US 12,611,746 B1 · Over-positioning grinding method of hard and brittle pipe fitting with large length-to-diameter ratio

Abstract

Provided is an over-positioning grinding method of a hard and brittle pipe fitting with large length-to-diameter ratio, which belongs to the field of grinding technologies. The existing machining method cannot increase the grinding accuracy of the external circles of the hard and brittle pipe fittings nor ensure the coaxiality of the external circles and internal circles of the ground hard and brittle pipe fittings, which leads to inconsistent wall thickness of the ground hard and brittle pipe fittings. In the present disclosure, by using the over-positioning supporting of the rigid mandrel, the support plate and the guide wheel for the hard and brittle pipe fitting in a machining process, the guide wheel is driven to rotate forward to push the hard and brittle pipe fitting with large length-to-diameter ratio into the grinding area, and the guide wheel contacts and drives the hard and brittle pipe fitting while rotating reversely.

An over-positioning grinding method of a hard and brittle pipe fitting with a large length-to-diameter ratio comprising:

at step S1, assembling and positioning of the hard and brittle pipe fitting;
penetrating a rigid mandrel through an internal hole of the hard and brittle pipe fitting with large length-to-diameter ratio such that the rigid mandrel is in clearance fit with the hard and brittle pipe fitting;
tensioning the rigid mandrel and maintaining the hard and brittle pipe fitting horizontally;
supporting a position at each end of the rigid mandrel and close to the hard and brittle pipe fitting by one vibration-damping device to lower vibration amplitude and frequency of the rigid mandrel in a machining process of the hard and brittle pipe fitting;
providing a support plate and supporting the hard and brittle pipe fitting by contacting with an external pipe surface of the hard and brittle pipe fitting;
at step S2, determining a grinding area:
disposing a grinding wheel and a guide wheel at one and other sides of the hard and brittle pipe fitting, respectively, and maintaining axes of the grinding wheel and the guide wheel at a same height;
adjusting heights of the grinding wheel and the guide wheel to ensure there is a height difference between the axes of the guide wheel and the grinding wheel and an axis of the hard and brittle pipe fitting;
opposing a guide supporting surface of the guide wheel in a forward direction by a grinding surface of the grinding wheel;
enclose the grinding area of the hard and brittle pipe fitting, and carry out over-positioning supporting for the hard and brittle pipe fitting in cooperation with the rigid mandrel by the grinding wheel, the guide wheel and the support plate;
obtaining the height difference between the axes of the guide wheel and the grinding wheel and the axis of the hard and brittle pipe fitting as below:
a radius of the external circle of the hard and brittle pipe fitting with large length-to-diameter ratio is Rw, a radius of the guide wheel is Rc, a radius of the grinding wheel is Rg, and the height difference between the axis of the hard and brittle pipe fitting and the axis of the grinding wheel is h;
when the grinding wheel comes in contact with the hard and brittle pipe fitting, an initial contact point of the grinding wheel and the hard and brittle pipe fitting is A, and a tangent line of the point A is l;
when the guide wheel comes in contact with the hard and brittle pipe fitting, an initial contact point of the guide wheel and the hard and brittle pipe fitting is B;
when the support plate comes in contact with the hard and brittle pipe fitting, an initial contact point of the support plate and the hard and brittle pipe fitting is C;
the axis of the hard and brittle pipe fitting is O, the center of the guide wheel is Oc, the center of the grinding wheel is Og, ∠AOC=α, ∠BOC=φ, upper ∠AOgOc=βg, upper ∠OgOcB=βc, β is a grinding angle of the grinding wheel, δ is an included angle between OA and a horizontal line, and an inclination angle of the supporting surface of the support plate is γ;
when there is an offset angle θ between the axis of the grinding wheel and the axis of the hard and brittle pipe fitting, the grinding wheel grinds at the offset angle θ a contour projection of the sectional grinding wheel perpendicular to a feed speed direction;
an elliptic curve equation in the xOgy is expressed as:
x
2
(
R
g
⁢
sin
⁢
θ
)
2
+
y
2
R
g
2
=
1
,
(
1
)
wherein Δy is utilized to represent a height difference from the tangent point A to the axis of the grinding wheel, and Δx is utilized to represent a horizontal distance from the tangent point A to the vertical axis y;
the following expression is obtained from the formula (1):
Δ
_
⁢
x
=
R
g
⁢
sin
⁢
θ
⁢
cos
⁢
β
g
(
2
)
Δ
_
⁢
y
=
R
g
⁢
sin
⁢
β
g
(
3
)
a slope of the tangent line l through the tangent point A on the elliptic curve is expressed as:
k=Δy/Δx:
k
=
-
cot
⁢
β
g
sin
⁢
θ
(
4
)
because the tangent value of the slope of the tangent line l is the included angle of the tangent line l and the X axis, the angle δ of the tangent line l and the x axis is obtained from the formula (4):
π
2
-
δ
=
❘
"\[LeftBracketingBar]"
arctan
⁢
(
k
)
❘
"\[RightBracketingBar]"
(
5
)
based on geometrical relationship, the following formula is obtained:
β
c
≈
h
/
(
R
w
+
R
c
)
(
6
)
h
=
y
+
R
w
⁢
sin
⁢
δ
(
7
)
β
=
β
+
δ
=
π
-
ϕ
-
α
(
8
)
the following is obtained by substituting δ, y, βc into the formulas (7) and (8):
β
=
h
R
w
+
R
c
+
π
2
-
❘
"\[LeftBracketingBar]"
arctan
(
-
cot
⁢
β
g
sin
⁢
θ
❘
"\[RightBracketingBar]"
)
(
9
)
h
=
R
g
⁢
sin
⁢
β
g
+
R
w
⁢
cos
⁢
(
❘
"\[LeftBracketingBar]"
arctan
⁡
(
-
cot
⁢
β
g
sin
⁢
θ
)
❘
"\[RightBracketingBar]"
)
(
10
)
in trigonometric function, when the angle is small, terms in formulas (9) and (10) are simplified as below:
arctan
⁡
(
-
cot
⁢
β
g
sin
⁢
θ
)
≈
-
π
2
+
sin
⁢
θ
cot
⁢
β
g
(
11
)
cot
⁡
(
β
g
)
≈
1
/
β
g
(
12
)
therefore, when the formulas (11) and (12) are substituted into the formulas (9) and (10), the following is obtained:
β
=
h
R
w
+
R
c
+
β
g
⁢
sin
⁢
θ
(
13
)
h
=
R
g
⁢
β
g
+
R
w
⁢
β
g
⁢
sin
⁢
θ
(
14
)
by combining the formulas (13) and (14), the following is obtained:
h
=
(
R
w
+
R
c
)
⁢
(
R
g
+
R
w
⁢
sin
⁢
θ
)
R
g
+
2
⁢
R
w
⁢
sin
⁢
θ
+
R
c
⁢
sin
⁢
θ
⁢
π
180
⁢
β
.
(
15
)
at step S3, guide wheel positioning:
moving the hard and brittle pipe fitting to the grinding area and moving the guide wheel toward the hard and brittle pipe fitting until the guide supporting surface of the guide wheel contacts and squeezes the external pipe surface of the hard and brittle pipe fitting so that a pre-pressure is present between the guide wheel and the hard and brittle pipe fitting:
moving the hard and brittle pipe fitting out of the grinding area and remaining the guide wheel in original position;
at step S4, cutter alignment:
driving the guide wheel to rotate forward to push the hard and brittle pipe fitting with large length-to-diameter ratio into the grinding area;
contacting and driving the hard and brittle pipe fitting by the guide wheel to advance while rotating reversely;
reversely rotating and performing micro feed toward the hard and brittle pipe fitting to realize cutter alignment operation by the grinding wheel;
at step S5, grinding the hard and brittle pipe fitting:
setting a rotation speed and a feed speed of the guide wheel and a rotation speed and a feed speed of the grinding wheel, and setting a grinding amount of the hard and brittle pipe fitting;
driving the guide wheel to rotate forward to push the hard and brittle pipe fitting with large length-to-diameter ratio into the grinding area, and contacting and driving the hard and brittle pipe fitting by the guide wheel while rotating the guide wheel reversely, and reversely rotating and performing the grinding wheel to feed toward the hard and brittle pipe fitting;
along with grinding and feeding of the grinding wheel, the guide wheel and the support plate perform feed toward the hard and brittle pipe fitting so as to always maintain the over-positioning supporting of the guide wheel, the support plate and the rigid mandrel for the hard and brittle pipe fitting.

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Over-positioning grinding method of hard and brittle pipe fitting with large length-to-diameter ratio

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Over-positioning grinding method of hard and brittle pipe fitting with large length-to-diameter ratio

Life of this patent

Abstract

Claims9