Design, Processing and Inspection of Geometric Angle of Turnable Turning Tools
With the increasing popularity of CNC machine tools, the application scope of indexable turning tools is continuously expanding. These tools offer fast processing speeds, stable dimensions, and the ability to quickly replace worn inserts, significantly improving machining efficiency and reducing tooling costs. This makes them a preferred choice in modern manufacturing environments.
**Design of Indexable Turning Tool Geometry**
The position of the insert groove in an indexable turning tool is primarily determined by three key angles: the main cutting edge angle (kr), the blade inclination (ls), and the rake angle (g0). Selecting appropriate values for these angles is essential for optimizing cutting performance and tool life.
**Table 1: Recommended Main Cutting Edge Angle (kr) Based on Machining Conditions**
| Processing Conditions | Main Cutting Edge Angle (kr) |
|------------------------|-------------------------------|
| Roughing with good rigidity | 45°–75° |
| Roughing with poor rigidity | 75°–90° |
| Finishing with good surface quality | 45° |
| Poor system rigidity | 60°–75° |
| Thin-walled or slender parts | 90°–95° |
| Intermediate cut or profiling | 45°–60°, 90°–95° |
**Table 2: Recommended Blade Inclination (ls) Based on Machining Conditions**
| Processing Conditions | Blade Inclination (ls) |
|------------------------|--------------------------|
| Finishing | 0°–5° |
| Roughing | -5°–0° |
| Intermittent cutting | -5°–0° |
| Machining hardened steel | -5°–-10° |
**Table 3: Recommended Rake Angle (g0) Based on Workpiece Material**
| Workpiece Material | Rake Angle (g0) |
|---------------------|------------------|
| Low carbon steel (roughing) | 13°–20° |
| Low carbon steel (finishing) | 20°–25° |
| Carbon structural steel (normalized) | 10°–15°, 13°–17° |
| Carbon structural steel (tempered) | 5°–10°, 8°–13° |
| Alloy structural steel (normalized) | 8°–13°, 10°–15° |
| Alloy structural steel (tempered) | 5°–8°, 5°–10° |
| Grey cast iron (HT15–32, HT20–40) | 5°–10° |
| High-strength steel | -5° |
**Table 4: Recommended Relief Angle (a0) Based on Workpiece Material**
| Workpiece Material | Relief Angle (a0) |
|---------------------|--------------------|
| Ordinary steel | 5°–12° |
| Ordinary cast iron | 6°–8° |
| High-strength steel | 10°–15° |
| Wear-resistant cast iron | 8°–12° |
The lead angle (kr) has a significant impact on the tool's life. Generally, reducing the lead angle can increase tool life. However, if the process system or workpiece lacks rigidity, decreasing the main cutting edge angle may increase radial force, leading to deformation, vibration, and reduced accuracy. Therefore, different lead angles are selected based on specific conditions. Refer to Table 1 for recommended values.
The blade inclination (ls) also greatly affects the cutting performance. It determines the chip flow direction. During finishing, a positive blade inclination is often used to prevent chips from scratching the machined surface. Additionally, the blade inclination influences the sharpness of the cutting edge. The recommended values for blade inclination are listed in Table 2.
The rake angle (g0) directly affects the strength and sharpness of the cutting edge. Increasing the rake angle reduces chip deformation, making cutting easier and extending tool life. However, an excessively large rake angle weakens the cutting edge, increasing the risk of chipping and shortening tool life. The selection of the rake angle depends on multiple factors, as shown in Table 3.
In addition to the rake and relief angles, the geometry of the insert itself is crucial in the design of indexable turning tools. When designing, it’s important to consider all relevant angles and their interactions.
**Modeling and Drawing Design**
Labeling of turning tool parameters is illustrated in Figure 1. Using AutoCAD 2000, the first step is to select the appropriate insert based on the machining conditions. Then, the rake and relief angles are subtracted to determine all necessary design parameters.
During solid modeling, the blade cannot be rotated exactly according to the desired blade angle and rake angle. Instead, it should be converted into the normal rake angle using the formula:
**tan(n) = tan(0) × cos(ls)**
The sequence for blade rotation during solid modeling should be: Main angle → Blade angle → Normal angle.
**Machining on Conventional Milling Machines**
Indexable turning tools can be milled on conventional machines, which helps ensure dimensional accuracy but increases processing costs. While ordinary milling machines are more cost-effective, they are typically limited to machining tools with a 0° rake angle.
Through extensive practice, the author has developed techniques for machining indexable turning tools with compound angles (i.e., blade inclination and rake angle not equal to zero) on conventional milling machines.
When machining small batches on a conventional milling machine, it is best to use universal flat pliers as fixtures. The more rotating axes the pliers have, the more convenient the machining becomes. However, the rigid structure of such pliers is usually weaker.
Using four-axis universal flat pliers (as shown in Figure 2), the steps are: clamp the tool, rotate axis 1 to form the main cutting edge angle, then rotate axis 3 to set the blade angle, followed by axis 2 to adjust the rake angle. At this point, the bottom of the insert pocket is parallel to the table plane. After rotating axis 4 to align the blade slot with the horizontal axis, the tool can be milled. After machining one back wall, rotate axis 4 again to machine the other side.
For three-axis universal flat pliers (Figure 3), the rotation sequence differs slightly. First, rotate axis 1 based on formula (2), then axis 2 according to formula (3):
**tan(q) = tan(g0)/tan(ls)**
**tan(a) = √(tan²(g0) + tan²(ls))**
Once the bottom of the insert is parallel to the machine table, proceed to mill the tool as described.
When producing large quantities of indexable turning tools on a conventional milling machine, adjustable horns on both sides and the bottom of the tool can be used to fine-tune the angles. These horns can also be fixed on the pliers, allowing for clamping with a single-axis flat plier.
**Angle Detection**
To detect the main cutting edge angle (kr), place the tool on a universal tool microscope and measure the angle f between the side base surface and the main cutting edge. The main cutting edge angle is then calculated as kr = 90° – f.
For detecting the blade inclination (ls) and relief angle (a0), place the tool on a flat plate and measure directly with a universal angle ruler. Measure ls along the direction of the main cutting edge, and for a0, measure along the direction perpendicular to the main cutting edge, then calculate using the formula:
**tan(a0) = tan(an) × cos(ls)**
Other dimensions can be measured using standard methods for conventional turning tools.
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