Created on 10.09

The Fabric Cutting Process in Denim Jeans Production

In the denim jeans production process, fabric cutting is a core link connecting "fabric preparation" and "sewing procedures". It requires precise alignment with pattern design to ensure each cut piece has consistent dimensions and neat edges, directly influencing the fit and production efficiency of the jeans. Its technological process mainly consists of the following 6 key steps, each with strict operating standards and technical requirements:  

1. Preparatory Stage: Ensuring "Zero Error" Between Fabric and Pattern  

Before cutting, it is necessary to address issues related to fabric characteristics and pattern adaptation to avoid dimensional deviations or waste in subsequent steps:  

1. Fabric Preshrinking & Relaxing

Denim fabric (especially unpreshrunk grey cloth) has a high cotton content and is prone to shrinkage and deformation after washing. Therefore, before cutting, the fabric must undergo steam preshrinking or natural hanging relaxation (usually hung for 24-48 hours) to release internal stress, reducing dimensional shrinkage of the fabric during subsequent sewing and washing. Skipping this step may result in finished jeans "shortening after washing" or "tightening at the waist".  

2. Pattern Confirmation  

The technical department creates a 1:1 paper pattern based on design drawings (e.g., straight-leg, wide-leg, skinny styles), marking details such as cut piece names (e.g., front panel, back panel, pocket lining, waistband), grain direction (the warp/weft direction of denim, which affects the drape when worn), and alignment marks (e.g., darts, pleats, pocket positions). The paper pattern must be proofread at least 3 times to ensure the error with the designed dimensions is ≤ 0.5cm.  

3. Fabric Spreading

Using an automatic fabric spreader (manual spreading racks are used in small factories), the denim fabric is laid flat in layers on the cutting table according to the grain direction of the pattern. The spreading height usually does not exceed 15cm (approximately 50-80 layers, depending on fabric thickness) to prevent deformation of the bottom-layer fabric due to excessive pressure. Meanwhile, each layer of fabric must be free of wrinkles and misalignment, with edges aligned (error ≤ 1cm) to avoid inconsistent cut piece sizes.  

2. Marking & Positioning: Creating "Identity Labels" for Cut Pieces  

To prevent confusion or incorrect orientation of cut pieces during sewing, precise marking is required on the spread fabric:  

1. Marker Making & Numbering

All pattern pieces are arranged on a marker in a "material-saving" manner (called a "marker plan"). An automatic numbering machine prints "cut piece number + size + layer number" on the edge of each fabric layer (e.g., "Front Panel-L-3/50", indicating the size L front panel of the 3rd layer), facilitating subsequent sorting and matching.  

2. Notching & Chalking  

A punching machine makes small holes (2-3mm in diameter) at key alignment positions of the cut pieces (e.g., the joint between the waistband and pants body, the sewing position of the pocket and front panel). Alternatively, special denim chalk (non-fading) is used to mark details such as darts and pleats on the reverse side of the fabric. This ensures precise alignment of cut pieces during sewing, avoiding issues like "crooked pockets" or "misaligned seam lines".  

3. Core Cutting Stage: Precise Cutting According to the Pattern  

Depending on factory scale and requirements, there are two main cutting methods: manual cutting and automatic cutting. The core goal is "neat edges and precise dimensions":  

1. Manual Cutting 

Small factories or custom orders often use a round-knife cutter (with a circular blade, suitable for straight-line cutting) or a band-knife cutter(with a long strip-shaped blade, suitable for curved cutting, such as pant leg arcs and pocket arcs). Operators hold the cutter and move it slowly along the edge of the pattern at a speed of 5-10cm/second, preventing fabric edges from fraying due to overheating (denim has high cotton content and is prone to fiber breakage when overheated).  

2. Automatic Cutting

Medium and large factories use CNC vibrating knife cutters (mainstream) or laser cutters:  

- Vibrating knife cutting: The marker plan is imported into a computer, and the knife cuts the fabric with high-frequency vibration (approximately 2000 times/second). It has a precision of ±0.1mm, making it suitable for thick denim (e.g., 12oz and above), with neat edges and no fraying.  

- Laser cutting: High-temperature laser is used to melt the fabric, suitable for thin denim or styles requiring patterned cutting (e.g., distressed holes, decorative pocket holes). However, temperature control is essential to prevent fabric yellowing.  

During cutting, a layer of "cutting paper" is covered on the fabric surface (to prevent the knife from sticking to the fabric), and cuttings are cleaned up promptly after cutting to avoid mixing with cut pieces.  

4. Cut Piece Inspection: Selecting "Qualified Cut Pieces"  

After cutting, each cut piece must be inspected one by one to eliminate unqualified ones, ensuring 100% qualification of cut pieces entering the sewing stage:  

1. Size Sampling Inspection

3-5 layers are randomly selected from each batch of cut pieces, and the dimensions of key cut pieces (e.g., front panel waist circumference, pant length, hip circumference) are measured. The error with the paper pattern must be ≤ 0.3cm; cut pieces exceeding the error range need to be recut.  

2. Edge & Defect Inspection 

Check if the edges of the cut pieces have frays (frays ≤ 0.5cm are acceptable; longer frays need trimming) or gaps (e.g., incomplete cutting, skewed cutting). At the same time, check if the fabric has defects (e.g., holes, color differences, yarn knots). Defects in "non-visible areas" of the cut pieces (e.g., the inner side of the waistband) can be retained, while those in "visible areas" (e.g., the front of the pants body) must be discarded and recut.  

5. Cut Piece Sorting: Classifying by "Order-Size-Cut Piece Type"  

The cut cut pieces are grouped according to marks to avoid confusion:  

1. Layer Sorting 

Operators take out the cut pieces of each layer separately according to the "layer number", preventing mixing of cut pieces from different layers (e.g., separating size L front panels from the 3rd layer and size M front panels from the 4th layer).  

2. Order-Based Packaging  

Cut pieces of the same order, style, and size (e.g., one pair of jeans requires 2 front panels, 2 back panels, 2 pocket linings, 1 waistband, and 2 pant leg patches) are sorted into one package. Labels are attached to mark "order number + style + size + quantity", and then the packages are transferred to the corresponding workstations in the sewing workshop.  

6. Scrap Handling: Environmental Protection and Cost Control  

Denim cutting scraps (accounting for 5%-10% of the total fabric volume) need to be handled standardizedly:  

1. Recyclable Scraps: Large scraps (e.g., ≥10cm×10cm) can be retained for making small accessories (e.g., denim labels, pocket decorative patches).  

2. Non-Recyclable Scraps: Small cuttings are collected centrally and handed over to professional environmental protection companies for processing (e.g., crushed into recycled cotton or sound insulation materials) to avoid environmental pollution.  

Summary of Key Technical Points  

1. Precision Control: The overall dimensional error must be ≤ 0.5cm, especially for key parts such as the waistband and hip circumference, which directly affect the fit.  

2. Fabric Protection: Prevent edge fraying caused by overheating of the cutter during cutting, avoid fabric wrinkles during spreading, and control the temperature during preshrinking (steam preshrinking temperature is usually 60-80℃).  

3. Efficiency Balance: Automatic cutting is 3-5 times more efficient than manual cutting but requires pre-machine debugging; manual cutting is suitable for small batches and complex patterns, requiring skilled operators.  

Through the above steps, denim fabric is transformed from "rolled grey cloth" into "cut pieces precisely matching the pattern", laying the foundation for subsequent sewing (e.g., seam joining, pocket attachment, waistband installation) and serving as one of the core processes determining the quality of denim jeans.

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