NATIONAL INSTITUTE OF
INDUSTRIAL ENGINEERING
PGDIE-42
Industrial Engineering
Assignment on Design Of Stapler:-
Presented By: -
PANKAJ KUMAR MOHLI
PGDIE 42
Roll NO. 56
GAURAV DUTTA
PGDIE 42
Roll No.32
INTRODUCTION
There are virtually as many types of staplers as there are
uses for them but we are considering the one used in the home or office. The
size of a mini stapler (as small a finger): to one requiring two hands to use.
And while there is no specific standard size of staple, the basic household (office)
type—with a wire size of .017 of an inch in diameter—are generally accepted as
typical. The average multi-use stapler operates with wire sizes averaging .050
of an inch in diameter.
Even with the potential of dozens of uses, staplers are most
frequently used in binding multi-page documents and other such related office
tasks. They are extremely inexpensive: a "typical" home or office
stapler costs less than $10.00, and a packet of 5,000 staples, less than $2.00.
RAW MATERIALS
A stapler comprises many components, most of which are metal
stampings and spring type parts. Main components
of a typical home or office stapler include the base; the anvil (the metal plate over which you put the document that you
want to staple); the magazine (which
holds the staples); the metal head
(which covers the magazine); and the
hanger (which is welded to the base and holds the pin that connects the
magazine and base). Rivets are used
to keep the parts together, and pins
are the hinge point for the top and bottom half. There are also rubber and plastic materials used both
in enhancing the product and in making the stapler cosmetically appealing. The
springs in a stapler typically perform two separate jobs: they keep the row of
staples lined up in the track and ready to be used, and they return the plunger
blade to its original up position. (The plunger blade acts as a guillotine, in
that it separates one single staple from the row of staples each time it is
forced down.)
The most recent
staplers are being made almost entirely of plastic. Currently, however, the
most popularly used staplers are still those made of metal. Thus, the following focuses solely
on the metal stapler and how it is manufactured.
The Manufacturing
Process
The parts of a stapler are formed in various ways before
coming together to form the finished item.
Forming the springs:
Two types of
springs are used in the basic stapler: the coil and the leaf. A coil spring is
made from metal that has the ability to withstand a constant pressure and
release and still maintain its shape. The
coil spring material is wound around an appropriately sized rod (similar to
winding a thin wire around a pencil) and is then heat-treated to a produce
changes in the metal's characteristics—changes that give the metal
"elasticity." The heat-treated coil spring can be pulled apart
and pressed together, within region, and still return to its original wound up
condition. A good example of a coil spring is the follow spring, which connects
the case to the follow block —the metal piece in the magazine that holds the
staples toward one end of the magazine.
Leaf springs, which resemble a diving
board, are typically made by either bending or rolling (slightly curling) a
thin piece of steel and then carefully heating it to a temperature that will
cause internal stresses. Thinly slicing a carrot lengthwise into strips and then placing them in
ice water causes the strips to curl up; this is the same effect observed when
springs are properly heat-treated. The steel maintains either a curled or flat
position and resists any bending motion applied to it. One example of a leaf
spring is the clearing spring, the part on the underside of the stapler that
allows you to unlatch the base from the upper assembly (the magazine and metal
head).
Sheet metal
parts such as the head and base are typically stamped between a punch and die,
while plastic parts can be injection molded.
Stamping of parts
Stampings
are typically made of flat sheet metal material of varying thicknesses that are
sandwiched between a punch and die. When the punch pushes on the material, it
"shears" a piece of material (the shape of the punch) out of the
sheet. A similar principle is applied when using a cookie cutter on rolled-out
dough. Stamping material can also be in the form of a coil of material that
looks something like a roll of paper towel. (The material type and thickness
depends on the configuration of the part being made). The coil allows automatic
feeding of the material across a punch and die using a coil feeder. The coil is
gradually unwound as parts are stamped out of it. This is a very cost-efficient
way of mass producing stampings because it does not require an operator to hold
the material between the punch and die. Most
of the major metal components besides springs and rivets, such as the base,
metal head, and anvil, are made in this way. The pins, stampings, and
springs are sub assembled in stages and then assembled together with the upper
and lower halves of the stapler frame. The last items to be assembled are the
feet (lanti-skid rubber pads) and the Snap-on plastic cap.
Brake forming
After a part
is stamped, it is usually then formed into a shape. If the shape is an
intricate one, another type of punch and die is used. The material may also be
heated in order to soften it, allowing the material to bend more easily. Most
stapler parts have somewhat square corners, so typically the material is bent
at 90 degree angles. There are now
machines that perform stamping and brake forming processes during the same
operation; they simultaneously punch out shapes and bend them to make the
appropriate parts. This eliminates the amount of setups and different
machines required to make all of the parts.
Rivets
A rivet is
usually made of a fairly strong steel material, but it must also have some
elasticity. A rivet is designed to hold parts in place just like a screw and
nut, except that the rivet is one piece and cannot be easily disassembled. One
end typically has a head on it (like a nail or a screw), and the other end is
usually hollow (either partially or along the whole length). Rivets are made by cutting off a piece of
bar stock and forging it to obtain the desired configuration. Forging is a
process similar to stamping, except that the starting material is almost to
size already. Forging will minimally
change the size and shape; the strength of the material, however, is
significantly increased.
Creating plastic moldings
Plastic
parts of staplers are made by injection
molding, in which a liquified plastic is injected into a die. The liquid
flows into the open void and is then cooled. As the die cools, the plastic
solidifies and takes on the shape of the die. The die is opened and the part is
removed.
Making the pin
The pin is
little more than a piece of bar stock, cut off to a certain length either with
a saw or on a machining center. Because the pins is used as a hinge point for
the top and bottom half of the stapler, it is usually made from a strong, heat-treatable metal.
Painting
As required to prevent rust, or for
cosmetic reasons, some of the components are painted. The parts are hung on
small racks, set on a conveyor and passed by a spray nozzle. Some automatic
painting operations employ electrostatic spraying, wherein the parts and paint
are electrically charged. The paint and the parts are given opposite
charges—for instance, the paint will be given a negative charge while the part
will be given a positive charge—because opposite electrical charges attract
each other. Electrostatic painting ensures that every possible space on the
part will be evenly painted. This method also eliminates wasted paint
(overspray).
Assembly
The pins,
stampings, and springs are sub assembled in stages and then assembled together
with the upper and lower halves of the stapler frame. For the bottom
subassembly, consisting of the base, hanger, anvil, and clearing spring, the
parts are placed in an assembly jig that holds them in position to allow the
rivets to be placed in the correct holes. Once the rivets are locked in place,
a tool called an orbital riveter spins the hollow end of the rivet until it
collapses outward and captures the parts together. The top half, consisting of
the magazine subassembly, the case, the follow spring, the driver-ram spring,
and the metal head, is assembled the same way in its own assembly jig.
The top and
bottom halves come together in another jig, and the pin that connects the two
is riveted into place. Finally, the finishing touches such as the feet
(anti-skid rubber pads) and the plastic cap are then snapped on.
Quality Control
Samples of all the components are
tested individually as they are manufactured. A certain percentage of parts are thoroughly checked
as they come off of the automatic machines. Critical dimensions are scrutinized
and adjustments are made to the machines or the tools are repaired/replaced as
they wear out.
Once the parts are assembled, they
are sample inspected for functionality and again a small number of units are
continuously cycled until they wear out. The component that wears out is checked for conformity to
determine whether it was normal wear or a design flaw.
An important
item determining longevity and product warranty is the use of factory
recommended staples. The use of incorrect staples is said to be attributed to
cause the majority of stapler malfunctions. It should be noted that some
stapler companies will service their staplers (for free or a nominal fee) only
if their staples, exclusively, are used in the unit.
To change the design to lower the
complexity of the baseline stapler
Simple
products are good products. So it's important to try to measure product
complexity. There are all kinds of ways to measure complexity, but almost all
of them target specific kinds of products.
What would
be really useful is a simple relationship that can give a relative measure of
the complexity of two similar things. If we had that, then we could compare
competing designs and decide which simpler (less complex) was.
Assuming a
systems perspective, everything is made up of other things that interact to
exhibit specific behaviors. Here's a simple, empirical relationship that does
the job.
C = 1/f * (NpNtNi)1/3
Where
C is the measure of complexity of the
product
f is the number of overall functions
that the product must provide (or the expected/required behaviors)
Np is the number of parts in the
product
Nt is the number of types of parts in
the product
Ni is the number of interfaces
between the parts.
The Future
Staplers,
like most other mechanisms, are continually adjusted and improved upon. As new
materials and processes are developed, many uses become incorporated into all
kinds of products, the stapler is no exception. Likewise the use for staplers
will continue to increase as one of the latest uses is in the medical field as
a substitute for stitches.
References
Books
Ewers,
William. The Staple Gun in Home and Industry. Sincere Press, 1971.
Periodicals
Capotosto,
Rosario. "Pop Goes the Stapler." Popular Mechanics. August, 1987, p.
19.
"Now, a
Stapler Can Become a Riveting Tool." Consumer Reports. February, 1987, p.
73.
McCafferty,
Phil. "Plastic Nails." Popular Science. April, 1987, p. 66.
— William L.
Ansel
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