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Currently, in stores you can easily buy almost any product necessary for the household. At the same time, the attention and creative efforts of amateur designers are increasingly directed to technically complex objects: tractors, all-terrain vehicles, cars and even aircraft. The approach of do-it-yourselfers to the implementation of planned projects is also changing; they are not afraid of the need to independently manufacture complex and precise parts, which, moreover, may be subject to strict requirements for strength. One of these typical elements, present in almost all energy-intensive designs, are helical coil springs of tension or compression. In this regard, we offer a technique that will help the production of responsible springs with the required quality and accuracy.

The proposed method of winding helical coil springs is implemented on a screw-cutting lathe using a special device consisting of a mandrel and copier. A mandrel with a hook in the form of a hole in the flange end is attached to the machine chuck to fix the beginning of the spring wire. A holder with a copier is installed in the tool holder. The copier is a shaft with a cut helical groove of variable pitch, which rotates freely in two bearings. Grooves at the beginning and at the end of the copier provide coiling of preloaded coils of the spring, and the central part - coiling of working coils with the required pitch and diameter.

The copier holder is a structure welded from a 40 mm steel plate, reinforced with a 10 mm strip rib, and two bearing housings. The right case is welded to the plate, and the left one is fixed with M12 bolts (to enable replacement of the copier).

Specific toolholder drawings are not provided as they are dictated by the type of screw-cutting lathe and coiled spring dimensions. The manufacture of the spring is carried out in the following sequence. First, the workpiece - a measured piece of wire with a 90 - 4 d long end bent at 5 ° is passed from below under the copier and installed in the hole-hook of the mandrel. Then the copier is rotated manually until the beginning of the groove coincides with the position of the wire. Its tension and constant contact with the helical groove of the copier are provided with significant bending resistance of the spring steel of the workpiece. The process of forming a spring begins by turning on the machine spindle at minimum speed. The wire is wound on the mandrel, and the pitch is set by the helical groove of the copier rotating in the bearings.

Scheme of winding cylindrical helical springs using a copier (click to enlarge): 1 - mandrel; 2 - removable bearing housing; 3 - wire; 4 - reinforcement rib; 5 - plate; 6 - cutter of a screw-cutting lathe; 7 - welded bearing housing; 8 - copier; 9 - three-jaw chuck

Below is a method for calculating the parameters of the mandrel and copier, providing the required spring dimensions.

Accepted designations in the calculations. Initial data (spring dimensions): n - number of working turns; n₁- total number of turns; t - step of the working part; D_o - inner diameter; D_Wed- average diameter.

Copier parameters: l - length of the working part; D_cop.- inner diameter of the groove; D_nl.- diameter of the neutral line of turns wound on the mandrel; k = D_nl./D_cop.- correction factor; T - pitch of the helix of the working part;

Т_n- the pitch of the helix of the input and output parts.

Mandrel: d_def.- diameter.

Intermediate calculated values: L - the length of one coil of the spring, excluding the pitch;

D_cf.def.- the average diameter of the coils of the spring wound on the mandrel;

X - tabular coefficient for determining the neutral line when bending;

β - coefficient taking into account the spring properties of the wire;

n_def.- the number of working coils of the spring wound on the mandrel, taking into account the elasticity of the wire;

L₁- the length of the wire passing through the working part of the copier; L₂- the length of the wire of the working coils of the spring, wound on the mandrel;

L₃- the length of the wire wound on the mandrel, taking into account the preloaded coils;

L₄- the length of the spring wire according to the drawing.

The decisive value in the calculation is the value that takes into account the elasticity of the wire during bending. It is used in determining the diameter of the mandrel and the number of turns of the correction. To determine the value of this quantity, the following sequence is recommended. In the first approximation, a mandrel with a diameter D_о. On a screw-cutting lathe, 5-10 turns of wire are wound onto the mandrel with a feed pitch approximately equal to the spring pitch. In this case, a special roller with a groove is installed in the tool holder. After winding, the untwisting angle of all turns of the spring ą is determined, the angle per turn is calculated and, finally, the coefficient B = ą₁/360°/, taking into account the elasticity of the wire of a given material.

Mandrel and wire parameters

For given spring sizes, according to the method described above, an increase in the circular arc of one coil by 30° after removal from a mandrel with a diameter of 42 mm was experimentally established, which corresponds to an increase in the coil length by 1,083 times (β = 30° 360° = 0,083).

On this basis,

D_cf.def.\u1d (L - βL) / π \u157d L (0,917 - β) / π \u3,14d 46xXNUMX / XNUMX \uXNUMXd XNUMX mm,

where L = π D_Wed= 3,14x50 = 157 mm;

d_def.= D_cf.def.- d = 46 - 8 = 38 mm

n_def.= 1,083n + 0,25 = 1,083 + 0,25 = ~10,

where 0,25 is the additional part of the coil, taking into account the tolerance of the number of working coils.

The diameter of the neutral line of the turn on the mandrel (Fig. 2) is calculated by the formula: D_nl.= d_def.+ 2dX.X - is determined according to Table 1 depending on the ratio d_def./ 2d (in our case 38 / (2x8) = 2,375) Using the interpolation method, we calculate X = 0,458 and round to 0,46. Then Dnl = 45,36 mm.

Table 1

(click to enlarge)

Dcop in the first approximation is taken equal to D_о= 42 mm.

Then the coefficient k = D_country./D_cop.= 45,36/42= 1,08. The length of the working part of the copier: = t n = 14x9 = 126 mm.

Estimated step of the working part of the copier: T \uXNUMXd l / (n_def.k) = 126 / (10x1,08) = 11,67 mm.

The resulting calculated step of the working part of the copier is rounded up to the nearest feed step of the screw-cutting lathe (T \u12d XNUMX mm) to ensure the possibility of cutting a helical groove. To maintain the specified spring pitch, the inner diameter of the copier groove is recalculated from the condition of the selected copier step: k = l / (T n_def.) = 126/(12x10) = 1,05. Then D_cop.= D_nl./k \u45,36d 1,05 / 43,2 \uXNUMXd XNUMX mm.

The number of turns of the input and output parts of the copier is chosen equal to 1,5.

The groove pitch of these parts is determined by the experimentally established formula: T = 0,875d = 0,875x8 = 7 mm, and is taken equal to the nearest feed pitch on the machine (7 mm). two screws M8. The conjugation of the grooves of the input and output parts of the copier with the groove of the working part is processed manually with an appropriate file, ensuring a smooth transition. Copier material - steel 8, heat treatment - hardening to hardness HRC45...38. To check the calculations, the length of the wire is determined: L₁= D_cop.π 1 / T \u43,2d 3,14x126x12 / 1425 \uXNUMXd XNUMX mm and compared with the length of the wire: L₂= D_nl.n_def.\u45,36d 3,14x10x1425 \uXNUMXd XNUMX mm. The length of the wire is also compared: L₃= D_nl.π(n_def.+ 2x1,083) = 45,36x3,14(10+2x1,083) = 1733 mm with wire length: L₄= (D_о+ 2d X) π n \u42d (2 + 8x0,46x14) x11, 1705xXNUMX \uXNUMXd XNUMX mm.

With a correct calculation, the error λ should not exceed 2,5%. In our case: λ = (L₃- L₄) 100%/L₄\u1733d (1705 - 100) 1705 / 1,6 \uXNUMXd XNUMX%.

Author: V. Vinichenko

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