Surface Finish

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Surface Finish

• An engineering component may be cast, forged,
  drawn, welded or stamped, etc.
• All the surfaces may not have functional
  requirements and need not be equally finished
• Some surfaces (owing to their functional
  requirements) need additional machining that
  needs to be recorded on the drawing

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Surface Roughness

• The geometrical characteristics of a surface
  include,
• Macro-deviations,
• Surface waviness, and
• Micro-irregularities.
• The surface roughness is evaluated by the
  height, Rt and mean roughness index Ra of the
  micro-irregularities.

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Surface roughness number

• Represents the average departure of the
  surface from perfection over a prescribed
  sampling length, (usually selected as 0.8 mm)
• Surface roughness number (Ra) is expressed in
  microns.
• Ra (h1h2-----hn)/n
• The measurements are usually made along a line,
  running at right angle to the general direction
  of tool marks on the surface.

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• Actual profile, Af
• It is the profile of the actual surface obtained
  by finishing operation.
• Reference profile, Rf
• It is the profile to which the irregularities of
  the surface is referred to. it passes through the
  highest point of the actual profile.
• Datum profile, Df
• It is the profile, parallel to the reference
  profile .it passes through the lowest point B of
  the actual profile

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• Mean Profile, Mf
• It is that profile, within the sampling length
  chosen (L) such that the sum of the
  material-filled areas enclosed above it by the
  actual profile is equal to the sum of the
  material void area enclosed below it by the
  profile.
• Peak to valley height, Rt
• It is the distance from the datum profile to the
  reference profile.
• Mean roughness index, Ra
• It is the arithmetic mean of the absolute value
  of the highest hi between the actual and mean
  profile.
• Ra 1/L ?x0 hi dx , where L is sampling
  length

xL
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Surface Roughness expected from manufacturing
processes
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Surface Roughness expected from manufacturing
processes
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Basic symbol only be used alone when its
meaning is explained by a note
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Roughness a obtained by any production process
Roughness a obtained by removal of material by
machining
Roughness a shall be obtained without removal of
any material
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If it is required that the required surface
texture be produced by one particular production
method, this method shall be indicated in
plain language on an extension of the longer arm
of the symbol
Indication of machining allowance where it is
necessary to specify the value of the machining
allowance, this shall be indicated on the left of
the symbols. This value shall be expressed in
millimeters.
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Generally to indicate the surface roughness, the
symbol is used instead of value. The relation is
given in following table.
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Machining Symbols
This symbol may also be used in a drawing,
relating to a production process , to indicate
that a surface is to be left in the state
,resulting from a preceding manufacturing
process, whether this state was achieved by
removal of material or otherwise
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Position of the Specifications of the Surface
Texture in the Symbol - The specifications Of
surface texture shall be placed relative to the
symbol as shown in figure.
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symbol Interpretation Interpretation
Parallel to the plane of projection of the view in which the symbol is used
Perpendicular to the plane of projection of the view in which the symbol is used
Crossed in two slant direction relative to the plane of projection of the view in which the symbol is used
Multidirectional
Approximately circular relative to the centre of the surface to which the symbol is applied
Approximately radial relative to the centre of the surface to which the symbol is applied
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Symbols with Additional Indications.
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Ways to represent roughness
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Separate note is written
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Surface finish grades specified
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Riveting
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Basic Dimensions
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Types of rivets
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Rivit Drawing
for the rest of the section we study in very
brief how to draw the riveting for the assembled
steel sections.
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In figure (a) the representation of the rivet
connecting two plates, in figure (b) shows the
counter shank rivet. In figure (c) it is a plan
view shows how to draw the rivets and description
of some important elements in the rivet drawing.
For figure (c) the line where all the rivets
should alignment to , is called the rivet line,
the distance between each two rivets is called
the pitch, where the distance between the first
rivet and the steel section edge is half pitch
and it is 6 cm. also if the line of rivets has
more than three rivets , then those rivets are
represented by only three rivets presented on the
drawing by the plus sign.
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Welding
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Introduction

• It is sometimes argued that it is unnecessary to
  specify welds on drawings and that the welder
  should be relied upon to deposit a suitable weld.
• This practice can be extremely risky because
• the type and size of the weld must be appropriate
  for the parent material and
• service conditions of the fabrication, and
• the necessary information and data are normally
  available only in the design office.

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Introduction

• Figure 1.1 illustrates (a) the instruction weld
  here and (bd)
• three ways to follow this instruction.

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Introduction

• Figure 1.1(b) shows a single fillet weld. This
  weld is simple
• and therefore cheap to apply
• but could be seriously deficient in performance.

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Introduction

• Figure 1.1(c) shows a double fillet weld, which
  takes
• longer to apply. Unless access is available to
  both sides of the joint,
• it will be impossible to weld it.

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Introduction

• Figure 1.1(d) illustrates a T-butt/groove weld.
  This weld normally
• requires edge preparation on a horizontal member,
  and therefore is
• more complex and
• expensive.
• However, it may be essential for certain service
  conditions.

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Introduction

• It can be seen from the previous examples that
  major problems will arise unless welded joints
  are carefully specified by the design office.
• The situation is particularly critical where, for
  example, work is placed with a subcontractor and
  the instructions need to be especially precise.

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The advantages of symbols

• symbolic representation can be used to cut down
  the time needed to complete the drawing and
  improve clarity.
• it may seem that the weld can simply be drawn as
  it will appear.

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Welding Symbols

• The symbols are placed on a horizontal reference
  line.
• This line is attached to an arrow line which
  points to the location of the weld (see Fig.
  2.1).
• In the ISO system there are two parallel
  reference lines, one solid and one dashed.
• In the AWS system a solid reference line is used.

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Welding Symbols

• Figure 3.1(a) illustrates a single-V butt/groove
  weld, which is the commonest form of edge
  preparation for this type of weld.

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Welding Symbols

• Figure 3.1(b) shows a square butt/groove weld.
  This weld will be limited to a maximum section
  thickness depending on the welding process used.

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Welding Symbols

• Figure 3.1(c) shows a single bevel butt/groove
  weld. This edge preparation is generally used
  when it is only possible to prepare one edge of
  adjoining sections.

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Welding Symbols

• Figure 3.1(d) illustrates a single-U butt/groove
  weld, which is used to restrict the quantity of
  weld metal required in sections greater than 12mm
  thick.

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Welding Symbols

• Figure 3.1(e) shows a single-J butt/groove weld.
  This weld is used to restrict the quantity of
  weld metal required in sections greater than 16
  mm thick when it is only possible to prepare one
  edge of adjoining sections.

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Welding Symbols

• Figure 3.1(f) illustrates a butt weld between
  plates with raised edges (ISO) or edge weld on a
  flanged groove joint (AWS).

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Welding Symbols

• Figure 4.1(a) illustrates a fillet weld. Unless
  otherwise indicated, the leg lengths are normally
  equal.

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Welding Symbols

• Figure 4.1(b) shows an edge weld.

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Welding Symbols

• Figure 4.1(c) shows a backing run or weld.

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Welding Symbols

• A flare-V-groove weld, shown in Fig. 4.1(d),

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Welding Symbols

• A flare-bevel-groove weld, shown in Fig. 4.1(e),

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Welding Symbols

• Figure 4.1(f) shows a plug or slot weld, which is
  a circular or elongated hole completely filled
  with weld metal.

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Welding Symbols

• Figure 5.1(a) shows spot welds.
• resistance spot weld requiring access from both
  sides.
• an arc spot weld made from one side of the joint.

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Welding Symbols

• Figure 5.1(b) illustrates seam welds.
• a resistance seam weld requiring access from both
  sides of the joint.
• an arc seam weld made from one side of the joint.

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Welding Symbols

• Figure 5.1(d) shows steep flanked butt welds.
• a steep flanked single-V butt weld
• steep flanked single-bevel butt weld.

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Welding Symbols

• Figure 5.1(c) indicates surfacing. In this
  symbol, the arrow line points to the surface to
  be coated with weld metal.

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Location of symbols

• Butt/groove welds
• Figure 6.1 (ac) shows the location of
  butt/groove welding symbols.

single-V butt weld
a single-bevel butt/groove weld
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Location of symbols

• Fillet welds

a T-joint with a single fillet weld.
a cruciform joint.
a double fillet weld on the left of the section
and a single fillet weld on the right-hand side.