ELECTRON AND LASER

BEAM HARDENINGMuhammed Labeeb

CONTENTS

▪ ELECTRON BEAM HARDENING

▪ LASER BEAM HARDENING

▪ REFERENCES

WHY HARDENING ?

▪ To increase hardness

▪ To reduce wear and tear

▪ If surface hardening is done, surface became hard and core remains soft, and so the material can withstand stress and fatigue.

▪ It is less expensive than through hardening

ELECTRON BEAM HARDENING

▪ EB hardening is a short surface hardening procedure for martensitically hardenable ferrous materials using the energy transferred by electron beams

▪ The rapid cooling of the austenite required for martensite formation occurs through self-quenching

▪ Typical hardening depths obtained by the EB hardening process range from 0.1 to 1.5 mm

▪ The hardening process advances from the surface toward the inner core regions of the component via heat conduction

▪ Offers the advantages of extremely low hardening distortion and relatively low energy consumption

▪ Vacuum is required to carry out EB hardening

ELECTRON BEAM HARDENING

▪ The thickness of the energy absorption layer is proportional of square of the acceleration voltage and inversely proportional to density of material

▪ Typical acceleration voltages of the beam range from 60 to 150 kV and typical electron range values are 10 to 50 μm

▪ By accurately controlling acceleration voltage, depth of hardening can be precisely controlled throughout the process

▪ Beam focusing and guidance is done by electromagnetic coils

▪ Precise application of the energy with respect to workpiece location is thus possible

ADVANTAGES

▪ Precise control and reproducibility of the energy input with respect to location and time

▪ No scaling or oxidation of component surfaces

▪ No preparation of surfaces to be hardened or of regions that have to be left untreated

▪ Compatible and easy to integrate with CNC/CAM processing methods

▪ High energy efficiency (Approximately 75% of the power generated by an electron beam is converted to heat)

▪ No waste products generated

▪ High process productivity

LASER BEAM HARDENING

▪ LB hardening is a surface hardening procedure for martensitically hardenable ferrous materials using the energy transferred by laser beams

▪ The rapid cooling of the austenite required for martensite formation occurs through self-quenching

▪ Heat generated by LB hardening is proportional to power density.

▪ The power density of a focused laser beam used for hardening is much lower than the power density of the small, intense focused spots used for welding and cutting

▪ A relatively broad area beam in the shape of a square or a rectangle, is used in LB hardening

LASER BEAM HARDENING

LASER BEAM HARDENING

▪ LB hardening requires reshaping of the output laser beam that is attained by the use of various optical systems

▪ Efficient use of the laser energy requires the introduction of a controlled absorbing coating on the material surface

▪ Chemical coatings, such as manganese phosphate and paints of graphite, silicon, and carbon, are generally used

▪ LB hardening gives low distortion, and high surface hardness, but initial cost is very high and energy conversion is only 10% of the input energy

▪ No vacuum is required and hence any intricate and large components can be hardened

COMPARISON

EB Hardening LB Hardening

• Needs vacuum

• Distance between source and component is

relatively small

• No application of heat absorption layers

• Beam guidance by electromagnetic coils

• Bulk components cannot be hardened due to

inability to place them in vacuum

• High efficiency

• No need of vacuum

• Distance between source and component is

relatively high

• Application of heat absorption layers required

• Beam guidance by mirrors and lenses

• Bulk components can be hardened easily

• Low efficiency

REFERENCE

▪ ASM Metals Hand Book, 9th edn, Vol 4, Heat Treating, ASM, Metals Park, (1983)