# Investigation of the Machining Stability of a Milling Machine with Hybrid Guideway Systems
## 1 Introduction  
For satisfying multipurpose or specific industrial applications, most of the modern milling machine centers nowadays have been designed and constructed by different modularized main components [1]. In the configuration of the machine tool, the arrangement of linear feeding mechanism plays an important role in determining machining performance because the various linear elements or other joints are weaker links of different structural components [2; 3]. Although modularized design concept brings various machine configurations under consideration, evaluation of dynamic performance of the candidates that can satisfy the required performance is a perquisite for fabricating the prototype [4; 5]. However, the feeding mechanism of the control axis has been verified to greatly affect the structural dynamic characteristics and machining stability [6]. The joints in the guideway system cannot be treated as a rigid interface; on the contrary, they form weak links between components and greatly affect the overall structural characteristics of the assembled machine [7; 8]. As a consequence, the modeling of an interface and the identification of the interfacial characteristics are of importance in the dynamic analysis of a machine tool structure. Currently, the horizontal milling machine with moving column has been constructed to achieve multiple machining functions. The configuration of the feeding mechanism is considered a dominant role for innovative design of such kind of machines. Generally, linear guides with rolling balls are appropriate for light duty milling machines, while linear roller guide moduli or sliding guideway systems were adopted in heavy duty milling machine to undertake more loads in machining. Essentially, each of the various guideway systems possesses different kinematical and dynamicproperties, which may thus bring the machine tool to demonstrate different dynamic performances. Research studies [9; 10] have shown that a rolling guide exhibits different vibration characteristics depending on preloaded amount. Regarding the sliding contact guide, the contact stiffness of a sliding surface is the function of surface finish, pairing of contact material, and interface pressure distribution [11]. The interface pressure was also verified to be an important factor affecting the contact stiffness and the machining performance [12]. The purpose of this study was to analyze the machining stability of a horizontal milling machine with hybrid guideway systems which were assembled with linear roller guides and sliding guides with coated antifriction layers. Currently, the finite element approach has been recognized as an effective tool in modeling the machine tool, which can accurately predict the dynamic behavior of the prototype designs without physically building any parts. This approach of designing prototype machines in software has been termed virtual prototyping [13; 14]. To be a realistic model for assessing the frequency responses of the milling machine, a finite element model incorporating the machine frame with a spindle unit was a prerequisite. Using the FE modeling approach, [PERSON] _et al._, [15; 16] demonstrated the dynamic compliance of the spindle to vary with the changing of the machine configuration. Various factors, such as the spindle bearing preload or structural geometry, influencing the FRFs at the tool tip were also investigated [17; 18]. The optimization of the machine tool design has been studied by incorporating the FE models for full machine analyses with the consideration of machining stability in process [19; 20]. Studies of [PERSON] _et al._, [21; 22] found the variation of the tool point dynamic response with the change of milling, which further caused great influences on the stability lobe curves. Their study also suggested that a precise estimation of the natural frequencies is of importance for lessening the uncertainty of the stability lobe curves.