# Design, Characteristic Analysis and Modeling of a Tailored Soft Robot for Phosphorite Grabbing
## 2 Structural Design and Manufacturing of TSRPG
### Manufacturing of SPA  
In this subsection, two SPAs are manufactured by using the thermoplastic injection molding technology, and silicone (brand: SMOOTH-ON, product model: Dragon skin 20, shore hardness: 20A) is the main material. For the convenience of the split mold, we usually first manufacture an unsealed SPA by injection molding. Then, we conduct another injection molding to form a confining layer to cover the unsealed SPA. Through the above two injection moldings, a complete SPA can be manufactured.  
According to Figure 4, the manufacturing processes of the unsealed SPA are listed below.  
* _Step 1: Design and manufacture molds_ To manufacture the SPA, the design and manufacturing of molds should be conducted first. The mold includes the lower mold and the upper mold. According to the structures and dimensions of the SPA (see Figures 1 and 2), the lower mold and upper mold are designed, whose 3D drawings are shown in Figure 4. Then, the lower mold and upper mold can be manufactured by 3D printing equipment or computer numerical control (CNC) engraving machines.
* _Step 2: Prepare fluid silicone_ This step involves preparing the fluid silicone that will be used for injection molding. Silicone is a flexible and soft material that is suitable for creating soft and compliant parts or components. To employ the integrated injection molding technology to manufacture the SPA, the silicone is prepared in a fluid state. In addition, the fluid silicone is usually mixed with a curing agent or catalyst to promote the curing process.
* _Step 3: Inject mold_ In this step, the prepared fluid silicone is injected into the cavity of the lower mold by using a syringe (Figure 4). The injection is carefully controlled to ensure that the entire cavity is filled with the fluid silicone without any air bubbles or voids.
* _Step 4: Mount upper mold_ Once the lower mold is filled with the fluid silicone, the upper mold is mounted onto it. The upper mold is designed to fit precisely onto the lower mold, forming a complete enclosure around the injected fluid silicone.
* _Step 5: Cure_ After the lower mold and upper mold are clamped, the curing process will be started. Curing is a chemical process. During the curing process, the fluid silicone undergoes polymerization and solidifies into the shape of the unsealed SPA. To accelerate the curing process, the molds are usually placed in oven equipment.
* _Step 6: Split mold_ After the curing process is complete, the upper and lower molds are split. Through the split mold process, the unsealed SPA can be obtained.
* _Step 7: Inspect_ In this last step, the manufactured unsealed SPA is carefully inspected. Any excess material or flash around the edges of the unsealed SPA may be trimmed or removed. Moreover, the dimensions and shapes of the manufactured unsealed SPA are carefully inspected to ensure its good quality.  
According to the above manufacturing processes, an actual unsealed SPA is manufactured. After that, to obtain a completed SPA, we conduct another thermoplastic injection molding to form a confining layer to seal the unsealed SPA. Similar thermoplastic injection molding processes are employed to accomplish the sealing task. According to Figure 5, we first design and manufacture a base mold. Next, the fluid silicone is injected into the base mold. After that, the unsealed SPA is placed onto the base mold. Then, the whole mold iscured by placing it into oven equipment. When the mold is split, a complete SPA, shown in Figure 6, is obtained. After inspection, the dimensions and shape of the SPA are qualified.