Ultrasonic Machining Process Guidelines

You must have done different machining processes like cutting, drilling, milling, knurling etc. and would have got acknowledged with lots of machining skills. In my previous article on machining processes I have mentioned its advantages over casting process and with appropriate accuracy machining process can be used for variety of engineering materials.

Apart from much advantages of conventional machining process there are many demerits like hard and brittle materials are not suitable for machining and even casted products can’t be machined easily.

Hence engineers developed modern machining process like ultrasonic machining (USM) and many more like that to overcome the disadvantages of machining process which I’ll discuss later.

The reason behind the replacement of the process is that unconventional process are far better than the conventional machining process from many aspects like dimensional accuracy, surface finishing, less time consuming, large production, efficiency and harder and brittle material can be easily machined.

Look being a mechanical engineer you have to find the new ways like using ultrasonic machining process etc. to raise the production rate when the demand is more than the supply. And to have better production rate you have to certainly think of using the modern machining process or find alternatives otherwise you won’t survive in the industry.

But you have to keep in mind the minimum cost that can be spent on adopting new technologies to enhance production rate. Skilled Engineers and researcher are masters in these and hence they always try to modify the conventional machining process to get better results and did a great job of developing unconventional machining processes which I am going to discuss below.

Before going to the deep discussion in the topic ultrasonic machining process let tell you some important reasons of adopting modern or unconventional machining process and the process that are involved within it.

Why Modern Machining Process

With rapid growth in the demand of harder and brittle material for various manufacturing products led to the development machining of harder and brittle material from time to time. This is because these materials are very difficult to machine through conventional means and hence required a stronger and convenient machining process that can overcome all the disadvantages of the conventional machining process.

For machining harder tool and brittle materials a much stronger tool is required which could be very uneconomical and simultaneously accuracy, surface finish and huge efficiency could not be achieved.

And with the advancement of machining technology and adopting modern machining processes all of the above problems are resolved and working tremendously with high production rate and low investment cost.

Not only this with modern machining processes like ultrasonic machining, the properties of the materials like chemical inertness, grin structure, physical properties, conductivity etc remains same throughout the process which is plus point of the unconventional process.

As I said many application demand tight tolerances, intricate shape and size with additive features like dimensional accuracy, surface finish and higher reliability which are not fulfilled by the conventional forming and sintering processes.

You might be thinking if there is problem in the tool then why not use the hardest material (Diamond) of the earth as machining tool. This is because it very costly and simultaneously cannot be harnessed in intricate shape and sizes. And more important it is very time consuming which doubles the investment cost.

Common Modern Machining Processes

• Abrasive Jet Machining (AJM)
• Chemical Machining (CHM)
• Electrochemical Grinding (ECG)
• Electric Discharge Machining (EDM)
• Ion Beam Machining (IBM)
• Laser Beam Machining (LBM)
• Plasma Arc Machining (PAM)
• Ultrasonic Machining (USM)
• Water Jet Machining (WJM)

Why Ultrasonic Machining

Ultrasonic machining process is none conducting (Heat and Electricity), none chemical machining process which doesn’t have any effect on the chemical and physical properties and also the grain structure remains same throughout the process.

This additive feature adds value to ultrasonic machining process over other and most important part is that it can machine harder material with dimensional accuracy and perfect surface finish. The cost of the production is also under control. The production rate can also be increased whenever needed.

Ultrasonic machining process is material removal process and can be used for both conductive and non conductive materials. As I said it can machine much harder material almost more 40RHC, hence it also called as ultrasonic impact grinding or vibration cutting and can be used for wide variety of materials with additive features.

You would have heard of LASER, which is also used in modern machining process but it has some disadvantage like heating effect of laser machining changes the grain structure. Hence it is has limited material choice. Although it has tremendous advantage like higher production rate, higher accuracy and surface finish.

EDM is also unconventional process and has wide variety of intricate shapes and size but it is limited to conductive material only and material which is not conductive would not be machined.

 All these demerits of different modern machining process gives higher ranking to ultrasonic machining process as it can machine hard and brittle material and can be conductive or non conductive.

Working of Ultrasonic Machining

In ultrasonic machining process an ultrasonic transducer is used to generate ultrasonic waves of frequency higher than 20KHz. And this frequency is given to the horn and tool assembly resulting in continuous impacting on the workpiece with that frequency.

Actually a low frequency electrical signal is made to fall through the ultrasonic transducer producing higher frequency mechanical vibration waves. And after that this mechanical vibration is given to the tool in a fixed direction or it is unidirectional.

The amplitude of the mechanical vibration produced in the tool is kept low almost 0.02mm and continuously hammers the work piece with the given frequency. Ultrasonic machining tool is made up of soft materials and hence some time static load acting in downward direction is given to compress it against the workpiece.

During the impaction of the tool to the workpiece slurry containing abrasive particles is allowed to pass through the gap between the tool and the workpiece. The slurry is made up of abrasive materials suspended in a liquid and made to fall in the cutting zone under pressure.

Some commonly and mostly used abrasive materials are like carbide, silicon carbide, diamond, born carbide and alumina with the chemical added. The abrasive materials both acts as a tool and workpiece which reduces the chance of surface damage.

As I said abrasive is made to fall in the cutting zone which acquires the area gap between the tool and workpiece. The vibration tool impacts the abrasive material which ultimately impacts the worpiece and a reverse image of the tool is imprinted on the workpiece.

You know that ultrasonic machining process is a material removal process and can be categorized in three categories as per mechanism. The first one is hammering of the abrasive materials on the workpiece, the second one is cavitation due to erosion and chemical effect and the third one is micro chiping due to the sliding of the abrasive materials over the workpiece.

The rate of material removal process in ultrasonic machining process depends on many factors like physical properties of the materials, size and shape of the abrasive grains used in the slurry, process parameters, frequency, amplitude etc.

All the above factors play a major roll for material removal in ultrasonic machining and thus have significant effect on the surface roughness and dimensional accuracy. If the material is too hard and brittle then less material is removed.

Materials That Can be Machined through Ultrasonic Machining

Ultrasonic machining process has very wide range of engineering materials that can be machined. And why it is so, you already know the reason behind. However, I have to give few names in front of you which are mostly machined through ultrasonic machining so that you can easily recognize it. Following are the engineering materials that are machined by this process:-

• Glass
• Engineering ceramics
• PCD (Polycrystalline Diamond)
• Quartz
• Single crystal materials
• Ferrite
• Graphite
• Glassy carbon
• Piezoceramics

There are any more if I have not mentioned here then let me know. However, apart from the engineering materials ultrasonic machining process is also capable of machining wide variety of shape and sizes like round shape, square shape, holes and cavities with varying depths etc.

From as small as 0.008 inches to a very large workpiece can easily be machined through ultrasonic machining process. Aspect ratio can be more than 25-to-1 and depends upon the shape and size of the worpiece.

Advantages of Ultrasonic Machining

• All hard and brittle materials can be machined in ultrasonic machining
• High dimensional accuracy
• High surface finish
• There is no change in the chemical & physical properties and also the grain structure remain same throughout the machining process
• Cracks and defects can easily be detected whatever is the orientation
• Higher production rate

Disadvantages of Ultrasonic Machining

• Highly qualified and skillful operator and integrity is required
• There is no certified record of the inspection as that of in radiography
• Some steels like austenitic steel may mask defects due to large grain size of the welds
• Lack in the concentration may mislead the readings which can cause damage and need to be repaired

Other Engineering Applications of Ultrasonic

• Casting and welding of metals
• Measurement of velocity of moving fluids
• Forming of plastics
• Measurement of density, viscosity and elastic constants
• Measurement of hardness and grain size determination of metals
• Flaw detection, leak detection etc
• Nondestructive residual stress determination

This was a brief information about ultrasonic machining if you want some more information comment below