As high-end manufacturing transforms greater precision, efficiency, and intelligence, precision mechanical parts are being increasingly widely applied in sectors such as the automotive and aerospace industries.
Their machining accuracy, surface quality, and production efficiency determine the performance and market competitiveness of the end products.
Turning-Milling Composite Machining Technology
Turning-milling composite machining is an advanced technology that integrates multiple machining functions, including turning, milling, drilling, and tapping, into a single process. It enables multiple machining operations to be completed in a single setup.
By effectively reducing clamping errors and enhancing part machining accuracy, it has become a core technological method for the machining of precision mechanical parts.
Industry Requirements and Production Pressures
Currently, the machinery industry faces urgent demands for energy conservation, emissions reduction, and lightweight upgrades.
Precision parts face continuously increasing machining accuracy requirements.
At the same time, manufacturing must balance mass production efficiency and cost control to support the industry’s shift toward large-scale production.
Current Industrial Challenges
Most enterprises currently face numerous challenges in the turning-milling composite machining of precision mechanical parts.
These challenges include a lack of systematic process routes, unreasonable process sequencing, and issues such as redundant machining and idle waiting time.
Operators set cutting parameters based on experience instead of considering part materials, machining characteristics, and equipment performance.
Tool and fixture configurations are unreasonable, lacking versatility and sufficient positioning accuracy;
Equipment operation and maintenance systems remain inadequate, which leads to high failure-related downtime.
At the same time, digital management levels remain low, and the system cannot support real-time collection or analysis of machining process data.
Research Direction and Objectives
Process optimization research draws on practical experience from turning-milling composite machining of precision mechanical components.
It develops a multidimensional and systematic study framework based on this foundation.
This study aims to resolve machining bottlenecks and improve machining accuracy and production efficiency.
It also seeks to reduce production costs and provide practical guidance for machining similar parts.
Theoretical Foundations and Current Status Analysis
Core Principles
Turning-milling composite machining integrates the core components of a turning spindle and a milling power head onto a single machine tool.
This configuration enables multiple machining operations to be completed in a single setup, including turning outer diameters, bores, end faces, and threads, as well as milling flat surfaces, grooves, and curved surfaces.
The centralization of processes is its core characteristic.
This technology reduces the number of part setups when compared with traditional multi-step machining methods.
It also mitigates the accumulation of setup errors and significantly improves dimensional accuracy and geometric tolerance control.
At the same time, it shortens part transfer and waiting times, substantially boosting overall production efficiency.
Multiple factors influence the quality and efficiency of turning-milling composite machining.
These factors include machining processes, cutting parameters, tool performance, fixture positioning, equipment operational performance, and the professional skills of operators.
Among these, the rational planning of the machining sequence forms the foundation of the process; the scientific setting of cutting parameters is the core key;
And the compatibility of tools and fixtures is a crucial guarantee of machining quality.
These three elements work in concert and complement one another, jointly determining the overall machining outcome.
Current Status and Challenges of Combined Turning and Milling
The field of combined turning and milling for precision mechanical parts in China demonstrates advanced technology but lacks standardized practices in actual application.
Most enterprises have equipped themselves with high-end machining equipment and possess the hardware foundation for high-precision, high-efficiency machining.
However, significant shortcomings appear in software-related aspects such as process planning, parameter setting, and equipment operation and maintenance.
This prevents the full realization of the equipment’s potential, resulting in machining quality and production efficiency that fall short of expectations.
1. Process Route Planning Issues
The following five aspects primarily reflect the core issues, with process route planning showing a lack of rationality.
Many enterprises still adhere to traditional processes and fail to leverage the advantages of turning-milling composite machining.
This results in poor process coordination, redundant machining, and time-consuming waiting periods.
It also reflects inadequate consideration of factors such as part deformation and incomplete stress relief during process planning, which in turn compromises part quality.
2. Lack of Scientific Cutting Parameter Setting
The setting of cutting parameters lacks scientific rigor.
Operators often determine cutting parameters based on personal experience.
This approach can lead to an excessive focus on machining quality, resulting in reduced machining efficiency and increased production costs.
Furthermore, the pursuit of machining efficiency can lead to excessive cutting forces, resulting in part deformation and rapid tool wear.
3. Tool and Fixture Configuration Deficiencies
The configuration of cutting tools and fixtures is inadequate.
Tool selection does not take into account the material and structural characteristics of the parts, and poor tool management leads to excessive tool wear.
Fixtures suffer from low positioning accuracy and poor versatility, which not only prolongs setup time but also increases machining costs.
4. Equipment Operation, Maintenance, and Digital Control Problems
The level of equipment operation, maintenance, and control urgently needs to be improved.
Many enterprises have high equipment failure and downtime rates; the lack of daily operation and maintenance leads to accelerated wear of key components, affecting machining accuracy.
Furthermore, the machining process lacks digital control; the system cannot monitor or analyze data, which constrains product quality and production progress.
5. Insufficient Operator Skills and Training
Operators lack sufficient professional skills.
Some personnel have not received specialized training in turning-milling composite machining and lack knowledge of process optimization and machining principles.
Consequently, they are unable to effectively handle machining anomalies, which in turn affects machining quality and efficiency.
Process Optimization Plan for Combined Turning and Milling of Precision Mechanical Parts
To address the aforementioned issues, drawing on practical experience in the machining of precision parts for internal combustion engine components, this paper uses internal combustion engine parts as an example.
It examines five key dimensions—machining processes, cutting parameters, tool and fixture configuration, equipment operation and maintenance, and digital control and management.
This approach aims to achieve simultaneous improvements in machining accuracy and production efficiency.
Optimization of Machining Process Routes
The core of process route optimization lies in fully leveraging the advantages of centralized turning-milling operations.
Process planning follows key principles, including separating roughing from finishing, ensuring rational sequence transitions, reducing the number of setups, and avoiding machining deformation.
It also takes into account the specific machining characteristics and material properties of the parts.
Process integration, stress relief, and sequence optimization shorten the machining cycle and improve machining accuracy.
Process Integration and Setup Reduction
Turning-milling composite equipment enables process integration and simplification by consolidating multiple traditional separate operations onto a single machine.
This integration allows multiple processes to be completed within a single setup, which reduces the number of setups and shortens machining time per part.
An internal combustion engine connecting rod serves as an example. The traditional machining process requires five setups.
After optimization, process planning reduces this to a single setup, enabling end face turning, drilling, and turning of the large and small ends in one operation. Separate precision grinding then processes both end faces.
Optimization reduces the number of setups from five to two, thereby improving machining efficiency.
Roughing, Finishing, and Stress Relief Strategy
Separation of roughing and finishing, along with stress relief, is necessary to address stress-induced deformation in parts.
Process planning schedules roughing and finishing separately and adds a stress relief process after roughing.
Natural aging is the preferred method to effectively release internal stresses and minimize part deformation.
In the case of high-precision internal combustion engine valve seat ring machining, low-temperature annealing is applied after rough machining.
This treatment improves control of form and position tolerance errors during subsequent finishing, achieving higher precision.
Process Sequence Optimization Guidelines
Process sequence optimization must be based on the machining characteristics of the part.
Arrange processes such as drilling and tapping after turning and milling to prevent metal chips from scratching the machined surfaces.
Schedule finishing operations during periods when equipment is running stably to minimize the impact of vibrations during startup.
For parts with multiple steps and grooves, adopt a sequence from the inside out and from rough to finish to reduce interference.
Process circumferential rectangular keyways using an intermittent, staggered approach to avoid thermal stress concentration or deformation.
Optimization of Cutting Parameters
A combined approach of theoretical analysis and process testing is used for optimization.
Workpiece material, machining characteristics, and machine tool performance are taken into account during this process.
Spindle speed, feed rate, and cutting depth are optimized to determine the optimal parameter combination, while prioritizing accuracy, balancing efficiency, and maintaining controllable costs.
This approach allows for theoretical analysis and the preliminary determination of parameters.
Based on metal-cutting theory, excessively high spindle speeds accelerate tool wear, excessively fast feed rates can cause part deformation, and excessive cutting depths compromise machining accuracy.
Mechanical properties of the part and equipment parameters define a preliminary range of cutting parameters. Process trials then determine the final parameter values.
A single-factor experimental method can be adopted for precision shaft parts made of 45 steel as an example.
The experiment selects a turning-milling machining center, carbide-coated cutting tools, a coordinate measuring machine, and related equipment.
These tools and systems measure machining accuracy, surface roughness, tool wear, and processing time per part under different parameter combinations.
Orthogonal experimental design analysis determines the optimal parameter combination.
Meanwhile, process planning sets differentiated parameters for rough machining, semi-finishing, and finishing.
Rough machining aims for efficient material removal, employing large cutting depths with moderate feed rates and spindle speeds;
Semi-finishing eliminates residual errors from rough machining, using moderate parameters;
Finishing ensures precision and surface quality, employing small cutting depths and feed rates, along with moderate spindle speeds.
Optimization of Tool and Fixture Configuration
Turning-milling composite machining requirements are integrated with workpiece characteristics to achieve optimization in three areas.
These areas include tool selection, management, and fixture design.
This approach improves positioning accuracy and clamping efficiency, reduces tool wear, and lowers production costs.
Tool Selection and Cutting Parameter Optimization
Tool selection and parameter optimization rely on choosing appropriate tools based on the workpiece material and machining characteristics.
YT15 and YW2 carbide-coated tools serve common steels such as 45 steel due to their high hardness and excellent wear resistance.
Ceramic tools or cubic boron nitride (CBN) tools are recommended for machining high-strength, high-hardness parts.
Solid, modular, or specialized form tools are selected based on the part’s machining characteristics.
Geometric parameters such as the rake angle and clearance angle are then optimized to ensure machining quality.
Tool Management and Lifecycle Control
Improvement of the tool management system and mechanisms is essential to enhance overall efficiency.
Classification management and labeling are implemented for tool inventory to ensure structured control.
Full traceability of tools throughout their lifecycle is achieved through these measures.
Use online monitoring equipment to track tool wear in real time, providing timely alerts for replacement when wear reaches critical thresholds to prevent impacts on machining quality.
Regrinding restores slightly worn tools, allowing their reuse and improving tool utilization.
Regularly analyze tool consumption data to optimize tool selection and cutting parameters, thereby achieving cost control.
Establish a standardized tool library to pre-match tools with corresponding cutting parameters, effectively reducing tool changeover time and improving machining efficiency.
Fixture Design and Positioning Optimization
Fixture design and optimization must focus on precision, versatility, and stability.
High-precision, versatile specialized fixtures are designed for improved stability and adaptability.
High-precision positioning methods such as single-face dual-pin and zero-point positioning systems are adopted to strictly control positioning errors within permissible limits.
Develop flexible fixtures to accommodate parts of different specifications, reducing the frequency of fixture changes and lowering auxiliary time costs.
Uniform clamping methods such as hydraulic or pneumatic systems are employed to apply clamping force smoothly.
This prevents part deformation caused by excessive clamping force and ensures machining accuracy.
Optimization of the Equipment Operation and Maintenance System
A scientific and comprehensive equipment operation and maintenance system is established based on the structural characteristics and operating specifications of turning-milling composite machining equipment.
This system focuses on reducing the frequency of breakdowns and downtime, thereby ensuring the machining accuracy and service life of the equipment.
A robust preventive maintenance mechanism replaces the traditional reactive maintenance model.
This system also incorporates the development of detailed, actionable maintenance plans.
Routine Maintenance and Periodic Inspection Strategy
Routine maintenance involves operators checking power supplies and lubrication, as well as cleaning metal shavings and oil residue from the equipment.
Maintenance schedules include weekly inspections of the spindle, guideways, and feed systems.
The system performs monthly precision testing and calibration.
It also carries out comprehensive maintenance and potential hazard inspections on a quarterly basis.
Define replacement cycles for wear-prone components and replace them promptly.
Automated Self-Inspection and Precision Calibration
Automated self-inspection procedures are additionally integrated into the system.
Upon startup, the equipment automatically checks parameters such as spindle speed and feed axis accuracy to ensure optimal operating conditions.
Environmental Control and Compensation Mechanisms
Strengthen equipment precision calibration and maintenance efforts.
Professional testing instruments such as laser interferometers and ball bar systems are utilized to periodically inspect equipment performance.
These instruments measure key precision parameters, including positioning accuracy and spindle rotation.
If deviations exceed the permissible range, adjust and calibrate the equipment promptly.
Strengthen management of the equipment operating environment by placing equipment in workshops with constant temperature and humidity and free from vibration.
Environmental parameters are monitored in real time, while machining parameters are adjusted using compensation algorithms.
This approach effectively mitigates the impact of environmental factors on equipment accuracy.
Failure Response and Maintenance Intelligence System
A professional maintenance team with clearly defined roles and responsibilities is established to improve the emergency response mechanism for equipment failures.
This arrangement ensures rapid response and efficient resolution of issues.
An equipment failure database records failure types, causes, and corrective actions in detail.
It identifies patterns in equipment failures and provides scientific guidance for preventive maintenance.
Develop standardized emergency response procedures for common failures to standardize operational steps and improve the efficiency of troubleshooting.
Remote assistance capabilities support real-time communication between operators and technical experts.
This enables rapid resolution of operational challenges and effectively reduces downtime caused by equipment failures.
Optimization of the Digital Monitoring and Control System
It is necessary to introduce digital monitoring and control technologies and establish a comprehensive digital monitoring and control system.
Real-time monitoring, data collection, and in-depth analysis of the machining process enable precise control of production quality and progress.
This approach further enhances overall production management efficiency.
Real-Time Machining Process Monitoring
Sensors for cutting force, vibration, temperature, and other parameters are installed on the equipment to enable real-time monitoring of key machining variables.
Immediate alerts occur when parameter anomalies are detected, reducing quality risks and preventing equipment failures.
Built-in laser measurement systems or contact probes automatically inspect critical dimensions after machining, as machine tools are equipped with these devices.
Inspection data is fed back to the CNC system to enable real-time parameter compensation, ensuring machining accuracy.
AI vision inspection technology is additionally integrated into the system.
It rapidly identifies surface defects on workpieces, achieving higher detection speed and accuracy than traditional manual inspection methods.
Data Collection, Analysis, and Digital Twin Modeling
A machining process data collection system is established for the data collection and analysis phase.
It collects parameters such as equipment operating status, machining quality indicators, and production progress in real time.
Centralized storage ensures full traceability of data throughout the entire process.
Specialized data analysis software is introduced to enable in-depth data mining.
It provides a scientific basis for process optimization, equipment operation and maintenance, and production management.
A digital twin model enables data traceability throughout the entire machining lifecycle.
The system can automatically generate visual production reports, intuitively presenting various production data to provide reliable data support for production optimization decisions.
Intelligent Production Planning and Scheduling Optimization
Optimization of production planning and scheduling must be based on digital control data as the core foundation.
Order requirements, equipment operating status, and process standards are integrated to formulate scientific production plans.
These plans clearly define the specific tasks and progress milestones for each piece of equipment and each production step.
Scheduling management software monitors production progress in real time.
It also enables timely adjustments of production plans and scheduling strategies when anomalies such as equipment failures or substandard product quality occur.
This approach ensures stable production continuity and prevents production stoppages.
Process Optimization Experiment Validation
Comparative tests were carried out before and after optimization to verify the feasibility and effectiveness of the proposed process optimization scheme.
Precision shaft components made of 45 steel from a specific internal combustion engine parts manufacturer served as test subjects.
Key indicators, including machining accuracy, production efficiency, and production costs, were measured and analyzed.
Test Conditions
The CKX6140 turning and milling machining center served as the test equipment, while precision shaft components made of 45 steel were used as the test parts.
Before optimization, standard YT15 carbide tools performed the cutting operations; after optimization, YT15-coated tools performed the cutting operations.
Before optimization, a standard three-jaw chuck secured the workpieces for clamping; after optimization, a high-precision flexible fixture secured the workpieces for clamping.
The measurement instruments selected included a coordinate measuring machine (CMM), a surface roughness meter, and a tool wear measurement device.
A total of 100 parts of each type underwent machining, enabling comparison of machining parameters before and after optimization.
Test Results and Analysis
Tables 1–3 show a comparison of part machining accuracy, production efficiency, and production costs before and after implementing the optimization plan.
As shown in the tables, part machining accuracy improved significantly after process optimization, and the machining pass rate increased substantially.
Process optimization significantly improves production efficiency, substantially increases equipment utilization rates, and reduces production costs.
The key reasons for these improvements include: process optimization reducing clamping errors and deformation;
Optimized cutting parameters lowering cutting forces and temperatures;
Optimized tooling and fixtures enhancing positioning accuracy and cutting performance; and equipment maintenance and control ensuring machining stability.
| Scheme Implementation | Dimensional Tolerance / mm | Geometric Tolerance / mm | Surface Roughness / μm | Qualification Rate / % |
|---|---|---|---|---|
| Before Implementation | 0.007 ~ 0.010 | 0.008 ~ 0.012 | 1.0 ~ 1.6 | 89.2 |
| After Implementation | 0.004 ~ 0.006 | 0.005 ~ 0.008 | 0.6 ~ 0.9 | 95.7 |
Table 1. Comparison of Part Machining Accuracy
| Scheme Implementation | Processing Time per Piece / min | Output / (pieces·h⁻¹) | Equipment Utilization Rate / % |
|---|---|---|---|
| Before Implementation | 12.3 | 4.9 | 78.5 |
| After Implementation | 9.8 | 6.1 | 91.3 |
Table 3. Production Cost Comparison
Conclusion
Based on actual production practices in the combined turning and milling of precision mechanical parts, this paper conducts a systematic study on process optimization to address various core issues encountered during machining.
Practical validation confirms that the multidimensional, systematic process optimization scheme demonstrates high feasibility and effectiveness.
It can significantly improve the machining accuracy and production efficiency of precision mechanical parts, effectively reduce production costs, and overcome the current bottlenecks in the turning-milling composite machining process.
This optimization scheme supports batch production of precision parts by improving process stability and repeatability.
It also offers practical reference value for machining similar precision components, demonstrating strong engineering applicability and industrial implementation significance.