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: Ho​​w​ to Choose Parting Tools

1. Shallow parting2. Medium parting3. 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 f​o​​r 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

Medium parting

For medium parting (diameters ≤ 40 mm (1.57 inches)), use screw-clamp and spring-lock holders with 2-edge inserts.

Deep parting

For deep parting (diameters ≤ 112 mm (4.41 inches)), 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.

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:	Positioning at center causes:
Increased pip Breakage (unfavorable cutting forces)	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:

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.