Based on the application of NX CNC machining technology in the rough machining stage of roughing, the software’s newly launched “adaptive milling” machining strategies and the classic machining strategies of ” impression milling” are analyzed and compared in combination with the typical, complete part production process. Using the advantages of programming, optimize the roughing method to quickly remove most allocations and improve processing efficiency.
1 Preface
CNC programming is the most fundamental work of CNC machining. The determination of each machining step and the selection of machining methods are important links in the analysis of the machining process before CNC programming. It is necessary to choose different machining methods according to different machining environments and different machining. compensation. This article focuses on the different processing methods of the two rough machining programming strategies newly launched in NX 12.0.2, “adaptive milling” and the classic “cavity milling”, combined with its application in the processing a typical part in real production, and discusses tool path and machining efficiency. They are compared and analyzed, and their different effects on the cutting process are summarized.
2 Treatment strategy
2.1 Impression milling
“Cavity_Mill” involves roughening the contour shape of the part by removing material in the plane cutting layer perpendicular to the fixed axis of the tool.[1]is a classic programming module commonly used for rough machining in NX series. It mainly has the following characteristics.
1) In the processing of parts or molds with complex three-dimensional surfaces and numerous islands, cavity milling can quickly carry out primary and secondary rough processing of the processed object and plays an important role in the rapid removal of excess material.
2) When applying “cavity milling”, an end mill of a certain diameter (indexable) is often used to follow the component/follow the periphery and other specific cutting modes and cutting directions in defining the cut layer and horizontal row spacing. The layer cutting method of “small cutting depth, large pitch distance” removes excess thickness and performs rough machining. That is, the side cutting amount (ae) is large, the back cutting amount (ap) is small, and the average chip thickness (hm) is not constant.
2.2 Adaptive milling
The high-speed machining command “Adaptive_Milling” newly launched in NX 12.0.2 is a very practical function for roughing and heavy cutting. This command uses adaptive cutting mode to rough out a certain amount of material on a plane cutting layer perpendicular to the fixed axis. It has the following main characteristics.
1) It is more suitable for rough machining with the component sidewall as a layer for straight-walled islands with large changes in sidewall cutting allowance and large processing depth, as well as for processing of objects with a flat bottom surface of the cavity.
2) When applying “adaptive milling”, an end mill of a certain specification is generally selected according to the cutting material, and the “small pitch distance, large cutting depth” method is used to remove the excess thickness, while maintaining the same advance. direction of the tool and always keeping the milling downward. That is, the side cutting amount (ae) is small, the back cutting amount (ap) is large, and the average chip thickness (hm) is constant.
It can be seen that under the condition that the two rough machining methods are applicable, two different CNC programs can be compiled for the rough machining of a workpiece, but there are essential differences in the processing concepts between programs. Generally, adaptive milling operations use cutting edge length as much as possible to increase cutting depth, thereby increasing machining efficiency, while “pocket milling” uses flat diameter percentage of the tool. So in actual production, can the newly added “adaptive milling” improve production efficiency compared with traditional “cavity milling”? We carry out a comparative analysis between the two through a treatment example.
3 Application examples
3.1 Characteristics of the parts
A certain type of media shown in Figure 1 is a certain type of aeronautical product component (semi-transparent display is white), the material grade is 7075, the required surface roughness value Ra = 3.2 μm and the local surface roughness value. Ra = 1.6 μm. The minimum package size for this part is 100mm × 94.828mm × 70mm. The blank before treatment is a round bar of φ 120 mm × 76 mm. The first batch of trial production quantity is 30 symmetrical pieces each.
a) Side view of the upper shaft b) Side view of the lower shaft
Figure 1 Support
The parts are made of aluminum alloy, which has high strength, good plasticity and good mechanical properties.[2]which is relatively common in the manufacture of aeronautical equipment and presents a certain representativeness. Calculated via NX 12.0 software, the volume ratio of the processed part compared to the pretreated blank reaches 1:7. The rough machining process will occupy most of the workpiece cutting time and is the key to improving production efficiency. Judging from the workpiece structure and the distribution of machining allowances, the roughing area has a large cutting depth and milling width, and the two roughing programming methods, “adaptive milling” and “pocket milling”, can be applied.
3.2 Treatment plan
In actual production, Ogilvy GS1000/5-T five-axis vertical machining center is used to realize the concentration of multiple working steps and reduce the use of tooling devices. The equipment has a small gantry structure and a cradle-type workbench. X, Y and Z are linear coordinate axes, A and C are rotary motion axes, the maximum spindle speed is 18,000 rpm, and the motor power is 40 kW.
According to the nature of the material to be processed and the specific processing needs, a three-edged aluminum alloy flat bottom milling cutter with a diameter of 16mm, a total length of 95mm, a blade length of 40 mm and a helix angle of 40° is selected for rough processing. The clamping length of ER32 (JT40) circlip handle ≤40mm.
The processing plan uses a self-centering chuck for clamping, and the entire processing content is carried out in two steps. Each working step is divided into 3 processing steps: roughing → secondary roughing (local corner cleaning) → finishing and hole machining.
3.3 Treatment process
Step 1: Process the main contour of the workpiece, circular cavity and holes everywhere, with a maximum processing depth of 57mm.
The roughing tool path analysis of traditional “cavity milling” programming is shown in Figure 2. The lower edge of the tool is mainly used for cutting, and processing is carried out using the “large radial pitch and small axial cutting depth” method. . The toolpath distribution is wide, the path is long, there are many axial layers and many tool jumps.
a) Toolpath b) 3D dynamic confirmation
Figure 2: Analysis of the path of the “Footprint milling” tool
The roughing tool path analysis of the newly added “adaptive milling” is shown in Figure 3. It makes full use of the side edge length of the cutter for cutting and uses “a small radial pitch and a large axial cutting depth” for processing. The cutting depth can reach approximately 2 times the diameter of the cutter. During processing, the side edge is mainly used for continuous milling to maintain the same cutting direction of the tool. Compared with the bottom edge cutting, the processing stability is higher and. tool life is longer. Cutting does not require multiple layers in the axial direction and can achieve high-speed machining.
a) Toolpath b) 3D dynamic confirmation
Figure 3 “Adaptive Milling” toolpath analysis
Step 2: Turn the part over and treat the boss, slope, cavity and holes on top. The maximum processing depth of rough machining is 20mm. The comparison of the tool paths of the two rough machining programming modules is shown in Figure 4.
a) Cavity milling b) Adaptive milling
Figure 4 Comparison of toolpaths of two roughing programming modules
Analyzing the processing characteristics of this stage of the process, it can be seen that there is a tapered wall (slope) between the two cutting layers. “Footprint milling” programming always adopts the top-down hierarchical cutting processing method, using an open toolpath and a cutting mode that follows the component to complete the rough machining and obtain a semi- uniform finish. “Adaptive Milling” programming can activate the “Ascending Cut” function in the cutting parameters dialog box according to the structural characteristics of the workpiece. By specifying the ascending step, the toolpath can be added between each cut. layer. . The additional toolpath intersects the cone wall from the bottom to the top of the layer with a slight change in the depth of cut (set by the Step Up parameter), thereby removing excess machining allowance and leaving no cut. Margins are minimal, consistent and uniform. distributed, which keeps the performance of the cutting tool stable during the semi-finishing process.
The “adaptive milling” strategy is specifically applied to the processing process of this step: when programming, by setting the parameters of the cutting layer and activating the “upward cutting” function, cut directly to the processing depth (in leaving a finishing allowance). out of the bottom plane, then cut from bottom to top around the cone wall to complete the rough machining of the boss slope and the top plane. From the comparison of the tool paths it can be seen that although both achieved ideal machining allowances after rough machining, the application of the “adaptive milling” processing method resulted in tool paths that were more simple and with higher cutting efficiency.
4 complete effects
4.1 Test results
In this example, the cutting parameters used by the “adaptive milling” and “pocket milling” programming modules in the actual processing and the cutting time of both are summarized in Table 1.
Table 1 Cutting parameters and cutting times of two programming modules
From the perspective of cutting parameters, the optimization of roughing parameters is based on the highest production efficiency as the goal and the maximum main power of the machine tool as the constraints. Ideally, users should set optimization parameters according to different processing stages to maintain a constant maximum main power state as much as possible, so as to maximize the amount of material removed per unit time. Due to differences in machining concepts, the cutting parameter settings are different between the “Adaptive milling” and “Pocket milling” programming modules.
Metal removal rate (Qmax)[3]Look, it is calculated using the metal removal rate formula Q=apaevf/1000. In this example, “cavity milling” Qmax=47.6 cm3/min is used and “adaptive milling” Qmax=153.6 cm3/min. It can be seen that the metal removal rate per unit time of “adaptive milling” strategy is three times that of “cavity milling”, and theoretically, the processing efficiency can be significantly improved. Judging from the actual cutting time, the “cavity milling” method takes a total of 33 minutes in the roughing stage of the two working steps, and the “adaptive milling” method takes a total of 11 minutes to the blank of a single piece. the time is shortened by 22 minutes and the production efficiency is greatly improved.
From the perspective of tool usage, after each of the two processing methods completed 30 processing tasks, the tool using “cavity milling” showed obvious passivation at the tip of the tool. tool, while the tool using “adaptive milling” showed that the edge remains sharp. enough. Compared with “pocket milling”, the “adaptive milling” method provides better cutting stability, so that more workpieces can be processed before the tool reaches the sharpening standard.
4.2 Comparative analysis
The workpiece processing entity is shown in Figure 5. Through practice and comparative analysis, it can be found that the two CNC roughing machining strategies “adaptive milling” and “cavity milling » have different impacts on the cutting process, which are summarized as follows.
a) Treatment
b) After treatment
Figure 5 Parts processing entity
(1) Cavity milling ① Since the back cutting amount (ap) is small and the side cutting amount (ae) is large, the tool is mainly cut with the bottom edge and repeated wear of the The front end of the tool is serious, and the granular chips generated have the ability to absorb cutting heat, relatively limited, the tool tip temperature is high and easy to wear. ② Due to the large side engagement (ae) and uneven average chip thickness (hm), the engagement angle during the cutting process is often very large and the amount of material cut by the tool is uneven, resulting in excessive cutting or even “full tool” phenomenon, so the force during the cutting process is large and unstable, and the tool load changes drastically, which will accelerate the wear of the tool and the spindle the machine tool, and is not suitable for high-speed cutting.
(2) Adaptive milling ① Due to the large amount of back cutting (ap) and small amount of side cutting (ae), the length of the tool cutting edge is more fully utilized, which greatly reduces wear repeated from the front end of the tool and the cutting force is more uniform. The high-speed flowing chips are thin and long, absorb and discharge more than 90% of the cutting heat, and have good heat dissipation effect, which can effectively control the cutting temperature, reduce workpiece deformation and increase tool life. ②The side cutting amount (ae) is small, the average chip thickness (hm) is constant, and the tool feed direction is maintained consistently, which makes the adaptive milling process very smooth. The tool always follows the milling direction downwards. a certain cutting depth. Method, peeling and milling layer by layer according to the amount of steps (line spacing) set by the processing parameters, and there are arc connections at the turning points. ③ Compared with cavity milling, the cutting angle during adaptive cutting is generally very small, the amount of material cut by the tool is always uniform, there will be no excessive cutting or even “complete tool”, and the stress on the tool and the machine tool is smaller. It is much more suitable for high speed cutting; and as the “adaptive milling” strategy has higher cutting parameters, smaller free stroke and greater processing stability, its metal removal rate (Qmax) is higher. ④ According to the processing characteristics of “adaptive milling”, combined with the tool material, workpiece material and cutting depth, the cutting angle can be adapted to the material to be processed by reasonably adjusting the number of pitch (line spacing). Adaptive milling is an excellent choice for high-speed milling of difficult-to-machine materials, significantly improving productivity and extending tool life.
In summary, the new “adaptive milling” processing strategy in NX 12.0.2, applied to the roughing stage of this example, is an excellent solution that can simultaneously improve processing stability and production efficiency.
5Conclusion
“Pocket milling” is the most commonly used machining strategy in CNC machining. It can be used for rough machining of most non-straight wall islands and parts with flat or curved bottom surfaces, as well as straight walls or side walls with small slopes. . finishing. The newly added “adaptive milling” operation is more suitable for rough machining of straight-walled islands with large cutting allowances on the side walls and large processing depth, as well as workpieces with a flat bottom surface .
The traditional “pocket milling” operation of NX 12.0 has the characteristics of completeness and versatility, while the new “adaptive milling” operation of NX 12.0.2 introduces more and more features when roughing specific processing conditions. A good choice is more like a powerful one. complement to the “cavity milling” operation, which can meet the highest production efficiency requirements with maximum processing reliability. Practice has proven that under conditions favorable for the application of “adaptive milling”, choosing the correct programming operation can achieve double the result with half the effort. In the manufacturing process of various types of equipment, “adaptive milling” can be applied to a very wide range of CNC machining of parts and components and deserves vigorous promotion.
Expert Commentary
The traditional “cavity milling” strategy of UG NX software is a classic programming module for rough machining of blanks. The cutter quickly removes most of the excess thickness so as to cut layer by layer in the direction of the depth of the cavity. the characteristics of “small cutting depth, large machining”. It has the characteristics of “step distance and rapid knife trajectory”. The new “adaptive milling” strategy in NX 12.0.2 is suitable for straight-walled islands and the bottom surface of grooves with large cutting allowances on the sidewalls. It provides more cutting capabilities when roughing the cavity for specific path selection and toolpath conditions. are more concise. Combining the two can achieve twice the result with half the effort.
The article is very popular and highly applicable. It integrates NX software programming and CNC milling processing. It highlights the advantages of the “adaptive milling” processing strategy in sidewall cutting. It cooperates with traditional “cavity milling” to meet specific or special conditions. The cavity processing structure quickly improves the roughing efficiency.
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