Research Article | Open Access
Efficient Series Expansions of the Temperature Field in Dry Surface Grinding for Usual Heat Flux Profiles
In the framework of Jaeger’s model for heat transfer in dry surface grinding, series expansions for calculating the temperature field, assuming constant, linear, triangular, and parabolic heat flux profiles entering into the workpiece, are derived. The numerical evaluation of these series is considerably faster than the numerical integration of Jaeger’s formula and as accurate as the latter. Also, considering a constant heat flux profile, a numerical procedure is proposed for the computation of the maximum temperature as a function of the Peclet number and the depth below the surface. This numerical procedure has been used to evaluate the accuracy of Takazawa’s approximation.
Straight grinding is a machining process that produces a smooth finish on a flat surface of a workpiece. In this process, there are hard abrasive grits stuck to the peripheral area of the grinding wheel, which perform the cutting when it rotates at high speed, removing the surface layer of the workpiece (see Figure 1). Also, the workpiece moves at a certain feed rate with respect to the wheel and contacts the latter at the grinding area, which is wide (see Table 1 for the nomenclature used). Jaeger’s model [1, Sect. 10.7.VII] is commonly used to calculate the temperature field in dry grinding. In this model, a two-dimensional approach is considered, in which the coordinate system is fixed to the wheel and centered on the middle of the grinding area, as shown in Figure 1. In surface grinding, the cutting depth is small, whereby the grinding area is assumed to be flat in Jaeger’s model.
The time-dependent temperature field of the workpiece in Jaeger’s model satisfies the convective heat equation [1, §1.7(2)]subjected to the initial condition,and to the boundary conditionwhere denotes the Heaviside function and is the dimensionless heat flux profile going to the workpiece, which is normalized to unity,
The temperature field in the stationary regime is reached when ; thus it does not depend on , and it is denoted as . In the stationary regime, the solution of the above equations (1)–(3) is given by [2, Eqn. 6-1]where denotes the modified Bessel function of the second kind of zero order [3, Chap. 51].
We can rewrite (5) in dimensionless form, setting the following dimensionless quantities: , , , and (Peclet number), whereis a characteristic length. Thereby,
On the one hand, on the surface, that is, , (7) is reduced to and when is an analytic function, closed form expressions for the dimensionless temperature on the surface can be obtained :wherewherepolynomials in . For instance, for a constant heat flux profile,and according to (10)-(11), we have
It is worth noting that the -axis given in  is just in the opposite direction as the one given in Figure 1. For coherence, all the formulas in this paper are referred to the coordinate system given in Figure 1. From the results given in , similar formulas to (12) can be derived for other heat flux profiles normalized to unity (4). For instance, considering a linear heat flux profile, we have
Also, for a parabolic heat flux profile, we obtainand, for a triangular one,where
Expression (19) comes from the numerical evaluation of (18) and a parameter fitting of the maximum temperature. Takazawa uses (19) to estimate how the hardness of the workpiece changes beneath its surface
The scope of this paper is two-folded. On the one hand, we derive some series expansions to calculate the integral given in (7) for the heat flux profiles considered above (see Figure 2). It turns out that the numerical evaluation of by using these series is considerably faster than the numerical integration of (7). On the other hand, we will provide a numerical procedure to calculate that allow us to evaluate the accuracy of Takazawa’s approximation (19).
This paper is organized as follows. Section 2 provides particular expressions of (7) for the different heat flux profiles considered above, that is, constant, linear, triangular, and parabolic. Section 3 is devoted to the calculation of the Taylor series of , whereby, taking , we get the main factor of the integrand given in (7). In Section 4, we use the result of the previous section to express as a series expansion for the different heat flux profiles considered in this paper. From these series expansions, we can recover the results given in (12) and (14)–(16) for the dimensionless temperature on the surface, that is, . As an example of this consistency test, we derive the latter for the case of a constant heat flux profile. Section 5 describes a quite efficient numerical procedure to calculate . In Section 6, we present some numerical simulations in order to compare the performance of the numerical integration of Jaeger’s formula (7) with the series expansions derived in Section 4 for the different heat flux profiles considered. Also, we evaluate the accuracy of Takazawa’s approximation (19) as a function of and . Finally, we collect our conclusions in Section 7.
2. Temperature Field for Usual Heat Flux Profiles
Consider now that is an analytic function within the contact area between the workpiece and the wheel; that is, ,
For a constant heat flux profile, thus (21) is reduced to
Taking into account the normalization condition (4), for a linear heat flux profile, we have hence
For a triangular heat profilewhere denotes the location of the apex in the triangular profile and is the following dimensionless parameter (see Figure 2):
Notice that when the heat flux occurs in an arbitrary interval, say , the dimensionless temperature is given bywhere and are both dimensionless parameters. Since the heat equation is linear, the temperature field that generates in the workpiece is given by the superposition of both parts of (27). Therefore, taking into account (29), we have
We can rewrite as follows:where we have set
Finally, for a parabolic heat flux profile, whereby
3. Taylor Expansion of the Integrand
In order to calculate , which is defined as an integral in (22), consider this more general form of the same integral,thereby
To expand in series, we calculate first the Taylor series of . For this purpose, according to [16, Eqn. 1.14.1(4)], we have this formula for the th derivative
Since the Taylor expansion of an analytic function is according to (37), we have
To calculate the radius of convergence of (39), let us set so, applying the ratio test, we have to determinate when , where
By using the asymptotic formula [17, Eqn. 10.41.2],we calculate (42) aswhere we have taken the definition of number [18, Eqn. 1.2]. Therefore, (39) converges absolutely when . Notice that we can convert (39) into (40) exchanging and , so (40) converges absolutely when .
4. Series Expansion of the Temperature Field
4.1. Calculation of
First, note that, performing the change of variables on the LHS of (48), we obtain thus
Therefore,where we have defined the following polynomials in :
Note that the degree of polynomial is and of polynomial is . According to Section 2, we need to calculate for ; thus we are going to derive particular expressions of for and , when . Thereby, taking , (49) is reduced to
Similarly, for , (54) is reduced to
Finally, for , we arrive at
4.2. Calculation of
For the calculation of the integral given in (47), we apply the definition of the lower incomplete gamma function [3, Eqn. 45:3:1]: so that, straightforwardly, we obtainand, performing the change of variables , we have
4.3. Calculation of
Applying the property given in (51), we have six different cases for the calculation of in terms of and . For the sake of clarity, here we use the following simplified notation: .that can be reduced to only three cases,
4.4. Calculation of
Now, we collect the previous results in order to calculate the dimensionless temperature field for the different heat flux profiles considered in the Introduction. First, consider a constant heat flux profile; thereby, according to (24) and (36), we have
Notice that, taking in (51), we have
Similarly, from (64), define
Similarly, from (64), define
For the parabolic case, we can follow similar steps as in the linear case, arriving at
Finally, taking into account (66) and using the above results for and , the dimensionless temperature field for , is calculated as follows:where
It is worth noting that is calculated properly with the formulas given for and in (75) and (78) when . Therefore, care has to be taken when we compute the dimensionless temperature for the triangular case as , as stated in (31).
Notice also that, in order to calculate the dimensionless temperature , we need to compute the series given in (70), (75), and (79) for and (71), (78), and (80) for . These series are all alternating series, which converges slowly when . However, we can accelerate the convergence of these alternating series by using Cohen-Villegas-Zagier algorithm . This algorithm approximates an alternating series as a weighted sum of the first values of by using a “Padé type approximation,” as long as is a reasonable well-behaved sequence. We will see in Section 6 that we need a small number of terms in order to get a good accuracy.
4.5. Temperature on the Surface
As mentioned before in the Introduction, can be calculated in closed form for the heat flux profiles considered in this paper. All these results can be obtained from the results of Section 4 taking . As a consistency test, we are going to derive here the expression given in (12) for a constant heat flux profile. For this purpose, note that when , the series given for , that is, (47), vanishes; thus, according to (35), we have
According to the limiting forms [17, Eqn. 10.3.2-3], we haveso that
Finally, according to (67) and applying again (51), the dimensionless temperature on the surface is which is equivalent to (12), taking into account (93). Therefore, for the computation of the temperature field with the series expansions given above, we will use directly the closed form formulas given in (12) and (14)–(16).
5. Maximum Temperature Beneath the Surface
As aforementioned in the Introduction, we present in this section a numerical method to compute the maximum temperature as a function of the Peclet number and the dimensionless depth below the surface, that is, . For this purpose, note that the integrand of (18) is positive, since , [19, Note ]. Therefore,
Also, directly from (95), we have
The behavior of given in (95) and (96) is shown graphically in Figure 3. Moreover, for each , exhibits and unique extreme value that matches the maximum value. Therefore, we can search for the maximum temperature at a given depth looking for the extreme value of as a function of , solving for the equation