Researches concerning friction influence on material flow in inverse extrusion of toothed gears.

Butnar, Lucian ; Pop, Nicolae ; Cioban, Horia 等

The paper presents aspects concerning material flow in manufacturing process of toothed gears, through inverse extrusion. The tribo-system of plastic deformation punch-toothed gear-active plate is very complex and it is characterized by elementary couples of friction that compose it. Friction punch-material and material-active plate has a great influence on material flow quality, extrusion process and on roughness of manufactured internal teeth. The researches present the way in which utilization of different lubricants on contact surfaces deformation tool-piece may have a favorable influence on flow quality and on manufactured toothed gear. Key words: extrusion, internal gear, flow, friction

1. INTRODUCTION

Extrusion of toothed or grooved pieces is a volume pressure procedure in which under the compression force action of punch, the material solicited on three-dimensional compression has to take through plastic flow, the space between punch and plate--figure 1. The punch is toothed and it generates copying, the teeth of internal toothed gear; the plate is smooth and it has circular contour. Depending on toothed gear material, used machinery, dimensional precision, form and the needed surface quality, extruded teeth, can be realized on cold, semi-warm and warm. The processed toothed gears measurement is limited especially by needed deformation forces which are very high (Tapalaga et al., 1986). These high forces need powerful equipments and also high price. Therefore, the procedure is applied especially in great series production. Extrusion procedure is used for a large scale of materials: plastics, metals and non-ferrous alloys and carbon and allied steels with low carbon equivalent content. Researches on inverse extrusion are less than researches for direct extrusion (Popa & Neagu, 1993) and those for inverse extrusion of pieces with thick walls and internal teeth are almost non-existent.

2. DEFORMATION TRIBO-SYSTEM

The bibliographic study shows the inter conditioning between: material flow for teeth forming, components in contact, these components characteristics, works environment, deformation tool roughness, toothed gear precision, technological process parameters multitude. These interdependences impose a systemic abortion for inverse extrusion process of internal toothed gears.

[FIGURE 1 OMITTED]

Comprising of elements, functions and levels into a unitary form, based on systems theory (Czihos, 1978) will conduce to a "building model" construction: definition for deformation tribo-system for inverse extrusion of a toothed gear--figure 1. During plastic deformation process, there are initializing and developing tribo-contacts between tool and gear surfaces, the ensemble tool-piece becoming a complex couple for plastic deformation. This complex couple and component elementary couples--table 1--have peculiarities to friction couples, which are characteristics for functioning machine elements:

* couples are submitting by very strong stress that produces material flow;

* mechanic characteristics are complete different--"strong" component (tool) is stressed in elastic domain and the "soft" component (piece) is stressed in plastic domain, through hardening;

* elementary deformation couples are instantaneously "strong" component is permanent and the "soft" component is other in each moment, being replacing by flowing, with new material stratums;

* deformation couple is very complex, having a numerous elementary couples (6) that will determinate a complex material flow and numerous influence factors;

* complex deformation couple comprises a fundamental elementary couple (superior couple of class II, stressed by deformation forces with essential roll for material flow, teeth forming and its quality), numerous (3) principal elementary couples (inferior couples of class III, stressed by friction forces or deformation force components); the others are secondary elementary couples (inferior couples of class IV, with negligible influences on teeth but important for interior material stratums flowing).

3. STUDY OF MATERIAL FLOW

The process is characterized through unitary efforts of intense spatial compression [sigma] > [[sigma].sub.c] needed for material flow through space between punch and active plate. Based on plasticity theory, it was realized tensions state scheme deformation state scheme on infinitesimal element with cubic form considered in different zones of material. On these volume elements it was established distribution of principal unitary efforts [[sigma].sub.x], [[sigma].sub.y], [[sigma].sub.z] and distribution of specific deformations [[epsilon].sub.x], [[epsilon].sub.y], [[epsilon].sub.z] on the three principal directions x, y, and z - --figure 2. Inverse extruded material can be divided (Butnar & Cioban, 2005) in four distinct zones:

* zone 1--deformation focus--placed under stamp, with [h.sub.f], depth, is strong strained on try-dimensional compression that produces reduces of element dimension on z direction and elongation on x and y directions;

* zone 2--placed under the punch level, in its exterior, strong strained and deformed where is registered reduces of element on y direction and elongation on x and z;

* zone 3--lateral wall of tubular piece with internal teeth;

* zone 4--non-extruded material.

Flowing stratums of material is influenced by some factors:

* extruded material and its proprieties;

* deformation grade;

* deformation speed;

* punch-material and material-active plate friction;

* produced piece dimensions.

Un-uniformity flowing of extruded material and toothed gear quality can be characterized by the quality indexed deformation focus high (Socaciu, 1996), relation 1:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)

where [[mu].sub.p], [[mu].sub.m] are friction coefficients between semi-product and punch and between semi-product and active plate, [beta] [congruent to] 1.1 ... 1.12--Lode coefficient; [epsilon]=[d.sup.2]/[D.sup.2]--deformation grade.

Growth of deformation focus high [h.sub.f1] means a superior quality of flank surface of teeth, of structural and physic-mechanical proprieties. In deformation process, is comprised a bigger volume of material. Difference between flowing speed of contiguous stratums is lower, deformation un-uniformity is attenuated and the risk for interior defects is much diminished.

4. EXPERIMENTATION RESEARCHES

Material flow process was researched through inverse extrusion of toothed gears with involutes internal teeth by modulus m=2.5 and z=28 teeth starting from a cylindrical semi-product with dimensions D=090 and H=30 mm. Material used was aluminum Al 99.5, semi-warm extruded, 265[degrees]C temp., on a hydraulic press PH200 with an extrusion mould, made through personal conception. Material deformation grade on reference diameter was [epsilon]=60.49%.

[FIGURE 2 OMITTED]

The punch and active plate were made of allied steel. Extrusion was in 4 different lubrication states of punch-material contact (friction coefficient [[mu].sub.p]) and material-active plate (friction coefficient [[mu].sub.m]): dry ([[mu].sub.p]=[[mu].sub.m]=0.64), with hydraulic oil H32EP ([[mu].sub.p]=[[mu].sub.m]=0.31), processing oil MET P1C ([[mu].sub.p]=[[mu].sub.m]=0.30) and graphite on oil support MET P1C, granulation 1 ... 2 [micro]m, ([[mu].sub.p]=[[mu].sub.m]=0.24). For flowing research and friction influence, the semi-product was made by 2 semi-cylinders and on separation plane was traced, by a pantograph milling machine, a fine rectangular net, with side 2.5 mm, precision 0.01 mm, canal width 0.5 mm and depth 0.3 mm.

Extrusion process has modified the net lines. Into separation plane, there was an complex flowing in concordance with the theoretical results. High determination of deformation focus [h.sub.f] was made by a measurement instrument through co-ordinate ZKM 05-250D, with precision 0.5 [micro]m, between internal frontal surface of toothed gear and the last "horizontal" line of the deformed net. Focus measurement was made on separation plane of teeth root and teeth tip, with the next results--figure 3.

5. CONCLUSION

Deformation focus grows with tool-piece friction reducing, that favors a uniform flow and a gear with unitary structure and proprieties. On lateral wall of gear are registered axial growths of "cell" that confirm material elongation. The "cells" growths higher in inferior part ([approximately equal to] 0.6 mm) and reduced in superior part ([approximately equal to] 0.08 mm). Lubricant presence favors deformation, "cell" growths being higher on graphite and reduced on mineral oils. Lubricant reduced deformations non-uniformity. On dry friction, on toothed wall of gear appear elongations of sliding lines very pronounced at a half of wall thickness. Using lubricant, this advance of central stratum, decreases. Deformation is most uniform using graphite, when the net lines remain approximate horizontal. The paper relieves the way which friction influences extruded material flow and piece quality. Future researches will analyze the phenomenon using method of finite element continued by flow PC simulation under tool-piece friction effect.

6. REFERENCES

Butnar, L., Cioban, H. (2005) Researches for material influence on quality indexes in inverse extrusion of toothed gears, Proceedings of Modern Technologies. Quality. Restructuring, Mazuru, S., pp.321-324, ISBN 9975-9875-4-0, Technical University of Moldova, May 2005, Chisinau

Czichos, H. (1978). Tribology, Elsevier Publishing Company, Amsterdam

Popa, A., Neagu, A., (1993). Influence of tilt angle of mould frontal surface on deformation ununiformity in direct extrusion. Proceedings of News in domain of technologies and warm manufacture machinery, pp. 52-56, Transylvania University, April 1993, Brasov

Socaciu, T., (1996). Researches and experiments cold exploitation of nonferrous alloys and steels using friction as active force, Ph.D. Thesis, Transylvania University, Brasov

Tapalaga, I., Berce, P. & Achimas, G. (1986). Metals cold extrusion, Dacia Publishing House, Cluj Napoca

Tab. 1. Elementary couples components of complex couple

 Elementary couples characteristics

 Elementary couple
 Contact type Force

[A.sub.III]--Toothed Generalized
 surface cylindrical [F.sub.p]--friction
 punch/material surface force

[B.sub.III]--Lateral Cylindrical [F.sub.p]--friction
 surface surface force
 plate/material

 [C.sub.III] Conical [F.sub.a]--deformation
([C.sub.II])*--Active surface force
 surface linear
 punch/material contact

 ([D.sub.II])*--Edge Linear [F.sub.a]--deformation
 punch/material force

 [E.sub.IV]--Frontal Plane F=[F.sub.p]+
 surface surface [F.sub.[alpha]]+[F.sub.n]
 punch/material Total force for extrusion

 [F.sub.IV]--Frontal Circular F=[F.sub.p]+
 surface plane [F.sub.[alpha]]+[F.sub.n]
 plate/material surface Total force for extrusion

 Elementary couples
 characteristics
 Elementary couple
 Couple class

[A.sub.III]--Toothed
 surface III Inferior
 punch/material

[B.sub.III]--Lateral III Inferior
 surface
 plate/material

 [C.sub.III] III Inferior
([C.sub.II])*--Active (II Superior)
 surface
 punch/material

 ([D.sub.II])*--Edge II Superior
 punch/material

 [E.sub.IV]--Frontal IV Inferior
 surface
 punch/material

 [F.sub.IV]--Frontal IV Inferior
 surface
 plate/material

Fig. 3. Variation of focus deformation with tool-piece friction

Focus high hf(mm)

 root tip

1 dry 11.06 13.91
2 H32EP 11.50 14.18
3 P1C 11.60 14.47
4 graphite 12.99 15.20

Note: Table made from bar graph.