Abstract
Chatter is a self-excited vibration that can occur during milling operations causing undesirable consequences such as poor surface finish and increased levels of tool wear. One possible solution to this problem is to optimise the dynamics of the machine by tuning parameters such as tool stickout length, e.g. by using receptance coupling substructure analysis. Unfortunately, experimental limitations of the method, such as the requirement to model interface dynamics and the inefficient optimisation process, have hindered its advancement to the industrial sector. This paper looks to resolve these issues by proposing a new structural modification method for chatter avoidance. Firstly, tool-holder diameter is investigated as a potential tuning parameter: a new experimental dataset demonstrates that this design parameter can have a significant and valuable impact on the chatter stability. Secondly, the direct structural modification method is introduced, allowing the tool-holder diameter to be modelled without any knowledge of the interface behaviour between tool and tool-holder. Thirdly, the inverse structural modification method is proposed, allowing tuning and stability optimisation by solving a single equation. Lastly, a new tunable-mass tool-holder is presented, allowing the dynamics of a milling machine to be tuned for each tool diameter and length range with a single tool-holder. This eliminates the need for manufacturers to purchase a wide range of tool-holders, a significant financial investment.
Highlights
High speed machining operations, such as milling, are widely used in many industries such as the aerospace sector
The tool-holder allows the user to tune the dynamics of the machine in order to optimise the stability threshold of a milling operation, without the need to purchase a wide range of tool-holders
This paper has presented a novel application of structural modification theory to the chatter avoidance problem
Summary
High speed machining operations, such as milling, are widely used in many industries such as the aerospace sector In these processes unstable self-excited vibrations, known as regenerative chatter, can occur due to the dynamic interaction between the tool-tip and the surface being machined. Structural modification is a frequency domain method by which different components of a structure can be modelled individually and later combined to form a global model. This allows for the separate components to be modelled using the most appropriate method (analytical, numerical, or experimental analysis); alleviating some of the problems associated with dynamic modelling. Relating this back to passive chatter avoidance; by solving the above equation with model as some standard tool-holder and model as some modification to that toolholder, it is possible to find a tool-holder diameter that will result in a dominant mode at the desired natural frequency , and (using Eq (1)) a stable peak at the desired spindle speed
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