NATIONALTRIBOLOGYCONFERENCE24-26 September 2003

THE ANNALS OF UNIVERSITY“DUNĂREA DE JOS“ OF GALAŢI

FASCICLE VIII, TRIBOLOGY2003 ISSN 1221-4590

167

THE CONNECTION BETWEEN PRODUCTIVITYAND TRIBOLOGY IN MANUFACTURING SYSTEMS

B. Ivkovic

Yugoslav Tribology SocietyS.J anjica 6, 34000 Kragujevac, Serbia

ABSTRACTRequirements for lowering friction in the contact zones of solid elements of

tribo-mechanical systems and slowing down the wear process of their criticalelements are consequences of needs for continuos decreasing of energy consumptionand costs of machining and maintenance of production equipment in industry.

As the industrial productivity is measured by Added Value per employdepends of production cost magnitude, with reference to energy consumption, toollife and working life of production equipment that means there is significantconnection between productivity and tribology in industrial systems.

KEYWORDS: productivity, tribology, manufacturing, added value.

1. INTRODUCTION

The productivity of manufacturing systems inboth developed and developing country depends forthe most part of the energy cost, machine cost, toolcost and lubricant cost, with reference to tribologicalprocesses in great numbers of tribomechanicalsystems that are exist in manufacturing equipment.

Productivity and reliability of manufacturingprocesses are the function of friction level in thecontact zone in the base tribomechanical systems andof wear intensity of the critical tribo elements.Though tribological (friction and wear) processescannot be stopped, they can be slowed down iftribological knowledge use during design andrealization of manufacturing processes.

In this paper is presented one consideration ofthe connection between manufacturing productivityand tribology in industrial systems, respectively theinfluence of the friction and wear processes on themanufacturing productivity.

2. MANUFACTURING SYSTEMPRODUCTIVITY

Manufacturing and industrial systems in generalwork toward the output of good and services usingboth material resources and labor. Based ondescriptions of manufacturing’s outputs and inputsone contemporary definition of productivity reads:Productivity is the measure of how specifiedresources are managed to accomplish timelyobjectives stated in terms of quantity and quality

The general expression for calculating theproductivity of a manufacturing system has the form:

InputOutputP =

where is output - goods and services and input -materials, energy, capital, work, etc.

Partial productivity indicators can be obtainedby varying the quantity used to measure output anddividing by individual input or groups inputs. Forinstance one of the most important partial productivityindicator to refer to labor productivity.

=

EmpoyeeDolar

EmpoyeesTotalValueAdded

Pl

The added value is the difference between theValue of shipments and cost of materials, supplies,containers, fuel, purchased electricity and contractwork (Annual Survey of Manufacturing).

The added value per employee, respectivelyproductivity of manufacturing systems, was about120,000 US dollar in 2000th year in Americanindustry. Manufacturing productivity in the otherdeveloped country is less in compare withproductivity that is obtained in United State ofAmerica in that year. Figure 1 shows productivityindex for a few developed countries, with reference tomanufacturing productivity.

Manufacturing productivity may vary widely fordifferent sectors of industry in the same country. Forinstance, added value per employee (manufacturingproductivity) in food industry is usually 30-40% lessof added value per employee that is obtained in themetal product sectors.

NATIONALTRIBOLOGYCONFERENCE24-26 September 2003

THE ANNALS OF UNIVERSITY“DUNĂREA DE JOS“ OF GALAŢI

FASCICLE VIII, TRIBOLOGY2003 ISSN 1221-4590

168

0 20 40 60 80 100USAFran

ceGerman

yJa

pan

Czech

Hunga

ry

in %

Fig. 1 Productivity index

The added value is function of production cost.It means that manufacturing productivity depends ofthe cost of machine tools, tools, lubricants, energy,transportation equipment and etc. Different level oftribology knowledge in manufacturing systems caninfluents on the level of production costs and addedvalue in great degree.

3. TRIBOLOGY INMANUFACTURING SYSTEMS

Tribology is customarily thought to encompassthe specific problems of friction, wear and lubrication,although the following opinion is increasinglyprevalent:

Tribology is a general concept embracing allaspects of the transmission and dissipation of energyand materials in mechanical equipment includingvarious aspects of friction, wear, lubrication andrelated fields of science and technology (3)

For manufacturing systems the term‘mechanical system” is understood to encompass allkind machining processes, machine tools, accessories,transportation and other equipment. The tribo-mechanical system is defined as an entity whosefunctional behavior relates to the interaction betweensurfaces in relative motion (3).

There are numerous tribo-mechanical systems inone manufacturing system that are parts of productionand other equipment. But many kinds of tribo-mechanical systems can be classified into four basicgroups (Fig. 2).

• Machining is carried out• Linear and other guides• Transmission of energy and motion• Information transmission take placeEach of the above groups has several subgroups.

For example, the first group could be said to containfour subgroups of tribo-mechanical systems in whichmaterial is formed by the various method of cutting,rolling, sheet metal forming and forging.

The other three tribo-mechanical groups may besimilarly divided into subgroups. However, regardlessof classification, tribology processes are developing inall kind of tribo-mechanical systems in the same way,respectively in so-called “basic tribo-mechanicalsystem”.

Fig. 2

However, regardless of tribo-mechanical type,the tribological process (friction and wear) to takeplace in the base tribo-mechanical system. Thestructure of all the base tribo-mechanical system issimilar and includes two solid elements in relativemotion in an environment filled with lubricant.

The consequence of tribological processes(friction and wear) are energy spending and loseutility of all kinds of tribo-mechanical systems. Boththese processes (friction and wear) have considerableeffect on the manufacturing productivity.

As energy cost is one part of production costevery decrease of friction in the contact zone of alltribo-mechanical systems that contain in productionand other equipment means bigger added value. Thus,

OtherLaborMaterialEnergyValueAdded

P+++

=

If other kind of production cost are constant thanproductivity depend of the level of energyexpenditure. Thus

CostEnergy

ValueAddedP =

Reduction of energy expenditure through frictioncontrol can potentially produce a considerableincrease manufacturing productivity.

The wear process (i.e. the wear resistance) oftribo-mechanical elements determines the reliabilityof the manufacturing processes and durability ofmachine tools, accessories, cutting tools and otherequipment.

NATIONALTRIBOLOGYCONFERENCE24-26 September 2003

THE ANNALS OF UNIVERSITY“DUNĂREA DE JOS“ OF GALAŢI

FASCICLE VIII, TRIBOLOGY2003 ISSN 1221-4590

169

If there is high wear intensity on criticalelements of numerous tribo-mechanical systems thatcontain in production and other equipment than manyparts of production costs are big. In that caseproductivity is small because:

saccessorie,toolmachine,toolofCostsAddedValueP =

Longer duration of tribo-mechanical elements asconsequence of wear slow down, means decrease toolcost, machine tool cost, accessories cost etc. andincrease manufacturing productivity.

4. THE CONTROL OF FRICTIONAND WEAR

The level control of tribological processes(friction and wear) in manufacturing system dependof the knowledge of tribological properties of triboelements.

It is known that tribological properties oflubricants and both solid elements of tribo-mechanicalsystem are determined by:

• magnitude of the friction force, namely thefriction coefficient in the contact zone oftribo-mechanical systems elements(energetic aspect) and

• critical magnitude of the correspondingparameter of wear at a critical element of atribo-mechanical system (economic aspect).

Tribological properties of lubricants and, as wellas of other elements of tribo-mechanical systems(elements made of solid materials) are of a relativenature, since they depend on conditions under inwhich the contact between the elements of a system isrealized. For example, the friction force depends onthe magnitude of the external load of the contact zone,and the friction coefficient depends on the sliding

speed, contact surfaces roughness, contact zonetemperature, etc.

The critical magnitude of wear of the criticalelement of a tribo-mechanical system occurs after ashorter or longer duration of contact, not only becauseof properties of the applied lubricant, for instance, butalso due to conditions in which the contact in thesystem is realized (materials of the system elements,sliding speed, contact zone load, etc.).

During comparison of tribologicalcharacteristics of a group of lubricants or solidmaterials, from any aspect, it is mandatory toexplicitly mention conditions under which the frictionforces and wear parameters were measured, duringand after the contact realization between the solidelements of the system.

It is very hardly to get tribological properties oftribo elements in real production conditions. It isreason because for creating of database of tribologicalproperties of solid materials, coatings and lubricantsthe laboratory methods are used.

Two type of tribological instruments are used inthe laboratories for determination the tribologicalproperties of all kinds tribo elements. These are

• tribometers with possibility to realize point,line and area contact,

• scratch testers for determination abrasionresistance of solid material and adhesionstrength between coating and substrate.

By measure friction force, respectively frictioncoefficient on any type of tribometer, the functionµ=f(t), for instance can be get in this form (Fig. 3)

The magnitude of wear on block as criticalelement of tribo-mechanical system ‘Block on Ring(or Disk)” is getting on the end of contact duration(Fig. 4).

Fig. 3 Experimental function µ=f(t).

NATIONALTRIBOLOGYCONFERENCE24-26 September 2003

THE ANNALS OF UNIVERSITY“DUNĂREA DE JOS“ OF GALAŢI

FASCICLE VIII, TRIBOLOGY2003 ISSN 1221-4590

170

Fig. 4 Wear scar on the block - the end of experiment.

Wear scar is measured on the RoughnessMeasurement System.

Data of solid materials abrasion resistance oradhesion strength between coating and substrate isgetting on Scratch tester. Figure 5 shows the shape oftwo experimental function µ-F(Fn), which refer totwo different coating on the same substrate.

The Scratch Test basically consists of simulatingthe sliding (motion) of the tips of asperities of thehard body over the surface (through the contact layer)of the body of a lower hardness, in presence ofvariable external load, which varies from a certainminimum to a certain maximum values.

As it is known, surfaces of solid bodies(elements of the tribo-mechanical systems) are roughwith asperities whose size, shape and mutualdistances depend on type of machining that was usedin their forming. The contact between the two solidbodies is always of a discrete nature (Fig. 1a). Radiusof the asperities tips is, usually, very small, and itranges, most frequently, around 0.1 to 0.3mm. InFigure 1b there is presented a tip of a cone made ofthe hard metal or diamond (used for measuringhardness according to the Rockwell method), whichsimulates the tip of a single asperity on the surface ofthe higher hardness body.

Two possible procedures can be used in theScratch test.

In the first procedure the contact between thehard metal or diamond cone and the part whoseabrasive resistance is being measured, is realized atthe beginning of contact, with minimal force FN,which equals, for instance, 5N. In the further processof contact realization, the normal force is varied at achosen rate, to a certain maximum value FN, whichequals, for instance, 100N.

The length of the sliding path, namely the weartrace of abrasive wear, is a function of the slidingspeed (of the object motion) and the rate of forcevariation.

Monitoring of the friction force and the acousticemission variation with variation of the normal force(normal load of the contact zone) during the contactrealization, enables determination of the "criticalvalue FNC" at which the significant increase of thefriction force and the acoustic emission occur. Afterreaching this critical value FNC, the phase of

accelerated destruction of the contact layer occurs, ofthe tested object, namely the coating on its surface.

Fig. 5 Abrasive resistance of two coatings.

In the second procedure the contact of the hard metalor diamond cone and the object whose abrasiveresistance is being tested, is realized with the constantforce FN, at the chose length of the sliding path.

5. CONCLUSION

The consequence of energy and other materialscosts decrease through reduce friction processes andslow down wear processes in numerous tribo-mechanical systems, which contain in production andtransportation equipment, is increase manufacturingsystem productivity.

The apply level of tribology knowledge inmanufacturing systems depend of the existing oftribological characteristics database.

REFERENCES

1. Ivkovic B., 2002, “Scratch Tester - Measurement of materialabrasive resistance and Coating Quality”, Balkantrib’ 02, pp. 641-646.2. Ivkovic B., 1988, “Manufacturing Process Productivity ThroughTribology”, J. of Robotic&Computer-Integrated Manufacturing,Vol. 4, No. 1/2, pp. 135-138.