PRESENTATION OF MANUFACTURING SCIENCE II Presented by Dushyant dixit (3 rd year) ME

Topic Standardization and interchangeability. Limits,fits and tolerances. Surface roughness.

OBJECTIVE for the awareness of topics mentioned in previous slide. for the availability of information,to all of you in future time.

Standardisation; it is the process of developing and implementing technical standards.Standardization can help to maximize compatibility,safety, repeatability, or quality. It can also facilitate commoditization of formerly custom processes. It refers to maintain the sizes of the parts within a close degree of accuracy.

NATIONAL AND INTERNATIONAL STANDARDS BODY The Bureau of Indian Standards (BIS); it is the national Standards Body of India working under the aegis of Ministry of Consumer Affairs, Food & Public Distribution, Government of India. It is established by the Bureau of Indian Standards Act, 1986 which came into effect on 23 December The Minister in charge of the Ministry or Department having administrative control of the BIS is the ex-officio President of the BISAs a corporate body.

, it has 25 members drawn from Central or State Governments, industry, scientific and research institutions, and consumer organizations. Its headquarters are in NewDelhi, with regional offices in Kolkata,Chennai, Mumbai, Chandigarh and Delhi and 20 branch offices. International standards bodies are ISO(International standard organization) and International Electrotechnical Commission(IEC).

Interchangeability; it normally employed for the production of identical items within prescribed limits of sizes. It’s significance is to ensures increased output with reduced production cost.

Concept of limits and fits As for example,a shaft may be designed to dia. of 40mm. This means,the nominal dia. Of shaft is 40 mm but the actual size will be slightly different, because it is impossible to manufacture a shaft of exactly 40mm dia., no matter what m/c is used.

in case the m/c element is mating part with another one,then diamentions of both the parts become important,because they decide the nature of assembly. The allowable variation in size for the mating parts is called limits and the nature of assembly due to such variation in size is known as fits.

Definition of terminologies For convenience, shaft and hole are chosen to be two mating parts.

Definition of Tolerance Tolerance is the difference between maximum and minimum dimensions of a component, ie, between upper limit and lower limit. Depending on the type of application, the permissible variation of dimension is set as per available standard grades.

Tolerance is of two types,bilateral and unilateral. When tolerance is presented on both sides of nominal size, it is termed as bilateral; unilateral has tolerance on one side.

Upper deviation ; it is the diff. Of dimention the max. Possible size of component and its nominal size. Lower deviation ;Similarly, it is the difference of dimension between the minimum possible size of the component and its nominal size. Fundamental deviation ; It defines the location of the tolerance zone with respect to the nominal size. For that matter, either of the deviations may be considered.

LIMIT GAUGES These are also called “go” and “no go” gauges. These are made to the limit sizes of the work to be measured. One of the sides or ends of the gauge is made to correspond to maximum and the other end to the minimum permissible size. The function of limit gauges is to determine whether the actual dimensions of the work are within or outside the specified limits. A double end gauge has the “go” member at one end and “no go” member at the other end. The “go” member must pass into or over an acceptable piece but the “no go” member should not. few examples;

FIT SYSTEM The nature of assembly of two mating parts is defined by three types of fit system, 1; Clearance, 2; transition and 3; interference fit.

Clearance Fit ; In this type of fit, the shaft of largest possible diameter can also be fitted easily even in the hole of smallest possible diameter. Transition Fit ; In this case, there will be a clearance between the minimum dimension of the shaft and the minimum dimension of the hole. If we look at the figure carefully, then it is observed that if the shaft dimension is maximum and the hole dimension is minimum then an overlap will result and this creates a certain amount of tightness in the fitting of the shaft inside the hole. Hence, transition fit may have either clearance or overlap in the fit.

Interference fit; In this case, no matter whatever may be the tolerance level in shaft and the hole,there is always a overlapping of the matting parts. This is known as interference fit.Interference fit is a form of a tight fit.

SURFACE ROUGHNESS Roughness is fine irregularities that are produced during a machining process (grinding, polishing etc.). Waviness is the result of unwanted vibration, run out, deflection, tool wear, misalignment etc. during the manufacturing process which results in widely spaced surface profiles. A number of standard parameters are used to describe surface roughness of engineered surfaces. Average roughness (Ra); it is the average of the individual heights (asperities) and depths from the arithmetic mean elevation of the profile.

Root mean square method; it is defined as the square root of the arithmetic mean of the squares of the ordinates. Mathematically, R.M.S. Value (in microns)= √[(y 1 2 +y y n 2 /n] where y 1,y 2,y y n are the ordinates measured on both sides of the mean line and n are the no. of ordinates.

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