25 in the R direction. Heat of the case weld portion 35 is less likely to escape to the surroundings as compared to that of the cover weld portion 25. For this reason, the case weld portion 35 is melted preferentially.

FIG. 4 shows a state after the vibration welding is completed. When the melt region 38 of the case weld portion 35 is melted, a weld layer 40 is formed between the case weld portion 35 and the cover weld portion 25. The case weld portion 35 and the cover weld portion 25 are joined to each other with the weld layer 40. The thickness of the weld layer 40 in the Z direction is less than the height 38z of the melt region 38 (see FIG. 3). When the melt region 38 is melted, an inner weld burr 41 and an outer weld burr 42 are generated. The inner weld burr 41 extends from the weld layer 40 in the −R direction, and the outer weld burr 42 extends from the weld layer 40 in the +R direction.

The inner weld burr 41 is accommodated in the inner space 41s, and the outer weld burr 42 is accommodated in the outer space 42s. The inner standing wall 41w (see FIG. 1) that covers a side of the inner space 41s in the −R direction prevents the inner weld burr 41 from flowing into the inside of the pump 1. The outer standing wall 42w (see FIG. 1) that covers a side of the outer space 42s in the +R direction prevents the outer weld burr 42 from flowing out to the outside of the pump 1.

As described above with reference to FIG. 2, the inclined surface 36 is formed at the tip end of the case weld portion 35. The inclined surface 36 is inclined from the inward side to the outward side in the R direction away from the cover weld portion 25. The volume of the melt region 38 per unit length in the R direction decreases from the inward side to the outward side in the R direction. For this reason, the volume of the outer weld burr 42 generated due to the melting of the melt region 38 is smaller than the volume of the inner weld burr 41.

The vibration welding causes powder burrs in addition to the weld burrs. A mechanism by which the powder burrs are generated will be described with reference to FIG. 5.

FIG. 5 is a graph showing changes in various portions due to the vibration welding. A horizontal axis of FIG. 5 represents a time, and a vertical axis represents a temperature and a thickness. The vibration welding includes a vibration step and a pressure holding step. The vibration step has a friction region I, a transition region II, and a steady state region III. The pressure holding step has a solidification region IV.

In the friction region I, friction between the case weld portion 35 and the cover weld portion 25 causes the temperature of the resin material that constitutes the two to rise. When the temperature of the resin material exceeds a melting temperature, the transition region II starts.

In the transition region II, the resin material softens and deforms above a glass transition point. In transition region II, the melting amount of the melt region 38 and the thickness of the weld layer 40 increase.

In the steady state region III, the melting of the resin material progresses, and the melting amount of the melt region 38 increases. In the steady state region III, the thickness of the weld layer 40 does not increase, and the inner weld burr 41 and an outer weld burr 42 are generated.

In the solidification region IV, the weld layer 40 cools and solidifies.

In the friction region I, the case weld portion 35 and the cover weld portion 25 rub against each other, and thus the powder burrs of the resin material are generated. The generated powder burrs scatter inside and outside the pump 1. The powder burrs remaining inside the pump 1 may affect the performance, durability, and the like of the pump 1. There is a demand for a pump in which the powder burrs are less likely to remain inside, and a method for manufacturing the pump.

As described above, the inclined surface 36 is formed at the tip end of the case weld portion 35. At the start of the vibration welding, only the flat surface 37 of the case weld portion 35 comes into contact with the tip end surface 27 of the cover weld portion 25. At the contact portion between the two, the friction region I starts. Since the contact area of the contact portion is small and the surface pressure thereat is large, the temperature of the resin material rises quickly. When the temperature of the resin material exceeds a melting temperature, the transition region II starts at the contact portion. Since the inclined surface 36 is formed at the tip end of the case weld portion 35, the transition region II starts quickly at the contact portion. In the transition region II, the resin material is softened and melted, and thus no powder burrs are generated. As a result, the generation of the powder burrs is suppressed.

The tip end of the case weld portion 35 is melted, and the cover weld portion 25 is moved in the −Z direction. The inclined surface 36 is inclined from the inward side to the outward side in the R direction away from the cover weld portion 25. The inclined surface 36 comes into contact with the tip end surface 27 of the cover weld portion 25 in order from the inward side in the R direction. On the inclined surface 36, the friction region I starts in order from the inward side in the R direction, and the powder burrs are generated. Here, on the inward side in the R direction of the portion of the inclined surface 36 in which the friction region I has started, the resin material is already melted. For this reason, the generated powder burrs are less likely to scatter to the inward side in the R direction. Most of the powder burrs generated on the inclined surface 36 scatter to the outward side in the R direction. As a result, it is difficult for the powder burrs to remain inside the pump 1.

FIG. 6 is a graph showing a relationship between the inclination angle θ of the inclined surface 36 and a weight of the powder burrs remaining inside the pump 1. A horizontal axis of FIG. 6 represents the inclination angle θ of the inclined surface 36 shown in FIG. 2. Cases in which θ is A deg and θ is B deg (A<B) are examples, and a case in which θ is 0 deg is a comparative example. In the comparative example in which θ is 0 deg, only the flat surface 37 is formed at the tip end of the case weld portion 35, and the inclined surface 36 is not formed. A vertical axis of FIG. 6 represents the weight of the powder burrs remaining inside the pump 1. The powder burrs remaining inside the pump 1 are collected from a cleaning liquid used to clean the inside of the pump 1 and are weighed.