یک رویکرد یکپارچه برای حمایت از طرح های مشترک از ابزار و ماشین آلات و برنامه ریزی فرایند

The configuration of machine tools and process planning problem are traditionally managed as independent stages, where the process plan is designed by considering a number of machine tool solutions available from catalogue. This strategy presents a number of disadvantages in terms of process results and machine capabilities fully exploitation. The current paper proposes an integrated approach for jointly configuring machine tools and process planning. The approach is structured in 4 major recursive steps that eventually ensure the accomplishment of the best trade-off between the machine tool static and dynamic behaviour, the process quality and the resulting economic efficiency. The benefits of the approach have been evaluated for a test case application in the railway and automotive sectors.

The design and configuration of machine tools is instrumental for European manufacturing competitiveness [1]. Coherently with the mass customization principles and the traditional European know how in the field of instrumental goods production, machine tools should result from a configuration process tightly related to the analysis of the families of products and process quality requirements rather than being a standard and rigid catalogue equipment. This makes the machine configuration and the process planning as two steps of the same problem where the machine tool geometric and kinematics features influence the accessibility to the workpiece operations along with the fixturing system configuration and the machine dynamic impacts on the final quality and costs of the workpiece. The relationships between machine tool configuration and process planning have been widely investigated by the scientific literature with reference to the following topics: the evaluation of machine capabilities to statically realize a process plan [2], the execution of a process plan across several resources [3], the energy efficient process planning [4], [5], [6] and [7] and, finally, evaluation of the impact of machine tool dynamic behaviour on the process planning definition [8]. However, the interest of these works is mostly focused on the impact of a specific machine tool architecture and performance on the process planning problem. The current paper presents an integrated approach to support the joint design of machine tools and process planning. The proposed approach is structured in four major steps as illustrated in Fig. 1. Full-size image (19 K) Fig. 1. The integrated approach. Figure options The first step consists in the analysis of the workpiece CAD model. The workpiece is analysed according to the STEP standard [9] through the identification of machining feature (geometrical description of the region of the workpiece to be machined), machining operations (selection of cutting tools, machining parameters and strategies) and machining workingsteps (MWS – association between a machining feature and a machining operation). On the basis of a number of alternative MWSs, Step 1 identifies the MWSs that globally better match the production requirements and machine behaviour. The geometric and technological information related to the family of products together with the data about the production demand and the forecasts about possible product evolutions are utilized in Step 2 related to the machine tool design. The outcome of this step is a domain of general-purpose machine tools that fit the production requirements from both the dynamic and static point of view Steps 1 and 2 are traditionally handled as independent phases as general-purpose machine tools are normally configured with no knowledge of the actual products to machine and the process planning is usually developed starting from an existing machine catalogue. Step 3 regards the dynamic simulation of the machine tool solutions resulting from Step 2 while executing the MWSs identified in Step 1. The dynamic behaviour of machine tools is evaluated against a number of Key Performance Indicators (KPIs) dealing with the energy consumption, tool wear, surface roughness, maximal required spindle power and torque. The KPIs are concurrently relevant to the MWS assessment as they could drive the adjustment of process parameters and to the machine tool design by leading to the tuning of the kinematic and dynamic characteristics. The last step of the approach concerns the selection of one or more fixtures and the definition of workpiece orientations as well as the association of the operations to a given orientation (workpiece setup) [10] and [11]. The outcome of this phase is the generation of alternative process plans feasible from the workpiece quality requirements [12]. Production time and costs are investigated and optimized on the basis of the MWS KPIs. The following section of this work will provide the reader with a more comprehensive description of each step of the proposed approach (from Sections 2, 3, 4, 4.1, 4.1.1, 4.1.2, 4.1.3, 4.1.4, 5 and 6). Section 7 will present an industrial test case considered to evaluate the approach benefits. Section 8 will outline the conclusions and future work.

The current work introduces an innovative approach for concurrent design of machine tools and process planning. The approach is structured as a sequence of steps leading to integrated machine and process solutions that globally optimize the production costs while considering a number of KPIs related to the machine tool static and dynamic behaviour as well as the quality of parts. The benefits of the proposed approach have been evaluated with reference to a test case provided by a supplier of the automotive and railway sectors. The results outline the possibility to develop customized solutions of machine tools and pallets that – compared to traditional resources – lead to a 8% of production cost reduction (involving tool wear costs and the cost of energy) while accomplishing the products quality constraints. Future work will mostly regard two aspects. The first one deals with the need to implement a software infrastructure embedding all the steps of the integrated approach so that the overall process can be automatically executed. The second aspect refers to the methodology enhancement by including a wider number of operation types, cutting tool types and machine tool types.