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07_Chapter 4 roughness

By Bernard Wells,2014-10-24 20:52
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07_Chapter 4 roughness

64 Chapter 4 Roughness

Chapter 4

Roughness

Chapter 4 Roughness 65

4.1 General terms and definitions

; surface profile: Profile that results from the intersection of the real surface by a specified plane.

; sampling length lr: Length in the direction of the X-axis used for identifying the irregularities characterizing the profile under evaluation.

; evaluation length lnLength in the direction of the X-axis used for assessing the profile under evaluation. In general, evaluation length equal five sampling length. ; profile peakAn outwardly directed (from material to surrounding medium) portion of the assessed profile connecting two adjacent points of the intersection of the profile with the X-axis.

; profile valley: An inwardly directed (from surrounding medium to material) portion of the assessed profile connecting two adjacent points of the intersection of the profile with the X-axis.

; ordinate value Z(x):Height of the assessed profile at any position x.

; profile peak height Zp: Distance between the X-axis and the highest point of the profile peak. Rp is the largest profile peak height Zp within a sampling length .

; profile valley depth Zv: Distance between the X-axis and the lowest point of the profile valley. Rv is the largest profile valley depth Zv within a sampling length.

; profile element width Xs: Length of the X-axis segment intersecting with the profile element.

4.2 Evaluation parameter

Amplitude parameters

; Arithmetical mean deviation of the assessed profile Ra: Arithmetic mean of the

absolute ordinate values Z(x) within sampling length.

66 Chapter 4 Roughness

l1RaZxdx;() 0l

; Maximum height of profile Rz: Sum of height of the largest profile peak height Zp and

the largest profile valley depth Zv within a sampling length.

Spacing parameters

; Mean width of the profile elements RSm: Mean value of the profile element widths Xs within a sampling length.

m1

RSmXs;i m;1i

4.3 Graphical symbols for the indication of surface texture

Basic graphical symbol

The basic graphical symbol shall consist of two straight lines of unequal length inclined at

approximately 60? to the line representing the considered surface, as shown in Figure 4-1.

The basic graphical symbol in Figure 4-1 should not be used alone (without complementary information).

Figure 4-1 Basic graphical symbol for surface texture

Expanded graphical symbols

; Removal of material required:If removal of material for example, by machining

is required for obtaining the specified surface, a bar shall be added to the basic graphical

symbol, as shown in Figure 4-2.The expanded graphical symbol in Figure 4-2 should not

be used alone (without complementary information).

Chapter 4 Roughness 67

Figure 4-2 Expanded graphical symbol indicating removal of

material required

; Removal of material not permitted:If removal of material is not permitted for obtaining the specified surface, a circle shall be added to the

basic graphical symbol, as shown in Figure 4-3.

Figure 4-3 Expanded graphical symbol indicating removal of

material required

Complete graphical symbol

; When complementary requirements for surface texture characteristics have to be indicated, a line shall be added to the longer arm of any of the

graphical symbols illustrated in Figures 4-1 to 4-3, as shown in Figure

4-4.

a) any manufacturing process permitted b) material shall be removed c) material shall bot be removed

Figure 4-4 Complete graphical symbol

; For use in the written text of for example, reports or contracts the

1)2)textual indication for Figure4-4, a) is APA, for b) it is MRR and for c)

68 Chapter 4 Roughness

3)NMR.

Marks:

Any process allowed.

Material removal required.

No material removed.

4.4 Composition of complete graphical symbol for surface texture

General

In order to ensure that a surface texture requirement is unambiguous, it may be necessary, in addition to the indication of both a surface texture parameter and its numerical value, to specify additional requirements (e.g. transmission band or sampling length, manufacturing process, surface lay and its orientation and possible machining allowances). It may be necessary to set up requirements for several different surface texture parameters in order that the surface requirements ensure unambiguous functional properties of the surface. Rules for comparison of the measured values with the tolerance limits

; The surface texture of the workpiece under inspection can appear homogeneous or be quite different over various areas.

; This can be seen by visual examination of the surface.

; In cases where the surface texture appears homogeneous, parameter values determined over the entire surface shall be used for comparison with the requirements specified on the drawings or in the technical product documentation.

; If there are separate areas with obviously different surface texture, the parameter values which are determined on each area shall be used separately for comparison with the requirements specified on the drawings or in the technical product documentation.

Chapter 4 Roughness 69

; For requirements specified by the upper limit of the parameter, those separate areas of the surface shall be used which appear to have the maximum parameter value.

The 16%-rule

; For requirements specified by the upper limit of a parameter, the surface is considered acceptable if not more than 16% of all the measured values of the selected parameter, based upon an evaluation length, exceed the value specified on the drawings or in the technical product documentation.

; For requirements specified by the lower limit of a surface parameter, the surface is considered acceptable if not more than 16% of all the measured values of the selected parameter, based upon an evaluation length, are less than the value specified on the drawings or in the technical product documentation.

; To designate the upper and the lower limits of the parameter, the symbol of the parameter shall be used without the “max.” index.

The max.-rule

; For requirements specified by the maximum value of the parameter during inspection, none of the measured values of the parameter over the entire surface under inspection shall exceed the value specified on the drawings or in the technical product documentation.

; To designate the maximum permissible value of the parameter, the “max.” index has to

be added to the symbol of the parameter (for example Rz1max.).

Position of complementary surface texture requirements ; The mandatory positions of the various surface texture requirements in the complete graphical symbol are shown in Figure 4-5.

70 Chapter 4 Roughness

Figure 4-5 Positions (a to e) for location of complementary

requirements

; The complementary surface texture requirements in the form of surface texture parameters,

numerical values, and

transmission band/sampling length,

shall be located at the specific positions in the complete graphical symbol in accordance with the following.

a) Position a Single surface texture requirement

Indicate the surface texture parameter designation, the numerical limit value and the transmission band/sampling length. To avoid misinterpretation, a double space (double blank) shall be inserted between the parameter designation and the limit value.

Generally, the transmission band or sampling length shall be indicated followed by an oblique stroke (/), followed by the surface texture parameter designation, followed by its numerical value using one text string. Example 1

0.0025-0.8/Rz 6.8 (example with transmission band indicated) Example 2

-0.8/Rz 6.8 (example with only sampling length indicated) Especially for the motif method, the transmission band shall be indicated, followed by an oblique stroke (/), followed by the value of the evaluation length, followed by another oblique stroke, followed by the surface texture parameter designation, followed by its numerical value.

b) Position a and b Two or more surface texture requirements

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Indicate the first surface texture requirement at position “a” as in a). Indicate the second surface texture requirement at position “b”. If a third requirement or more is to be indicated, the graphical symbol is to be enlarged accordingly in the vertical direction, to make room for more lines. The position “a” and “b” are to be moved upwards when the symbol is enlarged.

c) Position c Manufacturing method

Indicate the manufacturing method, treatment, coatings or other requirements for the manufacturing process etc. To produce the surface, for example, turned, ground, plated.

The surface texture parameter value of an actual surface is strongly influenced by the detailed form of the profile curve. A parameter designation, parameter value and transmission band indicated solely as a surface texture

requirement do not therefore necessarily result in an unambiguous function of the surface. It is consequently necessary in almost all cases to state the manufacturing process, as this process to some extent results in a particular detailed form of the profile curve.

There may also be other reasons for finding it appropriate to indicate the process.

The manufacturing process of the specified surface can be presented as text and added to the complete symbol as shown in Figures 4-6 and 4-7.

MRR turned Rz 3.1

a) in text b) on drawing

Figure 4-6 Indication of machining process

and requirement for roughness of resulting surface

72 Chapter 4 Roughness

NMR Fe/Ni15p Cr r; Rz 0.6

a) in text b) on drawing

Figure 4-7 Indication of coating and roughness requirement

Position d Surface lay and orientation

Indicate the symbol of the required surface lay and the orientation, if any, of the surface lay, for example, “=”, “X”, “M”.

The surface lay and direction of the lay emanating from the manufacturing process (e.g. traces left by tools) may be indicated in the complete symbol by using the symbols shown in Table 4-1 and illustrated

by the example in Figure 4-8. The indication of surface lay by the defined symbols (e.g. the perpendicularity symbol in Figure 4-8) is not applicable

to textual indications.

The direction of lay is the direction of the prevailing surface pattern, which is usually determined by the manufacturing process used. The symbols in Table 4.1 indicate the lay and direction of lay in relation to the drawing plane containing the surface texture requirement.

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Table 4.1 Indication of surface lay Graphical Interpretation and example

symbol

Parallel to plane of projection of view in

which symbol is used

Perpendicular to plane of projection of

view in which symbol is used

Crossed in two oblique directions

relative to plane of projection of view in

which symbol is used X

Multi-directional

M

Approx. circular relative t centre of

surface to which symbol applies

C

Approx. radial relative to centre of

surface to which symbol applies

R

Lay is particulate, non-directional, or

protuberant

P

If it is necessary to specify a surface pattern which is not clearly defined by these symbols,

this shall be achieved by the addition of a suitable note to the drawing.

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