Modeling dynamics of parallel milling processes in time-domain

The use of parallel milling processes is increasing in various industries due to several advantages of these machine tools. Parallel milling processes are the processes where more than one milling tool simultaneously cut a workpiece. Due to the increased number of cutting tools, they have the potential for considerable increase in productivity as a result of higher material removal rate (MRR). However, dynamic interactions between milling tools may reduce stability limits. Generally, direct dynamic coupling between two milling tools on such a machine is weak since they are located on different spindles. However, there can be a strong dynamic coupling in case of milling a flexible workpiece. In this case, the vibrations caused by one of the tools may have regenerative effects on the other one. In order to address this problem, a stability model that works in time domain has been developed. The model is capable of simulating cases where two flexible milling tools are cutting a flexible workpiece. Several example cases are simulated with the model and results are presented

Modeling dynamics of parallel turning operations

Parallel turning operations are advantageous in terms of productivity since there are more than one cutting tools in operation. However, the dynamic interaction between these parallel tools may create additional stability problems and the advantage of parallel turning may not be utilized to full extent. For that reason, dynamics and stability of parallel turning processes need to be modeled. In this paper, dynamics of two different parallel turning operations where two turning tools cut a common workpiece are modeled. In the first case, the tools are directly coupled to each other whereas in the other case the coupling occurs through the vibration waves left on the workpiece. For these two cases, stability models in frequency and time domain have been developed. The frequency and time-domain solution results are compared and a reasonable agreement is observed. The predicted stability limits are also compared with experimental results where good agreement is demonstrated

Tool orientation effects on the geometry of 5-axis ball-end milling

5-axis ball-end milling has found application in various industries especially for machining of parts with complex surfaces. Additional two degree of freedoms, namely, lead and tilt angles make it possible to machine complex parts by providing extra flexibility in cutting tool orientation. However, they also complicate the geometry of the process. Knowledge of the process geometry is important for understanding of 5-axis ball-end milling operations. Although there are considerable amount of work done in 3-axis milling, the literature on 5-axis ball-end milling is limited. Some of the terminology used in 3-axis milling is not directly applicable to 5-axis ball end-milling. Hence some new process parameters and coordinate systems are defined to represent a 5-axis ball end-milling process completely. The engagement zone between the cutting tool and the workpiece is more involved due to the effects of lead and tilt angles. In this paper, effects of these angles on the process geometry are explained by presenting CAD models and analytical calculations

Modeling dynamics and stability of 5-axis milling processes

5-axis milling is an important machining process for several industries such as aero-space, automotive and die/mold. It is mainly used in machining of sculptured surfaces where surface quality is of extreme importance. Being one of the most important prob-lems in machining, chatter vibrations must be avoided in manufacturing of these com-ponents as they result in high cutting forces, poor surface finish and unacceptable part quality. Chatter free cutting conditions for required quality with higher productivity can be determined by using stability models. Up to now, dynamic milling and stability models have been developed for 3-axis milling operations; however the stability of 5-axis proc-esses has never been modeled. In this paper, a stability model for 5-axis milling opera-tions is proposed. The model can consider the 3D dynamics of the 5-axis milling proc-ess including effects of all important process parameters including lead and tilt angles. Due to the complex geometry and mechanics of the process, the resulting analytical equations are solved numerically in order to generate the stability diagrams

5 eksen frezelemede kuvvet ve şekil hatalarının modellenmesi

Özet: 5 eksen freze operasyonları havacılık, otomotiv ve kalıpçılık sektörlerinde karmaşık yüzeylerin talaşlı imalatında sıklıkla kullanılır. Bütün bu operasyonlarda boyut toleransları ve yüzey kalitesi çok önemlidir. Parçada veya kesici takımda kesme kuvvetleri nedeniyle oluşan esnemeler kabul edilemeyecek parça kalitesine sebep olabilirler. İstenilen kalitenin daha yüksek bir verimlilik ile sağlanması için gerekli olan en iyi frezeleme koşulları süreç modelleri kullanılarak bulunabilir. Küresel uçlu freze takımı için geliştirilenler de dahil olmak üzere, freze modellerinin çoğu 3 eksen operasyonlar için geliştirilmiştir. Bu makalede, küresel uçlu takım kullanılan 5 eksen freze operasyonlari için geliştirilen bir kuvvet modeli sunulmaktadır. 5 eksen frezeleme için, kesme kuvvetlerinden dolayı oluşan kesici takım esnemeleri de formüle edilmektedir. Kesme kuvvetleri için modelin tahminleri deneysel sonuçlarla karşılaştırıldı ve doğrulandı.{|}5-axis milling operations are common in several industries such as aerospace, automotive and die/mold for machining of sculptured surfaces. In almost all of these operations, the dimensional tolerance integrity and surface quality are of utmost importance. Part and tool deflections under cutting forces may result in unacceptable part quality. Process models can be used to determine the proper or optimal milling conditions for required quality with higher productivity. Majority of the milling models have been developed for 3-axis operations, even the ones for ball-end mills. In this paper, a complete kinematics and force model is presented for 5-axis milling operations using ball-end mills. Tool deflections due to the cutting forces are also formulated for 5-axis milling. Model predictions for cutting forces are compared and verified by experimental results

Modeling of 5-axis milling forces and form errors

5-axis milling operations are common in several industries such as aerospace, automotive and die/mold for maching of sculptured surfaces. In almost all of these operations, the dimensional tolerance integrity and surface quality are of utmost importance. Part and tool deflections order cutting forces may result in unacceptable part quality. Process models can be used to determine the proper or optimal milling conditions for required quality with higher productivity. Majority of the milling models have been developed for 3-axis operations, even the ones for ball-end mills. In this thesis, a complete kinematics and force model is presented for 5-axis milling operations using ball-end mills. The effects of lead and tillt angles are included in the model, and presented in the thesis. Tool deflections due to the cutting forces are also formulated for 5-axis milling. Model predictions for cutting forces are compared and verified by experimental results

Mechanics and dynamics of multi-axis machining operations

Machining process with a single cutting tool is called multi-axis machining if more than 3-axis are involved in the operation. On the other hand, parallel machining processes where more than one cutting tool simultaneously cut a workpiece is also called multi-axis machining. 5-axis ball-end milling where a single cutting tool is employed, parallel turning and parallel milling processes with two cutting tools are in the scope of the thesis. Moreover, face-milling process with inserted tools is also modeled. 5-axis ball-end milling operations are common in several industries such as aerospace, automotive and die/mold for machining of complex sculptured surfaces. Additional two degree of freedoms, namely, lead and tilt angles make it possible to machine complex parts by providing extra flexibility in cutting tool orientation. However, they also complicate the geometry of the process. In these operations, productivity, dimensional tolerance integrity and surface quality are of utmost importance. Part and tool deflections under high cutting forces may result in unacceptable part quality, whereas using conservative cutting parameters results in decreased material removal rate. Process models can be used to determine the proper or optimal milling parameters for required quality with higher productivity. The majority of the existing milling models are for 3-axis operations, even the ones for ball-end mills. In the thesis, geometry, force and stability models are presented for 5-axis ball-end milling operations. The effect of lead and tilt angles on the process geometry, cutter and workpiece engagement limits, scallop height, and milling forces are analyzed in detail. In addition, tool deflections/form errors and stability limits are also formulated for 5-axis ball-end milling. The use of the model for selection of the process parameters such as lead and tilt angles which result in minimum cutting forces or maximum stability limits are demonstrated. The model predictions for cutting forces, form error and stability limits are compared and verified by experimental results. Parallel machining operations are advantageous in terms of productivity since there are more than one cutting tools in operation. Due to the increased number of cutting tools, they have the potential for considerable increase in productivity as a result of higher material removal rate (MRR). However, the dynamic interaction between these parallel tools may create additional stability problems and the advantage of parallel machining may not be utilized to full extent. For that reason, dynamics and stability of parallel machining processes need to be modeled. In the thesis, dynamics of parallel turning and parallel milling operations where two cutting tools cut a common workpiece are modeled. The predicted stability limits for parallel turning are also compared with experimental results where good agreement is demonstrated. Die manufacturing is a very critical part of the overall production chain in many industries. Depending on shape and size of a die, machining time can be very time consuming. Furthermore, since usually one die is manufactured, the chance for testing is very limited. Machining processes in die manufacturing can be limited by many factors. Process models can be used in order to select process conditions which will yield the required quality in the shortest possible time. In this study, force and chatter models are developed for face milling processes with inserted cutters. Using the developed models, process parameters are modified and their effects on productivity are demonstrated

Investigation of lead and tilt angle effects in 5-axis ball-end milling processes

5-axis milling is widely used in aerospace, die-mold and automotive industries, where complex surfaces and geometries are machined. Being special parameters of 5-axis milling, lead and tilt angles have significant effects on the process mechanics and dynamics which have been studied very little up to now. In this paper, first of all, effects of tool tip contact on the surface finish quality is presented, and conditions to avoid tip contact in terms of lead and tilt angles and depth of cut are stated. The effects of lead and tilt angles on cutting forces, torque, form errors and stability are investigated through, modelling and verified by experimental results. It is shown that the cutting geometry, mechanics and dynamics vary drastically and nonlinearly with these angles. For the same material removal rate, forces and stability limits can be quite different for various combinations of lead and tilt angles. The results presented in the paper are expected to help understanding of complex 5-axis milling process mechanics and dynamics in a better way. The results should also help selection of 5-axis milling conditions for higher productivity and machined part quality

Wind loads for stadium lighting towers according to Eurocode 1

The determination of actions on structures is an important step of in the design process. In nature, so many outer and inner actions are acting on structures continuously. The two most important ones of those actions are the earthquake and wind actions. For some structures, i.e. towers, high chimneys or lighting towers, the priority of these two severe actions can change. Wind forces can become a governing force on the design of these structures. Therefore, the determination of wind forces for these tall, slender and wind-sensitive structures becomes very important. Also, these tall and slender structures have a high ratio of height to least diameter that makes them more slender and wind-sensitive than any other structures. In this study, the determination of wind loads for a selected and modeled stadium lighting tower was given according to Eurocode 1 which is an international well-known standard. This study showed that it is difficult to calculate wind loads of stadium lighting towers according to Eurocode 1 because of the complexity of the document, insufficient explanation of some formulas like resonant response factor and unclear graph sections for the reader. This study is believed to enlighten the way of the users of Eurocode 1

Machining strategy development in 5-axis milling operations using process models

Increased productivity and part quality can be achieved by selecting machining strategies and conditions properly. At one extreme very high speed and feed rate with small depth of cut can be used for high productivity whereas deep cuts accompanied with slow speeds and feeds may also provide increased material removal rates in some cases. In this study, it is shown that process models are useful tools to simulate and compare alternative strategies for machining of a part. 5-axis milling of turbine engine compressors made out of titanium alloys is used as the case study where strategies such as flank milling (deep cuts), point milling (light cuts) and stripe milling (medium depths) are compared in terms of process time by considering chatter stability, surface finish and tool deflections