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Crankshafts

CrankshaftsThe asymmetrical, long and relatively slender crankshaft is the heart of any combustion engine, from mopeds to heavy trucks. It is also one of the most challenging components to machine. The design in combination with high tolerance demands and the challenging machinability of the material – forged steel or cast nodular iron – call for truly optimized tools and methods to succeed.

Crankshafts come in many shapes and sizes – from small ones found in two stroke engines in garden equipment to giant ones found in diesel engines in ships. Even crankshafts in automotive engines vary each one unique to its engine type.

A common challenge is the design of the crankshaft, as the instability of the component affects both cycle times and quality consistency. Presented below is a selection of typical crankshaft features that call for extra attention.

 


Main and pin journals

Producing main and pin journals are high volume operations with high expectations on low costs per part. Both features require dedicated machine equipment to achieve reliable performance and high quality.

 

Roughing

An internal rough milling concept provides a stable, exchangeable segment system with high process security and excellent tool life, giving a low cost per part.

However, for large volumes of small to medium-sized automotive crankshafts, an external concept is both flexible and productive, as you can use high cutting speeds and still achieve good chip evacuation and low cutting forces.



Turn-turn broaching for semi-finishing and finishing

For semi-finishing and finishing of the main journals, post ends and flanges, use an engineered turn-turn-broaching tool with indexable inserts for the best result.

​Turn-turn broaching is a smart combination of turning and turn broaching that provides productive, cost effective and flexible machining with short cycle times, high flexibility and fast tool-setting. The turning and turn broaching cassettes are mounted radially on a disk turret that moves into the crankshaft and along the bearings as the crankshaft rotates. Use Sandvik Coromant inserts for disc tools of up to 48 cassettes.

Main journals

 

Pin journals 

 

Oil hole

Needless to say, chip evacuation and precision are the main challenges when drilling the oil holes.

As all oil holes in a crankshaft are interconnected, they need to be drilled to perfection to be able to deliver lubrication efficiently to the contact points. With the new CoroDrill 865, combined with the dedicated pilot drill and efficient clamping, you can produce precise deep holes (IT8-IT9 and depths up to 25 x drill diameter) with high productivity in cast iron and steel materials.

High speeds and feeds reduce the cost per hole. Additionally, fast and efficient chip evacuation reduces machine downtime and increases tool life. Clamp with high precision chucks only. We recommend CoroChuck 930 for a secure process.

Continue using the CoroChuck-concept in the subsequent chamfering operation, combined with an engineered chamfer drill.

Oil hole

Flange and post end

Producing the flange and post ends require a number of different operations, including turning, drilling and tapping. Process security and predictable tool life are common challenges. Use traditional turning or turn-turn broaching, depending on the process design.

The drilling operation can be performed either with step or back chamfer depending on the crankshaft shape and process design. The tapping operation is best machined with a standard tap. Use a high precision chuck for clamping to ensure the tolerances.

 
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