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Sakurai S.,Keio University | Aoyama H.,Keio University | Sano N.,Nihon Unisys Excelutions Ltd.
Key Engineering Materials | Year: 2012

As the feed rate of cutting tools is influenced by the quality of NC programs, this causes two problems when cutting freeform surfaces using NC machine tools, one is the feed rate does not reach the specified value, and the other is the quality of the machined surface decreases due to the large acceleration and deceleration of the control axes. One reason for these problems is that the method to generate cutter location data does not take into consideration the sampling time of the NC controller. To improve these problems, the approximation of offset curves with a series of circular arcs has generally been proposed. But conventionally, circular arc interpolation algorithms are complicated and not rational. So, in this study, we proposed two simple NC program generation methods. (1) Approximate the offset form with circular arcs based on the location of the center of curvature. (2) Make the distance between the cutter location points of the NC data an integral multiple of the "feed rate command F × sampling time T". We also confirm the effectiveness of the proposed methods by simulations and experiments. © (2012) Trans Tech Publications, Switzerland. Source

Hokkyo T.,Keio University | Aoyama H.,Keio University | Sano N.,Nihon Unisys Excelutions Ltd.
Key Engineering Materials | Year: 2012

Generally, ball end mills are used for free-form surface machining. When machining curved surfaces with large curvature change using ball end mills, it is necessary to use tools with larger curvature of the cutting edges than the maximum curvature of the surface and minute pick feeds or to change tools for fitting the curvature of one part of the surface. However this causes poor machining efficiency. The curvature of the cutting edge of a flat end mill can be fitted to the curvature of a point on machined surfaces by adjusting the tool posture. Therefore, flat end mills can efficiently cut almost all curvature curved surfaces without tool change. This paper proposes two methods for deciding tool posture and tool path for 5-axis control machining based on minimum cusp height. To decide the tool path, one method defines tool paths along isoparametric curved lines, while the other defines tool paths along curved lines along the minimum curvature direction. The basic system was constructed based on the proposed method, and the effectiveness of the proposed method was verified. © (2012) Trans Tech Publications, Switzerland. Source

Ando S.,Keio University | Ikeda R.,Keio University | Aoyama H.,Keio University | Hiruma N.,Nihon Unisys Excelutions Ltd.
Key Engineering Materials | Year: 2010

Three-dimensional CAD systems contribute considerably to the detailed design processes of products. They are applied to the construction of 3D design models which are also utilized for design evaluation using a CAE system and for NC data generation using a CAM system. Since the functions of 3D CAD systems for constructing 3D models are increasingly being enhanced, they enable designers to easily construct 3D product models without design expertise. In detailed design work, designers are required not only to exactly define product shapes but also to assign attribute information such as dimensional tolerance, geometrical tolerance, roughness, machining process to be performed etc., which are essential for the manufacturing process. However, inexperienced designers often find it extremely hard to determine optimum attribute values and design values. In addition, it is more difficult to construct the required die/mold from the desired product shape taking into account forming errors caused by shrinkage during plastic injection and springback during press forming. This paper proposes a method to automatically assign required attribute information to each part of a designed product, to assist the model construction of a die/mold from a product shape, and to provide design support information on each part of a designed product to a designer. The proposed method is realized by assigning a Function Feature to each part; all the function features proposed in this paper are original. A CAD system based on the proposed method for injection molding and press forming was developed, and results of simple design experiments confirmed the usefulness of the CAD system and function features © (2010) Trans Tech Publications. Source

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