Effects of CNC Machining on Part Distortion2018-04-24
With recent increase in demand for more ultra precision machining designs for improving performance requirements, we are facing a great challenge in this kind of CNC machining services. Generally speaking, the greatest challenge when we machine these components is part distortion. For instance, assemblies with multiple enormous parts, of which removing up to 80% materials is necessary, have become common in aerospace, automobile, precision instrument industries. These kind of components might have similar appearance features such as thin wall, very long length, etc.
What Is Part Distortion?
Part distortion is defined as the deviation of part appearance from original shape after released from the fixture. In general, distortion could come from several variables such as type of material, inherent residual stresses in bulk material, residual stresses induced from CNC machining, part design, etc. In most of our cases, the dominant factor of part distortion is the inherent residual stresses in the part. If we look into the cause, these inherent residual stresses usually result from different manufacturing processes, i.e. quenching, stretching forging, extrusions, casting, welding, machining, forming, and etc.
Residual stresses induced from CNC machining may cause parts deforming.
How Can I Minimize Part Distortion?
Distortion is a common challenge in manufacturing industrial components. The suggestions to minimize or eliminate distortion shows as below:
1.) The length to thickness ratio of the part design is lower than 10:1.
2.) Pre-heat treating the metal part prior to manufacturing for stress relieve. For instance, the general stress relieve condition for AISI 4340 alloy steel is at 650-670°C for 2hrs, slow cooling furnace.
3.) Based on our experience of CNC machining services, distortion increases with the cutter size at constant feed, speed, depth of cut and material removal rates.
4.) Considering that WEDM process involves being fully-submerged, it imposes nearly no stress on the metal part.
With optimized manufacturing process flow, we are able to minimizing any deformation on all the CNC machined parts. Also, to select the suitable cutting tools and CNC machining parameters is of utmost importance. Note that the choice of cutting tools size is key to strike the balance between the productivity and geometrical constraints of the component. By the way, you can learn more about: