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Abstract Broaching is a very common manufacturing process for the machining of internal or external complex shapes into parts. Due to the process geometry, broaching tool is the most critical parameter of the broaching process. Therefore, optimal design of the tools is needed in order to improve the productivity of the process. In this paper, a methodology is presented for optimal design of the broaching tools by respecting the geometric and physical constraints. The method has also been implemented on a computer code. 52528
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1 INTRODUCTION Broaching is commonly used for machining of internal or external complex profiles that are difficult to generate by other machining processes such as milling and turning. Originally, broaching was developed for noncircular internal profiles and keyways. The process is very simple, and decreases the need for talented machine operator while providing high production rate and quality. Because of the straight noncircular motion, very high quality surface finish can be obtained. In addition, roughing and finishing operations can be completed in one pass reducing total cycle time. The main disadvantage of broaching is the inflexibility of the process in terms of process parameters. In broaching, all machining conditions, except the speed, are defined by the tool geometry, and thus, once a tool is designed it is impossible to change any process parameters such as depth of cut or chip thickness. This makes tool design the most important aspect of the broaching process. For improved productivity and part quality with reduced process cost, broach tools must be designed properly. In this paper, an approach for optimal design of broaching tools is presented with applications. This approach can be used for optimal design of broaching tools for a given part geometry and material. The optimization procedure has to respect the physical and process constraints. In broaching, usually the profile to be machined into the part is specified. However, it is possible to generate the same profile using many different combinations of broach sections with different tool geometries. Therefore, first of all, the number of sections and the basic tooth profile for each section have to be selected. In addition, tool geometry and parameters, such as tooth rise, pitch etc. for each section has to be defined.
Considering the number of possibilities, there is a need for a practical method for optimal design of broaching tools which is the topic of this paper. Optimization of machining processes has been the topic of many studies for a long time, starting with pioneering works of F. Taylor. Turning was the process under consideration in most of these studies due to its wide use and simpler geometry. Since the relationship between the cutting speed and tool wear was known, i.e. Taylor’s tool life equation, the most common purpose of these studies was the optimization of the cutting speed. Stephenson and Agapiou [1] give the general principles of economics in machining, and explain process optimization using common methods. Many different methods were employed, from genetic algorithms or combination genetic algorithms with fuzzy approaches [2, 3] to simulated annealing [4]. Also, iterative methods [5], or combinatorial methods that use databases [6], have also been used. Combinations of different approaches have also been utilized with a mixture of fuzzy basics [7]. Erol and Ferrel [8] also used fuzzy methods among many others. In most of these studies, the mechanics of the process such as forces, deflections, vibrations etc., other than tool wear, were not included in the analysis. Although there have been many studies on various machining processes, there has been only a few on broaching. The book by Monday [9] is perhaps the most comprehensive source on broaching. The broaching technology including tooling and machines is reviewed, and critical aspects of the process are analyzed. Kokmeyer [10] edited collection of works on broaching demonstrating the effectiveness of the process. Gilormini et al. [11] analyzed the cutting forces on a single broaching section, and compared them to the process forces in slotting and tapping. Sutherland, Salisbury and Hoge [12] presented a mechanistic model for force predictions in gear broaching. Terry, Kami and Huang [13] presented a knowledge based system for optimal design of broaching tools. Sanjeev et al. [14,15] used FEA to analyze the effects of burnishing. Budak [16] evaluated the fir-tree broaching tools used for waspaloy turbine discs based on the force and power monitoring system results.