- The part is a bowl-shaped sheet metal stamping with a wall thickness of 3.5 mm. The outer diameter of the bowl edge is φ(492.5±0.315) mm, the depth is 122.1 mm, and it features five tangent arcs. If converted to a machined part, its mechanical strength would be lower than that of the stamped sheet metal. However, based on Figures 1 and 2, the oil baffle is radially positioned and sealed by the outer diameter φ4690 -0.25 mm and axially positioned by the edge end face. The inner hole φ(155±0.0315) mm accommodates an oil seal for sealing. During operation, the oil baffle only prevents lubricating oil splashed by rotating components from leaking outside the machine and does not bear mechanical loads. Therefore, the mechanical strength of the machined part meets the requirements.
When converting the stamped sheet metal part to a machined part, the thin wall thickness makes it prone to deformation during machining, increasing processing difficulty. Thus, special attention must be paid to workpiece deformation and clamping during machining.
-
Technical Requirements Analysis
The outer diameter φ(492.5±0.315) mm, outer diameter φ4690 -0.25 mm, inner hole φ(155±0.0315) mm, and small end face require machining. The outer diameter φ4690 -0.25 mm is IT10 grade, and the inner hole φ(155±0.0315) mm is IT8 grade, with the highest surface roughness value of Ra=1.6 μm. The outer diameter φ4690 -0.25 mm serves for radial positioning and sealing, while the inner hole φ(155±0.0315) mm accommodates an oil seal for sealing. The edge end face provides axial positioning. The remaining surfaces are non-machined, with dimensional requirements meeting GB/T 1804 Roughness Grade C, ensuring the profile does not interfere with other rotating parts. Therefore, deformation control for the outer diameter φ4690 -0.25 mm and inner hole φ(155±0.0315) mm is critical. -
Selection of Blank Material
When converting the oil baffle to a machined part, casting is the optimal choice from a structural perspective, as it saves material and reduces machining costs. However:
- If cast steel is selected, molds are required for casting, and cast steel parts are prone to defects. When machined to a 3.5 mm wall thickness, leakage may occur.
- If cast iron is selected, molds are also required, and the large outer diameter increases the risk of cracking and leakage when machined to a 3.5 mm wall thickness.
The oil baffle's dimensions (φ(492.5±0.315) mm outer diameter, 130.6 mm total height) preclude the use of standard stock materials. Thus, forging is the only viable option. Die forging is suitable for small-batch production and, given the oil baffle's structure, can save material and reduce machining costs.
Material Selection:
The material must first meet design requirements, followed by considerations of machinability and cost-effectiveness. The design specifies No. 10 carbon structural steel, but No. 10 steel tends to stick to tools during machining and has poor rigidity, increasing the risk of clamping deformation and machining difficulty. After consulting with forging suppliers, No. 35 carbon structural steel is available for forging and offers better forgeability. For small-batch production, the price difference between No. 10 and No. 35 steel blanks is negligible. No. 35 steel has superior mechanical properties, better machinability, and meets usage requirements. Therefore, No. 35 carbon structural steel forgings are selected, with technical requirements complying with QJ 500A―1998 "Technical Conditions for Carbon Steel and Alloy Structural Steel Forgings."
The forging blank is shown in Figure 3, with a draft angle of 3°–5°.
- Process Flow Determination
Preliminary Analysis:
The oil baffle, converted from a stamped sheet metal part to a machined part, has a bowl-shaped structure with an outer diameter of 4690 -0.25 mm, internal depth of 122.1 mm, and wall thickness of 3.5 mm. Clamping may cause elastic or plastic deformation, and machining the 3.5 mm wall thickness under cutting forces may induce elastic deformation, necessitating increased workpiece rigidity. The forging blank, when machined into a thin-walled bowl-shaped part, involves significant material removal. Post-machining, internal stress redistribution may cause deformation, requiring timely stress relief during processing.
From the design perspective, controlling deformation of the outer diameter φ4690 -0.25 mm and inner hole φ(155±0.0315) mm is critical.
Key Control Points:
- Clamping deformation
- Deformation caused by internal stress post-machining
The process flow and machining methods must align with the enterprise's and subcontractors' actual capabilities, ensuring part quality, safety, and cost-effectiveness.
Finalized Process Flow:
Forging → Normalizing → Turning → Normalizing → Turning → Low-Temperature Annealing → Turning
Detailed Steps:
-
Forging and Normalizing:
- Subcontracted to a forging supplier. The buyer must approve the forging drawing and inspect the delivered forgings against it, including verifying normalizing records.
-
Turning (Rough Machining):
- Figure 4 shows the rough turning operation. The simple structure requires machining accuracy of GB/T 1804 Medium Grade m or lower. The blank weighs 138 kg (Figure 3).
- Preferred machine: Conventional vertical lathe C5112; alternative: Conventional horizontal lathe C630.
- Clamping: Four-jaw independent chuck for secure gripping of the φ508 mm blank.
- Steps:
a. Clamp the φ496 mm outer diameter (blank outer diameter φ508 mm) using the four-jaw chuck, with end face 1 as the reference. Align the inner hole with a scribing tool. Machine end face 2, outer diameter φ496 mm (35 mm length), inner hole φ150 mm, and internal profile.
b. Re-clamp the φ496 mm outer diameter with end face 2 as the reference, aligning the inner hole φ150 mm with a dial indicator (runout ≤0.2 mm). Machine end face 1 and the outer taper.
-
Normalizing:
- First normalizing eliminates overheating from forging; second normalizing refines grain structure, homogenizes the material, improves mechanical properties, and relieves stress.
- Parameters: Heat to 840–860°C, hold for 90–95 min, air cool.
-
Turning (Internal/External Profile Machining):
- Figure 5 shows the turning operation for the internal/external profiles, which consist of five tangent arcs. Conventional horizontal lathes are inefficient for this task, so a CNC lathe is preferred.
- Machine selection: Horizontal or vertical CNC lathe (e.g., Vturn-36).
- Clamping: Three-jaw self-centering chuck for faster setup.
- Steps:
a. Clamp the φ494 mm outer diameter (pre-machined φ496 mm). The left end face of φ494 mm is 105.5 mm from end face 1 (136 mm – 30.5 mm), and the clamped wall thickness is 18 mm (calculated from Figure 4). Use extended soft jaws for clamping, with end face 1 as the axial reference. Machine end face 2, inner hole φ(152±0.2) mm, and internal profile.
b. Re-clamp using the three-jaw chuck, with end face 2 as the axial reference, gripping the inner hole φ462.88 mm. Machine end face 1 and the external profile.
-
Low-Temperature Annealing:
- Relieves machining-induced stress and stabilizes dimensions before finish turning.
- Parameters: Heat to 580–600°C, hold for 70 min, furnace cool to below 250°C, then air cool.
-
Turning (Finish Machining):
- Figure 6 shows the finish turning operation, involving end faces and inner/outer diameters with IT8-grade accuracy and Ra=1.6 μm surface roughness. A conventional lathe (e.g., CW616E) suffices.
- Rationale for Conventional Lathe:
a. The 3 mm clamping area is deformation-prone; wide soft jaws and a backing plate are needed for gentle clamping.
b. Machining involves simple inner/outer diameters and end faces (no arcs). - Steps:
a. Clamp using the three-jaw chuck, with end face 2 as the reference, and wide soft jaws gripping the inner hole. Machine the φ(155±0.0315) mm hole end face (Ra=12.5 μm), outer diameter φ161 mm, and rough/finish the inner hole φ(155±0.0315) mm.
b. Re-clamp with end face 2 as the reference, lightly gripping the inner hole. Use the tailstock center to press the backing plate against the workpiece for axial support, then tighten the chuck. Rough machine the outer diameter φ4690 -0.25 mm and its bottom end face (leave 1.2 mm and 0.5 mm stock, respectively).
c. Loosen the chuck, then lightly re-clamp the inner hole. Finish machine the outer diameter φ4690 -0.25 mm and its bottom end face.