Variable Helix Angle End Mill Design for Vibration Reduction in CNC Milling
Table of Contents
CNC machine tool technology is a cornerstone of the mechanical processing industry.
Among the auxiliary equipment for CNC machine tools, cutting tools are consumables and instruments used to machine workpieces, and they have a decisive impact on factors such as machining efficiency, surface quality, and cost.
CNC Machine Tool Technology Overview
In recent years, China’s production of cemented carbide cutting tools has shown steady growth, a development largely attributable to the exceptional comprehensive performance demonstrated by cemented carbide milling cutters.
Cemented carbide milling cutters combine high hardness, excellent wear resistance, and outstanding red hardness, which can be maintained stably within a temperature range of 800–1000 °C.
This characteristic gives cemented carbide milling cutters a core advantage in achieving high-speed cutting.
In related studies, Phokobye and other scholars have also clearly pointed out that carbide milling cutters, as one of the most widely used milling tools in the industrial sector today, demonstrate outstanding performance.
Based on the above background, this paper will conduct a systematic study on solid-body milling cutters made of cemented carbide.
Vibration Problems in Milling Operations
Vibration is difficult to avoid during milling operations; it not only severely affects the cutting performance of the milling cutter but also significantly reduces the surface quality of the workpiece.
To address this issue, relevant scholars have conducted extensive research:
Many scholars conducted an in-depth analysis of the vibration-damping mechanism of traditional end mills.
They derived a formula to calculate the circumferential equal-division point edge length of end mills with unequal helix angles.
This work provides insights for improving the vibration resistance of end mills.
Cutting experiments confirmed the performance of this type of milling cutter. The experiments showed that this milling cutter effectively enhances vibration resistance.
It also improves the quality of machined surfaces.
Variable Pitch and Anti-Vibration Design Approaches
MEI et al. proposed an irregular pitch angle design for variable-pitch tools. This design suppresses vibration by disrupting the vibration mechanism.
It improves machining efficiency and stability. The researchers also established a design analysis method for variable-pitch milling cutters.
This method provides a new approach for optimizing the vibration resistance of milling cutters.
Variable Helix Angle Milling Cutter Innovation
In traditional milling cutter design, the helix angle is typically set to a fixed value; however, this design approach fails to meet the requirement for low cutting vibration in milling cutters.
To overcome this limitation, some reseacher proposed an innovative design for a vertical milling cutter with a gradually varying helix angle.
In this tool, the helix angle gradually increases along the fixed cutting edge, enabling precise control of the milling process.
Specifically, a smaller helix angle ensures the strength of the tool tip during initial contact with the workpiece, while the gradual increase in the helix angle helps mitigate the impact of increased milling depth on cutting forces.
This design not only enhances the cutting performance of the end mill but also improves the surface quality of the machined workpiece, offering new insights for technological advancements in the field of milling.
Research Objective and Experimental Approach
Based on this, this paper designs a variable helix angle carbide end mill.
Researchers optimized the helix angle structure to improve cutting performance.
They also conducted comparative cutting performance tests following standard experimental procedures. This approach ensures accurate and reliable experimental results.
Selection
Selection of Variable Helix Angle Parameters
The helix angle is a key parameter in milling cutter design, significantly influencing machining performance such as cutting forces, vibration, and efficiency.
In-depth research into its effects is crucial for optimizing milling cutter design and improving machining quality.
Classification of Helix Angle and Chip Flow Behavior
Helix angles are classified as left-hand or right-hand, with the direction of rotation determining the chip flow and the direction of cutting force:
Right-hand milling cutters eject chips upward and generate upward cutting forces; they have broad applicability and can be used in various scenarios such as face milling and slot milling, making them more widely used in practice;
Left-hand milling cutters eject chips downward and generate downward cutting forces; they are only suitable for specific applications such as side milling and through-hole milling.
Therefore, this paper selects a right-hand helix design.
Effect of Helix Angle Size on Cutting Performance
The size of the helix angle affects cutting edge strength, cutting force, and cutter life: a small helix angle corresponds to a small rake angle, resulting in high cutting edge strength but high radial cutting force; while a large helix angle has the opposite effect.
It should be noted that although an excessively large helix angle reduces the radial cutting force at a single contact point, the increased number of contact points involved in the cutting process may lead to an increase in the total radial cutting force, as shown in Figure 1.
In practical applications, the helix angle of end mills is typically selected to be between 30° and 45°.
Material Selection and Final Helix Angle Design
The end mill designed in this paper is made of cemented carbide with a compressive strength exceeding 6000 MPa (its physical properties are shown in Table 1), and is intended for machining high-hardness 45 steel.
After comprehensively considering edge strength, cutting forces, machining stability, and durability, the helix angle was ultimately set to 38°–41°.
| Physical Property | Hardness (HRA) | Tensile Strength (MPa) | Elastic Modulus (MPa) | Compressive Strength (MPa) |
|---|---|---|---|---|
| Value | 86 | 6000 | 4 × 10⁵ | 1000 |
Table 1 Physical Properties of Carbide Milling Cutters
Variable Helix Angle Design
The end mill designed in this paper is shown in Figure 2, which presents its circumferential development view and end face view.
The helix angle of the cutting edges in this mill is designed using a semi-gradual strategy. Specifically, each cutting edge is divided into five segments.
The helix angle of the first and third cutting edges remains constant at 41° in the first segment, then gradually decreases from 41° to 38° in the second segment.
It remains constant at 38° in the third segment and then gradually increases from 38° to 41° in the fourth segment, and finally returns to 41° in the fifth segment.
In contrast, the helix angle of the second and fourth cutting edges follows the opposite trend.
As shown in Figure 2, the design of this milling cutter exhibits distinct segmentation along the axial direction, which enhances damping characteristics.
This creates significant differences in the magnitude and time intervals of cutting force pulses, thereby effectively suppressing axial vibrations; its radial structure also serves to modulate cutting force pulses.
This milling cutter does not employ an unequal-pitch strategy, and it sets the angle between adjacent cutting edges at the end teeth uniformly to 90°.
This configuration increases the chip-carrying capacity of the end edges and significantly improves cutting performance, meeting the practical application requirements for dominant cutting in the lower half of the milling cutter.
Additionally, the remaining cross-sections of the milling cutter employ an unequal-pitch design, resulting in varying time intervals for the circumferential cutting force pulses.
In summary, the variable helix angle design effectively suppresses chatter during milling operations, thereby improving cutting stability and efficiency.
Physical Parameters of the End Mill
The end mill designed in this paper consists of two parts: the shank and the cutting head.
The cutting head is composed of four cutting edges, each of which includes a cutting tip, three cutting faces, a rake face, three end-tooth faces, and a cutting edge, as shown in Figure 3.
The cutter has a cutting edge length of 15 mm, four cutting edges, a core thickness of 3.75 mm, a head diameter of Ø6 mm, and a head length of 13.0 mm.
The shank has a diameter of Ø6.0 mm and a length of 27.0 mm. The specific parameters of the milling cutter are shown in Table 2.
| Parameter | Value (°) |
|---|---|
| End cutting edge rake angle | 3 |
| Peripheral cutting edge rake angle | 4 |
| Peripheral first relief angle | 8 |
| End cutting edge first relief angle | 8 |
| End cutting edge second relief angle | 16 |
| End tooth 1 flute angle | 30 |
| End tooth 4 flute angle | 35 |
| End tooth 2 flute angle | 35 |
| End tooth 3 flute angle | 30 |
Table 2 Parameters of Variable Helix Angle End Mills
Performance Testing and Analysis
Test Equipment
The cutting experiments were conducted on a VMC850E vertical machining center manufactured by Shenyang Machine Tool Works.
Its main technical specifications are as follows: maximum allowable load of 600 kg, maximum spindle speed of 8000 rpm, and maximum feed rate of 10,000 mm/min.
The INV3018C series data logger was used to measure vibration data.
Based on theoretical analysis and cutting experiments, the experimental parameters were determined as shown in Table 3.
| Cutting Depth (mm) | Cutting Width (mm) | Feed per Tooth (mm) | Spindle Speed (r·min⁻¹) | Feed Rate (mm·min⁻¹) | Machining Method |
|---|---|---|---|---|---|
| 6 | 0.4 | 0.025 | 2000 | 100 | Continuous |
Table 3: CNC Machining Parameters
Results of the Comparative Analysis
To ensure the accuracy and reliability of the comparative experiments, this study strictly adhered to the principle of control, minimizing differences in experimental factors between the experimental and control groups as much as possible.
To this end, two types of milling cutters were specially fabricated for the comparative study.
Milling cutter 1 features a fixed helix angle design, while milling cutter 2 is the variable-helix-angle end mill designed in this paper.
With the spindle speed of the machining center maintained at 2000 r/min, a comparative analysis of the vibration data from the cutting experiments of Milling Cutter 1 and Milling Cutter 2 was conducted, and the results are shown in Figure 4.
Compared to Milling Cutter 1, Milling Cutter 2 exhibits significantly enhanced vibration resistance during the cutting process, with an overall performance improvement of up to 25%.
This result indicates that the variable helix angle structure designed in this paper has a very significant effect on suppressing cutting vibrations in the milling cutter.
Results of Longitudinal Comparison
Through a comparison of the data, it can be observed that the cutting vibrations of the milling cutter are primarily concentrated in the X direction, which is consistent with the X direction serving as the feed direction of the milling cutter and the primary direction of the cutting force.
Therefore, this paper conducts a longitudinal comparative analysis of the time-domain plots of vibration acceleration in the X direction at different rotational speeds.
As shown in Figure 5, the cutting vibrations of Milling Cutter 1 are more significantly affected by rotational speed.
Not only does the amplitude of its vibration acceleration change with increasing rotational speed, but a distinct cutting chatter phenomenon also occurs at specific rotational speeds (such as 1500 r/min).
This chatter not only affects the stability of the cutting process but may also have a negative impact on machining quality.
As shown in Figure 6, the cutting vibrations of milling cutter 2 are more stable.
Although its vibration amplitude also varies with rotational speed, the range of fluctuation is small, and no significant cutting chatter occurs.
This indicates that milling cutter 2 possesses better vibration resistance and is capable of maintaining a stable cutting process at different rotational speeds.
In summary, Milling Cutter 2 maintains stable cutting performance at various rotational speeds and exhibits significantly better vibration resistance than Milling Cutter 1; therefore, it offers certain advantages in terms of machining efficiency.
Conclusion
Compared to the structural design of traditional helical angle milling cutters, optimizing the helix angle parameters to improve cutting performance can effectively suppress resonance during the milling process, reduce workpiece surface roughness, and significantly enhance machining quality.
Experimental results demonstrate that the end mill designed in this paper possesses high practicality, effectively extending tool life and enhancing machining stability, and thus holds promising market prospects and significant potential for widespread adoption.