The quality of the car itself is one of the important factors affecting fuel consumption and reducing pollutant emissions. At present, castings account for 10% to 20% of the quality of domestic automobiles, of which commercial vehicle castings account for about 20% of the vehicle quality, and passenger car castings account for about 10% of the vehicle quality. They are one of the important components of auto parts. Therefore, the lightweight of automobile castings is of great significance for reducing the quality of the entire vehicle and reducing pollutant emissions. Judging from the current development trend of lightweight automotive castings, its technical route can be realized from three aspects: casting material substitution, casting technology advancement and product structure optimization.

1. Casting material substitution

1.1 Application of high-performance casting materials in auto parts
For traditional cast iron and cast steel, the strength and toughness of the material can be improved by means of micro-, low-alloying, casting process control, and post-cast heat treatment to improve performance. For example, QT800-5 and ZGD1240-1450 developed through micro-, low-alloying and melting process control, and austempered ductile iron (Austempered Ductile Iron, ADI) obtained by applying austempering treatment.

1.2 Application of Lightweight Casting Alloys in Auto Parts
Among automobile aluminum alloy parts, cast aluminum alloy parts (gravity casting, low pressure casting and other special casting parts) account for 74% to 80%. For cast aluminum alloys, in addition to improving properties through alloying, the mechanical properties of materials can also be improved by controlling the forming process and subsequent heat treatment. Casting magnesium alloys and other non-ferrous casting alloys are limited by cost and molding process, and the actual amount is small, but with the improvement of industrial level, the development of manufacturing technology and the reduction of production cost, the application prospects are broad.

2. Lightweight design of casting products

2.1 Thinning
In the lightweight design of castings, thinning is the most effective and direct means to achieve lightweight design of castings. The thin-walled design of castings can be preliminarily passed through CAE simulation and topology optimization. Under the premise of meeting the performance of the parts, the parts with low load or high safety factor can be thinned to achieve the goal of reducing weight and costs. The wall thickness of cast iron parts after the thin-wall design optimization can generally reach 3-6mm, and the wall thickness of cast aluminum parts can reach 1mm. However, due to the influence of surface tension and viscous force on the filling of alloy liquid, thin-walled castings using ordinary sand gravity casting will be difficult to form or have a high rejection rate. Special castings such as investment casting, vacuum suction casting, and differential pressure casting are generally used. Process realization.

2.2 Hollowing
In addition to the thin-walled design of the casting to achieve light weight, the hollow design can also achieve the weight reduction effect. In terms of the hollow design of castings, there have been application examples of hollow cast aluminum brackets, cast iron hollow crankshafts and camshafts abroad.

2.3 Integration
Integrated design is a current trend in auto parts design and the only way for the lightweight development of auto castings. The main idea of ​​the design is to use casting methods to integrate parts of multiple molding processes into one part through structural optimization and reliability calculations, so as to achieve the goal of reducing manufacturing costs and lightweight. The integrated design can greatly reduce the quality of parts, but puts forward higher requirements on the casting process. Integrated design not only has stricter requirements on the casting process, but also puts forward higher requirements on the design level and material properties. It is necessary to continuously innovate and expand the level of integrated design and application effects.

3. Casting Technology Progress
The continuous upgrading of casting materials and lightweight design have higher and higher requirements for thin-walled, hollow, and integrated castings, which have further promoted the continuous improvement of casting processes and the application of new casting processes in auto parts. From the analysis of the development trend of lightweight castings, investment casting and (vacuum) high pressure casting molding processes have significant advantages.

3.1 Investment casting technology
After topology optimization, the local wall thickness of automobile castings can be reduced to 1~6mm. On the one hand, ordinary sand casting is difficult to form, and on the other hand, the appearance quality of parts is difficult to control. The use of investment casting not only has the advantages of high dimensional accuracy and good surface quality, but also can prepare castings with complex shapes, which is one of the key development directions of casting technology in the future. For ductile iron materials, if traditional sand casting is used, casting defects such as cold insulation and insufficient pouring are likely to occur, and the appearance quality of the product is difficult to guarantee. If investment casting is used, the wall thickness and appearance quality requirements of the parts can be met.

3.2 (Vacuum) High Pressure Casting Technology
High-pressure casting is a method in which liquid or semi-liquid metal is filled with die-casting mold cavity at high speed under high pressure and solidified rapidly under pressure to obtain castings. High pressure and high speed are the fundamental difference between high pressure casting and other casting processes, and they are also important features. High pressure casting has the advantages of high production efficiency, good product quality, good dimensional stability and high dimensional accuracy. The number of parts can be reduced through structural optimization. One high-pressure casting can integrate dozens of stamped parts, which are mainly used for the manufacture of shock absorber supports, door frame and other parts.

However, high-pressure casting has the shortcomings that it is easy to produce pores and cannot be heat-treated. Therefore, the mechanical properties of high-pressure castings are lower than that of metal gravity castings and low-pressure castings. The vacuum die-casting process uses special equipment to extract the air from the cavity of the die-casting mold and die-casting under vacuum conditions. Therefore, the porosity inside the casting can be effectively reduced, and the heat treatment can be strengthened to ensure the mechanical properties of the casting. At the same time, under vacuum conditions, the reaction force in the cavity can be reduced, and a small machine can be used to die-cast larger or thinner castings under a small specific pressure.

Substitution of casting materials, optimization of product structure and advancement of casting technology are not only the three main technical routes for lightweight automotive castings, but also an organic whole of collaborative innovation. Based on the rational application of high-performance and light-weight casting alloys, the optimization design of automobile casting product structure is carried out, supplemented by the advancement of casting technology as the key technical support for the realization of lightweight design ideas. At the same time, the lightweight design of automobile castings is integrated into the overall optimization design of the automobile to produce lightweight automobile castings with better cost-effectiveness, lighter weight and better quality.

Ningbo Suijin Machinery Technology can manufacture all kinds of lost wax investment castings and machining parts or called precision investment castings , material including carbon steel, alloy steel, and stainless steel. we also can according to the customers' requirement to compound the material, Our factory has a floor space of 33,000 square meters and another 18000 square meters of building area, which contain both casting foundries and CNC machining area. The two advanced lost wax casting and investment casting production lines have a capacity of 5000 tons lost wax castings and 1000 tons investment castings per year.