Boothroyd & Dewhurst’s DFA Analysis B&D offer eight rules or guidelines which are important during design for manual assembly (listed in decreasing order of importance): 1. Reduce part count and part types 2. Strive to eliminate adjustments 3. Design parts to be self-aligning and self-locating 4. Ensure adequate access and unrestricted vision 5. Ensure the ease of handling parts from bulk 6. Minimize the need for re-orientations during assembly 7. Design parts that cannot be installed incorrectly 8. Maximize part symmetry if possible or make parts obviously asymmetrical

Boothroyd & Dewhurst’s DFA Analysis (cont.) Step 1: Obtain information about the product or assembly from drawings, prototypes, or an existing product Step 2: Take the product or assembly apart and assign an identification number to each item as it is removed Step 3: Begin to reassemble the product beginning with the highest identification number and add the remaining parts one-by-one Complete one row of the DFA worksheet for each part Never assume that parts are grasped one in each hand and then assembled together before placing them in a partially-completed assembly Step 4: Complete DFA worksheet, computing total manual assembly time, cost, and design efficiency

DFA Worksheet Obtained from B&D Manual Handling Worksheet Obtained from B&D Manual Insertion Worksheet Design Efficiency EM = (3 x NM)/TM

Estimating Theoretical Minimum Number of Parts First Part; Theoretical # of parts = 1 Add a part Is there a need for significant movement between parts? Keep the two parts separate Yes Is there a need for interfacing parts to be isolated? No Yes Would assembly or disassembly of the product be prevented by combining two parts? No Yes Combine the two parts No Add zero to the minimum theoretical number of parts Add one to the minimum theoretical number of parts Add next part

Assumptions for BDI DFMA Parts are provided in bulk and randomly oriented in a bin. Parts are handled and inserted one at a time. Products weigh a few grams to a few tens of kilograms and are electro-mechanical in nature. Assembly sequence is optimized for one operator. 5

Assembly Time Estimate by Boothroyd/Dewhurst DFMA Estimate assembly time: Time to assemble a part: Time to handle a part Time to insert a part Time to assemble all parts, one at a time 5

BDI DFMA: Assembly Time Time to handle a part: Pick a part, orient & get ready to insert it 1.13 ~10 seconds depending on: Symmetry; Primary(-) & secondary(-) Size: Thickness, dimension, weight, … Handling ease: Tool, flexible, tangling, ... 5

BDI DFMA: Part Symmetry Primary (a-) symmetry: Rotational symmetry perpendicular to the axis of insertion a = 180o a = 360o 5

BDI DFMA: Part Symmetry Secondary (b-) symmetry: Rotational symmetry about the axis of insertion b = 0o b = 360o 5

? DFA Worksheet Part Orientation 3600 1800  asymmetry: rotational symmetry about an axis perpendicular to the axis of insertion  3600 1800 ? = =

DFA Worksheet Part Orientation  = ?  = 00  = 1800  symmetry: rotational symmetry about its axis of insertion  = ?  = 00  = 1800

BDI DFMA: Part Symmetry 5

BDI DFMA: Part Size 5

BDI DFMA: Assembly Time Time to insert a part: Time to insert and secure a part 1.5 ~ 12 seconds depending on: Ease of access: Visual & hand access Ease of positioning: Hold-down, alignment, insertion force, .. Securing requirement: Screw, snap, bending, soldering, …. Time to assemble all parts, one at a time 5

BDI DFMA: Assembly Time Time to insert a part Two-digit insertion codes for piston: _ _ _ _ 5

BDI DFMA: Assembly Time Time to insert a part Two-digit insertion codes for washer: _ _ _ _ 5

BDI DFMA: Assembly Time Handling Time 5

BDI DFMA: Assembly Time Insertion Time 5

BDI DFMA: Assembly Time Total Assembly Time 5

Pneumatic Pump Exercise with Boothroyd/Dewhurst DFMA 2

BDI DFMA: Pneumatic Pump Assembly Sequence: 6. Two screws 5. One cover 4. One spring 3. One piston stop 2. One piston 1. One main body Tool: A screw driver 5

BDI DFMA: Pneumatic Pump Assembly Time: 5

BDI DFMA: Pneumatic Pump Assembly Time: 5

BDI DFMA: Pneumatic Pump Assembly Time: 5

BDI DFMA: Pneumatic Pump Assembly Time: 5

BDI DFMA: Pneumatic Pump Assembly Time: 5

BDI DFMA: Pneumatic Pump Assembly Time: 5

BDI DFMA: Pneumatic Pump Assembly Time: 5

Part Reduction Method by Boothroyd/Dewhurst DFMA 2

BDI DFMA: Part Reduction Estimate assembly time: Identify critical parts & candidates for elimination/combination. Let’s assume a product consists of a number of parts: Are they all critical part? What if a part is missing or broken? What if two parts are replaced by a larger or different part Determine design efficiency 5

BDI DFMA: Part Reduction When ready to assemble a part, should this part: Move relative to all already assembled parts? Be made of different material from all already assembled parts? Be a separate part from all already assembled parts for assembly and disassembly? If any answer is a “yes”, this part is a critical part and may not be eliminated or combined! 5

BDI DFMA: Why Reduce Parts? A non-existing part never: Causes a quality problem Adds the cost Creates an inventory problem Requires design changes Creates a shortage problem Has a lead time 5

BDI DFMA: Pneumatic Pump Assembly Sequence: 6. Two screws 5. One cover 4. One spring 3. One piston stop 2. One piston 1. One main body 5

BDI DFMA: Pneumatic Pump Part Reduction: 5

BDI DFMA: Pneumatic Pump Part Reduction: 5

BDI DFMA: Pneumatic Pump Part Reduction: 5

BDI DFMA: Pneumatic Pump Part Reduction: 5

BDI DFMA: Pneumatic Pump Part Reduction: Yes 5

BDI DFMA: Pneumatic Pump Part Reduction: Yes 5

DFA of Pneumatic Pump According to the piston stop, the cover is a candidate for elimination or combination: Can the cover be eliminated? Can the cover be combined? If so with what? Fasteners are automatic candidates of elimination: How can the fasteners be eliminated? 5

Part Reduction Is the Key for Design Improvement Eliminating one part reduces at least 3 seconds. In addition a non-existing part is the best since it never: Requires purchasing and warehouse Needs inspection Causes a quality problem Needs design changes and drawing Be in shortage 5

DFA of Pneumatic Pump According to the piston stop, the cover is a candidate for elimination or combination: Can the cover be eliminated? No! Can the cover be combined? Yes! Combine with piston! Fasteners are automatic candidates of elimination: How can the fasteners be eliminated? Yes! Press-fit the cover! 5

New Design of Pneumatic Pump

BDI DFMA: Design Efficiency The pneumatic pump: Has 7 parts & needs 40.75 seconds to assemble Has 4 critical parts & 3 non-critical parts If the product is designed perfectly: Pump would consists of only four parts Each part would take 3 seconds to assemble Total assembly time would be 12 seconds Design efficiency from assembly view points is: Design Efficiency = 12/40.75 = 29% 5

BDI DFMA: Pneumatic Pump Assembly Time: What should we do to reduce handling time of the cover and insertion times of the cover and screws? 5

BDI DFMA Assembly Time 1.13 ~10 seconds to handle a part depending on: Symmetry; Primary(-) & secondary(-) Size: Thickness, dimension, weight, … Handling ease: Tool, flexible, tangling, … To reduce part handling time: More part symmetry: a- & b-symmetry Right part size : Thickness, dimension, … No flexible, tangling parts 5

To Reduce Handling Time Increase symmetry by introducing redundancy: a - symmetry from 360o to 180o Closed-end springs do not tangle 5

BDI DFMA Assembly Time 1.5 ~ 12 seconds to insert a part depending on: Visual & hand access Hold-down, alignment, insertion force, Securing: Screw, snap, bending, soldering, .. To reduce part insertion time: Easy visual & hand access No hold-down, easy alignment, low/no insertion force, .. Easy/No securing requirement: Snaps instead of screw, bending, soldering, …. 5

To Reduce Insertion Time The long shaft makes piston alignment easy The washer seat eliminates needs of holding 5

New Design of Pneumatic Pump Piston & piston stop are combined Cover is press-fitted 5

New Design of Pneumatic Pump BDI DFMA Assembly Time Analysis: 5

New Design of Pneumatic Pump BDI DFMA Assembly Time Analysis: Design comparison: 5

Design Guidelines for Assembly How to design a product for ease of assembly? Reduce the number of part Design each part for ease of handling Design each part for ease of insertion Examine trade-offs, other cost and other X’s 5

Design Guidelines for Assembly Reduce the number of part: Eliminate unnecessary parts Combine parts Reduce the different kinds of parts Reduce/eliminate fasteners 5

Design Guidelines for Assembly Design each part for ease of handling: Increase part symmetry but avoid near symmetric parts Avoid tangling, nesting and sticky parts Reduce/eliminate fasteners Avoid custom-designed parts & use standard parts Reduce part variability. If not possible, make difference pronounced 5

Design Guidelines for Assembly Design each part for ease of insertion: Design for top-down layered assembly Enhance self-locating & alignment capability Provide in-process verification process Design the base part for transportation & orientation & the last part to lock the assembly Avoid turnover & processing during assembly Design for one-hand assembly Design fixtures together with products 5

Design Guidelines for Assembly Examine trade-offs, other cost and other X’s: To hold a wash or provide a washer seat? Several standard parts or a single custom part? Different material? Different joining method? What about: Service & repair Packing and shipping Recycle ... Assembly is only one of many cost factors! 5