What Parts Of The Car Suspension System Require CNC Machining?

1. Requirements for sorting and processing the main parts of suspension systems
There are three main parts to the suspension system: elastic elements, shock absorbers, and steering mechanisms. Each module has important parts that need to be CNC machined.
Parts of the guiding mechanism
As a "joint" that connects the wheels and the body, the control arm must be able to handle longitudinal force, lateral force, and braking torque. The position of the installation hole directly impacts the wheel alignment characteristics, like the camber angle and caster angle. CNC machining can make sure that the hole tolerance is ≤± 0.05mm, which stops tires from wearing unevenly due to mistakes in assembly. For instance, CNC milling is used to make the front lower control arm of the Tesla Model 3. This makes it 15% lighter and 30% longer-lasting.
Steering knuckle: The steering knuckle is made up of the main pin hole, the wheel hub bearing mounting surface, and the brake caliper bracket. The quality of its machining has a direct effect on how the steering feels and how stable the brakes are. The BMW X5 steering knuckle uses integral forging and CNC five-axis precision machining technology, which makes it 20% lighter and 25% stiffer than the split welding construction.
Link for stabilizer: This part connects the stabilizer bar and suspension arm via threads. CNC thread milling can make the tooth profile accurate to within ± 0.01mm, which makes sure that the connection strength passes 100000 fatigue tests.
Parts that support elastic elements
Spring seat: The flatness of the spring seat should be kept within ≤ 0.02mm to keep spring bias from making strange noises. This is because the spring seat is where spiral springs or air springs are installed. Numerical control milling can do both seat surface machining and precise hole positioning in one step, which cuts down on the number of times the workpiece needs to be clamped.
Shock absorber bracket: This part has to be able to handle the force of the shock absorber's impact, and its welded construction needs to be fixed for deformation through CNC machining. For instance, after welding, the shock absorber bracket of a Toyota Corolla is machined with CNC accuracy to make sure that the verticality between the bracket and the body mounting surface is < 0.05mm.
Parts of structures that are complicated
Suspension arm with many links: To make them lightweight and strong, the connecting rods of multi-link suspension systems (such five-link rear suspension) need to be CNC machined. Audi A8's rear subframe connecting rod is made of aluminum alloy that has been forged and CNC milled. This makes it 40% lighter and 20% stiffer when bent.
Air spring piston: The piston of the air suspension system needs to be CNC machined to provide a precise chamber structure. This makes sure that the air spring's stiffness characteristic curve fulfills the design criteria. CNC machining is used to make the air spring piston for the Mercedes Benz S-Class. The air chamber sealing surface Ra is ≤ 0.4 μ m.
2. The technological benefits of CNC machining for making suspended parts
Ability to machine complex surfaces
Suspension parts often have three-dimensional surfaces (like the ball joint mounting surface of the control arm), holes that aren't round (like the brake caliper location hole of the steering knuckle), and thin-walled structures (like aluminum alloy suspension arms). Traditional machining methods need more than one clamp or unique fixtures, whereas CNC five-axis machining centers can do multi-faceted machining with just one clamp by linking the A/C axes. A five-axis machine tool can do the precision machining of the main pin hole, the wheel hub installation surface, and the brake caliper placement surface all at the same time while making steering knuckles. This makes sure that the coaxiality error of each part is less than 0.02mm.
Improving the adaptability of materials
Parts of the suspension need to be both light and strong. High-strength steel (like 42CrMo), aluminum alloy (like 6061-T6), and magnesium alloy (like AZ91D) are some of the most common materials. By changing cutting parameters like spindle speed and feed rate, CNC machining can make precise cuts in a variety of materials.
Control arm made of aluminum alloy: employing high-speed milling (speed > 10000rpm) to lower thermal deformation and surface roughness Ra ≤ 0.8 μ m;
High-strength steel steering tie rod: Low-temperature cutting technology (cutting fluid temperature set at -5 to 5 degrees Celsius) prevents work hardening and enhances tool life.
Magnesium alloy subframe: Using micro lubrication (MQL) technology to lower the amount of cutting fluid that gets into the environment and lower the cutting force to keep the material from becoming brittle.
Improving efficiency and flexibility in production
CNC machining can swiftly convert between different product models by changing the CNC program. This makes it great for making small quantities of personalized products in a variety of styles. For instance, the suspension geometry settings of a new energy vehicle chassis need to be changed since the battery arrangement is different. CNC machining can make new parts in 48 hours, but traditional casting procedures need to be remolded, which takes several months. Also, CNC machine tools can make up for material deformation and tool wear in real time using online measurement and adaptive machining technology. This raises the machining qualification rate to above 99.5%.
3. A typical case study for an application
Case 1: Working on the subframe of a Volvo XC 90
The Volvo XC90 has an aluminum alloy integrated die-casting subframe, and the steps for making it are as follows:
Rough machining: Use a three-axis CNC milling machine to get rid of the last bit of die-casting blank and leave a 0.5mm precision machining allowance;
Precision machining: A five-axis linkage machining center is used to finish the precision machining of the installation surface for the sub frame, the holes for the control arm connection, and the reinforcing ribs. This ensures that the surface is flat to within 0.03mm and the holes are within ±0.02mm.
Testing: Use a coordinate measuring machine (CMM) to check all the important dimensions, and then send the data back to the CAM system to improve the machining path.
This method makes the subframe 45% lighter and 10% stiffer, which helps the XC90 get a five-star safety rating from Euro NCAP.
Case 2: Processing the Air Suspension Piston for the BYD Han EV
The BYD Han EV air suspension piston must be able to withstand high pressure and seal well. The processing flow is as follows:
Turning machining: Use a CNC lathe to process the piston end face and outside circle. Make sure the cylindricity is ≤ 0.005mm.
Processing by milling: A five-axis machine tool is used to make the air chamber sealing groove, which has a groove width tolerance of ≤± 0.01mm. The surface is treated with micro arc oxidation technology to make it more resistant to wear and corrosion.
The piston can handle 3MPa of pressure and lasts for 2 million cycles, which lets the Han EV elevate its chassis by 150mm.