An unpositioned workpiece whose position is uncertain. As shown in Figure 3-29, the unpositioned workpiece (cuboid) is placed in a rectangular coordinate system. The cuboid can move in different positions along the X, Y, and Z axes, and can also rotate around the X, Y, and X axes. There are different positions, respectively, with,,,, and. The six degrees of freedom used to describe the uncertainty of the workpiece position,,,, and collectively referred to as the workpiece. Among them, , is called the freedom of movement of the workpiece along the X, Y, Z axis, , and is called the rotational freedom of the workpiece around the X, Y, Z axis. The correct positioning of the workpiece must first limit the degree of freedom of the workpiece. Let the space have a fixed point, and the bottom surface of the cuboid keeps in contact with the point, so the freedom of movement of the cuboid along the Z-axis is limited. If six fixed points are set as shown in Figure 3-30, the three faces of the cuboid remain in contact with these points, and the six degrees of freedom of the cuboid are limited. The three points in the XOY plane that are distributed in a triangle limit the three degrees of freedom; the two points in the horizontal plane in the YOZ plane limit the two degrees of freedom; the one point in the XOZ plane limits the one degree of freedom. . Limiting three or more degrees of freedom is called the main positioning reference. This principle of limiting the six degrees of freedom of the workpiece with six appropriately supported points of support is referred to as the six-point positioning principle. The distribution of supporting points must be appropriate, otherwise the six supporting points can not limit the six degrees of freedom of the workpiece. The three points in the XOY plane in Figure 3-30 should not be on a straight line. Similarly, the two points in the YOZ plane should not be arranged vertically. The six-point positioning principle is the basic principle of workpiece positioning. It is a geometric body with a certain shape that supports the actual production. The geometry used to limit the degree of freedom of the workpiece is the positioning element. Table 3-10 shows the degree of freedom of the workpiece that can be limited by common positioning elements. Second, from the workpiece processing requirements to determine the number of degrees of freedom the workpiece should be limited When the workpiece is positioned, the degree of freedom that affects the machining accuracy must be limited; the degree of freedom that does not affect the machining accuracy may or may not be limited, depending on the circumstances. According to the workpiece processing requirements, the degree of freedom that the workpiece must be limited is the primary problem that should be solved in the positioning of the workpiece. For example, Figure 3-31 shows an example of a guide plate for machining press plates. Due to the required depth A 2 in the groove direction, it is required to limit the freedom of movement in the Z direction. Since the bottom surface of the groove is required to be parallel to the C surface, the degree of freedom about the X axis and the degree of freedom about the Y axis are limited; The slot length A 1 is guaranteed so that the freedom of movement in the X direction is limited. Since the guide slot is at the center of the press plate and coincides with the oblong hole, the freedom of movement in the Y direction and the freedom of rotation around the Z axis are limited. In this way, the six degrees of freedom should be limited when machining guide slots. This type of positioning where the six degrees of freedom are all restricted is called full positioning. If the guide plate of Figure 3-31 is ground on a surface grinding machine, it is required to ensure the plate thickness B. Simultaneously, the processing surface and the bottom surface should be parallel. In this case, only three, three, and three degrees of freedom are required according to the processing requirements. This method of positioning with less than six degrees of freedom based on the actual limitations of part processing requirements is referred to as incomplete positioning. If the workpiece is processed in a certain process, the positioning method that is not limited according to the degree of freedom that the part processing requirements should be limited to is called underpositioning. Under-positioning is not allowed in parts processing. If a certain degree of freedom is limited by more than one positioning element at the same time, this positioning method is called over-positioning or repeat positioning. As shown in Figure 3-32, a part has two or more support points in the degree of freedom. This results in over-positioning.
Sodium hydroxid,with the chemical formula NaOH, is commonly known as Caustic Soda. It is a strong alkali with strong corrosivity, generally in the form of flakes,pearls or lumps.Industrial grade Caustic Soda contains a small amount of sodium chloride and sodium carbonate, and is white translucent crystal.Its aqueous solution has an astringent and creamy feel.Sodium hydroxide is prone to deliquescent in the air, so solid sodium hydroxide is often used as a desiccant.It is very soluble in water and emits a lot of heat when dissolved. It`s also soluble in ethanol and glycerin.
Sodium hydroxide (NaOH) is extremely versatile. Used in the production of paper, soap, dyes, rayon, metal smelting, petroleum refining, cotton fabric finishing, coal tar product purification, and food processing, wood processing and machinery industries.
The product is a strongly alkaline substance which belong to 8 grade dangerous goods. with strongly irritating and corrosive, dust or smoke can irritate the eyes and respiratory tract, corrode the nasal septum, direct contact between the skin and eyes and NaOH can cause burns, and misuse can cause digestive tract burns, mucosal erosion, bleeding and shock.So it`s highly corrosive and requires the "corrosive item" mark.
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Six-point positioning principle and selection of positioning datum
One and six positioning principles