What is the processing technology for automotive parts?

A car is made up of more than ten thousand parts, each of which must be processed and shaped through different techniques before being assembled into the vehicle. Today, let's take a look at the seven major processing techniques for automotive parts.

1. About Casting

Casting is a production method where molten metal is poured into a mold cavity, and after cooling and solidifying, the product is obtained.

In the automotive industry, many parts are made from cast iron, accounting for about 10% of the vehicle's net weight, such as cylinder liners, transmission housings, steering system housings, rear axle housings, brake drums, and various support brackets.

The production of cast iron parts generally uses sand molds. The main material of the sand mold is sand, mixed with binders, water, etc. The sand mold material needs to have a certain bonding compressive strength to be shaped into the desired form and withstand the erosion of high-temperature molten steel without collapsing easily. To cast a cavity that matches the shape of the workpiece in the sand mold, a wooden model, known as a wooden template, must first be made. The hot molten steel will shrink as it cools, so the size of the wooden template must be increased based on the original size of the casting according to the shrinkage rate, and the surface that needs to be cut must be correspondingly thickened.

Hollow castings must be made with sand cores and corresponding core wooden templates (core boxes). With the wooden template, the cavity sand mold can be flipped (the process is also known as "sand casting"). When producing the sand mold, consideration must be given to how the sand boxes can be separated to remove the wooden template, and also how the molten steel will be injected and fill the cavity to obtain high-quality castings. Once the sand mold is made, it can be poured, which means pouring the molten steel into the cavity of the sand mold. During pouring, the temperature of the molten iron is between 1250 and 1350 degrees, and the temperature during smelting is higher.

2. About Forging

In the automotive industry, casting is commonly used as a production method. Forging is divided into free forging and die forging. Free forging is a production method where metal blanks are placed on an anvil and shaped by impact or load (commonly referred to as "quenching"). The blanks for vehicle gears and shafts are produced using free forging.

Die forging is a production method where metal blanks are placed in the cavity of a forging die and shaped by impact or load. Die forging is somewhat like the process of dough being pressed into cookie shapes in a mold. Compared to free forging, the products produced by die forging have more complex shapes and more precise dimensions. Classic examples of die-forged automotive parts include engine crankshafts, front axles, and steering rods.

3. About Cold Stamping

Cold stamping dies or sheet metal stamping dies are production methods that cut or shape metal sheets under pressure in stamping dies.

Everyday items, such as pots, lunch boxes, and washbasins, are made using cold stamping methods. For example, to produce a lunch box, a rectangular blank with four rounded corners must first be cut out (referred to as "blanking"), and then this blank is pressed into the cavity using a die (referred to as "deep drawing"). In the deep drawing process, the flat sheet is transformed into a box shape, with the four sides bending upwards and the material at the corners gathering and showing wrinkles.

Automotive parts processed using cold stamping include engine oil pans, brake plates, vehicle frames, and most body parts. These parts are generally formed through blanking, punching, bending, flanging, and finishing processes. To manufacture cold-stamped parts, stamping dies must be created. Stamping dies are generally divided into two parts, one of which is installed on the side of the press and can move up and down, while the other is fixed below the press. During production, the blank is placed between the two stamping dies, and when the front and rear dies come together, the stamping process is completed. The efficiency of stamping is very high, and it can produce complex shapes with high precision.

4. About Welding

Electric welding is a production method that combines two metal parts by heating or simultaneously heating and pressing them together.

The common practice of holding a mask in one hand and a welding torch connected to a cable in the other hand is called manual arc welding, which uses the high temperature generated by the electric arc to melt the welding wire and the workpiece, thus joining them together.

Manual arc welding is rarely used in the automotive manufacturing industry. The most widely used method in car body production is welding. Welding is suitable for electric welding of cold-rolled steel plates. During operation, two electrodes apply pressure to two thick steel plates to make them fit together while energizing the contact points (with a diameter of 5-6 mm) to heat and melt them, thus creating a strong connection. When welding two body parts, a spot weld is made every 50-100 mm along the edges, creating a discontinuous multi-point connection between the two parts. To weld the entire car body, hundreds of spot welds are generally required. The strength requirement for spot welds is very high, with each spot weld able to withstand a tensile force of 5 kN, and even if thick steel plates are torn apart, the spot welds will not separate.

The common gas cutting in maintenance workshops uses acetylene combustion and O2 combustion to create a high-temperature flame that melts the welding wire and the workpiece to join them together. This high-temperature flame can also be used to cut metal, known as oxygen cutting. Gas cutting and oxygen cutting are quite flexible, but gas cutting has a larger heat-affected zone, causing deformation and changes in the alloy composition of the welded parts, which reduces their properties. Therefore, gas cutting is rarely used in the automotive manufacturing industry.

5. About Metal Cutting Processing

Metal material turning production processing is a production method that uses milling cutters to gradually drill metal material blanks; it allows products to obtain the required shape, specifications, and roughness. Metal material turning production processing includes two methods: milling and machining. Milling is a production method where workers use handmade special tools for cutting, which is flexible and convenient, widely used in installation and maintenance. Machining is achieved using CNC lathes, including turning, planing, milling, drilling, and grinding.

1) Milling: Milling is the technical process of processing products with a cutter at the lathe. CNC lathes are suitable for drilling various rotating surfaces, such as inner and outer cylinders or conical surfaces, and can also mill inner holes. Many shaft parts of vehicles and the blanks of transmission gears are processed at the lathe.

2) Drilling: Drilling is the technical process of processing products with a blade on a drilling machine. Drilling machines are suitable for processing flat surfaces, vertical planes, slopes, and grooves. The mating surfaces of the cylinder sleeve and cylinder head of the vehicle, as well as the mating planes of the transmission housing and cover, are all processed using drilling machines.

3) Cutting: Cutting is the technical process of processing products with a lathe tool on a CNC lathe. CNC lathes can process slopes, grooves, and even gears and inclined surfaces, which are commonly used in the production of various automotive parts. The molds for the cold stamping of vehicle bodies are processed using cutting. Computer-controlled CNC machine tools can produce workpieces with very complex shapes, which are key CNC lathes in intelligent machining.

4) Milling and Boring: Milling and boring are the main drilling methods for processing holes.

5) Cutting: Cutting is the technical process of processing products with grinding wheels on a CNC grinding machine. Cutting is a deep processing method that can achieve high precision and surface roughness of workpieces, and can also cut workpieces with very high strength. Some automotive parts that have undergone tempering treatment are deep processed using CNC grinding machines.

6. About Heat Treatment

The heat treatment process involves reheating, insulating, or cooling solid steel to change its structure, in order to meet the application standards or technical standards of the parts. The temperature of heating, the duration of insulation, and the speed of cooling can cause different structural changes in steel. Blacksmiths quickly cool heated cast iron parts in water (which is referred to as heat treatment by professionals), which can enhance the strength of aluminum parts; this is an example of the heat treatment process.

Heat treatment methods include quenching, tempering, heat treatment, and quenching. Quenching involves heating cast iron parts, insulating for a certain period, and then slowly cooling them in the furnace to obtain a fine and uniform structure, reducing strength to facilitate turning processing.

Quenching involves heating cast iron parts, removing them from the furnace after insulation, and then cooling them in the air, suitable for optimizing high carbon steel. Heat treatment involves heating cast iron parts, insulating, and then rapidly cooling them in water or oil to increase hardness.

Quenching is generally a later process in heat treatment, where heat-treated cast iron parts are reheated, insulated, and then cooled to stabilize the structure and eliminate ductility.

Many automotive parts need to retain the ductility of the core while changing the surface structure to increase hardness, which requires surface induction hardening or nitriding, cyaniding, and other heat treatment methods.

7. About Assembly

Assembly is the process of connecting and assembling various parts using connecting components (such as anchor bolts, nuts, pins, or locks) according to certain specifications, and then connecting and assembling various components into a complete vehicle.

Whether assembling parts into components or components into a complete vehicle, it is necessary to meet the mutual fitting relationship required by the design drawings, so that the components or the complete vehicle achieve the specified characteristics. For example, when installing the transmission onto the clutch housing, it is essential to ensure that the axis of the transmission input shaft aligns with the axis of the crankshaft. This core method is not adjusted by the assembly workers (millers) during assembly, but is ensured by design and production.

If you visit an automotive company, the most impressive sight is the vehicle final assembly line. On this assembly line, a vehicle is produced every moment. Taking the FAW Jiefang truck assembly line in China as an example, this assembly line is a 165m long conveyor chain, where vehicles move along the conveyor chain to each process and gradually assemble, with transport chains continuously delivering engine assemblies, vehicle cabins, wheel assemblies, etc., from each workshop to the corresponding processes on the final assembly line.

At the initial position of the conveyor chain, the window frame is first placed (upside down), then the rear axle assembly (including automotive leaf springs and rims) and the front axle assembly (including automotive leaf springs, steering rods, and rims) are installed onto the window frame, after which the window frame is flipped over to facilitate the installation of the steering system, exhaust system, brake system pipes, fuel tank and fuel pipes, cables, and wheels, and finally the engine assembly (including clutch, transmission, and central brake system) is installed, connecting the rotating shaft, and then the vehicle cabin and rear plate products are installed. At this point, the vehicle can drive off the assembly line.