Since DCT transmission housing of a certain automobile manufacturer was developed and put into production, pass rate has been low and fluctuated greatly. Pass rate of left box machine in one pass is 79%, and pass rate of right box machine in one pass is 70%, which seriously affects delivery of machine processing and waste of manufacturing costs. Through analysis of defective scrap parts, main reasons for scrapping are oil passage and large cavity leakage of left box, and blisters on valve plate surface, as well as shift steel ball holes and box closing surface blisters, large cavity leakage of right box. By analyzing causes from aspects of human, machine, material, method, environment and testing, analyzing each defect one by one, we found corresponding influencing factors and formulated effective improvement measures to achieve a pass rate of more than 94% for left and right box machines.

 

(1) DCT production workshop has stopped production for 2 years before producing DCT transmission housing. High-pressure point cold water path and circulating water path used for mold cooling have been severely rusted, affecting quality of cooling water. By testing water quality PPM of pure water, it has reached 54. Minimum inner diameter of core cooling water pipe in the mold core is 1.5mm. Poor cooling water quality can easily lead to frequent blockage of cooling water pipe, causing local elevation of mold and core, resulting in abnormal leakage of oil passages and large cavities. Through on-site analysis and evaluation, following improvement measures are formulated:
1) Replace pure water pipeline: Change pure water pipeline from pure water station to die-casting unit from ordinary steel pipes to stainless steel pipes to eliminate rust and impurities in pipelines;
2) Clean management of equipment end: remove impurities adhering to management wall of equipment end by cleaning pipeline between spot cooler equipment and mold end;
3) Add a filter: Install a filter at the end of ordinary circulating water (tap water) equipment with a filtration precision of 40 μm, which can basically filter out impurities and rust in water;
4) Add a purifier: Install a purifier at pure water equipment end, with a purification progress of 0.01μm, to purify small impurities in water.
(2) Check compressed air at equipment end on site to find out whether there is water vapor. During production process, after release agent is sprayed, if water blows out when blowing air into mold cavity, mold cannot be dried. Aluminum liquid entering mold cavity will easily form water vapor, causing shrinkage holes and pores in internal casting. At the same time, after lubricating oil is applied to spray chamber and blown away by blowing compressed air, if there is water blown out, a large amount of water vapor will be generated when aluminum liquid is poured in, which will be mixed in aluminum liquid and have a great impact on internal quality of casting. By formulating control measures, frequency of manual drainage at the front end of compressed air pipeline is increased from once a day to once per shift, automatic drainage is added at the end of pipeline, manual drainage is confirmed at equipment end every day to prevent occurrence of water problems in compressed air during spray blowing and pressure chamber lubrication.

 

(1) During daily mold inspection, use a mold pipe cleaning machine (adding citric acid) to clean and clear mold cooling water pipeline to ensure cooling effect of mold and core.
(2) Incorporate use of thermal imaging cameras to take pictures of mold surface temperature into daily monitoring, conduct daily filming, analysis, and handle abnormalities.
(3) For cores that are critical for leakage, during daily inspections, turn on cold water and check water flow.

(1) There are pores in valve layout of left box after processing, which affects sealing. Through CAE simulation analysis, current pouring system easily causes heat shrinkage on valve layout. Two streams of aluminum liquid gather on valve layout, resulting in poor molding quality. Through multiple designs and optimization of location and size of main runner, and through CAE simulation analysis, optimal solution is determined, which can effectively improve pouring quality of valve layout.

 

(2) Right box shift steel ball hole is processed with air holes, and porosity rate reaches 8%. Through composition and morphological analysis of defect location, it was determined to be a slag hole. Through CAE simulation, aluminum water is collected at position of 4# gate of main gate and 2# shift steel ball hole of side gate 3#, and slag holes are prone to appear after processing. By adding side gate 4# small gate, it is used to quickly fill 2# shift steel ball hole, aluminum water is collected and transferred to other non-processing positions.

 

(1) 2# shift steel ball hole is changed from side core pulling to side extrusion. Pressurization effect is not good. It is easy to squeeze aluminum skin on extrusion pin into casting, causing air slag holes. Through study of mold structure, it is possible to change side extrusion in fixed mold to top extrusion in mold plate, which will have a better extrusion effect on shift steel ball hole and effectively improve air hole defect at the top of shift steel ball hole.

 

(3) Because die-casting machine itself cannot move extrusion pin forward and backward twice during spraying process, it can only spray extrusion pin and cannot blow air onto it. By optimizing action of extrusion pin during spraying, from being able to only spray to being able to spray + blow, surface of extrusion pin is less likely to stick to aluminum. At the same time, extrusion start time is adjusted from 4.3s to 6.5s, which enhances extrusion effect, significantly improves extrusion pin sticking to mold.

 

Through process improvement, pass rate of DCT left box machine with one pass was increased to 96%, and pass rate of DCT right box machine with one pass was increased to 93%, completing set goals.