Copy Milling System Research Articles

Does abutment preparation affect abutment screw joint stability? An in vitro study

Statement of problemWhether preparation of an implant abutment decreases the stability of the abutment screw joint is unclear. PurposeThe purpose of this in vitro study was to evaluate the effect of the abutment preparation in laboratory conditions on the reverse torque value (RTV) of the abutment screw. Material and methodsSixty implants, implant analogs, and abutments obtained from 2 different manufacturers were used in the present study and divided into 2 groups (groups B and N) according to the manufacturer. Each group was then divided into 3 subgroups (n=10) according to the remaining wall thickness (control, 0.4 mm, 0.6 mm). All abutments were tightened to analogs with 15 Ncm, and standardized preparation was made with a custom-designed copy-milling system. All abutments were tightened to the implants with 30 Ncm, and then, the abutment screws were removed and RTVs were recorded. Subgroups were analyzed by using 1-way ANOVA (α=.05), and the independent-sample t test was used to compare groups. Relationships between categorical variables were analyzed by chi-square tests. One abutment screw from each subgroup was randomly selected and analyzed by using a scanning electron microscope. ResultsA statistically significant difference was found between RTVs of different manufacturers (group B=28.2 ±1.2 Ncm, group N=25.9 ±1.4 Ncm; P<.005). In group N, there was a significant difference among subgroups, control (26.7 ±1.4 Ncm), and 0.6-mm wall thickness (24.8 ±0.8 Ncm) (P<.05). A statistically significant relationship was found between preparation and RTV for the NucleOSS only (P<.05) and between manufacturer and RTV (P<.001). Scanning electron microscopy evaluations identified different screw head and thread designs. ConclusionsThe abutment screw joint stability of the BioHorizons implant was not affected by abutment preparation.

Development of Innovative Intelligent Machine Tool Based on CAM-CNC Integration Concept – Adaptive Control Based on Predicted Cutting Force –

A new methodology to generate instruction commands for prompt machine control as a replacement for the previously prepared numerical control (NC) programs is developed to realize an innovative intelligent machine tool. This machine tool can eliminate NC program preparation, achieve cutting process control, reduce the production lead time, and realize an autonomous distributed factory. In this study, the innovative intelligent machine tool based on the computer-aided manufacturing-computer NC integrated concept is developed. The special feature of this system is to generate instruction commands in real time for prompt machine control instead of using NC programs. Digital Copy Milling, which is a digitized version of traditional copy milling, is realized by using only the computer-aided design model of the product. In this system, the cutting-force simulation is performed simultaneously with the real-time tool path generation. Then, the tool feed rate can be controlled according to the predicted cutting force. Therefore, both the improvement of the machining efficiency and the avoidance of machining problems can be achieved. The instantaneous cutting force model predicts the cutting force. In this system, the work material is represented by the voxel model, and the uncut chip thickness is calculated discretely from the number of voxels removed. Thus, it is possible to predict the cutting force in the case of non-uniform contact between the tool and the work material. In this study, a machining simulation is conducted to validate the proposed method. The results of the simulation show successful tool feed speed adaptation based on the predicted cutting force. The results also show the effective reduction of the machining time. A case study of a custom-made product for dental prosthetics is examined as a good application of both the proposed adaptive control and the Digital Copy Milling system. Through this method, it is possible to improve the machining efficiency and prevent tool breakage.

被削材のボクセルモデルを用いたエンドミル加工の切削力シミュレーションと切削力の予測結果に基づく適応制御

A new cutting force simulator which calculates discretely uncut chip thickness by referring workpiece voxel model has been developed to predict cutting force in end-milling operation. This cutting force simulator can predict cutting force under the complex change of workpiece shape and the non-uniform contact between cutting edge and workpiece. Additionally, a new methodology to realize adaptive control or feed speed control based on the predicted cutting force is developed by integrating with the digital copy milling system which can generate tool paths in real-time during machining operation. This methodology can revise the tool feed speed based on the cutting force which predicted simultaneously with the real end-milling operation

A Comparative Study On The Marginal Fit Of Zirconia Cores Manufactured By CAD/CAM And Copy Milling Methods

Purpose: The marginal fit of zirconia cores that were produced by CAD/CAM and by copy milling systems was compared and analyzed to confirm the significance of the variation in dental technicians’ skill between the two systems. Materials and Methods: Using dental resin teeth and individual trays, 30 plaster casts were produced. Fifteen casts were assigned to be used with five different zirconia core manufacturing dental laboratories using the same CAD/ CAM system, which were designated as the CC group. The remaining 15 were assigned to be used with five different zirconia core manufacturing dental laboratories using also the same copy milling system and were designated as the CM group. The zirconia cores were fabricated and were cemented onto the casts. The vertical marginal opening was measured under an optical microscope at 75x magnification. The measured vertical marginal discrepancies were analyzed using an independent sample t-test, and the significance of the vertical marginal gap value for each dental laboratory was analyzed by performing the Kruskal-Wallis test. Results: The means and standard deviations for the marginal discrepancies of the CC and CM groups were found to be 102.73 ± 29.73 µm and 82.25 ± 22.37 µm, respectively. The independent sample t-test showed a significant difference between the two systems; the CAD/CAM system showed a larger vertical marginal gap than the copy milling system. The Kruskal-Wallis test indicated that no significant distributional differences were found between the dental laboratories in either the CAD/CAM or the copy milling systems. Conclusions: The copy milling system may produce more accurate zirconia restorations than the CAD/CAM system. The technician’s skill of a copy milling system may not be a determining factor influencing the accuracy of a single zirconia core.

Marginal Fit of Implant-Supported All-Ceramic Zirconia Frameworks

This study evaluated the effect of fabrication techniques and cyclic loading on the vertical marginal fit of implant-supported fixed partial denture (FPD) frameworks. Thirty implant-supported 3-unit FPD frameworks were fabricated on a model system, divided into 3 equal groups (n = 10). The first group (control) was constructed from base metal alloy; the other 2 test groups were constructed from all-ceramic zirconia using a computer-aided design/computer-aided manufacturing (CAD/CAM) Cerec 3 system and a copy milling (Zirkonzahn) system. A cyclic load of 200 N was applied to each framework for up to 50,000 cycles. Linear measurements were made in micrometers of the vertical gap between the framework and the implant-supported abutment at 16 predetermined points before and after cyclic loading. The frameworks were viewed using scanning electron microscopy to inspect any fractographic features. One-way analysis of variance was performed to compare the marginal discrepancy values of the control and the 2 test groups and for each group; a t test was applied to determine whether significant changes in the fit were observed after cyclic loading (α = 0.05). The CAD/CAM group showed significantly higher marginal gap mean values (80.58 μm) than the Zirkonzahn and control groups (50.33 μm and 42.27 μm, respectively) with no significant difference. After cyclic loading, the CAD/CAM group recorded the highest marginal gap mean value (91.50 ± 4.260 μm) followed by control group (72.00 ± 2.795 μm); the Zirkonzahn group recorded the lowest marginal gap (65.37 ± 6.138 μm). Cyclic loading significantly increased the marginal gap mean values in the control group only. A marginal chip was observed in one of the CAD/CAM ceramic frameworks. Within the limitations of this study, the fabrication technique influenced the marginal fit of the implant-supported 3-unit FPD frameworks. Cyclic loading failed to change the fit of all-ceramic zirconia frameworks, whereas significant changes were found in the metal frameworks.

Marginal Fit of Implant-supported All-Ceramic Zirconia Frameworks

Abstract Objective: This study evaluated the effect of fabrication techniques and cyclic loading on the vertical marginal fit of implant-supported FPD frameworks. Methods: Thirty implant supported 3-unit FPD frameworks were fabricated on a model system, divided into three equal groups (n=10). The first group (control) was constructed from base metal alloy and the other two test groups were constructed from All-ceramic Zirconia using CAD/CAM Cerec III system and copy milling (Zirconzahn) system. A cyclic load of 200 N was applied to each framework for up to 50,000 cycles. Linear measurements were made in micrometers (µm) of the vertical gap between the framework and implant-supported abutment at 16 predetermined points before and after cyclic loading. The frameworks were viewed using SEM to inspect any fractographic features. One way analysis of variance (ANOVA) was performed to compare the marginal discrepancy values of the control and the two test groups and for each group; T-test was applied to determine whether significant changes in the fit were observed after cyclic loading. (α=0.05). Results: CAD/CAM group showed significantly higher marginal gap mean values (80.58 µm) than Zirkonzahn and control groups (50.33 µm and 42.27 µm respectively) with no significant difference while, after cyclic loading, CAD/CAM group recorded the highest marginal gap mean value (91.50 ± 4.260 µm) followed by control group (72.00 ± 2.795 µm) while Zirconzahn group recorded the lowest marginal gap (65.37 ± 6.138 µm). Cyclic loading significantly increased the marginal gap mean values in the control group only. Marginal chip was observed in one of the CAD/CAM ceramic frameworks. Conclusions: Within the limitations of this study, the fabrication technique influenced the marginal fit of the implant supported 3-unit FPD frameworks. Cyclic loading failed to change the fit of all-ceramic Zirconia frameworks while; significant changes were found in the metal frameworks.

1408 加工除去領域のボクセルモデルを利用した仮想倣い加工システムの機能拡張(GS-13 生産加工,工作機械(2))

1408 加工除去領域のボクセルモデルを利用した仮想倣い加工システムの機能拡張(GS-13 生産加工,工作機械(2))

Direct Machining Operation Performed by Autonomous NC Machine Tool Controlled by Digital Copy Milling Concept

In order to shorten production lead-time, it is needed to eliminate time and efforts for process planning after product design. However, as far as a conventional NC machine tool is utilized, a reliable NC part program has to be prepared to achieve high cutting productivity and accuracy. It is a time consumed operation according to the fact that all cutting parameters are predetermined and coded as NC programs before the cutting operation to maintain the stable cutting operation and to avoid the cutting trouble for the whole cutting operation. The digital copy milling system which generates tool paths in real time has been developed to solve the problem mentioned above. In this study, a commercial process planning software is customized to integrate with the digital copy milling system for realizing an autonomous NC machine tool. The cutting operation performed by the digital copy milling system integrated with the commercial process planning software is compared to a conventional cutting operation performed by manual process planning using CAM software. The direct machining operation, which does not require any effort to prepare an NC part program, is performed successfully using a conventional NC machine tool associated with the digital copy milling system.

109 仮想倣い加工を用いた自律知能型NC工作機械制御法の確立 : CAMを使用した従来のNCデータ生成手法との比較(OS-3 最新工作機械・多軸複合加工)

An NC machine tool is widely employed in manufacturing systems. However, it is impossible to change cutting parameters, such as depth of cut and stepover, to maintain the stable cutting and to avoid the cutting trouble during machining operations, because cutting parameters are determined and coded as NC programs before the machining operation. The digital copy milling system which generates tool paths in real time is developed to solve the problem mentioned above. An NC machine tool associated with the digital copy milling system can perform autonomous and intelligent machining operations unconstrained by NC programs.

A New Architecture of Tool Path Generation for Five-Axis Control Machining

NC machine tools, which are widely employed in manufacturing systems, are basically driven by NC programs. However, it requires extensive amount of time and efforts to generate high quality tool paths before a machining operation. An NC program for five-axis control machining is more difficult to generate because the motion of machine tool is more complicated. In this paper, a new architecture is proposed to autonomously control the machine tool without an NC program for more rapid and flexible machining. A technique called digital copy milling is developed to generate the tool paths in real time based on the principle of copy milling. It means that the cutting parameters can be adaptively controlled in order to maintain stable cutting process and to avoid the cutting troubles. In the experimental verification, the improved digital copy milling system for five-axis control milling successfully detected and avoided tool collision in real-time.

Digital copy milling—autonomous milling process control without an NC program

Conventional NC machine tools do not generally allow the change of cutting conditions such as depth of cut and stepover during machining operations, once they are given machining commands as NC programs. For that reason, the NC programs must be prepared adequately and verified in advance, which requires extensive time and effort. It is therefore necessary to develop functions to generate the cutter path autonomously and control the cutting conditions adaptively during machining to optimize the cutting process, maintain stable cutting, and avoid cutting trouble. This paper proposes a new architecture to realize autonomous control of the cutting process without using NC programs. A technique called digital copy milling is developed to control the NC machine tool in real time. The digital copy milling system can generate tool paths in real time, based on the principle of copy milling. In addition, a new control strategy is developed to control the cutting conditions adaptively. A prototype of an autonomous controller was implemented in a three-axis control machining center. Thereafter, experimental milling tests were carried out to verify the effectiveness of the proposed system. The cutter paths were generated autonomously by the digital copy milling system. Results show that the cutting depth and stepover can be changed during milling tests. Cutting conditions were controlled adaptively.

Autonomous Machine Tool to Realize Flexible Machining Operation Unconstrained by NC program

In this paper, a new architecture is proposed to realize autonomous machining operation unconstrained by NC program. A flexible process and operation planning system is developed to generate cutting parameters dynamically for flexible machining operation. The flexible process and operation planning system can generate the production plan from the Total Removal Volume (TRV). The TRV is extracted from initial and finished shapes of the product, and the TRV is divided into machining primitives or machining features. The flexible process and operation planning system can generate cutting parameters according to the machining features detected. In addition, a technique called digital copy milling is developed to control the NC machine tool in real time. The digital copy milling system can generate the tool paths in real time based on the principle of copy milling, and it permits to change the operation sequence and the cutting parameters during the machining operation. A prototype of autonomous machine tool was implemented, and actual cutting tests were carried out to verify the effectiveness of the proposed system. It was proved that the direct machining operation which does not require any effort and time to prepare the NC program can be achieved.

Development of an innovative autonomous machine tool for dynamic product planning

In the area of machining, laborsaving and automation are comparatively realized mainly by the contribution of NC machine tools so far. However, conventional NC machine tools are not autonomous and intelligent because they don’t have any feedback mechanisms during machining operations. Therefore, in order to realize dynamic product planning for an innovative autonomous machine tool, it is indispensable that machine tools have feedback mechanism to adapt cutting parameters to monitoring information. As a matter of course, it is needed for the mechanism to include a function of tool path generation in real time. Because the real time tool path generation can perform to change not only feed speed but also depth of cut during an operation. In this paper, digital copy milling system that can generate tool paths in real time is developed by applying the traditional copy milling principle. And also, machining strategy is proposed to adapt cutting parameters considering cutting load, and integrated into the digital copy milling. Feedback machining control can be realized using the digital copy milling system with the proposed machining strategy. Furthermore, in order to achieve dynamic product planning, an automatic function of product planning is added by customizing commercial CAD software. By using this automatic planning system, even in case of a cutting trouble, it is possible to reschedule product planning immediately. Autonomous machining based on dynamic product planning can enable to realize high flexibility and high durability in machining operations.

Development of Digital Copy Milling System to Realize NC Programless Machining. 3rd Report. Machining Strategy for In-Process Adaptation of Cutting Conditions.

NC machine tool driven by NC programs is very useful to machine standardized products with high accuracy and productivity. However, conventional NC machine tools have no function to change cutting conditions during machining operations by themselves because NC programs instruct all cutting conditions before the operation. This is the biggest problem to realize an autonomous NC machine tool. To realize an autonomous NC machine tool, a new architecture is required to operate an NC machine tool without NC programs and to adapt cutting conditions in real time to maintain stable machining operation. This paper deals with implementation of a feedback machining control using digital copy milling system, which consists of function to generate tool paths in real time and machining strategy to adapt cutting conditions. The proposed digital copy milling system is verified to show its ability in cutting experiments.

Development of Virtual Copy Milling System to Realize NC Programless Machining. 2nd Report. Improvement of Collision Check and Realization of Contour-Line Machining.

An autonomous NC machine tool is required to have several functions, such as the optimization of outting conditions, and the avoidance of cutting troubles during machining operation. The virtual copy milling system has been developed to achieve these functions. This system based on copy milling principle is able to generate tool paths in real time. In this paper, the collision check between the stylus and the master model to generate tool paths is improved and completed to avoid over cutting. Furthermore, contour-line machining is realized besides scanning-line machining performed in the previous report. Experimental milling is succeeded to show NC programless machining of sculptured surface.

Development of Virtual Copy Milling System to Realize NC Programless Machining. Real Time Tool Path Generation for Autonomous NC Machine Tool.

NC programless machining which is realized by the virtual copy milling system have been demonstrated. In the virtual copy milling system which is developed in this study, a stylus and a master model in copy miling are defined as geometrical surface models, the stylus motion corresponding to the tool motion is simulated by applying copy milling principle. This method is simple enough to generate the tool motion in real time, because it detects only the collision between the stylus and the master model which are defined. Experimental cutting have been succeeded to show that the virtual copy milling system is able to perform NC programless milling of sculptured surface. The real time tool path generation accomplished by this system aims to be used for the adaptation of cutting conditions such as depth of cut and feed speed to maintain stable machining. The adaptation of cutting conditions is an important function to realize an autonomous NC machine tool towards 21st century.

310 NC プログラムを必要としない機械加工のための仮想倣い加工システム

The virtual copy milling system has been developed. In the virtual copy milling system, a stylus and a master model in copy milling are defined as geometrical surface models, and the stylus motion corresponding to the tool motion is simulated by applying copy milling principle. This method is simple enough to generate the tool motion in real time, and experimental cutting have been succeeded to show NC programless milling of sculptured surface. The real time tool path generation is indispensable for the adaptation of cutting conditions such as depth of cut and feed speed to maintain stable machining. In this study, the machining strategy for the adaptation of cutting conditions is proposed to realize an autonomous NC machine tool.