How to ensure that the CNC machining center does not deform when milling PA nylon workpieces

How to ensure that the CNC machining center does not deform when milling PA nylon workpieces

Pay attention to these 4 points to ensure that the CNC machining center does not deform the PA nylon workpiece when milling! The English abbreviation for nylon is PA, and the full Chinese name is polyamide. There are many types of nylon, including Pa6, Pa66, PA610, PA11, PA12, PA1010, PA612, PA46, etc. Nylon belongs to a type of engineering plastics, and CNC machining centers can process engineering plastics, including PA nylon. PA nylon has advantages such as high mechanical strength, good toughness, smooth surface, low friction coefficient, wear resistance, outstanding fatigue resistance, excellent electrical properties, easy dyeing, and easy forming.

PA nylon is used in transportation, machinery, cables and wires, automotive industry, electronic and electrical industry, etc.

PA nylon is specifically used for various bearings, gears, pulley pump impellers, blades, fans, air filter housings, radiator water chambers, brake pipes, engine covers, etc.

The CNC machining center's real-time milling of PA nylon workpieces results in deformation over time, making it difficult to ensure accuracy. So how can we avoid this situation from happening?

Pay attention to these 4 points to ensure that the CNC machining center does not deform the PA nylon workpiece when milling!

CNC machining centers do not deform when milling PA nylon workpieces, mainly starting from four aspects: clamping, cutting tools, cutting heat, and original internal stress of the material.

1. Firstly, it is clamping: no matter what material the workpiece is made of, there will always be clamping force during the clamping process, especially for very thin workpieces, which are prone to deformation. After unloading the clamping force, the elastic deformation of the workpiece will automatically recover. The size and machining size of the workpiece are not the same under the condition of no force and freedom. Once the clamping force is too large, it will exceed the yield limit of the workpiece, especially after a long period of clamping, which can easily cause plastic deformation of the workpiece. Therefore, the clamping part of the processed part does not match the machining size; Conversely, it can lead to loose clamping, high vibration during processing, and affect the final processing size and weight.

PA nylon material is different from metal materials in that it has characteristics such as easy deformation, low density, and easy processing. In CNC machining center tabletop clamping, it is very easy to deform due to clamping; After processing, the elasticity recovers, causing certain changes in the size and shape of PA nylon. Moreover, the greater the clamping force, the greater the deformation after processing. Therefore, when processing PA nylon workpieces, it is recommended to adopt a sequence of strong clamping for initial processing and slight clamping for precision processing, so that the clamping force will not affect the dimensional processing accuracy of the workpiece.

Alright, that's all for the clamping part.

2. Let's move on to the cutting tool: we need to avoid the excessive squeezing force caused by the tool itself when cutting PA nylon. Due to the continuous movement of the tool towards the inner side of PA nylon during cutting, removing the lateral cutting of the tool on PA nylon will also result in direct pushing pressure. If the pushing pressure is too high, it will not only affect the clamping stability of PA nylon workpiece, but also cause deformation of PA nylon workpiece. This will roughly result in excessive size deviation of PA nylon workpiece after elastic deformation recovery.

The comparison between tools with stronger stiffness and tools with weaker stiffness shows that the former has poor elasticity, which is more likely to cause thrust on PA nylon workpieces and cause deformation of the workpieces. Therefore, we suggest using relatively weaker alloy tools for machining accuracy, which is more suitable.

The sharpness of the blade also affects the machining accuracy. The sharper the cutting edge of the tool, the smaller the cutting resistance, the less the pushing force on the PA nylon workpiece, the smaller the deformation of the PA nylon workpiece, and the smaller the rebound phenomenon, thus ensuring dimensional accuracy. Therefore, we use alloy knives to process PA nylon workpieces, among which the triangular knife is better than the square knife. The edge can ensure surface roughness during precision machining of the workpiece, and using new blades can ensure dimensional accuracy more than old blades. It can also grind the blade to reduce the sharp angle of the blade.

3. It's cutting heat: No matter what part is being processed, a large amount of heat is generated, such as elastic deformation and plastic deformation generated during milling, chip separation, and the energy consumed by the friction between the tool and the workpiece. Most of these can be converted into heat energy. A small portion of these thermal energy will be carried away by chips or radiated by air, but a large portion will still be absorbed by the workpiece. The remaining heat energy will cause thermal stress in the internal profile of the workpiece, and as the processing continues, it will continuously generate heat energy. The thermal stress will continue to change, and finally the workpiece will undergo deformation, and in severe cases, it will crack.

However, for PA nylon workpieces, this material itself has weak thermal stability, and with a slight heat absorption, it is easy to deform.

If the heat generated during the cutting process is generated at the cutting point, assume:

1) The temperature of the workpiece is uniform before cutting;

2) The generated heat energy does not radiate outward;

3) If the cutting process is stable and uniform, then any point M (x0, y0, z0) of the workpiece is affected by the temperature of the moving point heat source as follows:

In the equation, Q（ τ) It is the instantaneous heat generated by a point heat source at any time; ρ Is the density of the medium; C is the specific heat capacity of the heat conducting medium; α Is the thermal conductivity coefficient of the thermal conductive medium; τ At any moment after the instantaneous heating of the heat source; The coordinates (x0, y0, z0) are fixed point positions and are known values; The coordinates (x, y, z) represent the position of the point heat source and represent the variation value; T is the temperature rise at a fixed point after the influence of a point heat source. From the equation, it can be seen that the closer the point heat source is, the greater the influence of its temperature is. The cutting surface is directly the heat source surface, which is the most heated, and the deformation caused by heating is also greater; Therefore, for workpieces with high machining accuracy requirements, they should be cooled down. Cooling can be achieved by methods such as kerosene flushing or coolant flushing.

4. Finally, there is the original internal stress of the material: during the machining process, we need to remove the original internal stress, which changes the overall structural correlation of the workpiece. This will cause the internal stress balance of the material to be disrupted, and a new internal stress balance needs to be found, causing the material to deform during cutting. So when processing metal materials, we should use methods such as quenching and tempering and vibration aging to eliminate internal stress, so as to ensure that the internal stress and structure of the material tend to be stable as much as possible and reduce mechanical processing deformation.

PA nylon casting production, producing large and small holes and pores; When the mold temperature is too high, shrinkage occurs in the nylon; On the contrary, due to the incomplete dissolution of the instantly separated polymer in the monomer, resulting in micropores; In addition, PA nylon is mixed with volatile or decomposable substances, which produce volatile products during casting, ultimately forming bubbles and pores. These large and small holes cause instability in PA nylon. If the structure is changed, the internal stress will change the balance and the material is prone to deformation.

The processing effect of PA nylon workpieces can be affected by four factors: clamping, cutting tools, cutting heat, and internal stress of the material.

The CNC machining center's milling of PA nylon workpieces and stable accuracy are mainly influenced by four factors: clamping, cutting tools, cutting heat, and material internal stress, and these four factors also affect each other. For example, if the tool wear is serious, it is necessary to increase the thrust of the milling cutter on the parts, so that the specialty can increase the heat generated by cutting, and the cutting heat changes the stress balance in the material. From this, it can be seen that when milling PA nylon workpieces on CNC machining centers, it is necessary to comprehensively consider the effects of these four factors and minimize the impact of each factor