Now light steel structure and steel grid are widely used in all kinds of buildings in our country. Because of its wide use, it promotes the development of modern industry in our country to a certain extent. In the production process of light steel and space truss, welding structure is widely used. Many practice and research found that the welded structure has its own regularity, if not correctly grasp, the use of welded structure will be limited, and even cause great loss of people's lives and property.

1.焊接接头

1. Welded joint

在焊接结构中，一般可选用不同方式焊接接头，有些接头方式是焊接工艺所特有的，有些是用铆接或螺栓接头套用来的。一般说来前者可更好地契合焊接结构作业功能的要求。常见的焊接接头有对接接头、T接头、角接头和搭接接头四种根本类型。

In the welding structure, generally can choose different ways of welding joints, some joint methods are unique to the welding process, some are used for riveting or bolt joint sleeve. Generally speaking, the former can better meet the requirements of welding structure operation function. The common welded joints are butt joint, T joint, corner joint and lap joint.

对接接头：不同板厚的对接接头方式不同，一般薄板可选用卷边接头，或选用不开坡口单面焊缝方式，板厚添加可选用带垫板不开坡口的单面焊缝接头，但引荐选用不带垫板的双面焊缝对接接头。为了保证焊透，对接接头可在单面开坡口或双面开坡口后焊接，坡口形状有v形、u形、x型和K型等。

Butt joints: butt joints with different plate thicknesses are different. Generally, thin plate can choose crimping joint or single side weld without groove. Single side weld joint with backing plate without groove can be selected for plate thickness addition, but double side weld butt joint without backing plate is recommended. In order to ensure the penetration, butt joint can be welded after single side or double side groove. The groove shape includes V-shape, U-shape, X-shape and K-shape.

关于埋弧主动焊工艺可选用与手弧焊相同的对接接头方式，但坡口上的尺度参数有必定的改变，如下图。

For the submerged arc active welding process, the same butt joint mode as manual arc welding can be selected, but the dimension parameters on the groove have certain changes, as shown in the figure below.

T形接头：同样有开坡口和不开坡口等方式，在该类接头中选用不开坡口角焊缝施焊类型为广泛，一般可选用等角或不同焊脚尺度的角焊缝。 角接头：其特性介于对接接头和T形接头之间，接头中焊缝可接近于对接焊缝和角焊缝。 搭接接头：这种焊缝由铆接或螺栓接头转化而来。搭接接头中一般要用角焊缝施焊，它能够是旁边面焊缝、瑞面焊缝或是联合焊缝、塞焊也是搭接接头焊接办法之一。

T-joint: there are also beveling and non beveling methods. In this kind of joint, non beveling fillet weld is widely used. Generally, fillet weld with equal angle or different leg size can be used. Fillet joint: its characteristics are between butt joint and T-joint, and the weld in the joint can be close to butt weld and fillet weld. Lap joint: this kind of weld is transformed from riveted or bolted joint. Generally, fillet weld is used in lap joint. It can be side face weld, side face weld, joint weld or plug weld. It is also one of the welding methods of lap joint.

2.焊缝

2. Weld

焊缝是由不同方式的焊接成形，主要分为对接焊缝（平面对接及曲面对接）角焊缝两种。

Weld is formed by different ways of welding, mainly divided into butt weld (plane butt and curved butt) and fillet weld.

焊缝按其外外表形状能够分为上凸及平面形状，而角焊缝除上述两种外，还可选用下凹焊缝。经很多的焊缝成形实验发现，上凸焊缝外表上看似乎是加强了焊缝，加大了焊缝的截面积，实践上，上凸焊缝对接头的作业是晦气的，不能增大焊接截面的抗拉强度，这是由于在荷载作用下，上凸焊缝使传力线发作歪扭。在焊缝向基体金属过渡处发作应力集 中而使焊缝与基体金属结合处断裂。为了进步对接焊缝的作业功能，可选用焊缝外形，这有利于力线的均匀传递，削减应力会集。关于角焊缝，可选用下凹焊缝，该焊缝外型使焊缝向基体金属形成滑润过渡，可有效地削减应力会集，因此可较大的进步焊接接头作业功能。

According to the external shape of the weld, it can be divided into convex and plane shape, while the fillet weld can also choose concave weld besides the above two kinds. Through a lot of weld forming experiments, it is found that the convex weld on the surface seems to strengthen the weld and increase the cross-sectional area of the weld. In practice, the convex weld is bad for the operation of the joint and can not increase the tensile strength of the welding section. This is because the convex weld causes the distortion of the force transmission line under the action of load. Stress concentration occurs at the transition from weld to base metal, resulting in fracture of the joint between weld and base metal. In order to improve the operation function of butt weld, the weld shape can be selected, which is conducive to the uniform transmission of stress line and the reduction of stress concentration. For the fillet weld, the concave weld can be selected. The appearance of the weld makes the weld form a smooth transition to the base metal, which can effectively reduce the stress concentration, so it can greatly improve the operation function of the welding joint.