توسعه و تجزیه و تحلیل عملکرد از طرح های کمی بیل زدن جدید

The purpose of this work is to present the development and experimental performance assessment of a new generation of spade drill bits. Rigorous point geometry and drilling force models that describe the topology of the drill and its cutting behaviour have guided the development of these new drills with unique topological features. It is shown, both analytically through simulations and through a systematic experimental study, that the performance of the newly developed topologies exceeds that of the commercially available designs. The new spade bits yield lower thrust and torque over the whole range of pragmatic operating conditions.

The spade drill bit is a very widely used tool for rough drilling in non-metallic materials in general and in wood and wood based products in particular. Its most widespread use is encountered in the home construction industry, predominantly for plumbing and electrical installations. A typical spade bit, the basic design of which has not changed for decades, is shown in Fig. 1 along with its major topological features. Moreover, spade bits have not received any attention in the technical literature, yet there is a pressing need to improve the performance of these tools. This need is dictated by the almost exclusive use of hand-held battery-operated cordless drills in conjunction with spade bits. The use of hand-held drilling units imposes the need to improve the performance of these tools in two respects: (1) reduced power consumption in order to prolong battery life, and (2) reduced thrust force to reduce operator fatigue. This, in turn, necessitates the examination of the suitability of the existing ubiquitous design and of the possibility of developing new bits with enhanced performance. Full-size image (4 K) Fig. 1. The spade bit. Figure options The aim of the present paper is, therefore, to develop new spade bit designs that outperform the tools currently on the market. In quantitative terms, in light of the above-stated requirements, performance will be judged in terms of the magnitude of drilling torque and thrust. The task of developing more effective designs will be based on a systematic approach, rooted in a sound theoretical foundation consisting of two essential components. The first is a thorough understanding of the geometric and manufacturing characteristics of spade drills, while the second pertains to the ability to predict their cutting mechanics related behaviour. The geometry of a generalized spade drill is shown in Fig. 2[1] and [2]. The definition of the major cutting edge rake surface in the form of a helical surface has allowed for a great deal of flexibility in defining different spade bit topologies using the same analytical model. The conventional spade bit, based on a flat/planar rake surface, shown in Fig. 1, is just a special case of this general topological representation. Zhao and Ehmann [2] have formulated the complete geometry of this drill as well as the geometry and kinematics needed for its manufacture. Full-size image (12 K) Fig. 2. Generalized helical spade bit geometry. Figure options In regard to cutting performance, Zhao and Ehmann [3] have developed a mechanistic model for force and torque prediction throughout all phases of the spade drill’s penetration into the material. The model includes the cutting actions of the chisel edge, drill tip and of the major cutting edges. The geometric and force models, together, have facilitated the development of a comprehensive software package that allows the simulation of all aspects of the spade drilling process [1]. This software will be used as the basis for the developments to be reported in this paper. In the subsequent sections, the design decisions and analysis of new spade drills will be outlined and their performance experimentally confirmed.

Based on the above reported developments and comparative performance analysis of the newly designed and commercial spade drill bits, the following conclusions can be drawn: 1. The newly formulated generalized helical drill bit allows for a high degree of flexibility in defining novel topologies that have desirable performance characteristics. 2. The mathematical models of the bit’s geometry and cutting performance constituting the basis for the simulation/design software used in these developments predict spade bit behaviour with a high degree of accuracy. 3. Four simple spade drill topologies were identified, designed, manufactured and evaluated. 4. The developed prototype bits and three commercial bits were compared in terms of their performance. Overall, most of the prototype bits have yielded a better performance in terms of both torque and thrust magnitudes than the commercial bits. 5. The most desirable topologies for the development of the final designs of better performing spade drills were identified and discussed.