CAD Detailing Methodology

Author: Ravindra Kulkarni
Company: IT Elite Systems Pvt. Ltd.

Overview

CAD detailing standards aim at reducing the errors in drafting to a maximum level. The standards are common for all type of detailing work. Final checklist is generated depending upon the nature of detailing work. The methodology explained in this paper, improves the effectiveness of detailing.

Introduction

Detailing job involves generating 2D manufacturing drawing. This job consists of generating views from a 3D model, dimensioning with tolerances, indicating other aspects related to surface, material and processes and so on. Following a proper methodology for detailing always ensures fewer errors, and less rework; resulting into the work of required quality.

The Drafting Standards

These standards need to be followed from modeling stage as naming of the components will start at that stage itself. So adhering to drafting standards from modeling stage will reduce the rework at detailing stage. Following are the conventions in drafting standards:

• File naming and folder structure: Naming of file and its folder start at modeling stage. Normally detailing is continued in the same model file. A coding that has project code (P), assembly code (A), sub assembly code (S) and serial numbers for different type of components (C) can work as a standard e.g. PPAASSCC. ·
• Component naming: Component naming is also an activity at modeling stage and a proper standard for naming needs to be followed.
• Title block structure: This mainly consists of
  • o drawing name and drawing number
  • o sheet numbering
  • o the persons involved in drawing, checking and approving the drawing
  • o the scale of the drawing
  • o projection method (1st or 3rd angle)
  • o material, heat treatment, surface related processes
• CAD standards like
  • Definition of model viewing (scene) for detailing.
  • Layout definition (naming, projection angle, scaling etc)
  • Layer names, colors, line types and components related to it
  • Format for Text, Text style
  • Format for dimensions, dimension style
  • Format for plot styles and line weights
  • Standard template for different paper sizes like A, B, C, D or A0, A1, A2, A3, A4 etc
• GD & T: The standards related to dimensioning, geometric & dimensional tolerances and fits

The Checklist

From the above standard a Checklist needs to be prepared for individual project. The checklist should be consisting of all the points related to standard drafting and specific points to that project. The detailing checklists will be different for component detailing, GA detailing and the Material Parts List.

The checklist will maintain the names of the detailer, peer reviewer and the review manager and the review dates. Thus the ownership and responsibility of the job will be well defined. The checklist helps us:

• review the detailing
• keep track of efforts put in
• improve repetitive mistakes
• providing correct quantities in parts list
• increase overall efficiency

The Methodology

This approach consists of following stages:

1. Check the model & Prepare it for detailing as per design concept:
   The model needs to be checked for following points so that it helps in automatic parts list & ballooning generation:
   • Correct naming of the components
   • Browser/ history maintained in a proper way
   • All hardware parts inserted
   • All design review points taken care off
2. Understand the drafting standards:
   A proper understanding of drafting standards related to specific project
   • helps the detailer detail more precisely
   • helps the reviewer check the drawing in line with customer requirements and
   • reduces rework in detailing
3. Understand the manufacturing process:
   This helps you decide the way dimensioning to be done. A proper way of dimensioning will clearly identify the important dimensions to be controlled in the manufacturing.
4. Generate the 2D views as per the standards:
   Once the understanding of the job is clear, the first task is to generate automatically the 2D views as per the scale and the projection angle.
5. Dimension & add tolerances with fits:
   After generation of views, dimensioning is done. Dimensioning is done with proper dimensional & geometric tolerances as per the GD&T. understanding the design and manufacturing aspect will help dimensioning precisely.
6. Indicate the surface roughness, material, processes:
   Every component drawing will have to specify component's material, roughness for critical surfaces and surface coating or heat treatment.
7. Add ballooning and Part list along with GA drawing:
   The proper browser/ history maintenance will provide automatic ballooning and parts generation. This will reduce the manual error and be accurate to 100%.
8. Peer check and correction:
   This is the first level check which takes care of minute details of detailing. Most of the errors get fixed in this checking itself.
9. Managerial check and approval:
   This is the second level verification. This aims at completeness of the drawing from design, drafting and manufacturing point of view. A drawing passing this stage is ready to be issued to the shop floor. More than 20% errors at this stage will need the detailer and the peer checker to be re-educated on the methodology once again.

We believe that a drawing through these 9 stages is ready for the final 10th stage- "Issue to Shop Floor".

Conclusion

The time allocated to checking the model & preparing it for detailing as per design concept increases the effectiveness as errors and re-work due to errors are minimized. The automatic generation of Material Parts List is another outcome of checking the model. This gives us correct parts list and saves us possible losses in material and time.

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