No abstract

Original scientific paper This paper deals with the reaming process optimization. The aim of optimization is that with controlled process suitable geometrical specifications could be achieved without final honing. To attain systematic improvements in manufacturing technology, transparent approach with the use of quality tools has been selected. SPC of bore cylindricity and surface roughness (Ra) of the original reaming process shows poor process capability and demonstrates shortcomings of the clamping device. Feed rate and spindle speed were identified as key factors in achieving required bore tolerances. Plan of experiments and process modelling was performed by DOE methodology. Regression analysis gives models for both responses, and they are adequate at 73 % and 96 % confidence level respectively. Optimization model was implemented in real production. Keywords: cylinder bore; Design of Experiments (DOE); honing; reaming; Statistical Process Control (SPC) Optimizacija proizvodnje visokopreciznog cilindraIzvorni znanstveni članak Rad se bavi optimizacijom postupka razvrtanja provrta tako da se kontroliranim postupkom mogu postići odgovarajuće geometrijske specifikacije bez završnog honanja. U svrhu sistematskog poboljšanja proizvodne tehnologije, izabran je transparentni postupak uz primjenu kvalitetnih alata. SKP cilindričnosti provrta i hrapavosti površine (Ra) originalnog postupka razvrtanja pokazuje slabu mogućnost obrade i ukazuje na nedostatke uređaja za stezanje. Brzina posmaka i brzina vretena prepoznati su kao ključni čimbenici u postizanju odgovarajućih tolerancija provrta. Plan eksperimenata i modeliranje postupka određeni su DOE metodologijom. Regresijskom analizom dobiveni su modeli za oba tražena odgovora (cilindričnost provrta i hrapavost površine) sa 73 % i 96 % pouzdanosti. Model optimizacije primijenjen je u stvarnoj proizvodnji.

Small batch production is mainly, due to the competitiveness of the market, oriented to achieve the required specifications with minimal manufacturing processes using standard cutting tools. Costume-made hydraulic valves are one of the unique cases of small batch production in combination with high tolerances requirements [1]. Honing represents the manufacturing process which enables achieving final geometric requirements for valve's cylinder bore and requires pre-processing on computer numerical control (CNC) machining centre with successive cutting processes drilling, milling and reaming. Specifications of the piston bore of the hydraulic valve housing prescribe cylindricity /○/ ≤ 12 µm and surface roughness Ra ≤ 1.6 µm after reaming and cylindricity /○/ ≤ 3 µm and surface roughness Ra ≤ 0.4 µm after honing.This paper deals with reaming process quality improvement. Experiment planning and process modelling were performed by design of experiments (DOE) methodology [2]. Measuring method for bore cylindricity was defined as suggested in [3] and [4] and surface topology with mean roughness parameter Ra [5]. Within the framework of an experimental investigation single and combined effects, as well as related reproducibility, of such parameters on bore geometry and surface finish were investigated.Factors that have been identified as key to achieve specifications (bolded factors in Fig. 1) have been studied within the experimental work. Authors in other reaming processes optimization studies investigated spindle speed n and feed rate f as numeric control factor [6] to [9]. In this study feed rate and spindle speed were recognized as the key productive operation factors as well.Studies The key non-productive operation factors that were analysed in this study were clamping device lack of rigidity and effect of surface cleanliness on measurements reproducibility. Clamping device weakness was minimized with focusing on only one (of three) clamping nest. Surface cleanliness impact was analysed with SEM analysis and was minimized with additional washing and degreasing. Influence of Non-Productive Operations on Product Quality