ISE 311Forging Lab

in conjunction with

Sections 3.1.2 (ch. 3), 19.3 & 19.4 (ch. 19) from the text book

“Fundamentals of Modern Manufacturing”Third Edition

Mikell P. Groover3/25/2008

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Outline

• Introduction• Forging – Basic Principles• Forging – Terminology• Objectives of the forging lab• Forging – materials and equipment• Forging examples – simulations• Summary

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Introduction

Upsetting or Upset Forging is the simplest case of open-die forging involving compression of a workpiece between two flat dies. Upset forging reduces the height of the workpiece but increases its cross-sectional area. We will consider upsetting of a round billet.

Under ideal conditions where there is no friction between the work piece and the dies, the billet deforms homogeneously (the cylindrical shape of the billet remains cylindrical throughout the process). But in practical conditions the billet tends to barrel since there is some friction.

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Introduction

The ring compression test is used to evaluate lubrication in forging by measuring forces and dimensional changes in the specimen.

In this test, a flat ring is deformed (upset) between two flat platens. As the height of the ring is reduced, its outside diameter increases.

If there were no friction between the dies and workpiece both the inner and outer diameters of the ring would expand. However, for large friction at material/ die interface, the internal diameter of the ring is reduced with increasing deformation.

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IntroductionHomogeneous upsetting of a cylindrical billet (without friction)

Practical upsetting of a cylindrical billet (with friction & barreling)

Figure 19.10, Groover

V1 = upper die velocity

Do, D, D1 = average billet diameters before, during and at the end of deformation

Figure 19.11, Groover

ho, h, h1 = billet heights before, during and at the end of deformation

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Introduction

Upsetting of a ring with good lubrication (μ is low) and bad lubrication (μ is high)

Figure 32.2, Kalpakjian

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Terminology

In homogeneous upsetting / no friction:

ho = starting height of workpiece (before deformation)

h = instantaneous height of the work piece (at an intermediate press stroke)

F = instantaneous upsetting force

A = instantaneous cross sectional area of the workpiece

h

hStrainTrue oln,

A

FStressTrue

(1)

(2)

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Terminology

In homogeneous upsetting:

K = strength coefficient, n = strain hardening coefficient

F increases with deformation (press stroke) since Yf and A both increase with deformation and strain (Eqs. (1), (3) & (4))

AYFForceUpsetting f

nf KstressflowY

(3)

(4)

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Terminology

Practical Upsetting of a cylindrical workpiece (with friction & barreling):

Where = coefficient of friction (0.05 – 0.3)

D = instantaneous workpiece diameter, mm (in),

h = instantaneous workpiece height, mm (in)

AYKF ff (5)

h

DKFactorShapeForging f

4.01 (6)

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The Ring Compression Test

The chart seen to the right gives the calibration curves for a specific ring geometry (OD:ID:Height = 6:3:2) and for different coefficients of friction, μ.

In this chart, the variation of the % change in internal diameter is given for % reduction in height of the compressed ring.

After the ring compression test is completed, the ID and height of the upset ring are measured and the % reduction of each is found. From the location of this experimental point on the chart, μ can be estimated.

Cold, warm and hot forging

The forging operation (and metal forming operations in

general) can be performed at various temperatures

ranges:

Where Tm is the melting temperature of the metal

Note: for most metals, recrystallization occurs between 30% and 50% of

The melting temperature

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Cold forging T < 0.3 Tm

Warm forging 0.3 Tm < T < 0.5 Tm

Hot forging T > 0.5 Tm and usually less than 0.75 Tm

Cold, warm and hot forging

Cold forging vs. Hot forging:

You have to think about the reasons behind each of the

above mentioned points12

Cold Hot

Strength/ hardness of the forged billet Higher Lower

Ductility/ ability to produce intricate shapes Lower Higher

Force/ energy/ machine capacity required Higher Lower

Load on the tools (dies) Higher Lower

Tool wear Less More

Dimensional accuracy Better Worse

Surface finish Better Worse

The need for heating equipment No Yes

Barreling (uniformity of deformation) Less More

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Objectives

This lab has the following objectives:• Understand fundamentals of the forging process• Observe the effects of frictional forces in forging

process• Compare material properties of forged parts with

respect to working temperature

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Objectives

Students will be able to:• Perform an upsetting test on specimens of two

different materials (steel and aluminum)• Use proper equipment terminology, and know the

parameters to control during the test• Measure and collect the force and height data and

observe the barreling effects• Compare the forces measured in the laboratory tests

with the calculated forces with and without friction effect

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Upsetting And Hot Forging

• Test Materials and Equipment– OBI (Open Back Inclinable) mechanical press with the LoadGard

system to measure the upsetting force– Upset tooling, tongs, acetylene torch– Specimens: (1) Aluminum, (2) Steel– Dial Calipers

• Safety Equipment and Instructions– Safety glasses with side shields are required during the entire lab period– Pay attention and follow the lab instructor’s directions– Do not use your hand to put or remove specimens on the die. Instead,

use the supplied tongs– Turn off the OBI press when ever you need to adjust the press slide

setting (shut height etc.)– Do not touch the forged specimens with your bare hands until they cool

down to room temperature

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Mechanical Presses Used in Forging

The drive system used in most mechanical presses is based on a slider-crank mechanism that translates rotary motion into reciprocating motion.

Shut height adjustment modifies the length of the connecting rod and changes the bottom position of the slide

Ram or Slide

Frame

Connecting Rod

Flywheel

Eccentric Shaft

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Slider-crank Mechanism

BDC = Bottom Dead Center Bottom position of the

slideTDC = Top Dead Center Top position of the slide

• The length of connecting rod determines the TDC and BDC or shut height. Its length can be modified.

• The total slide stroke S = 2r is unchanged

TDC

BDC Connecting Rod

Shut Height Adjustment

Force

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OBI press used for forging tests

Flywheel

Load reading system

Shut height adjustment

Power box to start and stop the press

Yellow pedal to cycle the press

Connecting rod

Press slide

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ForgingShims and shut height adjustment:

Screw for shut height adjustment

Handle to adjust the stroke

One of the 5 Shims

Slot to place handle and rotate slide screw

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The Loadgard and the power box of the press

Load Reading

Reset Button

Start Button

Stop Button

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Hardness testing machine

Hardness Reading

Indenter

Handle to load the specimen

Plate on which to place the specimen

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Forging

Test Specimen before deformation:• The upsetting can be

conducted with either a round bar or ring specimen.

• The round bar specimen is used for the current test.

• The specimen is placed on the lower die and deformation is applied using the motion of the top die.

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ForgingDial Calipers to measure the dimensions of the test specimen:

• The height of the specimen during testing is measured using dial calipers.

• As the specimen is compressed using 5 different slide positions, the dial calipers are used to measure the dimensions of the specimen after each stroke.

Specimen

Dial Calipers

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Simple Upsetting – Test Procedure

1. Obtain one steel billet and one aluminum billet from the lab instructor

2. Measure and record the initial dimensions of the billets (OD & height); OD is the outer diameter

3. Measure the hardness for the steel billet in three different locations.

4. Set the OBI press for the first step/shut height in the upsetting process (shim 1)

5. Using tongs, insert one of the billets into the tooling. Try to place it as close to the center of the upsetting platen as possible

6. Step on the yellow pedal to cycle the press one time

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7. Record the press load from the Loadgard system. (note: after recording the load, make sure to reset the Loadgard system in order to prevent false reading for the next measurement)

8. Use the tongs to remove the deformed billet9. Measure and record its new height10. Repeat steps 4-9 for each of the other billets11. Adjust the press for the next deformation (shims 2 through 5)

Repeat steps 4-9 for a total of 5 deformation steps. (caution: the flywheel on the punch press must stop, which means the OBI press must be turned off, before changing shut height)

12. Measure the hardness for the steel billet in three different locations

13. Mark the steel billet such that it can be identified as the cold forging sample and keep it for comparison with the hot forging sample

Simple Upsetting – Test Procedure

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Ring Compression – Test Procedure

1. Obtain one steel ring and one aluminum ring from the lab instructor

2. Measure and record the initial dimensions of the billets (OD: Outer Diameter, ID: Internal Diameter, & height)

3. Set the OBI press for the first step/shut height in the upsetting process (shim 1)

4. Place the specimen on the height block and place the block with the specimen on it as close as possible to the center of the upsetting platen

5. Step on the yellow pedal to cycle the press one time

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Ring Compression – Test Procedure

6. Set the OBI press for the second step/shut height in the ring compression test (shim 2)

7. Repeat steps 4 & 5 for the yellow shim

8. Measure and record all dimensions of the specimen (OD, ID, and height)

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Hot Forging – Test Procedure

1. Obtain one steel billet from the lab instructor

2. You will assume that the initial and final dimensions are the same as for sample 2 in part 1 (cold forging).

3. Measure the hardness for the steel billet in three different locations.

4. Set the OBI press for the final step/shut height in the upsetting process (shim 5)

5. Using the acetylene torch, heat the specimen until it is glowing red

6. Using tongs, insert the hot billet into the tooling placing it as close as possible to the center of the upsetting platen

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Hot Forging – Test Procedure

7. Step on the yellow pedal to cycle the press one time

8. Measure the load and the hardness (at 3 locations)

Note1: the specimen should be allowed to cool slowly (should not be quenched)

as this may affect the hardness.

Note2: The function of the flywheel in a mechanical press is to store kinetic

energy. This energy is used to form the workpiece. If the height reduction

reached in a single stage is very large, the energy required, which is taken from

the flywheel, may be large enough to slow down the flywheel very rapidly. To

avoid this, deformation is done in stages and enough time between these stages

is provided for the motor to build up the flywheel rotational speed to its idle

speed.

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Summary – Forging Lab

Specimen before and after the compression:

Original Specimen

Barreled Specimen after compression

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Summary – Forging Lab

4

2hDvolumebilletV o

Specimen before and after the compression:

Do D1 (avg)

h1

ho

h

VD

4.

1

D1 (average) can be calculated from volume constancy, i.e.,

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Summary – Forging Lab

Comparison of cold and hot forging:

Original steel specimen Steel specimenafter hot forging

Steel specimen after cold forging

(5 steps/hits)

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Summary – Forging Lab

Comparison of original ring specimens to deformed rings:

Original steelspecimen

Steel specimen after cold forging

(2 steps/hits)

Original aluminumspecimen

Aluminum specimen after cold forging

(2 steps/hits)

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Finite Element (FE) Simulations

The next several slides illustrate the simulation of the cylinder, ring, and hot cylinder compression tests, generated by FEA.

The following slides include:

- Cold upsetting of Al 1100 cylinders (σ = 25.2 ε0.304 Ksi)

- Comparison of Al 1100 and Steel AISI 1010 (σ = 103.8 ε0.22

Ksi) upsetting with respect to forging load

- Illustration of the effect of μ on the internal diameter in ring

compression test of Steel AISI 1010

- Comparison between the upsetting of Steel AISI 1015 at room

temperature (68 oF: σ=117.5 ε0.15 Ksi) and at elevated temperature

(1112 oF: σ=54.7 ε0.072 Ksi)

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Simple upsetting simulation

Cold upsetting of Aluminum 1100 σ = 25.2 ε0.304 Ksi

μ = 0.12

Stage A Stage B Stage C

Note the barreling

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Simple upsetting simulation

Load-Stroke curves for Al 1100 (previous simulation) and Steel

AISI 1010 σAl = 25.2 ε0.304 Ksi

σsteel = 103.8 ε0.22 Ksi

μ = 0.12

Note how material properties affect the upsetting force

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Ring compression simulation

Ring compression of Steel AISI 1010 (σ = 103.8 ε 0.22 Ksi) with two

different Friction coefficients: note how increasing μ reduces the final internal

diameter. This idea will be used in the lab to determine μ

Before

After (μ = 0.12)

After (μ = 0.3)

Note the change in internal diameter

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Hot vs. Cold upsetting

A comparison between cold and hot upsetting of steel: note the following:

1- The load in cold forging > hot forging

2- Barreling in cold forging < hot forging

Cold

Hot

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Summary – Upsetting Lab

This lab preparation material introduced:• The basic principles of the forging (upsetting, ring

compression, and hot upsetting) and the terminology used (stress, strain, barreling, forging shape factor)

• The objectives of and the expected outcomes from the evaluation of test results.

• The testing equipment and the test procedure• FE simulations