Connecting rod

Connecting rods are subject to high dynamic loads in engine operation. High-strength steel materials like 70MnVS4 or C70 are used to meet these requirements. Their role: To convert the linear motion of the piston into a rotating motion of the crankshaft. To minimise the moving mass, connecting rods are consistently optimised for weight. The result is a wide range of variants – from parallel and trapezoidal to step shapes. This variety poses stringent requirements for manufacturing, particularly in machining the small end of the connecting rod. Different geometries result in varying spot drilling situations that must be resolved with precision and cost-effectiveness. Cost-effectiveness is a priority in series production. The high quantities require stable processes, short cycle times and maximum tool lives.
Tool for precision machining of connecting rods at the small and big end

Key features

  1. Small end 
  2. Big end
  3. Bolt locating Surface / 4. Bolt hole bore

  • Tool for pre-machining the small end of a connecting rod

    1. Pre-machining

    Various connecting rod forms require flexible tool solutions. A special solid drill combines drilling, boring and chamfering on both sides. The challenge: stable processes despite varying geometries.

  • Tool for semi-finishing the small end of a connecting rod

    2. Semi-finishing

    Radially adjustable ISO inserts compensate for shape deviations and prepare the bore for the sleeve. Dimensional accuracy and even material distribution are crucial for subsequent fitting.

  • Fine boring tool for finish machining of the small end of a connecting rod

    3. Finishing

    Fine boring tools with PCD guide pads create the best surface qualities and circularities under 10 μm.

1. Small end

PROCESS CONDITIONS
  • Spot drilling and boring due to different connecting rod shapes
  • Surface requirements of maximum Ra 0.8 μm
  • Diameter tolerances of 6 μm
  • Circularities of 5 – 10 μm
  • Partly specified bore shapes such as the bell-mouthed shape
WP solid carbide drill for connecting rod machining

The right solution for every requirement

1. Pre-machining
WP solid drill
 
  • Short, sturdy tool design enables drilling from solid, boring and chamfering on both sides with just one tool.

Two tools for machining the connecting rod: semi-finishing and finishing operations

2. Semi-finishing and finishing machining
Fine boring tool

  • Pre-machining stage for maximum tool life and for the stringent quality requirements of the fine boring stage.

or


HPR replaceable head reamer

  • Multi-blade, regrindable replaceable head for short processing times and long tool lives.

Two tools for finishing the connecting rod in cylindrical and trumpet-shaped form

The right solution for every contour

3. Finishing
Fine boring tool

  • Pre-machining stage and adjustable WP fine machining stage for the most stringent quality requirements and maximum tool life.
     

or


Actuating tool

  • Additional U axis for semi-finishing and finishing machining for big and small end. Maximum contour flexibility and simple wear contour.

2. Big end

PROCESS CONDITIONS
  • Wear-resistant carbide on the crack notch
  • Different stock removal situations
  • Highest quality requirements for bore geometry
  • Circularities of 5 – 8 μm
  • Diameter tolerances of 10 μm
  • Defined surface values of ~ Rz 6 μm to Rz 11 μm
Two tools for machining the big end of the connecting rod: roughing and finishing operations

1. Pre-machining
Roughing tool

  • Stable, multi-blade tool design for the combination of multiple process steps (roughing, boring, chamfering
     

2. Finishing
Fine boring tool

  • Boring and fine boring for defined stock removal, maximum tool life and the most stringent quality requirements.

3. Bolt locating surface / Bolt hole bore

PROCESS CONDITIONS
  • Positional accuracy of +/- 0.10 mm
  • Surface finish requirement Ra 3.2 μm
  • Concentricity 0.20 mm
  • Diameter tolerances 0.05 mm to 0.10 mm
  • Bore design with multiple step changes
  • Materials difficult to machine with additional hard-forged outer skin
Connecting rod bolt head seating surface / bolt hole

1. Grooving/milling
Solid carbide milling tool

  • Face geometry that cuts across the centre for milling and grooving contact surfaces.

2. Pre- and finishing machining
Solid carbide step drill

  • Multi-stage one-shot design with Optimum chip breaking at boring stages.