Modeling the cost of varying surface finish demands during longitudinal turning operations

Summary, in English

Tolerances, including geometry, dimension, and

surface roughness, are an important part of production where

the desire to manufacture quality products have to be weighed

against the increase of manufacturing costs. The desired tolerance

will influence the choice of both manufacturing method

and machine tool. Given that machining is an adequate

production method, variation of the required tolerances will

imply a variation of the part cost which needs to be taken into

account during production planning. Thus, the term “tolerance

cost” is introduced. The paper presents a model for evaluating

the tolerance cost in respect to the surface roughness during

longitudinal turning operations, enabling a better comparison

between different production alternatives. Through knowledge

of the required surface roughness, it is possible to estimate

appropriate cutting conditions. Knowledge of the cutting

conditions and the part geometry then makes it possible to

calculate the cycle time, information which in turn may be

used for calculating the corresponding part cost. Through

using experimental data, it is proven that the required surface

roughness has a significant influence on the attained

manufacturing cost. For instance, while longitudinally turning

AISI 4140, it was shown that an improvement of the surface

roughness from Ra=3.2 μm to Ra=1.6 μm will entail an increase

of the part cost by roughly 20 %. Similarly, a decrease

of the required surface quality (larger Ra value) will imply a

significantly reduced part cost.