What is DFA when design for quality | Design for assembly

What is DFA?

DFA is defined as a process to design such that it can be assembled easily and at low cost. In DFA analysis is done on child parts and final product for any assembly problem early in the design stage. It is important as it potentially reduces the assembly cost.

Purpose of DFA?

  • To simplify the product so that cost of assembly is reduced.
  • To improve quality and reliability of the product.
  • It also reduce inventory cost and production equipment requirement.

Method of Assembly:

  1. Manual assembly: Capital cost is low. Cost per unit also low.
  2. Fixed automatic assembly: In an injection molded process as number of unit produced are more and unit cost is low.
  3. Robotic Assembly : Capital cost are more. Cost per unit is very low.

Design guidelines for manual assembly:

  • Eliminate need for operators to make decision or setting. Ensure fool proof assembly so that there is only one way whether sequence or orientation.
  • Ensure accessibility and visibility. Make everything self aligning.
  • Eliminate need for assembly tool and gauge. Make parts self locating and self orienting.
  • Number of parts should be minimum. Number of bolts and screw should be minimum.
  • Number of different parts should be minimum. Bolt and screw should be of same size.
  • Avoid part orientation during assembly.
DFA, Design for assembly

Design guidelines for automated assembly:

  • Use self aligning and self locating feature.
  • Minimise bolts / screws. Avoid if possible.
  • Use largest and heavy parts as base of assembly.
  • Use standard parts and material.
  • Use parts which can be fed automatically.
  • Design parts with low center of gravity. It makes parts more stable during assembly.
  • Reduce number of different parts.

Problems if DFA not done:

  • Every additional part is an opportunity for a defective part and assembly error.
  • Increase the total cost of assembly.
  • Make automation more difficult and more costly.
  • Cost related to purchasing, inventory increases.

Design for manufacturing (DFM) and design for assembly (DFA) should be done same time . Then it can be called design for manufacturing and assembly ( DFMA). Toyota understand the importance of Design for assembly and uses 15 – 20% less parts than other manufactures.

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