04 - pisarciuc - materials and machining technologies for sustainable development

7/30/2019 04 - Pisarciuc - Materials and Machining Technologies for Sustainable Development

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Nonconventional Technologies Review no. 4/2010

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MATERIALS AND MACHINING TECHNOLOGIES FOR SUSTAINABLEDEVELOPMENT

Cristian PISARCIUC1, Flavius A. SARBU1Transilvania University of Brasov, Romania,

[email protected],

[email protected]

Abstract: Technologies developing in the world are requiring the application of new achievements ofscience and technology, with direct implications on increasing of productivity, quality and reliability in order toreduce production costs for products. All these are evident in those goals but have also beneficial effects inlight of new regulations concerning environmental protection contributing as well to sustainable development.Currently, the industry benefits from a large number of processing methods and unconventionaltechnologies. Among technologies used today and which are applied on an increasingly large scale, areunconventional technologies, because they offer opportunities for manufacturing industry to use hard andsuperhard materials under conditions of maximum technical and economic efficiency. These technologies

are able to produce parts with complex shapes and types of surfaces, hard or impossible to obtain usingconventional processing technologies.

Keywords: unconventional technologies, environmental protection, sustainable development

1. INTRODUCTION

Products development with an acceleratedrate of production led, largely, to an increaseddemand for materials and products with special

physicochemical properties (hard, refractory,corrosion resistant, etc.). Using classicalmethods in processing these materials withhigh features, is, if not impossible, at least verycomplicated. The productivity of cuttingprocessing of such materials decreases withtheir hardness, while it remains almost constantfor erosion (electrical, electrochemical, water jetmachining, etc.). Up to 400 - 500 HB hardness,machining speeds through conventional meansare more productive; over those valuesunconventional processing technologies are far

more beneficial (figure 1) [1].

Fig.1. Productivity versus hardness

evaluation

Taking into account the great diversity ofmaterials used, geometric shapes andsurfaces dimensions made today, processing

productivity through various means, inrelation to the machinability of materials, canbe appreciated from the graph in figure 2.

Fig.2. Productivity versus machinabilityevaluation

It can be seen easily that, even taking intoaccount processing costs, for simple featuresconventional machining processes arerecommended, while for the most difficultmost unconventional machining are moreappropriate.

2. MATERIALS AND PROCESSINGMETHODS IN TERMS OFSUSTAINABLE DEVELOPMENT

Current development of industrialactivities shall be subject to reduction inconsumption of raw materials (steel - inparticular) and energy consumption. Inaddition, in view of sustainable development,

Conventionalmachining

Nonconventionalmachining

200 400 600 HBProductivityQm

m

/min

NonconventionalProcessing

Conventionalcutting

Machinabilityeasy difficult

Productivit
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harmonizing human activities with theenvironment the implications over naturemust be taken into account.

Although metal losses were significantly

reduced, the material consumption is stillhigh. Nowadays, iron and steel, bothwidespread in the engineering industry, areforming 83% of metal production and theweight of one tenth of world production ofmaterials [2].

Taking into account the negative effectsthat high consumption of metals has on theenvironment will result in a new factor to betaken into account when designing theproduct and its processing technology.

Thus, from material deployed throughout

a large part is discarded in the form of waste.Furthermore, to separate metal from ore areused, most often, toxic substances such ascyanide, mercury, sulphuric acid and others.The remaining material left after separation -waste - is stored in various areas that, in thisway, become extremely dangerous.

As the concentration of ore depositscurrently used for metal production falls, it isexpected that for every useful tonne togenerate more and more waste. If in 1990,

the copper is extracted from ores containingonly the metal at a rate greater than 3%today, following the application of effectivemethods of enrichment, becomes economicthe use of minerals, even at a concentrationof only 0.5%. Mining in these conditions isdone with the price of a large quantity of rockdisplaced and excessive energyconsumption, with obvious negative impacton the environment [3].

In order to reduce the consumption ofmetallic materials, several solutions are

available:- Use of metal materials with superior

physicochemical properties that are involvingless specific weight, over whole the product;

- Reducing, were is possible, the safetyfactor by appropriate redesign;

- Improving physical and mechanicalqualities of metallic materials by appropriatetreatment;

- Use of new technologies or otherprocessing methods to ensure a high index ofthe material utilization;

- Election of other materials capable toensure the same quality or better;

To summarize, in authors opinion, toreduce both consumption of materials andenergy researches can turn in two directions:

1. Researches on the development ofnew materials or to improve properties ofexisting ones;

2. Researches in development of

conventional processing technologies and /or using unconventional technology inmanufacturing.

Considering the first aspect, the materials,more exactly their properties, should provideresistance to the stresses, they will be subjectas finished parts. It can therefore be said thatproducts must meet both operational andtechnological requirements.

One of the most important properties ofmetal materials is tensile strength r.Researches has shown that with its

increasing occurs intensification of cuttingtools wear, a decrease of cutting speed(figure 3), an increase of specific cuttingenergy (figure 4), a temperature rise in thecutting area (with possible effect of changesof material properties during processing), etc.

Fig.3. The influence of tensile strengthover cutting speed

Fig.4. The influence of tensile strengthover specific cutting energy

The increase in hardness leads to a

decrease in machinability of steels and anincrease of cutting forces. Taking intoaccount the characteristics of steel toughnessis found that if this raises then specificmechanical cutting energy increase as well.


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Steels, and generally homogeneousmaterials, have a good thermal conductivity.However, there are cases, especially when areprocessing special varieties of steel, that this

property have small values. For example,thermal conductivity at 20 C is 0.140 fornormal carbon steel, compared to only 0.035 to0.065 for stainless steels. A low value ofthermal conductivity is reflected in the difficultevacuation of heat from the cutting area, a highconcentration of heat at the cutting tool level, allthose having negative impact over tool wear.

More and more higher-quality steels arerequired in relation to their resistance tocorrosion, which end in chemical compositionof stainless steel where are placed special

alloying elements as: Ni, Cr, Mo, V. etc.Some of these, however, adversely affect thecutting machining, contributing, as well, to anincrease in tool wear and cutting forces.

In terms of technological properties ofmaterials, particularly of the metal, the mostimportant is machinability through cuttingprocesses. Because a number of factors(manufacturing process, material and toolgeometry, cutting regime, cooling conditions,etc.) influences the chip formation, removal

material behaviour can be characterisedbased on a global criterion with a character ofgenerality. Figure 5 shows, in comparison,machinability through cutting processes ofsome most used materials [4]. As reference,standard martensitic stainless steel is usedwhose machinability through cuttingprocesses was assessed at 100%.

Mater

ial

Machinability %

11

109

87

65

4

3

21

50 100 150 200

Fig.5. Machinability through cuttingprocesses; 1. Ferritic stainless steels, 2.Martensitic stainless steels 3. Austeniticstainless steels, 4. Automatic steels 5.Carbon steels, 6. Steels alloys, 7. Iron,

8. Tool steels 9. Refractory Alloys,

10. Copper Alloys, 11. Aluminium Alloys

As can be seen, most of metallicmaterials do not present favourablecharacteristics in terms of cutting. In fact,

applying cutting processes - in the authorsopinion - is more related to a convenience inusing conventional methods andtechnologies. Thus, we prefer to invest time,

energy and money in developing new cuttingtools, made of performing materials instead in"investing" in more efficient methods andtechnologies.

Most of the times, because of thecompetitive economy, the first criterion takeninto account in the choice of material andprocessing technology is economical one.

Although it is an easy observation to benoted, depending on the nature of production(mass production, large or in small number),ratio between material price and processing

cost varies:- In mass production, due to automation

and mechanization of the production,processing cost is lower than that for material;

- In opposition, in small series production,the share of the cost of the material in thefinished piece is small compared with theprocessing costs.

Because of the way material is removed,through unconventional technologies, fromworkpiece, i.e. by erosion, the production

character has no influence over theproduction costs.In these conditions is less expensive to

use, when appropriate, more expensive butquality materials, coupled with a technologyoperation to ensure required economicefficiency.

Alongside metallic materials, industryincreasingly uses, more and more, non-metallic materials. Their use, for example inthe category of composite materials, has agreater interest as the overall energy costs

are higher.In machine building industry, coefficient

of metal utilisation (the ratio between theweight of the finished piece and blank) isaveraging 50 ... 60%, but in some cases, thispercentage drops to 15%. The total weight ofmetal processing chips is, for example, onethird in bars and laminates. Even whenproduced in large series, the waste can reachup to 30 ... 40% of the metal blank [5]. Beingmore accurate and precise, acting only wereis necessary, unconventional technologies

dramatically reduce the amount of materialwasted contributing this way to environmentalprotection.

It can be stated, as an overall conclusion,that the operating properties, technological and


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economic matters are closely interdependent.Thus, no matter how high it would be someoperating properties of a material, if it cannot beprocessed, i.e. has no technological

machinability, it cannot be used in theproduction of industrial products. Moreover,even if processing is possible, this should bedone in economic terms, in order to be aprofitable operation. Therefore, part designerand technologist must take into account alsothe properties of materials set out above.

Cutting technologies (conventionaltechnologies) are based on the phenomenon ofchip formation. Whatever the cutting processis analysed, under the cutting tool action overworkpiece material, a force is developed,

acting on the cutting layer. In case ofunconventional technologies forces emergedare negligible, meaning that is now load overthe machine or workpiece.

Of those mentioned so far, it appears thatthe cutting tool must have, in terms of itsform, a relatively complex geometric design.It also presents specificity due to bothmachine - tool (where processing is done),and from the processing itself. Tools used inunconventional machining, at most, are

having a negative form compared tomachined surface (electro dischargemachining, electro chemical machining) ornot having a form at all (laser, water jetmachining, electron beam machining etc.).

3. CONCLUSIONS

Although a known process, cutting ischaracterised by phenomena that prevent itsuse in all situations.

Regardless of the processed material,

cutting forces are developed duringmachining and, in most cases, presentimportant values. This aspect involves bothperformance materials for cutting edges ofcutting tools and machine tools capable toensure cutting conditions. Dynamic issuesemerged during cutting, related to both tool -workpiece interaction and machine operation,are not so obvious and further complicate theprocess.

Cutting, as machining process, cannot beapplied in all situations arising in engineering.

Limitations of the procedure are mostlyrelated to the technological concept (whichreally refers to the technological aspects andconstructive). Materials with special

properties, as well increasingly complexmachined parts, reveal the process limits.

In conclusion, technologist will have toconsider alternative methods of processing,respectively, unconventional, at least in one ofthe following cases:

- When machinability (using conventionalcutting processes) is very low, makingdifficult, inefficient and / or impossible the useof a conventional technology. The less effortis implied in this activity, the more positiveaspects arise in terms of sustainable

development and, as well, in environmentalprotection.

- When the surfaces to be obtainedpresent such forms, sizes or locations thateither applying of a classical processingmethod is uneconomic, or that in fact there nopractical method for obtaining the desiredsurface.

REFERENCES

[1] OBACIU, G., KLOCKE, F., MARINESCU, N.,

IVAN, M., SARBU, F.A., GHICULESCU, D.:Eletrochemical Machining of MetallicMaterials. Transilvania University, Brasov,Romania, ISBN 978-973-598-499-1, 2009 (inRomanian)

[2] GHEORGHE, C.: Ecological Products Designin Industry. Tehnica-Info, Chisinau, Republicof Moldavia, ISBN 978-9975-63-303, 2009 (inRomanian)

[3] TUREAC, I., MARASCU-KLEIN, V.,POPESCU, Maria, CIOARA, R.: ProductsSustainable Development in MachineBuilding. Transilvania University, Brasov,

Romania, ISBN 978-635-639-6, Romania,2006 (in Romanian)

[4] MARASCU-KLEIN, V.: Industrial Materials -vol I. Transilvania University, Brasov,Romania, ISBN 973-9474-9, 2000 (inRomanian)

[5] TUREAC, I., POPESCU, Maria, MARASCU-KLEIN, V., CIOARA, R.: Ecological Designand Sustainable Development with

Applications in Machine Building. TransilvaniaUniversity, Brasov, Romania, ISBN 978-635-639-6, 2006 (in Romanian)

04 - pisarciuc - materials and machining technologies for sustainable development

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