High-end Customized EVA Home Shoes
From mold manufacturing to mass production

Author: Felix    Position: Project Manager

This is a pair of high-end customized EVA home slippers produced for customers. In the second half of 2024, our British customer learned from our company’s website that we can customize the production of high-end EVA products. Our high efficiency enabled this product to transform from a drawing into a reality within three months.

Process applied: Compression molding

Post-processing applied: Screen printing

 Materials used: EVA 50A

Basic information：

There are three models of the product, namely SMALL, MEDIUM, and LARGE. Later, an Extra Large version was added. The weight of a single product is approximately 225g. The mold material is 7075 aluminum with high strength and good wear resistance. All adopt a left-right 1+1 layout. The mold manufacturing cycle is 15 days. For the first batch, there is one set of molds for each model. Later, it was increased to three sets of molds for each model. The production cycle of a single set of products is approximately 600 seconds. The production quantity of the first batch is 500 sets for each model; the formal production quantity is 2,000 sets per batch.

Product Requirements:

For the samples of the first batch, the customer provided detailed product requirement specifications, which included the details of both the surface and the interior of the shoes, as well as strict requirements for all the texture dimensions of the shoes.

1）：Dimensions: The dimensions of the shoes must strictly adhere to the requirements in the drawings, and all tolerances should be strictly controlled.

2）Surface Requirements: The surface of the shoes must reach a perfect level. There should be no defects such as shrinkage, burrs, dents, scratches, etc. At the same time, it is necessary to ensure that the shoes do not warp or deform in any way.

3）：Texture: The textures on the bottom and the sole surface of the shoes must comply with the requirements in the drawings, including the width and depth of the textures.

4）：Hardness: The material must be uniformly EVA. The hardness should be 50 degrees, and the deviation (both upward and downward) should not exceed 3 degrees, so as to ensure the comfort of the product.

Principle of Compression Molding Production:

Foaming compression molding is a common production process. It mainly involves steps such as heating, pressurizing, and cooling. The EVA material is extruded into the interior of the mold. After high-temperature foaming and pressurization, it takes on the specified mold shape. EVA compression molding production can achieve efficient and high-quality manufacturing, and it is suitable for mass production to meet market demands.

Advantages of Compression Molding:

1:Mold Manufacturing Cycle: Compression molding has significant advantages for mass production. Firstly, the structure of compression molds is relatively simple. Generally, the manufacturing cycle of a set of molds will not exceed 20 days. Therefore, the manufacturing cycle of compression molds is relatively short.

2):High Production Efficiency: Compression molding equipment usually has 6 or 8 mold pits. It can support the simultaneous production of multiple sets of molds. Since the production process is relatively long, for example, a 6-station equipment usually only requires 2 operators to ensure stable production, which greatly improves the production efficiency.

3):High Product Consistency: The dimensions and shapes of products produced through molds are very stable.

4):Excellent Product Performance: There are various hardness levels available for EVA materials. Meanwhile, this material is characterized by being lightweight, soft, comfortable, and wear-resistant.

5):High Material Utilization Rate: In addition to the runner system, the compression molding process generates little other waste materials, resulting in a high material utilization rate. Moreover, the waste materials can be recycled. (GREFEE 8-station Compression Molding Equipment)

Preliminary Review: 1) Parting Line Issue

In order to make the first appearance surface of the product more complete, the customer requires that the parting line be located at the texture position of the bottom of the product.

First, an uneven parting surface is very unfavorable for both mold manufacturing and subsequent production processes. Firstly, there will be many disadvantages during the mold manufacturing process. An uneven parting line will increase the processing difficulty of the mold. At the same time, it will also be very difficult during the mold matching process, and there is a possibility of flash occurring during the production process.

Second, when the parting line is located at a concave-convex position, it will cause an undercut situation in the front and rear molds of the mold, increasing the mold processing difficulty. In addition, during the production process, the undercut is not conducive to the removal of the product, and there is also a possibility of scratching the product.

Third, the undercut is not conducive to the cleaning and cooling of the mold during the production process, increasing the cleaning time and cooling time of the mold. Moreover, there may be insufficient cooling, which will affect the surface quality of the product.

Modification Plan: Our suggestion is to move the parting line of the product to a relatively flat position. This can ensure the flatness of the mold parting surface, save the mold processing cycle, reduce production risks, and also facilitate the subsequent maintenance of the mold.

Preliminary Review: 2) Gate Point Issue

The gate point suggested by the customer is located on the tail side of the shoe. The gate point at this position may bring many disadvantages to the product, mainly manifested in the following two aspects:

First, with the gate located at the rear side of the shoe, the material moves from the rear to the front and then loops back to the shoe opening. The complex flow path of the material results in a long molding time, and there is a possibility of causing surface quality problems of the product.

Second, this position is not conducive to the discharge of the gas inside the mold. The gas will accumulate at the front end of the shoe or at the shoe opening, which may lead to the formation of air pockets inside the product, thus affecting the surface quality.

Modification Plan: It is recommended to move the gate to the front end position where the thickness of the product’s plastic part is the greatest, which can accelerate the material filling speed and reduce the molding time. At the same time, an exhaust groove should be opened at the tail of the mold to exhaust the gas from the tail of the product without affecting the surface quality of the product.

Mold Manufacturing:

The core difference of shoe molds lies in that they are different from other types of molds. The core area does not require CNC machining. Instead, a wooden mold of the same proportion needs to be manufactured. Before manufacturing the shoe mold, a wooden mold should be made according to the shape of the product. The wooden mold serves as the master mold for manufacturing the sand mold and is used to form a cavity in the sand mold that is consistent with the EVA product. Then, the wooden mold is placed in the mold cavity, and finally, the aluminum liquid is poured into the cavity with the wooden mold, thus forming the core part of the mold. (Three wooden molds of different sizes)

Mold Materials:

Part Name：Spool Holder.Nut

EVA compression molds are much simpler compared to other molds. A compression mold is mainly composed of three major parts, namely the upper mold, the lower mold, and the mold core. All the mold materials are made of 7075 aluminum with high strength and good wear resistance.

Advantages of 7075 Aluminum:

1）：7075 aluminum has excellent thermal conductivity and can transfer heat rapidly. It can ensure that the EVA material is evenly heated during the heating process, shorten the molding cycle, and improve production efficiency.

2）：7075 aluminum has a relatively low density, making the mold lightweight. This enables rapid processing and also facilitates handling and installation.

3）：7075 aluminum can be processed to obtain a smooth surface, which helps to improve the surface quality of EVA foamed products.

Upper Mold Side: The upper mold side of the slipper mold is mainly used to form the top shape of the slipper on its surface. It usually features fine textures. The quality of the mold on the upper mold side determines the surface quality of the product. (Processing of the parting surface on the upper mold side)

Lower Mold Side: It cooperates with the upper mold and is mainly used to form the shape of the bottom of the shoe. (Surface processing of the lower mold side)

Mold Core: The mold core is located between the upper mold and the lower mold. It is mainly used to form the internal cavity part of the slipper. The internal dimensions and comfort level of the slipper depend on the mold core. (Simultaneous processing of multiple mold cores)

Before assembling the mold, clean and debug the mold to ensure the smooth progress of the mold trial.

Mold Trial and Production Trial:

Before the mold trial, we learned that the customer had the intention to visit the factory. In order to ensure that the customer could receive a perfect product during their stay in China, we conducted a mold trial in advance, adjusted the mold and the mold trial parameters to ensure that the product could meet the customer’s expectations.

On-site Mold Trial for the Customer:

On September 26th, the customer visited our factory and participated in the mold trial. During the mold trial that lasted for more than four hours, our communication was very smooth. Meanwhile, we also had a comprehensive communication on details such as mold manufacturing, production cycle, inspection requirements, and product packaging. We formulated detailed inspection standards, which provided inspection specifications for the subsequent mass production.

Quality Management Specifications for Mass Production:

Regarding the issues in the mold trial on September 26th, we made adjustments to the mold, material hardness, and equipment parameters. Then, we conducted another mold trial three days later. The samples after the mold trial were delivered to the customer on October 4th. After the customer tested all aspects of the product, the latest product was confirmed by the customer, and we started to prepare for the mass production of the first batch of 500 sets of products.

Taking this sample as the standard, we recorded and retained various parameters such as mold and equipment data, cooling time, etc. Based on this, we formulated a quality management system, including work instruction manuals and packaging specification manuals.

Mass Production:

The weight of each molded product is 450g, and the production cycle is approximately 600 seconds. The first batch consists of 500 black – colored items. Thanks to the professionalism of the production team and excellent quality management, the yield rate of this batch of products exceeds 98%, and the production cycle of this batch is successfully controlled within 10 days. (Product Finalization)

Trimming: Trim the burrs of each product after it has been finalized in shape and conduct a comprehensive cleaning of the product.

Inspection:

According to the quality management system and inspection specifications, we conduct meticulous inspections of every dimension of the product. Carry out a comprehensive inspection of the first product and take photos. Then, randomly inspect one set of products every hour and make records to ensure the quality of the mass-produced products. Count the quantity of the products that have passed the inspection every day and inform the customer.

Provide the size report of the randomly inspected products every day, and number each box of products to ensure that every product is traceable.

Packaging: Clean the qualified products and pack them with PE bags to prevent dust from adhering to the product surface.

Mass Production: The first batch of 500 customized sets received high praise in the market. Therefore, the production of the second batch of 2000 sets needs to be carried out quickly. Due to the production cycle, the production speed of one set of molds is far from meeting the market demand. In order to ensure the market demand, three sets of molds for each type in the second batch were quickly manufactured, totaling 12 sets of molds, and the mold trial was completed on October 25th. (Three sets of molds for each type in the second batch)

Production of the White Version:

Production of the Blue Version:

Mold Display

Timeline:Timeline:

The project was initiated in August. The mold trial was carried out in September, followed by the first small – batch trial production of 500 sets in October. Then, the mass production of 2,000 sets was carried out in November. The GREFEER engineering team has demonstrated a high sense of responsibility and strong execution ability, whether in overcoming technical problems or strictly controlling time nodes.

Conclusion:

At the end of September 2024, the customer visited the GREFEE factory. Through on – site communication, both sides got to know each other better and the distance between us was shortened. We further understood the customer’s needs and provided better services to the customer. This visit elevated our cooperation to a higher level. Meanwhile, the professionalism of our compression molding technology, the high – efficiency of mold manufacturing, the control of product quality, and the smoothness of communication with the customer have all been highly recognized by the customer. Finally, we welcome everyone to visit our production base in Shenzhen, China.