Optimized Cutting Tools for Thin-Walled FRP Component Machining

Using the turning of a thin-walled FRP (Fiber Reinforced Plastic) part as an example, several challenges arise during the machining process, such as slag, cracks, burrs, poor surface roughness, and frequent vibrations at the junction of the end face and the outer circle. To address these issues, multiple strategies were implemented, including selecting appropriate blades, optimizing tool paths, adjusting machining parameters, and modifying tools. These measures aimed to prevent defects in the turning process of thin-walled FRP parts. As a result, significant improvements were achieved in the surface quality of the parts, tool life, and machining efficiency, leading to considerable cost savings in the machining process.

 

01. Introduction

With the advancement of industrial technology, an increasing number of new materials are being utilized in industrial production, significantly enhancing product performance while reducing costs. Fiberglass Reinforced Plastics (FRP) are particularly popular due to their exceptional qualities, such as high strength, lightweight nature, excellent insulation, and corrosion resistance. However, their challenging cutting characteristics and high wear resistance often lead to tool wear and machining vibrations, which can negatively impact surface quality. These issues, to some extent, hinder the widespread adoption and development of this material, as it is considered a typical composite that is difficult to cut.

 

02. Problems in processing and analysis

2.1 Problem description

Figure 1 illustrates a thin-walled FRP (Fiber Reinforced Polymer) part, which is a composite material with overall dimensions of φ400mm × 9000mm. It features a tubular rotating body with a wall thickness of 2mm.

 

Additionally, it discusses methods to achieve mirror finishes on stainless steel without the need for secondary polishing operations.

 

 

When machining the outer circle of thin-walled FRP (fiber-reinforced plastic) components, issues such as tearing, slag buildup, cracks, and burrs often occur at the junction between the tool’s end face and the outer circle. Additionally, the surface roughness of the processed outer circle is often inadequate, and processing vibrations can frequently happen. These problems negatively impact the surface processing quality, tool longevity, and overall processing efficiency of the thin-walled parts. The defects found in FRP components are illustrated in Figure 2.

 

2.2 Problem Analysis

Unreasonable Selection of Tool Materials:
FRP (Fiber Reinforced Plastic) is a composite material that is difficult to cut. It has high tensile strength, low thermal conductivity, and high cutting temperatures, which contribute to a short tool life. The material tends to wear down tools quickly, leading to processing vibrations that affect surface roughness and make it difficult to maintain precise dimensions.

 

Unreasonable Selection of Cutting Parameters:
FRP is a non-homogeneous material characterized by interlayer structures and varying fiber orientations. This can lead to delamination and defects such as collapse and slag during machining. Due to the small connection force involved, unreasonable cutting parameters can easily result in excessive cutting forces and high heat, causing glass fibers to lift and create slag. Moreover, if the feed speed is not slowed down appropriately when the tool exits the workpiece, it can cause tearing of chips, leading to cracks and other issues.

 

Unreasonable Setting of Cutting Path:
During the machining of FRP materials, fiber elastic recovery can occur, making it challenging to control processing accuracy and surface roughness. For instance, when a 90° outer circle right-biased turning tool cuts the outer circle, the FRP material may rebound. This rebound leads to significant, temporary contact between the tool’s secondary back face and secondary cutting edge with the outer circle of the workpiece end face, resulting in intense cutting forces that can cause cracks and slag.

 

Inconsistency in Incoming Material State:
Artificially wound FRP parts often have irregular shapes and varying inner hole diameters, leading to poor cylindricity and uneven allowances. During turning, this can cause many empty cuts. The irregular, intermittent cutting impacts can generate processing vibrations, increasing cutting difficulty and reducing tool life. If the feed rate remains constant and cutting parameters are not adjusted and optimized based on actual conditions, the extended cutting times can adversely affect processing efficiency.

 

03 Tool improvement and countermeasures

3.1 Optimization of tool material

Considering the characteristics of FRP (fiber-reinforced polymer) materials and the initial state of the blank, the turning process involves a combination of rough machining and fine machining. During the rough machining of FRP materials, high-speed steel tools and uncoated carbide tools with small geometric angles tend to wear out more quickly and should be avoided. Instead, it is recommended to use YG-type negative indexable inserts that have larger geometric angles—specifically, a front angle of 10° to 20°, a back angle of 6° to 8°, and a cutting edge inclination of 3° to 5°. These inserts should also feature polished grooves and coatings (such as TiN, TiCN, or Al2O3).

These inserts offer sharp grooves, fast cutting speeds, smooth chip removal, and good economic efficiency. They effectively reduce friction between the chip and the front cutting edge, ensuring stable entry and exit during cutting. This minimizes chip adhesion to the cutting edge, resulting in higher surface quality and extended insert life.

When finishing a workpiece, it is advisable to use diamond turning inserts or cubic boron nitride tools, as illustrated in Figure 4. These tools possess higher hardness and heat resistance, making them sharper and more durable than traditional steel tools. Additionally, as friction is reduced, the chips produced change from a crushed form to C-shaped flakes, minimizing any tearing or pulling on the workpiece. This leads to reduced vibration and significantly improves cutting parameters, ultimately achieving higher processing accuracy and production efficiency.

3.2 Optimization of machining tool paths

The design of machining tool paths should ensure that as the machining tool cuts the end face of the workpiece, both the workpiece allowance and the cutting force gradually decrease. This helps avoid an abrupt loss of cutting force. The machining tool paths can be designed and optimized in three main ways, depending on the specific conditions, such as the machining characteristics of the part’s outer circle and the type of tool used.

1) The composite machining tool path using 45° and 90° offsets is illustrated in Figure 5. First, a 45° offset tool is employed to create a chamfer that is greater than 1.1 times the outer circle allowance at the cut-out end. Next, a 90° offset tool is used to divide the outer circle CNC machining program into two sections. When the cutting tool is approximately 5 mm away from the end of the machining process, the feed rate is reduced to half of the original rate. This adjustment decreases the force on the cutting edge, helping to prevent issues such as block collapse, material slag, and delamination at the point where the tool meets the workpiece.

2) The end of the glass fiber connection has a low force, making it easily separable under external pressure. To mitigate this, you can opt for a turning tool that feeds from the outside towards the inside. Additionally, employing a left and right compound offset tool processing method helps prevent tearing, collapse, and cracking at the ends.

To implement this, design and create a 90° left and right compound offset tool. The tool path for processing is illustrated in Figure 6. Begin by feeding the outer circle from the outer edges of the two end faces toward the center. Then, use the left outer circle turning tool to make a reverse cut of about 30mm at the exit point, followed by normal cutting with the right outer circle turning tool. Because excess material has already been processed and removed beforehand, this technique effectively prevents tearing, debris, and cracks at the end face.

3) The tool path for processing with a turning tool at an angle of 45° to 75° is illustrated in Figure 7. When using a turning tool with a main deflection angle within this range to machine the parts, it is important to reduce the feed rate accordingly, especially when the tool is rapidly cutting the end face.

3.3 Optimization of cutting parameters

In the processing of fiber-reinforced polymer (FRP) materials, cutting parameters play a crucial role in determining cutting efficiency, processing quality, and tool wear. To minimize cutting heat and force, it’s essential to properly control the cutting speed, feed rate, and depth of cut, avoiding excessively high values.

During rough processing, it is recommended to use a lower cutting speed in combination with a relatively higher feed rate and depth of cut to reduce cutting time and tool wear. Conversely, during fine processing, a higher cutting speed alongside a lower feed rate and depth of cut can be advantageous.

To ensure product quality and prevent surface roughness from falling short of drawing requirements, it is important to monitor tool wear throughout the processing. Tools should be replaced promptly as needed. The specific cutting parameters are detailed in Table 1.

To address the issues of empty cuts and inefficient processing caused by inconsistent incoming material conditions, the operator can manually adjust the horizontal and vertical cutting points based on the status of the incoming material. By increasing the back cutting amount, the operator can quickly position the tool at a higher cutting point on the blank, which helps to reduce empty cuts.

When vibrations occur during processing, the operator can intervene manually to modify the cutting parameters according to the current situation. Continuously adjusting the feed rate can change the excitation frequency of the CNC machinery parts, thereby reducing vibrations. If necessary, various damping materials, such as low-temperature alloys, wax, sand, or iron sand, can be used to fill the inner hole of the part. Additionally, materials like rope hoops, clamps, hoop sleeves, steel cable ties, or plastic cable ties can be employed to attach sandbags in non-processing areas of the outer circle of the workpiece. These methods can enhance vibration reduction and absorption, leading to more stable cutting performance.

 

3.4 Optimization of cooling method

Cutting heat significantly impacts the processing of FRP (Fiber Reinforced Polymer) materials, affecting several key aspects:

1. Tool Wear: Cutting heat accelerates tool wear, leading to a shorter tool life.
2. Thermal Deformation: It can cause thermal deformation of the workpiece, which negatively affects the geometric tolerance and dimensional accuracy of the parts.
3. Chip Accumulation: Chips may adhere to the front cutting edge of the tool, resulting in surface roughness that does not meet specifications.
4. Material Decomposition: High temperatures can accelerate the decomposition of glass fibers, leading to defects such as slag, cracks, and burrs on the parts’ end faces.

To mitigate these issues, it is essential to select a cutting fluid that offers good cooling and lubrication properties. The most recommended option is a water-based cutting fluid. This type effectively reduces the temperature of both the tool and workpiece in the cutting area and helps wash away accumulated chips, facilitating rapid cooling and smoother processing.

During machining, the cutting fluid should be continuously and adequately applied to maintain a stable temperature throughout the process. It is advisable to avoid using oil-based cutting fluids and pure gas for cooling. The chemical components in oil-based cutting fluids can react adversely with FRP materials, potentially reducing or altering the parts’ overall performance.

Using pure gas cooling involves blowing gas at high pressure into the machining area, which can disperse generated chips and dust uncontrollably. This not only compromises environmental safety but also poses health risks to the operator and increases equipment wear, ultimately decreasing the overall accuracy of the machinery.

 

3.5 Processing precautions

During the processing of thin-walled FRP (Fiber Reinforced Polymer) parts, a significant amount of fine dust and fibers is generated, which can pose health risks to workers. To ensure safety, operators must properly wear personal protective equipment, including dust masks, gloves, and safety glasses. It is also essential to utilize vacuum systems, maintain a clean working environment, and prevent dust from entering the internal mechanisms of the equipment.

Additionally, the processing of FRP parts carries potential risks of fire and explosion. Generated chips should not be allowed to accumulate; instead, they must be cleaned up promptly and safely. Equipment should be fitted with an effective chip removal system and proper ventilation.

In summary, technicians must thoroughly understand the processing characteristics of FRP materials and implement necessary safety precautions to protect both production and operators. By improving processes, issues such as slag, cracks, and burrs in the turning of thin-walled FRP parts can be effectively addressed, leading to enhanced surface quality and increased dimensional accuracy of the parts, thereby meeting process requirements. The results of the processing are illustrated in Figure 8.

 

04 Conclusion

Using the example of turning a thin-walled FRP (fiberglass reinforced plastic) part, this summary addresses common issues such as turning defects, inadequate surface roughness, and processing vibrations. By optimizing the cutting tool, adjusting the tool path, and fine-tuning the cutting parameters, we have developed a method to minimize defects during the CNC turning process. This approach effectively enhances surface quality, extends tool life, and improves processing efficiency for thin-walled FRP parts. The findings can serve as valuable references for processing other FRP products and are recommended for broader implementation.

 

 

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