Parting off
Parting-off is mainly performed in bar feed machines often used in mass production. The parting-off operation is usually only a small part of the component's total machining time and, therefore, not usually seen as a target area for time savings. However, after the parting sequence, some components still have additional features to be machined while in the sub spindle. If chips wrap around the component, they can prevent the clamping of the next component in the sub spindle. If this occurs, the machine will either produce scrap or stop. Chips wrapping around the finished component can cause problems in consecutive operations (heat treatments, deburring, assembly, etc.) and destroy the surface finish. Since parting-off is usually one of the last operations to be perform on the component, security is of great importance. If the tool breaks during parting, the component is usually scrapped. This may lead to long machine stoppages.
Parting off tips: how to choose parting tools
1. Shallow parting
2. Medium parting
3. Deep parting
As process security is of high importance, it is preferable to choose a tool with precision coolant. This will evacuate chips, reduce temperature and insert wear, and improve surface finish. Use a tool with the shortest possible overhang and a secure insert clamping for best stability. When parting-off a component, bar, or tube, it is important to save material and minimize cutting force. A narrow insert creates lower cutting forces and saves material. Choose an insert geometry designed for parting-off. These specialized inserts produce chips that are narrower than the groove. This results in a parting-off operation with good chip control and surface finish.
First choice for parting off
One- and two-edge solutions should be considered as the First Choice for different parting-off operations. Use inserts which are designed to produce chips narrower than the groove.
Shallow parting For shallow parting (diameters ≤ 12 mm (0.47 inch)), use 3-edge inserts for economic parting in mass production.
Medium parting
For medium parting (diameters ≤ 40 mm (1.57 inch)), use screw-clamp and spring-lock holders with 2-edge inserts.
Deep parting
For deep parting (diameters ≤ 112 mm (4.41 inch)), insert stability is crucial as this type of cut places high forces on the insert. Hence, a blade with a stable spring clamp and a single edge insert is the best choice.
Pip and burr free parting
For pip and burr free parting, use a sharp geometry with small corner radii. A front-angled insert will also reduce pip and burr. Front angled inserts will create side forces and are recommended only for short overhangs (<13 mm (0.51 inch)).
Small part machining
For small part machining, use an insert with the smallest width and sharpest cutting edges. For best process security, use a tool with precision coolant. If superior tool edge sharpness is not necessary, choose a 3-edge or 2-edge insert for a more economical solution or for larger diameters.
Parting off tips: how to apply parting off operations
Parting-off bars and tubes
Overhang (OH)
Minimize overhang. When parting-off bars, a shorter overhang and higher blade both decrease bending down (δ) by cubic function.
A short overhang increases stability dramatically. Part off close to the chuck. This is especially important when parting-off with thin inserts which require stable conditions and gentle handling.
- For an unavoidable long OH, use a light cutting geometry
- If the OH is less than 1.5 × H, use the recommended feed for the geometry
- If the OH exceeds 1.5 × H, reduce feed rate to the lower end of the recommended feed for the geometry
Tool center height
It is important to have the center height correct ±0.1 mm (±0.004 inch), especially when parting-off to center. For long overhangs, use a maximum deviation of +0.1 mm (+0.004 inch) above center to compensate for bending down.
Positioning below center causes:
- Increased pip
- Breakage (unfavorable cutting forces)
Positioning at center causes:
- Breakage (pushing through center)
- Rapid flank wear (small clearance)
Feed rate
Cutting through the center of a bar creates unnecessary toughness demands that can lead to insert breakage. Here, the insert is exposed to rubbing as the workpiece starts to move in the opposite cutting direction. This action exposes the insert to tensile stresses, resulting in breakages.
Calculating speed:
Reduce feed by up to 75% approx. 2 mm (0.08 inch) before center. Lower feed at the center reduces cutting forces and drastically increases tool life, while higher feed in the periphery improves productivity and tool life. To avoid breakage, stop feed approx. 0.5 mm (0.02 inch) before the center of the bar, and the cut-off part will drop due to its weight and length.
Feeding through center causes breakage
Sub spindle
When parting-off bars, a sub spindle can be used to pull the part off while significantly reducing toughness demands and increasing tool life. It can also allow for using a more wear-resistant grade, which in turn improves tool life even more. Perform the parting operation but stop feed approx. 1 mm (0.04 inch) before center. Then use a sub spindle to pull the part off.
Insert width
Use an insert that is as narrow as possible to save bar material and minimize cutting forces and environmental pollution.
Use the table to choose insert width, CW, depending on component diameter, D:
| D mm (inch) | CW mm |
|---|---|
| -10 (-0.4) | 1.0 |
| 10–25 (0.4–1.0) | 1.5 |
| 25–40 (1.0–1.6) | 2.0 |
| 40–50 (1.6–2.0) | 2.5 |
| 50–65 (2.0–2.6) | 3.0 |
Pip and burr free parting
Choose a left- or right-hand, front-angled insert to control the pip or burr when parting-off bars or tubes. A large front-angled insert decreases pips and burrs but may not produce a straight cut and can result in decreased chip control, poor surface finish, and short tool life. Use as small a front-angled insert as possible. For longer overhangs, use neutral inserts—the longer the tool, the bigger the problems with front-angled inserts.
| | Front angle | Neutral |
| Stability and tool life | Bad | Good |
| Radial cutting forces | Low | High |
| Axial cutting forces | High | Low |
| Pip/burr | Small | Large |
| Risk of vibration | High | Low |
| Surface finish and flatness | Bad | Good |
| Chip flow | Bad | Good |
Parting small diameter bars
Make sure the lowest possible forces are generated. Use an insert with the smallest possible width and sharpest edges.
Never use a tool as a bar stop!
This is not good for any tool, but for small insert widths, it will damage the tool.
Parting into a drilled hole
Avoid parting-off into the conical area because this causes blade deflection and can lead to tool breakage.
Thin-walled tubes
When parting off into thin-walled tubes, ensure the lowest possible cutting forces are generated. Use inserts with the smallest possible width and sharpest cutting edges.
Coolant
The use of coolant and lubrication has a large impact on process security in parting and grooving. In the Cutting Fluid and Coolant section, you will find more information and recommendations regarding over- and under-coolant, precision coolant, and pressure.
Y-axis parting
Y-axis parting is a completely new way of parting-off. In conventional parting off, most of the cutting force is generated by the cutting speed, the rest by the cutting feed. The resulting force is directed approximately 30 degrees into the tool. Thereby, the parting-off blades are loaded in their second weakest direction. The best way to overcome this is to reduce the blade overhang and/or increase the blade height. By turning the tip seat 90 degrees and utilizing the Y-axis on multi-task machines and turning centers to feed the tool, the resulting cutting force will be directed into the strongest direction of the tool. At a 60 mm (2.36 inch) blade overhang, this increases the bending stiffness more than six times. This results in a much more stable, silent, and vibration-free cutting process that provides better surface finish and allows higher feed rates and longer tool overhang. CoroCut® QD for Y-axis parting is the first choice for parting off in turning centers, multi-task machines and sliding head machines with Y-axis. It can machine large diameters up to 180 mm (7 inch), and is particularly suitable for reaching between the main- and sub-chuck with long overhangs. It is always beneficial to use Y-axis parting-off blades if the overhang is larger than the blade height.
How to apply
Y-axis parting in multi-task machines
The tool assembly is often long so it can reach between the main- and sub chuck. This means the total set-up is weak in the X direction compared to the Y-axis load, where the cutting force is directed into the tool assembly and into the machine spindle.
Conventional setup
Setup for Y-axis parting
The tool length is normally measured on an optical device outside the machine. The tool length will become the tool center height when parting-off, and it is important to have the center height correct, especially when parting-off to center.
Optical measuring outside the machine
If it is difficult to see the cutting edge, there is also a gauge plane on the tool. The plane is located:
- 5±0.05 mm (0.197±0.002 inch) above the cutting edge on E, F, G and H-tip seat (2, 2.5, 3 and 4 mm (0.079, 0.098, 0.118 and 0.157 inch))
- 5.5±0.05 mm (0.236±0.002 inch) above the cutting edge on J and K-tip seat (5 and 6 mm (0.197 and 0.236 inch))
Y-axis parting in turning centers
The tool assembly is often long and slender to reach between main- and sub chuck and allow parting off close to the chuck. The total setup is weak in the X-direction compared to the Y-axis load where the cutting force is directed into the tool assembly and turret.
Conventional setup
Setup for Y-axis parting
The tool length is normally measured with a probe inside the machine. The tool length will become the tool center height when parting-off, and it is important to have the center height correct, especially when parting-off to center.
If it is difficult to see the cutting edge, there is also a gauge plane on the tool. The plane is located:
5±0.05 mm (0.197±0.002 inch) above the cutting edge on E, F, G and H-tip seat (3 mm (0.118 inch))
5.5±0.05 mm (0.236±0.002 inch) above the cutting edge on J and K-tip seat (4 mm (0.157 inch))
Measuring with a probe inside the machine
Y-axis parting in sliding head machines
If it is difficult to touch the bar with the cutting edge, there is also a gauge plane on the tool. The plane is located:
5±0.05 mm (0.197±0.002 inch) above the cutting edge on E and F tip seat (3 mm (0.118 inch))
