The machining method of helical gear is explored.
Taking a typical helical cylindrical gear as an example, taking the four-axis machining center as the platform, with the help of CAXA software, cutting simulation verification and actual cutting of machine tool through VERICUT, the four-axis NC machining method of helical gear is preliminarily explored.
The processing of spur and helical cylindrical gears is usually completed by hobbing, gear shaping or gear grinding.
With the function development of the four-axis machining center, the process that was difficult to complete in the three-axis machining center in the past can be realized on the equipment of the four-axis machining center.
Taking a typical helical gear as an example, this post discusses its four-axis NC machining method.
2. Case analysis
The traditional machining method of helical gear needs to be realized by hobbing machine.
With the rapid development of NC technology, especially the development of four-axis linkage technology of machining center, the machining of helical gear has been gradually realized on NC machine tools.
This post explores the processing methods of helical gears.
Based on the software CAXA Manufacturing Engineer independently developed in China, the simulation verification is carried out with the help of VERICUT, and the processing of arbitrary helical gears and customized helical gears is realized on the platform of four-axis machining center.
The case is selected from the numerical control multi axis linkage machining technology competition in a mechanical industry vocational and technical competition in a year.
The helical gear to be processed is shown in Figure 1. Some parameters are shown in Table 1 and the material is LY12.
The difficulty of case processing is that the tooth inclination is 20 °, and the number of teeth is 20.
There is no special gear processing equipment on the competition site.
Each station is provided with a Chenbang four-axis processing center, which is required to complete simulation and actual processing, and complete a set of roller die mechanism matched with helical gear on site.
It runs automatically when powered on, and the gear matching requirements are high.
Fig. 1 Helical gear
|Tooth inclination / (°)||20 / pair of teeth|
|Number of teeth / piece||20|
|Graduation circle diameter / mm||80|
3. Method 1: general tool, stretch machining
CAXA Manufacturing Engineer software has rich four-axis and five axis machining functions.
First draw the helical gear entity, and then generate the tool path.
The path generation steps are as follows: select the machining methods of “machining → five axis machining → five axis limiting surface machining”, “machining → five axis machining → five axis parallel line” and “machining → path editing → five axis to four axis trajectory”.
Set the rough and finish machining tools, and select the general flat bottom cutter and conical ball cutter to generate the rough and finish tool path, and simulate the cutting verification, as shown in Fig. 2.
a) Rough machining path
b) Fine machining path
c) Simulate cutting effect
Fig. 2 Conventional helical gear machining tool path and cutting simulation
This processing adopts the five axis tool path processing function, and then turns it into four axis tool path, so that it can be realized on the more common four axis machine tool.
The above is the processing method of one tooth.
To process other teeth, you only need to rotate the tool path.
This method has strong adaptability.
It uses conventional cutting tools to copy and cut along the curved surface, and can be applied to the processing of helical gears of other sizes.
However, this method has low processing efficiency and low processing accuracy.
The curved surface is realized through tool splitting, which is suitable for single piece trial processing or small amount of processing.
When batch processing, the weakness of low efficiency and low precision appears.
Therefore, when products are processed in batches, it is urgent to find a more suitable processing method.
4. Method 2: customized cutting tools and profiling processing
4.1 Tool customization
Using design software, such as CAXA electronic drawing board, fill in the relevant parameters of helical gear according to table 1, the tooth profile can be obtained quickly, and then the data can be obtained according to the software.
According to the tooth profile, extract the CAD drawing data of the tooth profile, and provide it to the tool manufacturer to customize several gear knives.
As shown in Fig. 3, the diameter of the tool handle is 12mm, the length of the tool handle is 70mm, and the cutting edge part is customized according to the relevant data of the tooth profile.
Although the cost of customized tools is higher than that of general tools, in batch processing, customized tools have high processing efficiency, good processing quality and high overall benefits.
b) Physical object
Fig. 3 Customized gear cutter
4.2 Fixture fabrication
It can be seen from the analysis of this workpiece that its clamping size is short.
It is difficult to align and takes a long time.
Moreover, when machining the tooth profile, the tool and spindle are close to the four-axis chuck, which is easy to interfere, and it is difficult to clamp and align, which is not convenient for batch processing.
If you want to improve the processing efficiency, you need to customize the fixture, as shown in Fig. 4.
Fig. 4a is a movable part, which clamps the gear blank through the thread, and the clamping position is fixed each time, so the tool setting time is saved;
Fig. 4b shows the fixed part, which is fixed on the chuck.
The actual fixture is shown in Fig. 4c.
a) Moving parts
c) Physical object
Fig. 4 Custom fixture
4.3 Machining graphic element and tool path generation
1) Draw a line with an inclination of 20 ° between the tooth bottom circle and the helical gear, select “machining → four axis machining → four axis cylindrical curve machining”, set the tool and cutting parameters, generate a tool path, and then obtain other tool path paths through the path rotation array.
The path generation steps are shown in Fig. 5.
Fig. 5 Generation of tool path
2) Generate G code and verify with VERICUT.
Select the tool path path, generate G code, and then import VERICUT software to simulate the trial cutting process (see Fig. 6a).
After verification, import it into the machine tool.
The real object obtained by cutting is shown in Fig. 6b.
a) Simulated cutting
b) Physical object
Fig. 6 Simulated cutting and machining
Helical gears are usually machined on specific hobbing machines, and less use of more popular CNC machining centers.
Based on the four-axis machining center, this post attempts and explores the machining method of helical gear, and preliminarily explores the method of four-axis NC machining helical gear:
For single piece or a small amount of processing, profiling processing can be used;
For batch processing, it is recommended to use custom tools.
This method breaks through the limitation of helical gear processing on special equipment, and can be applied to more popular CNC equipment at present.