National Institute of Industrial Engineering

INDUSTRIAL ENGINEERING

ASSIGNMENT

ON

DESIGN OF WASHER

            

 Submitted by-

                       Shivam  Martolia(114)

                        Akash dutta(124)

DESIGN OF WASHER

DEFINITION

A washer is a thin plate (typically disk-shaped) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener, such as a screw or nut. Other uses are as a spacer, spring (belleville washer, wave washer), wear pad, preload indicating device, locking device, and to reduce vibration (rubber washer). Washers usually have an outer diameter (OD) about twice the length of their inner diameter (ID).

 TYPES OF WASHER

Washers can be categorized into three types;

·         Plain washers-which spread a load, and prevent damage to the surface being fixed, or provide some sort of insulation such as electrical.

·         Spring washers- which have axial flexibility and are used to prevent fastening loosening due to vibrations.

·         Locking washers -which prevent fastening loosening by preventing unscrewing rotation of the fastening device; locking washers are usually also spring washers. The term washer is also often used for disc shaped devices used as grommets..

We have designed a plane washer.

A plain washer (or 'flat washer') is a flat annulus or ring, often of metal, used to spread the load of a screwed fastening. Additionally a plain washer may be used when the hole is a larger diameter than the fixing nut.

                                         

MATERIALS

Common materials include steel, stainless steel, and plastic. Hardened washers are steel washers that have been heat treated. Other materials include aluminum, bronze, brass, , copper, felt, fibers, , iron, leather, rubber, silicon bronze, zinc, and titanium.

STANDARD METRIC FLAT WASHER SIZES:

INTERNAL DIA(di)	EXTERNAL DIA(do)	THICKNESS
1.1	3	.3
2.2	5	.3
3.2	7	.5
4.3	9	.8
5.3	10	1
6.4	12	1.6
7.4	14	1.6
8.4	16	1.6
10.5	20	2
13	24	2.5
15	28	2.5
17	30	3
19	34	3
21	37	3
25	44	4
31	56	4
40	72	6
43	78	7
46	85	7

PROCESSES INVOLVED

The various shearing process are:

·         Blanking: Blanking is the operation of cutting a flat shape from sheet metal .The article punched out is called the blank and is the required product of the operation. The hole and metal left behind is discarded as waste.

·         Piercing: It is a cutting operation by which various shaped holes are made in sheet metal. Punching is similar to blanking except that in piercing, the hole is the desired product, the material punched out to form the hole being the waste

·         Trimming: Trimming is done to remove the flash or unwanted excess material  from the previously formed components.

·         Shaving: This operation is done to cut the edges of the blanked part accurately and to maintain a close dimension. The shaving operation removes the uneven and rough edges of the blanked part.

 SHEARING ACTION:

The metal is brought to to the plasic stage by pressing the sheet between the two shearing blades so that fracture is initiated at the cutting points.The fractures on either side of the sheet further progressing downwards with the movement of the upper shear,finally resulting in the separation of the slug from the parent strip.

 

The material under the upper shear is subjected to both compressive and tensile stresses.In an ideal shearing operation,the upper shear pushes the metal to a depth equal to one third of its thickness. Because of pushing of the material into the lower shear, the area of the cross section of the metal between the cutting edge of the shear decreases and causes initiation of fracture.   

ANGULAR CLEARANCE:

After the final breaking ,the slug will spring back due to the release of stored elastic energy. This will make the blank cling to the face die unless the die opening is enlarged. This enlargement is referred to as angular clearance.

It depends on thickness ,material and shape of the stock used. The normal value is from .25 to .75 deg per side but occasionally a high value of 2 deg may be used.

SIMPLE  DIE AND  PUNCH

 

COMPOUND DIE AND PUNCH

              

 

CALCULATION OF CUTTING FORCE

Cutting force: It is the force which has to act on the stock material in order to cut out the blank. This determines the capacity of the press to be used for the particular tool.

Formula=(L*t* ),Where L=length of periphery to be cut in mm,

            t=thickness of sheet

         =shear stress

METAL	SOFT(Kg/mm^2)	HARD(Kg/mm^2)
Low carbon steel	22	60
Medium carbon steel	36	60
High carbon steel	40	70
Silicon	27	40
Aluminium	6	15
Aluminium alloys	8	37
Copper	17	24
Brass	15	24

Lets  select  the stock as aluminium, so the shear strength from the table is found out to be 15 kg/mm^2.

L=(∏*do+∏*di)

  =150.596mm

So F=(150.596*1*15)

       =2.258 tons

Stripping force= 20% of the cutting force

                           =(20% * 2.258) tons 

                          =.4516 Tons

The total force required to run the tool is (2.258+0.4516) Tons=2.7096 tons.

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References

·        MANUFACTURING TECHNOLOGY BY P.N. RAO

·        PRODUCTION ENGINEERING BY P.C. SHARMA