Detection and Elimination of Cracks on a Connecting Rod Forging Made of Aluminium Alloy 2014

The diploma thesis presented the process of resolving cracks on a connecting rod made of aluminium alloy 2014 and also defect detection using fluorescent penetrants. They described the problem encountered during the inspection of forgings with liquid fluorescent penetrant, i.e. defect detection, and its elimination. Subsequently, they described the process of resolving the problem in forging the connecting rod from aluminium alloy 2014, which led to the desired result, i.e. a ** forging without cracks** and thus to a reduction in the cost of forging production. Documentation from previous series was helpful in resolving the problem, such as temperature measurements, forging thickness, forces required for forming, and tool temperature during forging, which showed that we have a ** stable process** that did not change between series.

Problem

The diploma thesis presented the process of resolving cracks on a connecting rod made of aluminium alloy 2014 and also defect detection using fluorescent penetrants. They described the problem encountered during the inspection of forgings with liquid fluorescent penetrant, i.e. defect detection, and its elimination. In practice, the biggest problem proved to be graphite, which is used for lubricating the die cavity on the forging hammer, which remains in smaller cold laps and cracks.

Graphite repels the penetrant, which cannot enter the crack and thus does not show an indication on the forging during inspection. In practice, they eliminated the problem with prior visual inspection and removal of forgings before liquid penetration and re-pickling of forgings to remove graphite and other lubricants from cracks and cold laps.

Solution and Method

Subsequently, they described the process of resolving the problem in forging the connecting rod from aluminium alloy 2014, which led to the desired result, i.e. a forging without cracks and thus to a reduction in the cost of forging production. At the beginning of resolving the crack problem, they mistakenly thought that simply reducing the hardness of the input material would be sufficient, which proved during testing to be an inadequate solution, as they wanted to completely eliminate cracks and thus eliminate 100 per cent inspection of connecting rods with liquid ** fluorescent penetrant**, which means a significant saving of time in forging production and significantly reduces the amount of scrap.

Correction of the hammer tool proved to be effective. They achieved the expected goals and completely eliminated cracks on the connecting rods.

Results

Documentation from previous series was helpful in resolving the problem, such as temperature measurements, forging thickness, forces required for forming, and tool temperature during forging, which showed that we have a stable process that did not change between series. Before tool correction, they anticipated that they might have difficulties during forging with incomplete forgings due to easier material flow. During forging, the anticipation proved to be unfounded.

The tool correction itself proved, in combination with reducing the hardness of the input material, to be effective and sufficient for crack elimination. Before starting to resolve the problem, they wanted to investigate whether they could find a suitable solution in available literature and found that there is almost no suitable literature on the subject of aluminium forging or forging of alloy 2014 that could help them, so they had to rely on their own knowledge and past experience. Tool temperature fluctuation proved to be a major factor in forging defects, such as surface defects and incompleteness, which could not be achieved with ** flame preheating of the forging hammer**, so they introduced electric tool heating, but tool temperature fluctuation did not affect cracks on the forgings.

After forging several series, cracks on the connecting rod no longer appeared, so they began tool correction on other articles that they forge from alloy 2014 and had similar problems. In forging the connecting rod, tool correction and reduction of input material hardness for forging proved to be a good solution for tool durability. By reducing the forces for forming during forging, they certainly contributed to a longer service life of machines.

The greatest time saving in connecting rod production was obtained by eliminating 100 per cent inspection with penetrants, which they replaced with sampling 10% of forgings from individual series. Due to the reduced burden on heat treatment, which they burdened with an additional annealing operation to reduce the hardness of the input material, they agreed with the supplier to supply material in O condition, which has suitable hardness for forging. In forging aluminium alloys, there is certainly never a shortage of problems and new challenges that they will resolve in the future, in which previous experience and knowledge acquired over years of development will be of great help.

They also look forward to introducing robotisation for forging into their company, which will certainly enable greater competitiveness in the market and bring new challenges to their work.