Effect of cutting conditions and tool geometry on process damping in machining

Process damping can be a significant source of enhanced stability in metal cutting operations especially at low cutting speeds. However, it is usually ignored in stability analysis since models and methods on prediction and identification of process damping are very limited. In this study, the effects of cutting conditions and tool geometry on process stability in turning and milling are investigated. The previously developed models by the authors are used in simulations to demonstrate conditions for increased process damping, and thus chatter stability. Some representative cases are presented and verified by experimental data and conclusions are derived

Prediction of tool tip dynamics for generalized milling cutters using the 3D model of the tool body

In general, chatter is the main limitation to proper material removal in milling operations. Stability lobes are good tools to determine chatter-free cutting conditions in terms of spindle speed and cutting depth, which require the frequency response function (FRF) at the tool tip to be known. There are experimental methods to measure the tool tip FRF but this may be time consuming or even impossible for each tool and tool holder combination. Receptance coupling substructure analysis (RCSA) is a widely used approach to predict tool tip dynamics. This paper proposes the use of the RCSA approach with a stereolithographic (STL) slicing algorithm to enable the exact calculation of cross sectional properties such as area and area moment of inertia of the cutting tool from its 3D model opposed to the approximation methods. So that, the effect of flutes on cutting tool structure introduced in an exact manner and the RCSA approach becomes feasible for more complicated tool geometries with varying cross-sectional properties, i.e., tapered ball end mills, end mills with variable flute geometries, and so on. The solid model of the tool can be available by either the tool manufacturer or 3D measurement. Although, at the presence of 3D models, finite element methods (FEM) offer accurate simulation of the dynamic response for solid bodies, they suffer from the compromise between accuracy and computation time, as high number of elements is needed for accuracy. Thus, the use of analytical methods where possible improves the simulation time significantly. The proposed STL slicing algorithm is integrated with a previously developed RCSA method. The experimental results show that the proposed algorithm works more accurate in calculation of the cross-sectional properties and hence free-free response of the tool compared to the existing arc approximation methods. It is also shown that the proposed approach performs better than FEM solutions in terms of the computation time and the compromise between accuracy and computation performance. Finally, the proposed approach in prediction of tool tip dynamics for a robotic machining platform

Optimization of 5-axis milling processes using process models

Productivity and part quality are extremely important for all machining operations, but particularly for 5-axis milling where the machine tool cost is relatively higher, and most parts have complex geometries and high quality requirements with tight tolerances. 5- axis milling, presents additional challenges in modeling due to more complex tool and workpiece interface geometry, and process mechanics. In this paper, modeling and optimization of 5-axis processes with cutting strategy selection are presented. The developed process models are used for cutting force predictions using a part-tool interface identification method which is also presented. Based on the model predictions and simulations, best cutting conditions are identified. Also, for finish process of a complex surface, machining time is estimated using three machining strategy alternatives. Results are demonstrated by example applications, and verified by experiments

Simulation of multi-axis machining processes using z-mapping technique

Parameter selection in machining operations is curial for product quality and high productivity. Process parameters such as feed, spindle speed and depth of cuts are often chosen by trial-error methods. Mathematical models can be employed to predict the mechanics and the dynamics of the process. In this study, Z-mapping technique is utilized to simulate the process step by step by updating the workpiece according the given tool path where the cutter engagement areas are also determined. Using the numerical generalized process model, whole process is simulated for any milling tool geometry including intricate profiling tools, serrated cutters and tools with variable edge geometries

5 eksen frezeleme süreçlerinin modelleme yoluyla benzetimi ve eniyilenmesi

Özet: 5 eksenli frezeleme, havacılık ve kalıpçılık sanayilerinde karsılasılan karmasık yüzeylerin imalatında yaygın olarak kullanılmaktadır. Çok değiskenli ve karmasık bir mekaniğe sahip bu süreçlerin uygulanmasında uygun ve en iyi kesme kosullarının belirlenmesi verimlilik ve kalite açısından çok önemlidir. Genelde, 3 eksen frezeleme modellerini kullanarak hassas sonuçlar elde edilmesi çok mümkün değildir. Bu çalısmada, 5 eksen frezeleme süreçlerinin benzetimi ve en iyilemesi yapılmıstır. Geometrik modelleme için gerekli olan parametreler, verilen bir takım yolu dosyasından elde edilmistir. Elde edilen parametreleri kullanarak takım ve parça kesisim sınırları, eğilme-yatma açıları gibi kesme kosullarının hesaplanması anlatılmıstır. Bu değerler mevcut bir kuvvet modeline uygulanıp frezeleme kuvveti benzetimi yapılmıstır. Benzetimde elde edilen sonuçlara göre kesme kuvveti açısından kesme parametrelerinin en uygun değerleri bulunmustur. Hesaplanan eniyi değerler deneysel sonuçlarla doğrulanmıstır.{|}5 axis machining is widely used in die-mold and aerospace industries where complex surfaces are required to be manufactured. Identification of the optimum and appropriate cutting parameters of processes, which has complex mechanics, is very important from the productivity and quality perspectives. It is not possible to apply 3 axis machining models in these cases for accuare results. In this paper, simulation and optimization of 5 axis machining processes are performed. The required parameters for geometrical modeling are obtained from a CL-file. Calculation of cutting conditions such as engagement boundaries, lead-tilt angles from the obtained parameteres is shown. Those parameters are applied to an existing 5 axis force model, and then force simulations are performed. According to the simulation results, the best values of cutting parameters are identified from the milling forces point of view. The optimal values are verified with experimental results

Use of inverse stability solutions for identification of uncertainties in the dynamics of machining processes

Research on dynamics and stability of machining operations has attracted considerable attention. Currently, most studies focus on the forward solution of dynamics and stability in which material properties and the frequency response function at the tool tip are known to predict stable cutting conditions. However, the forward solution may fail to perform accurately in cases wherein the aforementioned information is partially known or varies based on the process conditions, or could involve several uncertainties in the dynamics. Under these circumstances, inverse stability solutions are immensely useful to identify the amount of variation in the effective damping or stiffness acting on the machining system. In this paper, the inverse stability solutions and their use for such purposes are discussed through relevant examples and case studies. Specific areas include identification of process damping at low cutting speeds and variations in spindle dynamics at high rotational speeds

Halit Ziya Uşaklıgil’in “Ayni Tata” ile Oğuz Atay’ın “Beyaz Mantolu Adam” Hikâyelerini Birlikte Okumak

Oğuz Atay, edebiyatımızda modern ve postmodern özellikler gösteren Tutunamayanlar romanı ile 1970’lerde bir kırılmayı gerçekleştirmiştir. Oğuz Atay’ın eserlerinde çoğunlukla Batılı yazarların tesiri görülmekle birlikte Türk edebiyatının önemli bazı isimlerini de takip ettiği, okuduğu bilinmektedir. Bu yazarlar arasında özellikle Halit Ziya’nın eserleri üzerine düşünen ve bazı tespitlerde bulunan Oğuz Atay, günlüklerinde yazarla benzer duyarlılıklara sahip olduğunu ifade eder. Romanlar söz konusu olduğunda dile getirilen bu benzerlik, çalışmamızın konusunu teşkil eden hikâyelerde de kendisini göstermektedir. Halit Ziya’nın “Ayni Tata” ve Oğuz Atay’ın “Beyaz Mantolu Adam” hikâyelerinde yabancılaşma ve toplumun dışına itilme konusu benzer karakterlerle işlenmiştir. Bu konu ve karakter benzerliğine karşın yazarların edebiyat anlayışlarının ve edebiyattan beklentilerinin farklı oluşu, hikâyelerdeki göndermeler ve anlatıcının konumunda görülen ayrılıklar eserleri farklı okumamızı sağlar. Çalışmamızda belirtilen hususiyetler göz önünde tutularak hikâyeler karşılaştırmalı olarak ele alınacaktır

Rapid extraction of machined surface data through inverse geometrical solution of tool path information

In the last decades, several process models have been developed for simulation of 5-axis milling cycles, where the simulation results are used for parameter selection or process improvement purposes. However, integrating the process models with milling cycles is not a trivial task especially for tool path modification purposes in 5-axis free-form milling. This is mainly due to the fact that tool path modification requires the machined surface information, i.e. surface location and surface normal vector, to be known. However, this information is not explicitly given in the tool path, i.e. cutter location source (CLS), file. In this paper, a novel and practical approach is proposed to analytically calculate the surface location and surface normal vectors directly from the already generated tool path in the form of CLS file. The proposed approach is applied on representative 5-axis milling cycles, and the results are verified through CAD model comparisons. It is shown that the proposed approach can calculate the machined surface data at a reasonable accuracy depending on the cutter location point density in the tool path file

Effect of MQL conditions on tool life in milling of AISI 316L stainless steel

In large-scale part manufacturing industries such as nuclear, aerospace and power generation, robotic milling is potentially a promising portable manufacturing technology to decrease the overall costs. The lack of enclosures around the robotic milling units blocks the use of flood coolant contrary to CNC machining centres. In such cases, the minimal quantity lubrication (MQL) technique is suitable, which on the other hand, agrees with the green manufacturing theme of the industry in the 21st century. However, the effect of MQL parameters such as the air pressure, oil flow rate, oil type, and pulse rate on tool life and surface integrity in end milling have not been well studied and understood yet. In this paper, the MQL technology is studied to understand its effects on tool life and surface integrity in end milling of nuclear manufacturing grade stainless steels such as AISI316L. The milling experiments are performed using a robotic milling cell. The tool life is assessed by measuring the wear land using optical microscopy techniques, whereas the surface integrity is assessed in terms of surface residual stress (XRD) and surface roughness (optical metallography). The results show that MQL conditions and the oil type significantly affects the tool wear, tool life and surface integrity. Improve surface roughness was observed at 15 strokes/min at 75 ml/h of fluid flow rate. It was observed that high stroke rate with increased oil flow leads to decrease in the surface residual stress. It was found that use of synthetic MQL oils do not help to increase tool life compared to dry cutting. When water-based synthetic oils were used, the stable wear progress duration was found to be very short

Geometrical Analysis and Optimization of 5-Axis Milling Processes

5-axis milling processes are widely used in industries where complex surfaces are machined, and cutter accessibility is limited due to geometrical constraints on the workpiece. Additional motion capability increases the accessibility of the cutting tool, so it becomes possible to machine complex surfaces despite the geometrical constraints. In most of these industries dimensional tolerance integrity, surface quality, and productivity are of great importance. Therefore, identification of optimal or nearoptimal process conditions, and selection of appropriate machining strategy for a given workpiece are required. Increased motion capability in 5-axis complicates the geometry and the mechanics of the process. Thus, optimization of 5-axis milling processes becomes a complex engineering problem. In order to solve such a problem, process models should be used together with geometrical analysis methods. In selection of appropriate machining strategy, surface characteristics should be known together with the process mechanics. In this thesis, a complete geometrical model is presented for 5- axis milling processes using ball-end mills. The developed model is integrated with an existing 5-axis process model in order to simulate the cutting forces throughout a given toolpath. Also, the effect of lead and tilt angle pair on process mechanics is investigated, and optimized values of those under various conditions are identified. In addition, a model suggesting the most appropriate strategy among various machining strategies for roughing and finishing operations for regular free form surfaces is presented. The developed models are verified through experiments and their applications are demonstrated on complex surfaces