Product Design for Manual Assembly

83

MANUAL HANDLING-ESTIMATED TIMES (s)

Parts are easy to grasp and manipulate Parts present handling difficulties (1)

Thickness >2 mm Thickness ≤2 mm Thickness >2 mm Thickness ≤2 mm

Key: 6 mm ≤ 6 mm ≤
Size Size Size Size Size Size Size Size
size size
>15 mm <6 mm >6 mm ≤6 mm >15 mm <6 mm >6 mm ≤6 mm
One hand >15 mm ≤15 mm
0 1 2 3 4 5 6 7 8 9

0 1.13 1.43 1.88 1.69 2.18 1.84 2.17 2.65 2.45 2.98
(α+β) < 360°
without the aid of grasping tools

1 1.5 1.8 2.25 2.06 2.55 2.25 2.57 3.06 3 3.38

360° ≤ (α+β)
< 540°
manipulated by one hand
Parts can be grasped and

2 1.8 2.1 2.55 2.36 2.85 2.57 2.9 3.38 3.18 3.7

540° ≤ (α+β) 3 1.95 2.25 2.7 2.51 3 2.73 3.06 3.55 3.34 4
< 720°

Parts need tweezers for grasping and manipulation

Parts can be manipulated without Parts require optical magnification

Parts need standard

(α+β) = 720°

Parts need special

and manipulation
optical magnification

tools for grasping

for manipulation

tools other than

Parts are easy to Parts present Parts are easy to Parts present
One hand grasp and handling grasp and handling
manipulate difficulties (1) manipulate difficulties (1)

tweezers
with
grasping aids
Thickness Thickness Thickness Thickness Thickness Thickness Thickness Thickness
>0.25 mm ≤0.25 mm >0.25 mm ≤0.25 mm >0.25 mm ≤0.25 mm >0.25 mm ≤0.25 mm
0≤β
0 1 2 3 4 5 6 7 8 9
≤ 180°
α ≤ 180°
manipulated by one hand but only

4 3.6 6.85 4.35 7.6 5.6 8.35 6.35 8.6 7 7

with the use of grasping tools

β = 360°
6
Parts can be grasped and

5 4 7.25 4.75 8 8.75 6.75 9 8 8

α≤β 6 4.8 8.05 5.55 8.8 6.8 9.55 7.55 9.8 8 9

≤ 180°
α = 360°

7 5.1 8.35 5.85 9.1 7.1 9.55 7.85 10.1 9 10

β = 360°
Parts present no additional Parts present additional handling difficulties
handling difficulties (e.g. sticky, delicate, slippery, etc.) (1)
α ≤ 180° α = 360° α ≤ 180° α = 360°
6 mm ≤ 6 mm ≤
Size Size Size Size Size Size Size Size
Two hands size size
>15 mm <6 mm >6 mm ≤6 mm >15 mm <6 mm >6 mm ≤6 mm
for ≤15 mm ≤15 mm
manipulation 0 1 2 3 4 5 6 7 8 9

Parts severely nest or 8 4.1 4.5 5.1 5.6 6.75 5 5.25 5.85 6.35 7
tangle or are flexible but
can be grasped and lifted
by one hand (with the
Two persons or mechanical

use of grasping tools if

Parts can be handled by one person without mechanical assistance
necessary) (2) Parts do not severely nest or tangle and are not flexible
assistance required for
Parts severely nest or

parts manipulation

Part weight < 10 lb Parts are heavy (>10 lb)

Two hands Parts are easy to Parts present Parts are easy to Parts present
tangle or are

or assistance grasp and other handling grasp and other handling

flexible (2)

required for manipulate difficulties (1) manipulate difficulties (1)

large size
α ≤ 180° α = 360° α ≤ 180° α = 360° α ≤ 180° α = 360° α ≤ 180° α = 360°
Two hands, two persons
or mechanical assistance 0 1 2 3 4 5 6 7 8 9
required for grasping
and transporting parts 9 2 3 2 3 3 4 4 5 7 9

Notes:
1. Parts can present handling difficulties if they nest or tangle, sick together because of magnetic force or grease coating, and so on, are slippery, or
require careful handling. Parts that nest or tangle are those that interlock when in bulk but can be separated by one simple manipulation of a single
part; for example, taper cups, closed-end helical springs, circlips, and so on. Parts that are slippery are those that easily slip from fingers or
standard grasping tool because of their shape and/or surface condition. Parts that require careful handling are those that are fragile or delicate,
have sharp corners or edges, or present other hazards to the operator.
2. Parts that nest or tangle severely are those parts that interlock when in bulk and both hands are needed to apply a separation force or achieve
specific orientation of inter-locking parts to achieve separation. Flexible parts are those that substantially deform during manipulation and
necessitate the use of two hands. Examples of such parts are large paper or felt gaskets, rubber bands or belts, and so on.

Figure 3.15
Original classification system for part features affecting manual handling time. (Copyright 1999 Boothroyd
Dewhurst, Inc. With permission.)
84 Product Design for Manufacture and Assembly

MANUAL INSERTION-ESTIMATED TIMES (s)

Alter assembly no holding down required Holding down required during subsequent
to maintain orientation and processes to maintain orientation
location (3) at location (3)

Easy to align and Not easy to align or Easy to align and Not easy to align or
position during position during position during position during
assembly (4) assembly assembly (4) assembly

No No No No
resistance Resistance resistance Resistance resistance Resistance resistance Resistance
Key:
to to to to to to to to
Part added
insertion insertion (5) insertion insertion (5) insertion insertion (5) insertion insertion (5)
but
not secured
0 1 2 3 6 7 8 9

Part and associated

0 1.5 2.5 2.5 3.5 5.5 6.5 6.5 7.5
tool (including
hands) can easily
reach the desired 1 4 5 5 6 8 9 9 10
location
Addition of any part (1) where neither
the part itself not any other part is

Due to 2 5.5 6.5 6.5 7.5 9.5 10.5 10.5 11.5

(including hands) cannot easily

obstructed
access or
finally secured immediately

reach the desired location

restricted
Part and associated tool

vision (2)
No screwing operation
or plastic Plastic deformation immediately after insertion
Due to
deformation Screw tightening
obstructed Plastic bending Riveting or similar immediately
immediately after
access and or torsion operation after insertion
insertion (snap/press
restricted
fits,circlips,spire
vision (2) Not easy to align or Not easy to align or
nuts,etc.)
position during position during

torsional resistance (4)

torsional resistance (5)

position during asse-

tance to insertion (5)

assembly assembly
Not easy to align or

Not easy to align or

mbly and/or resis-
Easy to align and

Easy to align and

Easy to align and

Easy to align and

position with no

position with no
Part secured

position and/or
position during

position during
immediately
No resistance

No resistance
Resistance to

Resistance to
resistance to

assembly (4)

assembly (4)
insertion (4)

insertion (5)

insertion (5)
to insertion

to insertion
Part and associated tool
(including hands) can
easily reach the desired
location and the tool 0 1 2 3 4 5 6 7 8 9
can be operated easily
Addition of any part (1) where the

being finally secured immediately

part itself and/or other parts are

3 2 5 4 5 6 7 8 9 6 8
(including hands) cannot easily

Due to
reach desired location or tool

obstructed
cannot be operated easily

accessor 4 4.5 7.5 6.5 7.5 8.5 9.5 10.5 11.5 8.5 10.5
Part and associated tool

restricted
vision (2)
5 6 9 8 9 10 11 12 13 10 12
Due to
obstructed
access and
restricted Mechanical fastening processes Non-mechanical fastening processes Non-fastening
vision (2) (part(s) already in place but not (part(s) already in place but not processes
secured immediately after insertion) secured immediately after insertion)
None or localized Metallurgical processes
plastic deformation
deformed during fastening)

adjustment of part(s). etc.)

(e.g. liquid insertion, etc.)

(e.g. orienting, fittings or
Bulk plastic deformation

Additional
(e.g. adhesive bonding,

Manipulation of parts
friction welding, etc.)

material required
(large proportion of

Chemical processes
or other processes

material required
similar processes

Screw tightening

part is plastically

or sub-assembly

Other processes
(e.g. resistance,
similar process

No additional

Separate
Weld/braze
Bending or

Riveting or

Soldering
processes

processes

operation
etc.)

Assembly processes
0 1 2 3 4 5 6 7 8 8
where all solid
parts are in place
9 4 7 5 12 7 8 12 12 9 12

Notes:
1. A part is the solid of nonsolid element of an assembly during an assembly process. A subassembly is considered a part if it is added during
assembly. However, adhesives, fluxes, fillers, and so on, used for joining parts are not considered to be parts.
2. Obstructed access means that the space available for the assembly operation causes a significant increase in the assembly time. Restricted vision
means that the operator has to rely mainly on tactile sensing during the assembly process.
3. Holding down required means that the part is unstable after placement or insertion or during subsequent operations and will require griping,
realignment, or holding down before it is finally secured. Holding down refers to an operation that, if necessary, maintains the position and
orientation of a part already in place, prior to, or during the next assembly operation. A part is located if it will not require holding down or
realignment for subsequent operations and is only partially secured.
4. A part is easy to align and position if the position of the part is established by locating features on the part or on its mating part and insertion is
facilitated by well designed chamfers or similar features.
5. The resistance encountered during part insertion can be due to small clearances, jamming or wedging, hang-up conditions, or insertion against a
large force. For example, a press fit is an interference fit where a large force is required for assembly. The resistance encountered with self-tapping
screws is similarly an example of insertion resistance.

Figure 3.16
Original classification system for part features affecting insertion and fastening. (Copyright 1999 Boothroyd
Dewhurst, Inc. With permission.)