I am honored that in this short period of three months, with the help of company leaders and colleagues, I have gained a profound understanding of precision casting from complete ignorance of casting. It also laid a solid foundation for my future work and study.
In the process of internship, I keep learning new knowledge and feel very satisfied, and I feel that I have made great progress. Especially during my internship in the manufacturing department, I learned a lot of advanced investment casting technology in a short time. There is also a Saturday regular meeting organized by the human resources department to discuss internship experience with all new colleagues, so that I can learn from others and make up for my shortcomings. In short, I am very grateful to the company for giving me this opportunity to study, and I am also very grateful to the leaders, masters and new and old colleagues who have worked hard together. Now I will make the following report on my three-month internship:
Entering the workshop as a trainee is the real beginning of my contact with investment and manufacturing. Everything is new to me. In the workshop, many simple problems may become difficult for me, but this is not the reason why I can't solve them. It is a process that everyone needs to go through. In the continuous study and exploration, cultivate their own independent learning ability and problem-thinking ability.
I first learned about the production process, and then gradually learned about the investment casting process and the control points of each process, as well as the basic knowledge of investment casting. The manufacturing department mainly includes several workshops such as molding, pouring, post-treatment, heat treatment and machining. The general production process of products is: pressing wax → checking wax → repairing wax → tree assembly → shell making → casting → spectral inspection → cutting, initial polishing → cleaning → initial inspection → welding repair → intermediate inspection → heat treatment → heat treatment inspection → processing gate → shaping → intermediate inspection → biting acid, shot blasting → sandblasting → pickling → plastic cleaning → pickling. Every process is arranged by the master. Under the careful guidance of the master, I have a certain understanding of the points that should be paid attention to in each process, the product defects that are easy to cause, and the reasons that lead to these defects.
1, Shell Workshop:
Wax pressing: this process is in direct contact with the product mold and is closely related to the work of R&D class. The whole shell workshop is the initial stage and the most critical stage of the product. Everything is difficult at the beginning, and the quality of wax patterns is directly related to the surface size and quality of products. Pay attention to the humidity, pressure, flow rate and holding time of wax injection during operation, as well as the causes of various defects (such as sag, bubble, shrinkage cavity, wax mold fracture, cold oil temperature stacking, insufficient wax injection, etc.) and their effects on subsequent products. As R&D personnel, we should pay special attention to the design methods of products with different structures, and the difference between mold cavity size and wax mold size.
Wax repair: mainly to repair the transition of mold closing line, flash and wax injection port on the surface of the cooled wax mold; Depression filling, bubble pick-up filling, oil pattern wiping, etc. All surface defects are well repaired. This process requires the operator to concentrate on preventing the wax parts from being accidentally scratched by the wax trimmer.
Tree organization: this process is closely related to the process class and directly reflects the process yield. Pay attention to the distance from the upper surface of the wax pattern on the tree to the upper edge of the sprue cup >: 90mm, the wax pattern spacing > 9mm, the wax pattern angle should be conducive to dewaxing, and the inner sprue length should be 12 ~ 25 mm for cutting. There are no depressions, notches, sharp edges and wax sticking at the welding place. Another principle that should be paid attention to is to ensure that all wax can be discharged when the workpiece is dewaxed.
Shell-making: The required materials include alkaline silica sol, zircon powder (used for preparing surface coating), zircon sand (used for sanding surface coating), coal gangue powder (used for preparing back coating) and coal gangue sand (used for sanding back shell). Shell-making process is complex, which needs attention, such as the control of the ratio of various materials, temperature, humidity and drying time. The quality of shell is directly reflected on the surface of casting, such as burrs, cracks, misfires, peeling, re-dissolution, shell cracking, bulging, sand inclusion and other defects, which are closely related to the preparation of slurry, stirring time, viscosity of slurry, temperature and humidity during drying.
Dewaxing and wax treatment: Pay attention to the temperature, pressure, time and operating procedures of dewaxing kettle, dewaxing water evaporator, dewatering bucket, static bucket and incubator. The dewaxing process should be rapid, and instantaneous dewaxing can be realized when the wax mold shell is pushed into the dewaxing kettle until the pressure reaches 0.56Mpa < 14S, thus reducing the damage of wax mold expansion to the mold shell. The pressure is controlled at 0.8~0.9Mpa for 9~ 18 minutes to ensure complete dewaxing.
Through the internship in the shell-making workshop, I not only learned about the various processes in the shell-making workshop, but also participated in the actual operation. More importantly, I had a preliminary understanding of the wax mold used for casting, and I also had a certain understanding of the properties and characteristics of shells made of wax and silica sol. For example, in the process of product design, some parts of the mold can not be realized, some parts of the shell can not be realized or there will be various defects in the wax mold. This will be of great help to my future work.
2. Pouring workshop
Pouring mainly includes roasting, smelting, pouring, shell vibration, cutting, initial throwing and other processes. Attention should be paid to the temperature and time of roasting, smelting and pouring, as well as the economic ingredients before the furnace. And the classification and reasons of various defects.
Melting is a very important link in the casting process. It not only strictly controls raw materials, melting temperature, melting time and the amount of deoxidizer added. It is also necessary for a smelting master to have professional technical knowledge and rich working experience in order to smelt qualified molten steel. The most important thing to pay attention to in the process of casting, vibrating shell and cutting is safety. We must strictly abide by the safety system and discipline to ensure safety first!
After the casting is cooled, it can be transferred to the vibrating shell process. Vibrating bombs are divided into mechanical vibrating bombs and artificial vibrating bombs. For some casting trees combined with transverse formwork, artificial vibrating formwork is needed, which is slow and inefficient. However, some casting trees combined with vertical dies can be vibrated by machines, which saves time and effort and has high efficiency.
So as to further remove the residual shell on the surface of the casting. Hanging shot blasting before cutting. It removes the residual shell of the whole casting tree by spraying cast iron sand shot in the hanging shot blasting machine. However, not all castings need shot blasting before cutting, and some products with simple structure and few residual shells in the inner gate can also be directly cut. When cutting, the casting can't be cut, but it can't leave too long inner gate, which is about 1-2mm.
Through the internship in the foundry workshop, I have a more intuitive understanding of every process in the foundry workshop. We have a deeper understanding of the performance of the shell, such as high strength at high temperature, good permeability and low strength at low temperature.
3. Post-treatment workshop
Post-treatment mainly deals with the surface quality and overall shape of products. Its working procedures are the most complicated, including shot blasting, sand blasting, pickling, pickling, coarse grinding, fine grinding, shaping, welding repair, electropolishing and grinding. It is closely related to the blank inspection in the quality inspection workshop, and the products constantly flow between them until they are qualified to enter the blank warehouse.
In the post-treatment process, there is no fixed process flow for the product, and the process flow is usually coordinated according to the product structure and on-site work arrangement. For example, in the cleaning process, there is no order of shot blasting, sand blasting and rough grinding, and coordination can be carried out according to the site conditions. In the cleaning process requiring pickling, shot blasting and sand blasting are carried out after pickling, and the pickling time is selected according to the product structure and quality requirements.
For products with high surface quality requirements. Need to be sandblasted. Sandblasting is a kind of high-speed sandblasting on the surface of casting with compressed air as the power, to remove the residual sand and oxide scale on the outer surface and inner hole of casting. There are clear requirements for the type, thickness and blasting pressure of sand used for sandblasting. Because excessive pressure is easy to cause product surface damage. During the operation, be careful not to put the casting directly at the nozzle of the spray gun. So as to prevent spray damage to the casting. The surface of the product after sandblasting is much more delicate than that after shot blasting.
Rough grinding is to grind the inner gate with abrasive belt until the height from the casting surface is less than 1mm, and then fine grinding. According to products with different surface quality requirements, abrasive belts with different thicknesses are selected for fine grinding. You must focus on fine grinding to avoid grinding the surface of the product.
The products transferred from inspection workshop to welding repair workshop are all products with surface defects. Generally speaking, the surface defects of products can be divided into two categories: protrusions and depressions. Outstanding defects include: flash, burr, steel ball or obvious wire clamping. Pit defects include: air holes, shrinkage cavities, cuts, scratches, etc. Grinding and welding repair are two methods to repair surface defects respectively. Grinding mainly uses pneumatic air guns, grinders and other grinding tools to install different models and types of grinding heads. Smooth and polish the protruding defects on the product surface. When repairing the protruding defects on the large surface of the product, the grinding head will be selected, which is faster. But there are some holes, ditches, grooves and other places where the sand grinding head can't be repaired well, so it is necessary to use steel grinding head. Because the steel grinding head is thinner, it will be more convenient to repair those smaller places. Welding repair is a method to repair concave defects, such as porosity, shrinkage cavity, incision and wear. Repair welding personnel choose covered electrode with the same material according to the casting. Repair the casting plane with exquisite professional technology. It has the same effect as grinding.
The purpose of shaping and welding is the same. It is to repair different types of defects in products in different ways to make unqualified products qualified. Mainly for the correction of deformed products. Generally, products with simple shape and thin wall thickness are easy to deform. As for those products with thick walls and complicated structures, they are not easy to deform. For some foreseeable deformation, measures such as cooling tools and reasonable placement are generally taken during wax pressing to prevent it, so as to reduce the deformation rate and repair rate.
Although there are two calibration hydraulic presses in the workshop, the utilization rate is very low, and only some simple and formal products can be used. Most products are trimmed by hand. Use metal bars, tooling, measuring tools and other instruments with low hardness to make the products smooth, round and vertical by tapping. So as to restore the original shape of the product and meet the technological requirements. Ensure dimensional accuracy.
Biting acid is to completely remove the residual shell and soften the oxide scale on the casting surface. Commonly used acids are nitric acid and hydrofluoric acid. Pickling generally refers to washing mixed acid, which is made up of nitric acid and hydrofluoric acid in a certain proportion. Biting acid and pickling have certain requirements on time and temperature. Pay attention to the casting when biting or pickling to prevent excessive biting or pickling. The surface of the casting is silvery white after pickling. It should be noted that carbon steel cannot be pickled.
Electrolytic polishing takes workpiece as anode and lead plate as cathode. In the electrolyte composed of sulfuric acid, phosphoric acid and ethyl glycerol, the metal surface is brightened by electrolytic reaction.
In the grinding operation, the mobile polishing machine drives the abrasive to grind the surface of the workpiece, and the vibration polishing machine polishes the surface of the workpiece. Polishing agent includes stone, corncob, etc.
4. Heat treatment workshop
Heat treatment consists of heat treatment and alkali explosion. I focus on the production process of heat treatment technology. Microstructure transformation mechanism of steel during heating and cooling: specific processes of various heat treatments; Defects of steel during heating and cooling; Microstructure transformation process of steel during heating and its influencing factors: definition, purpose, microstructure transformation process, performance change, application, applicable steel grades and parts range of various heat treatments.
Through three months' internship, I learned a lot of professional knowledge, but I deeply know that mastering in theory is not really mastering in technology. If technology is finally applied to production, it will inevitably encounter various problems in practice, and only by constantly discovering and solving problems in practice. Only by accumulating experience in practice can we truly master technology.
The three-month internship is coming to an end. Here I once again deeply thank the company leaders for giving me this opportunity to learn. I would also like to thank the teachers who carefully guided me during my internship. It was their words and deeds that made me familiar from the precision casting manufacturing that I knew nothing about. Although the internship time is very short, I can't master many aspects in depth, but please believe that in the future work, I will redouble my efforts to continue learning and enrich myself, so as to do better.
Do a good job and develop with the company.