Komkov N.M., Kapaeva S.D.

The East-Kazakhstan State Technical University

Ust-Kamenogorsk, the Kazakhstan Republic

The search of the cutting mechanism in the time of sharpening in an atmosphere of the water-soluble polymeric cutting-tool lubricant вп-4

The leading roles in the economic recovery play a machine-building industry particularly the metal cutting processes. At the same time much attention is giving to perfection of the machining operations, productivity and accuracy increasing, increasing of the cutting tool endurance. The industrial rhythm needs increasing of quantities and ranges of cutting tools and naturally it needs increasing of alloying components drain for the hard alloy production. The increasing of existing cutting tool endurance and durability is very significant in this situation. The choice of the cutting-tool lubricant may help to solve this problem.

Today in machine-building industry generally used the oil and the emulsion cutting-tool lubricants. The usage of which have an adverse effect to working conditions and technical conditions of cutting machines parts. Plus it is very they are difficult-to-make and while using it may take damage to environment.

The searching in technical literature shows that in influencing on the contact processes water-soluble polymeric cutting-tool lubricant is as good as the oil and the emulsion cutting-tool lubricants (CTL). So it is necessary to create the composition of water-soluble polymeric cutting-tool lubricant(CTL) which in its cooling abilities will be as good as emulsion CTL and in lubricating properties will be as good as oil CTL.

The new CTL must combine with opposite features such as low boundary tension i.e. good wetting quality, penetrability at the metal flaws and high viscosity for creating of more pressure in liquid between moving surfaces.

Different authors searched the water-soluble polymeric CTL in the processes of milling, glazing, threading, toothing, but not so much in sharpening. Although this handling type occupies a larger proportion in bulk of today’s metalworking in machine building.

This work devoted to increasing of turning tools durability by researching of water-soluble polymeric CTL influence to turning tools durability and machined surface quality of constructional and compound steel.

Different methods are using for the experimental definition of the isothermal curves П(h) of penetrating polymeric film pressure. First researches were done by Deryagin and Kusakov [1] who used gas bubbles with different radius R₀, which emerged to horizontally placed gentle smooth plate (Picture 1).

Disjoining pressure of gentle film defined by equation [1] in which is the gas pressure in bubble and P₀ is pressure in volumetric fluid phase, which close round the bubble. If we put P and P₀ in [1] we will have:

, ( 1)

Picture 1 – The bubble method of wetting films disjoining pressure isothermal curves reception.

Isothermal curves of disjoining pressure in plane of sliding are belonging from 8.95x10² – 7.77x10⁵ Pascal and film thickness in range of 400-25 A⁰.

At the breakdown force estimation we define average normal pressure of liquid between moving surfaces [2]:

, (2)

Where

V-peripheral speed of cutting, m/min

-rotating speed of detail, rad/sec

- dynamic viscosity

- kinematic viscosity

- liquid density

- loading coefficient, which is taken in according to [1]

Define the liquid pressure between contact surfaces of detail and cutting tool:

(3)

When microcrack size achieved amount more than 50 ⁰A to disjoining pressure will be added the pressure in liquid value, and it will increase:

7.77×10⁵+7.77×10⁵+1298025 = 2852025 Pa.

( =10^-8 sm. = 10^-10 sm.)

As the result of the disjoining activity of adsorbed polymeric film and pressure of the liquid CTL ВП-4, the sharpening process bypass with lower duty to cutting tool. This help to increase cutting tool endurance in 1.2-1.4, achieving of the R_a=1.1mkm undulation and worked pieces dimensional accuracy in high-velocity manufacturing of constructional and compound steel.

It follows that singularity of sharpening process course depend from the mechanism of plastic flow of metal in different mediums.

Study of the contact processes illustrate the nature of such events as friction, chip formation, cold-hardening, surface indulation of storages, wear of the cutting tools. The studies of chip formation process shown, that CTL is reducing the contact length between chip and cutting tool, essentially, because of the elastic contact zone reducing. CTL will take effect through the changing of average friction coefficient and defining the angle of coverage. The using of CTL which have the ability to penetrate into cutting zone allow to lower the friction coefficient and to change stress state of metal [3].

With this object in mind were created a number of new water-soluble polymeric CTL. Study of which revealed their action mechanism in chip formation and plastic flow character of machined metal while sharpening. For the researching of the plastically deformed cutting zone character were made metallographic samples of processed in different mediums details, and than were made a metallographic analysis of this samples. For comparative analysis were selected the standard liquid - CTL ЭГТ, which usually using in machine-building production and the best type of water-soluble polymeric CTL WP-4 (which were created in working process) [4].

Zone of the crystal grains (position 1) maximum plastic flow and the character of their streaming may be defined at the chip root microstructure situated at the picture 2.

1

2

ψ

Picture 2 – the сталь 20 chip root microstructure un CTL ЭГТ medium

The ranges of deformed metal crystal grains laying at an angle of ψ to the plane of sliding and nearly directly from facial layer. Such order of the deformed metal crystal gains cause the hard surfacing and increasing of micro-hardness of chip and processed detail facial layer. Which in its turn cause the increasing of the cutting tool wear.

The process which is visible on the picture is the process of metal tearing from cut surface by cutter. This process cause chatter marks at the processed surface.(Picture 2, position 2). As a result the processed surface indulation appear. The value of this indulation in the CTL ЭГТ medium situated at the graph of indulation as a function of cutting speed(Picture 3).

Picture 3 – The processed detail surface finish dependence of tool back-surface(h3) wear value in finish sharpening of the сталь 20 by carbide-faced tool T15K6.

The researching of the chip root microstructure which was processed in the medium of the CTL ВП -4(Picture 4) has show following results:

2

ψ

1

Picture 4 – the сталь 20 chip root microstructure in water-soluble polymeric CTL ВП-4 medium

At the micrography of the metallographic sample which has been processed in the medium of the CTL ВП-4 we can see singularity of chip deformed crystal gains order, their defined form and orientation. The value of angle is smaller and it proves that value of the frictional force lower under the effect of polymeric interfacial film CTL ВП-4. The strips of deformed zones of chip metal crystal gains parallelism (picture 4, position 1) while saving the constancy of texture angle, testifying about absence of burst layer secondary deformation. The effect of which cause the increasing of chip micro-hardness and abrasive wear of cutting tool. This factor explain the difference of surfaces cold hardening degree, which were processed in different mediums(Picture 5).

V, m/min

1 - without CTL; 2 - CTL ЭГТ;3 – CTL ВП-4.

Picture 5 – the work-hardening degree(H) dependence of cutting speed(V) in finish sharpening process.

Also at the micrograph of metal chip root which has been processed in the CTL WP-4 medium was marked the character of facial layer and indulation(picture 4,position 2). Also at the micrograph evidently viewed decreasing of the indulance lugs height.

The action mechanism of water-soluble polymeric CTL ВП-4 (Picture 6) consist in appearing of the disjoining force P_p, resulting of which and N_p fit in vector with sliding force Pτ. This involves to total force(resulting) increasing.

(4)

This resulting force exceed the yield limit of the processing material, and then happen its destruction (Picture 7). Intercrystalline bond breaking of processing metal is affected by adsorbed polymeric film of CTL ВП-4 and by the pressure of liquid. It cause the disjoining effect at the cutting zone i.e. it cause the Rebinder effect.

So it allow to make such conclusion that the CTL mechanism depend of chemical composition and of physical features of liquid with water-soluble polymers.

The CTL created at the base of water-soluble polymers leads to thermal exchange increasing, because of high thermal capacity of water which exist copiously in CTL composition. The increasing of the cutting tool hardness and its load drop caused by decreasing of temperature in contact zone. It is the first cutting mechanism.

The decreasing of frictional force and action angle caused by existence of polyatomic alcohols and surface acting agents at the CTL ВП-4 compositions which cause the lubricating effect.. It is the second cutting mechanism.

Picture 6 – the cutting mechanism with using of water-soluble polymeric

CTL ВП-4.

0,0025мммм

Picture 7 – sliding surface zone with the scoth forming by adsorb film of polymeric CTL ВП-4 (×2100)

And the third cutting mechanism – disjoining mechanism – may able because of opposite features combination in CTL composition. It means two features: The decreased boundary tension and the increased viscosity. The existing of monoatomic alcohols, organic acids and sulphates at CTL composition is decreasing the liquid boundary tension and increasing wetability of contact surfaces. It creating the ability of liquid penetration to microcracks and promoting to destruction of processed metal. And the existing of cooling liquid, furcated high-polymeric chains of water-soluble polymers at CTL composition coupled with surface acting agents allow to significantly increase the kinematic viscosity of liquid. It helps to arise the disjoining effect, which cause the Rebinder effect.

The cutting mechanism has been recommended as the most efficient mechanism for the increasing of cutting tool durability.

The list of literature:

1 Deryagin B.V., Kusakov M.M. “Experimental researching of the surfaces solvation” News of the Academe of Sciences of the USSR. Gray chemistry. 1937. №5. page 1119-1152.

2 Yakushev A.I., Vorontsov L.N., Fedotov N.M. “Interchangeability, standardizing and technical metrology”. M.:Machine-building.1986.page 350.

3 Kostetskiy B.I., Nathanson M.E., Berigatskiy A.I. “Mechanical process in boundary friction”.M.:Science.1972.page 170.

4 Patent №17885 of the Kazakhstan Republic. Cutting-Tool Lubricant for mechanical process of metal/Komkov N.M., Kapaeva S.D.;16.10.06.bull.№10.page 2.