Mill+: tool for stable and quality milling

2024/12/09 Gorka Urbikain Pelayo - Gipuzkoako Ingeniaritza Eskola (EHU). CFAA Fabrikazio Aeronautiko Aurreratuko Zentroa (EHU). | Daniel Olvera Trejo - Institute of Advanced Materials for Sustainable Manufacturing, Tecnológico de Monterrey. Iturria: Elhuyar aldizkaria

• Industria
• Softwarea
• Ingeniaritza

Milling is common in mechanical manufacturing and is one of the most valuable processes for the piece. But it's very sensitive to vibrations, especially the so-called chatter, which are very dangerous for parts. This problem is due to the fact that the shear system does not have sufficient stiffness or damping when the shear is made under certain conditions. This phenomenon, in addition to producing noise, worsens the quality of the piece and reduces the service life of the herramienta.Cuando occurs the Chatter phenomenon, the vibrations of the cutting tool exacerbate the working surface or produce irregularities; on the other hand, the tool is eroded faster and, therefore, reduces productivity and increases the costs of the process [1-3].

Although the problem of vibrations is old, it currently poses new challenges, since higher standards must be ensured in machining processes. When the cutting system cannot be changed or does not want to change, the solution is to change the cutting parameters. This is the main argument for using the application below.

What is Mill+ and how does it solve the chatter vibrations problem?

Mill+ is an application developed by the University of the Basque Country [4,5] and the Tecnológico de Monterrey [6] thanks to a long collaboration of years, and is designed to prevent and control vibrations that occur in milling. MATLAB App Designer offers stability maps via an interface in the environment so that the operator can select the most appropriate cutting parameters, such as the head turn speed (\(n)) and axial shear depth (\(a_p\)). These maps show combinations of parameters that produce a stable process or unpleasant vibrations, (\( n\) ,\(a_p\)), especially as a couple.

Functions of the Mill+ application

In order to achieve an effective and high quality milling process, it is necessary to select the appropriate cutting parameters. These parameters, such as turning speed, tooth advancement and cutting depth, directly affect the quality of the piece, the productivity and the durability of the tools. From these parameters new, more elaborate (and predictable) are created: some variables – cutting power, cutting forces, chip flow, surface roughness… – play a fundamental role.

The understanding and control of these variables, besides helping to increase productivity, ensures the stability and overall quality of the milling process.

Therefore, the developed tool offers the following simulation capabilities:

1. Multivariate visualization. It allows predicting the stability and surface roughness that will be obtained with the selected cutting parameters. In this way, the operator can predict whether the process is stable and what finish can be obtained. This helps to find a balance between stability and superficial quality, since it must be borne in mind that both aspects are different. A balance shall be sought between the productivity (or withdrawing rate of the chip) and the surface finishing of the part. Of course, the latter becomes more important in finishing processes.
   

   Figure 2.Resultados: color stability maps (left) and multivariable views (right).
2. Calculation of dynamic forces. The application allows to simulate the cutting forces at any point in the network. Thus, the evolution of dynamic forces over time can be observed. In addition, it allows a rapid conversion (FFT) of Fourier into the force profile to accurately determine whether or not a chatter phenomenon occurs. The criterion is as follows: If in the FFT the highest moments of the forces coincide with the multipliers of the frequency of strokes between the teeth, the process is stable and in the milling a forced vibration occurs (characteristic in the milling). Conversely, if the higher moments start to separate from the collision frequencies (and their multipliers) and appear around the system's own frequencies, this indicates that there is a chatter phenomenon.
3. Optimization of productivity and quality. The Optimization tab provides a balance between productivity and surface finishing quality. Optimal location for the application user (\(n)and\(a_p\)You can adjust the coordinates according to the value limits initially defined by it: the chip removal rate or chip flow rate (blue dots) and the minimum roughness that has been considered objective \(R_a\)(purple dots). From these two conditions, a point in the diagram is suggested. In the image, the starting point (red) is seen at the center of the map and the optimal point (green) tries to achieve the best balance between the two characteristics.
   

   Figure 3.Optimizacion productivity and quality: looking for balance.

 

Who is Mill+ going to?

Mill+ aims to be useful for both industry professionals and students in the academic field. Professionals will be able to perform a rapid analysis before milling operations and optimize parameters and reduce the probability of errors; the application is easy to use and does not require much training to integrate into the workflow. In the academic field, it is already used at the Tecnológico de Monterrey and at the University of the Basque Country to teach the vibrations and stability of the milling process, so that they can see and analyze how cutting parameters affect the behavior of tools and work pieces and they can better understand the theory and apply it in practical situations.

 

Bibliography

[1] Tlusty, J. Polac, M. The stability of machine tools against self-excited vibrations in machining. International Research in Production Engineering Conference, 1963, pp. 465-474.

[2] Altintas, Y. Manufacturing Automation: Metal Cutting Mechanics, Machine Tool Vibrations, and CNC Design, 2012, Cambridge University Press.

[3] Schmitz, T., As for Miguel Strogoff and Miguel Strogoff, the two gentlemen, one of them Smith and the other K. Machining dynamics: Response to Improved Productivity. Springer, 2009

[4] Urbikain, G. Artetxe, E. López de Lacalle, L.N., Numical simulation of milling forces with barber-shaped tools considering runout and tool inclination angles. Applied Mathematical Modelling, 2017, vol. 47, pp. 619–636.

[5] Urbikain G. Modelling of static and dynamic milling forces in inclined operations with circle segment end mills. Precision Engineering, 2019, vol. 56, pp. 123–35.

[6] Olvera D., Elias - Zuñiga A., D. Martínez Alfaro H., López de Lacalle L.N., Rodríguez C.A., Campa F.J. Determination of the stability lobes in milling operations based on homotopy and simulated annealing techniques. Mechatronics, 2014, vol. 24(3), pp. 177–85.