Choosing a tool
Endmill geometry can have a large effect on machining forces and required torque. Selecting a suitable tool is therefore very important, and millalyzer can help to identify one.
Millalyzer cannot take all machining conditions into account. Check you selection with the cutting tool manufacturer’s recommendation regarding material compatibility and maximum chip thickness. For example, millalyzer force and torque predictions will often favor sharp-edged endmills (large rake angles and small cutting edge radius). Such tools are very susceptible to chipping and dulling in hard materials (e.g. steel) and would therefore degrade very quickly.
The second tab shows a list of currently configured tools. Millalyzer ships with a small built-in database of solid endmills for aluminum machining (currently 81 tools). Given the very large number of tools that are available on the market for different applications, it is very likely that the user will need to edit their own tool geometry. For this purpose there is a tool editor, shown to the right.
Although there are what may appear a large number of values to configure, many only affect the structural model (tool stiffness). So, if tool deflections are of no interest, these values need not be accurate. Nominal cutting forces depend on:
- Cutting diameter [DC]
- Diameter of the cylindrical section of the endmill
- Flute cout [NOF]
- Number of cutting edges around the circumference. More flutes mean less space per chip; please note that millalyzer does not model chip evacuation.
- Helix angle [FHA]
- Spiral angle of the flute with respect to the tool axis. A straight flute, as in some wood routing tools, corresponds to helix angle zero. Larger helix angles (45° to 55°) are common on finishing tools that are meant to be used in side-milling with small values of radial engagement and moderate chip thickness. Smaller helix angles (20° to 35°) are used on endmills for larger engagement (or slotting) because the chips are more reliably transported out of the cut.
- Radial rake angle [GAMF]
- The rake angle is a measure of the edge sharpness. A higher rake angle means a sharper tool, smaller forces, but also a more fragile cutting edge that chips easily. Many manufacturers of high-end endmills specify this value in their catalogues (Coromant, SECO, Ceratizit, WNT, Dormer-Pramet and others) using the symbol 𝛾 (gamma, or GAMF) but some do not. General-purpose endmills that are suitable for use in steel and other materials tend to have radial rake angles in the range 5°-8°, while tools that are advertised especially for use in aluminum are often ground to 12°-20°. See the sketch below for a definition of the radial rake angle. Large rake angles yield smaller cutting forces, but are also weaker and may break or chip sooner, especially in hard materials.
- Cutting edge radius [EDRD]
- Set this value to zero to run the simulaon for a perfectly sharp edge. Edges with very small radius tend to chip soon, while a large edge radius can make the tool last longer but also increase machining forces. High-quality endmills are often lapped or honed to create a well-defined cutting edge radius that provides good tool life for the intended material (smaller radius for aluminum/brass, larger radius for carbon steel, even larger for austenitic stainless steels or heat-resistant alloys).
The combination of large rake angle and small edge radius is common in tools for plastics. Coatings, on the other hand, always increase the edge radius because they can only be applied after grinding, so that the coating thickness essentially adds to the radius. Many common commercial (PVD, arc) coatings are only 1-5 µm thick, others (CVD or PVD-SFC) lie in the range 4-18 µm.
- Unequal helix angle
- Some high-end endmills have flutes with slightly different helix angles. This can sometimes help to alleviate chatter. To define such a tool, check the box and enter the difference between the highest and lowest flute helix angle. A common value for this is 2 degree. With uneven helix angles, some adjacent flute pairs will converge with increasing distance from the tool tip, which reduces chip space. Therefore, tools with unequal angles often have short length of cut [APMX]. Note that millalyzer will accept large helix angle variations, even if they are geometrically detrimental or impossible.
- Uneven flute spacing
- Most tools have their flutes evenly spaced around the circumference. Enable this option for tools where the flute indexing (circumferential spacing) differs. As for unequal helix angle, this feature can reduce chatter tendencies in some cases, but will reduce the width of at least one gullet. Unequal indexing has an effect on the tool tip as well, while variable helix angles have not.
Additional tool parameters are used to assemble a finite-element model that is used to compute how the endmill bends along its length.
- Can be tungsten carbide (VHM) or high-speed steel (HSS). Carbide is a composite of a mixture if very hard ceramic materials (mostly carbides and nitrides) that is sintered and infused with Cobalt. Different tools use different fraction of Cobalt binder content, which has a strong effect on material properties. More Cobalt (up to 25%) reduces the hardness (and elastic modulus), but increases toughness, while less Cobalt (down to 5%) yields a stiffer, harder material that is very brittle. Carbide in tools for cutting aluminum often have around 10% carbide, but that ca vary between manufacturers.
- Exposed length [LXP]
- This is the length of the tool sticking out of the tool-holder (stickout). This is the single most important quantity for tool deflection. The value given for the endmills in the built-in collection are the minimum amounts that can be achieved.
- Detail dimensions
- Neck diameter [DN], neck [LN] and taper length [LT] are used to set the dimensions of the finite-element model. These values should be chosen correctly if tool deflection or tool stress/failure is of interest.