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Forged connecting rods

1.What are connecting rods?

Connecting rod is the key part of car engine parts, is also a typical and important complex closed die forging parts.Manufacturing fine degrees,inner and outer quality of connecting rods will directly affect the engine performance and level.Connecting rod causes high-frequency alternating stress inside in the high speed run up process of engine.It will have to bear shock pressure detonated by every stroke gas in cylinder and crankshaft torsional inertia force.When the hair motor's speed is 3000 ~ 5000 r/min, the loading frequency is very high.Because the connecting rod is working at high speed under the fatigue load,so,there is high requirement on the strength of the connecting rod.In addition,due to keep the crankshaft always operate at a high speed in an equilibrium state,so the weight of the connecting rod must also be controlled in a certain range.

Plastic forming and machining process of connecting rod are difficult,for the purpose of this forging production and machining process,which it is easy to appear the quality problem.The occurrence of these quality problems involve many factors. So for a long time,drop forging manufacturers are always continuously improving and discussing the material,forging process and mechanical processing manufacturing technology.Its purpose is to satisfy thetechnical performance and use requirements of products,and to be able to reduce costs,improve efficiency and increase economic benefits to the greatest extent at the same time.

2.Classifications of connecting rods

1)By material

Quenched and tempered steel connecting rod and non quenched and tempered steel connecting rod

Quenched and tempered steel connecting rod is to point that connecting rods finally meet the performance requirements by heat treatment of quenching and high temperature tempering after forging.Non quenched and tempered steel connecting rods refers that connecting rods meet the performance requirements through the control of cooling speed after forging.

2)By structure

Split type connecting rods and integral type connecting rods

Split type connecting rod is refers to the connecting rods that the body and cover is separated during forging.While Integral connecting rod is refers to the connecting rods that the body and cover is forged in a whole  and then seperated by subsequent processing.

3.Forged connecting rods

With the development of automobile industry,the increase of the engine power,the requirement about the quality of the connecting rod is becoming more and more high.Therefore,choosing the appropriate forging materials, the reasonable forging process,play a crucial role on the performance of the connecting rod.

Forged connecting rod process is:blanking-heating-roll forging-closed die forging-trimming punching-heat treatment-shot blasting-correction.

1)Blanking

Common ways of blanking are:cutting and sawing (sawing is preferred) is often used. Due to uneven and not round shear section,if you want to roll forging blank, the manipulator have the danger of falling off blanks,so sawing is better.

2)Heating

In order to improve the working environment,the quality of billet heating,and is advantageous for the mechanized automatic production,we usually use medium frequency induction heating.Fir consumption of induction heating is low,generally below 0.5%,and the oxide skin is shin,easy to remove.Due to production has certain rhythm,therefore,in order to reduce billet heating temperature of two heads,blank can not exceed chamber mouth before out of chamber,usually control by adjusting the stroke switch.Heating temperature will direct affect the outer and inside quality of forged connecting rods.Low temperature will be benifit on the strength and subsequent heat treatment  of connecting rods.But too low temperature will result in bad metal flow and fast mold wear.If mold withstand big hitting power,it will be easy casue cracking of forged connecting rod But if the heating temperature is too high,the plasticity of connecting rods will be too high,lead to defects like too fast metal flow,discontent,serious surface oxidation defects. Therefore, under the condition of guarantee forming,the lower the heating temperature,the better the forged connecting rods will be.

3)Roll forging

Roll forging quality will directly affect the quality of forged connecting rod,so when roll forging,we should pay attention to the following:

a.surface quality of roll forging dies:due to the long service life of roll forging die,but in use after a period of time,surface of roll forging die will be not so smooth due to metal flow, resulting in fold of roll forging billets.
b.entry point of each roll forging is not consistent,so circular arc of transition section is small.
c.surface of billet is uneven,exists scratches.
d.wearing of roll forging die makes uneven billet distribution,more in the middle and less in two sides.

Because of the existence of these problems,they can cause defects of connecting rod,such as folding,fold lines,unfull filling.To ensure the quality and reduce defects of roll forging,we should pay attention to the following:

a.when design roll forging die,each roll forging shape and size should be determined rationally.
b.reasonable distribute of each extension coefficient,and determine the appropriate type slot.
c.reasonable to determine the forward slip value.d.accurate calculation of the section size and slot size of roll billet.

4)Closed die forging

Main equipments of connecting rod mainly include hot die forging press,electro hydraulic forging hammer,active friction press and die forging hammer.

a.After pre forging,move forged connecting rods to final forging die,but the effect of removing oxide skin is obvious when flip mobile.
b.Flat press undeformation section of roll forged connecting rods,so that it will be easy to locate,and remove scale,at the same time of flattening and blowing scales.
c.Production rhythm is consistent with the greatest degree,it can ensure the forging temperature after trimming, is conducive to the follow-up working procedure quality control,in order to improve the quality of forged connecting rods.

5)Trimming punching

Trimming punching of forged connecting rod is usually processing in hot condition,making use of waste heat after forging,the trimming stress will be small.On the press by using trimming punching compound die,finish at a time.Trimming punching process often encounter the following problems: a.the uneven residual burrs:caused by the unmatch of punch die or too large gap,generally the punch die clearance take 0.5 ~ 0.8 mm.b.cutting deformation:cutting die can be made wavy,can prevent the deformation. In addition to the above reasons,unmatch of forging die and trimming die is also one of the reasons.c.in order to prevent the deformation of trimming,can use high precision double point trimming press or design guiding device on punching die.

6)Collection

Collection of forged connecting rod is simple, mainly to control of flatness and thickness of connecting rods.

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