Cautions CNC machining shaft parts

Michin.Mu

Rapid Prototyping & Rapid Manufacturing Expert

Specialize in CNC machining, 3D printing, urethane casting, rapid tooling, injection molding, metal casting, sheet metal and extrusion

Follow me on:

Cautions CNC machining shaft parts

What is shaft parts

Shaft part is a common type of parts, its structure is a rotating body and the length is greater than its diameter generally. It’s widely used in supporting transmission parts, transmission torque and load to bear for various mechanical equipments. The machining of Shaft parts must follow certain rules. Here list out some CNC machining tips & machining cautions of shaft parts.

Basic processing route of shaft parts

The main processing surface of shaft parts is the cylindrical surface and the common special-shaped surface. Therefore, select most suitable processing method for various requirements of accuracy levels and surface roughness. The basic processing route can be summarized into the following four points.

The first type of processing route is from rough turning to semi-finishing turning and then finish turning, which is the mainly processing route option for the outer circle processing of shaft parts with common materials.

The second type of processing route is from rough turning to semi-finishing turning, then to rough grinding and finally takes fine grinding. For ferrous metal materials (such as mold steel, alloy steel, or hardened materials after heat treatment, etc.), and the part need to do quenching treatment with highly requirements of accuracy and surface roughness, such processing route will be the best option, as grinding processing is ideal choice for the strict requirements of surface roughness.

The third type of processing route is from rough turning to semi-finishing turning, then to finish turning and diamond turning. Such kind of processing route is dedicated to use for machining non-ferrous metal material (aluminum, brass, etc), as the hardness is low for non-ferrous metal material and easy to block the gaps between sand grains. Usually using grinding processing can’t meet the requirement of the surface roughness and have to take finish turning and diamond turning.

The last type of processing route is from rough turning to semi-finish turning, then rough grinding, fine grinding, and finally polishing processing. Such processing route usually applied for the ferrous metal materials after quenching treatment, and the parts also with highly requirements of accuracy and surface roughness.

Pre-processing of shaft parts

Before turning the outer circle of shaft parts, there are some preparatory processes must be carried out which called pre-processing of shaft parts. The most important preparatory process is straightening. As the workpiece blank usually got deforming during the manufacturing, transportation and storage process. In order to make sure reliable clamping and evenly distributed of machining allowance, will take straightening process through various presses or straightening machines in the cold state.

Locating datum for machining shaft parts

Firstly, use the center of the workpiece as CNC machining locating datum. In the processing of shaft parts, the coaxiality of various cylindrical surfaces, taper holes, threaded surface and the perpendicularity of end faces to the rotary shaft line are important manifestation of location accuracy. Those surfaces are generally based on the centerline of the shaft as the design reference, and use center line for positioning which conform to the principle of criteria coincidence. The center line is not only limited to as the locating datum of CNC turning, but also as the locating datum and inspection datum for other machining processes, and conforms to the principle of datum unification. When two center holes are used for locating, it can maximize machining of multiple outer circles and end faces in one clamping.

Secondly, use the outer circle and center hole as CNC machining locating datum. Such method effectively overcomes the shortcomings of poor rigidity center hole locating, especially machining the heavy workpiece, the center hole locating will easy lead unstable clamping, and cutting parameters can’t be large also. And use the outer circle and center hole as CNC machining locating datum can avoiding such problem happens. During the rough turning, use the outer circle and center hole as CNC machining locating datum can withstand the larger cutting torque during turning processing, which is common locating method for shaft part machining.

Thirdly is using the two outer circle surfaces as CNC machining locating datum. When processing the inner hole of the hollow shaft, the center hole cannot be used as location datum, so we have to use the two outer circle surfaces as location datum. When machining the main shaft of a machine tool, the two supporting journals are often used as the locating datum, which can effectively guarantee the coaxiality requirements of the tapered hole relative to the supporting journal, and eliminate errors caused by datum misalignment.

Finally is use the taper with the center hole as CNC machining location datum. Such method is most commonly used in the outer circle surface turning of the hollow shaft parts.

Clamping of shaft parts

The processing of the taper and taper center shaft must with highly machining accuracy, the center hole is not only the locating datum of its own manufacturing, but also the datum for finish turning the outer circle of the hollow shaft, which must ensure the taper and the taper surface of tapper center shaft have highly coaxiality with the center hole. Therefore, when choosing the clamping method, it should be noted that the number of taper installations should be reduced as much as possible, which aim for reduce the errors caused by repeat install the parts. In actual machining, after the taper installed, generally speaking, it will not be removed or replaced in the middle of processing until the processing is completed.