The crankshaft oil passage holes serve as channels for lubricating oil, facilitating lubrication. The engine oil in the crankcase flows into these passages and reaches the connecting rod journals and main journal, thereby lubricating the areas where the bearing shells come into contact with the crankshaft.

Formation of burrs in crankshaft oil passage holes

The oil passage holes are composed of straight oil passage holes and inclined holes in the connecting rod journals. Burrs mainly form at the junctions where the two oil passage holes meet, as well as at the points where each oil passage hole meets the corresponding journal surface (at the inlet and outlet of the main journal surface, and at the inlet of the connecting rod journal surface).

Especially after the oil passage holes are drilled in the crankshaft, during heat treatment, some oxide scale forms and adheres to the inner wall of the holes. This accumulated oxide scale and burrs are difficult to remove, whether by blowing with an air gun or brushing, during the final cleaning of the crankshaft.

Burrs in the crankshaft oil passage holes directly affect the quality of the finished product, as well as its assembly and performance.

Burrs on the oil passage holes and the scale formed inside them during heat treatment will gradually fall off during crankshaft installation due to the action of oil pressure circulation and the harsh working conditions of the entire machine. This can affect the mating surfaces between the crankshaft journal and bearings, as well as the formation of the oil film between them. Eventually, this can lead to bearing damage and crankshaft seizure.

Main processes for deburring crankshaft oil passage holes

1. Manual labor:  

Manual grinding is done using electric tools and silicon carbide or wire brush pipes. This method is inefficient, resulting in inconsistent quality. It requires a lot of time for inspection and rework. Additionally, there are high costs associated with material consumption and labor expenses.

2. Electrochemistry:  

Burrs on parts are removed through electrolytic reactions. This process requires precise fixture design and has limitations regarding burr size. If the burrs exceed the specified limits (usually less than 0.1 mm), short circuits can occur, potentially damaging both the fixtures and the contact surfaces of the parts. This method is not environmentally friendly and falls under special equipment regulations.

3. High-pressure Water:

The purpose of deburring is achieved through the impact force of a high-pressure water jet. This method requires a sophisticated design of the fixture and is difficult to control during processing. It can easily damage areas that don’t need to be processed, resulting in inconsistent quality. It’s best suited for removing small burrs only. This process falls under special equipment regulations.

4. Abrasive Flow:  

This process uses a polymer-based adhesive material as the medium to grind the interior of parts through extrusion. It is suitable only for grinding small-batch parts with large, straight holes or grooves. However, when it comes to small or intersecting holes, it’s difficult to completely remove the abrasive residues after deburring. The efficiency is low, and the cost of using abrasives later in the process is very high.

5. Cross-hole deburring machine:  

Using water as the medium and adding approximately 20% abrasive, this process utilizes fluid dynamics to effectively grind the internal cross-holes in the parts. It requires minimal design considerations for the fixture, as long as a proper flow path is ensured. While removing burrs from the cross-sectional areas, it also polishes the inner surfaces of the parts, helping to remove oxide layers, rust, eliminate crack sources, and improve surface roughness. The process is efficient; pressure adjustment allows it to handle variations in burr size of the incoming materials (except in cases involving extrusion and flanging). Additionally, the cost of abrasive usage is low over time. Currently, this technique is most effective for removing burrs from crankshaft oil passage holes.

The comparison images of the crankshaft oil passage holes before and after deburring are as follows:

Currently, the rheological deburring process is widely used in deburring complex holes and grooves in various industries, including valve bodies, fuel circuit boards, fuel injection systems (injectors, high-pressure common rails), VVT rotors, and aircraft engines (bearing cages). In comparison, its application in deburring crankshaft oil passage holes is relatively much simpler.