Optimization of the setup position of a workpiece for five-axis machining to reduce machining time

Five-axis machining is commonly used for complicated features due to its advantage of rotary movement. However, the rotary movement introduces nonlinear terms in the kinematic transform. The nonlinear terms are related to the distance between the cutter location (CL) data and the intersection of the two rotary axes. This research studied the possible setup positions after the toolpaths have been generated, and the objective was to determine the optimal setup position of a workpiece with minimal axial movements to reduce the machining time. We derived the kinematic transform for each type of five-axis machines, and then, defined an optimization problem that described the relationship between the workpiece setup position and the pseudo-distance of the axial movements. Eventually, an optimization algorithm was proposed to search for the optimal workpiece setup position within the machinable domain, which is already concerned with over-traveling and machine interference problems. In the end, we verified the optimal results with a case study with a channel feature, which was real cutting on a table-table type five-axis machine. The results show that we can save the axial movements up to 16.76% and the machining time up to 10.70% by setting up the part at the optimal position.

A novel error compensation method for multistage machining processes based on differential motion vector sets of multiple contour points

Modeling the variation propagation based on the stream of variation (SoV) methodology for multistage machining processes (MMPs) has been investigated intensively in the past two decades, however little research is conducted on the variation reduction and the existing work fails to be applied to irregular features caused by the machining-induced variation varying with the positions of the contour points on the machined surface. This paper proposes a novel error compensation method for MMPs through modifying the tool path to reduce variation for general features. The method based on differential motion vector (DMV) sets of multiple contour points is presented to represent the deviation of the irregular feature. Then the conventional SoV model is further extended to more accurately describe variation propagation for irregular features considering the actual datum-induced variations and the varying machining-induced variations, especially the deformation errors for the low stiffness workpiece. Based on the extended SoV model and error equivalence mechanism, the datum error and fixture error are transformed to the equivalent tool path error. Then the original tool path is modified through shifting the machine zero point of machine tools with no need for changing the original G code and workpiece setup. A real cutting experiment validates the effectiveness of the proposed error compensation method for MMPs with an average precision improvement of over 60%. The application of the extended SoV model significantly contributes to compensating more complex error sources for MMPs, such as the clamp force, the internal residual stress, etc.

A Coupling Approach Combining Computational Fluid Dynamics and Finite Element Method to Predict Cutting Fluid Effects on the Tool Temperature in Cutting Processes

In metal cutting processes, the use of cutting fluids shows significant effects on workpiece surface quality by reducing thermomechanical loads on cutting tool and workpiece. Many efforts are made to model these thermomechanical processes, however without considering detailed heat transfer between cutting fluid, tool, and workpiece. To account for heat transfer effects, a coupling approach is developed, which combines computational fluid dynamics (CFD) and finite element method (FEM) chip formation simulation. Prior to the simulation, experimental investigations in orthogonal cutting in dry and wet cutting conditions with two different workpiece materials (AISI 1045 and DA 718) are conducted. To measure the tool temperature in dry as well as in wet cutting conditions, a two color pyrometer is placed inside an electrical discharge machining (EDM) drilled cutting tool hole. Besides tool temperature, the cutting force is recorded during the experiments and later used to calculate heat source terms for the CFD simulation. After the experiments, FEM chip formation simulations are performed and provide the chip forms for the CFD mesh generation. In general, CFD simulation and experiment are in reasonable agreement, as for each workpiece setup the measured temperature data are located between the simulation results from the two different tool geometries. Furthermore, numerical and experimental results both show a decrease of tool temperature in wet cutting conditions, however revealing a more significant cooling effect in a AISI 1045 workpiece setup. The results suggest that the placement of drilling holes has a major influence on the local tool temperature distribution, as the drilling hole equals a thermal resistance and hence leads to elevated temperatures at the tool front.

A Coupling Approach Combining CFD and FEM Methods to Predict Cutting Fluid Effects on the Tool Temperature in Cutting Processes

In metal cutting processes the use of cutting fluids shows significant effects on workpiece surface quality by reducing thermomechanical loads on cutting tool and workpiece. Many efforts are made to model these thermomechanical processes, however without considering detailed heat transfer between cutting fluid, tool and workpiece. To account for heat transfer effects, a coupling approach is developed which combines CFD (Computational Fluid Dynamics) and FEM (Finite Element Method) chip formation simulation. Prior to the simulation, experimental investigations in orthogonal cutting in dry and wet cutting conditions with two different workpiece materials (AISI 1045 and DA 718) are conducted. To measure the tool temperature in dry as well as in wet cutting conditions, a two color pyrometer is placed inside a EDM drilled cutting tool hole. Besides tool temperature, the cutting force is recorded during the experiments and later used to calculate heat source terms for the CFD simulation. After the experiments, FEM chip formation simulations are performed and provide the chip forms for the CFD mesh generation. In general, CFD simulation and experiment are in reasonable agreement, as for each workpiece setup the measured temperature data is located between the simulation results from the two different tool geometries. Furthermore, numerical and experimental results both show a decrease of tool temperature in wet cutting conditions, however revealing a more significant cooling effect in a AISI 1045 workpiece setup. The results suggest that the placement of drilling holes has a major influence on the local tool temperature distribution, as the drilling hole equals a thermal resistance and hence leads to elevated temperatures at the tool front.

Penerapan Lean Manufacturing Untuk Meminimasi Waste Delay Pada Workstation Curing di PT Bridgestone Tire Indonesia

Lean Manufacturing is a method used to increased productivity and costs reduction by minimizing waste in the production process. This study describe the use of lean manufacturing with Single Minutes Exchange Of Dies tools on the PSR’s production floor in PT XYZ, which is engaged in automotive manufacture form making of car tires. Research stage begins by analyzing waste using mapping tool and identification causes of waste in workstation curing. The next stage is analyzing every step of machine setup that occurs are workpiece setup, mold setup, curing setup, and finishing setup. Based on observations, the amount of the initial state setup time is 194,05 minutes. The improvement begin by convert internal activities setup into external setup, reduction of operator displacement activity, elimination of adjusment, and apply a parallel operation by using two operators. So the total setup time can be reduced is equal to 127,41 minutes.Keyword : Lean manufacture, SMED, Setup time, Workstation curing Lean Manufacturing merupakan metode yang digunakan untuk meningkatkkan produktivitas dan pengurangan biaya dengan cara meminimasi pemborosan dalam proses produksi. Penelitian ini menjelaskan penggunaan Lean Manufacturing dengan tool Single Minutes Exchange Of Dies (SMED) pada lantai produksi PSR di PT XYZ, yang bergerak dalam bidang Automotive Manufacture berupa pembuatan ban mobil. Tahap penelitian diawali dengan melakukan analisis waste dengan Mapping tools dilanjutkan dengan mengidentifikasi penyebab pemborosan pada workstation curing. Tahap Selanjutnya adalah menganalisis tahapan proses setup mesin curing yang terdiri dari setup benda kerja, setup mold, setup curing, dan setup finishing. Berdasarkan hasil pengamatan, jumlah waktu setup keadaan awal adalah 194,05 menit. Perbaikan yang dilakukan adalah dengan mengkonversi aktivitas internal setup menjadi eksternal setup, pengurangan aktivitas perpindahan operator, eliminasi adjusment, dan menerapkan operasi paralel yaitu dengan menggunakan 2 operator. Sehingga total waktu setup yang dapat direduksi adalah 127,41 menit.Kata kunci: Lean manufacture, SMED, Waktu setup, Workstation curing

Contribution of Five-Axis Machine Geometric Errors and Workpiece Setup Errors to On-Machine Laser Scanning Measurement

On-machine scanning measurement of workpiece geometry has a strong advantage in its efficiency, compared to conventional discrete measurement using a touch-trigger probe. When a workpiece is rotated and tilted, position and orientation errors in workpiece setup with respect to the machine’s rotary axes can be a significant contributor to the measurement error. The machine’s geometric errors also influence the measurement error. To establish the traceability of on-machine laser scanning measurement with workpiece rotation, this paper kinematically formulates their contribution to measured profiles. As a practical application example, this paper studies the sensitivity of work-piece setup errors and rotary axis geometric errors on the error in laser scanning measurement of an axis-symmetric part.