Non Traditional Machining Processes (NTP)

Prof. Dr. Taha Ali El-TaweelProfessor of manufacture engineering

Faculty of Engineering, Menofiya University

Ultrasonic machining (USM)

Ultrasonic machining (USM) Principle of USMUltrasonic machining (USM) is the removal of hard and brittle materials using an axially oscillating tool at ultrasonic frequencies [18–20 kHz]. During that oscillation, the abrasive slurry is continuously fed into the machining zone between a soft tool and the workpiece. The abrasive particles are, therefore, hammered into the workpiece surface and cause chipping of fine particles from it.

The machining system

The machining system is composed mainly from: magnetostrictor, concentrator, tool, and slurry feeding arrange.

The magnetostrictor is energized at the ultrasonic frequency and produces small-amplitude vibrations.

Magnetostriction

The magnetostrictor used in USM has a high-frequency winding wound on a magnetostrictor core and a special polarizing winding around an armature.

Magnetostrictor material converts the magnetic energy to a mechanical one.

Coefficient of magnetomechanical coupling:

Ew is the mechanical energy Em is the magnetic energy.

Variation in a wave of elongation along the length of the magnetostrictor

Mechanical amplifier

The elongation from magnetostrictor of length of l = 0.5 are 0.001-0.1m.USM required 0.01mm, can be obtained from “concentrator”

Types:• Cylindrical• Stepped• Conical• Exponential• Hyperbolic

Materials for the tool• Tool tips must have high wear resistance and fatigue strength.• Tungsten carbide, Copper, and Silver steel

Abrasive suspensionAbrasive slurry is usually composed of 50 percent (by volume) fine abrasive grains (100–800 grit number) of boron (B4C), aluminum oxide (Al2O3), or silicon carbide (SiC) in 50 percent water.

Slurry injection methods

The slurry is continuously fed to the machining zone in order to ensure efficient flushing of debris and keeps the suspension cool during machining.

Mechanism of material removal

The material is removed in the form of grains by: - Shear deformation - Brittle fracture of work material- Impact- Cavitation erosion- Chemical reaction

Material Removal Rate (MRR)

Relative machinability ratings for some materials

Factors affecting USM performance

Amplitude of tool vibration

Effect of process condition on MRR

Amplitude of tool vibration

Effect of grain size

Effect of cocentration and hardness

Effect of concentration and hardness

Effect of impact hardness of W.P material

H=F/4hd

H: w.p. material hardness (Brinell number)d: the diameter of the embedded sphere F: the force appliedh: the impact indentation depth

Effect of tool and w.p. on impact with grain

t+w= (d-x)t, w: tool and w.p. indentationx: distance separating themy= aosin,t+w= ao - ys

ys: distance moved down by the tool from mean position

The rad. of of inden. on w.p.rw= [w d]1/2

Fracture /gritVo= 2/3[w d]2/3

Fc: the contact load

w /d<<1 Hw=Fc/w d Fc = d Hw w Hw/ Ht= w/t =qw= (d-x)/(1+q)

Effect of shape of the tool

Effect of static load

Effect of static load

MRR

SURFACE FINISH

» Micro-hole drilling

The entrance The exit

Micro air turbine.Center pin diameter 70 µm; rotor diameter 350 µm

Finishing

» Manufacturing of 3D s tructures

» Finishing EDMed parts

USM applications

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