## Chapter 6: Example DFMA Analysis Using DFA Index

### Introduction

Now that the foundation has been laid for the application of DFMA, we are ready for implementation. This chapter will present a step-by-step DFMA design analysis using a new measure called the DFA index.

Key Terms:

Manual Assembly : product assembled using human labor.

: product assembled using machines dedicated to that product.

: product assembled using reconfigurable robots.

: product assembled using mix of manual and automated methods.

### Determining Part Size

Rectangular Parts

- Find the smallest rectangle that encloses the part.
- Thickness = shortest side
- Size is the length of the longest side.

Cylindrical Part Thickness

- Cylindrical or regular polygon (5+ sides) cross-section and diameter is less than the length.
- Thickness = radius of the smallest cylinder that will enclose part.

### DFA Index Definition

The design for assembly (DFA) Index is an efficiency measure which compares the current design to the theoretically simplest design with the minimum number of parts. The DFA is expressed as a percentage (%) and as DFMA is applied the percentage should increase with 100% being the maximum value. DFA Index can be calculated using a theoretical time to handle and assemble; however, whenever possible the actual time to handle and assemble will be utilized. However, in the early design stages, we often don’t yet know these actual times. Therefore, it is critical that individuals from the assembly process be part of the DFMA team and provide input on challenges with the existing design as well as estimates of actual handling and assembly times. The use of DFMA analysis software can be very beneficial in making more accurate estimates of time and providing added the benefit of monitoring against industry best practices and standard times.

**E _{MA} = 100 x N_{MIN} × T_{A} ÷ T_{MA}**

N_{MIN} = theoretical minimum part count

T_{A} = theoretical minimum handling and assembly time for any part (2.93 seconds, often rounded to 3 seconds)

T_{MA} = Actual total handling and assembly time for the design concept

### DFMA Process

**Initial Design (Baseline) Evaluation**

- Step 1: Begin with a new concept design (or an existing product assembly) with a full bill of materials and dimensional data.
- Step 2: Determine the current total number of components
- Step 3: Determine the cost of each component
- Step 4: Determine the Total Component Part Costs
- Step 5: Determine the Steps to Assemble the product
- Step 6: Determine the Handling Time each part with consideration to product geometry, symmetry, and handling challenges.
- Step 7: Determine the Assembly time for each component with consideration to tools required, holding methods, and assembly challenges.
- Step 8: Determine the Total Handling, Assembly and the combined Handling and Assembly time.

**Evaluate Initial Design to Determine Theoretical Minimum Parts**

- Step 9: Use the DFMA Functional Analysis to Determine which parts are
**essential** - Step 10: Clearly identify (list)) these essential parts
- Step 11: Total the number of essential parts (T
_{min}) - Step 12: Calculate the DFA Index of the Initial Concept

**Explore Design Improvements (Redesign) for Manufacture and Assembly**

- Step 9: Brainstorm design changes with an emphasis on removing or minimizing the
**non-essential**parts. - Step 10: For each concept, clearly identify
**what is being changed and why**. - Step 11: Develop a new bill of materials
- Step 12: Determine the current total number of components
- Step 13: Determine the cost of each component
- Step 14: Determine the Total Component Part Costs
- Step 15: Determine the Steps to Assemble the product
- Step 16: Determine the Handling Time each part with consideration to product geometry, symmetry, and handling challenges.
- Step 17: Determine the Assembly time for each component with consideration to tools required, holding methods, and assembly challenges.
- Step 18: Determine the Total Handling, Assembly and the combined Handling and Assembly time.
- Step 19: Calculate the DFA Index of the Initial Concept using the same Tmin from step 11.

**Evaluate the potential DFMA improvement**

Step 20: For each concept, compare the new concept to the initial design in the following areas:

- DFA Index
- Number of component parts
- Total Component part costs
- Total time to Handle and Assemble
- Total Handling and Assembly Costs
- Total Cost

For more information check out the following links to additional information:

### Design Analysis

What is included in the total cost?

- Material cost for component
- Tooling costs (mold cost) = Total cost / # of units to be produced
- Setup of Machinery Costs
- Handling and assembly cost for entire assembly
- Overhead costs for facilities, support staff, etc.

DFA Software:

- Calculates handling and assembly time and costs
- DFA index
- Allows design modification to show DFA improvements.

DFM Software:

- Calculates material and tooling costs + equipment set up and overhead

Pros:

Little or no labor

Less expensive than soft automation

Cons:

Limited to single product/family

Little flexibility (improving)

High volumes

Pros:

Flexibility and repeatability

Cons:

Capital cost and changeover time

Pros:

Part presentation

Overcomes some human limitations

Cons:

Cost of labor