tailieunhanh - Machining and Monitoring Strategies Part 5

Tham khảo tài liệu 'machining and monitoring strategies part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Machining and Monitoring Strategies 471 with the rotational axis but intersects it at the centre of gravity of the assembly s body . Under such conditions the force vectors equalise but are 180 apart. 3. Dynamic unbalance - dual-plane. Such a condition of the toolholder assembly arises when the axis does not coincide with the rotational axis and is not either parallel to nor intersecting this axis . see Fig. 232 . For any rotating tooling assembly estimating the cutter unbalance is possible using the following variables M cutter holder mass s mass centre e displacement of mass centre r distance from centre of tooling to the centre of gravity of mass m w angular velocity m mass unbalance U cutter unbalance 9549 a constant. Determining the relative unbalance U of a rotating tooling assembly can be found by the following expression s U MX e or alternatively U m X r i . It is usual to express unbalance in terms of the product of the mass times distance typically using the units g-mm . Finding the magnitude of centrifugal force produced by the rotating tooling assembly with a given unbalance can be established as follows F UX w ii . Where Th is the angular velocity in units of radians sec-1. The formula to find Th is expressed by 2 X n X rpm . V ------ iii . 60 Therefore by combining formulae i and iii in ii we can obtain the magnitude of centrifugal force F as follows F m X r X 2 X nX rpm 60 2 iv . As established in equation iv the centrifugal force caused by tooling unbalance will increase by the square of the speed in a similar manner to the spindle nose taper swelling . growth previously mentioned. Nonetheless assuming that this specific toolholder initially has a low unbalance this will become a problem if the rotational speeds are increased beyond 10 000 rev min-1. For example with most toolholders exhibiting single-plane unbalance25 research experimentation has shown that the initial unbalance of a typical tooling assembly will be of the order 250 g-mm. .