = 250 rpm, feed rate = 1000 mm/min and lubrication = greese.

A forming tool [Figure 3] and a clamping system have also been designed and fabricated to implement ISF for production of the ankle support. The forming tool is made of high-speed steel material with hemispherical head of diameter 12 mm. The diameter of a ball-head is selected 12 mm because 10-15 mm diameters are best suitable for the deep forming operation.{Figure 3}

The CNC machine to perform forming made use of a dedicated clamping system made up of mild steel material as shown in [Figure 4]. The complete clamping system is composed of a static frame, fixed on the machine working table, the blank holder, to hold the sheet over the backing plate [Figure 5]. The whole apparatus is clamped to the bottom corners of the working table of the CNC. The working area of the forming process was 240 mm by 240 mm.{Figure 4}{Figure 5}

After all the production formalities till the tool profiling, the parameters taken during ISF are shown in [Table 3]. The production process has been kept at quite slow speed in order to produce good surface as a slow process controls dimensional accuracy and also diminishes the spring back effect. The formation of the ankle foot part took about near 45 min and generated tool path is shown in [Figure 6]. The Interior and exterior part of ankle support produced from Incremental sheet Forming process is shown in [Figure 7].{Figure 6}{Figure 7}{Table 3}

 4. Analysis of Ankle Foot Part

In order to investigate the load bearing capability of the ankle support, force analysis is carried out on the CAD model of the ankle part [12] . This force analysis is done in the ANSYS workbench; static structural analysis is chosen in this workbench. For this analysis system, some properties related to ankle and material is required [Table 4], which are considered from past literatures [11] .{Table 4}

In this part of the ankle support, firstly geometry and related properties of the material are imported. Geometry is imported in either Initial Graphics Specification or Standard for the Exchange of Product data format, which are supported by ANSYS workbench. Meshing operation is also done on the ankle part for the applying load and fixed support. Meshing is done on this part after giving a certain thickness (2 mm) [Figure 8].{Figure 8}

After the force and fixed support applying, come to the solution portion, which is in the form of Von-misses stresses and total deformation. Three different loads 1000 N, 2000 N, and 3000 N are applied with Young's modulus values and a Poisson's ratio value. Results come out in the form of stress and strains with colored graphs, which shows the different condition of the ankle part with different values [Figure 9]. Then from analysis of different loads, it has been seen from the table that which load is safe for the ankle part.{Figure 9}

From [Table 5], it is observed that minimum stress and strain occurs at load of 1000 N and 32.2 GPa, Young's modulus. The value of Young's modulus has no effect on the equivalent (von-misses) stresses. The strain value is changing with the change in Young's Modulus. This is due the fact that a single material mainly possesses the common value of Young's modulus. From this, it is concluded that 1000 N is the safest load for the Ankle Foot Part Prosthesis.{Table 5}

 5. Concluding Remarks

As ISF is still not a fully assessed process, some interesting applications start to appear in the world scenario especially in the medical field. In this work, a paradigm is presented through which the RE technique has been implemented with ISF process. This work presents modification in the earlier work [4] for the easy tool path generation of the CAD model. In addition, a force analysis is carried out which enlightens that which product is better for which type of patient and what material should be used for the different patients. It is also revealed RE in conjunction with and ISF form a hybrid mixture that can form any shape or design.


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