Impact of the manufacturing phase on the life cycle of machined products (2012)

Impact of the Manufacturing Phase on the Life Cycle of Machined Products Nancy Diaz, Moneer Helu, Kevin Ninomiya, David Dornfeld Laboratory for Manufacturing and Sustainability, Dept. of Mechanical Engineering, University of California, Berkeley Abstract Growing global energy demands require manufacturers to implement strategies to improve energy efﬁciency over the entire product life cycle. These strategies must consider the complexity of modern manufacturing systems by evaluating impacts at both the process- and facility-level while also considering the effect of any strategy on part quality to ensure a salable product that meets its intended function. This paper presents three studies that focus on how green machining strategies can be implemented on the shop ﬂoor and how they subsequently affect facility planning and the product use phase. The results of these studies highlight the need for a holistic perspective that emphasizes resource efﬁciency over consumption reduction to provide green products. Keywords: Energy, green machining, product life cycle 1 INTRODUCTION Global energy demand is expected to grow by 53% between 2008 and 2035 [1]. China and India are projected to more than double their energy demand by 2035. Previous literature has shown that the manufacturing phase can have a substantial effect on the environmental impact of a product, particularly when ﬂows beyond electrical energy are considered [2]. This is especially true since manufacturing decisions can have a direct effect on a products use phase impacts. Therefore, we must continue to propose and implement efﬁcient and realistic strategies to reduce natural resource consumption in all phases of a product's life cycle. This paper first characterizes energy in the manufacturing phase for both process- and factory-level assessments. We initially validate the energy model from Diaz et al. [3] for a toolpath with varied MRR [4]. The energy model is then utilized in a facility energy assessment conducted by means of a discrete event simulation (DES) to identify green operation strategies [5]. While it is important to implement green strategies during the manufacturing phase, we cannot ignore the effects of these strategies on machine tool service costs and surface quality. Effects on part quality are particularly important to consider since part quality must remain sufﬁcient to ensure that the product meets its intended function and provides value to the manufacturer and customer. Furthermore, these effects can also impact resource efﬁciency over the entire product life cycle [6]. For example, improvements in part precision generally lead to greater operational efficiency and longer service life [7]. Thus, any change in the manufacture of a part must be holistically considered across the entire product life cycle. 2 VALIDATION OF THE ENERGY MODEL FOR VARIED PROCESS RATES Gutowski et al. [8] showed that the speciﬁc electrical energy requirement of manufacturing processes was inversely proportional to the process rate. Based on this work, Diaz et al. [9]—[10] and Kara et al. [11] developed a method to model the speciﬁc electrical energy of machining centers that will be utilized in this paper. The model was previously used to predict the energy consumed to manufacture parts produced under a constant material removal rate (MRR) with 91.95% to 97.63% accuracy [11]. © 2012 The Proceedings of MTTRF 2012 Annual Meeting 2.1 Methodology To assess the validity of this model for complex parts, we conducted experiments on the Mori Seiki NVD1500 for a toolpath with variable MRR. The electrical energy required for milling was estimated for an inclined spiral design on an ANSI 1018 steel workpiece with ﬂood cooling. Machining occurred over 87% of the total cycle time of 259 seconds. The part design was broken down into 9 features as shown in Figure 1; each feature indicates a change in the MRR. The same part was machined six times to gage repeatability. 2450mm I 88'90“q“ 127.(g9mm Figure 1: Spiral geometry and feature label of part design for energy characterization experiments The MRR as a function of elapsed time was then used to estimate the energy consumption with Equations 1 and 2 for areas of constant (feature x+1 in Figure 2) and variable MRR (feature x in Figure 2), respectively: EC0M.Yl : V * ( k MRR +b) (1) N = N * Atz (k + b * MRRW.) (2) i:I where V is the volume of material removed, k and b are constants to the speciﬁc energy model [10], N is the subintervals per feature, and At the processing time for the feature. For each scenario, the average MRR of each subinterval, MRRaVg‘i, was used to calculate the energy consumed per feature, Em. The energy consumed for part manufacture was thereafter found by summing Eva, 97