Let’s delve into the final stage of the shoe manufacturing process, which is the Assembly Process.
What Is the Assembly Process?: Shoe Manufacturing
The Assembly Process involves assembling the components prepared in the previous stages into a finished product. The components prepared up to this stage mainly consist of two parts: the upper and the sole. To combine these two parts, three key processes or lines need to be followed:
- Molding Process: This process shapes the upper to ensure it adheres well to the sole.
- Assembly Process: This is the main process where the upper and sole are glued together to create the finished shoe.
- Finishing Process: After the shoe is completed, it goes through finishing touches, quality checks, and packaging.
The Assembly process of shoes, being the final stage, is considered one of the most crucial processes.
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Assembly Process : Shoe Manufacturing
The process of assembly follows the sequence below. While the specific steps may vary depending on the shoe model or manufacturer, the essential processes are as follows:
- Back Part Molding
- Sewing Strobel
- Lasting
- Guage Marking
- Buffing
- Priming
- Cementing
- Attaching
- Pressing : Deep Well Press
- Curing
- Inserting Insole
- Quality Check
- Boxing
Molding Process
Back Part Molding
This step involves molding the heel part of the upper, known as the back part. Most shoes have a rigid support in the heel called the back count. As the upper is sewn together, the back count does not take its final shape and requires molding using a Back Part Molding Machine.
Sewing Strobel
Up to this point, the upper is essentially a component without a bottom. The part that gives the shoe its sole shape is called Strobel. This process involves sewing the Strobel to the upper. When the Strobel is sewn to the upper, the shoe’s sole shape is finally achieved. Since this process is manual, the skill of the worker is crucial, as it can impact subsequent processes and the overall quality of the shoe. A Strobel Sewing Machine is used in this process.
Lasting
Lasting is a relatively straightforward process in which the upper is placed on a three-dimensional plastic model called a last, resembling the shape of a human foot. Lasting involves attaching the upper to the last. While this process seems simple, it is crucial that the worker correctly fits the upper to achieve the right balance and centering, ensuring no issues with shoe deformation or adhesion in later stages.
Assembly Process
Gauge Marking
Gauge Marking involves marking lines on the upper using a pen, starting from the Strobel-sewn part to where the sole will be attached in subsequent processes. It is done on an Engineered Pad, a concept similar to the Golden Sole, which ensures the most accurate shape for the sole. This process employs a Gauge Marking Machine.
Buffing
The Buffing process involves using a Buffing Tool to shave the bottom part of the upper, following the lines marked during Gauge Marking. Buffing roughens the surface, allowing for better adhesion when glue is applied later. Buffing is particularly crucial for leather products. The worker’s skill in this process also affects the quality of adhesion.
Priming
Priming is a pre-treatment to ensure proper adhesion between the upper and sole. While the specific adhesive used in the Cementing process may vary, most cases involve priming the upper and sole. The purpose of priming is to alter the surface’s properties, facilitating better adhesion in the next step. Since the upper is often made of fabric, and the sole of materials like EVA or PU, priming is essential to ensure effective adhesion. After priming, the upper and sole primers are dried in a chamber.
Cementing
Cementing is the process of applying adhesive to the upper and sole. A suitable amount of cement is applied to both, and then they are allowed to dry. The overall process is similar to Priming.
Attaching Upper and Sole
After drying, the upper and sole are finally combined. The lines marked during Gauge Marking serve as a guide for matching the upper and sole. Depending on the type of shoe, additional fixtures may be necessary. Worker skill is crucial in this process to ensure that there are no gaps at the boundary where the upper and sole meet.
Deep Well Press
In this step, a hydraulic machine applies pressure from all sides to the shoe, ensuring proper adhesion. This process is vital for the shoe’s durability and adhesion quality. Weak adhesion could result in defects when the consumer wears the shoe.
Finishing Process
Curing
The completed shoe may look finished, but it requires some time to stabilize the bond between the upper and sole. Therefore, the shoe is left to mature at room temperature for a specific period. This process is essential to ensure the shoe’s adhesive strength is stable.
Inserting Insole
The insole refers to the shoe’s footbed. After completing the curing process and removing the last, the insole is inserted into the shoe. Depending on the shoe, adhesive like hot melt may be applied to the insole. After inserting the insole, paper is usually crumpled and inserted to maintain the shoe’s shape.
Quality Check
Before packaging, a final inspection is carried out to check the size and appearance of the shoe, ensuring its quality.
Boxing
This marks the final stage of shoe production. The shoes are placed in retail boxes, stickers are applied, and the shoes are prepared for shipment.
This concludes the basic information about shoe manufacturing.
Taking another look at the overall process of making shoes from the beginning will be even more helpful for better understanding.
