The rapid development of modern manufacturing has led to increasingly stringent requirements for the precision, quality, and production efficiency of mechanical parts.

As critical components in mechanical transmission systems, the machining precision and surface quality of bushing-type parts directly impact the overall performance of the machine.

Traditional turning and milling methods suffer from issues such as fragmented processes, low machining efficiency, and difficulty in ensuring precision.

These limitations make it challenging to meet the modern manufacturing industry’s demand for high-quality, high-efficiency machining of bushing-type parts.

Advantages of Turning-Milling Composite CNC Machining

In contrast, we use CNC machining technology widely in mechanical processing because of its high precision, high efficiency, and high flexibility.

As a major branch of CNC machining technology, turning-milling composite machining integrates turning and milling functions into a single machine tool.

This integration enables the efficient and precise machining of complex parts.

Applying this technology to the machining of bushing-type parts can effectively address the issues inherent in traditional machining methods, thereby improving machining efficiency and product quality.

This study aims to design a machining plan based on turning-milling composite CNC machining processes.

We tailor the plan to the structural characteristics and machining requirements of bushing-type parts.

It will involve process parameter optimization and machining process simulation, with the goal of providing technical support for the efficient and precise machining of bushing-type parts.

The anticipated outcomes of this study will offer new insights and methods for the efficient and precise machining of bushing-type parts.

These outcomes will promote the application and development of turning-milling composite CNC machining technology in the field of mechanical manufacturing.

Overview of Combined Turning and Milling CNC Machining Technology

• Basic Concepts

Combined turning and milling CNC machining technology is a highly efficient machining method that integrates turning and milling operations.

By performing multiple machining functions on a single CNC machine tool, it significantly improves machining efficiency.

At its core, this technology relies on the CNC system to precisely control the machine tool.

This enables us to perform turning and milling operations continuously on the same workpiece without repeated clamping and adjustments.

The fundamental principle of turning-milling composite CNC machining technology involves controlling the machine tool’s spindle and feed axes via the CNC system.

This control enables the tool to move in different directions.

We primarily use the turning component to machine the outer circles, inner bores, and end faces of rotationally symmetric parts.

We apply the milling component to machine complex contours and grooves.

The combination of these two processes enables turning-milling composite CNC machining technology to meet the machining requirements of various complex parts.

Compared to traditional turning and milling processes, turning-milling composite CNC machining technology offers significant advantages.

It reduces the number of workpiece setups, thereby avoiding the accumulation of errors caused by repeated clamping and improving machining accuracy.

At the same time, this technology enables continuous multi-process machining.

It shortens the waiting time between operations.It also significantly improves production efficiency (as shown in Figure 1).

• Technical Features

Turn-mill composite CNC machining technology plays a significant role in modern manufacturing due to its unique characteristics.

(1) High-precision Machining Capability.

Through precise control by the CNC system, turning-milling composite CNC machining technology can achieve micron-level machining accuracy.

This is particularly important for the machining of parts with high precision requirements, such as bushings.

It not only ensures that the dimensions and shapes of parts meet design requirements but also significantly improves the fit accuracy of parts.

(2) Extremely High Machining Efficiency.

Traditional turning and milling processes typically require multiple setups.

In contrast, turning-milling composite CNC machining technology completes multiple operations in a single setup.

This reduces waiting time between operations and minimizes setup errors, thereby significantly improving production efficiency.

For example, when machining bushing parts, this technology simultaneously performs external turning, internal boring, and face milling, significantly shortening the machining cycle.

(3) Versatile Machining Capabilities.

Traditional turning and milling processes generally handle only a single type of machining task.

In contrast, turning-milling composite CNC machining technology enables a single machine tool to perform multiple machining functions, including turning, milling, drilling, and tapping.

This versatility allows turning-milling composite CNC machining technology to meet the machining demands of various complex parts.

It further expands the scope of machining.It also improves equipment utilization.

CNC Turning and Milling Process for Bushings

• Technical Analysis of Bushings

The bushing part discussed in this paper is made of 45 steel.

The raw material is a bar stock measuring 110 mm × 120 mm.

The part’s locating references are the centerlines of 35H7 and 100f9, as well as the bottom end face of the bushing.

Additionally, when machining the 35H7, we impose stricter requirements on the specific position of the 100f9 outer diameter.

We must keep it within a 0.05 mm tolerance range.We must also specify all part dimensions completely.

All tolerances must meet industry standards.

• Selection of Machine Tools and Fixtures

When we machine bushing parts using a standard CNC machine, we typically require multiple setups to complete all processes.

This not only increases processing time but also raises the likelihood of machining errors.

To address this issue, this paper selects the HTC2050Z turning and milling center for machining.

Equipped with a FANUC 0i-TC CNC system and a tool magazine with a capacity of 12 tools, this machine can meet a wide range of machining requirements.

Regarding fixture selection, the HTC2050Z turn-mill center comes standard with a three-jaw chuck, which provides stable clamping force to ensure positioning accuracy during machining.

To guarantee machining accuracy, we select the outer diameter and end face of the left end of the bushing part as the rough and finish reference surfaces.

We machined the left-end outer diameter and end face into rough reference surfaces via turning.

We then clamped and positioned the workpiece using the three-jaw chuck to ensure the precision of subsequent machining operations.

In CNC machining, the selection of the programming origin directly affects machining accuracy.

In this case, the programming origin is set at the right end face of the bushing part, with the positive directions of the X-axis and Z-axis aligned accordingly.

This facilitates programming operations for the operator.

It effectively reduces machining errors.It improves machining efficiency.

It enhances the machining accuracy of each process step.

As a result, it ensures the quality of the final product (as shown in Figure 2).

• Principles for Formulating Key Composite Reinforcement Process Plans

(1) Reference Surface First Principle.

During the machining process, we should select and machine the reference surface first.

We then use it as the positioning reference for subsequent machining operations.

For bushing parts, the selection and machining accuracy of the reference surface directly affect the machining accuracy of subsequent operations.

When formulating machining process plans, operators should prioritize the machining of the reference surface to ensure its accuracy meets the requirements of subsequent operations.

(2) Rough Machining Before Finishing Principle.

Under the “rough before finish” principle, we must perform rough machining first to remove the majority of the material allowance.

We then perform finish machining to achieve the final dimensional accuracy and surface quality requirements.

For bushing parts, we primarily use rough machining to rapidly remove material and reduce machining time.

We then use finish machining to ensure the final dimensional accuracy and surface quality of the part.

Therefore, when we formulate machining process plans, personnel must reasonably arrange the sequence of rough and finish machining.

This helps us comprehensively improve machining efficiency and quality.

(3) Principle of Process Consolidation.

The principle of process consolidation involves grouping multiple machining operations together to reduce the number of setups and improve machining efficiency.

This is particularly important in the machining of bushing parts.

These parts involve numerous operations, such as turning, milling, and drilling.

Operators must fully implement this principle to effectively minimize setups and enhance efficiency.

When we formulate a machining process plan, we should arrange the sequence of operations reasonably based on the structural characteristics and machining requirements of the part.

We should also strive to complete multiple machining tasks in a single setup.

Design of Machining Process Routes

CNC machining technology offers advantages such as high precision, high efficiency, and high automation, and can significantly improve part quality and production efficiency.

In the machining of bushing parts, the design of the turning-milling composite CNC machining process route is particularly critical.

Through the rational design of the machining process route, it is possible to effectively reduce machining time, improve machining accuracy, and lower production costs.

This paper will focus on the key aspects of designing a turning-milling composite CNC machining process route for bushing parts.

It will particularly emphasize the toolpath design for internal turning to ensure the safety of the machining process.

• Toolpath for Milling Flat Surfaces

In the turning-milling composite machining of bushing parts, the design of the toolpath for milling flat surfaces is a critical factor in improving machining efficiency.

To achieve efficient cutting, this paper proposes using a rectangular ring-cutting method in the XY directions and cutting in layers in the Z direction, with a layer height of 2 mm.

Rectangular Ring-Cutting Strategy in the XY Plane

Rectangular ring cutting is a highly efficient toolpath method.

By forming multiple annular cutting paths in the XY plane, it effectively reduces idle travel time and improves cutting efficiency.

In practice, the tool rapidly moves from the initial position to the edge of the workpiece to begin the first layer of cutting.

The tool then performs annular cutting along the edge of the workpiece, with the cutting path gradually contracting inward to form multiple annular paths.

The width of each annular path is adjusted based on the workpiece dimensions and tool diameter.

Between each annular path, the tool switches paths via rapid traverse (G00) to minimize idle travel time.

When the tool reaches the center of the workpiece, the first layer of cutting is completed.

Through this rectangular annular cutting method, the tool forms multiple annular paths in the XY plane, effectively reducing idle travel time and improving cutting efficiency.

Layered Cutting Method in the Z Direction

In the Z direction, a layered cutting method is employed, with a cutting depth of 2 mm per layer.

The tool begins cutting from the workpiece surface at a depth of 2 mm.

After we complete the first layer of rectangular ring cutting in the XY plane, the tool rapidly moves to the starting position of the next layer.

It then continues the rectangular ring cutting.We maintain a cutting depth of 2 mm for each layer.

The tool then cuts downward layer by layer until the predetermined cutting depth is reached.

This layered cutting method effectively controls the cutting depth, ensuring machining quality while improving cutting efficiency.

• Feed Paths for Boring

Internal boring presents greater challenges than external turning.

Due to limited space, the feed and retract paths of the tool are restricted, making collisions between the tool and the workpiece or fixture more likely.

Furthermore, the direction of cutting forces in internal boring is opposite to that in external turning.

This can easily cause tool vibration and workpiece deformation, thereby affecting machining accuracy.

To prevent tool collisions during internal turning, the starting point should be selected outside the right end face.

This ensures the tool has sufficient space for adjustment and positioning before entering the bore, thereby avoiding collisions with the workpiece.

Starting the cut from outside the right end face creates an outward-to-inward machining path.

This path facilitates control of cutting forces and feed rates, reducing tool vibration and workpiece deformation.

Starting the feed from outside the right end face allows chips to be naturally evacuated, preventing chip buildup inside the bore and extending tool life.

Internal Turning Toolpath Design and Machining Strategy

When designing the feed path for internal turning, a layered cutting approach is adopted to reduce cutting forces and tool vibration.

Material is removed layer by layer, with the cutting depth for each layer selected based on the tool’s strength and the workpiece material’s properties;

The toolpath for internal turning employs a helical feed method.

It advances gradually from the outside in, effectively controlling cutting forces and feed rates.

This approach also reduces tool vibration and workpiece deformation.

Application of the G90 Internal Cylindrical Fixed Cycle

To improve machining efficiency and accuracy, we use the G90 internal cylindrical fixed cycle for internal turning.

This enables repeatable machining within a fixed cycle.It reduces programming workload.It also enhances machining efficiency.

When applying the G90 internal cylindrical fixed cycle, the operator first moves the tool to a position outside the right end face of the bushing part and sets the starting point.

Based on the workpiece dimensions and machining requirements, the cycle parameters for the G90 command are set, including cutting depth, feed rate, and cutting speed.

Next, the G90 command is initiated, and the tool performs internal turning according to the preset cycle parameters.

After each cycle, the tool automatically returns to the starting point to prepare for the next cycle.

Following each cycle, the machining quality is inspected to ensure that the internal bore dimensions and surface finish meet the requirements.

• Drilling Feed Path

During the hole-making fixed cycle, the machine rapidly positions to the initial position (Point R).

It performs the hole-making operation and executes tasks such as tool movement and pausing at the bottom of the hole.

The machine then automatically returns to the plane of Point R.

The end face hole 35H7 on the bushing part has a depth of 80 mm, and the 2-M6 pilot hole has a depth of 25 mm.

The drilling method uses a fixed cycle for step-by-step drilling, with depth control utilizing a reciprocating chip removal fixed cycle.

Drilling operations are strictly performed in accordance with G83 requirements.

When the center point of the radial hole 2×15H7 deviates from the workpiece’s rotary axis, the operator must promptly switch the power tool to a radial power tool.

Machine Setup and Mode Switching

Additionally, before the machine tool operates, we must activate the hydraulic switch to adjust the milling power axis, X-axis, Y-axis, and rotary axis.

We return these axes to their initial positions.We also ensure that they do not contact the tailstock.

When the rotary axis returns to the home position, enter the CO code into the system to switch to MDI mode.

Use the M70 and M71 commands in accordance with the machining requirements for the sleeve component:

Use the M70 command for turning operations and the M71 command for end-face drilling to ensure successful transition to rotary axis mode (as shown in Table 1).

Once the internal bore, external turning, and all end-face drilling operations are complete, switch to the power spindle for milling to perform radial drilling and surface milling operations.

Table 1. Common M Codes for Powered Tools

CNC Turning-Milling Process Design and Toolpath Optimization

The design of the CNC turning-milling combined machining process for bushing components is a critical factor in ensuring machining quality and production efficiency.

In the design of the toolpath for internal turning, the selection of the starting point and the optimization of the toolpath are particularly important.

By selecting an appropriate starting point and employing layered cutting and helical feed methods, we can effectively prevent tool collisions and other safety incidents.

This approach also improves machining quality and efficiency.

Furthermore, utilizing the G90 internal cylindrical fixed cycle can further improve machining efficiency and precision, reduce programming workload, and enhance process safety.

At the same time, during actual machining, the machining process route should be flexibly adjusted based on the specific workpiece material, dimensions, and machining requirements.

Continuous optimization of the machining process route will further improve the machining quality and production efficiency of bushing components.

This will help meet the demands of modern manufacturing for high-precision, high-efficiency machining.

Conclusion

In summary, through an in-depth study of turning-milling composite CNC machining technology, this paper demonstrates its significant advantages in the machining of bushing components.

Through precise CNC system control and optimized machining process route design, turning-milling composite CNC machining technology improves machining accuracy and efficiency.

It also significantly reduces the number of setups and the accumulation of errors.

As the manufacturing industry’s demand for high-precision, high-efficiency machining continues to grow, turning-milling composite CNC machining technology will play an increasingly important role in the future.

Future research can further explore its application in machining more complex parts.

It can also investigate how technological innovations can enhance its machining capabilities and efficiency.