In CNC machining of metal parts, thin-walled structures (usually less than 3mm in thickness) are prone to deformation due to their weak rigidity, resulting in dimensional deviations, inadequate form and position accuracy, and even direct scrapping of the parts. These types of parts are widely used in aerospace, automotive, electronics and other fields, and their machining deformation has always been a common problem in production. This article combines processing experience to systematically sort out the main causes of deformation in the processing of thin-walled metal parts, and provides targeted control techniques to provide reference for improving production qualification rates.
1、 The main causes of deformation in the processing of thin-walled metal parts
The deformation of thin-walled metal parts is caused by multiple factors such as material properties, clamping methods, cutting parameters, and process arrangements. It is necessary to accurately identify the causes:
1. Material properties and initial stress effects
Thin walled non-ferrous metal components such as aluminum alloys and copper alloys have strong plasticity and are prone to plastic deformation during processing;
Residual internal stress in the casting and rolling process of raw materials can cause bending and warping of the parts due to stress release after material removal during processing;
Thin walled components have a small cross-sectional area, low moment of inertia, and weak resistance to cutting and clamping forces. Slight external forces can cause deformation.
2. Deformation caused by improper clamping force
Excessive force during clamping can directly cause elastic deformation of the parts, especially when clamping thin-walled flat parts with pliers. The pressure of the jaws can easily cause the middle of the parts to protrude and both ends to lift up;
Unreasonable selection of clamping points, failure to avoid weak areas, resulting in local stress concentration and causing local deformation;
Lack of auxiliary support results in vibration deformation of the suspended parts of the clamped parts under cutting force.
3. Deformation caused by cutting force and cutting heat
Improper selection of cutting parameters, excessive feed rate, and deep cutting depth can lead to a sudden increase in cutting force, causing displacement and deformation of the parts;
The cutting heat generated during high-speed cutting is conducted to the surface of the part, causing local temperature to rise and uneven cooling shrinkage of the material after expansion, leading to thermal deformation;
The wear of cutting tools or the lack of sharpness of cutting edges increase cutting resistance, intensify part vibration and deformation.
4. Unreasonable arrangement of processing technology
Improper connection between rough machining and precision machining processes leads to direct precision machining without releasing stress after rough machining, resulting in deformation after precision machining due to residual stress;
Unreasonable cutting path planning, such as one-way cutting leading to concentrated force on one side of the part, or failure to use symmetrical cutting methods, resulting in unbalanced deformation;
If the excess is removed at once, the material will suddenly decrease significantly, and the stress release will be too concentrated, leading to increased deformation of the parts.
2、 Practical control techniques for machining deformation of thin-walled metal parts
Targeted measures can be taken in terms of clamping optimization, parameter adjustment, process improvement, stress control, and other aspects to address the aforementioned deformation reasons
1. Optimize the clamping method to reduce clamping deformation
Adopting a flexible clamping scheme, using soft materials such as rubber pads and copper sheets to wrap the jaws, increasing the contact area, dispersing clamping force, and avoiding local compression and deformation;
Reasonably select clamping points and support points, prioritize clamping parts with strong rigidity, and add auxiliary support to weak parts (such as using adjustable support nails and hydraulic top pins);
Thin walled flat parts can be clamped using vacuum suction, utilizing atmospheric pressure to uniformly adsorb the surface of the part, avoiding local stress caused by mechanical clamping, especially suitable for the processing of large-area thin-walled plates;
Thin walled shaft components are clamped using expansion sleeve fixtures, which evenly transmit clamping force through the elastic deformation of the expansion sleeve, reducing damage and deformation to the workpiece.
2. Scientifically setting cutting parameters to reduce cutting deformation
When selecting a reasonable cutting speed for processing thin-walled non-ferrous metal parts such as aluminum alloys, a higher cutting speed (150-300m/min) should be used to reduce cutting force and heat generation; When processing thin-walled parts with strength such as stainless steel, choose medium low speed cutting (80-150m/min) to avoid excessive cutting force;
Optimize feed rate and cutting depth, adopt the strategy of "small cutting depth, large feed rate" to reduce single cutting force, while controlling the total cutting allowance to avoid removing too much material at once;
Choose appropriate cutting tools, such as sharp hard alloy or diamond cutting tools, to reduce friction and cutting resistance between the tool and the workpiece; The tool rake angle can be appropriately increased to reduce cutting force and minimize material plastic deformation.
3. Improve processing technology, control stress and deformation
Adopting the process route of "rough machining aging treatment precision machining", after rough machining, most of the excess is removed, and then natural aging or low-temperature aging treatment is carried out to release residual stress, followed by precision machining to avoid deformation caused by stress release during precision machining;
Adopting a symmetrical machining strategy, such as using symmetrical cutting at both ends and alternating processing of inner and outer walls when machining thin-walled sleeve parts, to ensure uniform force distribution and reduce deformation of the parts;
Optimize the cutting path and use bidirectional cutting instead of unidirectional cutting in flat machining to reduce unilateral stress; The cavity processing adopts the method of spiral cutting and arc transition to avoid the impact cutting force caused by sudden turning;
Reserve reasonable machining allowance, and reserve 0.2-0.5mm precision machining allowance after rough machining to ensure that the deformation caused by rough machining can be corrected during precision machining, while avoiding errors that cannot be corrected due to insufficient allowance.
4. Control cutting heat and reduce thermal deformation
Fully utilize cutting fluid, select cutting fluid with good cooling performance, spray cutting fluid into the cutting area through a high-pressure nozzle, timely remove cutting heat, and reduce the surface temperature of the parts;
Reasonably arrange the pause time during the processing. For thin-walled parts with long processing cycles, pause for a period of time to allow the parts to cool naturally and avoid deformation caused by heat accumulation;
Avoid dry cutting during high-speed cutting, as dry cutting can cause a sharp increase in cutting heat, especially when processing non-ferrous metals, which can lead to tool sticking and thermal deformation. It must be used in conjunction with cutting fluid.
5. Strengthen the monitoring and subsequent processing of the machining process
Perform trial cutting before batch processing, check the deformation of the first part, adjust the clamping method or cutting parameters based on the test results, and ensure stable subsequent processing;
During the processing, monitor the status of the parts through visual observation, sound judgment, and other methods. If abnormal vibration is found, adjust the cutting parameters or check the tool status in a timely manner;
After precision machining is completed, the dimensions of the parts are checked. If there is slight deformation, it can be corrected through cold pressing correction and other methods to ensure that the parts meet the design requirements.
2、 Precautions in daily processing
Choose raw materials with lower internal stress and prioritize those that have undergone aging treatment to reduce stress release and deformation during processing;
Regularly check the condition of cutting tools, replace worn or broken tools in a timely manner, and avoid exacerbating part deformation due to tool problems;
Operators need to standardize the clamping operation, avoid arbitrarily increasing the clamping force, develop the habit of "light clamping and slow testing", and ensure that the clamping is firm and does not deform.
Conclusion
The deformation control of CNC machining of thin-walled metal parts lies in "reducing external interference, releasing internal stress, and controlling cutting heat accumulation". By optimizing the clamping method, scientifically setting cutting parameters, improving machining processes, and other measures, the probability of deformation can be effectively reduced and the qualification rate of parts processing can be improved. In actual production, it is necessary to flexibly adjust control techniques based on the specific structure, material characteristics, and processing equipment of the parts, while accumulating processing experience for different types of thin-walled parts, forming targeted processing plans, and providing guarantees for high-precision thin-walled part processing.
