Tool life enhacement in cold bolt forging process: effect of forging stage design

Abstract

In this paper, tool failure evolution in cold forging process of special M10x32 dog-point bolts was investigated with Simufact.forming finite element software. In the first part of the study, material flow in the five different forging stages were modeled and contact and tool stresses were determined. Simulations revealed that simultaneous forming of the flange, head and socket of the bolt with dog-point section causes excessive tensile stress evolution on the stationary die which leads to tool fracture. To prevent the failure, forming of dog-point section was shifted to further forging stage and preparation angle for dog-point was decreased to 40°. In addition, monolithic tool design was replaced with split insert design. Simulations carried out with these designs showed that tool stress was decreased about 70%. Finally, forging trials were also conducted with the updated tools and tool life was seen to increase about 3.8 times.

Keywords

• Cold forging,bolt,simulation,tool,failure

Cıvata soğuk dövme işleminde kalıp ömrünün arttırılması: dövme kademe tasarımının etkisi

Abstract

Bu çalışmada özel M10x32 dog-point cıvataların soğuk dövme işleminde meydana gelen kalıp hasarı Simufact.forming sonlu elemanlar simülasyon programı kullanılarak incelenmiş ve dövme kademe tasarımlarında değişimler yapılarak kalıplar üzerinde meydana gelen yüksek gerilme değerlerinin azaltılması amaçlanmıştır. Çalışmanın ilk kısmında cıvataya ait beş farklı dövme kademesinde meydana gelen malzeme akışı modellenerek belirlenmiş, kalıp kırılmasının yaşandığı dövme kademesinde oluşan kontak basınçları ile kalıp gerilmeleri tespit edilmiştir. Simülasyonlar cıvata kafa ve flanş kısmının dog-point’in oluşturulduğu dövme kademesinde aynı anda şekillendirilmesi nedeniyle sabit kalıp üzerinde yüksek çekme gerilmesinin oluştuğunu ve kalıbın bu nedenle hasara uğradığını tespit etmiştir. Bu durumu engellemek amacıyla dog-point kısmı bir sonraki dövme kademesine alınmış ve hazırlık açısı 40°’ye düşürülmüştür. Buna ek olarak tek parça olan dövme kalıbı tasarımı iki parçalı tasarım ile değiştirilmiştir.  Bu tasarımlar ile gerçekleştirilen simülasyonlar dövme kalıbındaki gerilmenin yaklaşık %70 oranında azaldığını göstermiştir. Son olarak yenilenen kalıplar ile yapılan üretim denemelerinde kalıp ömrünün 3.8 kat arttığı görülmüştür.

Keywords

• Soğuk dövme,cıvata,simülasyon,kalıp,hasar

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