Metal cutting, or simply machining, is one of the oldest processes for shaping components in the manufacturing industry. It is estimated that 15% of the value of all mechanical components manufactured worldwide is derived from machining operations. However, despite its obvious economic and technical importance, machining remains one of the least understood manufacturing operations due to low predictive ability of the machining models.

The old "trial-and-error" experimental method, originally developed in the middle of the 19^th century is still in wide use in metal cutting research and development activities. Its modern form, known as the "Unified or Generalized Mechanics Approach", has been pursued by Armarego and co-workers for years and then spread as the mechanistic approach in metal cutting. It was developed as an alternative to the metal cutting theory because the latter did not prove its ability to solve even simplest practical problems. Some researches even argued about "advantages of experimental research over theoretical models."

Although a number of books on metal cutting have been published, none of them provides critical comparison of different theories of metal cutting in their discussion of the corresponding models of chip formation which constitute the very core of the metal cutting theory. After reading these books, a practical specialist in metal cutting does not feel to be sufficiently equipped with knowledge on the advantages and drawbacks of different models so he/she may wonder which particular model of chip formation to use in a given practical case. Besides, a great number of papers were published on the subject providing contradictive results and thus adding even more confusion to the matter.

In my personal opinion, no progress in the theory of metal cutting and in the proper evaluation of experimental results can be achieved regardless of tons of time and money spent unless the proper definition of the metal cutting process is used:

Metal cutting is a forming process taking place in cutting system components that are so arranged that by their means the applied external energy causes the purposeful fracture of the layer being removed. This fracture occurs due to the combined stress including the continuously changing bending stress that is the cause of cyclic nature of this process.

and unless the following is accepted as a pre-requisite:

• The single shear plane model is totally rejected due to its complete inadequacy to reality.  All other 'shearing' based models (starting with Lee and Shafer model and finishing with Oxley model) should follow as well without any mercy.

• The relevant mechanical properties of the work material are considered. The shear strength or the flow shear stress cannot be considered as adequate characteristics in this respect because, considered alone, the stress does not account on the energy spent in cutting. Therefore, all naive attempts to find out the so-called "flow curve" should be abolished ASAP. 

• Physics of metal cutting should be considered.  All ungrounded notions as extremely high strain rate, inapplicability of the principle of minimum energy etc. should be forgotten ASAP.  Instead, a 3-D state of stress even in the simples case of orthogonal cutting should be considered.  The combination of cutting parameters (regime, geometry, tool materials properties, etc) under which a given work material has the least resistance to cutting should be established .

• System consideration of metal cutting becomes a common mindset and dominating notion.  It should be recognized that metal cutting is a cyclic process so that the frequency of chip formation should be determined first.  Then, the variation of the cutting force, temperatures and contact conditions within each cycle should be considered.  The clear system objective as to separate the layer being removed with minimum possible energy should be considered as a criterion of optimization of the metal cutting process.

  To start, I would recommend you first to read this book.

  

  Why you have to spend your money and time to read this book? Because it is just different from anything you've seen and learned on metal cutting. I just fed up with the existing set of legend unjustly called the "theory of metal cutting." Just ask yourself a few simple questions: " What the existing "theory" can actually predict?" or "Could I recall a practical problem that has been solved using the existing theory?" or even "How the essential parameters of the cutting process as the cutting speed, feed rate, flank (relief) angle, radius of the cutting edge (tool sharpness), inclination angle of the cutting edge, etc. are accounted in the existing "theory"? The answers are: No, No, and No. The conclusion should be a kind of simple: Why do I need this theory at all? Don't you wish to know why it happed and what to do about it? Would you like to learn that the theory of metal cutting can be of very practical nature answering you vital questions on machining? If the answers are Yes and Yes then please read the book. You can find the detailed review on this book in Applied Mechanics Reviews, Vol.53, No. 12, Dec2000, pp.B125-126.