Typical Machining Processes for Mechanical Manufacturing

CNC machining

Shaft Parts Machining

Function of Shaft Parts

Shaft parts are primarily used to support transmission components and transmit torque. Common shaft parts include plain shafts, hollow shafts, half shafts, stepped shafts, spline shafts, cross shafts, eccentric shafts, screws, crankshafts, and camshafts.

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Materials, Blanks, and Heat Treatment of Spindle Parts

Spindles commonly use materials such as 45 steel, with high-precision spindles using 40Cr, bearing steel GCr15, and spring steel 65Mn. For high-speed, heavy-load spindles, low carbon alloy steels such as 20CrMnTi and 20Mn2B are used. Blanks are often round bars and forgings, while large or complex shafts use castings. Heated forgings ensure metal fibers are evenly distributed along the surface, enhancing tensile, bending, and torsional strength.

bronze machining

Heat treatment processes include normalizing or annealing, quenching, and surface hardening to refine grains, relieve forging stress, reduce material hardness, and improve machinability. High-precision shafts also undergo low-temperature aging treatment.

Main Technical Requirements for Shaft Parts

  • Dimensional Accuracy: Main surfaces are bearing journals (with IT 5IT7 accuracy) and mating journals (with IT6IT9 accuracy).
  • Geometric Accuracy: Includes roundness, cylindricity, etc., with errors limited within dimensional tolerances.
  • Positional Accuracy: Includes coaxiality, radial runout, etc.
  • Surface Roughness: Bearing journals have 0.21.6μm roughness, while mating journals have 0.43.2μm.
  • Others: Heat treatment, chamfering, deburring, and appearance finishing requirements.

Clamping Methods for Shaft Parts

  1. Two Center Holes Positioning: The important outer cylindrical surface is used as the rough reference to machine the center hole, which then serves as the precise reference.
  2. Outer Surface Positioning: Suitable for hollow or short shafts.
  3. Plug or Drawbar Mandrel Positioning: Used for machining the outer surface of hollow shafts.

Key Requirements for CA6140 Spindle

  • Bearing Journal: High accuracy affecting rotational precision.
  • Morse Taper No.6: Used for installing centers or tool shanks, requiring coaxiality with the bearing journal axis.
  • Tapered Surface and End Face: Locating surfaces for chuck or lathe fixtures.
  • Thread: For fixing and adjusting spindle bearing clearance, requiring coaxiality with the bearing journal.

Machining Process for Lathe Spindle Parts

Process Flow Table

No.Process NameProcess ContentLocating ReferenceEquipment
1Material PreparationMaterial preparation
2ForgingDie forgingVertical precision forge
3Heat TreatmentNormalizing
4SawingSawingSaw machine
5Milling & DrillingMilling end face and drilling center holeBlank outer roundCenter hole machine
6Rough TurningRough turning outer roundCentersMulti-tool semi-automatic lathe
7Heat TreatmentQuenching
8Large End MachiningTurning large end outer round, short taper, end face, stepCentersHorizontal lathe
9Small End MachiningProfiling small end outer roundCentersProfiling lathe
10Deep Hole DrillingDrilling φ48mm through holeBoth ends bearing journalsDeep hole drill
11Small End TaperingTurning small end taper (1:20 taper plug, contact rate ≥50%)Both ends bearing journalsHorizontal lathe
12Large End TaperingTurning large end taper (Morse No.6 taper plug, contact rate ≥30%), short taper, end faceBoth ends bearing journalsHorizontal lathe
13DrillingDrilling holes on the large end faceLarge end inner taperRadial drill
14Heat TreatmentLocal high-frequency quenching (φ90g5, short taper, Morse No.6 taper hole)CentersHigh-frequency quenching equipment
15Precision TurningPrecision turning all outer rounds, slotting, chamferingCentersCNC lathe
16Rough GrindingRough grinding φ75h5, φ90g5, φ100h7 outer roundsPlug centersCombined cylindrical grinder
17Rough Grinding TaperRough grinding large end inner taper (Morse No.6 taper plug, contact rate ≥40%)Front bearing journal and φ75h5 outer roundInternal grinder
18Spline MillingMilling φ89f6 splinePlug centersSpline milling machine
19Key Slot MillingMilling 12f9 key slotφ80h5 and M115mm outer roundVertical milling machine
20Thread TurningTurning three threads (matching nuts)Plug centersHorizontal lathe
21Precision GrindingPrecision grinding all outer rounds and endsPlug centersCylindrical grinder
22Rough Grinding ConesRough grinding 1:12 outer conesPlug centersSpecial combined grinder
23Precision Grinding ConesPrecision grinding 1:12 outer cones, D end face, short taperPlug centersSpecial combined grinder
24Precision Grinding TaperPrecision grinding Morse No.6 inner taper (remove plug, contact rate ≥70%)Front bearing journal and φ75h5 outer roundSpecial spindle taper grinder
25DeburringDeburring, chamfering end holesHandwork
26InspectionFull inspection according to drawingsFront bearing journal and φ75h5 outer roundSpecial gauge

Key Points and Process Analysis

  1. Division of Processing Stages: Rough and finish machining are separated, following the principle of “rough before finish.” Important surfaces (especially bearing journals) are processed as the main line, interspersed with other surface processing steps.
  2. Selection of Locating References: Using two center holes as the locating reference; positioning with bearing journals for taper turning; using plug center holes for rough and precision grinding outer rounds; positioning with outer rounds for rough grinding tapers; final taper grinding with bearing journals as reference.
  3. Arrangement of Process Sequence: Center drilling first, deep hole drilling before semi-finish turning the outer round, secondary surfaces processing after finish turning or rough grinding the outer round.
  4. Main Process Methods: Center hole processing, outer round processing, spline processing, precision taper grinding.

Spindle Inspection

  • In-process Inspection: Using automatic measurement devices to control the machining process based on measurement results without interrupting processing.
  • Post-process Inspection: Dimensional accuracy with external micrometers, high-volume production using smooth limit gauges, surface roughness with roughness samples, high precision using optical instruments.

Bracket and Box Parts Machining

Function of Bracket and Box Parts

Box parts are foundational components of machines, connecting relevant parts such as shafts, sleeves, and gears into an integral whole, maintaining their correct relative positions, transmitting torque, or altering speed to complete specified movements.

Materials and Blanks for Box Parts

Box parts are commonly made of gray cast iron, with aluminum alloy used for car and motorcycle crankcases. Cast blanks are often used, and post-casting artificial aging or annealing is required to reduce residual stress.

Process Analysis

  • Selection of Rough References: Usually, important holes and another hole spaced apart are used as rough references to ensure uniform machining allowance.
  • Selection of Precision References: Assembly references or specially machined surfaces and two holes are often used to ensure consistency.
  • Process Concentration and Priority: High precision positional requirements are concentrated in the same process to minimize clamping times and ensure precision.

Hole Series Machining

Box parts have various hole series, including parallel holes, coaxial holes, and intersecting holes. Methods include using previously machined holes for guidance, boring machine rear column guide sleeves, and flip boring.

Box Inspection

  • Surface Roughness Inspection: Visual or sample comparison, optical instruments for small Ra values.
  • Dimensional Accuracy Inspection: Plug gauges for high-volume production, internal micrometers or pneumatic gauges for high precision.
  • Flatness and Straightness Inspection: Flat rulers, thickness gauges, autocollimators, or level instruments.
  • Coaxiality Inspection: Using test rods.
  • Hole Spacing and Parallelism Inspection: Vernier calipers or micrometers, coordinate measuring machines for high precision.

Bracket Machining Example

No.Process NameProcess ContentTypeEquipment
1CastingCasting blank
2Heat TreatmentAnnealing
3MarkingMarking center lines and processing linesHandworkMarking table
4PlaningPlaning bottom surfaceShaper
5TurningDrilling and boring bearing holes, turning end facesLathe
6HandworkMarking bearing hole lines
7HandworkDrilling screw holes and countersinking protrusionsDrill press
8InspectionInspection according to drawings

Box Machining Example

No.Process NameProcess ContentTypeEquipment
1CastingCasting blank
2Heat TreatmentArtificial aging
3PaintingPrimer painting
4MarkingMarking center lines, connecting holes, pins, screw holesMarking table
5PlaningRough and finish planing fitting surfaces and top surfaceShaper
6MarkingMarking according to processing surfaceMarking table
7DrillingDrilling connecting holes, screw holesRadial drill
8HandworkTapping threads, scraping fitting surfaces, assembling
9MillingRough and finish milling bearing hole end surfacesEnd mill
10BoringRough and finish boring bearing holesHorizontal borer
11HandworkDeburring, cleaning, marking
12PaintingPainting non-machined surfaces
13InspectionFull inspection according to drawings

Cylindrical Gear Machining

Gear Structure and Classification

Gears are classified based on structure and application, including spur gears, helical gears, herringbone gears, spiral gears, internal gears, etc.

Gear Accuracy Requirements

  1. Motion Accuracy: Ensure precise motion transmission and constant transmission ratio, with maximum angle error not exceeding specified limits.
  2. Smooth Operation: Ensure smooth transmission with minimal vibration, impact, and noise.
  3. Contact Accuracy: Ensure uniform load distribution during transmission to prevent premature wear or breakage.
  4. Backlash: Ensure proper clearance for thermal expansion, elastic deformation, and assembly errors, facilitating lubrication and oil film formation.

Gear Materials and Heat Treatment

Gear materials are selected based on usage requirements and working conditions. Common materials include medium carbon steel, medium carbon alloy steel, low carbon alloy steel, and cast steel. Gear blanks are chosen based on material, shape, size, usage conditions, and production volume, commonly including cast iron, bar stock, forgings, and cast steel blanks.

Gear Machining Methods

Gear machining methods are divided into forming methods and generating methods. Forming methods include gear milling, gear shaping, and forming gear grinding, while generating methods include gear hobbing, gear shaping, gear shaving, gear grinding, and gear honing. The machining process is divided into forming the gear blank, rough machining, semi-finish machining, heat treatment, and finish machining.

Gear Machining Process Flow Table

No.Process NameProcess ContentLocating Reference
1ForgingForging blanks
2Heat TreatmentNormalizing
3Rough TurningRough turning shape, leaving allowance
4Finish TurningFinish turning, leaving grinding allowanceOuter and end face
5Gear HobbingHobbing gear teeth, leaving grinding allowanceInner hole and end face A
6ChamferingChamfering to sizeInner hole and end face A
7DeburringDeburring
8Heat TreatmentSurface hardeningGear teeth
9Key SlottingSlotting keyways to sizeInner hole and end face A
10Grinding SurfaceGrinding flat surfacesInner hole and end face A
11Grinding BoreGrinding bore to sizeInner hole and end face A
12Gear GrindingGrinding gear teethInner hole and end face A
13InspectionFull inspection according to drawings

Gear Blank Machining

Gear blank machining is crucial, as it establishes the reference for gear tooth machining and inspection. Gear tooth measurements are based on the pitch circle diameter, and accurate pitch circle diameter is essential for correct tooth thickness measurement.

Gear End Machining

Gear end machining includes rounding, chamfering, deburring, and de-burring. Rounded or chamfered gear teeth facilitate meshing, reducing impact. Chamfering removes sharp edges and burrs. End machining is usually performed after gear hobbing or shaping and before gear shaving.

Sleeve Parts Machining

Structure and Classification of Sleeve Parts

Sleeve parts support or guide movement, such as cylinder liners, oil cylinders, drill sleeves, and sliding bearings. Sleeve parts are relatively simple but difficult to machine, requiring high geometric and positional accuracy.

Blanks and Materials for Sleeve Parts

Sleeve parts blanks are often cast or forged with holes, and materials include steel, cast iron, bronze, brass, high-quality alloy steel, and Babbitt alloy. Sliding bearings often use copper and high-quality alloy steel for high strength and hardness requirements.

Machining Methods for Sleeve Parts

Machining sleeve parts requires ensuring the coaxiality of the inner and outer diameters and perpendicularity of the end face to the axis. Basic methods include drilling, reaming, boring, honing, and cold extrusion.

Sleeve Parts Machining Process Flow Table

No.Process NameProcess ContentEquipment
1Material CuttingCutting materialSaw machine
2Rough TurningTurning end face, drilling through holeLathe
3Semi-finish TurningSemi-finish turning outer diameterLathe
4Heat TreatmentEnsuring carburizing depth 0.8-1.2mm, hardness HRC58-62
5Grinding Inner/OuterGrinding outer diameter, inner boreUniversal grinder
6Honing Inner BoreHoning inner bore to size, grinding arcLathe
7InspectionInspection according to drawings

Key Points

  1. Reducing Cutting Force and Heat: Separate rough and finish machining, sufficient cooling and lubrication during machining.
  2. Reducing Clamping Force: Change radial clamping to axial clamping, use transition sleeves or spring sleeves for even radial clamping.

Connecting Rod Machining

Structure, Materials, and Requirements of Connecting Rods

Connecting rods transmit motion and force, subjected to significant dynamic loads. Medium and large connecting rods consist of a rod body and a rod cap, made from 45 steel or 40Cr, 45Mn2, and increasingly ductile iron. The blank is forged.

Connecting Rod Machining Process Flow Table

No.Process NameProcess ContentEquipmentLocating Reference
1ForgingForging blanks
2Heat TreatmentQuenching
3Magnetic InspectionMagnetic inspection
4Rough & Finish MillingRough and finish milling fitting surfacesPlanar grinder
5Rough & Finish MillingRough and finish milling both surfacesVertical milling machineEnd face
6Grinding Fitting SurfaceGrinding fitting surfacesMulti-station special machineLarge and small end face
7Drilling & ReamingDrilling and reaming small end hole, chamferingLarge and small end face
8Rough & Finish MillingRough and finish milling fitting surfacesLarge and small end face
9Drilling & ReamingDrilling and reaming positioning holesSmall end hole and end face
10Tapping & DrillingTapping and drilling screw holesPositioning holes
11Drilling & CounterboringDrilling and counterboring screw holesPositioning holes
12CleaningCleaning
13InspectionInspection according to drawings
14DemagnetizationDemagnetization

Connecting Rod Process Arrangement

The sequence includes rough milling, fine grinding end surfaces, drilling and reaming small end holes, rough and finish milling fitting surfaces, half round hole and joint boring large end holes, grinding fitting surfaces, drilling and reaming positioning holes, fitting assembly, grinding assembly end surfaces, semi-finish boring large end holes, fine boring large and small end holes, drilling small oil holes, chamfering, honing large end holes, pressing small end bushings, milling small end hole end surfaces, fine boring small end bushings, disassembling assembly and numbering, milling bearing positioning grooves, aligning assembly, demagnetization, cleaning, and inspection.

Connecting Rod Inspection

  • Positional Accuracy: Checking parallelism of large and small end hole axes.
  • Flaw Detection: Inspecting for internal quality using flaw detection methods.
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