Lehrstuhl für Technologie der Fertigungsverfahren Laboratorium für Werkzeugmaschinen und Betriebslehre Manufacturing Technology I Exercise 2 Measuring and Testing in Manufacturing Technology Werkzeugmaschinenlabor Lehrstuhl für Technologie der Fertigungsverfahren Prof. Dr. - Ing. F. Klocke RWTH - Aachen Steinbachstraße 53 52065 Aachen
Table of Contents Table of Contents 1 Introduction... 3 2 Criteria for the selection of a measuring instrument... 4 3 Definition of measuring equipment... 5 4 Use of measuring instruments... 7 4.1 Measuring in prototype manufacture... 7 4.2 Measuring in small batch manufacture (max. 20 parts / lot)... 9 4.3 Measuring in a mass production environment... 10 4.4 Measuring surface roughness... 12 Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 2
Introduction 1 Introduction The objective of metrology is to ensure that the requirements specified in relation to a product are met in the manufacturing department, thus ensuring that the subsequent function is guaranteed. One of its duties is therefore to determine the dimensions of workpieces and their deviations from a given constructional dimension. The extent of these deviations, or of the manufacturing error, depends on the manufacturing uncertainty which is influenced by the following factors, among others: Material Machine Operator Ambient influences Tool Basically, a distinction can be drawn between systematic and random nonconformities. In contrast to random or stochastic errors, systematic errors tend to be system based and to be duplicable under the same boundary conditions. They can be corrected by implementing appropriate measures. The causes of systematic faults may be geometrical faults in the machine guideways or machine flexibility. By contrast, random, or stochastic faults cannot be described systematically. They find expression in the variation range around an average value and may be attributable to process vibration, to tool wear or to the characteristic features of the tester. Statistical evaluation techniques must be used in order to distinguish between systematic and random faults. Typical times for testing quality characteristics are at goods-in, during manufacture and in the final checks following manufacture or assembly. Depending on the importance of the characteristic and of the measuring work involved, this testing may be random, statistical or, when safety-relevant criteria are involved, 100 % - testing. Suitable measuring instruments and techniques, capable of recording the individual faults in a certain workpiece separately from the other are required in order to evaluate the workpieces. Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 3
Criteria for the selection of a measuring instrument 2 Criteria for the selection of a measuring instrument Parts are measured and tested in dependence on a very wide range of basic conditions. First, it is essential to take account of the measuring frequency when selecting suitable measuring equipment. Here, a distinction is drawn between: Single part manufacture Small batch manufacture and industrial scale manufacture. It is also important to take due account of the measuring tolerance required. This will further reduce the number of instruments available for the measuring operation in question. Likewise, not every measuring instrument is capable under the boundary conditions previously outlined, to measure any geometrical form. Here, a distinction can be drawn between: Prismatic measurements Angular measurements Roundness measurements. All of these measurements can be recorded using a wide range of different measuring principles. These measurement principles can be categorised as follows: electrical mechanical optical pneumatic Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 4
Definition of measuring equipment 3 Definition of measuring equipment In order to demonstrate the range of measuring instruments available, the measuring range of selected measuring instruments will first be discussed. Measuring equipment Measuring range Display accuracy Characteristics and application Dial gauge Calliper gauge Mikrokator Pneumatic measuring instrument Comparator Block gauge Linear measurement indicator Laboratory microscope 3D-co-ordinate measuring machine Inductive probe Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 5
Definition of measuring equipment Measuring instrument Measuring range Display accuracy Characteristics and application DMS Sine bar with block gauge Universal angular measuring Instrument External micrometer (screw alone) Universal angular measuring Instrument External micrometer (screw alone) When measuring instruments are to be used to measure other measuring instruments, the display accuracy of the instrument conducting the measurement must be higher by a factor of at least 10 than that of the instrument being measured. Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 6
4 Use of measuring instruments The measuring instruments listed in Table 1, are suitable for use in the conditions outlined in Chapter 2 for a wide range of measuring tasks. These are explained in the following, on the basis of a wide range of parts: 4.1 Measuring in prototype manufacture The shaft pin shown in Fig. 1, is to be manufactured as a single part. 2 12 cm 1 1 = 20-0,2 5 cm 2 = 50 +0,02 3 3 = 5-0,05 4 = 15 +0,1 4 Fig. 1: Shaft extension Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 7
The following measuring instruments can be used for dimensions 1, 2, 3 and 4: Measuring instrument for dimension 1: Measuring instrument for dimension 2: Measuring instrument for dimension 3: Measuring instrument for dimension 4: A suitable measuring set-up for testing Dimension 4, might look like this: Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 8
4.2 Measuring in small batch manufacture (max. 20 parts / lot) Some of the measuring instruments listed in 4.1 can be substituted by more instruments more suitable for testing dimensional tolerances in small batch production of the part shown in Fig. 1. Measuring instrument for Dimension 1: Measuring instrument for Dimension 2: Measuring instrument for Dimension 3: Measuring instrument for Dimension 4: Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 9
4.3 Measuring in a mass production environment The part shown in Fig. 1 is now to be mass-produced. Measuring instruments with adapted measuring frequency can be used in this application. In mass production settings, a distinction is drawn between random sampling and 100% control. The following measuring instruments can be used for random sampling: Measuring instrument for Dimension 1: Measuring instrument for Dimension 2: Measuring instrument for Dimension 3: Measuring instrument for Dimension 4: Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 10
The following measuring instruments can be used for 100%-testing: Measuring instrument for Dimension 1: Measuring instrument for Dimension 2: Measuring instrument for Dimension 3: Measuring instrument for Dimension 4: Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 11
4.4 Measuring surface roughness Many functional areas of parts require not only that a certain measuring tolerance is met but also that certain roughness values are observed, in order to ensure that the part can be used successfully over a long period. It is therefore vital to be able to determine surface roughness, for bearing seats, gear wheels etc. The following physical principles of measurement can be applied using probes in order to measure the surface profile: 1.) 2.) 3.) 4.) The surface profile shown in the following was scanned using a commercially available inductive probe and can be analysed in terms of its roughness values R zdin and R max without computer-assisted evaluation. 1 µm 1 µm l Fig. 2: Surface profile Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 12
R max = R zdin = Additionally, the same surface profile can be used to determine the material contact area ratio M r when c = 2 µm. The same profile is shown again in order to facilitate the determination of the value. 1 µm 1 µm l Fig. 3: Surface profile M r = Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 13
In addition to the characteristic surface values which can be determined graphically, other characteristic surface values can be determined in a minicomputer-assisted evaluation. The most common characteristic values are: 1.) 2.) 3.) Manufacturing Technology I - Exercise 2 Measurement and Testing in Manufacturing Technology 14