26-05-2014, 11:40 AM
Working Drawings and Assemblies
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INTRODUCTION
Production or working drawings are specialized engineering drawings that provide information required to make the part or assembly of the final design. Working drawings rely on orthographic projection and many other graphical techniques to communicate design information for production. Though there is a common method for representing mechanical parts for production, many industries use specialized production drawings. In addition to standard mechanical drawings, two types of specialized drawings, piping drawings and welding drawings, are described in this chapter.
Reprographics is the storage, retrieval, and copying of engineering drawings. Reprographics techniques such as diazo printing, and the digital techniques used with CAD are covered in this chapter.
BASIC CONCEPTS
Engineering drawings are used to communicate designs to others, document design solutions, and communicate design production information. These types of drawings are called working drawings or production drawings.
Documenting is the process of communicating and archiving design and manufacturing information on a product or structure. The documents created include drawings, models, change orders, memos, and reports.
Detail drawing
A detail drawing is a dimensioned, multiview drawing of a single part, describing the part’s shape, size, material, and finish, in sufficient detail for the part to be manufactured based on the drawing alone. Standard parts are not drawn as details because they are normally purchased, not manufactured, for the assembly.
When more than one detail is placed on a sheet, the spacing between details is carefully planned, including leaving sufficient room for dimensions and notes.
assembly drawing
An assembly drawing shows how each part of a design is put together. If the design depicted is only part of the total assembly, it is referred to as a subassembly. An assembly drawing normally consists of:
A parts list or bill of materials (BOM) showing the detail number for each part, the quantity needed for a single assembly, the description or name of the part, the catalog number if it is a standard part, and the company part number.
Leader lines with balloons, assigning each part a detail number, in sequential order and keyed to the list of parts in the parts list.
Assembly drawings are used to describe how parts are put together as well as the function of the entire unit; therefore, complete shape description is not important. The views chosen should describe the relationships of parts and the number of views chosen should be the minimum necessary to describe the assembly.
Dimensions are not shown on assembly drawings unless necessary to provide overall assembly dimensions, or to assist machining operations necessary for assembly. Also, hidden lines are omitted in assembly drawings, except when needed for assembly or clarity.
An outline assembly gives a general graphic description of the exterior shape. Outline assemblies are used for parts catalogs and installation manuals or for production when the assembly is simple enough to be visualized without the use of other drawings.
A sectioned assembly gives a general graphic description of the interior shape by passing a cutting plane through all or part of the assembly. Sectioned assembly drawings are used for the manufacture and assembly of complicated devices.
SUMMARY
Working drawings are a fundamental part of any manufacturing or construction business. These drawings document the manufacturing and construction process for simple-to-complex assemblies. Typically, a set of working drawings includes dimensioned detail drawings, assembly drawings, and parts lists normally developed based on ANSI standards.
Most assemblies contain standard parts such as fasteners or mechanisms. These parts all have to be specified on the working drawings using ANSI standards. A basic knowledge of how these standard parts function in a product is critical both to its design and how it is notated on the drawings. Many industries have their own specialized drawings such as piping drawings and welding drawings. These drawings also have standardized methods of representing parts and processes on the drawings.
Traditionally, drawings have been created on paper, which must be stored, retrieved, and copied through a process called reprographics. Increasingly computers are being used to not only generate the original drawings, but also manage their storage, copying, and distribution electronically.