A pre-stretching and drawing type overlock waist seam process

Abstract

This invention discloses a pre-stretching and pulling overlocking waist seam process, belonging to the field of garment sewing technology. This invention targets waist side panels with an inward curve. Before sewing, it creates curvature-adaptive gradient stress-relieving cuts on the seam allowance of the inward curve edge to release the shrinkage stress at the fabric edge. Then, the panel is subjected to multi-point vector pulling, applying differentiated stretching forces along the curved edge to obtain a uniform pre-stretch amount. While maintaining the stretch, simultaneous overlocking is completed, followed by a two-stage heat setting process: first, moistening and relaxing, then high-temperature drying, to permanently fix the three-dimensional curve. This invention fundamentally eliminates the wrinkling, lifting, dimensional shortening, and loosening problems inevitably caused by concentrated shrinkage stress when sewing curved waist seams in traditional overlocking processes. The sewn waist seam flatness can reach level 5, the dimensional deviation rate is close to zero, and the shape retention is excellent after multiple washes, significantly improving the finished quality and fit of high-end shirts, dresses, and other waist-cinching garments.

Description

Technical Field

[0001] This invention belongs to the field of garment sewing and processing technology, and specifically discloses a pre-stretching and pulling type overlocking waist seam process. Background Technology

[0002] In high-end shirts, fitted dresses, and fashionable trench coats—clothing styles that need to showcase the beautiful curves of the waist—the side seams at the waist of the front and back pieces are often designed as inward-curving arcs, achieving a slimming effect through the shrinkage of the side seams. Currently, the standard sewing method for this curved side seam in the industry is the ordinary overlock sewing process. The procedure involves directly aligning and stacking the edges of the pre-cut front and back curved side seam pieces, with the right sides of the fabric facing each other, and then feeding them into an industrial overlock sewing machine in one go. The overlock machine completes the combined operations of trimming, sewing, and overlocking. This method is simple and fast, and can meet basic quality requirements for straight or outward-curving sewing. However, when the sewing object is changed to an inward-curving concave arc piece, this conventional process exposes its inherent, long-standing, unresolved technical flaws. The geometric length of the edge of the inward-curving piece is naturally longer than the chord length or the actual length of the overlock stitch that should appear after sewing. In ordinary overlock sewing, the edges of the fabric piece are forcibly pushed forward by the overlock machine's feed dogs, while simultaneously subjected to the resistance of the needle piercing and the tension of the sewing thread. The combined effect of these three forces generates a strong compressive stress on the concave edge of the fabric piece, pointing towards the center of the seam path. This forces the fabric piece to be compressed and shortened along the seam direction, resulting in a significant reduction in the actual length of the fabric piece after sewing, a phenomenon known as "excess" in garment technology. When excess material is unevenly distributed along the entire waist seam, localized excess material manifests as wrinkles, ripples, and sags, the so-called "wrinkling and sag" defects. These defects not only severely damage the garment's smoothness and visual sophistication but also make the designer's originally planned fitted waistline become loose and shapeless, losing its three-dimensionality and lines, greatly reducing the garment's fit and comfort.

[0003] Regarding the technological challenges of shaping the waistline of garments, existing technologies have proposed several improvements. For example, Chinese patent CN108175141B, "Waistline Curve Shaping and Back Waistline Seam Opening Technique," discloses a method for shaping the waistband of trousers with a curve. The technical approach involves pre-sewing the waistband and lining with a specific allowance, then using a steam iron with a "top-edge shaping and bottom-edge pulling" technique to heat-shape and pull the pre-sewn straight waistband, forcibly transforming it into a curve. A retractable opening is then added to the back waistline seam. This process is essentially a post-processing correction method of "sewing first, then ironing," where the heat-shaping effect acts on the pre-defined seam structure, offering no guidance on solving the problem of wrinkling during waistline sewing, which is the focus of this patent. Chinese patent application CN111820490A, entitled "A Method for Cutting, Shaping, and Ironing Trousers," discloses a method for shaping the buttocks, crotch, and knees by shaping and ironing the entire trouser piece along an S-line. This shaping is applied to large trouser pieces and does not involve the overlocking process for the waistband seams. Chinese patent application CN108221351B, entitled "A Method for Cutting and Ironing Fabric for Garment Production," discloses a continuous equipment and method for integrated fabric cutting, ironing, and rolling, but does not involve any improvements to the sewing process for curved pieces. In summary, existing technologies lack an effective process to proactively overcome the fundamental contradiction of inward-curving trouser pieces being compressed and wrinkled during the overlocking process.

[0004] To address the aforementioned technical challenges, the present invention aims to provide a pre-stretching and pulling overlocking waist seam process. The core concept of this process is to achieve a paradigm shift from "post-contraction correction" to "pre-stretching to offset, in-process balancing and fixing, and post-contraction relaxation and stabilization." Through pre-sewing stress-relieving structural design, precise control of the stretching direction and size, and maintenance of dynamic force balance during the sewing process, a high-quality waist seam that is completely flat, dimensionally accurate and stable, and possesses a natural three-dimensional curvature is ultimately obtained, significantly improving the sewing quality of waist-cinching garments. Summary of the Invention

[0005] This invention aims to solve the technical defects of existing conventional overlock sewing processes when sewing waist seams with inward curves, such as wrinkling, lifting, dimensional shrinkage, and loosening of the pattern due to the concentration of compressive stress at the edges of the fabric pieces. To address this, this invention provides a pre-stretching and pulling overlock sewing process for waist seams. Before sewing, a gradient cut with adaptive curvature is made on the concave side seam allowance of the fabric piece to release shrinkage stress. Then, multi-point vector pulling is applied to the curved edge to obtain a uniform pre-stretch. While maintaining the pulled state, dynamic tension is used to coordinate the overlock sewing process to complete the stitching. Finally, a two-stage heat setting process of "first moistening and relaxing, then high-temperature drying" permanently fixes the three-dimensional curvature. The purpose of this invention is to fundamentally eliminate stress deformation during the waist seam sewing process, obtaining a three-dimensional waist seam with a flatness level of 5, a dimensional deviation rate close to zero, and excellent washability, significantly improving the finished product quality and fit of waist-cinching garments.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A pre-stretching and pulling overlock seam technique includes the following steps: S1. Pre-treatment of Gradient Cuttings in Fabric Pieces: Based on the pre-designed garment pattern, cut out the front and back pieces of the waistband with inward-curving edges, and leave a seam allowance of 0.6-1.2cm at the curved edges. Along the curved edge of the waistband, measure and record the radius of curvature of each section using the equal arc length method, thereby dividing the area into high-curvature and low-curvature regions. On the seam allowance of the inward-curving edge of the fabric piece, make multiple (≥2) stress-relieving cuts with a depth not exceeding 1 / 2 of the seam allowance width, perpendicular to the curved edge or inclined inward at 75°-90°. In high-curvature regions where the radius of curvature is less than a preset threshold, the spacing between stress-relieving cuts is set to 0.4-0.8cm; in low-curvature regions where the radius of curvature is greater than or equal to the preset threshold, the spacing between stress-relieving cuts is set to 1.5-4.0cm, so that the distribution density of stress-relieving cuts is positively correlated with the local curvature. S2. Vector Pre-stretching Pull: Precisely align the curved edges of the waist seams of the front and back pieces processed in step S1, with the right sides of the fabric facing each other and the inward curved edges facing upwards and laid flat on the workbench; use a gauge clamp with tension indicator to clamp and fix the two ends of the waist seam curve, and then select at least three evenly distributed vector stretching points along the waist seam curve path. At each point, use a hook or clamp to apply an outward stretching force along the outer normal direction of the tangent of the curve at that point. The magnitude of the stretching force at each point is positively correlated with the local curvature at that point, so that the fibers at each part of the inward curved edge are stretched and extended in the optimal direction, and the total stretching is controlled to be 2%-5% of the original curved edge length; during the stretching process, simultaneously smooth the fabric along the warp direction with a smooth scraper to eliminate interlayer voids and fine wrinkles, so that the piece is in a uniformly taut and wrinkle-free pre-stretching stable state. S3. Dynamic Tension Coordinated Overlock Sewing: Maintaining the overall pre-stretched state of the cut pieces established in step S2, the curved edge of the cut piece assembly in a stable tensioned state is fed uniformly between the roller and presser foot of the overlock sewing machine. The deviation between the feed dog speed of the overlock sewing machine and the operator's manual feed speed is controlled within ±5%. At the same time, the pressure of the presser foot of the overlock sewing machine is adjusted to apply uniform damping tension opposite to the feed direction to the moving cut pieces to counteract the instantaneous reverse compressive stress generated when the needle punctures and the thread tightens. The overlock sewing of the curved waist seam is completed in the above dynamic force balance system, with the stitch density set to 12-14 stitches per centimeter. S4. Phased Heat Setting: After sewing, lay the finished waist seam flat on a vacuum ironing board. In the first phase, use a steam iron to continuously spray saturated steam at a pressure of 0.3-0.5MPa at a distance of 1-2cm from the surface of the fabric for 10-15 seconds. This allows the fabric fibers to fully absorb moisture and swell. During this process, keep the waist seam free and unrestrained, allowing the microscopic residual stress accumulated inside the fibers during the pulling and sewing process to be fully released through the chain segment movement of the fiber macromolecules. In the second phase, quickly raise the iron temperature to 120-150℃, place a pure cotton ironing cloth on the surface of the waist seam, and apply a uniform pressure of 50-150Pa along the arc direction of the waist seam from one end to the other using a pushing and ironing technique until the fabric is completely dry and cooled, forming a permanent and stable inward-curving three-dimensional waist seam.

[0007] In this invention, the "stress-relieving notch" described in step S1 is not an arbitrary destruction of the cut piece, but a precisely designed pre-treatment process. The working principle of the stress-relieving notch is that along the concave arc edge, the fabric fibers are in a state of high internal stress due to their geometric shape. This internal stress is the root cause of strong shrinkage during subsequent overlocking. By creating stress-relieving notches, it is equivalent to introducing regular breakpoints in the fiber continuum, cutting off long-distance stress transmission chains, and decomposing the large-scale shrinkage trend into small-scale local adjustments. Furthermore, the "gradient distribution" stress-relieving notch strategy proposed in this invention, that is, the stress-relieving notches are denser in high-curvature areas (areas with greater curvature), is based on the following mechanical understanding: the greater the curvature of the concave arc, the greater the difference between its edge length and chord length, that is, the greater the amount that needs to be extended, and the more concentrated the compressive internal stress on the fibers in this area. By using densified stress relief shears, more stress relief points and greater degrees of freedom can be provided in high-demand areas, thereby achieving a precise match between stretchability and stretching requirements. This avoids the problems of insufficient stretching in high-curvature areas and excessive stretching in low-curvature areas that exist in uniform stress relief shear schemes.

[0008] The "vector pre-stretching pull" described in step S2 is a significant improvement over traditional simple bidirectional stretching. Traditional two-end stretching only applies force to the entire fabric piece, and the direction of the force is unidirectional, which cannot adapt to the complex geometric requirements of curved shapes. The "multi-point vector pull" method of this invention selects multiple points on the curved path and applies a pull force to each point in the direction of the outward normal to the tangent of the arc at that point (i.e., the direction that "pushes" the arc outward). This pull force direction is completely consistent with the ideal direction in which the fiber needs to be stretched to offset shrinkage, achieving vector optimization of force and greatly improving stretching efficiency. At the same time, the magnitude of the force at each point is positively correlated with the local curvature of that point, ensuring that areas with large curvature receive greater stretching driving force, ultimately achieving uniform stretching of the entire arc. This refined pull control can be achieved through simple multi-axis adjustable tooling or intelligent fixtures with tension feedback, allowing the operator to make precise adjustments based on visualized force values.

[0009] Step S3, "dynamic tension-coordinated overlock sewing," is the core of the entire process. If the tension is removed before feeding the sewing machine after pre-stretching, the cut piece will instantly elastically retract, losing most of the pre-stretching effect. Therefore, this process requires "maintaining the stretched state" during overlock sewing. At this time, the curved edge of the cut piece is in a dynamic equilibrium of being actively stretched outward. To ensure that this state is not disrupted during high-speed sewing, this invention further proposes a dual control mechanism of "speed synchronization" and "reverse damping." The feed dog's pushing speed is synchronized with the operator's (or auxiliary feeding device's) feeding speed, avoiding pushing or pulling caused by speed differences; while the reverse damping tension applied by the presser foot constitutes a stable "tension background," which can absorb and buffer the impact reverse compressive stress generated at the moment of needle piercing and thread knot tightening, preventing the stress from being too large instantaneously superimposed and squeezing the edge of the cut piece back into a wrinkled state. This dynamic force balance system is designed to ensure that the overlock stitches are accurately formed on the stretched, ideal cut piece, and the stitches themselves are transformed from a source of shrinkage stress into a fixed framework of the ideal shape.

[0010] Step S4, the "stress relaxation and pull-dry setting two-stage heat setting," is crucial for stabilizing the three-dimensional shape of the finished product. The initial saturated steam humidification relaxation stage utilizes the stress relaxation characteristics of textile fibers, particularly cotton, linen, and regenerated cellulose fibers, under high temperature and humidity conditions. With sufficient humidity and heat, the activity of the macromolecular chain segments in the amorphous region of the fiber increases dramatically, allowing the intermolecular hydrogen bonds and van der Waals forces that were forcibly stretched or compressed during drawing and sewing to break down and rebuild, thus macroscopically releasing the residual elastic energy accumulated internally. This stage is essential to prevent the finished product from slowly shrinking and deforming during subsequent washing and wearing. The subsequent high-temperature pull-drying and ironing setting, under a new, stress-free or low-stress condition, rapidly removes moisture, allowing the fiber macromolecular chain segments to re-establish stable intermolecular forces in their new positions, thereby permanently fixing the ideal three-dimensional arc shape.

[0011] A pre-stretching and pulling overlock seam technique includes the following steps: S1. Pre-treatment of gradient seam allowances in the cut pieces: Multiple stress-relief seams are made on the concave side seam allowance of the waist-side cut piece with an inward-curving edge. The distribution density of the stress-relief seams is positively correlated with the local curvature of the inward-curving edge; the quantitative relationship is: stress-relief seam spacing (cm) = α / radius of curvature (cm), where α is 0.5-2.0cm. 2 The smaller the radius of curvature (the larger the curvature), the smaller the slit spacing. S2. Vector pre-stretching: After aligning the waist seam edges of the front and back pieces, select multiple action points along the inner curved edge, and apply an outward pulling force to each action point along the outer normal direction of the arc tangent at its position, so that the inner curved edge obtains a uniform pre-stretch amount. S3. Dynamic tension coordinated overlock sewing: Maintaining the pulled state of step S2, the cut piece is fed into the overlock sewing machine for sewing. By synchronously controlling the feeding speed and applying reverse damping tension to the cut piece, the overlock sewing is completed under dynamic force balance. S4. Phased heat setting: First, the sewn waist seam is moistened to release sewing stress, and then it is dried and ironed to form a stable, inward-curving three-dimensional waist seam.

[0012] Preferably, in step S1, the seam allowance reserved at the inward-curved edge is 0.6-1.2cm; the depth of the stress-relieving cut does not exceed 1 / 2 of the seam allowance width, and its direction is perpendicular to the curved edge or inclined at 75°-90° towards the inside of the curve; the distribution density of the stress-relieving cut is specifically set as follows: based on the radius of curvature, high and low curvature areas are divided, and in the high curvature area, the cut spacing is set to 0.4-0.8cm; in the low curvature area, the cut spacing is set to 1.5-4.0cm; the stress-relieving cut is processed by laser cutting or ultrasonic cutting to ensure that the cut edge is fused and does not come apart; the depth of the stress-relieving cut is 1 / 3 to 1 / 2 of the seam allowance width, and the cut shape is V-shaped or straight.

[0013] Preferably, in step S1, the threshold for dividing the high curvature region and the low curvature region is: the curvature radius value corresponding to one-third of the total arc length of the waist seam; that is: when measuring along the waist seam arc from one end to the other, when the cumulative arc length reaches 1 / 3 and 2 / 3 of the total arc length, the curvature radius values ​​at these two points are used as the dividing threshold; the region with a curvature radius less than the threshold is the high curvature region, and the region with a curvature radius greater than or equal to the threshold is the low curvature region.

[0014] Preferably, in step S2, the pre-extension amount is controlled to be 2%-5% of the length of the inward arc edge; the magnitude of the pull force applied at each point is positively correlated with the local curvature at that point, and is operated by a gauge clamp with a pull force indicator or a multi-axis adjustable pull tool; the multi-point coordinated vector pre-extension pull shaping operation is completed by a multi-axis adjustable pull tool, which includes a base plate, a fixed clamp, a movable clamp, and a pull sensor; the fixed clamp fixes both ends of the waist seam, and the movable clamp applies pull force along the arc normal direction at a preset angle and position, and the pull sensor provides real-time feedback of the force value at each point.

[0015] Preferably, in step S2, the quantitative correlation between the magnitude of the pull-out force at each point of application and the local curvature is: F = k × C, where F is the target pull-out force (in N) and C is the local curvature (in m). -1 ), defined as the reciprocal of the radius of curvature at that point, i.e., C=1 / R; k is a proportionality constant related to the fabric type and the target elongation, with a value range of 0.5-5.0 N·m. For lightweight fabrics such as chiffon, k is 0.5-1.5 N·m; for heavy fabrics such as cotton poplin, k is 3.0-5.0 N·m; and for medium-weight fabrics such as polyester-cotton blends, k is 1.5-3.0 N·m.

[0016] Preferably, in step S3, the deviation between the push speed of the overlock sewing machine's feed dog and the feed speed of the cut piece is controlled within ±5%. The reverse damping tension is achieved by adjusting the presser foot pressure of the overlock sewing machine, and the stitch density is set to 12-14 stitches per centimeter. The overlock sewing machine is a four-thread or five-thread industrial overlock sewing machine, and the feed dog has a three-row feed dog structure to improve the synchronization and stability of pushing multi-layer cut pieces. The reverse damping tension of the presser foot is achieved by adjusting the presser foot spring pressure to 0.5-1.5 kgf. The conversion coefficient between the reverse damping tension and the presser foot spring pressure is approximately 0.3-0.5 N / 0.1 kgf, that is, for every 0.1 kgf increase in the presser foot spring pressure, the reverse damping tension increases by approximately 0.3-0.5 N. After the overlock sewing is completed, a uniform micro-texture is formed on the edge of the waist seam allowance. This texture is naturally formed by the pre-stretched fabric under dynamic tension overlock sewing.

[0017] Preferably, in step S4, the phased heat setting specifically includes: the first stage, using a steam iron to spray saturated steam onto the waist seam for 10-15 seconds, with the iron 1-2 cm away from the fabric, so that the fabric fibers absorb moisture and swell and are in a free state to release stress; the second stage, using an iron at a temperature of 120-150℃, using a pushing ironing technique along the arc direction of the waist seam to dry and set the fabric; the humidity of the saturated steam is not less than 95%, and the suction function of the ironing board is kept off during the steam spraying stage; during the pushing ironing stage, the iron moving speed is 3-8 cm / s, the bottom of the iron is at a 5°-15° angle to the fabric, and 50-150 Pa pressure is applied to match the rate of moisture evaporation of the fabric.

[0018] A garment panel component with an inwardly tapered waist seam is sewn using the pre-stretching and pulling overlocking waist seam process described in this invention. The edge of the waist seam has a uniform micro-texture that has been pre-stretched and pulled and locked by the overlocking stitch. The garment panel component described in this invention is the front and back seam assembly of the waist side seam of shirts, dresses, and coats.

[0019] The drawing fixture mentioned in this invention specification refers to a multi-axis adjustable drawing fixture.

[0020] The core innovations are as follows: ① Curvature-Adaptive Gradient Stress Relief Cutting Stress Management: Unlike any existing technology that maintains the integrity of the cut pieces or uses uniform cutting, this invention dynamically adjusts the density of stress relief cuts based on the curvature changes of the waist seam, employing a "gradient cutting" method. Its physical essence is the non-uniform, differentiated pre-planning of the required stress relief and extension freedom at various points along the concave arc edge. High-curvature areas have denser stress relief cuts, providing ample space for release and extension; low-curvature areas have sparser stress relief cuts, maximizing fabric structural strength while ensuring necessary extension. This positively correlated "curvature-density" stress relief cutting layout is the prerequisite for ensuring subsequent uniform extension.

[0021] ② Multi-point stretching method based on vector mechanics: Unlike the traditional "one-dimensional" force control approach of stretching from both ends, this invention pioneers a "multi-dimensional vector" stretching method that applies differentiated force values ​​along the arc normal. By discretizing the waist seam arc into multiple force application points, and applying a stretching force perpendicular to the tangent of the arc at that point (i.e., outward along the outer normal) and proportional to the local curvature of that point to each point, the fabric fibers are stretched directionally along the natural path most conducive to resisting shrinkage. This method greatly improves the uniformity of stretching and energy utilization efficiency, avoiding local over-stretching or under-stretching, which is the key to this technology.

[0022] ③ "Feed-Push-Damping" Balance in the Sewing Process: Instead of "presetting" a static shape before sewing, this system maintains a stable dynamic force balance throughout the entire sewing process. The system consists of three components: the forward force of the operator feeding the fabric into the sewing machine, the forward pushing force of the sewing machine's feed dogs, and the backward damping force generated by the presser foot through pressure adjustment. The feeding speed is synchronized with the pushing speed, avoiding pushing or pulling on the fabric; the reverse damping force sensitively counteracts the unavoidable instantaneous reverse compression pulses when the needle penetrates and the thread is knotted and tightened. These three forces achieve dynamic balance at the moment of sewing, transforming the overlock sewing process into a precise operation performed on a stable tension plane, completely eliminating micro-wrinkling caused by force fluctuations.

[0023] ④ A two-stage heat-setting process based on the principle of fiber stress relaxation: Unlike traditional ironing that directly heats and flattens, this invention adds a crucial "saturated steam humidification and free relaxation" stage before ironing. This process allows the elastic potential energy locked inside the fibers during sewing and stretching to dissipate completely through free shrinkage or swelling after the fiber macromolecular chains gain sufficient mobility under high temperature and humidity. Only after the internal stress is cleared to zero, and then subsequent drying and ironing are performed, resulting in a new shape that is thermodynamically more stable and permanently set without slowly shrinking over time. This "release first, fix later" process logic significantly improves the dimensional stability and washability of the finished product.

[0024] Beneficial technical effects: 1. Elimination of Wrinkling and Rigging: This process solves the problem of compression wrinkling at curved edges, which is unavoidable with ordinary overlock stitching. According to the AATCC 124 standard rating, the flatness of the waist seam using this process can reach level 4.5 or higher, compared to the flatness of around level 1.5 with ordinary processes, achieving a quality leap from "severe wrinkles" to "almost invisible wrinkles." The deviation between the waist seam size and the design size is controlled within 0.2%, solving the problems of "edge rigging" and curvature deformation.

[0025] 2. Shaping and Maintaining a Crisp, Three-Dimensional Curve: Multi-point vector stretching precisely pre-shapes an ergonomically contoured inward curve for the waist seam. Dynamic tension overlocking securely locks this curve in place, while two-stage heat setting ensures its stability. The finished waist seam features smooth, natural lines, achieving a crisp, three-dimensional look without requiring any support from the wearer, perfectly executing the designer's waist-slimming intent. After five standard washes, its three-dimensional shape and flatness retention rate exceeds 95%, far surpassing the significant shape degradation observed after washing with traditional processes.

[0026] 3. The process of this invention is applicable to a wide range of fabrics: The fabrics of this invention are not limited by chemical composition. Whether it is chiffon fabric with smooth fibers, loose structure, and easy wrinkling during sewing, or high-count, high-density woven cotton fabric with dense fibers, high stiffness, and strong internal stress, or common polyester-cotton and viscose blended fabrics, they can all be easily adapted by adjusting the tensile force and stress release shear parameters, and all can achieve processing results superior to traditional processes, solving the processing difficulties of non-elastic fabrics in waist-cinching designs.

[0027] 4. Controllable and standardized operation, low industrial production cost: The core equipment of this process consists of simple, low-cost mechanical or pneumatic auxiliary tooling, eliminating the need for expensive fully automated equipment. Process parameters such as curvature, force, speed, and time are quantified and standardized, reducing the technical threshold and human error for operators, and shortening the training cycle. This process can be directly implemented on existing industrial overlock sewing machines by adding fixtures and adjusting equipment parameters, resulting in a very high return on investment and suitability for large-scale promotion. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the pre-processing of the cut pieces in Embodiment 1 of the present invention, showing the distribution of minute stress-relieving cuts on the waist side cut pieces and seam allowances, and the pull-out state of the cut pieces.

[0029] Figure 2 The image shows a comparison between the finished waist seam products of this invention and those of ordinary overlock sewing. The left side shows the finished product of ordinary overlock sewing, while the right side shows the finished product of pull-out overlock sewing. It is clear that the finished product of ordinary overlock sewing has wrinkles and drooping edges, while the finished product of this invention is flat, smooth, and has a natural curvature. Detailed Implementation

[0030] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0031] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of those skilled in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or identical to those described in the embodiments of this invention may be used to implement this invention.

[0032] Unless otherwise stated, the test methods, detection methods and preparation methods disclosed in this invention all adopt conventional techniques in this technical field.

[0033] All fabrics used in the following examples and comparative examples were purchased from large domestic textile fabric markets and were all untreated, conventional garment fabrics. The overlock sewing process used an EF4-V61 four-thread high-speed industrial overlock sewing machine manufactured by Brother Industries, Ltd. of Japan. This machine features differential feed adjustment and presser foot pressure fine-tuning. The ironing process used an MG-600 full-steam iron and a matching rocker ironing table with blowing and suction functions manufactured by Shanghai Weishi Machinery Co., Ltd. The ambient temperature was 25±2℃ and the relative humidity was 60±5%. The multi-point stretching fixture used for pre-stretching was designed and manufactured in our laboratory. It consists of an aluminum alloy base plate, four universal precision vises, and a matching tension spring scale, enabling multi-angle clamping and quantitative stretching of curved cut pieces. In the following examples and comparative examples, except for the process steps themselves, the external conditions such as fabric, thread, equipment, and operating environment were kept consistent to ensure the reliability of the comparison results. For ease of understanding, the "inwardly curved edge" mentioned in this invention refers to the concave curved side edge of the cut piece; "stress relief notch" is abbreviated as "notch"; "pre-stretch amount" and "stretch amount" are synonymous; "high-temperature drying and ironing" and "drying and shaping" are synonymous.

[0034] Example 1: Construction of waist seam for chiffon shirt (low curvature) The fabric selected is a commercially available 8mm double crepe chiffon (the fabric has not undergone special pretreatment), its fiber composition is 100% polyester, its weight is 80g per square meter, and its warp and weft density is 42×38 threads / cm. 2Based on the standard women's shirt pattern of size 170 / 88A, the front and back waist panels on both sides are cut. This embodiment focuses on the operation of the waist seam on one side. The waist seam edge of the panel is designed as an inward concave arc with a total arc length of 28.5cm. After segmented measurement, the maximum curvature occurs near the midpoint of the arc with a radius of curvature of 45cm, and the minimum curvature occurs near the endpoint with a radius of curvature of 120cm. The overall average curvature corresponds to a radius of curvature of 60cm. The seam allowance is set to 1.0cm. According to the process rules of this invention, the waist seam arc is divided into high and low curvature regions based on a curvature radius of 60cm. The region with a curvature radius of 45cm < 60cm in the middle section of the arc is determined as the high curvature region, and the regions with a curvature radius of 120cm > 60cm at both ends are determined as the low curvature region. After marking the seam allowance of the gathered curved edge of the fabric piece with sharp chalk, make stress-relief cuts using sharp tailor's scissors: in high curvature areas, the spacing of the stress-relief cuts is set at 0.6cm, the depth of the cuts is 0.3cm (1 / 3 of the seam allowance width), and the direction is perpendicular to the curved edge; in low curvature areas, the spacing of the stress-relief cuts is set at 4.0cm, with the same depth and direction. A total of 7 stress-relief cuts are made. Place the front and back fabric pieces face to face, ensuring the waist seam edges are precisely aligned, with the gathered curved edge facing upwards on the base plate of the pulling fixture. Fix the two ends of the waist seam curve with clamps at both ends, and then select 3 vector pulling points equidistantly along the curve path, located at 1 / 4, 1 / 2, and 3 / 4 of the curve length, respectively. A tension spring scale with a range of 0-5N and a scale division of 0.05N is used to apply a pulling force (R=0.45m, F=1.5N, C=1 / R=2.22m) along the outer normal direction of the arc at each of the three points. -1The force is calculated as k = 1.5 / 2.22 ≈ 0.68 N·m, where the force at the midpoint (high curvature area) is 1.5 N and the force at both ends (low curvature area) is 0.8 N. Under tension, the entire inward-curving edge extends uniformly outward. The original 28.5 cm arc length, measured with a soft ruler, increases to approximately 29.3 cm after stretching, with an extension of 0.8 cm and an elongation rate of 2.8%. While maintaining this stretching state, a smooth horn scraper is used to gently smooth the fabric along the warp direction to eliminate any gaps between the upper and lower pieces. While maintaining this tension, the pieces are fed into an overlock sewing machine with adjusted parameters. The overlock sewing machine is set to a stitch density of 12 stitches / cm, the differential ratio is adjusted to 1:1.1 to slightly increase the feed dog speed, and the presser foot pressure is adjusted to 0.8 kgf to create appropriate reverse damping. The operator feeds the fabric slowly at a stable speed synchronized with the machine, maintaining a consistent pulling sensation throughout the process. Once no localized shrinkage is observed, the sewing is completed. After sewing, the waist seam is laid flat on an ironing board. The suction is turned off, and a steam iron is used to spray saturated steam 1.5cm above the fabric for 12 seconds. The fabric will be observed to fully absorb moisture, soften, and slightly expand. Then, the suction is turned on, and the iron temperature is quickly adjusted to 130℃. A piece of pure white cotton cloth is placed on the waist seam, and the iron is pushed and ironed from left to right along the arc at a speed of 5cm / s (moving in an "S" shaped trajectory, with the bottom of the iron at a 10° angle to the fabric, applying 100Pa pressure). Each section is moved back and forth twice until the fabric is completely dry. The suction is then turned off, allowing it to cool naturally to room temperature. The chiffon waist seam produced in this example is smooth and even, with no wrinkles or ripples visible from any angle. The length along the arc is measured to be 28.5cm, perfectly matching the design dimensions.

[0035] Example 2: Construction of waist seam for a high-density woven cotton shirt (medium curvature). Selected high-count, high-density cotton poplin woven fabric, with a yarn count of 80S / 2×80S / 2 and a warp and weft density of 140×90 threads / inch. 2The fabric is finished with mercerizing. The back and side panels are cut according to the standard men's 175 / 92A pattern. The waist seam has a relatively large curvature, with an arc length of 32.0cm, and a high curvature threshold of 50cm. The seam allowance is 1.2cm. In this embodiment, the high curvature area (curvature radius < 50cm) accounts for approximately 60% of the arc length. Stress relief cuts are made at 0.5cm intervals and at a depth of 0.6cm (half the seam allowance). To ensure the fabric stretches more easily under high-density, stiff fabric, the stress relief cuts are intentionally angled inwards at approximately 80°. In the low curvature area, stress relief cuts are spaced 3.0cm apart and 0.6cm deep, perpendicular to the edge. A total of 15 stress relief cuts are made. The fabric is aligned and fixed to the pulling fixture as described above, and vector pulling is performed at four equally spaced points along the arc. Due to the fabric's high stiffness, the pulling force applied at each point was increased accordingly, with a force of 3.5N at the midpoint and 1.5N near the end. The total elongation reached approximately 1.3cm, with an elongation rate of 4.1%, near the target upper limit, ensuring sufficient elongation of the high-stiffness fabric. The fabric was fed into an overlock sewing machine with a thread density of 13 stitches / cm and presser foot pressure adjusted to 1.2kgf to provide stronger reverse damping. After sewing, saturated steam was sprayed for 15 seconds, and the high-density cotton fabric was observed to soften significantly. Subsequently, it was vigorously ironed at 150℃ to stretch the fabric, moving it along an arc from left to right at a speed of 5cm / s (moving in an "S" shaped trajectory, with the iron bottom at a 10° angle to the fabric, applying 100Pa pressure). The all-cotton poplin waistband sewn in this example exhibited extremely clean lines, without any wrinkles or sagging, with a full and crisp curve and a strong three-dimensional effect.

[0036] Example 3: Construction of the waist seam for a polyester-cotton blend dress (high curvature arc) A 65 / 35 polyester / cotton blend plain weave fabric, weighing 120g per square meter, was selected. This fabric was used for an extremely fitted dress with a high curvature at the waist, with an arc length of 24.0cm. However, the curvature is concentrated and narrowed, with a minimum curvature radius of only 18cm at the midpoint. The high curvature threshold was set at a radius of 30cm, therefore, the arc length exceeding 80% was defined as a high curvature zone. The seam allowance was 0.8cm. In the high curvature area, the stress-relieving notch spacing was further reduced to 0.4cm, and the depth was strictly controlled to 1 / 3 of the seam allowance, i.e., 0.26cm, to prevent damage to the structural strength of the high-stress area due to excessively deep stress-relieving notches. The direction was perpendicular to the edge. The stress-relieving notch spacing in the low curvature area was 2.0cm. A total of 18 stress-relieving notches were made. Pulling was performed using a 5-point synchronous vector stretching method, with a force of 3.8N applied at the midpoint and decreasing sequentially at adjacent points. The total elongation was strictly controlled at 5%, i.e., an elongation of approximately 1.2cm. Careful observation ensured that the high curvature area exhibited uniform stretching rather than localized tearing deformation. During sewing, the stitch density was set to the densest setting of 14 stitches / cm, and the presser foot pressure was adjusted to 1.2 kgf to provide stronger binding force to fix the high-extension shape. After sewing, steam was sprayed for 10 seconds, and then immediately ironed at 120°C to dry. The iron was moved from left to right along the curvature at a speed of 4 cm / s (moving in an "S" shaped trajectory, with the bottom of the iron at a 10° angle to the fabric, applying 100 Pa of pressure) to prevent excessive temperature from affecting the luster of the blended fabric. The extremely high curvature waist seam treated in this embodiment still achieved a smooth and wrinkle-free finish with a natural and smooth curvature. Furthermore, due to the reasonable stress-relieving cut gradient design, no edge wavy deformation occurred in the high curvature area.

[0037] Comparative Example 1: Standard Overlock Sewing Process for Chiffon Fabric Using the same chiffon fabric and cut pieces as in Example 1 (without any stress-relieving notches), and without any pre-stretching or shaping, the waist seam edges of the front and back pieces were directly aligned and fed into the same overlock sewing machine using conventional methods. Ordinary overlock sewing was performed using the same stitch density (12 stitches / cm) and presser foot pressure as in Example 1. During the sewing process, it was observed that the fabric gathered and wrinkled after pressing. After sewing, the waist seam exhibited extremely significant continuous fine wrinkles and wavy edges. The effective length, measured along the center of the waist seam stitch with a soft measuring tape, was 27.1cm, which is 1.4cm shorter than the designed waist seam length of 28.5cm, corresponding to a length deviation rate as high as -4.9%. Even with repeated pressing with 130℃ steam ironing as in Example 1, the wrinkles could only be slightly reduced, not completely eliminated, and the length did not recover significantly. The entire waist seam had a loose shape and lacked any aesthetic appeal.

[0038] Comparative Example 2: Chiffon fabric with only stretching and no cutting process The same chiffon fabric and cut pieces as in Example 1 were used, but no stress-relief notches were made on the seam allowances. All subsequent operations were identical to those in Example 1, including pre-stretching to 3% total elongation using multi-point vector pulling, and performing stretched overlocking and phased shaping under the same parameters. Because no stress-relief notches were made, the continuous fiber network of the fabric constituted strong structural resistance. When the same 1.5N / 0.8N pulling force as in Example 1 was applied, the force could not be effectively transmitted through the fibers to the central area, resulting in a very "mushy" feel during pulling and difficulty in stretching. To achieve a macroscopic elongation of 3% similar to Example 1, the midpoint pulling force was forced to be increased to 2.8N. Excessive concentrated stress caused localized stretching and deformation marks to appear on the fabric during the pulling process. After overlocking, the waist seam was improved compared to Comparative Example 1, but scattered fine uneven ripples were still visible. Especially in the high curvature area where stress was originally concentrated, there were still slight residual wrinkles. Its static flatness rating could only reach about level 3, which was far inferior to Example 1.

[0039] Comparative Example 3: Chiffon fabric with evenly cut edges and simple end-pulling process Using the same chiffon fabric and cut pieces as in Example 1, stress-relief cuts with a uniform spacing of 1.8 cm (divided into 16 equal parts based on an arc length of 28.5 cm) and a depth of 0.3 cm were made on the seam allowance of the inward-curved edge. The cuts were perpendicular to the edge and were uniformly applied regardless of the curvature. Then, instead of using multi-point vector stretching, a traditional method was employed: simply holding the two ends of the cut piece with both hands and stretching it bidirectionally along the line connecting the two ends, stretching it by hand to approximately 3% of the total elongation, similar to Example 1. Subsequent operations were the same as in Example 1. Because the stress-relief cuts were uniformly distributed, the edge of the high-curvature area required a larger elongation per unit length, resulting in the same number of stress-relief cuts as the low-curvature area, leading to relatively insufficient elongation. Conversely, the low-curvature area might become too loose due to excessive stress-relief cuts, and thus be over-stretched under stretching at both ends. Although the overlocked finished product avoids the most severe shrinkage, careful inspection under side lighting reveals that the fabric on both sides of the waist seam shows extremely slight uneven twisting, and the consistency and smoothness of the shape are significantly different from those in Example 1.

[0040] Performance testing and result comparison To scientifically and objectively evaluate the process effect, the samples prepared in the above embodiments and comparative examples were tested according to the following generally accepted standards: Appearance smoothness (grade): Referring to the three-dimensional smoothness sample photo in AATCC 124-2018 "Smoothness of Fabrics After Household Washing" standard, five trained observers independently rated the waist seam area in a standard D65 light source and darkroom environment. The final result is the mode or mean. Grade 5 indicates the smoothest surface, and Grade 1 indicates extremely severe wrinkling.

[0041] Size deviation (%): Use a soft measuring tape with an accuracy of 1mm, close to the center of the waist seam overlock stitch, measure the actual net length of the waist seam after sewing, and compare it with its design length. Calculate the size deviation rate according to the formula (actual length - design length) / design length × 100%.

[0042] Washability and shape retention (smoothness after washing, grade): Washing and tumble drying were performed according to procedure 5A in GB / T8629-2017 "Test Procedures for Home Washing and Drying of Textiles". After five complete cycles, the smoothness of the waist seam was graded again according to method 1 above. This indicator directly reflects the durability of the shaping effect.

[0043] The results of each test are detailed in Table 1 below.

[0044] Table 1 shows the test results for each example and comparative example. As can be clearly seen from the data in Table 1 above, the embodiments of the present invention have achieved technical effects far exceeding those of the comparative examples in all test indicators, and the underlying mechanism has an inherent logical consistency. Comparative Example 1, which is a conventional overlock sewing process, has no means to counteract compressive stress. The aggregate shape of the fabric in three-dimensional space is forcibly changed by the seam, resulting in irreversible macroscopic plastic compression wrinkles that are difficult to eliminate even with ironing. Furthermore, the fiber memory effect after washing causes the wrinkles to recover and worsen. The results of Comparative Example 2 demonstrate that simply stretching without simultaneous stress release (without stress release slits) results in extremely uneven stretching force and stretching shape due to the inherent cohesive network resistance of the fabric. Local overstretching or understretching inevitably occurs, and the residual microscopic internal stress becomes the root cause of shrinkage and wrinkling after washing. Comparative Example 3 reveals the shortcomings of combining uniform stress release slits with simple stretching. The degree of freedom of stretching (the space provided by the stress release slits) and driving force (tensioning force) obtained in high-demand areas are supplied at a global average, resulting in unevenness and deformation differences, with slight surface distortion. The embodiments of this invention effectively resolve the mechanical contradictions leading to wrinkling through "curvature adaptation" of stress-relieving cut density, "vector and magnitude adaptation" of pulling force, and "dynamic force balance adaptation" of the sewing process. Based on this, the final "two-stage heat setting" process fixes the final perfect shape in a molecularly stable form. This series of interconnected innovations gives this invention outstanding substantive features and significant progress compared to existing technologies.

[0045] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A pre-stretching and pulling type overlock seam technique, characterized in that, Includes the following steps: S1. Pre-treatment of gradient notches in the cut piece: On the concave arc side seam of the waist side cut piece with an inward arc edge, multiple stress-relieving notches are made. The distribution density of the stress-relieving notches is positively correlated with the local curvature of the inward arc edge. S2. Vector pre-stretching: After aligning the waist seam edges of the front and back pieces, select multiple action points along the inner curved edge, and apply an outward pulling force to each action point along the outer normal direction of the arc tangent at its position, so that the inner curved edge obtains a uniform pre-stretch amount. S3. Dynamic tension coordinated overlock sewing: Maintaining the pulled state of step S2, the cut piece is fed into the overlock sewing machine for sewing. By synchronously controlling the feeding speed and applying reverse damping tension to the cut piece, the overlock sewing is completed under dynamic force balance. S4. Phased heat setting: First, the sewn waist seam is moistened to release sewing stress, and then it is dried and ironed to form a stable, inward-curving three-dimensional waist seam.

2. The process according to claim 1, characterized in that: In step S1, the seam allowance reserved at the inner curved edge is 0.6-1.2cm; the depth of the stress-relieving cut does not exceed 1 / 2 of the seam allowance width, and its direction is perpendicular to the curved edge or inclined to the inner side of the arc at 75°-90°. The distribution density of the stress-relieving cuts is specifically set as follows: based on the radius of curvature, high and low curvature regions are divided. In the high curvature region, the cut spacing is set to 0.4-0.8cm; in the low curvature region, the cut spacing is set to 1.5-4.0cm. The stress-relieving cuts are processed by laser cutting or ultrasonic cutting to ensure that the cut edges are fused and do not come apart. The depth of the stress-relieving cuts is 1 / 3 to 1 / 2 of the seam allowance width, and the cut shape is V-shaped or straight.

3. The process according to claim 2, characterized in that: In step S1, the threshold for dividing the high curvature region and the low curvature region is the curvature radius value corresponding to one-third of the total arc length of the waist seam.

4. The process according to claim 1, characterized in that: In step S2, the pre-extension amount is controlled to be 2%-5% of the length of the inward arc edge; the magnitude of the pull force applied at each point is positively correlated with the local curvature at that point, and is operated by a gauge clamp with a pull force indicator or a multi-axis adjustable pull tool; the multi-point coordinated vector pre-extension pull shaping operation is completed by a multi-axis adjustable pull tool, which includes a base plate, a fixed clamp, a movable clamp, and a pull force sensor; the fixed clamp fixes both ends of the waist seam, and the movable clamp applies pull force along the arc normal direction at a preset angle and position, and the pull force sensor provides real-time feedback of the force value at each point.

5. The process according to claim 4, characterized in that: In step S2, the quantitative correlation between the pull force at each point of application and the local curvature is: F = k × C, where F is the target pull force, C is the local curvature, defined as the reciprocal of the radius of curvature at that point, i.e., C = 1 / R; k is a proportionality constant related to the fabric type and the target elongation, with a value range of 0.5-5.0 N·m. For lightweight chiffon fabrics, k is 0.5-1.5 N·m; for heavy cotton poplin fabrics, k is 3.0-5.0 N·m; and for medium-weight polyester-cotton blended fabrics, k is 1.5-3.0 N·m.

6. The process according to claim 1, characterized in that: In step S3, the deviation between the feed speed of the overlock sewing machine's feed dog and the feed speed of the cut piece is controlled within ±5%. The reverse damping tension is achieved by adjusting the presser foot pressure of the overlock sewing machine, and the stitch density is set to 12-14 stitches per centimeter. The overlock sewing machine is a four- or five-thread industrial overlock sewing machine with a three-row feed dog structure to improve the synchronization and stability of pushing multi-layer cut pieces. The reverse damping tension of the presser foot is achieved by adjusting the presser foot spring pressure to 0.5-1.5 kgf. The conversion coefficient between the reverse damping tension and the presser foot spring pressure is 0.3-0.5 N / 0.1 kgf. After the overlock is completed, a uniform micro-texture is formed on the edge of the waist seam allowance. This texture is naturally formed by the pre-stretched fabric under dynamic tension overlock.

7. The process according to claim 1, characterized in that: In step S4, the phased heat setting specifically includes: the first stage, using a steam iron to spray saturated steam onto the waist seam for 10-15 seconds, with the iron 1-2cm away from the fabric, so that the fabric fibers absorb moisture and swell and are in a free state to release stress; the second stage, using an iron at a temperature of 120-150℃, using a pushing ironing technique along the arc direction of the waist seam to dry and set the fabric; the humidity of the saturated steam is not less than 95%, and the suction function of the ironing board is kept off during the steam spraying stage; during the pushing ironing stage, the iron moves at a speed of 3-8cm / s, with the bottom of the iron at a 5°-15° angle to the fabric, and applies a pressure of 50-150Pa to match the rate of moisture evaporation of the fabric.

8. A garment panel component with an inwardly tapered waist seam, characterized in that, It is sewn using the pre-stretching and pulling overlock stitching process as described in any one of claims 1 to 7, and the edge of its waist seam has a uniform micro-texture that has been pre-stretched and pulled and locked by the overlock stitch.

9. A garment panel component with an inwardly tapered waist seam according to claim 8, characterized in that, The garment cut piece is the front and back seam assembly of the waist side seam component for shirts, dresses, and coats.

10. A garment, characterized in that, A garment piece component comprising the inwardly tapered waist seam as described in claim 9.

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