Precision Improvement Methods for Gate and Riser Grinding Using Five-Axis Technology

To tackle the issues of low precision, poor efficiency, and inconsistent quality in the post-processing of casting gatings and risers, this paper explores an optimized five-axis machining process for high-precision grinding. We designed and optimized an automated grinding device that integrates a three-axis slide, a rotary module, and a dual-station turntable. Additionally, we established a trajectory generation mechanism that combines manual teaching with external input. Key parameters, such as travel speed, tool overlap rate, and contact angle, were optimized, leading to the development of a reusable grinding process system. This method effectively reduces grinding time, improves surface quality and dimensional consistency, and enhances both automation and machining stability.

 

1 Introduction

The removal and surface grinding of casting gatings and risers significantly impact the appearance quality and dimensional accuracy of the finished product. Traditionally, this step has relied heavily on manual labor, leading to high labor intensity, low efficiency, and inconsistent results. To enhance the automation level and machining quality in processing casting gatings and risers, it is essential to develop an efficient and stable automated grinding process system that can meet the high-precision grinding requirements for complex casting gatings and risers.

2. Current Status and Problems of Grinding Process

2.1 Overview and Bottlenecks of Traditional Grinding Methods

In traditional manual grinding and the removal of risers and gating gates, operators typically use portable angle grinders and grinding wheels. While this manual grinding method is cost-effective and adaptable, it has several drawbacks, including high labor intensity, low efficiency, and inconsistent results. When producing castings that require high consistency in large batches, traditional manual grinding methods often lead to quality defects, such as missed areas, over-grinding, and significant deviations that can compromise the consistency of the grinding quality. Additionally, manual grinding poses occupational health hazards, including dust pollution and risks associated with tool handling, which can impede the workshop’s transition to more advanced, automated processes.

 

2.2 Existing Machine Tool Structure and Process Limitations

To enhance automation levels, some companies are trying to retrofit traditional gantry machining centers for casting grinding applications. However, these machines are primarily designed for metal cutting, which means their structural rigidity, range of motion, and control systems are not suitable for cleaning the complex curved surfaces of casting risers and gating gates. As a result, grinding operations on these machines depend significantly on advanced CNC programming and skilled operators. This reliance increases personnel training costs and limits the equipment’s versatility and flexibility.

 

2.3 Analysis of Grinding Accuracy, Efficiency, and Consistency Issues

The surface of the casting riser and the gating gate area is uneven, featuring complex transition structures and various materials. Traditional manual grinding, as well as semi-automatic machine tool grinding, often fail to produce consistent grinding paths. In areas with sharp curvature changes, the tool angle and the contact state between the tool and the workpiece become unstable. This instability can lead to inadequate grinding in some regions or excessive surface cutting, which can severely impact both the appearance and performance of the casting. Furthermore, reusing process parameters with precision is challenging, and grinding results can vary significantly between different operators or under different equipment conditions. As a result, it is difficult to ensure consistent product qualification rates.

 

3. Five-Axis Grinding Device Structural Design and System Composition

3.1 Overall Structural Composition

The structure of the grinding device has been optimized. The overall design (see Figure 1) features a frame composed of a base and a shell. Internally, it incorporates X, Y, and Z-axis linear slide modules, a rotary module, and a dual-station turntable, enabling five-axis linkage control. The three-axis linear slides are equipped with ball screw modules. A fixed frame is mounted on the X-axis slide, and it contains a nested Z-axis slide. The Z-axis slide is connected to the Y-axis slide to ensure high-precision spatial motion control.

The rotary module is positioned at the end of the Y-axis, allowing it to rotate along the sliding direction. The turntable is connected to a servo motor that drives the grinding tool, enabling flexible adjustments of its posture to suit complex curved surfaces. The dual-station turntable consists of a turntable base, a motor, and a reducer. The two workpiece turntables on either side can rotate either synchronously or independently, facilitating a seamless transition between loading and grinding tasks, which improves work efficiency and cycle continuity.

 

3.2 Control System and Operation Mode

The grinding device features an integrated equipment control system that allows for the unified scheduling of five-axis motion components. Its core controller operates in two modes: manual teaching mode and external import mode.

In manual teaching mode, the operator can adjust the slide speed and magnification using the controller. The tool moves along a standard casting gating path, allowing the operator to record key teaching points and motion patterns (either linear or circular). This information is then used to automatically generate preliminary grinding process documents.

In external import mode, the system imports the casting CAD model and tool parameters. It combines these with simulation software to design and verify the grinding trajectory, ultimately converting this into a directly executable process document.

 

3.3 Auxiliary Device Design

The design of the auxiliary structure ensures stable equipment operation and maintains a clean working environment. To protect moving CNC turning parts, a scale-like dust cover is installed between the fixed frame and the outer shell in the X-axis direction. Additionally, scale-like dust covers are placed on both sides of the Y-axis module to prevent metal dust from entering the moving mechanism, thereby extending its service life.

For chip collection, a device is installed on the base below the grinding area, which, along with the multi-hole chip collection openings on the top, effectively centralizes the cleaning of grinding residue and enhances maintainability. Furthermore, a dedicated positioning fixture is installed on the turntable for quick and stable casting installation, ensuring the repeatability and consistency of the grinding path while optimizing stability and production efficiency in the grinding process.

 

4. Five-Axis Grinding Path Generation Process Optimization

4.1 Manual Teaching Path Generation Method and Parameter Setting

In manual teaching mode, the operator uses the controller to control the X, Y, and Z-axis slides, as well as the rotary module. They manually guide the grinding tool along the contour of the standard casting’s gating gate. Whenever the tool reaches a critical position, the controller records the current position as a teaching point, including the movement mode and speed parameters between adjacent points.

Key parameters during the grinding process include the three-axis movement speed and magnification, as well as the rotation speed and magnification of both the rotary module and the servo motor. All of these parameters can be easily adjusted through the interface. Once the teaching process is complete, the system automatically generates a preliminary grinding process file for verification and adjustments.

This method is particularly suitable for grinding non-standard parts and offers advantages such as intuitive operation and controllable paths.

 

4.2 External Model Import and Simulation Optimization Path Generation Process

The external import mode automates the generation and optimization of the grinding path using digital modeling and simulation. First, the process begins by acquiring a three-dimensional CAD model of the casting. From this model, the edge of the gating gate is extracted to create a two-dimensional outer contour drawing. The system then generates an initial grinding trajectory based on factors such as the casting material, dimensions, grinding thickness, and tool characteristics.

Next, both the casting model and the grinding device model are imported into simulation software to create a simulation environment. This environment includes process parameters like speed, acceleration, and rotational speed. A virtual grinding task is then executed. If there is any deviation between the simulated trajectory and the casting model, the path is corrected and verified again until the accuracy is satisfactory before actual grinding begins.

Finally, the validated grinding path is converted into a process file that can be directly executed by the grinding device.

 

4.3 Analysis of the Influence of Motion Mode on Grinding Effect

Different motion modes have a significant impact on path smoothness and surface quality. Linear motion is ideal for areas with minor contour changes or flat surfaces, allowing for high-speed, large-area grinding. However, it may lead to abrupt changes in the path or overcutting in corners and areas with sudden curvature changes. On the other hand, circular motion is more suitable for continuous curved surfaces and boundary transition areas. It helps maintain the stability of the tool posture, improves contact uniformity, and enhances both surface consistency and grinding accuracy.

In practice, it is beneficial to combine both motion modes. An intelligent controller can assess the geometric relationship between teaching points and automatically select the optimal motion type for the task at hand.

5. Process Parameter Optimization During Grinding

5.1 X, Y, Z Axis Travel Speed ​​and Magnification Settings

The travel speeds of the X, Y, and Z axis linear slides play a crucial role in determining the rhythm and precision of the grinding process. In both manual teaching and automatic operation modes, the system allows for separate adjustments of speed and magnification parameters. This enables dynamic speed adjustments for different segments of the grinding path.

When grinding complex curved surfaces or corners, it is important to reduce both speed and magnification to enhance the accuracy of the trajectory. Conversely, when grinding flat areas, increasing the speed can improve efficiency.

The strategy for setting speed must take into account factors such as tool load, material hardness, and path curvature to achieve an optimal balance between efficiency and quality.

 

5.2 Grinding Depth, Tool Path Overlap Rate, and Contact Angle Adjustment

To maintain stable processing, it is important to control the grinding depth properly. The path overlap rate, which influences the coverage of the grinding process, should generally be kept between 20% and 50%. This range ensures that there are no areas missed during grinding and prevents overlapping marks. Additionally, the contact angle affects both cutting efficiency and surface quality; therefore, it should be automatically adjusted according to the tool’s shape and the contour of the workpiece.

 

6. Comparative Analysis of Optimization Results

Compared to traditional manual grinding methods, the optimized system significantly reduces processing time by approximately 35%. The average time per piece has decreased from 7.8 minutes to 5.1 minutes. Additionally, the surface roughness (Ra value) has improved, decreasing from 3.2 μm to 1.8 μm, which greatly enhances surface quality. The dimensional consistency error of parts within the same batch is now controlled within ±0.15 mm, which is far better than the ±0.5 mm observed with the traditional method.

Furthermore, the reusability of milling process documents greatly minimizes programming and debugging time. The adjustment time per piece has been reduced from 20 minutes to less than 5 minutes, leading to significant improvements in production efficiency and process stability.

 

7. Conclusion

This paper presents a method for optimizing processes using a five-axis linkage structure to automate the grinding of casting risers and gating gates. It includes strategies for path generation, process parameter settings, and error compensation mechanisms. Research shows that this method can significantly enhance grinding accuracy and production efficiency, while also offering good scalability and adaptability to different processes.

 

 

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