**1. Introduction**

The plastic mulching technique is one of the most widely used and effective technical measures to improve soil water storage capacity and plant water use efficiency [1,2]. At present, cotton sowing in Xinjiang is based on the method of sowing on film, which is carried out on the soil covered with the film [3,4]. The duckbilled dibbler is used for sowing on film in Xinjiang. The duckbill of the dibbler will cut the film at the sowing position and form holes in the soil. The welding quality of the duckbill of the dibbler is the key to affecting the quality of the hole and the speed of operation [5].

The number of welded duckbills in Xinjiang is about millions every year. Before 2017, the welding method of cotton planter duckbill was manual welding. Welding workers manually position, fix, and weld the three parts of the duckbill, static duckbill, hinge, and girdle. Manual welding has the following problems: unstable welding quality, low efficiency, high labor intensity, and low degree of automation. In 2017, we developed a semiautomatic duckbill welding robot. This semi-automatic welding robot needs to be loaded, positioned, fixed, and unloaded manually, and the welding operation is completed by the

robot. The welding robot improves the welding efficiency of the duckbill. The purpose of this study is to further improve duckbill welding automation, welding efficiency, and welding quality, as well as reduce the labor intensity of welding duckbills.

There are many ways to improve welding efficiency and welding quality. For example, on the one hand, some research can be conducted on harmonic drive transmission [6–8]. This method can improve the welding quality by improving the positioning accuracy of the welding robot manipulator. On the other hand, according to the characteristics of the welding object and the welding requirements, a special welding robot can be designed to replace manual welding [9–13]. For example, Süleyman ERSÖZ et al. [14] proposed a robot system that can automatically complete measurement and welding operations for products that are difficult to manually complete standard measurement or welding operations. Namkug Ku et al. [15] designed a self-driving mobile welding robot for doublehull structures in shipbuilding. Stephen Mulligan et al. [16] developed and demonstrated an autonomous, mobile welding robot capable of fabricating large-scale customized structures. Jiang Yi et al. [17] designed a series-parallel-series hybrid structure mobile welding robot for welding corrugated plates of liquefied natural gas (LNG) membrane tanks. At present, there is little research on the application of special welding robots in the field of duckbill welding of the cotton planters.

Different from the traditional plane welding operation, the weld of the duckbill part is a fillet weld. Its processing technology is complex, the welding workload is large, and the weld is prone to defects [18]. The traditional welding process relies on experience to determine the amount of deformation, the reasonable welding method, and welding process parameters, which rely on experience and cannot fully and quantitatively grasp the law of welding deformation. With the development of finite element technology, the welding simulation is fully applied to the actual production and used to guide the process design and gradually became an effective means to provide technical support for the control of process measures in the welding robot manufacturing process [19–22].

To design a duckbill welding robot to improve the welding quality, stability, and welding efficiency of the duckbill parts of the cotton seeder, this study first analyzes the characteristics of the duckbill parts and then uses Simufact Welding software to simulate and analyze the duckbill welding process, which effectively provides technical support for the welding deformation control process measures of the duckbill welding robot in the manufacturing process. Finally, a cotton seeder duckbill welding robot is designed, and the reliability of the welding robot is verified by the welding test. The research results provide ideas for further improving the quick automatic feeding, clamping, positioning, and welding of the duckbill of the dibbler, as well as provide basic and technical support for the automatic welding of the duckbill of the dibbler.

#### **2. Welding Object Characteristics**

### *2.1. Assembly Structure of Duckbill Welding Parts*

The assembly relationship diagram of duckbill welding parts is shown in Figure 1. The dibbler is one of the key components of the cotton mulching seeder, which is used to complete the seeding process. Sowing quality has a significant impact on crop growth and yield [23,24]. The duckbill part cuts the film at the seeding position during the seeding operation and forms holes in the soil. The duckbill is welded by three parts: the static duckbill, hinge, and girdle. The welding quality has a very important influence on the hole-forming effect of the dibbler and the seed falling position.

**Figure 1.** The assembly relationship diagram of duckbill welding parts.

#### *2.2. Material Properties of Duckbill Welding Parts*

As shown in Figure 2, the duckbill of a cotton seeder is composed of a girdle, static duckbill, and hinge, and its structural parameters are shown in Table 1. The material of duckbill parts is Q235, which is an ordinary carbon structural steel. The chemical composition and mechanical properties are shown in Table 2. Q235 has low carbon and alloy element content and excellent welding performance. Generally, special process measures, such as preheating and post-weld heat treatment, are not required during welding. However, when the incorrect welding form is adopted, the appearance of the weld will also appear poor, forming cracks.

**Figure 2.** Physical drawing of the duckbill welding parts of the cotton seeder.

**Table 1.** Structural parameters of duckbill welding parts.


#### **Table 2.** Material properties of Q235.


#### *2.3. Weld and Welding Requirements Analysis*

As shown in Figure 3, the weld of the duckbill welding part is two fillet welds, which are: weld 1 formed by the static duckbill and the hinge and girdle, and weld 2 formed on another back symmetrical surface.

**Figure 3.** The weld diagram of duckbill welding parts.

An inappropriate welding process will increase the deformation of duckbill welding, resulting in the following problems: (1) the girdle and seeding wheel being difficult to assemble; (2) the following performance being affected; and (3) the quality of the hole being unstable. Duckbill parts in the process of sowing operation need to film soil punching and work under great pressure. The duckbill parts of the welding quality requirements are very high, including the ability to weld duckbill weld surface without cracks, crater shrinkage, and welding tumor defects.
