The effect of the rake angle and feed speed in planing on the surface roughness of beech.

Skaljic, Nedim ; Obucina, Murco ; Beljo-Lucic, Ruzica 等

1. INTRODUCTION

Beside physical, mechanical, and anatomical properties of the wood the quality of details and finished products is influenced by numerous factors like: direction of cutting, geometry of the blade and its sharpness, thickness of the cut part, lack of precision of the sharpening tool, technological parameters (speed of cutting, speed of movement, etc.). (Usta et. al., 2007). Quality of processing includes the precision of processing and quality of the processed surface. These two mutually dependent indicators of the processing quality, which depend on numerous factors, represent the most important conditions in achieving required quality of the product. Morphologic properties of the surface which was created through mechanical processing of the wood carries a lot of information on the quality of technological procedure with which the surface came to existence. Full understanding and evaluation of the geometric condition of the wood surface and wood material provides mostly technical information in solving the problems like capabilities of gluing, impregnation, strength of joints, control of the blade sharpness, and decrease of waste. The relation between the surface roughness and wearing of the tools is known (Koch, 1964). Monitoring of the roughness can provide valuable information on the condition of the blade and vice versa. The strength of the glued joints and other mechanical properties of the wood products are also dependent of the surface roughness (Marian et. al., 1958). Studies show that smooth surfaces require relatively small amount of paint for surface protection (Richter, 1995).

In the manufacturing process the occurrence of fault in processing is inevitable. If the deviations of the real properties of the quality are in the frame of tolerance boundaries, then the detail is considered to be properly processed in technological sense. But, it often happens that dimensions of the detail are within the tolerance boundaries, but that details are different in the quality of processed surface. The sanding is the most common and for surface quality processing most influential operation during the surface preparation phase. That is why this paper will research the influences of the processing regime of planning on the quality of the processed surface and possibilities to leave out the sanding operation through the use of appropriate processing regime using planning in the preparation of the surface.

2. MATERIAL AND METHODS

2.1 Test materials

Solid beech planks of 21 mm x 70 mm x 600 mm in size, the moisture content of average 9.63% and with the grain orientation along the main axis of the specimen (parallel) were obtained from a local supplier in Croatia. However, structures of wood knotted are not avoided, which are the natural characteristics of the hardwoods. They were conditioned at a temperature of 20 [+ or -] 2[degrees]C and 65 [+ or -] 5% relative humidity. The beech with average density has been 664 kg/[m.sup.3].

Machining process was conducted with a cabinet planer (Weinig Powermat 400). Only the top spindle of the machine with two knives was used at 125 mm tool diameter. The knives were made of industry standard high-speed steel. The feed speeds used were 6 m/min, 12 m/min, 18 m/min and 24 m/min. The knife rake angles used were 15[degrees], 20[degrees] and 25[degrees] and a depth of cut of 2.0 mm.

2.2 Tests of wood surface roughness

For each experiment a total of 10 planks were used. Measurements in five different randomly selected spots of the surface from each plank were averaged. Surface roughness tests were conducted using a Mitutoyo Surftest SJ 201, and were carried out according to DIN 4768 [5]. Table 1 lists the characteristics of the tracing process. The values of the roughness were determined with a precision of [+ or -] 0 .01 urn.

The Mitutoyo Surftest SJ 201 which is being used for current research is shown in figure 1.

[FIGURE 1 OMITTED]

An example of the R profile obtained with our device is presented in figure 2.

[FIGURE 2 OMITTED]

3. RESULTS AND DISCUSSION

The Ra values obtained according to the samples and the principles mentioned above are given in table 2.

A relationship has been found in the present investigation that the surface roughness decreases when the feed rate decreases and lowest surface roughness is achieved with the rake angle of 20[degrees] (Fig. 3).

[FIGURE 3 OMITTED]

All data were analyzed by a computerized statistical software. In general, better results for the machining performance are obtained with the decreasing feed speed. In the open literature, it has been reported that increasing feed speed caused strong machining defects. The results (involving three rake angles and four feed rates) are given in Table 3.

4. CONCLUSIONS

In this work, effect of various machining of beech lumber on her surface roughness characteristics was investigated. In the light of preliminary results of this study, a stylus method can accurately be used to evaluate surface roughness of machined samples. Surface roughness of the samples exposed to different relative humidity levels and other machining properties of such species could be evaluated to provide an initial data for finishing applications.

5. REFERENCES

Koch, P. (1964). Wood Machining Processes. Ronald Press Company, New York 530p.

Marian, J.E.; Stumbo, D.A. & Maxey C.W. (1958). Surface texsture of wood as related to glue-joint strenght. Forest Prod. J. (12): pp. 345-351.

Richter, K.; Feist, W.C. & Knabe M.T. (1995). The effect of surface roughness on the performance of finishes. Part 1 Roughness characterization and strain performance. Forest Prod. J. 45(7/8):pp. 91-97.

Usta I., Demirci S., Kilic Y., (2007), Comparison of surface roughness of Locust acacia (Robinia pseudoacacia L.) and European oak (Quercus petraea (Mattu.) Lieble.) in terms of the preparative process by planing. Building and Environment, 42, pp. 2988-2992.

*** DIN 4768 (1990). Determination of values of surface roughness parameters, [R.sub.a], [R.sub.z], [R.sub.max], using electrical contact (Stylus) instruments. Concepts and measuring conditions.

Tab. 1. Characteristics of stylus tracing

Tracing length ([L.sub.t]) 12,5 mm
Tracing speed 0,5 mm
Pick-up length ([[lambda].sub.c]) 2,5 mm
Stylus tip radius 5 [micro]m
Stylus tip angle 90[degrees]

Tab. 2. Arithmetic means ([micro]m) of the surface roughness
values according to the test variables

 Cutting Operation Rake Feed speed Arithmetic
direction angle (m/min) Means
 ([degrees]) Ra ([micro]m)

 6 4,58
 15 12 5,76
 18 6,07
 24 6,35

 Radial Planing 20 6 3,86
 12 5,16
 18 5,68
 24 6,18

 25 6 4,46
 12 5,19
 18 6,47
 24 6,85

Tab. 3. The results of analysis of variance for surface roughness
indicating significant effects for the influencing factors of the
rake angle (A) and feed rates (B)

 i j MI VAR SD

 1 1 4,581 1,176 1,085
 1 2 5,756 1,739 1,319
 1 3 6,067 1,041 1,020
 1 4 6,348 1,300 1,140
 2 1 3,856 0,881 0,938
 2 2 5,163 1,165 1,079
 2 3 5,676 1,591 1,261
 2 4 6,184 1,417 1,190
 3 1 4,461 1,178 1,085
 3 2 5,191 0,928 0,963
 3 3 6,471 1,278 1,130
 3 4 6,854 1,260 1,122
Sources SS dF MS F
 A 33,181 2 16,591 13,314
 B 405,080 3 135,027 108,358
 AB 21,135 6 3,522 2,827
 ER 732,714 588 1,246
 T 1192,110 599

Factor A

A[1]=1137,600 [A.sub.sr]=5,688
A[2]=1043,930 [A.sub.sr]=5,220
A[3]=1148,850 [A.sub.sr]=5,744
i=1 j=2 t= 3,758
i=1 j=3 t= 0,451
i=2 j=3 t= 4,210

Factor B

B[1]=644,870 [B.sub.sr]=4,299
B[2]=805,520 [B.sub.sr]=5,370
B[3]=910,680 [B.sub.sr]=6,071
B[4]=969,310 [B.sub.sr]=6,462

i=1 j=2 t= 4,443 i=2 j=3 t=4,872
i=1 j=3 t=12,316 i=2 j=4 t=7,589
i=1 j=4 t=15,032 i=3 j=4 t=2,716

DF: degrees of freedom, SS: sum of square, MS: mean of
square