Nie udalo sie połączyć z bazą! EJPAU .
Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.

Volume 10
Issue 3
Topic:
ELECTRONIC
JOURNAL OF
POLISH
AGRICULTURAL
UNIVERSITIES
. , EJPAU 10(3), #09.
Available Online: http://www.ejpau.media.pl/volume10/issue3/art-09.html


 

ABSTRACT

The goal of this paper is to demonstrate the method of the application of the theory of the work of cutting distribution from the flat cutting to milling. Calculating the work of cutting and work of cutting components based on forces measured at flat cutting is easier but less precise, and the cutting conditions are less similar to the industrial ones. Determining the work of cutting distribution based on measuring of forces in milling gives more accurate and realistic results but there is a necessity to apply more complicated and expensive measurement equipment.

Key words: .

INTRODUCTION

One of the methods to describe specific work of cutting is to use the pendular labormeter [13]. The method is based on the usage of the energy of pendulum, where the tool is mounted, to cut. Two ways can be used in this method: single-cut principle, and multiple-cut principle. In single-cut method the loss of the energy used to cut of the single chip is measured. In the multiple-cut principle the whole energy of the pendulum is consumed to cut. In this case the specific work of cutting is calculated as energy of pendulum in relation to volume of wood turned into chips. The efficiency of the whole pendular labormeter has to be taken into consideration when calculating the specific work of cutting.

The other way to describe the specific work of cutting is to use the specific force of cutting which is measured for model parameters (pine wood, 13% of MC, 60° of cutting angle, sharp tool, 50 m·s-1 cutting speed etc.) and apply it to particular conditions with special conversion coefficients [15].

More practical description of the specific work of cutting is to measure the power of the main machine tool motor [7, 16]. This method can be applied in actual industrial conditions. The essence of this method is to measure the electrical energy, consumed by motor, to cut the known wood volume in known time. But, this method is less precise because of the motor and gear efficiency. Another disadvantage of this method is that in many cases the measured power changes consist only small part of the whole consumed energy, which can be the main source of mistakes.

Modern methods to calculate the specific work of cutting are generally based on measuring the cutting force. According to Orlicz [15] the cutting force is the force moving the knife in his motion direction which is needed to overcome the cutting resistance. The main and most important elements in the measuring equipment are actually the piezoelectric force sensors and the sequel of strain gauges. These kinds of sensors are the most popular in investigations [1, 3, 5, 8, 14]. The forces measured in this way are the base to the work of cutting calculation [9] and to calculate the work of cutting distribution to work of new surface creation (work of fracture/fracture toughness under “real-life” cutting conditions) and work of chip deformation [3, 10, 12, 17]. A direct relation between linear cutting and rotary cutting, in which rotary cutting was simulated based on linear cutting, was also investigated [4]. But the above mentioned measurement of cutting forces and calculation of work of cutting distribution were described and explained only in relation to flat cutting using the microtome technique. There are no publications about the methodology of calculating the work of cutting distribution in rotating cutting, i.e. milling.

The goal of this paper is to demonstrate the method of the application of the theory of the work of cutting distribution from the flat cutting to milling.

Work of cutting distribution in flat cutting

According to Huang et al. [9] the work of cutting consists in work of fracture (work of new surface creation) and work of chip deformation (work of curling) (Fig. 1). In flat cutting the work of cutting is described by the cutting force and the cutting path [12]:

       [J]
          (1)

 

Fig. 1. Graphical method for the determination of the cutting and plastic work [9]

This work, referred to the surface of cut material, defines work (energy) of cutting per surface unit (specific work of cutting):

   [J/m2]
    (2)

If the specific work of cutting relates to a few different thicknesses of cut layers, the plot on the Cartesian co-ordinate systems is a linear function y = ax + b, where “a” component is the specific work of chip deformation ED and “b” is the specific work of new surface creation ES. Thus, the equation of the work of cutting distribution is:

   [J/m2]
    (3)

where “h” is the chip thickness (in flat cutting the height of cutting layer).

Obviously, determination of the specific work of new surface creation is based on the theoretical extrapolation of the above mentioned plot to an intersect Y-axis. It means 0-thickness cut layer.

Practically, the distribution of the specific work of cutting is calculated from the forces measured during cutting on the microtome. The microtome technique makes it possible to reach a precise height of a cut layer, but the cutting speed is much lower then in actual industrial conditions [9]. Nevertheless, the results of the work of cutting, calculated in this way, can be easy applied in other ways of machining, because the microtome technique is an example of a cut with an elementary blade.

Work of cutting distribution in milling

In planning and milling chips have the “comma” shape [6]. The thickness of such chip is linearly changing from zero to maximum [18] (Fig. 2). According to this it is possible to apply the work of cutting distribution theory to milling. But in milling there is a possibility of calculating the work of cutting, work of new surface creation and work of chip deformation, based on the data from forces measuring during one chip creation. It is important that when a forces measurement is conducted during cutting with the “industrial” cutting speed, the time of single chip creation is very short. To achieve accurate force measurement results, the force sensors and the whole data acquisition equipment has to enable the data registration with the high frequency. For example, for a cutting speed about 50 m·s-1, cutting diameter 125 mm and a height of cutting layer 1mm, the time of single chip creation is about 0.22 ms. To obtain 10 readouts of forces in this time (to plot the force vs. cutting time dependence for a single cut) the acquisition equipment has to work with a 44.7 kHz frequency.

Fig. 2. Calculated chip shape and chip thickness as a function of time [18]: a-calculated chip shape, b-chip thickness as a function of time

In milling, the work of new surface creation can be calculated directly from the Fx force. As it is shown in Fig. 3, at the start of the chip creation (start of the new surface creation), there is only one force – Fx0. Thus, the Fx0 force is at this moment the cutting force Fc0, and there is no the repel force Fr. On the Fig. 4 the forces ordination at the mean chip thickness is shown. In this situation the feeding force Fx and the normal force Fy are non-zero. To calculate the cutting force Fc, the Fx and Fy must be pointed out. To varying the forces descriptions on Fig. 3 and 4 the “mean” index is added for forces at the mean chip thickness.

Fig. 3. Forces ordination in milling at the zero chip thickness (description at Fig. 4)

Fig. 4. Forces ordination in milling at the mean chip thickness
m) – measured, (c) – calculated
Fx – force parallel to feed [m]
Fy – force normal to feed [m]
Fo – outcomes force from Fx and Fz [c]
Fc – cutting force [c]
Fr – repel force [c]
Fx0 – Fx in the time of crack initiation [m]
Fc0 – Fc in the time of crack initiation [m]
D – cutting diameter
n – tool rotation direction
h – height of cutting layer
u – feed of material
ψ/2 – half of the cutting angle
δF – angle between Fx and Fo force

At a mean chip thickness, there are two forces, in two directions: parallel Fx mean and normal Fy mean to feed direction. To calculate the distribution of the work of cutting, the value of the cutting force Fc mean is required:

   [N]
    (4)

where

   [N]
    (5)

The value of the specific work of cutting in milling can be calculated as:

   [N]
    (6)

where “τ” is the length of the chip (length of the arc of the cut).

The value of the specific work of new surface creation can be calculated from the equation:

    [J/m2]
    (7)

And, the value of the specific work of chip deformation can be calculated as:

    
    (8)

where “hm” is a mean chip thickness.

Fig. 5. Feeding and normal forces measuring example for a single chip (on the basis of [18]): Fx0=Fc0 – feeding force when the crack starts, Fx max – feeding force at the maximum chip thickness, Fy max – normal force at the maximum chip thickness

In Figure 5 an example of the forces measuring for the single chip of MDF milling is shown. Sinn et al. [17] uses the Fx0 force to calculate the fracture toughness [2]. As it is shown in the figure, the normal force for the Fx0-time is non-zero. Sinn et al. [18] says that due to a small penetration angle of less than 11° it is correct to apply the chip-thickness-force model directly for the feeding force.

CONCLUSIONS

The work of cutting distribution theory came into existence as the method of the calculating of the work of new surface creation (work of fracture) and work of chip deformation, based on the force measurement results in flat cutting. Despite that the speed of cut in flat cutting, using microtome technique, is lower than cutting speed in industrial conditions, results of these calculations can be applied to other machining ways. Thanks to a lower speed of cut, there is a possibility of using less complicated and cheaper measurement equipment. The calculation of the work of new surface creation is a theoretical approximation of the chip thickness to 0, because there is probably no possibility of measuring the forces in cutting with 0-mm thin chip in practice.

As it is shown above, it is possible to apply the work of cutting distribution theory to rotary cutting such as planning and milling. Calculating the work of cutting, work of new surface creation and work of chip deformation based on the forces measured in rotary cutting is more realistic and more accurate. But to conduct investigations of the cutting speed which is similar to industrial cutting speed more complicated and modern force measuring equipment is required.

ACKNOWLEDGMENTS

The author is very grateful to dr Gerhard SINN, from the Institute of Physics and Materials Science, University of Natural Resources and Applied Life Sciences, Vienna, for helpful and pertinent remarks, and matter-of-fact discussions during preparation of this paper.

REFERENCES

  1. Aguilera A., Martin P., 2001. Machining qualification of solid wood of Fagus silvatica L. and Picea excelsa L.: cutting forces, power requirements and surface roughness. Holz a. Roh- u. Werkst. 59, 483-488.

  2. Atkins A. G., 2003. Modelling metal cutting using modern ductile fracture mechanics: quantitative explanations for some longstanding problems. Int. J. Mech. Sci. 45, 373-396.

  3. Beer P., Ede Ch., Gindl M., Stanzl-Tschegg S., 2002. Cutting tests of laminated particle board regarding work of fracture and chips plastic deformation. Wood Science and Engineering in the Third Millennium Proc. “Transilvania”, University Brasov, Romania.

  4. Beer P., Sinn G., Mueller U., Gindl M., Stanzl-Tschegg S., 2003. Influence of cutter blunting on milling of particleboard. Proc.16th IWMS. Matsue, Japan.

  5. Eyma F., Meausoone P. J., Martin P., 2004. Strains and cutting forces involved in the solid wood rotating cutting process. J. Mat. Proc. Technol. 148, 220-225.

  6. Fischer R., 2004. Micro processes at cutting edge-some basic of machining wood. Proc.2nd Int. Symp. Wood Machining. Vienna, Austria.

  7. Furukawa H., Tsutsumoto T., Banshoya K., 2003. Cutting performance of edge-sharpened diamond-coated milling tools. Proc. 16th IWMS. Matsue, Japan.

  8. Goli G., Marchal R., Uzielli L., Negri M., 2003. Measuring cutting forces in routing wood at various grain angles. Study and comparison between up- and down-milling techniques, processing douglas fir and oak. Proc.16th IWMS. Matsue, Japan.

  9. Huang X., Jeronimidis G., Vincent J.F.V., 2000. The instrumented microtome cutting tests on wood from transgenic tobacco plants with modified lignification. Proc. 3rd Plant Biomechanics Conf. Freiburg-Badenweiler.

  10. Kowaluk G., Dziurka D., Beer P., Sinn G., Tschegg S., 2004. Analysis of work of chip formation during cutting of blades with growing blunt. Proc. 4th Int. Conf. Chip and Chipless Woodworking. Stary Smokovec-Tatry, Slovakia.

  11. Kowaluk G., Dziurka D., Beer P., Sinn G., Stanzl-Tschegg S., 2004. Influence of ammonia addition on particleboard properties. Proc. 2nd Int. Symp. Wood Machining. Vienna, Austria.

  12. Kowaluk G., Dziurka D., Beer P., Sinn G., Stanzl-Tschegg S., 2004. Influence of particleboards production parameters on work of fracture and work of chips formation during cutting. EJPAU, Wood Technol. 7(1) www.ejpau.media.pl

  13. Marzymski W., 1961. Wpływ zawartosci kleju mocznikowo – formaldehydowego i cisnienia prasowania na wartosc pracy własciwej skrawania płyt wiórowych [Influence of the urea – formaldehyde glue content and the pressing pressure on the value of the specific work of cutting of the particleboards]. Przem. Drzew. 9(61) 22-25 [in Polish].

  14. McKenzie W. M., Ko P., Cvitkovic R., Ringler M., 2001. Towards a model to predict cutting forces and surface quality in routing layered boards. Wood Sci. Technol. 35, 563-569.

  15. Orlicz T., 1988. Obróbka drewna narzędziami tnacymi [Wood processing with the cutting tools]. SGGW-AR Warsaw [in Polish].

  16. Saljé E., Stühmeier W., 1988. Milling laminated chipboard with tungsten carbide and PCD. Ind. Diamond Rev. 4, 319-326.

  17. Sinn G., Beer P., Gindl M., Patsch R., Kisselbach A., Standler F., Stanzl-Tschegg S., 2005. Analysis of cutting forces in circumferential flat milling of MDF and particleboard. Proc. 17th IWMS. Fachhochschule Rosenheim, Germany.

  18. Sinn G., Beer P., Stanzl-Tschegg S., 2006. Analysis of cutting forces in circumferential flat milling of particleboard. Proc. Int. Conf. Integrated Approach to Wood Structure, Behaviour And Applications, Joint Meeting of the ESWM and COST Action E35. Florence, Italy.

 

Accepted for print: 28.08.2007



Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.


Nie udalo sie połączyć z bazą!