Module-II of PDPT

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2.3 UPSET FORGING DIE DESIGN

In upset forgings, as a rule, no reduction in cross section occurs and, therefore, the stock to be chosen is of

the smallest area of cross section of the component. Also, very small or negligible flash is provided in upset

forgings. Depending on the shape of the upsetting to be done, the number of passes or blows in the die are

to be designed. The amount of upsetting to be done in a single stage is limited. To arrive at the safe amount

of upsetting in a given pass, the following three rules are to be satisfied to achieve defect free upset

forgings.

Rule No.1:

The maximum length of the unsupported stock that can be gathered or upset in a single pass is not

more than three times the stock diameter. Beyond this length, the material is likely to buckle under the axial

upset.

Figure 2.3.1: Application of rule one for proper upsetting

Rule No.2:

If the stock longer than three times the diameter is to be upset in a single blow, then the following

conditions should be complied. The die cavity should not be wider than 1.5 times the stock diameter and

free length of the stock outside the die should be less than half the stock diameter. When these conditions

are not complied, the stock would bend.

Figure 2.3.2: Application of rule two for proper upsetting

Module-II of PDPT

Lecture Notes of Chinmay Das

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Rule No.3:

For upsetting the stock which is longer than three times the diameter and free length of stock

outside the die is up to 2.5 times the diameter, the following conditions should be satisfied. The metal is to

be confined into a conical cavity made in the punch with the mouth diameter not exceeding 1.5 times the

stock diameter and the bottom size being 1.25 times the stock diameter. Also, it is necessary that the

heading tool recess be not less than two thirds the length of the working stock or not less than working

stock minus 2.5 times the stock diameter.

Figure 2.3.3: Application of rule three for proper upsetting

The above are the absolute limits for proper upsetting. But in practice it may be possible to cross these

absolute limits.

Location of Cavities

The upset cavities may entirely be kept in the gripper dies or in the heading tool or part in the

gripper and part in the heading tool. The choice of

location mainly depends on the severity of the

upsetting and the convenient location of flash for

trimming. Simple forgings requiring smaller upsetting

may contain the complete die cavity in the heading

tool. Also complex shapes requiring severe upsetting

are obtained with the die cavity completely in the

gripper die.

For very simple shapes, one pass may be enough to

obtain the final shape, but majority of forgings require

three or more passes. If trimming of flash is included,

then an additional pass is required. All these passes are

arranged on the die block in an order and the stock is

moved from one pass to the other sequentially. While

designing the heading tool or the punch to slide into the

gripper die, it is necessary to provide clearance

between the two such that no seizure takes place due to

uneven expansion or due to scales of the punch and die.

Figure 2.3.4: Location of cavities

This clearance should be of the order of 0.125 to 0.200 mm. The length of gripping portion of the gripper

die should be maintained between 3 and 4 times the stock diameter.

Module-II of PDPT

Lecture Notes of Chinmay Das

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Figure 2.3.5: Gripper die section

Stock size, mm R, mm A, mm C, mm

10 5 0.05 0.40

16 8 0.06 0.40

20 10 0.08 0.40

22 11 0.09 0.40

25 12.5 0.10 0.40

32 16 0.13 0.80

40 20 0.15 0.80

45 22.5 0.17 0.80

50 25 0.18 0.80

65 32.5 0.19 1.20

75 37.5 0.20 1.20

Table –I: Gripper die dimension

Figure 2.3.6: Upset forging products

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Reference: 1. Manufacturing Technology by P.N.Rao, TMH , page 272 -275

2. Dies, Moulds and Jigs by V. Vladimirov, MIR Publishers, page 301-304

3. Manufacturing Engineering and Technology by Kalpakjian and Schmid, Pearson Education, page

353-355

Review Questions 1. Why lower taper angles are provided in upset forging dies?

2. In which case cavities are made in header tool of upsetting die?

3. The steel bolt is manufactured by which process and how?

4. Why negligible or no flash is provided in upset forging die?

5. Write various materials used for manufacture of forging die.

6. How is stock requirements determined in the case of upset forging?

7. What is the basis for the design of upset forging dies? State various rules.

8. What methods are available to a die designer when the stock length is too long compared to its

diameter while upsetting?

9. What are the advantages and limitations of upset forging?

10. Why cold shuts are not observable in upset forging process?