608901411-Ch-1-Metrology-and-Measurement - Copy.pptx

Metrology

1. Introduction to Metrology Metrology word is derived from two Greek words such as metro which means measurement and logy which means science.  Metrology is the science of precision measurement. The engineer can say it is the science of measurement of lengths and angles and all related quantities like width, depth, diameter and straightness with high accuracy .  Metrology demands pure knowledge of certain basic mathematical and physical principles. The development of the industry largely depends on the engineering metrology. Metrology is concerned with the establishment, reproduction and conservation and transfer of units of measurements and their standards. Irrespective of the branch of engineering, all engineers should know about various instruments and techniques.

2. Objective of Metrology To standardize the measuring methods To maintain the accuracies of measurement. Complete evaluation of newly developed products. Determination of the process capabilities and ensure that these are better than the relevant component tolerances . Determination of the measuring instrument capabilities and ensure that they are quite sufficient for their respective measurements. Minimizing the cost of inspection by effective and efficient use of available facilities. Reducing the cost of rejects and rework through application of Statistical Quality Control Techniques. To prepare designs for all gauges and special inspection fixtures .

3. Need of Inspection/ Metrology To ensure the material, parts and components conform to the established standards To meet the interchangeability of manufacture T o p r o vi d e the m e ans of findin g the p r o b l em a r ea f o r meeting the established standards T o p r odu c e the part s h a ving ac c e p t able qual i ty l e v e l s with reduced scrap and wastage T o pu r c hase goo d qu a l i ty of r a w m a t er i als, t o ols a nd equipment that govern the quality of finished products T o t a k e necessa r y e f f orts t o measu r e and r e du c e the rejection percentage To judge the possibility of rework of defective parts

4. Metrology and Manufacturing

5. Metrology and Manufacturing

6. Elements of Metrology Standard The most basic element of measurement is standard without which no measurement is possible. Standard is a physical representation of unit of measurement . Different standards have been developed for various units including fundamental units as well as derived units . Workpiece Work piece is the object to be measured/measured part Variations in geometry and surface finish of the measured part directly affect measuring system’s repeatability Compressible materials like plastic or nylons pose a different type of problem that any gauge pressure will distort the material. This can be avoided by fixing of gauging pressure as suggested by the industry so that everyone will get uniform results

7. Elements of Metrology Instruments Instrument is a device with the help of which the measurement can be done The instrument must be selected based on the tolerance of the parts to be measured, the type of environment and the skill level of operators It should be remembered that what type of instruments the customer prefer to measure . Person There must be some person or mechanism to carryout the measurement Modern gauges are increasingly easy to use but the failure to adequately train the operating personnel will lead a poor performance

8. Effects of elements of metrology on Precision and Accuracy Accuracy of Measurements: The purpose of measurement is to determine the true dimensions of a part. But no measurement can be made absolutely accurate. There is always some error. The amount of error depends upon the following factors: The accuracy and design of the measuring instrument The skill of the operator Method adopted for measurement Temperature variations Elastic deformation of the part or instrument etc The true dimension of the part cannot be determined but can only by approximate. The agreement of the measured value with the true value of the measured quantity is called accuracy. If the measurement of dimensions of a part approximates very closely to the true value of that dimension, it is said to be accurate . The term accuracy denotes the closeness of the measured value with the true value. The difference between the measured value and the true value is the error of measurement. The lesser the error, more is the accuracy.

9. Accuracy: Accuracy may be defined as the ability of an instrument to respond to a true value of measured variable under the reference conditions. It refers how closely the measured value agrees with the true value. The difference between the measured value and the true value is know as Error of measurement. Precision: Precision may be defined as the degree of exactness for which an instrument is designed or intended to perform. It refers the repeatability or consistency of measurement when the measurements are carried out under identical conditions Precision and Accuracy Effects of elements of metrology on Precision and Accuracy

10. Effects of elements of metrology on Precision and Accuracy

11. Effects of elements of metrology on Precision and Accuracy

12. Factors affecting elements of metrology Factors affecting the standard of measurement Coefficient of thermal expansion Elastic properties of a material Stability with time Calibration interval Geometric compatibility Factors affecting the workpiece to be measured Coefficient of thermal expansion of material Elastic properties of a material Cleanliness, surface finish, surface defects such as scratches, waviness etc., Adequate datum on the workpiece Thermal equalization

13. Factors affecting the characteristics of an instrument Scale error Repeatability and readability Calibration errors Effect of friction, zero drift, backlash etc., Inadequate amplification Deformation when heavy workpieces are measured Constant geometry for both workpiece and standard. Factors affecting person Training/skill Ability to select the measuring instruments and standard attitude towards accuracy Planning me a sur eme n t t echniques f o r minim u m c o s t, consistent with precision requirements etc. Factors affecting elements of metrology

14. Factors affecting environment Temperature, humidity, atmosphere, pressure etc., Clean surrounding and minimum vibration enhance precision T emp e r a tu r e equ a li z a ti o n bet w e e n s t anda r d , w orkpie c e and instrument. Therm a l e x pansio n e f f e cts du e t o he a t r adi a t ion f r o m li g h ts, heating elements, sunlight and people. Manual handling may also introduce thermal expansion. Factors affecting elements of metrology

15. Higher accuracy can be achieved only if, ail the sources of error due to the above five elements in the measuring system are analyzed and steps taken to eliminate them. The above analysis of five basic metrology elements can be composed into the acronym. SWIPE, for convenient reference where, S - STANDARD W- WORKPIECE I - INSTRUMENT P-PERSON E – ENVIRONMENT Factors affecting elements of metrology