Analysis of Machining Process of Typical Sleeve Parts

1. Structure Characteristics and Process Analysis of Sleeve Parts

The processing technology of sleeve parts varies according to their functions, structural shapes, materials, heat treatment and size. According to its structure and shape, it can be divided into two categories: short sleeve and long sleeve. In their processing, their clamping methods and processing methods are very different, which are described below.

(1) Analysis and processing of bearing sleeve processing technology

As shown in Fig. 1.1, the bearing sleeve is made of ZQSn6-6-3, and the quantity of each batch is 200 pieces.

Fig. 1.1 bearing sleeve

1.1.1 Technical conditions and process analysis of bearing sleeve

The bearing sleeve belongs to a short sleeve, and the material is copper as shown in the diagram of tin blue Figure 1.1 bearing sleeve. The main technical requirements are: Φ 34js7 outer circle pair Φ The radial circular runout tolerance of 22H7 hole is 0.01mm; Left end face Φ verticality tolerance of 22H7 hole axis is 0.01mm. The outer circle of bearing sleeve is of IT7 accuracy, and fine turning can meet the requirements; The internal hole accuracy is also IT7, and reaming can meet the requirements. The machining sequence of the inner hole is: drilling – drilling – reaming.
Since the radial circular runout of the outer circle to the inner hole is required to be within 0.01mm, it cannot be guaranteed to clamp with soft jaws. Therefore, when fine turning the outer circle, the inner hole shall be used as the positioning reference, so that the bearing sleeve can be positioned on the small taper mandrel and clamped with two centers. In this way, the processing datum and measuring datum can be consistent, and the drawing requirements can be easily met.
When reaming the inner hole, it shall be machined in one clamping with the end face to ensure that the perpendicularity between the end face and the axis of the inner hole is within 0.01mm.

1.1.2. Processing technology of bearing sleeve

Table 1.1 shows the machining process of bearing sleeve. When rough turning the outer circle, the method of machining five pieces at the same time can be adopted to improve the productivity.
Table 1.1. Processing Process of Bearing Sleeve

Number	Process name	Process content	Positioning and clamping
1	Material preparation	Bar stock, processing and blanking according to five in one
2	Drill center hole	Turn the end face and drill the center hole; Turn the other end of the lathe and drill the center hole.	Outer circle of three jaw clamp
3	Rough turning	Vehicle excircle Ф 42, 6.5mm long, outer circle Ф 34Js7 is Ф 35mm, empty tool groove 2 × 0.5mm, the total length is 40.5mm, and the groove is divided Ф twenty × 3mm, chamfer at both ends 1.5 × 45 °, 5 pieces of the same processing, the same size.	Central hole
4	Drill	Drill hole Ф 22H7 to Ф 22mm single piece	Soft claw clamp Ф 42mm outer circle
5	Turning, hinge	The total length of the end face shall be 40mm to the dimension; Interior hole Ф 22H7 is Ф 22mm; Turning trough Ф twenty-four × 16mm to size; Reaming Ф 22H7 to size; Chamfer both ends of the hole.	Soft claw clamp Ф 42mm outer circle
6	Fine turning	Vehicle Ф 34Js7 (± 0.012) mm to dimension	Ф 22H7 hole spindle
7	Drill	Drilling radial oil hole Ф 4mm	Ф 34mm excircle and end face
8	Inspect

(2) Analysis of Hydraulic Cylinder Machining Process

The hydraulic cylinder is a typical long sleeve part, which is quite different from the short sleeve part in processing method and workpiece installation method.

1.2.1. Technical conditions and process analysis of hydraulic cylinder

The materials of hydraulic cylinder generally include cast iron and seamless steel pipe. Figure 1.1 shows the hydraulic cylinder made of seamless steel pipe. In order to ensure the smooth movement of the piston in the hydraulic cylinder, there are requirements for cylindricity of the inner hole of the hydraulic cylinder, straightness of the inner hole axis, perpendicularity between the inner hole axis and the two end faces, and the inner hole axis supports the outer circle at both ends( Φ 82h6). In addition, there are special requirements: the inner hole must be smooth and clean without longitudinal nicks; If the material is cast iron, its structure shall be tight without sand holes, pinholes and looseness.

Fig. 1.2 hydraulic cylinder

1.2.2. Machining process of hydraulic cylinder

Table 1.2 shows the machining process of hydraulic cylinder
Table 1.2. Machining Process of Hydraulic Cylinder

Number	Process name	Process content	Positioning and clamping
1	Mixed ingredients	Cutting seamless steel pipe
2	Turning	1. Vehicle Ф 82mm outer circle to Ф 88mm and M88 × 1.5mm thread (for process)	One end of the three jaw chuck clamp and the other end of the big tip.
		2. End face and chamfer	One end of the three jaw chuck clamp is laid on the center frame bracket Ф 88mm.
		3. Turning car Ф 82mm outer circle to Ф 84mm	One end of the three jaw chuck clamp and the other end of the big tip.
		4. The total length of turning end face and chamfer is 1686mm (machining allowance is 1mm)	One end of the three jaw chuck clamp is laid on the center frame bracket Ф 88mm.
3	Deep hole push boring	1. Semi precision push boring to Ф 68mm	M88 for one end × The 1.5mm thread is fixed in the fixture, and the other end is laid on the center frame.
		2. Finish boring to Ф 69.85mm
		3. Fine reaming (boring with floating boring cutter) to Ф 70 ± 0.02mm, surface roughness Ra is 2.5 μ m
4	Rolling hole	Use a rolling head to roll the hole to Ф 70 mm, surface roughness Ra is 0.32 μ m	One end is fixed in the fixture with thread, and the other end is laid on the center frame.
		1. Remove process thread and turn Ф 82h6 to size, cut R7 groove
5	Turning	2. Bore the inner cone hole 1 ° 30 ′ and turn the end face	One end of the soft claw clamp is positioned with a hole on the other end.
		3. Turn around, car Ф 82h6 to size, cut R7 groove	One end of the soft claw clamp and the other end of the center frame bracket (dial gauge alignment hole).
		4. Bore the inner cone hole 1 ° 30 ′ and turn the end face	The soft claw clamps one end and the other end.

2. Main Technological Problems in the Processing of Sleeve Parts

The main technological problem of sleeve parts in machining is to ensure the mutual position accuracy of inner and outer circles (that is, to ensure the coaxiality of inner and outer circle surfaces and the perpendicularity requirements of axis and end face) and prevent deformation.

2.1. Ensure mutual position accuracy

To ensure the coaxiality between the inner and outer circular surfaces and the perpendicularity between the axis and the end face, the following three process schemes can generally be adopted:
(1) The inner and outer circular surfaces and end faces shall be machined in one installation. This process scheme can ensure high mutual position accuracy because it eliminates the influence of installation error on machining accuracy. In this case, the main factor affecting the coaxiality between the inner and outer circular surfaces of the parts and the perpendicularity between the hole axis and the end face is the accuracy of the machine tool. This process scheme is generally used in the case where the part structure allows to process all the surfaces with position accuracy requirements in one installation. In order to facilitate the clamping of workpieces, the blanks are often made of multi piece bar stock, which is generally arranged to be processed on automatic lathes or turret lathes and other machines with concentrated processes. The bushing part shown in Figure 1.2 is a typical part adopting this scheme. See Table 1.3 and Figure 1.3 for the processing process.
Table 1.3. Machining Process of Bar Blank

Number	Process content	Positioning datum
1	Machining end face, rough machining excircle surface, rough machining hole, semi finish machining or finish machining excircle, finish machining hole, chamfering, cutting (see Figure 1-4)	Cylindrical surface and end face (for fixed material)
2	Machining another end face and chamfer	Excircle surface
3	Drilling lubricating oil hole	Excircle surface
4	Processing oil tank	Excircle surface
	Finish machining the cylindrical surface (if the bushing is not required highly, this process can be replaced by the finish turning in process 1)

Fig. 1.3 bushing parts

(2) All machining shall be carried out in several installations. First, the hole shall be machined, and then the cylindrical surface shall be machined with the hole as the positioning datum. This method is used to process the sleeve. As broaching, rolling and other process schemes are often used for hole finishing, the production efficiency is high, and the processing error caused by the poor rigidity of boring bar and grinding wheel bar during boring and grinding can be solved. When machining the outer circle of the sleeve with the hole as the benchmark, the small taper mandrel with good rigidity is often used to install the workpiece. The small taper spindle is simple in structure and easy to manufacture. The spindle is installed with two centers, and its installation error is very small, so high position accuracy can be obtained. The shaft sleeve shown in Figure 1.4 can be processed with this scheme. See Table 1.4 for the processing process.

Fig. 1.4 machining the bushing on the turret lathe

Fig. 1.5 axle sleeve

Table 1.4. Machining Process of Single Blank Shaft Sleeve

Number	Process content	Positioning datum
1	Rough machining end face, drilling, chamfering	Outer circle
2	Rough machining of excircle, other end and chamfer	Hole (with plum blossom tip and adjustable tip)
3	Semi finishing hole (reaming or boring), finishing end face	Outer circle
4	Finishing hole (broaching or pressing hole)	Hole and end face
5	Finish machining of excircle and end face	Inner bore

(3) All machining shall be carried out in several installations. First, the outer circle shall be machined, and then the inner hole shall be machined with the outer circle surface as the positioning datum. In this process, if the workpiece is clamped with a general three jaw self centering chuck, the coaxiality of the workpiece will be reduced due to the eccentric error of the chuck. Therefore, it is necessary to use a fixture with high centering accuracy to ensure that the workpiece has a high coaxiality. This processing scheme is generally adopted for long sleeves.

2.2. Methods to prevent deformation of thin-walled sleeve

In the process of machining, thin-walled sleeve is often deformed due to the influence of clamping force, cutting force and cutting heat, resulting in reduced machining accuracy. If the heat treatment process is not properly arranged for the thin-walled sleeve requiring heat treatment, it will also cause uncorrectable deformation. The following measures can be taken to prevent deformation of thin-walled sleeve:

(1) Reduce the influence of clamping force on deformation

① The clamping force should not be concentrated on a part of the workpiece. It should be distributed over a larger area to reduce the pressure on the unit area of the workpiece and thus reduce its deformation. For example, when the outer circle of the workpiece is clamped with a chuck, a soft jaw can be used to increase the width and length of the jaw, as shown in Figure 1.5. At the same time, the soft jaw should adopt the technological measures of self boring to reduce the installation error and improve the processing accuracy. Figure 1.6 shows the use of slotted sleeves to clamp thin-walled workpieces. Due to the large contact surface between the slotted sleeves and the workpieces, the clamping force is evenly distributed on the outer circle of the workpieces, which is not easy to deform. When the thin-walled sleeve takes the hole as the positioning reference, it is better to use the expansion mandrel.
② A fixture used to clamp the workpiece axially. As shown in Fig. 1.7, the workpiece is clamped axially by the nut end face, so the radial deformation caused by the clamping force is very small.

③ Make an auxiliary convex edge on the workpiece to strengthen the rigidity, and use a claw with special structure to clamp during processing, as shown in Figure 1.8. When the machining is finished, the convex edge is cut off.

Fig. 1.6 clamping the workpiece with soft jaws

Fig. 1.7 simply install and clamp thin-walled workpieces with slotted sleeves

(2) Reduce the influence of cutting force on deformation

Common methods are as follows:
① Reducing the radial force can usually be achieved by increasing the main deflection angle of the tool.
② The internal and external surfaces are processed at the same time to offset the radial cutting forces.

Fig. 1.8 axial clamping of workpiece

③ Rough and finish machining shall be carried out separately, so that the deformation generated during rough machining can be corrected during finish machining.

(3) Reduce the error caused by thermal deformation

In the process of machining, the workpiece will expand and deform due to cutting heat, thus affecting the machining accuracy of the workpiece. In order to reduce the influence of thermal deformation on machining accuracy, sufficient cooling time shall be reserved between rough and finish machining, and sufficient cutting fluid shall be injected during machining.

Heat treatment also has a great impact on sleeve deformation. In addition to improving the heat treatment method, the heat treatment process should be arranged before finishing, so that the deformation caused by heat treatment can be corrected in subsequent processes.

Source:  China Sleeves Manufacturer: www.epowermetals.com

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]