Introduction: CR04 and Chain Bridge steels using both

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Last updated: May 16, 2019

Introduction: QMAC Silos manufacture largestorage bins mainly for the agricultural industry. A key component of the silois the cone end ring that is attached to the end of the base cone. The cone endrings are formed using Tata steel CR04 steel. QMAC silos are in the process ofchanging material supplier to a company called Chain Bridge who can supplyequivalent steels from other European mills. The main issue with this is thatthe alternative steel appears to fracture during the forming process where thebolt holes are located in the blank.

Preferably Qmac would still like to formthe part with the bolt holes in place. In this project we are to determine thecharacteristic differences between the two types of steel or indeed if there areany significant differences and analysis these. Aims and Objectives:The aim for this project is to:get an understanding of the materialcharacteristic’s for 2mm Tata CRO4 and Chain Bridge mild steel sheet materialunder different constraintsDetermine potential solution that Qmac could useto stop the deformation of the bolt holes during forming Objectives and deliverables: Gain information on the Qmac product and the end rings themselves through site visit/CAD drawings End ring formation process what is involved to form end ring? How are the holes achieved on the sheet metal? Information on ASTM standards for tensile testing, Specimen standard for tensile testing, shape and size of specimen Review of research for potential solutions and equations Gain knowledge in tensile testing and metal forming processes Tensile testing of Tata CR04 and Chain Bridge steels using both an-isotropic and isotropic orientations Analyse the strains produced when forming the 62-degree end ring Stress concentration calculations for area around the holes Knowledge of using Roark’s Formulas for stress and strain calculations Using Roark’s formulas determine the stress and strain on the metals and produce stress and strain relationship graphs to reflect findings Feedback information to Qmac with any recommended changes to the forming process that would reduce the changes of deformation from happening around the bolt holes on the end cones.

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  Literature review: This is the review of material thatis relevant to my project as separated into appropriate sub headings below:Material:For the end ring manufacture Qmacare using Cr04 / DC04 steel. This steel has the Europeanstandard EN 10130: 2006, It is specified as a Cold rolled low carbon steel flatproduct for cold forming. This steel has been designed especially to cope withthe stress and strains produced during cold forming processes.

(Tata Steel , 2017 ) Technical data sheets will besoured for the two different steels. Cold working: Cold working, is a metal formingprocess that is carried out at room temperature. In cold working, plasticdeformation of process causes strain hardening.

The force required to shape apart is much larger than if the part was being hot worked. At cold workingtemperatures, the ductility of a metal is limited, and only a certain amount ofshape can be created on the material before it starts to deform. This is acrucial point when looking at the ring end as because it has pre drilled holesadded more fracture areas that are more susceptible to a high stressdeformation area. The main problem with the cold working process is that themetal has a poor ductility and is prone to stress concentrating and tearingaround the forming area.

The advantage of cold forming is that the ring endwill be stronger and harder due to strain hardening that happens during theprocess. Cold forming causes directional grain orientation, which can becontrolled to produce desired directional strength properties for the finishedpart this directly relates to the part being analysed. (The library of manufacturing , 2017 ) Process for forming end ring:The process of making the end ringsis as follows, 2mmDC04 Sheet is punched into blanks with holes Theblank is rolled into a cylindrical shape Theends of the rolled cylinder are MIG welded to form one pieceThiscylindrical blank is then formed cold working into the conical shape using ahydraulic press with a die.  Factors affecting material after formingprocess:Spring Back:According to (Gate, 2015) Spring back isconsidered as one of the major problems in press forming which occurs duringthe unloading of the formed part from the forming tools.

For the accurateprediction of spring back, unloading behaviors of cold rolled steel DC04 forthe process should be investigated and a strategy for the reduction of springback based on variable blank holder force considered. This is related to Qmacend rings as there could be potential in the forming process for spring backand this has a potential to deform the material and could lead to stressconcentrations around where the holes are deforming. (Bauer, 2016) Suggests that in therolling process distribution of residual stresses in the blank and thedirection of the stress tensors allows for a definition of the blank in therolling process even before the pressing process. He suggests that thetemperature and friction of the rolling process can induce additional stresseson the material.

This could potentially increase stress concentrations in therolled blank tubes formed by Qmac before they press flange the formed pipeallowing for deformations to occur at a faster and more aggressive rate. Variability in process: There could be variability in theprocess due to wear on tooling which could cause induced stress areas on thesheet when in the forming process. Over time tooling will degrade and becomeout of specification this should be checked on a regular basis to ensure allforms are produced within spec to avoid any addition stresses and materialthinning and thickening which could cause potential failures.

 Differing hydraulic pressures couldbe used to form the component this could cause an excessive compression forceon the formed part and could cause it to give way (deform) around vulnerableareas such as the bolt holes on this part. (The library of manufacturing , 2017) Thickness variations of incoming material, thethickness of the DC04 sheets could vary from batch to batch and this couldcause an effect on the overall stress and stain when cold forming the ring end.There is also potential that thin areas could have increased stress concentrationand in some cases thin wall and sheer/deform due to this factor. Depending onthe thickness it could have a different effect on the forming process and couldcause molecular variations on the structure of the finished part.(Tekkaya, 2012) Poor punch tool quality       Effectof temperature during forming process:Properties of a metal change withan increase in temperature. Therefore, the metal will react differently to theoperation if it is performed under different temperatures and the end ring havediffering characteristics because of this process.

  Friction between the tooling and metal being formed:Metal forming processes are normally a form applied with highpressures between two contacting surfaces (top and bottom mould form). Acertain amount of friction will be necessary for the forming process, butexcessive friction is always avoided as best. Friction increases the amount offorce required to perform the forming operation, causes wear on tooling, andcan affect metal flow causing failure fatigue and creating defects in the formedpiece.

Lubricants can usually help to reduce the friction factor of theprocess. Lubrication is applied to contacting surfaces to reduce frictionforces. Lubricants used in forming processes are different depending on thetype of metal forming process, the temperature at which the operation occurs,and the type of metal that is being formed.  Formability and Factors affecting formability: What is formability? Formability is the ability of sheetmetal to undergo shape change without failure by necking or tearing.

It is themeasure of the value of deformation a material can withstand before thinning ora fracture occurs. This is a measure that is essential when manufacturing oranalysing materials as materials can vary in each batch produced so should bereviewed on a regular basis.(Industrial Metallurgists, 2017 )Factors affecting formability; Micro cracking:”An anticipated failure mode iscaptured where formability is limited by severe macro-cracking preceded bylocalization with void sheeting” (Soyarslan, 2011)This is where a micro crack appearsand can become large enough to create a void in the metal.

At this void therewill be the lightly hood of a failure as the key properties of the metal haveexceeded their elastic limit and will yield when forming operation isattempted. Chemical composition:Where the chemical form of the DCO4metal could differ to that of which is in its specification this could causeirregular deforming in areas where the composition is different and could causeareas of high stress in the forming process of the end ring. Many metal alloyshave specific compositions to achieve a desired strength, microstructure, orcorrosion resistance, Composition Analysis can be used to determine if the CRO4has any impurities or other unusual elements present that could causefailures.

  Chemical composition is testedby the following methods, Metallography and Energy Dispersive X-RaySpectrometry (EDS), Inductively Coupled Plasma (ICP), X-Ray PhotoelectronSpectroscopy (XPS) all these methods would involve sample material being sentaway for analysis. This has shown that many metals have had differing chemical compositionsthan what was on their specifications. (Polymer Solutions, 2017)

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