Production drawing

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Production drawings[1][2][3] (sometimes called working drawings) are complete sets of drawings detailing the manufacturing and assembly of products. They are orthographic views of any machine parts and assembly. Production drawings are defined as 'drawn (graphic) information, prepared by the design team for use by the construction or production team, the main purpose of which is to define the size, shape, location and production of the building or component'. For instance, if the engineering drawings called for a screw to be fastened to a specific torque, the production drawings would typically elaborate the tool to be used to fasten the screw, and how it should be calibrated. If the screw is in an inconvenient place the drawings might also elaborate that the fastening is to be done at the beginning of assembly procedure, before access becomes confined.[4]

The details of material, the number of components needed for the assembly, etc., are given in the title block of production drawing. The sub-assembly or main assembly of a component where it will be assembled should also be indicated by production drawing.

"A component or part drawing is termed as production drawing". It is an authorised documents to produce the component in the shop floor. It should also mention the no. of parts that are required for making of assembled unit, of which the part is a member.

Production drawings show how to manufacture products. Engineering drawings are taken by production engineers and they then decide how best to manufacture the products described in factories or industries. These drawings are widely used. Machine operators, production line workers and supervisors all use production drawings for obtaining manufactured products. Design engineers use orthographic or pictorial views to record their ideas, these are called "working cases". These sketches are used for both the component and assembly drawings.

Set of production drawings[edit]

There are three main sets of production drawings:

1)Detailing of each non-standard part on drawing sheet, usually one part per sheet.

2)Assembly drawing showing all parts on one sheet.

3)A bill of material (BOM) essentially of each part.

Elements of production drawings[5][edit]

The basic elements of production drawing are as follows:

  1. Size and shape of component that is to be used
  2. Format of drawing sheet
  3. Process sheets
  4. Projection method
  5. Limits,fits and tolerances of size,form and position
  6. Production method
  7. Indication of surface roughness and other heat treatments
  8. Material specifications
  9. Conventions that are used

Principle of dimensioning in production drawing[edit]

Principles in dimensioning- Following are the basic principle of dimensioning:

  1. Each feature shall be dimensioned once only on that drawing module
  2. No more dimensions than necessary should be shown on the drawing
  3. As far as possible, dimensions should be placed outside the drawing view
  4. Dimensions should be represented by visible outlines, rather than from hidden lines
  5. Dimensioning of centre line should be avoided except when it passes through centre hole
  6. Intersecting projection or dimension line should be avoided
  7. If the space for dimensioning is insufficient at that time arrow heads may be reversed and adjacent arrow heads may be replaced by dots

Dimensioning technique[edit]

[6]

DIMENSIONING TECHNIQUE

Any engineering drawing requires the specification in term of dimensions. This information should be complete so as to manufacture the required component. Dimensions are classified according to following types: -1. Functional dimensions, 2. Non-functional dimensions, 3. Auxiliary dimensions.

Functional dimensions[edit]

The dimensions that are essential to describe the function of part or space.

Non-Functional dimensions[edit]

The dimensions that are not essential for the functional requirement,but are still required for manufacturing are called as non-functional dimensions.

Auxiliary dimensions[edit]

It is an additional information given on the drawing.This dimension does not govern manufacturing or inspection of parts. Arrangement and indication of drawing:-This dimensions are arranged in following manners:

  1. Chain dimensioning:-This method can be used only where the possible accumulation of tolerances does not affect the functional requirements.
  2. Parallel dimensioning:-In this type of dimensioning,a number of single dimension lines are drawn parallel one two another and are spaced so as to accommodate the dimensional values.
  3. Running dimensioning:-This type of dimensioning are similar to that of parallel dimensioning,only difference is that the dimensions are superimposed in one line.In this case the origin point should be marked.
  4. Co-ordinate dimensioning:-In co-ordinate type of dimensioning,the location of each hole and its size can be given by specifying X and Y co-ordinates from the defined origin and tabulated them.

Production drawing in limits,fits and tolerance[edit]

[7]

Limit system[edit]

The terms used in limit system are as: 1)Tolerance 2)Limits 3)Deviation

  1. Tolerance:-Deviation from basic value is defined as Tolerance.It can be obtained by taking difference between maximum and minimum permissible limits.
  2. Limits:-Two extreme permissible sizes between which the actual size is contained is called as limits.
  3. Deviation:-It is algebraic difference between a size and corresponding basic size.There are two types of deviations:-
  1. Upper deviation
  2. Lower deviations.

Fundamental deviation is either the upper or lower deviation,depending on which is the closest to the basic size.

Tolerances[edit]

[8]

Due to

  1. Human errors,
  2. Setting of machine, etc.

it is nearly impossible to manufacture an absolute dimension as specified by the designer.There arises deviation in dimensions from basic value.This deviation of dimensions from basic value is known as TOLERANCE.

Mechanical Tolerance Definitions

The figure shows mechanical tolerances which occurs during operations.

Fits[edit]

[9]

The relation between two mating parts is called as a fit. Depending upon the actual limits of the hole or shaft sizes,fits may be classified as clearance fit,transition fit and interference fit.

clearance fit[edit]

clearance fit means that there is clearance between mating parts.In clearance fit there is always a positive clearance between the hole and shaft.

transition fit[edit]

The transition fits may result in either an interference or clearance, depending upon the actual values of the tolerance of individual parts.

Interference fit[edit]

Interference fit is obtained if the difference between the hole and shaft sizes is negative before assembly.Interference fit is generally divided as minimum and maximum interference.

The two extreme cases of interference are as follows:

Minimum interference[edit]

It is magnitude of difference(negative)between the maximum size of the hole and minimum size of the shaft in an interference fit before assembly.

Maximum interference[edit]

It is the magnitude of the difference between the minimum size of hole and the maximum size of the shaft in an interference or a transition fit before assembly.

Hole Basis and shaft basis system: In working out limit dimensions for three classes of fits; two systems are in use, i.e. two basis system(hole and shaft) a)hole basis system: Here,the size of shaft is obtained by subtracting the allowance from the basic size of the hole. Tolerances are then applied to each part separately here,Lower deviation of hole is zero.The letter symbol indication for this is 'H'. b)shaft basis system: Here,upper deviation of shaft is zero and the size of hole is obtained by adding the allowance to the basic size of the shaft.The letter symbol indication is 'h'.

Production drawing in surface roughness[edit]

[10] The properties and performance of machine component are affected by degree of roughness of various surfaces, the higher the smoothness of surface better is the fatigue strength and corrosion resistance.Friction between mating parts is also reduced due to better surface finish. Surface roughness: The geometrical characteristics of the surface are as follows:

  1. Macro-deviations,
  2. Surface waviness,
  3. Micro irregularities.

We can evaluate surface roughness by height,and mean roughness index of micro-irregularities. Surface roughness is defined by following useful terms,

  1. actual profile,
  2. reference profile,
  3. datum profile,
  4. main profile,
  5. mean roughness index,
  6. Surface roughness number, etc.

Surface roughness number:The surface roughness number[R(a)]represents the average departure of the surface from the projections over the sampling length which is expressed in micrometers. It is given by,R(a)={h1+h2+h3+.....+hn}/n Surface roughness can be measured using some of the following terms,

  1. Surface gauge,
  2. straight edge,
  3. Profilograph,
  4. Profilometer,
  5. Optical flat, etc.

Production drawing and process sheets[edit]

Production drawing roughness skew is given in following figure:

Surface roughness skew2

Process sheets[edit]

The production drawing of a component is usually accompanied by a sheet,known as process sheet;which indicates the sequence of operations recommended for manufacturing it.It should list the machinery,tooling and skills for each act or event.the process sheet should consist of following:

  1. Description of the job,
  2. Component number,
  3. Size and weight,
  4. Cycle time,
  5. Drawing number,
  6. Sequence number, etc.

Uses of process sheets[edit]

Following are some of the uses of process sheets:

  1. An overall view of the various operations that are to be performed for a job.
  2. Assistance in layout of the plant,during the product design.
  3. It serves in the areas of cost estimation,standard costs,production control and the evaluation for productivity.
  4. Information for methods study personnel,to optimise the production process.

Principle of production drawing[edit]

Production drawings are to be prepared on standard size drawing sheets.The correct size of sheet and size of object can be visualized from the understanding of not the views of it but also from the various types of lines used, dimensions, notes, scales, etc. To provide the correct information about the drawings to all the people concerned,the drawings must be prepared. In India standards are according to Bureau of Indian Standards (BIS).

Drawing sheets[edit]

In production drawing standard size sheet are generally used to save paper and facilitate convenient storage of drawing. In specifications of sheets its sizes,design of size,size of title block & its position,thickness of borders & frames etc. to be considered.

Sheet size[edit]

The basic principle to be considered in sizes of drawing sheets are (a) X:Y=1:1.414 (b) XY=1 where X and Y are the sheet. For the reference size A4 having a surface area of 1 sqr. meter X=210mm and Y=297mm .

Title block[edit]

The title block should lie within the drawing space such that, the location of it, the containing the identification of the drawing, is at bottom right hand corner. The direction of viewing of the title block should correspond in general with that drawing. The block can have a maximum length of 170 mm .

See also[edit]

References[edit]

  1. ^ K.L. Narayana. Production Drawing. New Age International. ISBN 81-224-0953-9. 
  2. ^ bhatt, N.D. machine drawing. charotar publishing house. ISBN 978-81-85594-95-8. 
  3. ^ reddy, venkata (2009). production drawing. new age international. ISBN 978-81-224-2288-7. 
  4. ^ miller, john (1932). production drawings. rice institute. 
  5. ^ narayana, K. machine gawing. ISBN 81-224-0953-9. 
  6. ^ Machine Drawing & Computer Graphics,Farazdak Haideri,NIRALI PRAKASHAN. ISBN 978-93-8072-527-7
  7. ^ PRODUCTION DRAWING,K.L.Narayana ,NEW AGE INTERNATIONAL PUBLISHERS. ISBN 81-224-0953-9
  8. ^ Machine Drawing & Computer Graphics,Farazdak Haideri, NIRALI PRAKASHAN. ISBN 978-93-8072-527-7
  9. ^ MACHINE DRAWING,P.Kannaiah, NEW AGE INTERNATIONAL PUBLISHERS. ISBN 978-81-224-1917-7
  10. ^ Pohit, Goutam (2002). MACHINE DRAWING WITH AUTOCAD. PEARSON Education. ISBN 81-317-0677-X.