Integrisani pristup konstruisanja u funkciji razvoja nove generacije reznih elemenata za bagere kontinualnog dejstva

Abstract

Proces kopanja kod bagera kontinualnog dejstva neposredno vrše vedrice sa reznim elementima (rezni zubi i nož vedrice) koji se nalaze na frontu rezanja. Da bi se stenski materijal razorio potrebno je na njega delovati određenom silom, koja zavisi od vrste stenskog materijala, tehnologije iskopavanja, geometrije reznih elementa i dr. Rezni zubi svojom oštricom dospevaju na ograničene površine stenskog materijala i vrše naprezanja dovoljna za njihovo razaranje. Primenom reznih zuba raspoloživa sila rezanja se koncentriše na malu dužinu rezanja, i na taj način se olakšava prodiranje kompletne vedrice u materijal. Razoreni materijal se preko odgovarajućih površina reznih elemenata transportuje u kašiku. Da bi ispravno izvršili svoju osnovnu funkciju, rezni zubi moraju zadovoljiti više zahteva, kao što su povoljna geometrija, visoka otpornost na abrazivno habanje, velika mehanička čvrstoća i žilavost itd. Faktori na koje se mora obratiti pažnja pri konstruisanju su geometrija zuba, dimenzionisanje zuba, izbor materijala, montaža zuba na vedrici I tehnologija njegove izrade. Zbog toga je proces konstruisanja reznih zuba kod bagera kontinualnog dejstva vezan za sledeće probleme: a) Kompleksnost procesa konstruisanja vezana za visok nivo korelacije osnovnih svojstava konstrukcije, zbog čega su krajnji izgled, dimenzije i tehnologija izrade reznih zuba veoma osetljivi na tekuće izmene tokom procesa konstruisanja; b) Veliki uticaj specifičnih zahteva korisnika i težnja unikatnoj proizvodnji, zbog čega je pored fleksibilnosti u tehnologiji izrade, neophodno je obezbediti fleksibilnost u svim fazama realizacije reznih zuba, počevši od rane faze razvoja i procesa konstruisanja; c) Složenost definisanja spoljašnjeg opterećenja i usvajanje odgovarajućih pretpostavki, kao osnova pri proračunu nosivosti i optimizacije oblika reznih zuba; d) Specifičnost tehnologije izrade reznih zuba, koja se ogleda u definisanju velikog broja kompleksnih tehničko-tehnoloških parametara livenja; e) Izrada fizičkog prototipa reznog zuba zahteva značajno vreme pripreme i realizacije, dok je ispitivanje fizičkog prototipa na bageru u eksploatacionim uslovima otežano i zahteva značajne vremenske i finansijske izdatke. Postojeća znanja i odgovarajuća literatura ne objašnjavaju i ne daju preporuke za rešavanje predhodnih problema. Zbog toga ne postoji sistemski pristup, pa se proces konstruisanja izvodi na bazi iskustva i minimalnih poboljšanja postojećih rešenja, koristeći se pri tom grubim pretpostavkama i izvođenjem zaključaka bez ulaženja u suštinu problema. Ovakav pristup predstavlja problem u trenutku kada se želi napraviti iskorak i generisati konstrukciono i tehnološki bolje rešenje reznih elemenata, kao što je to slučaj sa razvojem nove generacije modularnih reznih zuba. U okviru doktorske disertacije razmatrana je problematika uvođenja sistemskog procesa konstruisanja reznih elemenata, kroz koncept integrisanog razvoja proizvoda. Ovakav pristup predstavlja alternativu postojećem stanju procesa razvoja reznih elemenata, koji se na relativno jednostavan način može inkorporirati i primeniti u proizvodnom procesu. Cilj primene integrisanog pristupa konstruisanja je u tome da pre same izrade reznog elementa postoji jasna predstava o tome kako će proizvod izgledati, kako i na koji način će usvojena tehnologija proizvodnje uticati na krajnji kvalitet, kako će se ponašati u radnim uslovima i dr. Takođe, obezbeđuje se prednost koja se ogleda u smanjenju troškova, samim tim što se u većem delu analize tokom konstruisanja koriste CAD/CAE/CAM alati, čime se značajno smanjuje vreme potrebno za testiranja u laboratoriji ili eksploatacionim uslovima. Sa druge strane, smanjuje se vreme od trenutka postavljanja zahteva za proizvodom do njegovog dolaska na tržište, jer se smanjuje broj razvojnih ciklusa, automatskim odbacivanjem nezadovoljavajućih rešenja konstrukcije. Težište ovakvog pristupa se prenosi na konceptualno projektovanje I preliminarno konstruisanje, čime se utiče na kasnije smanjenje broja konstrukcionih izmena I izmena u proizvodnom procesu. Ovakvim pristupom se obezbeđuju osnovni uslovi i realizuje težnja ka unikatnoj proizvodnji reznih elemenata, posebno prilagođenih specifičnim uslovima radne sredine, bageru, vedrici, itd.

The process of digging in continuous excavators is directly performed by the buckets with cutting elements (cutting teeth and bucket knife) which are positioned on the front of excavators. In order to destroy rock material, it is necessary to exert sufficient force on it, which is dependent on the type of rock material, digging technology, shape of cutting elements, etc. The edges of cutting teeth settle on limited surfaces of rock material and exert pressure sufficient for their destruction. By the use of cutting teeth the available cutting force is concentrated on a small cutting length, thus facilitating the penetration of the entire bucket into the material. The destroyed material is lifted into the bucket by way of appropriate surfaces of cutting elements. In order to properly perform their basic function, cutting teeth must meet several requirements, such as appropriate geometry, high resistance to abrasive wear, high mechanical strength and resilience, etc. The factors that must be considered when designing are teeth geometry, teeth sizing, selection of materials, installation of the teeth on the bucket and its manufacturing technology. Therefore, the process of designing cutting teeth of continuous excavators involves the following issues: a) The complexity of the design process related to the high level of correlation between basic properties of construction, which is why the final appearance, size and manufacturing technology of cutting teeth are very sensitive to the changes in the design process b) Due to strong influence of specific demands of users and tendency towards unique manufacture, it is necessary to ensure flexibility both in manufacturing technology and at all stages of cutting teeth manufacture, starting with the early stages of development and design process; c) The complexity of defining the external load and adoption of appropriate assumptions as the basis for ascertaining the lifting power and optimizing the shape of cutting teeth; d) The specific technology of cutting teeth manufacture, which is reflected in defining a large number of complex technical and technological parameters of casting; e) Manufacture of a physical prototype of the cutting tooth requires considerable time for preparation and implementation, while the testing of the physical prototype on the excavator in exploitation conditions is difficult and requires both longer period of time and considerable financial expenditures. The existing knowledge and appropriate literature neither explain nor provide recommendations for solving the aforementioned problem. Due to the lack of a systematic approach, the manufacturing process is performed on the basis of experience and minimal improvement of existing solutions, using only rough assumptions and drawing conclusions without addressing the problem itself. This approach presents a problem when a more constructive and technologically advanced solution of cutting elements is to be produced, as is the case with the development of a new generation of modular cutting teeth. The issue addressed in this PhD thesis refers to the introduction of a systematic process of designing cutting elements, through the concept of integrated product development. Such an approach presents an alternative solution to the current state of the development process of cutting elements, which can be incorporated and applied in the production process comparatively easily. The main goal of applying an integrated approach to constructing is to form a clear idea of how the product will look like prior to manufacturing the cutting elements, how the adopted production technology will affect the ultimate quality, how it will function in working conditions, etc. Moreover, the advantage of this approach is reflected in the reduction of costs, on account of the fact that CAD/CAE/CAM tools are used in the major part of the analysis during the design. This significantly reduces the time required for the testing in laboratory or exploitation conditions. On the other hand, there is a reduction in the time starting from the moment of the product demand to its launch on the market, because the number of development cycles is reduced by automatic rejection of unsatisfactory design solutions. The focus of this approach is transferred to the conceptual design and preliminary construction, which affects the later reduction in the number of structural changes and changes in the production process. This approach provides the basic conditions and enables the tendency towards unique production of cutting elements, specifically tailored to the specific conditions of working environment, excavators, bucket, etc.