CN102896660A - Non-delamination drilling method based on drilling force control for carbon fiber reinforced polymer (CFRP) laminate - Google Patents

Abstract

The invention discloses a non-delamination drilling method based on drilling force control for a carbon fiber reinforced polymer (CFRP) laminate. In the method, in a process of drilling a carbon fiber reinforced polymer (CFRP) laminate with a drill bit, the drilling axial force of the drill bit is controlled to be always smaller than a drilling delamination critical thrust value Fa, wherein Fa is determined by the following steps of: establishing a delamination stable state equation of the CFRP laminate; establishing a polar equation of a small-deflection sheet and a CFRP laminate defection formula of the drill bit during drilling to evaluate the maximum deflection value X of the CFRP laminate; establishing a bending deformation energy formula of the CFRP laminate during drilling, and evaluating the bending deformation energy U of the CFRP laminate during drilling of the drill bit; and determining a drilling delamination critical thrust value Fa according to the evaluated maximum deflection X, the bending deformation energy U and the established delamination stable state equation of the CFRP laminate. Due to the adoption of the method, non-delamination drilling processing of the CFRP laminate is realized, the delamination damage defect of drilling is avoided, the product quality is improved, the cost is lowered, and the efficiency is increased.

Description

Based on the carbon-fiber-reinforcomposite composite material layer plywood of drill thrust control without the layering boring method

Technical field

The present invention relates to a kind of brill processing method, be specifically related to a kind of carbon-fiber-reinforcomposite composite material layer plywood of controlling based on drill thrust without the layering boring method, belong to the Machining Technology field.

Background technology

Carbon fibre reinforced composite (Carbon Fiber Reinforced Polymer, be called for short CFRP) be a kind of novel take carbon or graphite fibre as strengthening the polymer matrix composites of body, because it has that intensity is high, specific stiffness is high, fatigue performance is good and advantage is widely used in making on the Advanced Aircraft the main force support structure spare such as designability is strong, such as parts such as aircraft covering, wallboard, wing intermediate beam, fuselage bulkhead and hatch doors.In the machining of CFRP, drilling is to use maximum, most widely used a kind of materials processing mode, also is simultaneously the final link of aerospace component assembling.The quality of drilling drilling quality is directly connected to assembly quality and the service life of whole aircraft.Because the characteristics such as the distinctive anisotropy of CFRP and interlayer contact intensity are low make it become a kind of typical difficult-to-machine material.In the CFRP boring procedure, except the drilling defective that traditional metal materials can occur (scale error in hole, deviation from circular from, site error, the error of perpendicularity etc.), also can produce the distinctive defective of composite, main manifestations is: entrance is peeled off layering, outlet layering, interlayer layering, is torn and burr, hole perimeter surface fiber extraction etc., and wherein delamination damage is topmost drilling defective.According to statistics, when aircraft is in the end assembled, because of the scrappage that causes of boring layering up to more than 60%.

CFRP laminate boring lamination defect is a kind of I type crackle (opening mode crack) that is caused by the drilling axial force and the debonding damage between layers that causes, thereby the key that realization is holed without layering is to control the thrust of CFRP laminate when the drilling layering, make it less than the critical thrust value that produces lamination defect, and then realize processing without the layering drilling.At present, the method that adds mostly by experiment the mathematics match of determining of relevant layering critical thrust value is found the solution indirectly, namely by measuring and record CFRP laminate drilling axial force value and corresponding lamination factor under different cutting parameters, then set up functional relation between axial force and the lamination factor by the numerical fitting method, and then the critical thrust value when solving without layering.The method is large for the initial data dependence, and solving precision often depends on the precision of collection capacity and the fitting function of initial data; And the delamination damage of CFRP laminate usually is not easy to observe and detect in the actual drilling processing, especially between layers delamination damage, the material that often needs a person with the qualifications of a general cuts and cleans and can observe by chemical agent, the experiment experience that when delamination area is determined, usually depends on again the operator, the human factor impact is larger, and experimental implementation is loaded down with trivial details and error is large.

Through the retrieval to existing document, do not find that so far the carbon-fiber-reinforcomposite composite material layer plywood is without the open report of layering boring method.

Summary of the invention

The object of the invention is to overcome the deficiency of existing carbon-fiber-reinforcomposite composite material layer plywood boring method, provide a kind of carbon-fiber-reinforcomposite composite material layer plywood of controlling based on drill thrust without the layering boring method, it is based on Plate Theory, fracture mechanics and Elasticity relevant knowledge, critical thrust value when determining different drill bit drilling CFRP by setting up the critical thrust model, and in reality boring control drill bit thrust less than this critical thrust value, and then realize the CFRP laminate without the layering Drilling operation.

The present invention is achieved by the following technical solutions:

A kind of carbon-fiber-reinforcomposite composite material layer plywood of controlling based on drill thrust is without the layering boring method, it is characterized in that, in the process of the described carbon-fiber-reinforcomposite composite material layer plywood of drill bit drilling, control the drilling axial force of described drill bit all the time less than boring layering critical thrust value F _a

Described boring layering critical thrust value F _aDetermined by following step:

The first step, set up the layering stable state equation of described carbon-fiber-reinforcomposite composite material layer plywood:

F _a·dX-ΔU-G _IC·dA＝0

Wherein, W is that the drilling axial force is done work along laminate amount of deflection direction,

Δ U is crooked potential energy,

F _aBoring layering critical thrust value,

DX be the carbon-fiber-reinforcomposite composite material layer plywood along the differential displacement of maximum defluxion on the drill bit direction of displacement,

G _ICBe on the I type crackle that is caused by axial force the critical crack on the per unit area propagate can,

DA is the elementary area of surface energy area, and this surface energy area refers to the delamination area maximum area;

Second step, the carbon-fiber-reinforcomposite composite material layer plywood is reduced to a thin-plate member, and the carbon-fiber-reinforcomposite composite material layer plywood deflection formula the when polar equation by setting up Thin plate under small deflection and drill bit drilling, obtain the maximum immunity value X of carbon-fiber-reinforcomposite composite material layer plywood;

The polar equation of described Thin plate under small deflection is:

$(\frac{{\∂}^2}{\∂r^2}+\frac{1}{r}\frac{\∂}{\∂r}+\frac{1}{r^2}\frac{{\∂}^2}{\∂{\mathrm{\θ}}^2})(\frac{{\∂}^{2}w}{\∂r^2}+\frac{1}{r}\frac{\∂w}{\∂r}+\frac{1}{r^2}\frac{{\∂}^{2}w}{\∂{\mathrm{\θ}}^2})=\frac{q}{D}$

Wherein, $D=\frac{E{h}^3}{12(1-{\mathrm{\μ}}^2)}$

D is the bending rigidity of carbon-fiber-reinforcomposite composite material layer plywood,

W be the carbon-fiber-reinforcomposite composite material layer plywood in the amount of deflection of drilling direction,

Q is the load that acts on the face unit are in the carbon-fiber-reinforcomposite composite material layer plywood;

Described laminate deflection formula is:

$w=\∫\frac{1}{r}\∫r\∫\frac{1}{r}\∫\frac{\mathrm{qr}}{D}d{r}^4+\frac{1}{4}A{r}^2(\ln r-1)+\frac{1}{4}B{r}^2+C\ln r+E$

Wherein, w be the carbon-fiber-reinforcomposite composite material layer plywood in the amount of deflection of drilling direction,

Q is the load that acts on the face unit are in the carbon-fiber-reinforcomposite composite material layer plywood,

A, B, C and E are undetermined constant;

Described maximum immunity value is:

$X=\underset{\max }{\lim }w$

Wherein, X is that the carbon-fiber-reinforcomposite composite material layer plywood is at the maximum immunity value of drilling direction;

The 3rd step, the flexural deformation of described carbon-fiber-reinforcomposite composite material layer plywood energy formula when setting up drilling, and according to the maximum immunity value X of the carbon-fiber-reinforcomposite composite material layer plywood of trying to achieve in the second step in the drilling direction, the flexural deformation of carbon-fiber-reinforcomposite composite material layer plywood energy U when obtaining the drill bit drilling;

Described carbon-fiber-reinforcomposite composite material layer plywood flexural deformation can formula be:

$U=\frac{D}{2}\underset{D_1}{\∫\∫}{(\frac{d^{2}X}{d{r}^2}+\frac{1}{r}\frac{\mathrm{dX}}{\mathrm{dr}})}^2\mathrm{dxdy}$

Wherein, U is the flexural deformation energy of carbon-fiber-reinforcomposite composite material layer plywood,

D is the bending rigidity of carbon-fiber-reinforcomposite composite material layer plywood,

D ₁Integral area,

X is that the carbon-fiber-reinforcomposite composite material layer plywood is at the maximum immunity value of drilling direction;

The 4th step, according to the flexural deformation of the maximum defluxion X of the carbon-fiber-reinforcomposite composite material layer plywood of trying to achieve in the second step, the carbon-fiber-reinforcomposite composite material layer plywood of trying to achieve in the 3rd step can U and the first step in the layering stable state equation of the carbon-fiber-reinforcomposite composite material layer plywood set up, determine boring layering critical thrust value F _a

The drilling axial force of the described drill bit of described control is all the time less than boring layering critical thrust value F _aTo realize by the drilling parameter of adjusting this drill bit.

Compared with prior art, the invention has the beneficial effects as follows: based on the basic reason of CFRP (carbon-fiber-reinforcomposite composite material layer plywood) boring delamination damage generation, pass through Plate Theory, fracture mechanics, the method that Elasticity and energy method combine, critical thrust model when deriving drill bit drilling CFRP, and then the critical thrust value can determine under specific bit and the certain material boring layering time, the drilling axial force of control drill bit is all the time less than this boring layering critical thrust value in actual production processing, realized the CFRP laminate without the layering Drilling operation, thereby avoided the delamination damage defective that produces in the boring, reduced the product rejection that causes because of lamination defect, improved production efficiency, reduce production cost, promoted product quality.

Description of drawings

Fig. 1 is CFRP laminate Simplified equivalent model among the present invention.

Fig. 2 is deformation energy integral domain schematic diagram of the present invention.

Fig. 3 is CFRP laminate fixed boundary condition schematic diagram of the present invention.

Fig. 4 is load rough schematic view of the present invention.

The specific embodiment

The carbon-fiber-reinforcomposite composite material layer plywood of controlling based on drill thrust of the present invention is without the layering boring method, the predictability that is difficult to for CFRP laminate boring layering critical thrust, based on Plate Theory, fracture mechanics and Elasticity correlation theory, set up CFRP laminate boring layering critical thrust model, thereby determine boring layering critical thrust value F _a, and in the process of drill bit drilling CFRP laminate, control the drilling axial force of described drill bit all the time less than boring layering critical thrust value F _aThereby, realize the CFRP laminate without the layering Drilling operation.

Described boring layering critical thrust value F _aDefinite step specifically comprise: be the principle that strain energy (the drilling axial force is poor along the acting of CFRP laminate amount of deflection direction and the laminated bending of plate potential energy of CFRP) equals to form the surface energy of the required absorption of new crack surfaces just according to CFRP laminate boring layering critical condition, the layering stable state equation of model CFRP laminate; Then be converted into based on the deflection equation under the polar coordinates by the fundamental differential of coordinate transformation method with Thin plate under small deflection, according to CFRP laminate suffered equivalent-simplification power situation and load boundary condition, obtain the maximum immunity value of CFRP laminate when boring; Utilize afterwards the Elasticity correlation theory, and the binder course plywood adds the border rigid condition in man-hour in drilling, the flexural deformation of CFRP laminate can formula and the inner stored flexural deformation energy of CFRP laminate when obtaining drilling when setting up drilling again; Utilize at last maximum immunity value, flexural deformation energy and the layering stable state equation of trying to achieve, determine boring layering critical thrust value F _a

Below in conjunction with accompanying drawing embodiments of the invention are further described, the present embodiment is implemented under take technical solution of the present invention as prerequisite, provided detailed embodiment and concrete operating process, but protection scope of the present invention is not limited to following embodiment.

Embodiment

Adopting diameter in the present embodiment is the hard alloy twist drill drilling processing T300/250F CFRP laminate of 4.9mm, definite specifically may further comprise the steps of its boring layering critical thrust, please in conjunction with consulting Fig. 1, Fig. 2 and Fig. 3:

The first step, drill bit is when drilling CFRP laminate, be about to the moment of layering at material, the drilling axial force is done work along CFRP laminate amount of deflection direction, its part is converted into the crooked potential energy of matrix inside for overcoming the flexural deformation of CFRP laminate, another part then is converted into the required surface energy of plate Inner hierarchical crack expansion.When strain energy (the drilling axial force is poor along the acting of CFRP laminate amount of deflection direction and the laminated bending of plate potential energy of CFRP) when just equaling to form the surface energy of the required absorption of new crack surfaces, hierarchical crack is in stable state, and drilling this moment axial force value is CFRP laminate boring layering critical thrust value F _a

Fluted drill is when drilling CFRP laminate, and its layering stable state is:

W-ΔU＝ΔS

Wherein: W=F _aDX; Δ S=G _ICDA

That is: F _aDX-Δ U-G _ICDA=0

Wherein, W is that the drilling axial force is done work along laminate amount of deflection direction,

Δ U is crooked potential energy, required surface energy when Δ S is Crack Extension,

F _aBoring layering critical thrust value,

DX be the CFRP laminate along the differential displacement of maximum defluxion on the drill bit direction of displacement,

G _ICBe on the I type crackle that is caused by axial force the critical crack on the per unit area propagate can,

DA is the differentiation element of surface energy area, and this surface energy area refers to the delamination area maximum area.

Second step is reduced to a thin-plate member with the CFRP laminate, and assert the deflection value of its drilling direction much smaller than the thickness of plate, and the middle face of CFRP laminate is neutral, and plate Inner is without film power, i.e. the flexural deformation of CFRP laminate belongs to the small deflection distortion; Adopt the coordinate transformation method fundamental differential of Thin plate under small deflection to be converted into the polar equation of Thin plate under small deflection; In drilling process, all be condition about hole circle heart symmetry by the load on the circle of contact plate portion and boundary condition according to drill bit, and amount of deflection is the function about r, with the irrelevant condition of θ, deflection equation in the time of can drawing general drill bit drilling CFRP laminate, the suffered equivalent-simplification power situation of CFRP laminate during again in conjunction with the specific bit drilling, can draw the deflection formula of CFRP laminate when drilling, deflection formula is got the maximum immunity value X that greatest limit can be obtained laminate.

The polar equation of described Thin plate under small deflection is:

$(\frac{{\∂}^2}{\∂r^2}+\frac{1}{r}\frac{\∂}{\∂r}+\frac{1}{r^2}\frac{{\∂}^2}{\∂{\mathrm{\θ}}^2})(\frac{{\∂}^{2}w}{\∂r^2}+\frac{1}{r}\frac{\∂w}{\∂r}+\frac{1}{r^2}\frac{{\∂}^{2}w}{\∂{\mathrm{\θ}}^2})=\frac{q}{D}$

Wherein, $D=\frac{E{h}^3}{12(1-{\mathrm{\μ}}^2)}$

D is the bending rigidity of carbon-fiber-reinforcomposite composite material layer plywood,

W be the carbon-fiber-reinforcomposite composite material layer plywood in the amount of deflection of drilling direction,

Q is the load that acts on the face unit are in the carbon-fiber-reinforcomposite composite material layer plywood;

Described laminate deflection formula is:

$w=\∫\frac{1}{r}\∫r\∫\frac{1}{r}\∫\frac{\mathrm{qr}}{D}d{r}^4+\frac{1}{4}A{r}^2(\ln r-1)+\frac{1}{4}B{r}^2+C\ln r+E$

Wherein, w be the carbon-fiber-reinforcomposite composite material layer plywood in the amount of deflection of drilling direction,

Q is the load that acts on the face unit are in the carbon-fiber-reinforcomposite composite material layer plywood,

A, B, C and E are undetermined constant;

Described maximum immunity value is:

$X=\underset{\max }{\lim }w$

Wherein, X is that the carbon-fiber-reinforcomposite composite material layer plywood is at the maximum immunity value of drilling direction.

In the present embodiment, during fluted drill drilling CFRP laminate, the suffered active force of CFRP laminate can equivalence for by apex point and be parallel to the concentrfated load of drill bit direction of feed, as shown in Figure 4.

Because F _a=π qb ²B → 0, q is the load that acts on middle the unit are, b is the operating radius of q; When r=0, w and

Should be the fixing condition in finite value and CFRP laminate border: during r=a, w=0,

Again according to above-mentioned laminate deflection formula, then can solve this moment CFRP laminate and along the amount of deflection of drilling direction be:

$w=\frac{F_a}{8\mathrm{\πD}}[\frac{1}{2}(a^2-r^2)+r^2\ln \frac{r}{a}]$

Therefore, the CFRP laminate along maximum defluxion on the drill bit direction of displacement is:

$X=w_{\max }=\underset{r=0}{\lim }w=\frac{F_a{a}^2}{16\mathrm{\πD}}$

The 3rd step, the flexural deformation of described carbon-fiber-reinforcomposite composite material layer plywood energy formula when setting up drilling, and according to the maximum immunity value X of the carbon-fiber-reinforcomposite composite material layer plywood of trying to achieve in the second step in the drilling direction, the flexural deformation of carbon-fiber-reinforcomposite composite material layer plywood energy U when obtaining the drill bit drilling;

Described carbon-fiber-reinforcomposite composite material layer plywood flexural deformation can formula be:

$U=\frac{D}{2}\underset{D_1}{\∫\∫}{(\frac{d^{2}X}{d{r}^2}+\frac{1}{r}\frac{\mathrm{dX}}{\mathrm{dr}})}^2\mathrm{dxdy}$

Wherein, U is the flexural deformation energy of carbon-fiber-reinforcomposite composite material layer plywood,

D is the bending rigidity of carbon-fiber-reinforcomposite composite material layer plywood,

D ₁Integral area,

X is that the carbon-fiber-reinforcomposite composite material layer plywood is at the maximum immunity value of drilling direction.

In the present embodiment, D ₁For take the circular area of fluted drill diameter as size, and can formula with the above-mentioned CFRP laminate of the laminate maximum defluxion X substitution flexural deformation of trying to achieve in the second step, plate internal strain energy in the time of then can getting fluted drill drilling CFRP laminate

The 4th step, according to the flexural deformation of the maximum defluxion X of the carbon-fiber-reinforcomposite composite material layer plywood of trying to achieve in the second step, the carbon-fiber-reinforcomposite composite material layer plywood of trying to achieve in the 3rd step can U and the first step in the layering stable state equation of the carbon-fiber-reinforcomposite composite material layer plywood set up, determine boring layering critical thrust value F _a

In the present embodiment, according to second step and the 3rd CFRP laminate maximum defluxion that solve of step and the flexural deformation energy of laminate, again with the layering stable state equation both sides in the first step respectively to a differentiate, then have

Get G _IC=140J/m ², E=18.4GPa, υ=0.3, h=0.25mm, boring layering critical thrust is when then solving fluted drill drilling T300/250F laminate:

$F_a=\mathrm{\π}\sqrt{32G_{\mathrm{IC}}D}=\mathrm{\π}\sqrt{\left[\frac{8G_{\mathrm{IC}}E{h}^3}{3(1-v^2)}\right]}=\mathrm{\π}\sqrt{\frac{8\×140\×18.4\×{0.25}^3}{3(1-{0.3}^2)}}=34.1N$

The present embodiment is adjusted the drilling parameter by the control device on the drilling device when actual drilling CFRP laminate, the drilling axial force value of control fluted drill is all the time less than 34.1N, finally realize the CFRP laminate without the layering Drilling operation.

Adopt the method for the invention, only need know the physical parameters such as elastic modelling quantity, Poisson's ratio and thickness of slab of CFRP laminate in the actual processing, can determine easily the critical thrust value F of CFRP laminate boring layering _a, and then the drilling axial force value of control reality is all the time less than this boring layering critical thrust value F _aThereby, realize the Drilling operation without layering.Described method has overcome loaded down with trivial details property and the inaccuracy of the experiment prediction of prior art, has reduced the product rejection that causes because of lamination defect, has improved production efficiency, has reduced production cost, has promoted product quality.

Claims (3)

1. a carbon-fiber-reinforcomposite composite material layer plywood of controlling based on drill thrust is without the layering boring method, it is characterized in that, in the process of the described carbon-fiber-reinforcomposite composite material layer plywood of drill bit drilling, control the drilling axial force of described drill bit all the time less than boring layering critical thrust value F _a

2. the carbon-fiber-reinforcomposite composite material layer plywood of controlling based on drill thrust according to claim 1 is characterized in that described boring layering critical thrust value F without the layering boring method _aDetermined by following step:

The first step, set up the layering stable state equation of described carbon-fiber-reinforcomposite composite material layer plywood:

F _a·dX-ΔU-G _IC·dA＝0

Wherein, W is that the drilling axial force is done work along laminate amount of deflection direction,

Δ U is crooked potential energy,

F _aBoring layering critical thrust value,

DX be the carbon-fiber-reinforcomposite composite material layer plywood along the differential displacement of maximum defluxion on the drill bit direction of displacement,

G _ICBe on the I type crackle that is caused by axial force the critical crack on the per unit area propagate can,

DA is the elementary area of surface energy area, and this surface energy area refers to the delamination area maximum area;

Second step, the carbon-fiber-reinforcomposite composite material layer plywood is reduced to a thin-plate member, and the carbon-fiber-reinforcomposite composite material layer plywood deflection formula the when polar equation by setting up Thin plate under small deflection and drill bit drilling, obtain the maximum immunity value X of carbon-fiber-reinforcomposite composite material layer plywood;

The polar equation of described Thin plate under small deflection is:

$(\frac{{\∂}^2}{\∂r^2}+\frac{1}{r}\frac{\∂}{\∂r}+\frac{1}{r^2}\frac{{\∂}^2}{\∂{\mathrm{\θ}}^2})(\frac{{\∂}^{2}w}{\∂r^2}+\frac{1}{r}\frac{\∂w}{\∂r}+\frac{1}{r^2}\frac{{\∂}^{2}w}{\∂{\mathrm{\θ}}^2})=\frac{q}{D}$

Wherein, $D=\frac{E{h}^3}{12(1-{\mathrm{\μ}}^2)}$

D is the bending rigidity of carbon-fiber-reinforcomposite composite material layer plywood,

W be the carbon-fiber-reinforcomposite composite material layer plywood in the amount of deflection of drilling direction,

Q is the load that acts on the face unit are in the carbon-fiber-reinforcomposite composite material layer plywood;

Described laminate deflection formula is:

$w=\∫\frac{1}{r}\∫r\∫\frac{1}{r}\∫\frac{\mathrm{qr}}{D}d{r}^4+\frac{1}{4}A{r}^2(\ln r-1)+\frac{1}{4}B{r}^2+C\ln r+E$

Wherein, w be the carbon-fiber-reinforcomposite composite material layer plywood in the amount of deflection of drilling direction,

Q is the load that acts on the face unit are in the carbon-fiber-reinforcomposite composite material layer plywood,

A, B, C and E are undetermined constant;

Described maximum immunity value is:

$X=\underset{\max }{\lim }w$

Wherein, X is that the carbon-fiber-reinforcomposite composite material layer plywood is at the maximum immunity value of drilling direction;

The 3rd step, the flexural deformation of described carbon-fiber-reinforcomposite composite material layer plywood energy formula when setting up drilling, and according to the maximum immunity value X of the carbon-fiber-reinforcomposite composite material layer plywood of trying to achieve in the second step in the drilling direction, the flexural deformation of carbon-fiber-reinforcomposite composite material layer plywood energy U when obtaining the drill bit drilling;

Described carbon-fiber-reinforcomposite composite material layer plywood flexural deformation can formula be:

$U=\frac{D}{2}\underset{D_1}{\∫\∫}{(\frac{d^{2}X}{d{r}^2}+\frac{1}{r}\frac{\mathrm{dX}}{\mathrm{dr}})}^2\mathrm{dxdy}$

Wherein, U is the flexural deformation energy of carbon-fiber-reinforcomposite composite material layer plywood,

D is the bending rigidity of carbon-fiber-reinforcomposite composite material layer plywood,

D ₁Integral area,

X is that the carbon-fiber-reinforcomposite composite material layer plywood is at the maximum immunity value of drilling direction;

The 4th step, according to the flexural deformation of the maximum defluxion X of the carbon-fiber-reinforcomposite composite material layer plywood of trying to achieve in the second step, the carbon-fiber-reinforcomposite composite material layer plywood of trying to achieve in the 3rd step can U and the first step in the layering stable state equation of the carbon-fiber-reinforcomposite composite material layer plywood set up, determine boring layering critical thrust value F _a

3. the carbon-fiber-reinforcomposite composite material layer plywood of controlling based on drill thrust according to claim 1 is characterized in that without the layering boring method, and the drilling axial force of the described drill bit of described control is all the time less than boring layering critical thrust value F _aTo realize by the drilling parameter of adjusting this drill bit.

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