Based on the application of NX CNC machining technology in the rough machining stage of blanks, this paper analyzes and compares the newly introduced “Adaptive Milling” and the classical “Cavity Milling” strategies. By combining these methods with the production process of typical parts, the programming advantages are comprehensively utilized to optimize roughing methods, rapidly remove the majority of excess material, and improve machining efficiency.
CNC programming is the fundamental task in CNC machining. Determining the machining stages and selecting the appropriate methods are critical steps in process planning prior to programming. Different machining environments and varying material allowances require tailored machining strategies. This study focuses on the different roughing approaches of NX 12.0.2’s “Adaptive Milling” and the classic “Cavity Milling” strategies. By examining their application in the production of a representative part, the toolpaths and machining efficiencies are compared to summarize their distinct impacts on the cutting process.
2. Machining Strategies
2.1 Cavity Milling
“Cavity Milling” achieves roughing by removing material from layers perpendicular to a fixed tool axis to shape the part contour. It is a classic roughing module in the NX series, with the following characteristics:
- For parts with complex 3D surfaces and multiple islands or mold components, cavity milling can quickly perform primary and secondary roughing, playing a key role in rapid material removal.
- Typically, a specific diameter (indexable) end mill is used, following either part contours or surrounding boundaries. By setting the cut layer depth and horizontal spacing, material is removed in a “small cut depth, large step-over” manner. That is, the radial cut (ae) is large, axial cut (ap) is small, and the average chip thickness (hm) is non-uniform.
2.2 Adaptive Milling
The newly introduced NX 12.0.2 “Adaptive Milling” command is designed for high-speed roughing and heavy cutting. It removes material from layers perpendicular to a fixed axis using an adaptive toolpath strategy, with the following main features:
- Better suited for parts with significant variation in sidewall material allowance, deep straight-wall islands, and cavities with flat bottoms, performing roughing layer by layer along the sidewalls.
- Typically, an appropriately sized end mill is selected based on the material. Using a “small step-over, large cut depth” approach, material is removed while maintaining a consistent tool feed direction and conventional climb milling. That is, radial cut (ae) is small, axial cut (ap) is large, and the average chip thickness (hm) remains constant.
Thus, for parts where both strategies are applicable, two distinct CNC programs can be created for roughing, each reflecting fundamentally different machining philosophies. Adaptive Milling maximizes tool engagement along the cutting edge to increase cutting depth and efficiency, whereas Cavity Milling relies on a percentage of the tool diameter. To evaluate the production efficiency improvement brought by Adaptive Milling, a comparative machining example is presented.
3. Application Example
3.1 Part Features
Figure 1 shows a type of support component for an aerospace assembly (semi-transparent areas indicate the blank). Material: 7075 aluminum alloy, with surface roughness requirements of Ra = 3.2 μm and local surface roughness of Ra = 1.6 μm. The part’s minimum bounding dimensions are 100 mm × 94.828 mm × 70 mm, machined from φ120 mm × 76 mm cylindrical blanks. The first trial batch consisted of 30 symmetrical pieces.
Figure 1. Support Part
7075 aluminum alloy is strong, ductile, and mechanically reliable, making it common in aerospace components. NX 12.0 simulations show the volume ratio between blank and finished part is approximately 7:1, with roughing consuming the majority of total cutting time. The roughing areas have significant cutting depths and widths, making them suitable for both Adaptive Milling and Cavity Milling.
3.2 Machining Plan
The production uses an Aumate GS1000/5-T five-axis vertical machining center, which allows multiple operations without changing fixtures. The machine has a small gantry structure, cradle-type table, linear X, Y, Z axes, rotary A and C axes, 18,000 rpm maximum spindle speed, and 40 kW drive power.
A three-flute, aluminum alloy flat-end mill (16 mm diameter, 95 mm overall length, 40 mm cutting length, 40° helix angle) is used for roughing, held by an ER32 collet (JT40) with a clamping length ≤ 40 mm. The part is clamped using a self-centering chuck and machined in two steps, each divided into three stages: roughing → secondary roughing (local corner cleanup) → finishing and hole machining.
3.3 Machining Process
Step 1: Machining the main body, circular cavities, and various holes, maximum depth 57 mm.
Cavity Milling roughing toolpath (Figure 2) primarily uses the tool tip, with radial large step-over and small axial cut depth. Toolpath coverage is broad, with long paths, multiple axial layers, and frequent retracts.
Figure 2. Cavity Milling Toolpath Analysis
a) Toolpath b) 3D simulation
Adaptive Milling roughing toolpath (Figure 3) utilizes the side cutting edges with a small radial step-over and large axial cut depth. Cutting depth can reach roughly twice the tool diameter, primarily using continuous climb milling along the side edges. Fewer axial layers are needed, improving machining stability, tool life, and high-speed capability.
Figure 3. Adaptive Milling Toolpath Analysis
a) Toolpath b) 3D simulation
Step 2: Part flipped, machining top bosses, slopes, cavities, and holes, max roughing depth 20 mm. Toolpath comparison (Figure 4) shows:
Figure 4. Toolpath Comparison of Two Roughing Modules
a) Cavity Milling b) Adaptive Milling
Analysis shows tapered slopes between layers. Cavity Milling continues top-down layer cutting, following part contours to achieve uniform semi-finish allowance. Adaptive Milling enables “bottom-up” cutting, adding toolpaths between layers with small depth changes, reducing leftover material to a minimal, uniform distribution—beneficial for stable semi-finishing. The strategy directly machines bottom surfaces, then slopes, ensuring a cleaner, more efficient path.
4. Comprehensive Effects
4.1 Experimental Results
Cutting parameters and machining durations for both strategies are summarized in Table 1.
Machining Parameters Table
| Spindle Speed | Feed Rate | Step 1 Cutting | Step Cutting | |||
|---|---|---|---|---|---|---|
| Machining Strategy | Milling Cutter Specs | n<sub>f</sub> (r/min) | v<sub>f</sub> (mm/min) | Cutting Step Parameters | Time/min | Time/min |
| ET | $m (a,) | «Imm, GIA (a) = | ||||
| BEE Nom | ms | 3500 | 85% of Tool Flat Radius | = | . | |
| : Heel on m, TK | HH (a,) + SVRITHERER 100%, | |||||
| Adaptive Milling (mm) | a<sub>e</sub> | 5000 | f<sub>er</sub> (a,): TERRI IIB |
Table 1. Cutting Parameters and Duration
Optimized roughing parameters aim for maximum productivity while respecting machine power constraints. Adaptive Milling and Cavity Milling differ due to philosophical differences.
Metal removal rate (Qmax) is calculated via Q = apaevf / 1000. Here, Cavity Milling Qmax = 47.6 cm³/min, Adaptive Milling Qmax = 153.6 cm³/min—Adaptive Milling achieves roughly three times the removal rate. Total roughing time for 2 steps: Cavity Milling 33 min, Adaptive Milling 11 min, saving 22 min per part. Tool wear analysis shows Cavity Milling tools exhibit tip dulling after 30 parts, while Adaptive Milling tools remain sharp due to improved stability.
4.2 Comparative Analysis
Figure 5. Machined Part
a) During machining b) After machining
Cavity Milling:
- Small axial cut and large radial cut lead to repeated tip wear. Chips absorb limited heat, resulting in high tip temperature and accelerated wear.
- Variable chip thickness and large radial engagement produce uneven material removal, high cutting forces, and unstable machining, unsuitable for high-speed cutting.
Adaptive Milling:
- Large axial cut and small radial cut maximize tool edge usage, reduce tip wear, and distribute cutting forces evenly. Thin, long chips carry away over 90% of heat, maintaining low temperatures and reducing part deformation.
- Constant chip thickness and consistent feed direction result in smooth, controlled layer-by-layer climb milling, with small engagement angles and uniform material removal. High-speed cutting is possible with increased stability and higher metal removal rate.
In summary, NX 12.0.2’s Adaptive Milling strategy in roughing enhances both stability and production efficiency.
Cavity Milling is widely used for roughing parts with non-straight walls or flat/curved cavity bottoms, as well as finishing of shallow walls. Adaptive Milling is more suited for parts with large sidewall allowance variations, deep straight-wall islands, and flat-bottomed cavities.
While NX 12.0 Cavity Milling is comprehensive, NX 12.0.2 Adaptive Milling provides additional, optimized options for roughing under specific conditions, improving both reliability and efficiency. Proper selection of Adaptive Milling can achieve significantly higher productivity, making it highly applicable in CNC machining of various aerospace components.
