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1 2004

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Ocena możliwości zmniejszenia różnościenności rur w procesach ciągnienia

Nowak S., Mroczkowski M.

Rudy i Metale Nieżelazne

2004

R. 49, nr 10-11

517-521

W artykule prezentowane są wyniki badań i analizy zmienności grubości ścianki rur wytwarzanych w procesach wyciskania a następnie walcowania pielgrzymowego lub ciągnienia. Analizowana jest ewolucja różnościenności. Oceniono możliwości jej zmniejszania, zwłaszcza w procesach ciągnienia z użyciem narzędzi wewnętrznych.

The paper presents results of research and analysis concerning variability of dimensions, mainly in terms of thickness of walls of tubes made in various technologies. High requirements as to stability of wall thickness may result directly from assembling needs or necessity to ensure repeatability of the post bending shape of the product. The latter is connected with so called de-springing and correlated with requirements concerning mechanical properties - repeatability of sigma (epsilon) curve and module of elasticity. Reasons of variability of wall thickness and other parameters of any product obtained from plastic working or other processes may be divided into two groups. The first group includes variability of dimensions, and possibly properties of the input. The second group results from input tube treatment processes. As far as the second group is concerned we may consider variability in relation to three factors. 1. Repeatability of tools we use - this problem refers to average value in various batches of products. 2. Variability of process conditions leading to variability of tool dimensions - mainly because of elastic deformations and other forms of wear. 3. Ability of the process to reduce variability in case of a group where we cannot actively change dimensions in the course of process without changing tools. The paper deals with analysis of various technologies: extruding-pilgrim rolling-drawing; extruding-floating and fixed plug drawing, forming tubes from strips and welding with reduction and calibrating. Two methods of description of variability have been applied. The first is naturally associated with variability - it is a statistic description. The other is associated with a characteristic feature of input preparation process, especially extruding, and is expressed by eccentricity of external and internal circles. The paper aims at answering the following questions: 1. In what cases distribution of wall thickness at the tube perimeter is determined with eccentricity and in what cases it is random variable and how to describe such cases in terms of a single sample or a batch of tubes with consideration of evolution of such variability. 2. Are pilgrim rolling and drawing processes capable of reducing wall thickness understood as relative differentiation.