COMPUTER-AIDED DESIGN Computer-Aided Design 35 (2003) 395±401
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In¯uence of tool path strategy on the cycle time of high-speed milling Manuel Monreal a,1, Ciro A. Rodriguez b,* a
Department of Mechanical Engineering, Instituto TecnoloÂgico y de Estudios Superiores de Monterrey, Av. Eugenio Garza Sada #2501, Monterrey, NL 64849, Mexico b Center for Integrated Manufacturing Systems, Instituto TecnoloÂgico y de Estudios Superiores de Monterrey, Av. Eugenio Garza Sada #2501, Monterrey, NL 64849, Mexico Received 2 July 2001; revised 23 October 2001; accepted 24 November 2001
Abstract This work at ®rst look discusses the in¯uence of the tool path strategy on the cycle time of high-speed milling operations. Experiments and predictions were focused on pocketing operations with a zig-zag tool path, quantifying the signi®cant discrepancy between the programmed feed rate and the actual average feed rate. A mechanistic approach for cycle time evaluation is proposed. The mechanistic model construction is based on the experimental measurement of the machine tool acceleration and speci®c geometric assumptions regarding tool motion. For high feed rates, the proposed approach is capable of capturing the in¯uence of the zig-zag tool path orientation on the machining cycle time. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: High-speed milling; Cycle time; Tool path
1. Introduction In the context of high-speed milling operations, the tool path strategy has a signi®cant in¯uence on the cycle time. This means that, for the removal of the same amount of material, the type of tool motion utilized will produce signi®cantly different results in terms of cycle time. Under these conditions, process planning for high-speed milling operations can be dif®cult. The objective of this work is to establish a methodology for the prediction of cycle time, during high-speed milling operations and for any type of tool path strategy. The paper is organized as follows. First, the machine tool requirements for die and mold production are established, providing the context to measure the cycle time as a function of the tool path strategy. This study is focused on zig-zag milling patterns at different angles relative to the pocket orientation. Experiments show that, under conditions of suf®ciently high feed rate, there is a signi®cant discrepancy between the ideal cycle time (i.e. traveled length/programmed feed rate) and the actual cycle time. Next, the proposed methodology for cycle time prediction is explained. Finally, under conditions of high-speed milling, a good match between actual cycle * Corresponding author. Tel.: 152-81-8158-2056; fax: 152-81-83284123. E-mail address:
[email protected] (C.A. Rodriguez). 1 Tel.: 152-81-8358-1400 x5431; Fax: 152-81-8358-1400 x5433.
time and predicted cycle time is shown as evidence of the suitability of the proposed methodology. The proposed methodology for cycle time prediction is directed towards the end user of high-speed milling technology. Therefore, strong emphasis is placed on the simplicity of the approach and the minimal use of sophisticated metrology equipment. The results presented here are a continuation of previous work in the same topic [1]. The main issue in this work is the discrepancy between the prediction of cycle time provided by the CAM systems (ideal cycle time) and the actual cycle time. At high feed rates, CAM systems ignore the dynamics of the machine tool and therefore are unable to estimate the actual cycle time. While other works have concentrated on improving CAM systems with process considerations [2,3], there has been relatively little attention to the in¯uence of machine tool dynamics on cycle time. 2. High-speed milling for die and mold production Fig. 1 shows a selection of machine tool capabilities for high-speed milling. The machines are classi®ed into three categories: (a) vertical spindle with linear drives, (b) vertical spindle with ball screw drives and (c) horizontal spindle with ball screw drives. Horizontal milling centers are more suitable for pallet automation. Therefore, these milling centers are mainly
0010-4485/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S 0010-448 5(02)00060-X
M. Monreal, C.A. Rodriguez / Computer-Aided Design 35 (2003) 395±401
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Spindle Speed, n (rev/min)
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Copper Graphite
25 Ball End Mill Type solid WC/brazed PCD 2
