4.1. Composition of Expert Panel and Establishment of Evaluation Items
This study invited experts with relevant backgrounds in the field of CNC machine tools to conduct interviews and surveys, including 4 experts from the industry sector, 10 from research institutions, and 2 from the academic sector, totaling 16 experts, as shown in
Table 3.
Semi-structured interviews were carried out inviting SIX experts and scholars for in-depth interviews, including industry experts, research institution experts, and academic scholars, through experts and scholars with different backgrounds and roles. The experiences provided by the following experts were consolidated in the semi-structured in-depth interviews on the perception and experience of the development trends of computer numerical control machine tools.
Expert1: Factors influencing the improvement of feed precision in computer numerical control machine tools are as follows: rigidity of the feed system, rigidity of the guide (track) system, rigidity of the main structure, matching of the inertia ratio between the servo motor and the feed system, matching of the servo control, accuracy of the ball screw, accuracy of the guide (track) system, accuracy of the bearings in the feed system (supporting the ball screw). Regardless of how the main body structure is designed, there must be its “system natural frequency”, so the accuracy of the dynamic balance of the spindle can be corrected according to the detection technology of the dynamic balancing equipment to set the standard for dynamic balance correction.
Expert2: The controller is the heart of the computer numerical control machine tool. In equipment production, the controller is required to achieve precise machining purposes for the entire machine, enhance the user-friendly operation interface, accelerate operators’ mastery of various interface settings, and improve production efficiency. Intelligent control can be achieved by constructing more auxiliary modules and improving compensation systems in the controller.
Expert6, Expert9: The construction aspect of the main structure of computer numerical control machine tools can be divided into the main structure and the spindle and bearing system. With the development of numerical control machine tools being ready for many years, further development will focus on improving the spindle and bearing system, enhancing the structural rigidity, reducing the weight of the machine, and lowering production costs, which are essential considerations for the next stage of manufacturing production.
Expert15: The feed mechanism and the servo motor are interrelated, and through the transmission of information from the servo motor, the feed mechanism is moved. The tuning technology of the servo can quickly adjust the axial dynamic error, enhancing the dynamic performance and part accuracy of the CNC machine tool.
Expert16: Intelligent manufacturing is the challenge that manufacturers will face in the future. If intelligent handling (AGV) can be introduced without increasing production costs and combined with robotic arms, it will provide significant assistance in addressing labor shortages and experience transfer, moving towards the goal of Industry 5.0 human–machine collaboration.
Following the confirmation of research aspects and technical projects, the next step involves drafting the sub-technical projects of the technical projects. Throughout the interview process, experts and scholars drew on their experiences in production and research of computer numerical control machine tools to discuss the current development status and future directions of the eight technical projects listed in
Figure 6. After consolidation by this study, a total of 34 sub-technical projects were identified. Consulting with 16 experts and scholars to avoid differences in language interpretation with experts and scholars, this study adopts a more cautious attitude and seeks advice from experts and scholars to revise the sub-technical projects of “B-1 Body Structure”, “B-2 Spindle and Bearing System”, “B-3 Feed Mechanism and Servo Motor”, “B-4 Controller”, “B-7 Cloud Database and Data acquisition”, and “B-8 Intelligent Manufacturing”. The revised sub-technical projects are numbered 1, 2, 3, 4, 6, 8, 9, 10, 12, 31, and 32, as shown in
Table 4.
4.2. Analysis of Results from the Expert Questionnaire Survey Using the Fuzzy Delphi Method
A fuzzy Delphi method expert questionnaire survey on the research aspects, technical projects, and sub-technical projects of computer numerical control machine development trends compiled after expert interviews was conducted. The perceived importance was analyzed by 16 experts and scholars based on the questionnaire results, establishing dual triangular fuzzy numbers after statistical analysis of the most optimistic and most conservative cognitive scores acceptable in experts’ semantic thinking, eliminating extreme values by two standard deviations, calculating the geometric mean of the minimum and maximum values acceptable to experts, conducting a grey zone test to determine if the experts’ cognition has converged, and deriving the consensus degree values (Gi) of experts on each sub-technical project, as shown in
Table 5. All 34 sub-technical projects exhibit the phenomenon of dual triangular overlap, with 26 projects reaching a consensus degree value of 80 or above at the threshold of importance consensus, indicating that experts and scholars consider this indicator to be extremely important. The test values of the other eight sub-technical projects are negative, indicating significant disagreement among experts and failure to converge; thus, they are removed.
Experts and scholars believe that optimizing the rigidity of the numerical control machine tool main body structure in aspect “A-1 Numerical Control Machine Tool Main Body Structure” and technical item “B-1 Main Body Structure” can reduce production costs by lightweighting the overall structure. Verifying the correctness of sensor placement through visual comparison and data matching of workpiece and tool path overlap is crucial to avoid overcutting and spindle collisions. Experts and scholars in the aspect “A-1 Numerical Control Machine Tool Main Body Structure” and technical item “B-2 Spindle and Bearing System” believe that improving the assembly precision of the spindle and bearings, along with the addition of sensor components, can detect the temperature generated by the spindle during high-speed operation. This facilitates timely feedback for temperature adjustment of the cooling system. In terms of rotational speed, high spindle speed and torque effectively enhance production efficiency. High spindle dynamic balance standards, combined with the design of the main body structure to avoid resonance points, help reduce resonance during machine operation.
Experts and scholars in the aspect “A-2 Control System” and technical item “B-3 Feed Mechanism and Servo Motor” believe that intelligent servo tuning technology, combined with overall machine rigidity, allows for rapid adjustment of axial dynamic errors. The slight movements of the feed mechanism and servo motor contribute to improved processing accuracy. Experts and scholars in the aspect “A-2 Control System” and technical item “B-4 Controller” believe that constructing auxiliary modules can enable operators to quickly master the machine and enhance system compensation. This includes addressing errors caused by structural displacement, tool wear leading to processing errors, and feed mechanism movement errors, achieving intelligent control.
Experts and scholars in the aspect “A-3 Intelligent Manufacturing” and technical item “B-5 Troubleshooting” believe that establishing remote connection services to address issues with controllers and drivers that cause machine downtime is crucial. Remote connection allows for timely troubleshooting of system-generated faults, reducing machine downtime and minimizing the impact on production capacity. Experts and scholars in the aspect “A-3 Intelligent Manufacturing” and technical item “B-6 Intelligent Monitoring” believe that utilizing internet communication and (visual) monitoring technology is beneficial for fault detection, diagnosis, and monitoring of CNC machine tools. Experts and scholars in the aspect “A-3 Intelligent Manufacturing” and technical item “B-7 Cloud Database and Data Collection” believe that collecting and analyzing processing parameters, setting processing conditions, and measuring tool wear data can lead to a comprehensive processing environment through the establishment of a cloud database.
4.3. Analysis of Expert Questionnaire Survey Results Using Fuzzy Analytic Hierarchy Process (FAHP)
This study investigates the development trends of CNC machine tools. In the previous section, after analysis using the fuzzy Delphi method by experts and scholars, 26 important consensus indicators for technical items were obtained. In this section, further analysis explores three aspects, eight technical items, and the 26 sub-technical items in the hierarchical structure. Experts and scholars conduct pairwise comparisons of indicators and their importance, determine the consistency index (C.I.) and consistency ratio (C.R.) through pairwise comparisons of indicators, and establish triangular fuzzy numbers to evaluate the indicators. The weight values of technical item indicators in the overall hierarchical structure are calculated, and the importance levels are ranked.
The three main dimensions of the development trend of CNC machine tools, “Body structure of the numerical control machine tool”, “Control System”, and “Intelligent Manufacturing”, are displayed in
Table 5 with the weight values and importance ranking in the hierarchical structure. From
Table 5, it is observed that the Consistency Index (C.I.) is 0.0587, below 0.1, and the Consistency Ratio (C.R.) is 0.1013, also below 0.1, passing the consistency test. The importance level of the evaluated indicators by experts and scholars is consistent. Experts and scholars consider the “A-2 Control System” dimension to be the most important, followed by the “A-3 Intelligent Manufacturing” dimension, and finally the “A-1 Body structure of the numerical control machine tool” dimension. This indicates that experts and scholars believe that the “A-2 Control System” dimension is the future important development trend for computer numerical control machines. Subsequently, combining with the “A-3 Intelligent Manufacturing” dimension, aiming to move towards Industry 5.0.
The eight technical items under the three main dimensions are categorized as “B-1 Body Structure”, “B-2 Spindle and Bearing System”, “B-3 Feed Mechanism and Servo Motor”, “B-4 Controller”, “B-5 Fault diagnosis”, “B-6 Intelligent Monitoring”, “B-7 Cloud Database and Data acquisition”, and “B-8 Intelligent Manufacturing”. Their weight values and importance levels in the hierarchical structure are presented in
Table 6. According to
Table 6, the Consistency Index (C.I.) for the technical items is 0.0671, which is less than 0.1, and the Consistency Ratio (C.R.) is 0.0476, also less than 0.1, passing the consistency test. The importance level of the evaluated indicators by experts and scholars is consistent. Experts and scholars consider the development sequence of the technical items, with the “B-3 Feed Mechanism and Servo Motor” technical item being the most important, followed in sequence by “B-4 Controller”, “B-6 Intelligent Monitoring”, “B-2 Spindle and Bearing System”, “B-5 Fault diagnosis”, “B-8 Intelligent Manufacturing”, “B-7 Cloud Database and Data acquisition “ technical items, and lastly the “B-1 Machine Structure” technical item.
In the hierarchy structure, the weight values and importance levels of the sub-technical items under “B-1 Body Structure”, such as “ B-1-1 Machine tool main body structure (including machine base, column, bed, spindle head), if a structural model can be established, using topological optimization design to achieve optimal structural rigidity and material lightweighting” and “B-1-2 Set up position sensors, visually compare the overlap of data workpieces and tool paths to ensure correctness, and prevent overcutting and spindle collisions” are ranked as shown in
Table 7.
Table 7 reveals that experts and scholars view the development sequence of the sub-technical items, ranking the “B-1-1 Machine tool main body structure (including machine base, column, bed, spindle head), if a structural model can be established, using topological optimization design to achieve optimal structural rigidity and material lightweighting”, as the most important, followed by “B-1-2 Set up position sensors, visually compare the overlap of data workpieces and tool paths to ensure correctness, and prevent overcutting and spindle collisions”.
In the hierarchical structure, the weight values and importance levels of the sub-technical items under “B-2 Spindle and Bearing System”, such as “B-2-1 Enhancing the assembly precision of the spindle and bearing system, appropriate tolerances can prevent unnecessary deformation and temperature rise during bearing operation” “B-2-2 Add sensors to the spindle and bearing system to detect the temperature generated during high-speed rotation of the spindle, facilitating feedback to the cooling system for timely temperature adjustment”, “B-2-3 Precision machining of high-precision product components, matching the spindle with cutting conditions based on material properties and tooling, high spindle speed and torque effectively enhance production efficiency” and “B-2-4 Enhance spindle dynamic balance, incorporate structural design to avoid resonance points, reducing resonance during machine operation” are ranked in terms of importance as shown in
Table 8. According to
Table 8, the Consistency Index (C.I.) for the technical items is 0.0285, which is less than 0.1, and the Consistency Ratio (C.R.) is 0.0317, also less than 0.1, passing the consistency test. The importance level of the evaluated indicators by experts and scholars is consistent. Experts and scholars consider the development sequence of the sub-technical items, ranking “B-2-1 Enhancing the assembly precision of the spindle and bearing system, appropriate tolerances can prevent unnecessary deformation and temperature rise during bearing operation” as the most important, followed by “B-2-4 Enhance spindle dynamic balance, incorporate structural design to avoid resonance points, reducing resonance during machine operation”, “B-2-2 Add sensors to the spindle and bearing system to detect the temperature generated during high-speed rotation of the spindle, facilitating feedback to the cooling system for timely temperature adjustment”, and lastly “B-2-3 Precision machining of high-precision product components, matching the spindle with cutting conditions based on material properties and tooling, high spindle speed and torque effectively enhance production efficiency”.
Concerning the sub-technical items of ‘B-3 Feed Mechanism and Servo Motor’, “B-3-1 Utilizing servo intelligent tuning technology in conjunction with overall machine rigidity to swiftly adjust axial dynamic errors, thereby improving the dynamic response characteristics and part accuracy of CNC machine tools”, and “B-3-2 Optimizing the micro displacement of the feed mechanism and servo motor will help improve product processing accuracy”, the weight values and levels of importance within the hierarchical structure are as indicated in
Table 9. According to
Table 9, experts believe that among the sub-technical projects, “B-3-1 Utilizing servo intelligent tuning technology in conjunction with overall machine rigidity to swiftly adjust axial dynamic errors, thereby improving the dynamic response characteristics and part accuracy of CNC machine tools” is of utmost importance, followed by “B-3-2 Optimizing the micro displacement of the feed mechanism and servo motor will help improve product processing accuracy” of products.
The sub-technical items of ‘B-4 Controller’, ‘B-4-1 The controller serves as the brain of the numerical control machine tool, responsible for coordinating information management and compensatory actions, enhancing its user-friendly interface, and contributing to the transition towards Industry 5.0’, ‘B-4-2 Constructing an auxiliary module in the controller—developing intelligent machining setup software to enable operators to quickly complete machining settings’, ‘B-4-3 Enhancing the controller’s compensation system, allowing for real-time compensation for errors caused by structural displacement during operation, achieving intelligent control’, ‘B-4-4 Enhancing the controller compensation system to promptly compensate for processing errors caused by tool wear, while also incorporating tool life and precision management functions to achieve intelligent control’, ‘B-4-5 Enhancing the controller compensation system to promptly compensate for feed mechanism movement errors, achieving intelligent control’, and ‘B-4-6 Connecting sensors and measurement equipment to communicate, utilizing data collection to provide feedback to the controller system, improving machine processing speed (cost) and precision (quality)’, are ranked by their weight values and levels of importance in the hierarchical structure as shown in
Table 10”. According to
Table 10, the consistency test analysis of the technical projects shows a Consistency Index (C.I.) of 0.0085, which is less than 0.1, and a Consistency Ratio (C.R.) of 0.0068, also less than 0.1, indicating that the consistency test has been passed. The importance level of the evaluated indicators by experts and scholars is consistent. Experts and scholars consider the development sequence of sub-technical projects, with ‘B-4-4 Enhancing the controller compensation system to promptly compensate for processing errors caused by tool wear, while also incorporating tool life and precision management functions to achieve intelligent control’ as the most critical, having a weight of 0.2167. This indicates that experts prioritize the perfection of the controller compensation system in the development of Computer Numerical Control (CNC) machine tools, significantly benefiting the machining of parts. This is followed by ‘B-4-3 Perfecting the controller compensation system to compensate for errors due to structural displacement during operation, achieving intelligent control’, ‘B-4-1 The controller serves as the brain of the numerical control machine tool, responsible for coordinating information management and compensatory actions, enhancing its user-friendly interface, and contributing to the transition towards Industry 5.0.’, ‘B-4-5 Enhancing the controller compensation system to promptly compensate for feed mechanism movement errors, achieving intelligent control’, ‘B-4-6 Connecting sensors and measurement equipment to communicate, utilizing data collection to provide feedback to the controller system, improving machine processing speed (cost) and precision (quality)’, and finally ‘B-4-2 Constructing an auxiliary module in the controller—developing intelligent machining setup software to enable operators to quickly complete machining settings’.
The sub-technical items of ‘B-5 Troubleshooting’, ‘B-5-1 Set up remote connection services to handle machine shutdowns due to controller problems, enabling prompt resolution of system malfunctions remotely to minimize machine downtime and production capacity impact’, ‘B-5-2 Set up remote connection services to handle machine stoppages due to driver problems, allowing for prompt resolution of system faults remotely to reduce machine downtime and minimize the impact on production capacity’, and ‘B-5-3 Remote monitoring and fault detection do not require manual intervention, capable of predicting and immediately rectifying problems, thus decreasing machine downtime’, are ranked in terms of weight values and importance levels in the hierarchical structure as shown in
Table 11.
Table 11 reveals that the consistency test analysis of the technical items shows a Consistency Index (C.I.) of 0.038, which is below 0.1, and a Consistency Ratio (C.R.) of 0.0066, also below 0.1, indicating that the consistency test has been passed. The importance level of the evaluated indicators by experts and scholars is consistent. Experts and scholars believe that in the sequence of development for sub-technical projects, ‘B-5-1 Set up remote connection services to handle machine shutdowns due to controller problems, enabling prompt resolution of system malfunctions remotely to minimize machine downtime and production capacity impact’ is of utmost importance. This is followed by ‘B-5-3 Remote monitoring and fault detection that do not require manual intervention, capable of predicting and immediately resolving issues to minimize machine downtime’, and lastly, ‘B-5-2 Set up remote connection services to handle machine stoppages due to driver problems, allowing for prompt resolution of system faults remotely to reduce machine downtime and minimize the impact on production capacity’.
In the sub-technical items of ‘B-6 Intelligent Monitoring’, ‘B-6-1 Intelligent manufacturing utilizes Internet communication and monitoring technologies to conduct fault detection, diagnosis, and monitoring for CNC machine tools’, and ‘B-6-2 Visual monitoring of CNC machines in real-time processing conditions, with sensor data feedback, can prevent errors, promptly eliminate faults, and ensure stable machine operation’. The weight values and importance levels are ranked in the hierarchical structure as shown in
Table 12.
Table 12 indicates that experts and scholars consider the development sequence of sub-technical projects to prioritize ‘B-6-1 Intelligent manufacturing utilizes Internet communication and monitoring technologies to conduct fault detection, diagnosis, and monitoring for CNC machine tools’ as the most important. This is followed by ‘B-6-2 Real-time visual monitoring of CNC machines, along with feedback from sensing components, which can prevent errors, promptly resolve faults, and ensure stable machine operation’.
In the sub-technical items of ‘B-7 Cloud Database and Data acquisition’, ‘B-7-1 Setting up a cloud database enables quick cross-matching for debugging and offers the best machining parameters, leading to a comprehensive processing environment’, ‘B-7-2 Connecting network devices to machine tools for CNC program analysis enables feedback for optimizing tool paths in subsequent processing, making it vital analytical data for machine monitoring systems’, ‘B-7-3 Creating a data collection system for analyzing CNC machine data collection technology facilitates swift adjustment of processing conditions (such as feed rate and speed)’, and ‘B-7-4 Creating a data collection system for analyzing tool wear measurement data allows for instant feedback for tool wear compensation, enhancing the smart tool life management system’, the weight values and importance levels are ranked in the hierarchical structure as shown in
Table 13.
Table 13 reveals that the consistency test analysis of the technical project shows a Consistency Index (C.I.) of 0.0285 and a Consistency Ratio (C.R.) of 0.0317, both below 0.1, indicating the test has passed the consistency examination. The importance level of the evaluated indicators by experts and scholars is consistent. The consensus among experts and scholars indicates that the importance levels of the evaluation indicators align. They consider ‘B-7-4 Creating a data collection system for analyzing tool wear measurement data allows for instant feedback for tool wear compensation, enhancing the smart tool life management system’ as the most critical. This is followed by ‘B-7-2 Connecting network devices to machine tools for CNC program analysis enables feedback for optimizing tool paths in subsequent processing, making it vital analytical data for machine monitoring systems’, then ‘B-7-3 Creating a data collection system for analyzing CNC machine data collection technology facilitates swift adjustment of processing conditions (such as feed rate and speed)’, and finally ‘B-7-1 Setting up a cloud database enables quick cross-matching for debugging and offers the best machining parameters, leading to a comprehensive processing environment’.
In the sub-technical items of ‘B-8 Intelligent Manufacturing’, ‘B-8-1 With experienced masters able to communicate, we can move towards the goal of human–machine collaboration in Industry 5.0’, ‘B-8-2 Connecting and communicating automated equipment (such as robotic arms) is a step towards the goal of human–machine collaboration in Industry 5.0’, and ‘B-8-3 Combining intelligent handling (AGV) with robotic arms is a step towards transitioning from Industry 4.0 to Industry 5.0’, the ranking of weight values and importance levels in the hierarchical structure is shown in
Table 14.
Table 14 reveals that the consistency test analysis of the technical project shows a Consistency Index (C.I.) of 0.0001 and a Consistency Ratio (C.R.) of 0.0002, both below 0.1, thereby passing the consistency examination. The importance level of the evaluated indicators by experts and scholars is consistent. Experts and scholars believe that in the sequence of development for the sub-technical project, ‘B-8-3 Combining intelligent handling (AGV) with robotic arms is a step towards transitioning from Industry 4.0 to Industry 5.0’ is of paramount importance, with a weight value of 0.4831. This indicates that the integration of smart transport and robotic arms is seen as the future production trend for manufacturers; thus, incorporating these devices into CNC machine tools will further advance towards Industry 5.0. Following this, ‘B-8-2 Connecting and communicating automated equipment (such as robotic arms) is a step towards the goal of human–machine collaboration in Industry 5.0’, and finally ‘B-8-1 With experienced masters able to communicate, we can move towards the goal of human–machine collaboration in Industry 5.0’.
In the fuzzy hierarchical analysis method, from the aforementioned results of the analysis, the weights and importance rankings of each level are obtained and have passed the consistency index test, indicating that the dimensions, technical projects, and sub-technical projects all meet the standards of consistency. To determine the overall hierarchical structure constructed in this study, the proportion of sub-technical projects in the total weight must be calculated through hierarchical linkage to obtain their global weight values and importance rankings.
Table 15 is a statistical table of hierarchical linkage analysis results, intended to serve as a reference for future development trends for CNC machine tool manufacturers.