GIÁO TRÌNH KHAI THÁC PHẦN mềm TRONG GIA CÔNG KHUÔN mẫu chapter IX bulk forming processes

Chapter IX: Bulk Forming Forging 1Content: Forging • Introduction • Examples of Application • Overview to Basic Forging Processes • Open-Die Forging • Forging Machine Tools • Closed-Die

Trang 1

Chapter IX: Bulk Forming (Forging) 1

Content:

Forging

• Introduction

• Examples of Application

• Overview to Basic Forging

Processes

• Open-Die Forging

• Forging Machine Tools

• Closed-Die Forging

• Forging Temperature

• Forging Defects

• Forging Dies

• Current Trends

Description of Forging

Advantages of Forging Process:

• High material utilization

• High production rates

• High process stability

• High recyclability of products

Forging consists of a group of manufacturing processes which are

mainly deformation processes The two other types of processes are

separating (parting) and joining processes.

In order to reduce stresses and forces and to increase formability,

forging is usually carried out after heating to a temperature range at

which recovery and recrystallization occurs Hence the workpieces after

forging do not show a permanent work hardening.

Advantages of Forged Products:

• Improved grain structure

• Higher fatigue strength & ductility

• Better surface quality than in casting

• Beneficial grain flow (fibers)

Trang 2

Material Fibers (Grain Flow)

Forging Industry Association

The beneficial grain flow in forged parts leads to a longer

fatigue life & higher ductility than machined or casted parts

ASM Handbook

Forging Production

2.368.000

35.000

1.360.000

9.600.000

0 3.000.000

6.000.000

9.000.000

12.000.000

Turkey (1989)

Germany (1999)

Europe (1998)

World (1998)

Tekkaya/Hirschvogel

Trang 3

Examples of Application:

Various Parts

IDS

Front Axle of a Truck

Daimler Benz AG

Trang 4

Automobile Front

Wheel Suspension

Examples of Application: Truck Gear Box

Daimler Benz AG

Trang 5

Examples of Application: Vehicle Power Shaft

Gelenkwellenbau Gmbh

Aircraft Landing Gear Structure

Airbus Industrie

Trang 6

Basic Forging Processes

Open-Die Forging

Closed-Die Forging

Hot Forging

Warm Forging Cold Forging

Precision Forging Near-Net-Shape-Forging Net-Shape Forging

Isothermal Forging

Hot versus Cold Forging

Hot Forging

• Production of discrete parts

• Greater technical and

economical importance

• Low stresses, no/low

work-hardening, homogenized

grain structure

• High formability

• Medium to low accuracy

• Scale formation

• Forging temperatures:

– Steel: > 1000oC (up to 1150 oC)

– Al-Alloys: 360oC-520oC

– Cu-Alloys: 700oC-800oC

Cold Forging

• Production of discrete parts

• Processes covered: extrusion

forging, upsetting, coining

• High stresses, strain

hardening, high die loads

• Limited formability

• Near-net shape or net shape

• High surface quality

Trang 7

Open-Die versus Closed-Die Forging

Open-Die Forging

• Aim: To achieve a convenient

mass distribution or shape for the

successive operations

(machining or closed-die forging)

• Simple tools, whose geometry do

not depend on the product

geometry

Closed-Die Forging

• Aim: Achieve best possible dimensional and shape accuracy

of the product

• Tools whose geometry is product dependent

Open Die Forging

Cogging

Video

Upsetting Heading (with no given form)

Spreading Radial Forging (with no given form)

Kalpakjian

Geiger

Lange

Trang 8

Basic Processes of Open-Die Forging and

Achievable Cross-Section Changes

• Cogging (material displacement)

• Spreading (material displacement)

• Upsetting, heading (material concentration)

Complete Plastification During Cogging

Lange

Trang 9

Closed Die Forging (1)

Impression Die Forging

Video

Closed Die Forging (no flash) Coining

Heading

Video

Kalpakjian

Closed Die Forging (2)

Roll-Forging

Skew-Roll-Forging

Upsetting in a Die

Kalpakjian

Trang 10

Closed

Die

Forging

(3)

Radial Forging (Swaging)

Kalpakjian

Terminology for Impression Die

Forging

Kalpakjian

Trang 11

Material Flow in Closed-Die Forging

Geiger/Lange

Lange

Work W

Stroke

s

plastic region rigid region

workpiece

dc

r z

s

r

s

r

s

f sz,f

sz,f

Mechanics of Closed-Die Forging

Trang 12

Effect of Flash Dimesions

Die Land - Ratio b/s

1200

1000

800

600

400

200

0

szmax

30

25

20

15

10

5

0

5500

5000

4500

4000

3500

3000

2500

55

50

45

40

35

30

25

s zmax

Dm

W

F

80 mm

Vieregge

Stress and Force Computation in

Impression Die Forging: Slab Method

In the flash land the axial stress is given according to the slab

method by Siebel as:

max

1 2

b s

= − ⋅  + ⋅ ⋅ 

Simple method to estimate the forging load:

max max

P z

where, the total projection area A p is given by:

P dc F

A : Projection area of die cavity, A : Projection area of flash

Trang 13

s plastic region

rigid region rigid region

d D

Stress and Force Computation in Impression

Die Forging: Upper Bound Method

• The material within the die cavity does not

plastify anymore as the maximum force is

recorded, since all free places are filled already

• The material flow happens only in the material

slab of thickness s, i.e the flash thickness The

shape of the die cavity is therefore immaterial

Assumptions for die with steep and deep cavities:

f

F

s s

⋅

max

f

F

(v Mises)

(Tresca)

0.3 < µ < 0.5 (0.577)

Lange

Typical Hot Flow Curves for Ck45

0

100

200

300

400

Equivalent plastic strain

1

40 s

ε & = −

1

8 s− 1

1.6 s− 1

40 s− 1

8 s− 1

1.6 s−

T = 1000 o C

1.6 s−

MSC/AutoForge

Trang 14

Forging Press Characteristics

Lange

Forging Presses (1)

Trang 15

Forging Presses (2)

Knuckle Joint

Gravity Drop Hammer

Kalpakjian

Example for Forging Sequences

Trang 16

Examples of Forged Parts

Courtesy Kanca

Closed-Die Forging without Flash:

Example

Trang 17

Force-Displacement Diagram

Punch Stroke in mm

Upsetting

Corner Filling

Johne

Material Flow

Punch

Die

unfilled corner plastic zone

sticking zone Workpiece

Lange

Trang 18

Forging Temperature

• Lower Temperature: Significantly larger than the

recyrstallization temperature

• Upper Temperature: As large as possible, but if too

large:

– Oxidation or melting of impurities at the grain boundaries

– Excessive grain grow (overheating)

– Increased scale formation and decarburization

– Tendency of fracture on the blank surface

• Workpiece temperature is neither in time nor in space constant:

– Heat losses due to radiation and conduction

– Heat gain by friction and forming work

Forging Defects

Kalpakjian

Trang 19

Forging Dies: Failure

Kannappan

Wear (abrasion) Thermal fatigue Mechanical fatigue Plastic deformation

Forging Dies: Design

• Positioning the forging stages

• Design of die land and flash gutter

• Design of the die cavity

– Design for material flow and die layout

– Design for dimensional accuracy

– Design for ease of machining

Trang 20

Current Trends

• Thixo-Forging:

– Combination of casting and forming

– Thixotropic state: both liquid and solid

states co-exist

– Materials: basically aluminum and

magnesium alloys

– Advantages:

• Low forging loads

• Complicated shapes can be forged in

one stage

• Near-net forming (as compared to

casting)

• Large wall thickness differences

possible

– Disadvantages:

• Very tight temperature window

• Advance tool technology necessary

• Not all materials can be thixoforged

• Precision Forging of

Gears

– Precision forging: Forging with higher precision than described in the standards – Higher tool costs are compensated by saving post-machining costs

Computer Aided Forging

unkown owner

Định dạng
Số trang	20
Dung lượng	9,32 MB