CN114952182A - Internal thread step-by-step cold extrusion process - Google Patents
Internal thread step-by-step cold extrusion process Download PDFInfo
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Abstract
According to the internal thread step-by-step cold extrusion process, the diameter formula of the bottom hole in the internal thread cold extrusion process is calculated, so that the quality of a workpiece is ensured; and step-by-step cold extrusion is carried out, so that the torque in the extrusion process is greatly reduced, the consumption speed of the screw tap is greatly reduced, the process cost is reduced, the roughness of the internal thread can be reduced by step-by-step extrusion, the residual stress and the hardened layer in the extrusion process at each time are reserved, the fatigue strength of the workpiece is improved, and the service life of the workpiece is prolonged.
Description
Technical Field
The invention relates to a step-by-step cold extrusion process for internal threads.
Background
With the development of the internal thread processing towards the direction of high performance, low cost and low energy consumption, the cold extrusion forming process is adopted to become an important component for improving the mechanical property of the internal thread and solving the problem of metal chip residue in the internal thread of the blind hole, and the blind hole has wide application prospect in the fields of aviation, aerospace, high-speed trains, important mechanical engineering and the like.
The internal thread cold extrusion has high precision of the formed thread and good surface integrity, and keeps the cold work hardening state of the surface and the subsurface of the internal thread after the cold extrusion, thereby improving the thread connection strength and the fatigue resistance life.
The cold extrusion forming process of the internal thread is to use a cold extrusion screw tap to enable metal to generate plastic flow through the extrusion effect of the ridge teeth on a preset bottom hole of a workpiece under the condition of room temperature, and then the internal thread is formed.
Compared with the cutting forming of the internal thread, the cold extrusion forming of the internal thread has the following advantages:
the thread machining precision is high, the cold extrusion forming process of the internal thread belongs to elastic-plastic deformation, and due to the good guidance of the extrusion screw tap, the formed thread has small error, and the machining precision of 4H or 5H can be achieved by common materials.
Secondly, the surface roughness is low, the ridge teeth of the extrusion tap part are very flat to the tooth surface of the internal thread in the cold extrusion forming process of the internal thread, and the surface roughness can reach Ra0.4-Ra0.8.
And thirdly, the tensile strength and the fatigue resistance are improved, and the internal thread extrusion is a process of enabling metal to generate plastic flow through the plastic deformation of the metal to fill the whole tooth form. Therefore, the formed thread surface structure is fibrous and distributed along the tooth shape, and a processing hardened layer and residual stress exist on the thread root and the tooth flank, so that the tensile strength and the fatigue resistance of the thread are greatly improved.
And fourthly, because the internal thread is not cut, the internal thread has no residual metal chips, and the internal thread of the blind hole can avoid the short circuit accident of the electrical element caused by the metal chips.
The cold extrusion internal thread is not widely used in aerospace, and the cold extrusion process is only used for extruding blind hole internal thread products with the extrusion M less than or equal to 2. And the yield strength sigma s is less than or equal to 250mPa at low hardness; the material is used. The reasons for this are the following:
the cold extrusion internal thread process has the advantages of improving the fatigue strength of products, improving the precision of workpieces, reducing the roughness, having no metal chips in internal threads of blind holes and the like.
Secondly, the bottom hole diameter of the internal thread is subjected to cold extrusion, and a proper and practical calculation method cannot be found.
And thirdly, the size of the bottom aperture of the internal thread directly influences the tooth height rate (small diameter size) and the size of the cold extrusion torque. Large aperture, small tooth height and unqualified products. The diameter of the hole is small, the tooth yield is qualified, but the torque is large, the screw tap is easy to wear, and the screw tap is easy to break and cannot be processed. This is a major reason that limits the widespread use of cold extrusion.
Disclosure of Invention
In order to solve the technical problem, the invention provides a step-by-step cold extrusion process for internal threads.
The invention is realized by the following technical scheme.
The invention provides an internal thread step-by-step cold extrusion process, which comprises the following steps:
s1, calculating a functional relation between the diameter of the bottom hole and the nominal diameter and the thread pitch of the internal thread of the workpiece;
in the process of extruding the workpiece by the tap, the volume V2 of the metal thread extruded by the tap is equal to the volume V1 of a thread groove generated by extruding the extruding ridge of the tap into the inner wall of the workpiece,
V 1 ＝V 2 (1)
V 1 ＝2π×〔(h 1 /3×(2a 1 ﹢b 1 )/(a 1 ﹢b 1 ))﹢d 0 /2〕×(a 1 ﹢b 1 )/2×h 1 (2)
V 2 ＝2π×〔(h 2 /3×(2a 2 ﹢b 2 )/(a 2 ﹢b 2 ))﹢d 1 /2〕×(a 2 ﹢b 2 )/2×h 2 (3)
a 1 ＝0.125P (4)，
b 1 ＝0.125P﹢0.5774(d﹣d0) (5)，
a 2 ＝0.875P﹣0.5774(d﹣d0) (6)，
b 2 ＝0.25P (7)，
h 1 ＝(d﹣d 0 )/2 (8)，
h 2 ＝(d 0 ﹣d 1 )/2 (9)，
d 1 ＝d﹣1.0825P (10)，
b 1 ﹢a 2 ＝P (11)
bringing formulae (2) to (11) into formula (1) to obtain d 0 ≈d-0.60P。
S2, correcting the diameter d of the bottom hole according to the numerical value of the thread tolerance zone 0 ＝d 1 ﹣(0.43～0.60)P，
Wherein, a 1 Width of thread crest of thread groove, b 2 Crest width of the thread extruded for the tap, h 1 To a depth of penetration into the thread groove, h 2 Height of thread for extruding thread from tap, P is pitch, d 1 Is the minor diameter of the thread, d is the nominal diameter of the internal thread of the workpiece;
s3, selecting the diameter of the bottom hole according to the workpiece material and then processing the bottom hole;
and S4, performing cold extrusion processing on the internal threads of the workpiece step by using a screw tap.
The distribution processing steps are as follows:
s41, performing primary cold extrusion on the internal thread of the workpiece by using a small-diameter screw tap with the diameter smaller than the nominal diameter of the internal thread of the workpiece and the pitch same as that of the internal thread of the workpiece, so that the displacement volume of the metal on the inner wall of the workpiece is the displacement volume V of the complete internal thread 1 64 to 75 percent of the total weight of the composition;
and S42, performing primary cold extrusion by using a standard tap with the diameter equal to the nominal diameter of the internal thread of the workpiece and the thread pitch same as that of the internal thread of the workpiece to obtain a complete internal thread.
The rotation speed of the machine tool in the steps S41 and S42 is 25r/min, and special cold extrusion oil is used in the extrusion process.
The diameter of the small-diameter tap in the step S41 is calculated by the following method:
V3＝(64％～75％)V1 (12)，
V3＝2π×〔(h 3 /3×(2a 3 ﹢b 3 )/(a 3 ﹢b 3 ))﹢d 0 /2〕×(a 3 ﹢b 3 )/2×h 3 (13)，
h 3 ＝(d 3 ﹣d 0 )/2 a 3 ＝0.125p (14)
b 3 ＝0.125P﹢0.5774(d 3 ﹣d 0 ) (15)
substituting formulae (2), (13) to (15) into formula (12)
d 3 ＝d－(0.1～0.15)P。
V3 is the volume of the minor diameter tap squeezed into the thread groove, a 3 The crest width h of the minor-diameter screw tap extruded into the thread groove 3 Depth of the minor-diameter tap into the thread groove, d 3 Is the nominal diameter of the small diameter tap.
And if the bottom hole of the workpiece is a through hole, performing step-by-step machining by using the combined screw tap.
The combined screw tap comprises a small-diameter section and a standard section, wherein the small-diameter section is smoothly connected with the standard section through a transition section, the other end of the small-diameter section is smoothly connected with a positioning head, and the other end of the standard section is connected with a clamping handle.
The diameter of the small-diameter section is the diameter relation of the standard section: d Small ＝d Sign board ﹣(0.1～0.15)P。
The clamping handle is a thick handle or a thin handle.
The diameter of the clamping handle of the thick handle is larger than that of the standard section, and the clamping handle is smoothly connected with the standard section.
The diameter of the clamping handle of the thin handle is smaller than that of the standard section.
The invention has the beneficial effects that:
1. the diameter formula of the bottom hole in the cold extrusion process of the internal thread is calculated, so that the quality of the workpiece is ensured.
2. The extrusion process is divided into two times of extrusion, so that the torque in the extrusion process is greatly reduced, the consumption speed of the screw tap is greatly reduced, and the production cost is reduced;
3. the step extrusion can reduce the roughness of the internal thread, the residual stress and the hardened layer in each extrusion process are reserved, the fatigue strength of the workpiece is improved, and the service life of the workpiece is prolonged.
Drawings
FIG. 1 is a schematic view of a thread form construction of the present invention;
FIG. 2 is a torque schematic of the internal thread extrusion process of the present invention;
FIG. 3 is a graph of the tooth height rate versus thread connection strength of the present invention;
FIG. 4 is a plot of bottom hole diameter versus extrusion torque for the present invention;
FIG. 5 is a schematic view of a combination upset tap construction of the present invention;
FIG. 6 is a schematic view of a fine-shank combination extrusion tap of the present invention;
FIG. 7 is a schematic cross-sectional view of the tapping section of the present invention;
FIG. 8 is a cross-sectional view of the clamping shank of the tap of the invention;
FIG. 9 is a profile view of a step extrusion of M3 threads according to the present invention;
1-small diameter section, 2-transition section, 3-standard section, 4-clamping handle and 5-positioning head.
Detailed Description
The technical solution of the present invention is further described below, but the scope of the claimed invention is not limited to the described.
The internal thread step-by-step cold extrusion process comprises the following steps of:
s1, calculating a functional relation between the diameter of the bottom hole and the nominal diameter and the thread pitch of the thread;
in the process of extruding the workpiece by the tap, the volume V2 of the metal thread extruded by the tap is equal to the volume V1 of a thread groove generated by extruding the extruding ridge of the tap into the inner wall of the workpiece,
V 1 ＝V 2 (1)
V 1 ＝2π×〔(h 1 /3×(2a 1 ﹢b 1 )/(a 1 ﹢b 1 ))﹢d 0 /2〕×(a 1 ﹢b 1 )/2×h 1 (2)
V2＝2π×〔(h 2 /3×(2a 2 ﹢b 2 )/(a 2 ﹢b 2 ))﹢d 1 /2〕×(a 2 ﹢b 2 )/2×h 2 (3)
a 1 ＝0.125P (4)，
b 1 ＝0.125P﹢0.5774(d﹣d 0 ) (5)，
a 2 ＝0.875P﹣0.5774(d﹣d 0 ) (6)，
b 2 ＝0.25P (7)，
h 1 ＝(d﹣d 0 )/2 (8)，
h 2 ＝(d 0 ﹣d 1 )/2 (9)，
d 1 ＝d﹣1.0825P (10)
b 1 ﹢a 2 ＝P (11)
bringing formulae (2) to (11) into formula (1) to obtain d 0 ≈d-0.60P。
S2, correcting the diameter d of the bottom hole according to the numerical value of the thread tolerance zone 0 ＝d﹣(0.43～0.60)P，
Wherein, a 1 Being threads of thread groovesCrest width, b 2 Crest width of thread extruded for tap, h 1 To a depth of penetration into the thread groove, h 2 Height of thread for extruding thread from tap, P is pitch, d 1 Is the minor diameter of the thread, d is the nominal diameter of the internal thread of the workpiece;
s3, selecting the diameter of the bottom hole according to the workpiece material and then processing the bottom hole;
and S4, performing cold extrusion processing on the internal thread of the workpiece step by using a screw tap.
The step-by-step processing steps are as follows:
s41, performing primary cold extrusion on the internal thread of the workpiece by using a small-diameter screw tap with the diameter smaller than the nominal diameter of the internal thread of the workpiece and the pitch same as that of the internal thread of the workpiece, so that the displacement volume of the metal on the inner wall of the workpiece is the displacement volume V of the complete internal thread 1 64 to 75 percent of the total weight of the composition;
and S42, performing primary cold extrusion by using a standard tap with the diameter equal to the nominal diameter of the internal thread of the workpiece and the thread pitch same as that of the internal thread of the workpiece to obtain a complete internal thread.
The machine tool rotating speed in the steps S41 and S42 is 25 r/min.
The diameter of the small-diameter tap in the step S41 is calculated by the following method:
V 3 ＝(64％～75％)V 1 (12)，
V 3 ＝2π×〔(h 3 /3×(2a 3 ﹢b 3 )/(a 3 ﹢b 3 ))﹢d 0 /2〕×(a 3 ﹢b 3 )/2×h 3 (13)，
h 3 ＝(d 3 ﹣d 0 )/2a 3 ＝0.125p (14)
b 3 ＝0.125P﹢0.5774(d 3 ﹣d 0 ) (15)
substituting formulae (2), (13) to (15) into formula (11)
d 3 ＝d－(0.1～0.15)P。
V 3 Volume of the minor-diameter tap squeezed into the thread groove, a 3 The crest width h of the minor-diameter screw tap extruded into the thread groove 3 Depth of the minor-diameter tap into the thread groove, d 3 Is the nominal diameter of the small diameter tap.
And if the bottom hole of the workpiece is a through hole, performing step-by-step machining by using the combined screw tap.
Example 1: the invention finds the reason that the screw tap is easy to break in the cold extrusion process of the internal thread,
as shown in fig. 2, cold extrusion of internal threads can be carried out in three main stages:
a) a pressing stage, b) a pressing and correcting stage, c) correcting the torque of each stage of the pressing stage.
The screw tap material: w18WCr4V, W6M05Cr4V2Al, W7Mo4CrV2Co5 high speed steel and cemented carbide. High-speed steel, hard alloy, some are coated. TiN, TiALN coatings;
judging the strength of the screw tap:
τ max ＝Mnmax/Wn≤〔τ〕，τ max maximum working shear stress.
[ tau ]: allowable stress of material, M n Torque, Wn: torsional section modulus.
Tap torsional section modulus W n ＝πD 3 And D, the minor diameter of the tap. If D is small, τ max It is easily larger than [ tau ] to cause the screw tap to break. This is why particularly small taps are prone to breakage. The hardness of workpiece material HRC is more than 25, cold extrusion is very difficult, such as M2 threads, the hardness of material 022Cr19Ni5MO3Si2N is more than HRC30, the torque is extremely large, and the screw breakage is very much. The alloy extrusion screw tap has the advantages of large brittleness, easy brittle failure and tooth breakage, and inferior service performance (effect) to that of a high-speed steel extrusion screw tap.
Example 2: analysis of the relationship between thread height and thread connection Strength
Analyzing factors influencing torque in the production process:
1. the lubricant is the rotating speed of a machine tool (drilling machine), and the common lubricant adopts special extrusion oil with a small friction coefficient;
2. rotation speed of machine tool (drilling machine), according to yield strength sigma of material s The HRC is determined by the magnitude of the rotation speed, and is generally controlled at a lower rotation speed.
3. The biggest factor influencing the torque is the diameter of a reserved threaded bottom hole, the diameter of the bottom hole is small, and the tooth height rate is high. Generally, the tooth height can be controlled by more than 70%.
As shown in fig. 3, when the thread height exceeds 70%, the connection strength of the thread is not significantly increased and the required extrusion torque is significantly increased.
The thread height of the internal thread increases along with the reduction of the diameter of the bottom hole of the workpiece in the cold extrusion forming process of the internal thread. Generally, under the condition of meeting the internal thread connection strength, the high tooth height rate is not required to be excessively required, namely, the diameter of a bottom hole is selected to be smaller. The small diameter of the workpiece is required to be qualified in production. However, when HRC is more than 25 or sigma s is more than 450mPa, the screw plug gauge (T, Z) is ensured to be on and off, and the small diameter d1 is qualified, the extrusion tap can not ensure a certain processing yield. For example, M2 and 022Cr19Ni5MO3Si2N (HRC30) are adopted, one tap can only be processed into 2-5 parts, cold extrusion internal threads are adopted for processing at high cost, and for high-temperature alloy used by aerospace enterprises, the hardness HRC of stainless steel materials is more than 30, and the hardness HRC of titanium alloy materials is more than 30. If the internal thread is subjected to cold extrusion, the torque is too large, and the screw tap is greatly abraded and even breaks. The bottom hole diameter size is very torque sensitive. The cold extrusion internal thread processing method is not adopted.
Example 3, the bottom hole diameter was analyzed as a function of torque.
As shown in fig. 1, taking a common thread as an example, the volume of the rotator at a1 in the figure is:
V 1 ＝2π×〔(h 1 /3×(2a 1 ﹢b 1 )/(a 1 ﹢b 1 ))﹢d 0 /2〕×(a 1 ﹢b 1 )/2×h 1 ，
wherein h is 1 ＝(d﹣d 0 )/2，
a 1 ＝0.125P，
b 1 ＝0.125P﹢0.5774(d﹣d 0 )，
h 1 ＝(d﹣d 0 )/2，
Wherein, a 1 Width of thread crest of thread groove, h 1 Depth of penetration into the thread groove, P is pitch, d 1 Is a small diameter of the thread.
A is a 1 ，b 1 ，h 1 Substituting into a formula to solve, can obtain:
V 1 ＝a(d﹣d 0 ) 3 ﹢b(d﹣d 0 ) 2 ﹢C(d﹣d 0 ). Wherein a, b, c > 0. a 0.048125 pi, b (0.3125P + 0.14435 d) 0 )π、c＝0.0625πPd 0 ，V 1 Is (d-d) 0 ) Increasing the function. Let X be d-d 0 The volume change formula of the A1 rotating body is dV 1 ＝(3aX 2 2bX + C) dx, knowing dV1 due to the volume change and (d-d) 0 ) There is a very sensitive relationship. V1 ═ f (x) is a nonlinear function. This is the cold extrusion internal thread deformation (V and d) 0 ) The important features of (a).
The metal deformation, plasticity and deformation resistance are related to the deformation magnitude of the displacement volume degree, the displacement volume of the cold extrusion thread is related to the cubic, quadratic and first order of (d-d 0) along with the increase of the displacement volume deformation, and the displacement volume is related to the deformation displacement according to the cold extrusion thread structure state. To illustrate the change dv of the internal thread extrusion volume (3 aX) 2 2bX) the characteristic of the dx nonlinear relationship is the most important factor that restricts the wide use of cold-extruded internal threads! The diameter of the reserved bottom hole is not accurately controlled, the precision is not enough, the tooth form of a workpiece is directly influenced, the tooth height is T, Z, and the pass percent of small-diameter sizes is reduced. Affecting residual stress, mechanical properties, fatigue life, etc. The extrusion tap is affected from adhering to the workpiece, the degree of wear is even broken in the internal thread bottom hole. Therefore, the cold extrusion internal thread processing, the material, the hardness and the thread diameter are all strictly limited.
Establishing a mechanical model of the cold extrusion forming process of the internal thread, analyzing the stress condition and the contact angle and the contact arc length of each stage, and calculating the torque of each stage:
according to the structure of the working part of the extrusion tap, the cold extrusion forming process of the internal thread can be divided into three main stages: the extrusion stage 1, the extrusion and correction simultaneous stage 2, and the correction stage 3, wherein the torque of each stage is shown in figure 2. The torque variation trend in the whole internal thread cold extrusion forming process is as follows: in the stage I, the workpiece is continuously extruded by the thread-extruding tap ridge teeth, the metal plastic deformation of the workpiece continuously occurs, and the torque of the whole stage is continuously increased; in the stage II, the extrusion effect and the correction effect exist at the same time, and the torque in the stage is increased firstly and then reduced; in the stage III, along with the derivation of the extrusion tap, the ridge teeth of the extrusion tap participating in the correction continuously reduce, and the torque value continuously reduces. Therefore, the maximum value of the forming process torque can be used as an index for calibrating the whole forming process torque.
The maximum torque value calculation formula in the quoted internal thread extrusion process is as follows:
T＝3.92×10 -4 σ s H V m 0.8783 n 0.014 L1 0.2718 L2 0.6298 φ 0.05 K -1.396 z 0.1039 (d－d 0 ) 2 P
wherein, σ s is the yield stress (MPa) of the material of the extrusion workpiece, HV is the Vickers hardness of the material; m is the average friction coefficient between the extrusion tap and the workpiece; n is the machine tool rotation speed (r/min); d0 is the diameter (mm) of the bottom hole of the prefabricated workpiece; l1 is the extruded filament taper length (mm); l2 denotes the correction section length (mm); phi is the extrusion cone angle (°); k is the shovel back amount (mm); z is the number of edge teeth; d is the nominal diameter (mm) of the major diameter of the extrusion screw tap; p is the thread pitch (mm) of the extrusion tap.
From this equation, it can be seen that the torque T is primarily proportional to the workpiece material σ s, HV, indicating that the harder the material, the greater the torque, the greater the yield hardness, and the greater the torque. It is related to the coefficient of friction (m), but the degree of influence is not σ s, HV is large, and is known from the functional relationship of T. Most importantly, T and (d-d) 0 ) 2 About, T ═ K (d-d) 0 ) 2 Non-linear is a quadratic relationship.
Calculated by mathematical least squares from the experimental data: t398.1 × (22-d) 0 ) 2 . 28 The relative error between the calculation and the experiment is shown in the table 1.
TABLE 1T 398.1 × (22-d) 0 ) 2.28 Comparison table of calculation results and test results
Calculated by mathematical least squares from the experimental data: t39.8 × (8-d) 0 ) 3.35 It is counted
The calculated relative error with the test is shown in table 2.
TABLE 2 term T ═ 39.8 × (8-d) 0 ) 3.35 Comparison table of calculation results and test results
According to the experimental result, the torque T ═ K (d-d) 0 ) 2～4 And since the parameters of the material chemical composition, texture, σ s, HV, extrusion tap size, friction coefficient, etc. are not changed during the product processing, K > 0 is a constant.
Example 4, the minimum value of the bottom hole diameter was calculated.
As shown in FIG. 1, triangle OAB is similar to triangle OCD due to a 1 0.125P, so b 1 ＝0.125P﹢0.5774(d﹣d 0 )，
Triangle MFG is similar to triangle MDE due to b 2 0.25P, so that 2 ＝0.875P﹣0.5774(d﹣d 0 ) And b is 1 ﹢a 2 ＝P。
Volume V of the rotating body of A1 in FIG. 1 according to the law of constant volume of plastic deformation 1 Should be equal to the volume V of A2 rotating body 2 I.e. V 1 ＝V 2 ，
A1 is isosceles trapezoid of section of thread groove squeezed by the thread tap, a1 (area): a. the 1 ＝(a 1 ﹢b 1 )/2×(d﹣d 0 )/2. A2 is a tap extruded isosceles trapezoid in cross section, a2 (area): (a) 2 ﹢b 2 )/2×(d 0 －d 1 )/2，
a 1 ＝AB＝P/8＝0.125P b 2 ＝FG＝0.25P
d 1 ＝d﹣1.0825P；
According to Gulujin's 2 nd law V2 pi LAMiddle L 1 ＝X 1 ﹢d 0 /2，L 2 ＝X 2 ﹢d 1 /2。X 1 、X 2 The distance between the center of the isosceles trapezoid and the bottom edge is, and A is the area of the isosceles trapezoid.
V 1 ＝2π×〔(h 1 /3×(2a 1 ﹢b 1 )/(a 1 ﹢b 1 ))﹢d 0 /2〕×(a 1 ﹢b 1 )/2×h 1 ..................(1)
Wherein h is 1 ＝(d﹣d 0 )/2，
V 2 ＝2π×〔(h 2 /3×(2a 2 ﹢b 2 )/(a 2 ﹢b 2 ))﹢d 1 /2〕×(a 2 ﹢b 2 )/2×h 2 Wherein h is 2 ＝(d 0 ﹣d 1 )/2......(2)
V 1 ＝V2；
Solving this equation: d 0 ≈d－0.60P。
This function d 0 d-0.60P is A1 volume of revolution 1 Complete shift V 2 This displaced volume position state is an ideal state, i.e. V 1 The volume is fully squeezed into the two-sided tooth cavity, the ideal state is that the torque is maximum, and d 0 Is the minimum value of the bottom hole diameter.
And a minor diameter d of the thread 1 There are tolerances, the tolerances being implemented in GB/T197-2018 common thread tolerance & fit, d 1 The tolerance is positive difference, and d is paired according to the value of the tolerance band 0 D is corrected to d-0.60P 0 ＝d 1 0.43-0.60P, the non-ferrous metal is selected from aluminum alloy M3 × 0.5, and the diameter of the bottom hole is selected
Alloy steel 30CrMnSiA
1Cr18Ni9Ti
Titanium alloy
The diameter precision of the bottom hole in the production is reserved 2 bits behind the decimal point, namely the percentile, 0.01mm level,
example 5 tap torque during cold extrusion was reduced by step extrusion.
Using mechanical model T ═ K (d-d) 0 ) 2 And (6) carrying out analysis.
Torque T and d-d 0 Is a square relation, so in d-d 0 Between them add a d 3 And d is 3 The pitch of the internal thread of (d) is the same as that of the internal thread of (d), and d is added 3 The rear torque formula is:
T＝K(d﹣d 0 ) 2 ＝K(d﹣d 3 ﹢d 3 ﹣d 0 ) 2 ＝K〔(d﹣d 3 )﹢(d 3 ﹣d 0 )〕 2 ＝K(d﹣d 3 ) 2 ﹢K(d 3 ﹣d 0 ) 2 ﹢2K(d﹣d 3 )(d 3 ﹣d 0 )。
let d 0 ＜d 3 ＜d，d﹣d 3 ＞0，d 3 ﹣d 0 0, the conclusion is as follows: t ═ K (d-d) 0 ) 2 ＞K(d﹣d 3 ) 2 ﹢K(d 3 ﹣d 0 ) 2 Similarity of K (d-d) 0 ) 2 ＞K(d﹣d 3 ) 2 ，③K(d﹣d 0 ) 2 ＞K(d 3 ﹣d 0 ) 2 。
According to the characteristics of the relation between the cold extrusion internal thread torque and the diameter of the bottom hole, the conclusion of mathematical derivation of the steps is combined to divide one cold extrusion internal thread tapping or forming into two times. Due to the fact that the extrusion times are too many, a plurality of special screw taps with different diameters and the same screw pitch need to be machined, machining cost is increased, the situation that threads are disordered due to the fact that the inner wall of a workpiece deforms for many times due to the fact that the extrusion times are too many is caused, and therefore two-time step-by-step cold extrusion forming is adopted. The extrusion torque drop of such a step-forming is very fast because T and (d-d) 0 ) Is a nonlinear function and is a quadratic relation.
Although the first cold extrusion brings certain residual stress, the internal thread of M22 multiplied by 1.5 is generally less than or equal to 0.35mm, and the first step extrusion (d) is carried out due to the step extrusion 3 ﹣d 0 ) The surface residual stress is relatively reduced, and the depth of the hardened layer is relatively reduced. However, the substrates HV and σ s are unchanged. Assume that the second torque T2 fully superimposes on the T1 basis:
T1＝K(d 3 ﹣d 0 ) 2 then the second time T2 is T1K (d-d) 3 ) 2 ＝K(d 3 ﹣d 0 ) 2 ﹢K(d﹣d 3 ) 2 ＜K(d﹣d 0 ) 2 I.e., less than the torque required to form the internal thread by one cold extrusion.
And residual stress, case hardening due to d 3 ＞d 0 ，(d 3 ﹣d 0 )＜(d﹣d 0 ) Naturally, it is smaller and shallower than the primary forming, i.e., the second time the torque is superimposed on the first time T1, it must be less than the torque of the primary forming. However, after the cold extrusion of the internal thread, the residual stress of the 2 nd step extrusion is larger than the first residual stress, and the work hardening is increased. And an increase in the lamination stress of the thread surface will certainly increase its fatigue life.
As shown in table 3, the high hardness of the high temperature alloy and the stainless steel was subjected to primary cold extrusion internal thread forming and step-by-step secondary cold extrusion internal thread forming experiments, and the lubricating oil used was SKS tapping exclusive oil. The obtained tooth form is shown in FIG. 9.
TABLE 3M 3X 0.5 Cold extrusion test
Table 3 the test data demonstrate that the stepped extruded female thread forming torque is less than the one-shot extruded female thread forming torque.
Example 6 energy conservation was used to determine the displaced volume relationship of each step in a step extrusion process.
Torque T and (d-d) 0 ) Functional relation further theoretical analysis, functional relation V of metal displacement volume of inner wall of workpiece 1 ＝f(x)＝ax 3 +bx 2 +cx
X＝d﹣d 0 For a workpiece in which the internal thread d is defined by the design, i.e. is constant, then d 0 Increase X decrease, d 0 Decreasing X increases.
Demonstration from energy conservation, T and (d-d) 0 ) The plastic deformation process is considered as an adiabatic process, and the work (or power) performed by the external force is equal to the sum of the increase in the object and the total work (or power) required for the metal deformation.
If the kinetic energy is K and the internal energy is U, the total energy is changed to delta K + delta U + delta A + delta Q according to the first law of thermodynamics when the state is transited to another state within a tiny time interval delta t,
wherein δ A is the volume force F i With area force P i The work done, δ Q, is the heat dissipated by the object to the surrounding medium.
The change formula of the external force doing work is delta A ═ integral multiple V [F i δu i ﹢(σ ij,j δu i ﹢σ ij δu i , j )]dV is closely related to V, etc., and is an integral of volume, and the change of volume affects the work done by external force.
The internal extrusion thread is subjected to torque work, and the internal extrusion thread TdQ is delta A, dQ torsion angle unit and radian.
When the torque rotates one revolution, dQ is 2 pi, forming one pitch.
T＝1/2π∫ V [F i δu i ﹢(σ ij,j δu i ﹢σ ij δu i,j )]dV..........(1)
Let V become V 1 ﹢V 2 The properties may be added by a fixed integral.
T＝1/2π∫ V [F i δu i ﹢(σ ij,j δu i ﹢σ ij δu i,j )]dV＝1/2π∫ V1 [F i δu i ﹢(σ ij,j δu i ﹢σ ij δu i,j )]dV(T 1 )﹢1/2π∫ V2 [F i δu i ﹢(σ ij,j δu i ﹢σ ij δu i,j )]dV(T 2 ).......(2)
I.e. T ═ T 1 ﹢T 2 Due to T 1 ﹥0，T 2 Is more than 0, so T 1 ﹤T,T 2 And (4) draining. It is shown that the extrusion torque per step in the step extrusion is smaller than the extrusion torque for only one forming.
δu i Small displacement, δ u i And d 0 And (d-d) 0 ) It is related. Although the displacement of particles within a deformed body is difficult to describe accurately, δ u i Qualitatively knowing δ u i ＝f(d﹣d 0 )。
From δ a volume integral, T ═ f (d-d) can be qualitatively known 0 )＝a(d﹣d 0 ) 4 ﹢b(d﹣d 0 ) 3 ﹢C(d﹣d 0 ) 2 a.b.c＞0。 (3)
From the formula (3), T ═ K (d-d) can be found 0 ) y And (4) function equivalence (function values corresponding to a, b, c and K can be found), wherein K is related to a workpiece material, a screw tap structure, a friction coefficient and the like, and the value range of y is 2-4. Table 1: t397.1 × (22-d) 0 ) 2.28 Table 2: t39.8 × (8-d) 0 ) 3.35 . Further explanation verifies that y is 2-4.
Because y is 2-4, we are T-K (d-d) 0 ) 2 The analysis of the torque of extruding the internal thread step by step is smaller than the torque of extruding the internal thread only once, the effect is obvious, and the theoretical analysis is correct. The actual y-K (d-d) effect is self-evident (more than T-K) 0 ) 2 ) The practicability is stronger. This is demonstrated by the experimental data in table 3.
By calculation of the displacement volume, the first time the volume (64-75%) V1 (d) should be displaced 3 d-0.1-0.15P, (d3 same as d pitch) first internal thread extrusion d 3 The larger value is taken, the second extrusion screw tap can be ensured to smoothly enter the first reserved tooth-shaped threaded hole, the disordered buckling and the disordered teeth can not be caused, and the reduction of the number of drill bits and the number of the added teeth can be eliminatedThe diameter precision error of the bottom hole is eliminated, the unevenness of the surface of the drilled hole is eliminated, the roughness is reduced, and secondary fine drilling supplementary processing (step drilling method) is not needed. The step-by-step tapping method can further improve the surface precision, reduce the roughness, reserve the residual stress and the hardened layer, improve the fatigue strength and the service life of the product, and simultaneously, the d0 can be relatively selected to be a smaller value, thereby improving the tooth height and further improving the mechanical property. The first extrusion process can replace a fine drilling process, and the cost is not increased.
Example 7, as shown in fig. 5 and 6, the combined tap of the present invention was formed by connecting a positioning section 5, a small-diameter section 1, a transition section 2, a standard section 3, and a grip holder in this order, by extruding through-hole threads twice without replacing the tap, during processing, the positioning section 5 is butted with a bottom hole of a workpiece, the screw tap rotates and then gradually enters the bottom hole, the inner wall of the workpiece is extruded for the first time through the ridge teeth on the small-diameter section 1, so that the inner wall of the workpiece forms threads with lower tooth height, then the transition section 2 is connected with the small-diameter section 1 by the prefabricated screw thread, so that the inner wall of the workpiece is gradually extruded by the standard section 3, the thread with the lower tooth height formed by the first extrusion generates residual stress, and the standard section 3 continuously extrudes the surface of the thread on the basis, deepens a hardened layer of the thread, and increases the surface precision and the thread integrity of the thread.
The clamping handle shown in fig. 5 is a thick handle, can adapt to larger torque and is suitable for processing high-strength threads, while the clamping handle shown in fig. 6 is a thin handle, so that the torque of the extruded internal threads is reduced, the clamping handle is suitable for continuous extrusion processing of a plurality of internal thread through holes, and the efficiency is improved.
Claims (10)
1. A step-by-step cold extrusion process for internal threads comprises the following steps:
s1, calculating the functional relation between the diameter of the bottom hole of the workpiece and the nominal diameter and the thread pitch of the internal thread of the workpiece;
in the process of extruding a workpiece by using the screw tap, the metal volume V of the threads extruded by the screw tap 2 Volume V of thread groove generated by extruding the screw tap extrusion ridge teeth into the inner wall of the workpiece 1 The phase of the two phases is equal to each other,
V 1 ＝V 2 (1)，
V 1 ＝2π×〔(h 1 /3×(2a 1 ﹢b 1 )/(a 1 ﹢b 1 ))﹢d 0 /2〕×(a 1 ﹢b 1 )/2×h 1 (2)，
V 2 ＝2π×〔(h 2 /3×(2a 2 ﹢b 2 )/(a 2 ﹢b 2 ))﹢d 1 /2〕×(a 2 ﹢b 2 )/2×h 2 (3)，
a 1＝ 0.125P (4)，
b 1 ＝0.125P﹢0.5774(d﹣d 0 ) (5)，
a 2 ＝0.875P﹣0.5774(d﹣d 0 ) (6)，
b 2 ＝0.25P (7)，
h 1 ＝(d﹣d 0 )/2 (8)，
h 2 ＝(d 0 ﹣d 1 )/2 (9)，
d 1 ＝d﹣1.0825p (10)，
b 1 ﹢a 2 ＝P (11)，
bringing formulae (2) to (11) into formula (1) to obtain d 0 ≈d-0.60P。
S2, correcting the diameter d of the bottom hole according to the numerical value of the thread tolerance zone 0 ＝d 1 ﹣(0.43～0.60)P，
Wherein, a 1 Width of thread crest of thread groove, b 2 Crest width of thread extruded for tap, h 1 To a depth of penetration into the thread groove, h 2 Height of thread for extruding thread from tap, P is pitch of internal thread, d 1 Is the minor diameter of the thread, d is the nominal diameter of the internal thread of the workpiece;
s3, selecting the diameter of the bottom hole according to the workpiece material and then processing the bottom hole;
and S4, performing cold extrusion processing on the internal threads of the workpiece step by using a screw tap.
2. The internal thread step-by-step cold extrusion process of claim 1, wherein: the step-by-step processing steps are as follows:
s41, makingPerforming primary cold extrusion on the internal thread of the workpiece by using a small-diameter screw tap with the diameter smaller than the nominal diameter of the internal thread of the workpiece and the pitch same as that of the internal thread of the workpiece, so that the displacement volume of the metal on the inner wall of the workpiece is the displacement volume V of the complete internal thread 1 64 to 75 percent of the total weight of the composition;
and S42, performing primary cold extrusion by using a standard tap with the diameter equal to the nominal diameter of the internal thread of the workpiece and the thread pitch same as that of the internal thread of the workpiece to obtain a complete internal thread.
3. The internal thread cold step extrusion process of claim 2, wherein: the rotation speed of the machine tool in the steps S41 and S42 is 25r/min, and special cold extrusion oil is used in the extrusion process.
4. The internal thread cold step extrusion process of claim 2, wherein: the diameter of the small-diameter tap in the step S41 is calculated by the following method:
V 3 ＝(64％～75％)V 1 (12)，
V 3 ＝2π×〔(h 3 /3×(2a 3 ﹢b 3 )/(a 3 ﹢b 3 ))﹢d 0 /2〕×(a 3 ﹢b 3 )/2×h 3 (13)，
h 3 ＝(d 3 ﹣d 0 )/2 a 3 ＝0.125p (14)，
b 3 ＝0.125P﹢0.5774(d 3 ﹣d 0 ) (15)，
substituting expressions (2), (13) to (15) into expression (12) to obtain:
d 3 ＝d－(0.1～0.15)P。
V 3 volume of the minor-diameter tap squeezed into the thread groove, a 3 The width of the crest of the small-diameter screw tap extruded into the thread groove h 3 Depth of the minor-diameter tap into the thread groove, d 3 Is the nominal diameter of the small diameter tap.
5. The internal thread cold step extrusion process of claim 2, wherein: and if the bottom hole of the workpiece is a through hole, performing one-step combined machining by using the combined screw tap.
6. The internal thread cold step extrusion process of claim 5, wherein: the combined screw tap comprises a small-diameter section (1) and a standard section (3), the small-diameter section (1) is smoothly connected with the standard section (3) through a transition section (2), the other end of the small-diameter section (1) is smoothly connected with a positioning head (5), and the other end of the standard section (3) is connected with a clamping handle (4).
7. The internal thread cold step extrusion process of claim 5, wherein: the diameter relation between the small diameter section (1) and the standard section (3) is d Small ＝d Sign board ﹣(0.1～0.15)P。
8. The internal thread cold step extrusion process of claim 5, wherein: the clamping handle (4) is a thick handle or a thin handle.
9. The internal thread cold step extrusion process of claim 8, wherein: the diameter of the clamping handle (4) of the thick handle is larger than that of the standard section (3), and the clamping handle (4) is smoothly connected with the standard section (3).
10. The internal thread cold step extrusion process of claim 8, wherein: the diameter of the clamping handle (4) of the thin handle is smaller than that of the standard section (3).
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| JP2000266024A (en) * | 1999-03-16 | 2000-09-26 | Niigata Eng Co Ltd | Method of working female thread part |
| CN1883875A (en) * | 2006-07-05 | 2006-12-27 | 潍柴动力股份有限公司 | Method for processing screw hole in connecting rod body of Steyr diesel engine and dedicated extruded tap therefor |
| JP2007125680A (en) * | 2005-11-07 | 2007-05-24 | Asahi Tec Corp | Method for manufacturing plated female screw and screw tap |
| CN103464842A (en) * | 2013-08-23 | 2013-12-25 | 西安交通大学 | Internal thread vibration and extrusion tapping process |
| CN109604488A (en) * | 2018-12-21 | 2019-04-12 | 哈尔滨理工大学 | A kind of extruding method of magnesium alloy AZ31 internal screw thread |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000266024A (en) * | 1999-03-16 | 2000-09-26 | Niigata Eng Co Ltd | Method of working female thread part |
| JP2007125680A (en) * | 2005-11-07 | 2007-05-24 | Asahi Tec Corp | Method for manufacturing plated female screw and screw tap |
| CN1883875A (en) * | 2006-07-05 | 2006-12-27 | 潍柴动力股份有限公司 | Method for processing screw hole in connecting rod body of Steyr diesel engine and dedicated extruded tap therefor |
| CN103464842A (en) * | 2013-08-23 | 2013-12-25 | 西安交通大学 | Internal thread vibration and extrusion tapping process |
| CN109604488A (en) * | 2018-12-21 | 2019-04-12 | 哈尔滨理工大学 | A kind of extruding method of magnesium alloy AZ31 internal screw thread |
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