How Can CNC Machining Improve The Consistency Of Automotive Parts?

一,The main idea behind CNC machining technology is to change the way we think about things from "experience driven" to "data-driven."
Traditional mechanical processing depends on the abilities and knowledge of the people who work on it, and it is finished by manually changing the machine's settings. This mode has two big problems: first, human factors can cause errors to change (for example, not replacing worn tools on time, clamping placement variation, etc.), and second, it's hard to get the same processing results from different batches and machines. For instance, when using a typical lathe to machine crankshafts, you have to make sure the dimensions are correct by clamping and measuring them by hand numerous times. The error range is frequently more than ± 0.1mm, and the machining results might be very different depending on who is doing it.
With numerical control machining technology, computer program instructions control cutting tools and mechanical movements. This is a big change from "manual experience" to "data-driven." The main part of the procedure is
Digital modelling: making 3D models of items with CAD software and setting important parameters like surface roughness and dimensional tolerances;
Process planning: Use CAM software to build tool paths and improve cutting parameters including feed rate, cutting depth, and spindle speed.
Sending the program: Send G-code instructions to the CNC machine tool to control multi-axis linkage machining.
Online detection: a quality control system with built-in sensors that watches the machining process in real time and automatically fixes mistakes.
For example, when machining engine cylinder blocks, a five-axis CNC machining centre can do multi-faceted machining of cylinder holes, oil passages, threaded holes, and more all at once. This avoids repeated clamping errors and keeps the cylinder bore cylindricity error to within 0.005mm, which is much better than the old process of 0.02mm.
二, The most important technology approach for making CNC machining more consistent
1. Multi-axis linkage machining: lowers the number of times you have to clamp and gets rid of positioning inaccuracies.
To do different types of surface machining, traditional machining needs to clamp pieces together many times. Each time they are clamped, they may not be in the right place. For instance, traditional methods need three clamping steps to process the gearbox housing, which can add up to 0.15mm of error. In contrast, five-axis CNC machining only needs one clamping step to finish all surface processing, and the positioning error can be kept to 0.01mm.
In this case, a car company uses five-axis CNC machining to make aluminium engine cylinder blocks. The scrap rate has gone down from 12% to 0.8%, and the dimensional accuracy has gone up by 85% compared to earlier approaches.
2. High speed cutting (HSM) technology: improving cutting settings and keeping machining quality stable
High-speed cutting (up to 3000m/min or more) and feed rate (up to 400%) lower cutting force and heat deformation, which keeps machining quality stable. When cutting titanium alloy blades, for instance, the normal cutting speed is only 800m/min and the surface roughness Ra is ≥ 1.6 μm. High-speed cutting can lower surface roughness to Ra ≤ 0.4 μm and make tools last three times longer.
The technical principle: When you cut at high speed, the temperature in the cutting zone goes up, the material gets softer, and the cutting force goes down. At the same time, the chips form faster, which means that heat conduction to the workpiece happens faster, which helps limit thermal deformation.
3. Adaptive control and real-time compensation: change the settings on the fly to deal with changes in the material
Different batches of automobile components materials (such aluminium alloy and high-strength steel) have different performance characteristics (like hardness and toughness). Traditional production needs to be stopped and started often to change parameters. The CNC system has sensors (such force sensors and temperature sensors) that keep an eye on things like cutting force, vibration, temperature, and other characteristics in real time. It then automatically changes the feed rate, cutting depth, and other settings to make sure the machining is always the same.
When processing high-strength steel crankshafts, the CNC system notices a rapid rise in cutting force and immediately lowers the feed rate by 20% to protect the tools from damage while keeping the dimensions consistent.
4. Digital inspection and quality traceability: establishing a closed-loop control system
By using online detection tools like laser scanners and coordinate measuring machines, numerical control machining can accomplish closed-loop control of "processing detection feedback." For instance, when manufacturing gears, the CNC machine tool can automatically check the tooth profile mistake once the machining is done. If it goes beyond the limit, the compensation program will kick in to reprocess the parts, making sure that they all fit the design specifications. The MES system also keeps track of the processing parameters and inspection data for each part so that quality can be tracked.
Support for data: One gearbox maker's digital inspection cut the gear tooth profile inaccuracy from 0.008mm to 0.003mm and the rejection rate from 8% to less than 1%.
三, Real-world example: Using CNC machining to keep the essential parts of a car consistent.
1. Machining the crankshaft of the engine: Five-axis linkage and fast cutting
The crankshaft is a very important moving part of the engine, and how well it fits determines how well the engine works. Traditional workmanship involves several processes, a lot of clamps, and a lot of mistakes. A particular business uses a five-axis CNC machining centre and makes things more consistent by doing the following:
Do all surface processing in one clamping to cut down on positioning mistakes;
For high-speed cutting, the optimisation parameters are: feed rate up to 1200mm/min, cutting depth of 0.5mm, and surface roughness Ra < 0.4 μ m.
Online detection compensation: After processing, automatically check the coaxiality of the spindle neck and connecting rod neck. If the mistake is too big, the tool route will be immediately changed.
Effect: The machining cycle for the crankshaft is cut by 60%, the uniformity of the dimensions is improved by 90%, and the scrap rate goes from 5% to 0.2%.
2. Processing of gearbox gears: gear hobbing and grinding are done together
The precision of the tooth profile of gears has a direct effect on how well they work and how much noise they make. In traditional handicraft, gear rolling and grinding are done separately, with a lot of clamping cycles. Gear grinding is also likely to cause heat deformation. To make things more consistent, a certain company uses CNC gear hobbing and grinding composite machine machines with the following technologies:
Synchronous machining: Hobbing and grinding are done on the same machine to keep from having to clamp twice;
Adaptive grinding: Change the grinding pressure automatically dependent on how hard the gear material is to keep it from getting too hot and changing shape.
Digital twin simulation: Use a virtual environment to simulate the machining process and find the best tool paths and settings.
The gear tooth profile error has gone down from ± 0.012mm to ± 0.005mm, the noise has gone down by 3dB, and manufacturing efficiency has gone up by 40%.