# Design and Verification of a New Fixture for Machining of Porous Blocks for Medical CAD/CAM Systems
## 1 Introduction  
Taking into account the rapid technological development that is primarily focused on production with maximum efficiency and minimum costs, the role of fixtures today presents one of the key elements in this whole process [1, 2, 3]. Their primary role is the accurate locating and clamping of objects in defined working positions during the various processes that take place, such as machining, measurement, etc. [4, 5]. Therefore, their dynamic behavior has a direct impact on the accuracy, quality, and cost-effectiveness of the machined workpiece [6, 7]. By being able to provide several key advantages, such as automation of many different tasks, speed-up production times, increasing precision for performing tasks with a higher degree of accuracy and precision, and allowing flexibility for handling a range of different tasks, fixtures today present production equipment which can contribute to an efficient production process [8]. However, with the natural progression of these fixtures through their adaptability and flexibility that they provide, in addition to their standard use in the machining industry, their application has also been extended to other sectors such as medicine, dentistry, etc. [9, 10, 11]. Also, the application of finite element method (FEM) analysis has a wide use today, and as such, has found its way into medical applications as well, such as dentistry [12, 13], maxillofacial [14], or cranial reconstruction [15]. By providing numerical results in a virtual environment, they are providing an immense contribution towards a better understanding of how different processes behave under certain environments. Biocompatible porous blocks (also referred to as scaffolds) can be made using several different techniques such as solvent casting/particle leaching, thermally induced phase separation (TIPS), electro-spinning, gas foaming, and additive manufacturing [16, 17, 18, 19]. Machining of various reconstructive anatomy such as grafts or implants from these small to medium size biocompatible porous blocks still presents a challenge, as they are usually manually shaped. However, this drawback has some limitations regarding the complexity of the implant that can be shaped, but also adequate fit of the shaped implant to the site. The application of CAD/CAM systems eliminates this drawback, as virtually any shape can be manufactured while maintaining the perfect fit between the graft/implant and the recipient site for improved integration [20; 21]. The application of fixtures in the field of medicine today includes their wide application in surgery, diagnostics, rehabilitation, and for research purposes as well [22]. In each of these areas, fixtures have become a key factor in achieving high standards of accuracy and success in various medical procedures. While in rehabilitation, fixtures enable the stabilization and support of different orientations [10], they have also found their use in virtual environments where haptic virtual fixtures (VFs) are being used for force feedback mechanisms that enhance human performance, increase accuracy, and reduce the time taken to perform certain tasks [9]. Design of the personalized stereotactic fixture is also developed which is being used for implanting depth electrodes in patients where it allows surgeons to precisely guide instruments and reduce patient trauma [23]. Other applications of fixtures are also for manufacturing parts with thin ends (like the hip joint) by providing support during machining [24]. They are also being used for optimization tasks in cranioplasty [25], and when it comes to the production of medical equipment fixtures have been also used for the production growth of different medical equipment as well [11]. With the rising use of additive manufacturing (AM) technologies, additively manufactured fixtures for bone measurements are also being developed [26], as well as for the treatment of amputees [27].