Reserches regarding the choosing of the type device for long cylindrical surfaces rotorolling.

Sava, Ovidiu ; Lupescu, Octavian ; Popa, Ionut 等

1. INTRODUCTION

The solutions diversity that can be used in the devices construction for superficial cold plastic deformation (SCPD) process applications through rolling or rotorolling is relatively high, this work imposing, at one moment, to take some decisions to use any type of device to process the distinguished piece surfaces. There are known the Saturov researches in rotorolling area concerning the usage, as a rolling tool, of a long cylindrical roll that realize a principal rotation motion, as well as, another rotation one, towards a normal piece surface axis, in the instantaneous tool-piece contact point (Saturov, 1979).This solution, proposed and patented by Saturov, can be accepted as a "history" for the rotorolling appearance and respectively, as a mechanical hardening process for metallic surfaces.

The author's proposed new method consists in a technological equipment for SCPD through rotorolling, in figure 1 being possible to follow the working head principle kinematic schema.

This is endowmented with 3 cylindrical rolls, frontal cam type, star connected, executing a [n.sub.c] rolling motion towards the main head axis. The used rolls also recive:

--a [n.sub.s] rotation motion around their axis, due to the friction contact with the working piece, whose speed is [n.sub.p];

--a [s.sub.t] low ampliude alternatig rectilineal motion, due to a pusher contact with their frontal rolling surfaces, that also compress or relax an elastic element; finally it takes place a [n.sub.p1] rotation motion (planetary) of the entire rolls star, all around the central device axis.

[FIGURE 1 OMITTED]

The entire assembly realise also the [s.sub.a] displacement towards the piece, to obtain the rotorolling pressure force, together with the [s.sub.l] longitudinal head feed, on the pieces axis direction.

The planetary motion also determines a second rollers pass when, the B point arrives in the A initial position point but, not necessity, on the same elemantary unit piece surface. This depends by the longitudinal rolling head feed size and also, by the speed working piece.

2. APPLICATION AREA

The researches objective was from the beginning, the SCPD application trough rotoroling to rigid heavy shifts, on their smooth cylindrical surfaces without sills (panel drawing roller on). Especially it was followed the surfaces hardening through rotorolling, as well as to some working regim parameters values, the realization of any calibration and finishing of these. The speciality literature (Lupescu O. 1999) show that the process is possible to be used for individual and serial production, the hardening degree of the superficial layer (until 0, 5-1, 5 mm) exceeding in many cases 350 units HV (Lupescu O & Baciu M, 2002). Another objective of the author's researches was to choose one of the constructive variant which can be used, based on some criteria that can allow to give of an optimal final decision (Lupescu O, 2005). In this meaning the paper authors appeal to the "utility" concept, defined for the first time by Newmann and Morgenstern in 1947 and representing, the conventional rate-setted value gived by a governor to some variable, taking into account a certain estimation criterion.

3. METHOD USED

To elaborate the decision algorithm, the authors began, considering as a variable, the device constructive solution, the possible variants technically taked into account being: [D.sub.1]-unbalanced device for hardening long external cylindrical surfaces; [D.sub.2]- unbalanced device for hardening long external cylindrical surfaces and for the interface connector radius; [D.sub.3]-balaced device for hardening smooth cylindrical surfaces, short and long; [D.sub.4]-device for rotorolling with rigid contact, unbalanced, for long external cylindrical surfaces hardening.

The used criteria to estimate this variants were established as being: the constructive solution price [x.sub.1] (determining any production process) and respectively, total device rigidity [x.sub.2] (justified choise by his conection and dominant influence upon the processing precision and also, upon the obtained performances, in the case of this technological process application). In table 1 are gruped the known elements for these four analysed variants. The each constructive variant estimation, reported to the considerate criteria was noted with [x.sub.ij] = consequences, subscript parameters significance being as follow: the first one represents the solution estimation - i, and the second one, the criterion estimation - j. Rate-setting into 1 and 0 limits the [u.sub.ij] utilities, those can be rendered as subjective probability using the proposed variants for the SCPD device.

The values deduction of those utilities involves, first of all, the extreme adjustment for: [u.sub.12] = 1 (maximum utility) for the lowest cost and respectively [u.sub.31] = 0 (minimum utility) for the highest cost. For the other consequences, the utilities are granted proportionally with the respectively consequences, through linear interpolation, between the maximum and minimum utilities, using relation 1 and 2 (Lupescu O, 2005):

[u.sub.ij] = [x.sub.ij] - [x.sub.minj]/[x.sub.maxj] - [x.sub.minj] (1)

[u.sub.ij] = [x.sub.maxj] - [x.sub.ij]/[x.sub.maxj] - [x.sub.minj] (2)

The first relation can be applied for the utilities deduction, in the case in which these varies directly proportional with the consequences values and the second one can be used for those utilities granted inverse proportional with the consequences.

4. RESULTS

In the case of [x.sub.1] criterion, using those presented before and the reation 2, one obtain for [D.sub.1] and respectively [D.sub.2] devices:

[u.sub.11] = [x.sub.max1] - [x.sub.11]/[x.sub.max1] - [x.sub.min1] = 9400-5500/9400-3000 = 0,6 (3)

[u.sub.41] = [x.sub.max1] - [x.sub.41]/[x.sub.max1] - [x.sub.min1] = 9400-3700/9400-3000 = 0,89 (4)

Calculating also the utilities for the [x.sub.2] criterion, but using the relation 1, one obtains the results from table 2.

If for each estimated criterion is granted a significance [k.sub.j] coefficient, one can determine a sum utility for the [D.sub.i] variant, using relation 5:

u([D.sub.i]) = [m.summation over (j=1)] [k.sub.j] x [u.sub.ij] (5)

where:

--"m" is the number for the established criteria utilities and [k.sub.j] are the significance coefficients for the j criteria. These coeficients can be choosed in the way to verify relation 6:

[m.summation over (j=1)] [k.sub.j] = 1 (6)

In the mechanical cutting processing case the speciality literature (Bragaru A. & Stancescu C, 1977) recomands that [k.sub.1] > [k.sub.2], the cost determining, with priority, the choise of the technological variant, the processing precision being not so much related to the costs, but especially, to the cutting regim parameters and other factors. In the SCPD process the working device rigidity becomes the primary criterion (implied [k.sub.2] > [k.sub.1]), this essentially determining the performances obtained at the process application, more then the contact force (specific pressure between tool and piece), who became one of the work regim parameters. In this conditions, the coefficients importance weight, statically determinated, being: [k.sub.1] = 0,42 and [k.sub.2] = 0,58 (the difference between them being smaller than in the case of the cutting proceses because, in the rotorolling case, the device costs are bigger, fact that approach the cost importance between those of the device rigidity), one obtaine the sum utilities using the system:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (7)

One impose as an optimal decision the variant to which correspond the maximum sum utility, this being in this case the constructive solution [D.sub.4]. In the productive activity some consequences can appear with a value or another one, in some probability limits. Those can take more values depending by the concrete conditions in which the production process is deployed.

5. CONCLUSIONS AND FUTURE RESEARCHES

From [D.sub.1], [D.sub.2], [D.sub.3], [D.sub.4] devices, the constructiv solutions analaysis allows an optimal variant establishment, taking into account the following conclusions:

* the tool-piece contact type is necessary to be established through the device constructiv solution and influence both the rigidity and the costs measure of these;

* the rotorolling tools number from the device (1, 2 or more), through which one transmit the contact force on the processed piece, depends and is invers proportional with his rigidity;

* the future researches will be centered to increase the rotorolling force, using a tools-head with hidraulicaly constructive action;

6. REFERENCES

Bragaru A. & Stancescu C. (1977). Bazele optimizarii proceselor tehnologice- Indrumar de laborator (Bases of technological processes optimization--Laboratory handbook), Publsher Polytechnic Institute of Bucharest

Lupescu O., (1999). Netezirea suprafefelor prin deformare plastic (Surfaces polishing through plastic deformation), Publisher Technical--INFO, ISBN 9975-910-67-X, Chisinau

Lupescu O., (2005). Ingineria calitafii in procesele de deformafie plastica superficiala la rece (Quality engineering in cold superficial plastic deformation processes), Publisher Politehnium, ISBN: 973-621-104-5, Iasi

Lupescu O. & Baciu M. (2002). The characterization of mechanical treatment at SPD at cold through rolling as a tribological process, Proceedings of Meridian Engineering, pg. 29-32, ISSN 1683-853-X, Vol 12, No. 3, Chisinau

Saturov G.F. (1979). Sposob uprocineniia poverhnostei tilindriceskim instrument, Surfaces hardening method with cylindrical tool, Patent description nr. 662329

Tab. 1. Calculating utilities for [D.sub.i] variants
and [x.sub.j] criterion

VARIANTS CONSEQUENCES

 Criterion [X.sub.1] Criterion [X.sub.2]
 (cost-lei) (rigidity--daN /mm)

[D.sub.1] 5500 1220
[D.sub.2] 3000 1960
[D.sub.3] 9400 3500
[D.sub.4] 3700 3350

Tab. 2. Calculating utilities for [D.sub.i] variants
and [x.sub.j] criterion

VARIANTS CONSEQUENCES

 Criterion [X.sub.1] Criterion [X.sub.2]

[D.sub.1] 0,6 0
[D.sub.2] 1 0,3
[D.sub.3] 0 1
[D.sub.4] 0,8 0,9