PROBLEM xxxxx is a large engineering company, manufacturing steel products for the building industry. As the company has grown over the last few years, the products produced have not only increased in volume but the high quality standard and minimal tolerance to which they are manufactured has become more of a customer requirement and therefore an important company objective.
One particular high sales volume product, is assembled using numerous steel bracket components which themselves are milled to size on a CNC lath. At present the company have two of these machines each manufacturing between 150 and 170 steel brackets per day, on a 3 rotation shift pattern.
The steel bracket itself should be 100 mm long with a tolerance factor of + / - 1 mm, therefore the smallest dimension the bracket could be is 99 mm and the largest dimension being 101 mm to achieve a set quality standard.
Prediction and chaos
Normal distribution. Shows the quartile and interq...
English: Nishiguchi. Boxplot and a probability den...Any thing outside this numerate quality range will result in the end product being assembled incorrectly. Each machine automatically measures the component at the end of the milling cycle and this is logged in the machines computer database, the measurement has a 1/20th mm accuracy. As part of the British Quality Standard, every twentieth component is also measured manually by the machines operator using engineering callipers with the same accuracy of a 1/20th mm.
The CNC laths are both the same model and when purchased from the supplier, were said to be accurate within + / - 0.5 mm. However the machines are now 3 years old and have had continuous five days per week, 49 weeks per year working life, with standard maintenance checks. The operators therefore feel that due to the age of the laths and the level of work they have undertaken, the machine accuracy has been...