Bükme ve kesme kalıpları, kesme kalıplarının bilgisayar destekli tasarımı

Abstract

Seri üretimin en önemli araçlarından olan sac metal kalıpçılığının kesme ve bükme kalıplarının nasıl yapılacağını, kalıp parça boyutlarının nasıl belirleneceği tezde anlatılmaya çalışılmıştır. İlk grupta kesme kalıplan ele alınmıştır. Kesme kalıplan ile ilgili önemli olan kesme boşluğu, boşluk açısı gibi kavramlar ve bunların etkisi ile üretilen parça üzerinde oluşan durumlar anlatılmıştır. Daha sonra kesme kalıpları sınıflandırılmıştır. Gelen adımda ise kalıp parçalan tek tek ele alınarak, nasıl boyutlandırılacağı, boyutlandırılırken nelere dikkat edileceği üzerinde durulmuş ve şekiller ile gerekli boyutlar için tablolar verilerek desteklenmiştir. İkinci grup olarak üçüncü bölümde bükme kalıplan anlatılmaya çalışılmıştır. Daha sonra V bükme kalıplan ve U bükme kalıplan tanıtılmış ve kalıp parçalaman boyutlarının nasıl bulunulacağı anlatılmıştır. Üçüncü grup olarak dördüncü bölümde Visual Basic'de plaka kayıtlı kalıp parçalarının boyutlandıran bir bilgisayar programı yapılmıştır. Program yapılması istenen parça durumuna göre kayıt plakalı, kalıp parçalarının boyutlarını resimlerini vermektedir.

Die design is very important at industry. Mass production is obtained by die. Quality of products does not belong to people. In this thesis, it is described shearing and bending die. In addition to it is prepared a computer program about shearing die. This program gives the dimensions of tools of die. While preparing this program, Visual Basic is used. Shearing consists of three stages. At the first stage, punch touches on the sheet and applies force to sheet. At the second stage, punch and die plate start to cut the sheet. The force applied to the sheet by punch starts to increase. The sheet is pushed into the hole of the die plate. At the third stage, punch plunged 60 % of the material thickness to the sheet. End of this stage sheet is broken. At shearing die, die clearance is very important case. The die clearance is clearance the die plate and punch. It effects the blanked and pierced surface. There is no general rule for selecting the clearance value since parameters are very. But there is table for selecting the clearance value. The clearance value in table depends on shear stress of material which is used for producing the product and thickness of materials. In addition to there is formula for finding the die clearance value like below Sp=2x0.005xSx fa (1) Sp = Die Clearance ( mm ) S = Material Thickness (mm) rb = Shear Stress of Material ( daN/mm2 ) XIX The blanking or piercing clearance can be selected on the appearance of the blanket or pierced surface, inaccuracies, further operations, and functional aspects. If no special conditions are placed on the blanked surfaces, the blanking clearance is generally chosen to result in minimum force requirements. The die clearance is applied the punch or die plate. If it is made piercing, the die clearance is applied the die plate. If it is made blanking, the die clearance is applied the punch, that is, dimensions of the punch is made little as the die clearance. Figure 1 shows the die clearance. -*.- Punch _^ Die Plate Figure 1. The die clearance The relief angle is the second important case at shearing dies. The relief angle in the openings of shape Figure 2 reduces the friction between the cut piece and die plate and faculties pushing the cut piece through the die opening. Guidelines concerning the height (or thickness) of the cylindrical piece and the relief angle to be selected very considerably. % I _L 22 (a) a (t>) " (c) Figure 2. Opening or hole designs in die plate Punches and die plate are made in one piece when it is feasible from both the economically and the manufacturing standpoints. Split tooling is used for pieces with larger dimensions. In this case the various tool elements are made separately and screwed or plotted onto the supporting plate. Split tooling is also uses in cases where a grinding operation is required for the tooling and the operation can not be carried out in the unsplit condition. An example of the tooling used for stator and XX rotor shown in Figure 3. In this case the punch and die plate are made from separate pieces and joined together. Figure 3. Sheet utilization in blanking various pieces for stator and rotor The selection of material for punches and die plate is generally based on economical considerations and hence on various factor. The important factors are wear resistance stresses acting on the tooling, and workability of tool material. Die plates and punches made from steel are generally hardened if more than a few pieces are to be produced. Bending belongs to the most widely applied types of sheet metal forming. It extends from the mass production of minute work pieces to the fabrication ofsagle parts in ship building and the construction of large machinery. I n addition to sheet material, pipe, strip, wire, and base stock of varied cross sectional shapes formed by bending in a multitude of processes. In the majority of cases bending is carried out at room temperature. However, for large cross sections forming at elevated temperatures is preferred in order to limit forming forces and to avoid embrittlenient by work hardening. Die bending involves bending of the sheet between punch and die plate until the work piece contacts the side of the die. Bottoming of joining, that is, pressing the sheet flat against the die side. The most important die bending process, bending in a V - shaped die and in a U - shaped die. This thesis describes U and V bending dies. U - die bending is the bending a U - shaped part in a single die. Parts are composed of two legs or walls, usually parallel by a web Figure 4. XXI »> ı! it At^^l / ^ l-ıq*p_:-- r~7 (a) (b) Figure 4. U - die bending (a) without pressure pad. (b) with pressure pad U - die bending without pressure pad; in die bending, the process is characterized by different stage of deformation. The punch establish contact with the sheet and effects elastic bending, which produces a circular arc in the domain of the web due to constant moment distribution. The legs of work piece fold upward, close the punch, as it moves into the die plate, and the curvature of the web is increased. No significant deformation takes place from this point on until the web touches the bottom of the die plate on joining begins. During joining the curvature of the web changes from convex to concave. U - die bending with pressure pad, the pressure pad is intended to keep the web from bending by pressing it against the bottom of punch throughout the entire bending process. Joining becomes superfluous as a result. Except for this difference, The bending process is identical to bending without pressure pad. V - die bending is the bending of a V - shaped a in a single die. V - bending starts at the moment establishes contacts with the sheet, and is completed either the legs of the work pieces become tangent to the die face or when smallest internal xxn radius of the work piece becomes smaller of the punch. In both cases, the tool geometry effects the subsequent deformation of the sheet and than it comes coining stage. Coining has the purpose of removing the undefined geometry of the sheet curvature by forcing the sheet conform to the shape of the punch - die plate system. The shape assumed by the part during coining is determined to a considerable extent by the inner curvature of the peak of the part. V - die bending can be carried out by closed dies; that is, the bottom of the die has a radius equal to sum of punch radius plate thickness, or by a semi closed die, in which the bottom of the die has a smaller radius plus plate thickness. Figure 5 shows 90° V - die bending with small punch radius. Figure 6 shows 90° V - die bending with large punch radius. Figure 5. Shows 90° V - die bending with small punch radius. Figure 6. Shows 90° V - die bending with large punch radius.