4 Things You Need to Know about the Shaft Parts Manufacturing Process

1. Structural characteristics and technical requirements of general shaft parts

General shaft parts are divided into four categories according to their structural characteristics: light shafts, stepped shafts, hollow shafts and shaped shafts (including crankshafts, half shafts, camshafts, eccentric shafts, cross shafts and splined shafts, etc). If the ratio of the length and diameter of the shaft (L / d) to be divided, and can be divided into rigid shafts (L / d ≤ 12) and flexible shafts (L / d ≥ 12) two categories.

a. Structural characteristics of general Shaft parts are rotating body parts, the length is greater than their diameter, and are usually composed of external cylindrical surfaces, tapered surfaces, threads, splines, keyways, transverse holes, grooves and other surfaces.

b. Technical requirements for general shaft parts

• Dimensional tolerances Shaft parts of the main surface is often divided into two categories: one is with the inner ring of the bearing with the outer journals, namely the bearing journal, used to determine the position of the shaft and support the shaft, the dimensional tolerance level required higher, usually IT5 ~ IT7; another class with various types of transmission parts with the journal, namely with the journal, its tolerance level is slightly lower, often IT6 ~ IT9.
• Geometric tolerances include shape tolerance, orientation tolerance, position tolerance and runout tolerance.

1. Shape tolerance mainly refers to the roundness tolerance and cylindricity tolerance of important surfaces such as journal surface, outer conical surface, and taper hole. The error shall generally be limited to the dimensional tolerance; for precision shafts, the shape tolerance shall be specified separately on the part drawing.
2. Directional tolerances refer to the tolerance of perpendicularity of the important end faces to the axis, the tolerance of parallelism between the end faces, etc.
3. The positional tolerances refer to the tolerances of the inner and outer surfaces, the coaxiality of important axis surfaces, etc.
4. The runout tolerance mainly refers to the radial runout tolerance of inner and outer surfaces, important shaft surfaces, etc.

• Surface roughness The machined surfaces of shafts have surface roughness requirements, which are generally determined by machining possibilities and economy. The surface roughness of the bearing journals is often Ra0. 2 to 1. 6 μm, and that of the mating journals of the transmission parts is Ra0. 4 to 3. 2 μm.

2. Machining process analysis and selection of positioning datum for general shaft parts

a. Machining process analysis of general shaft parts. For parts with high accuracy requirements, the rough and finish machining should be separated to ensure the quality of the parts. Shaft parts processing can generally be divided into three stages: rough turning (rough turning of the outer circle, drilling the center hole, etc.), semifinish turning (semi-finish turning of the outer circle, step and repair the center hole and secondary surface, etc.), rough and fine grinding (rough and fine grinding of the outer circle) . Each stage is roughly defined by the heat treatment process.

b. Selection of positioning datum for general shaft parts. The most common positioning reference for general shaft parts is the two center holes. Because the shaft parts of the outer surface, thread surface coaxially and end face perpendicularity of the axis is the main item of geometric tolerance, and the design reference of these surfaces are generally the centerline of the shaft, the use of two center hole positioning can comply with the principle of coincidence of the reference; and because most processes use the center hole as the positioning base, can maximize the processing of multiple outer and end faces, which is also consistent with the principle of unity of the reference. However, two center holes cannot be used as a datum in the following cases.

• When roughing the outer circle, in order to improve the rigidity of the workpiece, the surface of the outer circle of the shaft is used as the positioning base, or the outer circle and the center hole are used as the positioning base, i.e. one clamping and one top.
• When the shaft is a through-hole part, the center hole, which is the locating surface, disappears during machining due to the drilling of the through-hole, and in order to use the center hole as the locating surface after the through-hole has been machined, three methods are often used.

1. When the diameter of the central hole is small, a 60° inner taper with a width of not more than 2 mm can be directly inverted at the hole instead of the central hole.
2. When the shaft has a cylindrical hole, a tapered plug can be used with a taper of 1:500. When the taper of the shaft hole is small, the taper of the plug is the same as the taper of the positioning holes at both ends of the workpiece.
3. If the shaft bore is tapered and the taper of the shaft through-hole is large, a mandrel with a tapered plug, referred to as a tapered plug mandrel, may be used.

When using tapered plugs or tapered plug arbors, care should be taken not to replace or disassemble them until the center bore is no longer in use after finishing each machined surface.

3. Materials and heat treatment of general shaft parts

a. Materials and blanks for general shaft parts

• General shaft parts materials commonly used 45 steel, high precision shaft can be selected 40Cr, GCr15, 65Mn, can also choose ductile iron; high-speed, heavy-duty shaft, choose 20CrMnTi, 20Mn2B, 20Cr and other carburized steel or 38CrMoAl nitriding steel.
• Commonly used billets for general shaft parts are round bars and forgings; large shafts or shafts with complex structures use Casting. After heating and forging, the billet can be heated so that the internal fibers of the metal are evenly distributed along the surface, resulting in high tensile strength, bending strength and torsional strength.

b. Heat treatment of general shaft parts

• Forging blanks before processing, are required to arrange normalizing or annealing treatment, so that the internal grain refinement of steel, eliminate forging stress, reduce material hardness, improve machinability.
• Tempering is generally arranged after rough turning and before semi-finishing turning to obtain good overall mechanical properties.
• Surface hardening is usually scheduled prior to finishing to correct local distortion caused by hardening.
• Shafts with precision requirements must also be subjected to low-temperature aging after partial hardening or rough grinding.

4. Example of machining a general shaft part

Example 1: Spline shaft

a. Part drawing analysis

• The spline shaft shown in above is based on the common axis of the two journals ϕ45js5, the coaxial tolerance of ϕ53. 55g6 to the datum is ϕ0. 005 mm, and the axial runout tolerance of the two ϕ53. 55g6 end faces to the datum is 0. 005 mm.
• Part material is 45 steel.
• Tempered to a hardness of 220 to 250 HBW.

b. Process Analysis

• The part is a splined shaft and the centering method is OD centering.
• In the machining process, the roughing process is followed by overall tempering and then finishing.
• In single piece or small batch production, horizontal lathe is used, rough and finish turning can be done on one lathe; in larger batch, rough and finish turning should be done on different lathes.
• ϕ 45 js5 and ϕ53.55g6 have high cylindrical accuracy, so the finish turning process leaves a grinding allowance and the final grinding is done with a cylindrical grinder.
• In order to ensure concentric center bores at both ends, the center bore of the shaft is initially used only as a temporary center bore; finally, during finishing, the center bore is reworked or ground and then positioned with the finished center bore.

c. Machining Processes (see Table, Unit: mm)

Example 2: Shaft

a. Part drawing analysis

• The shaft shown in the above picture is based on the common Shaft of the journals ϕ50h6 and ϕ60js6 at the right end. The tolerance of the coaxiality of the outer circle ϕ80-0. 005 mm and the outer circle ϕ60js6 (middle position) to the datum is 0. 005 mm.
• The material of the part is 45 steel.
• Tempered hardness of 220 to 250 HBW.

b. Process Analysis

• During the machining process, the roughing process is followed by an overall tempering process and then a finishing process.
• In single piece or small batch production, using ordinary lathe, rough and finish turning can be done on one lathe; in larger batch, rough and finish turning should be done on different lathes.
• ϕ80(-0.005 -0.020) mm cylinders, ϕ60js6 cylinders and ϕ50h6 cylinders with high accuracy requirements are left for grinding in the finishing process and finally ground with a cylindrical grinder.
• In order to ensure concentric center bores at both ends, t h e shaft center bore is initially used only as a temporary center bore. Finally, during finishing, the center bore is reworked or ground and then positioned with the finished center bore.

c. Machining Processes (see Table, Unit: mm)

Example 3: Eccentric Shaft

a. Part drawing analysis

• The eccentric shaft shown in above is based on the common Shaft of the two journals of the outer circle of ϕ75(-0.03 -0.06) mm.
• Part material is 45 steel.

b. Process Analysis

• The part is an eccentric shaft, ϕ110 (-0.03 -0.09) mm outer circle and ϕ75 (-0.03 -0.06) mm outer circle of the common shaft of both journals to ensure an eccentricity of 6 mm, two central holes should be machined on the left and right sides of the part: one centered on the ϕ75 mm outer axis and the other centered on the ϕ110 mm outer axis.
• In single piece or small batch production, using ordinary lathe, rough and finish turning can be done on one lathe; in larger batch, rough and finish turning should be done on different lathes.
• ϕ75 (-0.03 -0.06) mm with high cylindrical accuracy, with grinding allowance for the finishing process and finally with the cylindrical grinding machine to grind.

c. Machining Processes (see Table, Unit: mm)

Example 4: Motor shaft

a. Part drawing analysis

• The motor shaft shown in above is based on the common Shaft of the two journals with 1:12 tapered circle and ϕ80 mm ± 0. 005 mm outer circle.
• The part material is 20CrMnTi steel.
• The depth of the carburized layer is 0. 5 to 0. 8 mm, and the hardness is 60 to 65 HRC after quenching and tempering

b. Process Analysis

• The dimensional and geometric tolerances and surface quality of the 1:12 tapered circle, ϕ80mm ± 0.005mm outer circle, ϕ64g6 outer circle and ϕ150f7 outer circle are very high.
• The gears are machined after finishing, using a self-centering chuck ϕ80 mm ± 0.5 mm. 0.005 mm OD, squared ϕ64g6 OD.
• In single piece or small batch production, using ordinary lathe, rough and finish turning can be done on one lathe; in larger batch, rough and finish turning should be done on different lathes.

c. Machining Processes (see Table, Unit: mm)

Example 5: Slender Shaft

a. Part drawing analysis

• The slender shaft shown in above is based on the common Shaft of the two journals ϕ22f7 and ϕ16h6.
• Part material is GCr15 steel.
• Heat treatment: Hardened and tempered to 60 to 65 HRC.

b. Process Analysis

• The dimensional and geometrical tolerances and surface quality of the ϕ22f7 outer circle, ϕ16h6 outer circle and ϕ20mm ± 0.005mm outer circle are very high.
• Milling of 2×6P9 keyway is scheduled to be done after the finishing process.
• In single piece or small batch production, using ordinary lathe, rough and finish turning can be done on one lathe; in larger batch, rough and finish turning should be done on different lathes.

c. Machining Processes (see Table, Unit: mm)

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