Internal grooving
Long overhangs and poor chip evacuation are two of the challenges with internal grooving. Long overhangs can cause problems with both deflection and vibrations. Vibrations and poor chip evacuation can cause insert breakages. Difficulties with chip evacuation can also lead to poor surface finish. The most common internal grooving process is radial grooving; however, multiple grooving (A) and plunge turning (B) can also be used.
Internal grooving application tips
- Precision coolant with high flow improves chip control and evacuation
- A smaller bar improves chip evacuation but reduces stability
- To avoid vibration, the setup should have the shortest overhang with the lightest cutting geometry
- Vibration can be avoided by using several cuts with a narrower insert. End with a finishing operation (see illustration (A) right)
- An internal groove can also be machined with a single cut followed by plunge turning (B). Start at the bottom, and machine from the back of the hole to the front to obtain best chip evacuation
- Use a smaller insert width and corner radii for lower cutting forces
- For accurate machining with lower vibration and precise height, use a clamping solution designed to support this, for example EasyFix™ sleeves
For overhang 5−7 × D, use carbide reinforced dampened bars
L = 5−7 × D
For overhang 3−6 × D, use dampened or carbide bars
L = 3−6 × D
For overhang below 3 × D, use steel bars
L ≤ 3 × D
Internal grooving strategies
Roughing with radial feed
Always start closest to the bottom of the hole (1) and work outwards to make room for the chips. Use the recommended feed. Further cuts (2 and 3) should be 0.5–0.8 × insert width. Since the cutting force will be lower at this point, you can increase the feed by 30‒50%.
Roughing with side turning
Side turning provides better chip control and chip breaking. Start closest to the bottom of the hole and machine outwards to the entry. Do not feed from and against the shoulder, leave 0.2 mm (0.008 inch) steps between the passes.
Side turning is a more stable process than cutting with radial feed, it will generate lower radial forces that cause vibrations. Be aware that side turning is less productive than radial cutting due to the lower depth of cut (ap).
Roughing with non-linear tool path
A non-linear tool path provides good chip control and tool life. The wear of the insert is distributed along a large part of the cutting edge. The -RM geometry is ideal for non-linear tool paths. Non-linear turning is useful when the bottom of the feature has a large radius.
Finishing
It is always difficult to achieve good chip control when finishing, especially when machining fillets. It is important to separate the material to be removed by making three cuts.
- Make the first cut close to the corner radius nearest to the bottom of the hole.
- Start the second cut closest to the bottom of the groove, and machine to the corner radius on the inner diameter.
- The third cut finishes the groove wall closest to the entry of the hole and the corner radius.
Internal coolant
Use internal grooving tools with internal coolant supply even if the maximum coolant pressure in your machine is low. Coolant improves chip evacuation and decreases the risk of chip jamming in the groove, especially in grooves deep in a hole. To achieve better chip evacuation, use the highest possible coolant pressure.
External Grooving
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Internal turning
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Face grooving
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