Raw Material Pretreatment: Building Processing Foundation
Material Selection and Testing
Select materials conforming to GB/T 699(45 steel) and **GB/T 3077** (35CrMo alloy structural steel), verify carbon, chromium, molybdenum and other element contents through direct reading spectrometer; complete tensile and hardness tests using universal material testing machine to ensure raw materials meet:
Tensile Strength: ≥ 600 MPa
Brinell Hardness: HB 170–210
Meeting processing and usage strength requirements.
Straightening and Cutting
- Straightening Process**: Use hydraulic bar straightening machine to control straightness error ≤ 0.08 mm/m, avoiding outer diameter deviation caused by raw material bending
- Cutting Process**: Cut according to “finished length + 2–3 mm allowance” through fully automatic bar cutting machine, ensuring single-piece length tolerance ±0.1 mm
Forming Processing: Optimizing Pre-Conditions for Centerless Grinding
Cold Heading Forming
Multi-station cold heading machine completes head forming such as hex head and cylindrical head, precisely controls head height and across-flats width through custom molds, with head coaxiality ≤ 0.05 mm after forming, avoiding head deflection affecting subsequent grinding accuracy.
Rough Turning Pre-Processing
For high-precision products such as automotive engine bolts, CNC lathe rough turns bar outer diameter and reserves **0.15–0.2 mm** grinding allowance, reducing centerless grinding finish grinding load and improving overall processing efficiency.
Centerless Grinding Core Processing: Staged Control of Accuracy and Efficiency
Using “centerless positioning, grinding wheel – regulating wheel coordinated drive” as the core, achieve high-precision processing through two steps: rough grinding and finish grinding:
Rough Grinding Process
Remove most of the allowance, control outer diameter to “finished size + 0.03–0.05 mm”, with surface roughness **Ra ≤ 0.32 μm**.
Finish Grinding Process
Through one-time processing, finally achieve:
- Outer Diameter Tolerance**: ±0.01 mm
- Surface Roughness**: Ra ≤ 0.32 μm
- Same Batch Dimensional Consistency**: ≤ 0.003 mm
Threading
Prioritize thread rolling process, using cold extrusion to make thread metal flow lines continuous, improving thread strength; thread tapping correction can be combined when high precision is required.
Head Detail Processing
Perform finishing on head structures such as hex and cross slots, remove burrs, ensuring assembly fit.
Surface Treatment
After processing, perform phosphating, galvanizing, or Dacromet treatment according to actual product use, improving corrosion resistance while enhancing thread friction for anti-loosening.
| Item Classification | Specific Parameter Description | Parameter Value |
|---|---|---|
| Thru-feed Grinding | Grinding diameter | 10—100mm |
| Maximum grinding length | 210mm | |
| Plunge-feed Grinding | Grinding diameter | 10～100mm |
| Maximum grinding length | 195mm | |
| Grinding Wheel Specification (Gri.wheel spec) | Specification | P500×200×305 |
| Guide Wheel Specification (Reg.wheel spec) | Specification | PDA350×200×203 |
| Grinding Wheel Speed (Gri.wheel speed) | Speed | 1250r/min |
| Guide Wheel Speed (Reg.wheel speed) | Speed | 10～200r/min (Stepless) |
| Guide Wheel Swivel Angle (Reg.wheel swivel angle) | In vertical plane | -2°～5° |
| In horizontal plane | 0°～3° | |
| Feed Rate per Division of Micrometer Feed Dial | Feed rate of handwheel per division | 0.002mm |
| Feed Rate per Division of Dresser Dial | Dressing device graduation | 0.01mm |
| Height from Centerline of Grinding Wheel & Guide Wheel to Workrest Base | Height from centerline of gri.wheel & reg.wheel to workrest | 255mm |
| Total Power of Machine | Total power | 21.66KW |
| Grinding wheel electromotor | 18.5KW | |
| Guide wheel electromotor | 2.2KW | |
| Overall Dimensions of Machine | Dimension | 2675×1505×1615mm |
| Net Weight of Machine | Weight | Approximately 4500Kg |
| Machining Accuracy | Roundness | 0.002mm |
| Cylindricity | 0.003mm | |
| Surface Roughness Ra | Ra0.32μm |
