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Machining Ceramics with Rotary Ultrasonic Machining Processing with Low-frequency

Ultrasonic machining is the removal of material by the abrading action of grit-loaded liquid slurry circulating between the workpiece and a tool vibrating perpendicular to the workface at afrequency above the audible range.
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  • M20-R
  • Rps-sonic
  • M20-R

Machining Ceramics with Rotary Ultrasonic Machining Processing with Low-frequency


Introduction

Ultrasonic machining is a mechanical type non-traditional machining process. It is employed to machine hard and brittle materials (both electrically conductive and non conductive material) having hardness usually greater than 40 HRC. The process was first developed in 1950s and was originally used for finishing EDM surfaces. In ultrasonic machining, tool of desired shape vibrates at ultrasonic frequency ( 19 to 25 kHz. ) with an amplitude of 15-50 Microns over work piece. Generally tool is pressed down with a feed force F. Between the tool and work, machining zone is flooded with hard abrasive particles generally in the form of water based slurry. As the tool vibrates over the work piece, abrasive particles acts as indenter and indent both work and tool material . Abrasive particles , as they indent , the work material would remove the material from both tool and work piece. In Ultrasonic machining material removal is due to crack initiation, propagation and brittle fracture of material. USM is used for machining hard and brittle materials, which are poor conductors of electricity and thus cannot be processed by Electrochemical machining ( ECM) or Electro discharge machining (EDM). The tool in USM is made to vibrate with high frequency on to the work surface in the midst of the flowing slurry. The main reason for using ultrasonic frequency is to provide better performance. Audible frequencies of required intensities would be heard as extremely loud sound and would cause fatigue and even permanent damage to the auditory apparatus.


In the UM process, a low-frequency electrical signal is applied to a transducer, which converts the electrical energy into high-frequency (~20 KHz) mechanical vibration (see Figure 2). This mechanical energy is transmitted to a horn and tool assembly and results in a unidirectional vibration of the tool at the ultrasonic frequency with a known amplitude. The standard amplitude of vibration is typically less than 0.002 in. The power level for this process is in the range of 50 to 3000 watts. Pressure is applied to the tool in the form of static load.

A constant stream of abrasive slurry passes between the tool and the workpiece. Commonly used abrasives include diamond, boron carbide, silicon carbide and alumina, and the abrasive grains are suspended in water or a suitable chemical solution. In addition to providing abrasive grain to the cutting zone, the slurry is used to flush away debris. The vibrating tool, combined with the abrasive slurry, abrades the material uniformly, leaving a precise reverse image of the tool shape.

Ultrasonic machining is a loose abrasive machining process that requires a very low force applied to the abrasive grain, which leads to reduced material requirements and minimal to no damage to the surface. Material removal during the UM process can be classified into three mechanisms: mechanical abrasion by the direct hammering of the abrasive particles into the workpiece (major), micro-chipping through the impact of the free-moving abrasives (minor), and cavitation-induced erosion and chemical effect (minor).2

Material removal rates and the surface roughness generated on the machined surface depend on the material properties and process parameters, including the type and size of abrasive grain employed and the amplitude of vibration, as well as material porosity, hardness and toughness. In general, the material removal rate will be lower for materials with high material hardness (H) and fracture toughness (KIC).


Parameters of Ultrasonic Machining:

The ultrasonic vibration machining method is an efficient cutting technique for difficult-tomachine materials. It is found that the USM mechanism is influenced by these important parameters. 

 Amplitude of tool oscillation(a0)

 Frequency of tool oscillation(f) 

 Tool material 

 Type of abrasive

 Grain size or grit size of the abrasives – d0 

 Feed force - F 

 Contact area of the tool – A 

 Volume concentration of abrasive in water slurry – C 

 Ratio of workpiece hardness to tool hardness; λ=σw/σt

Item

Parameter

Abrasive Boron carbide, aluminium oxide and silicon carbide 
Grit size(d0)  100 – 800
Frequency of vibration (f)  19 – 25 kHz 
Amplitude of vibration (a) 15 - 50 µm
Tool material Soft steel titanium alloy
Wear ratio  Tungsten 1.5:1 and glass 100:1 
 Gap overcut  0.02-0.1 mm


1 (1)

Features:


  •       Simple installation

  •       Improve the surface integrity of the material being processed for true cold cutting

  •       Reduce the cutting resistance during tool processing and reduce the residual stress on the surface of the machined material

  •       High-speed machine tool processing can be used to improve machining efficiency in low-speed machine applications

  •       Customized JT, BT, HSK, straight shank and other specifications according to the user's machine tool spindle

  •       Suitable for hard and brittle materials, such as: glass, ceramic lamps are more difficult to process materials.


What's the Principle of ultrasonic machining?

      Through ultrasonic to achieve a very large impact acceleration (about 104-105 times the acceleration of gravity) under the action of a vibration frequency of 20-50KHz (ie, 2000-50,000 times per second), and the cutting direction of the machine is combined with the main motion of the machine. High frequency vibration, the material is first crushed and then removed.


      Ultrasonic milling is microscopically a pulse cutting. The effective cutting time of the tool is very short. The tool is completely separated from the workpiece more than 80% of the time, and the workpiece is intermittently contacted by the machined surface, which greatly reduces the cutting resistance of the tool and avoids the common cutting. The phenomenon of letting the knife phenomenon is greatly reduced on the surface residual stress of the workpiece.

Ultrasonic machining, or strictly speaking the "Ultrasonic vibration machining", is a subtraction manufacturing process that removes material from the surface of a part through high frequency, low amplitude vibrations of a tool against the material surface in the presence of fine abrasive particles. The tool travels vertically or orthogonal to the surface of the part at amplitudes of 0.05 to 0.125 mm (0.002 to 0.005 in.).[1] The fine abrasive grains are mixed with water to form a slurry that is distributed across the part and the tip of the tool. Typical grain sizes of the abrasive material range from 100 to 1000, where smaller grains (higher grain number) produce smoother surface finishes



 Ultrasonic machining is suitable for machining of hard, brittle materials including:


Glass
Sapphire
Alumina
Ferrite
PCD
Piezoceramics
Quartz
CVD Silicon Carbide
Ceramic Matrix Composites
Technical Ceramics

  


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