Evaluating Process Machinability

The machinability time-series chart can be used to evaluate tool breakage risk during machining.

Tool breakage occurs when any of the following exceeds 100% and persists for longer than one simulation step: Yielding Stress Ratio, Max Spindle Torque Ratio, or Max Spindle Power Ratio. If the value significantly exceeds 100% — roughly speaking, above 200% — tool breakage can occur even without sustained duration.

Note: The default simulation uses per-revolution milling mode, where one simulation step equals one spindle revolution.

Yielding Stress Ratio is a percentage indicator with the tool material's breakage force as the denominator. The numerator is the simulation step's absolute force MaxAbsForce_N(API). Compared to using the absolute force value directly as a limit, the ratio incorporates tool material mechanics and more accurately reflects the tool's actual safety margin. The optimization target force OptPreferedForce_N(API) represents the desired MaxAbsForce_N after optimization.

For small tools, breakage is typically caused by insufficient tool force capacity, and breakage is based on the Yielding Stress Ratio.

For small-to-medium tools, breakage is typically caused by insufficient spindle performance, and breakage is based on the Max Spindle Torque Ratio or Max Spindle Power Ratio. When cutting resistance exceeds spindle performance, the machine feed rate remains constant but the spindle speed continuously decreases, causing the feed per tooth to continuously increase, which drives cutting forces to spike until tool breakage or machine stoppage.

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Tool Breakage Solutions

Modify the toolpath to reduce cutting width/depth, or use HiNC's optimization feature to adjust feed rates, bringing the Yielding Stress Ratio, Max Spindle Torque Ratio, and Max Spindle Power Ratio below 100%.

Thermal Plastic Deformation of Cutting Edge

If the Thermal Yield Ratio exceeds 100%, thermal plastic deformation of the cutting edge occurs, accelerating wear. Unlike the Yielding Stress Ratio, Max Spindle Torque Ratio, and Max Spindle Power Ratio, this is a long-term indicator — exceeding 100% does not cause immediate effects.

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Thermal Plastic Deformation Solutions

After addressing tool breakage issues, reduce the spindle speed to allow sufficient time for the cutting edge to dissipate heat.

Note that whether the coolant is properly directed at the cutting edge has a significant impact. If the coolant is not aimed at the cutting edge, it effectively reduces the heat dissipation coefficient.

Tool manufacturers typically provide recommended machining conditions, and the Thermal Yield Ratio obtained by simulating under those conditions usually exceeds 100%. This is because the manufacturing formulations of tool materials differ from HiNC's conservatively set default values. If you consider machining conditions with a Thermal Yield Ratio above 100% to be reasonable, you can adjust the thermal properties of the tool material so that the calculated Thermal Yield Ratio approaches 100%.