Plunge milling removes metal by feeding the cutter straight into the workpiece rather than sweeping sideways. The approach lowers radial load, lets you run high feed per tooth, and protects fragile tools on deep pockets or hard steels. Follow this guide to set up plunge toolpaths, pick cutters, tune feeds, and avoid chip traps.
Table des matières
- Why switch to plunge milling on tough jobs
- How plunge cuts differ from conventional milling
- Tool design and insert geometry for plunge
- Calculating feed, speed, and step-over
- Chip evacuation and coolant rules
- Plunge milling in soft vs hard materials
- Programming strategies for corner clearance
- Cycle time and tool life comparison
- Machine stability and fixturing tips
- Need complete CNC cutting services?
- Quick recap of plunge milling setup
Why Switch To Plunge Milling On Tough Jobs
Side milling makes the tool bend when radial step-over is high. In titanium or Inconel the bend sparks chatter and burns edges. By plunging, cutting force points into the spindle axis, so:
- Deflection drops 50 %–70 % on long reach tools.
- You can run higher feed per tooth without vibration.
- Chip thickness stays even, giving more predictable wear.
How Plunge Cuts Differ From Conventional Milling
Three motion elements change when you plunge:
- Tool path. Paths are a grid of vertical pokes, not a helical sweep.
- Feed vector. Feed moves along Z for cut, small X–Y for reposition.
- Chip flow. Chips eject upward, so high-pressure coolant is critical.
Tool Design And Insert Geometry For Plunge
Dedicated plunge cutters use double-edged inserts with positive rake and center point. The following table lists popular cutter families and their max depth per plunge.
| Cutter series | Insert size mm | Max plunge depth mm | Corner angle ° | Typical material |
|---|---|---|---|---|
| Sandvik CoroMill 300 | 12 | 2.5 | 90 | Alloy steel |
| Kennametal KSEM PLUS | 16 | 3.0 | 85 | Titane |
| Iscar Heliturn LD | 10 | 2.0 | 80 | Cast iron |
| Seco Minimaster Plunge | 8 | 1.5 | 90 | Aluminium |
Pick insert grade with thick PVD coating for heat and interrupted entry.
Calculating Feed, Speed, And Step-Over
Because chip thickness equals feed per tooth on a vertical cut, feeds run higher than in slotting. The chart shows safe starting feeds at 1 × dia depth.
Material | vc m/min | fz mm/tooth | D cutter mm ------------------------------------------------------ Aluminum 6061 | 300 | 0.25 | 20 Mild steel 1018 | 180 | 0.18 | 20 Stainless 304 | 120 | 0.12 | 16 Ti-6Al-4V | 60 | 0.10 | 16 Inconel 718 | 35 | 0.07 | 12
Step-over in X–Y is usually 20 %–40 % of cutter diameter. Smaller step-over leaves islands for tool stability but raises passes.
Chip Evacuation And Coolant Rules
Vertical chips stack if coolant fails. Follow these coolant rules:
- Through-tool high-pressure 50 bar minimum in steel.
- Flood at 12 L/min when through-tool unavailable.
- Purge compressed air between plunges for blind pockets.
For gummy titanium add 5 % chlorine-free sulfurized oil to emulsion to cut built-up edge.
Plunge Milling In Soft Vs Hard Materials
The benefits shift with hardness. The next table compares cycle savings.
| Stock removal 20 mm deep, 50 × 100 mm pocket | Aluminium 6061 | Stainless 304 | Ti-6Al-4V |
|---|---|---|---|
| Conventional slot time min | 1.6 | 3.8 | 8.5 |
| Plunge time min | 1.7 | 2.2 | 4.1 |
| Time saved % | -6 % | 42 % | 52 % |
Plunge rarely helps in soft alloys but cuts half the time in super-alloys.
Programming Strategies For Corner Clearance
CAM systems name plunge paths “zig-zag,” “grid,” or “helix pack.” Follow three rules:
- Keep start point near center to equalize wall forces.
- Use helical entries on first poke to avoid tool shock.
- Leave 0.2 mm stock, then finish with light side mill to erase scallops.
Cycle Time And Tool Life Comparison
You can reveal total gain with the cost matrix below.
| Paramètres | Side mill Ti 6-4 | Plunge Ti 6-4 |
|---|---|---|
| Cycle time min | 12.0 | 6.0 |
| Insert edges/part | 3 | 1 |
| Tool cost $ | 12 | 8 |
| Machine cost $15/h | 3.0 | 1.5 |
| Total per part $ | 15.0 | 9.5 |
Even with higher feed, plunge lowers edge wear because chip load points axially through a stiff spindle.
Machine Stability And Fixturing Tips
Radial load is low, yet axial impact can knock thin fixtures. Clamp rules:
- Use a solid backstop under pocket floor if possible.
- Add step shims on jaws to shorten unsupported length.
- Watch Z-axis ballscrew torque; scale back feed if spindle power dips.
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Quick Recap Of Plunge Milling Setup
- Pick a dedicated plunge cutter with positive-rake inserts.
- Set feed per tooth close to drill data, not end-mill data.
- Plan Z cuts in 80 %–100 % of insert length; leave 0.2 mm finish stock.
- Force high-pressure coolant to clear chips or step-over clogging will break tools.
- Compare cycle time and tool cost; expect >40 % saving in hard alloys.
Apply these steps and plunge milling will become your go-to method for deep, hard-metal pockets without breaking cutters—or the budget.
