THE EFFECT OF THE SPINDLE SYSTEM ON THE POSITION OF CIRCULAR SAW TEETH A STATIC APPROACH

Transcription

1 TRIESKOVÉ A BEZTRIESKOVÉ OBRÁBANIE DREVA THE EFFECT OF THE SPINDLE SYSTEM ON THE POSITION OF CIRCULAR SAW TEETH A STATIC APPROACH Roman Wasielewski - Kazimierz A. Orłowski Abstract In the paper causes and error analysis o circular saw teeth positions in relation to the workpiece in static conditions are presented. Mentioned errors originate rom the circular sawing machine spindle system. For the exemplary circular saw spindle system determined error values are perormed. Key words: circular sawing machine, spindle system INTRODUCTION Sawing o wood with circular saws is a typical example o cutting with multi-blade tools. In that kind o cutting, the position accuracy o ollowing tool blades is a crucial actor which aects a cutting process and machining inal eects. Position tooth errors may cause: deterioration in cutting conditions, changes in loads o individual teeth and the tool as a whole, and also a decrease in accuracy and surace quality ater cutting. Circular saws belong to the group o multi-blade tools and are highly sensitive to position tooth errors in the cutting process. Changes in tooth loads may cause their additional position errors, and intensiy disadvantageous cutting eects because o a small value o the circular saw stiness [3]. The tooth position errors may by analysed in the static or dynamic conditions. In the static system, the tooth position is an eect o the tooth position accuracy in the saw blade, accuracy o clamping on the spindle, and the spindle axis o rotation static accuracy. In dynamic conditions, cutting system vibrations caused by cutting orces and dynamic orces originating rom spindle rotary motion are additional actors aecting position o the teeth. However, these orces are a unction o the static teeth position. Hence, the static analysis is a basis or determination o the spindle system eect upon the circular saw tooth position during sawing process. CIRCULAR SAW TOOTH POSITION ERRORS IN THE SAWING SYSTEM In the sawing system the circular saw tooth position errors in relation to the workpiece depend on tooth position errors in relation to its axis o rotation, and also position errors o the axis o rotation in relation to the assumed working plane P (Fig. 1). In these two cases, the spindle system greatly eect on mentioned error values.

2 306 THE EFFECT OF THE SPINDLE SYSTEM ON THE POSITION OF CIRCULAR SAW TEETH... The position o the circular saw axis o rotation is an eect o the whole spindle system deormation during sawing process (Fig. 1). Y Z M X P Pe YZ p FN XZ p y F x Fig. 1. Deormation o the circular sawing machine spindle system It is assumed that in the theoretical (rigid, undeormable) system, the circular saw is located in the assumed working plane P. This plane is perpendicular to the spindle axis o rotation Z and parallel to the assumed eeding direction v. In the true system, spindle loads reerred to the spindle axis o rotation (geometrical axis), caused by the resultant cutting orce F and the orce F N (originating rom the driving system), produce both deormation o the spindle and the bearings. Thus, the saw blade position changes and relocates to the working plane P e as a result o these displacements. The position o the working plane P e in relation to the assumed working plane P may be determined in two the most characteristic or sawing directions: assumed eed speed direction X and in direction Y perpendicular to the latter (X). In dependence o both the cutting orce action direction angle Ψ and the angle o the driving orce direction Ψ, spindle end displacements x and y, and also tooth displacements XZ p and N YZ p in two characteristic directions may have dierent values. In the examined static approach displacements o the axis o rotation depend mainly on [1]: - actors connected with the load system cutting orces and driving orces; - actors connected with the spindle longitudinal and crosswise dimensions, - actors connected with bearings a bearing type and initial stress. Tooth position errors in the sawing system, besides the circular saw blade displacement to the working plane P e, may additionally arise rom the radial run-out and the axial run-out o teeth in relation to the circular saw working plane P e (Fig. 2).

3 ROMAN WASIELEWSKI - KAZIMIERZ A. ORŁOWSKI 307 a) b) Bo tot. 0,5 Bot 0,5 Bou 0,5 Bop Bp tot. Dp Op dw 0 0' 0,5 (Tw+To) 0,5 Bw 0,5 Bp e tot. D P D T d Tw+To L Fig. 2. Circular saw teeth position or collar clamping system on the spindle: a) tooth radial run-out, b) tooth axial run-out In commonly known designs o circular sawing machine spindles the saw is directly seated on the pin spindle (Fig. 2a), which an axis o rotation is placed in the point 0. The radial tooth position accuracy is a result o the machine ixing and saw clamping elements quality o work. The value o this accuracy depends on; - radial run-out o the spindle pin Bw, - dimensional tolerance o the spindle pin diameter Tw, - dimensional tolerance o the saw hole To, - radial run-out o teeth in relation to the saw hole Bp. Furthermore, assuming that inaccuracies o the machine ixing and saw clamping elements quality o work in the radial direction are an eccentricity in character, thus, the saw teeth geometrical centre occupies location at point 0, which is remote rom the axis o rotation at a distance o the total eccentricity e tot., and saw teeth have radial run-out o Bp tot. In many cases, the clamping accuracy o the circular saw in the axial direction is even worse. It concerns mainly systems in which the circular saw is directly ixed on the spindle pin, or i it is seated with the additional use o the adapter ring (additionally dimensional tolerances o both the outside diameter and the inside diameter o the adapter ring should be taken into account). In the commonly used designs o circular sawing machine spindles, the circular saw is ixed in the axial direction with the use o the sliding headed bush (sliding collar), which is seated on the spindle pin (Fig. 2b). I the axial pressure is unsymmetrical to the collar, in

4 308 THE EFFECT OF THE SPINDLE SYSTEM ON THE POSITION OF CIRCULAR SAW TEETH... relation to the spindle axis, the circular saw may take up the position as in Fig. 2b. In these conditions an axial accuracy o the circular saw teeth is a result o the machine ixing and saw clamping elements quality o work, and its value depends on: - collar axial run-out Bou caused by an angular rotation o the collar (angle α at the collar length L in the ranges o the sum o the spindle pin dimensional tolerance Tw and the collar hole To; - collar axial run-out Bot caused by axial run-out o the collar in relation to the collar hole; - axial run-out o teeth in relation to saw blade Bop. Cleanness o the saw blade suraces and collar suraces is an another signiicant actor aecting circular saw ixing accuracy. Local impurities on these suraces may cause additional teeth displacements in the axial direction, which values are a unction o the ratio o the outside circular saw diameter to the collar diameter D p /D T. ANALYSIS OF TEETH POSITION IN THE SAWING SYSTEM An example o the eect o the circular sawing machine spindle system upon position o circular saw teeth in the sawing system is perormed in Fig. 3. For the traditional design issue o the spindle system (Fig. 3a) there are shown positions o circular saw teeth in the Fig. 3b. In the presented example o wood cutting with rotational speed n, when the process consumes cutting power P c, the resultant cutting orce F and the driving orce F N have values as in Fig. 3b. It was also assumed that: these orce action directions are parallel to each other, their senses are the same and spindle bearings are rigid. In these conditions, a spindle delection causes movement o the circular saw to the plane deined with the displacement o the spindle axis o rotation F and teeth displacement p. Values o these displacements are perormed in Fig. 3b [2]. Mentioned displacements originating orm the spindle delection are totalized with position inaccuracies arising rom the method o clamping o the saw on the spindle, and also with inaccuracies o teeth positions in the saw blade. For the analyzed sawing design system values o the total teeth axial run-out Botot and teeth radial run-out Bptot are presented in Fig. 3b [4]. These values were estimated on the basis on the commonly used, by the circular saw producers, dimensional tolerances o the quality o work. On the grounds o the presented analysis it is visible that or the common applied issues o circular sawing machine spindle systems total values o the spindle delections, radial run-out and axial run-out o teeth reach considerable values. The component o delection caused by the driving orce has the biggest value among other constituents. Unloading the driving system as it is shown in Fig. 3c, the spindle orm the driving system is only loaded with a torque without the bending moment (originating previously rom the driving orce F N ). This solution signiicantly improves the circular saw position in the cutting process. Furthermore, in this design a value o the teeth axial run-out is irst o all a unction o the saw clamping method. Limitation to the minimum o the ixing element number may also reduce a value o the tooth run-out (Fig. 3c). The urther improvement o the system accuracy needs an increase o both the circular saw quality o work and the spindle accuracy.

5 ROMAN WASIELEWSKI - KAZIMIERZ A. ORŁOWSKI 309 a) b l a d dw Dp Dt Dp = 400 b = 65 Pc = 6 kw Dt = 125 l = 381 n = /min d = 30 a = 85 dw = 35 p b) = 0,028 F = 90 N p = 0,085 FN = 1112 N Bo tot = 0,418 Bp tot = 0,111 Bp tot Bo tot F FN P Pe c) Bp tot P Bo tot Pe = 0,002 F = 90 N p = 0,005 FN = 0 Bo tot = 0,144 Bp tot = 0,111 F Fig. 3. Analyses o circular saw teeth positions: a) spindle system, b) teeth position errors o the spindle orm Fig. 3a, c) teeth position errors o the modernized spindle system (unloaded with a bending orce rom the driving system)

6 310 THE EFFECT OF THE SPINDLE SYSTEM ON THE POSITION OF CIRCULAR SAW TEETH... RESULTS In the sawing system the circular saw tooth position errors in relation to the workpiece depend mainly on tooth position errors in relation to its axis o rotation, and also position errors o the axis o rotation in relation to the assumed working plane P. The position o the working plane is irst o all a unction o the spindle system stiness and the motion transer method. Moreover, values o axial run-out and radial run-out o the circular saw teeth depend on the saw clamping method on the spindle and quality o work o the whole spindle system. REFERENCES [1] KOCH J., ILCZYSZYN J., KRZYŻANOWSKI J., 1982: Wrzeciona obrabiarek (Machine tool spindles, in Polish). Wydawnictwa Naukowo-Techniczne, Warszawa, 220p. [2] ORŁOWSKI K., 2005: Analyses o static displacements o a spindle applied in typical circular sawing machines. Annals o Warsaw Agricultural University : Forestry and Wood Technology. No 57, pp [3] STAKHIEV J.M., 2000: Today and tomorrow circular saw blades: Russian version. Holz als Roh- und Werksto Vol. 58: [4] WASIELEWSKI R., 2005: Clamping precision o a circular saw blade on a spindle o a sawing machine. Annals o Warsaw Agricultural University: Forestry and Wood Technology. No 57, pp