In order to verify the feasibility of sand casting pouring process, the sample trial production of broken axle housing is carried out according to the semi closed pouring process determined above.
Through multiple rounds of production, the first 2 pieces and the second 8 pieces were equally divided into 10 cm sections for verification, as shown in Figure 1. The original defective parts and key parts were inspected with a 10x magnifying glass. It was found that there were no visible cracks in the product and no holes with a diameter of more than 3 mm. After five batches of production, a total of 630 sand cast axle shells were produced. According to the sampling proportion, 2 pieces per 100 pieces were selected for equal distance cutting, and a total of 31 axle shells were cut. No defects were found in sand cast axle shells.
Air tightness test, also known as tightness test, is an important index to judge whether there are internal defects in the axle housing by observing the change of bubbles after the sand casting axle housing is processed and sealed with tooling, immersing the sand casting axle housing in water according to a certain pressure and maintaining it for a certain time. It is an important index to judge whether the axle housing has oil leakage and oil leakage. The test site is shown in Figure 2.
Limited by economic conditions, this product adopts the direct pressure test method. Its principle is that under the condition of stable environment, inflate the test workpiece until the tested workpiece is filled with gas, and then close the pressure valve. Under the condition that the test workpiece is relatively sealed, visually check whether there are bubbles within a certain time. Therefore, it is judged that the air tightness of the workpiece is good, The workpiece is qualified, otherwise, the workpiece is unqualified.
(1) Clean the outer surface of sand cast axle housing, remove the sludge and iron slag on the surface, and complete the preparation of axle housing pressing tooling. The hydraulic test tooling of sand cast axle housing is shown in Figure 3. Add hb-223 water-based antirust agent into the clean water for pressure, and the preparation ratio – antirust agent: water = 1:10.
(2) As shown in Figure 3, use the tooling corresponding to the sand casting axle housing to seal each connecting surface. When sealing, add a rubber pad with a thickness of 6mm on the contact surface between the sand casting axle housing and the tooling and fasten it with bolts. A combined washer is added at the threaded through hole for sealing. When tightening each oil filling / drain hole with screw plug, add O-ring for sealing.
(3) Connect compressed air. Connect one end of the air pipe to the connector on the tooling and the other end to the compressed air source on the pressure regulating valve to ensure that the connecting pipeline has no air leakage.
(4) Lifting and pressing. Lift the sand cast axle housing and tooling components above the water tank, slowly place them 10-20cm below the water surface, slowly pressurize them until the ventilation pressure is 0.5MPa, and the continuous pressurization time of each piece is not less than 10min. Check whether there are bubbles at all parts of the sand cast axle housing. If there are bubbles, check the bubble position and mark it.
(5) Remove tooling. After pressurization, close the air source, relieve the pressure, lift the sand casting axle housing and tooling components out of the water tank, and remove the air pipe and pressurization tooling.
(6) Place the leaked sand mold casting axle housing in the designated nonconforming product area, place the qualified axle housing in the designated area for sequence transfer, remove and dry the water stains on the surface of the sand mold casting axle housing, put the pressing tooling back to the tooling placement bench, and clean the pressing site.
In the product test, 8 products in the third batch and 12 products in the fourth batch were selected for air tightness test. Through the above inspection table, it can be found that during the pressurization of the second batch of axle housing produced by the semi closed new casting process, there was no leakage of sand casting axle housing, and the casting quality of axle housing was significantly improved. By the end of 2019, a total of more than 6000 sand cast axle housings have been produced, 174 unqualified products have been found, and the defective product rate has been controlled below 3%, which has achieved good results.