Lecture 01MEC 263 ArijitSen Faculty Department of Mechanical Engineering IUBAT
What is Metrology? • The word Metrology is derived from Greek word which means measurement. • Metrology is the Science of Measurement, includes all aspects both theoretical and practical with reference to measurements, whatever their uncertainty, and in whatever field of science or technology they occur. • The metrologist has to understand the underlying principles to be design and develop new instruments and also to use the available instruments in the best possible way. • (Ref: Jain, Ch – 1 , Article 1.1)
Objectives of Metrology • While the basic objective of a measurement is to provide the required accuracy at minimumcost, metrology would have further objective in a modern engineering plant with different shops like Tool Room, Machine Shop, Press Shop, Plastic Shop, Pressure Die Casting Shop, Electroplating and Painting Shop, and Assembly Shop, as also Research, Development and Engineering Department. In such an engineering organization, the further objectives would be as follows :
Objectives of Metrology • a) Thorough evaluation of newly developed products, to ensure that components designedare within the process and measuring instrument capabilities available in the plant. • (b) To determine the process capabilities and ensure that these are better than the relevantcomponent tolerances. • (c) To determine the measuring instrument capabilities and ensure that these are adequatefor their respective measurements.
Objectives of Metrology • (d) To minimize the cost of inspection by effective and efficient use of available facilities, and to reduce the cost of rejects and rework through application of Statistical Quality Control Techniques. • (e) Standardization of measuring methods. This is achieved by laying down inspectionmethods for any product right at the time when production technology is prepared.
Objectives of Metrology • (f) Maintenance of the accuracies of measurement. This is achieved by periodical calibration of the metrological instruments used in the plant. • (g) Arbitration and solution of problems arising on the shop floor regarding methods ofmeasurement. • (h) Preparation of designs for all gauges and special inspection fixtures.
Need of Inspection • In order to determine the fitness of anything made. • To minimize variation of assembly parts and establish control over sizes the parts. • To minimize the cost of reworks. • To develop precision inspection methods and instruments. • (Ref: Jain, Ch – 1 , Article 1.2)
Accuracy, precision and uncertainty Low AccuracyHigh Precision High AccuracyLow Precision High AccuracyHigh Precision (Ref: Jain, Ch – 1 , Article 1.4)
Error • `Difference between true value and measured value. • Cause of error: • Effect of Environment • Effect of Support • Effect of alignment • Dirt • Vibration • Metallurgical effects • Deflection (Ref: Jain, Ch – 1 , Article 1.6)