Lightweight milling head tools
The cutting heads for milling machines
The traditional design of cutting heads for milling has the goal to optimize the static and dynamic behavior of the system composed by the milling machine, the cutting head and the workpiece. More recently, the technological evolution of milling processes is moving towards increased productivity and reduced energy consumption than in the past.
The process throughput and the energetic needs of plants are inspiring innovative solutions in designing the cutting heads and the electronic controls of machines.
Of course, the preservation, and hopefully the improvement, of the quality levels of tooling performances is the real challenge behind the recent requirements.
The machine-tool-workpiece system is characterized by mutual interactions that directly determine many functional parameters such as accuracy, vibration amplitude, natural frequencies, cutting speed, and power consumption.
The design requirements associated with tooling accuracy and dynamic vibrations were normally managed with stiffness and inertia properties of the cutting head, which are both proportional to the mass. High mass provides high static strength and dynamic inertia. However, heaviness leads to drawbacks on the milling velocity, on the energy consumption, and on handling operations.
These limitations are in contrast with the more recent targets of advanced milling processes. Then, companies and research centers are providing the first attempts of advanced and modified versions of cutting heads with low mass.
The design for additive manufacturing
The redesign approach is inspired by the additive manufacturing (AM) building processes, and it is based on two steps, namely concept and design phases. The redesign started from a standard component provided by the company Fiudi. The eight design steps include the AM process constraints, such as temporary supports, part orientation, volumes oversizing for tooling, and powder management and extraction.
The automatic algorithms for topology optimization implemented in commercial software can not provide satisfactory solutions in this case, due to the strong coupling between geometrical and functional properties. For these reasons, all the intermediate steps are conceived by the designer by reshaping the component and calculating the stress-strain fields. In the final version, the weight reduction is about 35%.
More than weight reduction, the redesign must provide dramatic functional evolution of the cutting head. The lubrication system efficiency is enhanced thanks to parabolic channels and inner reservoir which increase uniformity, cooling, cleaning and lubrication of the cutting tools. Separate parts are merged together, while keeping almost the same outer appearance.
Modeling and simulation
The combination of structural and fluidic simulations is mandatory to optimize the shape and functionality of the component at the same time. The mass reduction leads to changes in stress and torsional stiffness, while channels shape and size determines the lubricant flow characteristics. The new channel design is able to exploit the rotational velocity of the cutting head to increase the output pressure of the lubricant and to improve the flow uniformity among the channels.
Validation and testing
The operative conditions are reproduced in the lab to measure static and dynamic properties under controlled loading conditions.