A Generative CAPP system for sheet hydroforming of CP Titanium

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 6, June 2013)

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A Generative CAPP system for sheet hydroforming of CP

Titanium

F. Forouhandeh

1

, S. Kumar

2

, S. N. Ojha

3

, T. Omkar Prakash

4

1_{Ph.D. Scholar, Department of Mechanical Engineering IIT BHU & lecturer, Department of Engineering, Shahrood Branch,}

Islamic Azad University, Shahrood, Iran

2_Professor,4_{M.Tech Student,}_{Department of Mechanical Engineering IIT BHU}

3

Professor, Department of Metallurgical Engineering IIT BHU Abstract—Sheet hydro forming (SHF) process is found to

be special for different kind of sheet metal component manufacturing. Commercially pure titanium grade 1(CP Ti) is paid much attention due to its lightness, high specific ratio of strength to weight and property of anti-rust. CP Ti shows low ductility at room temperature, and requires thermal activation to increase its ductility and formability. Studying the behavior of the process by finite element-computer aided engineering process has now become very popular and therefore symmetric and nonsymmetric shaped products have been taken to study the forming behavior of CP Ti metal under SHF using FEM solver DEFORM-3D. The finite element result is used to investigate the effective stress distribution, maximum forming load and thickness distribution under various process parameter conditions and at different temperatures. Furthermore the SHF process has been optimized in order to get the uniform thickness and defect free product. Based on several parametric studies and simulation result, a generative process planning system for sheet hydroforming has been proposed to help engineers. In the absence of CP Titanium grade 1 sheet, fabricated setup has been tested for Aluminum, Copper and low carbon steel sheets.

Keywords— Commercially Pure Titanium, Sheet hydro forming, Deform 3D, computer aided process planning

I. INTRODUCTION

Metal forming of light alloys has become very popular due to high strength to weight ratio product formation by forming processes. Automobile, Sanitary, aerospace etc are very common due to the capability of light alloys to be formed in variety of shapes by variety of forming operations. Hydro forming has become very popular forming process today to meet the challenges of these industries. Tube forming [THF] and sheet hydro-forming [SHF] are relatively complex manufacturing process.

The process is better than the conventional

manufacturing via stamping and welding such as: (i) Part consolidation resulting in weight reduction of the component, (ii) weight reduction through more efficient section design and tailoring of the wall thickness, (iii) reduced tooling cost, (iv) improved structural strength and stiffness, (v) less number of secondary operations, (vi) reduced dimensional variation, (vii) significant reduction in spring back effects and (viii) reduced scrap rate. The analysis and performance of the process depends on many factors such as part geometry and design, material and process parameters and the boundary condition of forming. The best and easy way to study the behavior of the process for these alloys is by Finite Element method and Computer Aided Engineering based procedure. The technology of product manufacturing by THF and SHF is developing very fast to shape complex profiles of products. Nowadays, commercially pure Titanium (CP Ti) is being paid much attention due to its properties of lightness, high specific ratio of strength to weight, strength against high temperature, anti-rust and good adaptability for a living body. Sheet hydro forming of CP Ti sheets is especially important for the production of thin-walled structural components used in the electronics and aerospace products, such as the cover cases of notebook and camera, mobile phone. But low ductility, high spring back and sensitivity against atmosphere elements especially Oxygen above recrystalization temperature of Titanium makes some limitations for any kind of metal forming.

The working principle for sheet hydroforming is shown in figure1 as an example. After blank setting and blank holding, when the punch pushes the sheet metal into the die cavity, within which oil or other liquids are contained, high pressure that can press the sheet metal tightly onto the punch will be generated. Then, the effect of friction retention is affected.

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At the same time the liquid in the die cavity will flow out between the upper surface of the die and the sheet

metal. Therefore, fluid lubrication that will reduce

frictional force is produced.

Main limitations during sheet hydro forming are wrinkling due to low blank holding force and tearing due to high blank holding force or high forming load or speed that

it has been shown in figure 2. There are some

investigations about Sheet hydroforming like Zhang.

et.al.[1]investigated a brief review of recent developments

in the area of hydro forming and their relevant history with process variations for forming tubular and flat components. Applications of shell type products have also been reported in most of German aircraft.

Hein.et.al.[2] carried out an investigation about hydro

forming of sheet metal pairs and numerical and experimental study wherein Hydro forming of sheet metal pairs (a new class of HF) has also been investigated concerning different models, simulations and experiments on unwelded sheet metal pairs. It is found that numerical simulations and experimental study influence various parameters on the process feasibility and the result of experiments confirmed the FEM simulations results.

Novontny. et.al.[3] carried out an investigation about

SHF of Al-alloys (AA6016-T4) and illustrated the advantages of SHF over other alloys. It is formed that SHF of Aluminum alloy has good mechanical properties.

Zhang. et.al.[4] proposed a movable die for SHF process and carried out numerical and experimental study to improved the forming characteristics of alloys. The limit drawing ratio of the sheet was improved. This process is especially suitable for forming of small batch production of sheet metal parts with complicated shapes.

Zampaloni. et.al.[5] carried out numerical and

experimental investigations in stamp hydro forming by using pressurized viscous fluid.(for aluminum(3003-H14-Aluminum) alloy). Wherein, one or both surfaces of the sheet metal are supported with a pressurized viscous fluid to assist with stamping of the part thus (no need to female die). The pressurized fluid has several purposes: a) Supports the sheet metal from the start to the end of the forming process ,thus : better deformation. b) Delays the onset of material failure. c) Reduces wrinkle formation. Experiments, shows draw depths improvements up to 31% before the material failed.

Zhang. et.al.[6] has carried out a new SHF technology

using a movable die comparing between THF and SHF and used a movable female die in SHF. Where in SHF technology are summarized w.r.t increase in the feeding of materials and local deformation capacity for SHF.

Development of SHF technology is still much slower than THF technology.

Lang. et.al.[7] investigated resent development of SHF

for lightweight components and expressed the requirements

of press control equipments.

Ahmetoglu. et.al.[8] carried out numerical and

experimental research about application of viscous pressure forming(VPF)for non-symmetric steel, aluminum and nickel parts. FEM simulation and blank holding force control was used for optimization the process conditions. It has been discussed effect of process variables upon the achievable part geometry. Comparison between FEM results and experiments illustrated simulation was used to predict material flow with high accuracy.

Merklein. et.al.[9] carried out numerical and

experimental study for joining tube and double sheet in hydro forming. Both of tube and sheets were formed simultaneously jointed. The finite element analysis and laboratory trials were used to design the die cavity so as to avoid the wrinkling of material tearing and the collapsibility of the tube section during forming. The analytical model of the author predicts the experiment conditions well.

Abedrabbo. et.al.[10] carried out an important

investigation about wrinkling behavior of Aluminum alloys during SHF. In this research FEM and experimental study have been implemented for 6111-T4 aluminum alloy. It shows that, the use of pressurized fluid delays the onset of material rupture and acts as a blank holding force to control wrinkling in the flange area. An optimum fluid pressure profile generated by FEM was applied in SHF to make the deep-drawn hemispherical cup without tearing and with minimal wrinkling in the flange area. The FEM model predicts the location of the material rupture in pure stretch and wrinkling characteristics of the Aluminum alloy sheet.

Lang. et.al.[11]carried out numerical and experimental

study of hydromechanical deep drawing (HDD) by using

very thin middle layer in multi-sheet hydro forming. The main advantage of SHF has been to be uniform pressure transferred to everywhere. Some features on the formed forced internal, external and middle layers including high drawing ratio, wall thickness distributions, free wrinkling and fracture were also discussed.

Hama. et.al.[12]carried out numerical and experimental

study on elliptical deep drawing using an elastoplastic FEM (code STAMP3D) program. Where in simulated result could predict experimental result about the thickness strain distribution. The comparison between conventional process and SHF process (numerically and experimentally shows that SHF gives better formability.

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Murr. et.al.[13] carried out investigation about

metallurgical and microstructural characterization of a hydro formed steel part. Microstructural characterization by light optical metallography (LOM) and transmission electron microscopy (TEM), (including grain structures) was carried out.

Hojjati. et.al.[14] simulated super plastic forming in hydro forming process. The investigation of Aluminum alloy 5083 in hydro forming process was simulated at three different constant pressures, and effect of pressure on thickness distribution and final dome height were evaluated. Paper shows the work on Titanium alloys (Ti-6Al-4V,Ti-6Al-2Sn-4Zn-2Mo) and Aluminum alloys (5083,7475)are typical examples of metallic super plastic materials. It is observed that Low flow stress and high sensitivity of flow stress to strain rate are the main feature of super plastic deformation.

In the recent competitive product development paradigm, product cost, time-to-market and product quality are three overriding issues. In the up-front design process, the first 20% of design activities commits to about 80% of product development cost and product quality issues. How to conduct "right the first time" design is critical to ensure low development cost, high product quality and short time-to-market. To address these issues, state-of-the-art technologies are needed through CAE technology to help practitioners to generate, verify, validate and optimize the design solutions before they are practically implemented and physically realized.

CAE simulation technology is to use numerical techniques to quantitatively represent the working behavior of a physical system and imitates the dynamic and physical behaviors of the system in working processes and conditions. In metal forming processes, the plastic flow of metal and die deformation constitute a physical system which can be simulated by the Numerical approaches through the modeling of plastic flow of metal and the elastic or elastic-plastic deformation of die. The numerical results arising from the simulation are correspondingly related to the physical content of the metal forming system to be simulated. Currently, most CAE simulations employ commercial CAE packages, in which the finite element technique is the kernel technology.

Use of FEA for SHF process simulations is now a standard development tool after investigations and validations conducted by many researchers since early 1990s. Application of commercial FEA packages, such as

LS-DYNA, PAM-STAMP, ABAQUS, MARC,

AUTOFORM, DEFORM, etc. have been used successfully for stamping and forging processes into SHF.

Finite element analysis in conjunction with experimental validation has been used for better understanding of the process. It should be noted, however, that it is quite expensive to experimentally validate a process where the geometry is complex in nature, and thus finite element simulation alone can provide a valuable insight and understanding of the process and help in new prototype or product design and development. In this paper cup shape and non-symmetric products under sheet hydroforming processes have been simulated using FE solver using updated Lagrangian formulation.

There have been traditionally three recognized approaches to Computer Aided Process Planning in literatures as variant, semi-generative and generative approaches. With rapid development of new techniques, a combination of two or more of these approaches is used as a hybrid approach.

Sarang and Kumar[15,16] have reported several attempts (Table 1) to develop automated process planning system for manufacturing process such as machining, grinding, unconventional machining, sheet metal working, forging, wire drawing, deep drawing,

injection molding and extrusion etc. This work based on generative, variant or hybrid approaches, aims to develop knowledge based system, an expert system, etc. using either group technology, and feature based rules, decision trees, CSG trees, decision support system or combinations to develop a CAPP system.

Kumar and Sreenivasulu[16] proposed a generative CAPP system for Tube hydroforming. A methodology for symmetric design has been developed.

The above literature indicates that the scope of hydro formed components is very high for the coming future and there is a need for CAE based CAPP system for quick disposal of SHF industrial problems. It is because of this reason a systematic CAPP system for hydro forming products is being proposed in the paper.

In this paper, a methodology for systematic and non-symmetric designs of metal forming systems via CAE simulation has been developed. The FEM package DEFORM-3D is used to simulate of sheet hydro forming process of semispherical cup shape and also non-symmetric products of pure titanium metal sheet at elevated temperatures. The finite element results are used to investigate the effective stress and thickness distribution and maximum forming load under various process parameter conditions, including the blank holding force and drawing at different temperatures. Finally a generative computer aided process planning (CAPP) system for sheet hydroforming process has been proposed.

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II. SIMULATION PROCEDURE

To start simulation it is necessary to represent the metal forming system with detailed geometry comprising of work piece, die, punch etc. Then it should be converted into suitable formats like .stl, dat, .key etc. so that it can be imported into simulation solver. Blank holder can be created as a solid model or as a applied pressure in particular area. Fluid will be applied in upper (lower) or both surfaces of sheet.CAE engineers need to create the simulation-related models for the given deformation system like physical model, mathematical model and numerical model. The physical model idealizes the real engineering problems and abstracts them to comply with certain physical theory with assumptions. For example, material of the sheet is assumed Elasto-Plastic. The mathematical model specifies the mathematical equations such as the differential equations needed to be solved by FEM analysis. It also details the boundary and initial conditions as well as the process and geometry constraints. The numerical model describes the element types, mesh density and solution parameters. Usually, some of the solvers have the in built capacity to represent such models but most of the time the user has to create and import the information related to this. In FE based CAE simulation process, there are four

steps, viz., pre-processing, simulation, post-processing, and

results analysis and evaluation. After the simulation is over, the calculated results need to be analyzed and evaluated. If the simulation results and solutions are not satisfactory, the suggested changes and modification can be made for next iteration of the simulation.

III. SOLID MODELLING

To conduct a SHF simulation using computer, first it needs to create the computer models of the deformation system and the metal forming process. Blank holding has been applied as a selected area between two concentric circles outside the die cavity and inside the sheet for axisymmetric and non-symmetric cases. The solid models of die for cup shape and sheet (blank) for both cases are built as shown in figure 3 and 4. The area inside the black circle in figure 4 is under fluid pressure and outside area is under blank holding pressure. Applied fluid pressure and blank holding pressure are up to 5Mpa and 2MPa (linear type function) respectively.

IV. PROCESS PARAMETERS AND MATERIAL DATA USED IN

PREPROCESSING OF SIMULATION

Tooling setup

--- Blank diameter (mm) 100 Die corner radius (mm) 1.2 for axisymmetric, 3 for non-symmetric

Initial temperature (◦C) 25, 100, 150 Blank material Commercial Pure / Unalloyed Titanium grade 1

Thickness (mm) 0.4

Mechanical properties[17]

…..……… Youngs modulus E (GPa) 105 Ultimate Strength (MPa) 241

Yield Strength (MPa ) 172 Poisson’s ratio, (ν) 0.3

Flow stress curve Obtained from (Fig. 6)

Friction coefficient, μ 0.08 Thermal properties[17]

……… Thermal conductivity (sheet) (N/s C) 20.8 Heat capacity (sheet) (N/mm2 C) 0.52 Emissivity 0.3 Melting point (◦C) 1671

Figure 5 shows isometric and details geometry of die for non-symmetric product. The work piece (figure4) has been meshed with 24646 nodes and 240608 tetrahedral mesh elements (for both cases) in the sheet hydroforming simulation. Sparse FE solver and Newton-Raphson iteration method has been used to the elastic-plastic material as a work piece. Deformation and thermal boundary condition has been added in the simulation.

V. RESULT AND DISCUSSIONS

Several cases have been simulated for different parameters for both axisymmetric and non-symmetric products. The main aim is getting proper deformation without any defects like wrinkling, tearing and incomplete deformation. Fluid pressure has been applied from 4 to 6 MPa and blank holding pressure from 2 to 4 Mpa (linear type function). Temperature has been changed from room

temperature to 150oC. Die fillet has been changed from 1 to

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The process has been optimized to meet defect free deformation and minimized thinning and also to some extent uniform thickness distribution. Following figure indicates optimized die filling process. In presented sheet hydro forming process, there is pressurized fluid from upside which presses the material into the die cavity.

Figure 7 shows step 5th and 100th (end step) of filling of die

cavity due to pressurized fluid for axisymmetric cup shape product. Figure 8 shows 25th and 430th (end) steps of die filling of non-symmetric. All figures are for optimized condition with 5MPa fluid pressure, 2MPa (linear type

function) blank holding pressure and 100 oC temperature. It

is clear that number of steps for non-symmetric part more than axisymmetric one due to time needs for filling of bottom corners.

Figure 9 and 10 show area under fluid pressure and blank holding force for both cases, respectively.

V-1. Effective stress and strain

Figure 11 shows effective stress distribution during SHF process of axisymmetric cup shape. Maximum value is 1120 MPa near the center because of maximum deformation, while in non-symmetric one maximum value, 300MPa occurs in bottom corners because of maximum curvature and also bottom floor due to max deformation. Figure 12 shows effective strain in both cases.

V-2. Thickness distribution

Ten points have been evaluated under slicing of final shape for measuring the thickness of axisymmetric shape (figure 13). There is no oxidizing and brittleness in sheet because process has been done under recrystalization temperature. Fifteen points have been selected coincident to maximum length of non-symmetric shape from centroid (figure14). Effect of contact friction coefficient on thickness distribution of final axisymmetric shape and non-symmetric one have been shown in Figures 15 and 16 respectively. It is clear that minimum thinning has taken place when the friction coefficient value is 0.08 (for both cases). Thickness distribution curve is not so smooth in non-symmetric shape (even in 0.08) due to inhomogeneous distribution of material while there is no fracture, wrinkling or tearing even in corners.

Figure 17 shows optimum load cycle at the end of SHF process for both cases. Maximum required load for deformation of axisymmetric shape will be around 47 KN and for non-symmetric one will be around 206 KN. Figure 18 shows effective stress distribution of die at the end of SHF process for both cases. Maximum values of effective stress of die for axisymmetric and non-symmetric cases are 68.9 MPa and 111 MPa respectively.

Die steel AISI-H13 has been selected as a die material

due to it can tolerate up to 700 ◦C temperature. Perimeter of

sheet/blank is a circle with 25 mm radius and after deformation is like a circle with around 96 mm diameter (almost for both cases).

V-3. Damage distribution

Figure 19 shows damage distribution for both cases. It is clear that maximum damage in symmetric shape has taken place in near the center due to maximum deformation and for non-symmetric one in bottom corners. Maximum values for symmetric shape and non-symmetric one are1.31 and 1.22 respectively. The regions are considered to be most sensitive for tearing and wrinkles. To decrease this damage a proper loading path and suitable thickness selection is necessary.

VI. COMPUTER AIDED PROCESS PLANNING

Factors affecting the process planning are shape, size, tolerance, surface finish, component type and material, quantity to manufacture, etc. These factors are considered while selection of dies, design and manufacturing parameters for the process. To reduce the human efforts computer assistance is necessary.

It consists of following stages-

VI-1. Design and development of the CAPP system for SHF

CAPP system is designed for SHF to generate most economical process plan for components of simple or complex nature using sheet hydro forming dies. This task is accomplished by dividing CAPP activities in to two major phases. One is to design CAPP modules, and other is the implementing phases. In the first phase, different modules and mathematical/simulation procedures of the proposed CAPP are discussed, whereas implementation is aimed to transform the theory into practice by the use of available information. Fig. 20 shows the schematic flowchart for the proposed CAPP system.

VI-2. Design and Design of modules

System flow chart for the proposed CAPP system is shown in Figure 20. It comprises of the following major modules incorporating different sub modules as (1) Modeling, (2) Process and (3) parameter design module.

VI-2-1. Design and Modeling of die

The 3D drawing for various shapes as proposed by designer for symmetrical or unsymmetrical hydroforming die is drawn accurately using AutoCAD. The *.stl file is created corresponding to each component layout.

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Drawing details from a given component layout for products to be hydroformed in the form of geometrical data imported as a input.

VI-2-2. Process and parameter Design:

Different inputs to the die design module are SHF process parameters, specification of the sheet, friction conditions, and information on the type of hydroforming

shape. The hydroforming process selection is based on

commonly used sheet hydroforming processes such as sheet hydro-forming and tube hydro forming. It depends on the product and application required.

The proposed CAPP system is developed for SHF under cold and warm conditions. Specification of the sheet/blank involves input of sheet material such as the material properties and the geometry.

Relevant mechanical and metallurgical properties such

as yield strength (σy), ultimate strength (σu), poissions ratio

(µ), heat transfer coefficient, temperature etc. are required for the evaluation of the process parameter. These properties are organized and stored in the form of database such that it can be suitably updated and edit as per requirement. Selection of a particular material is automatically fetches and all the data about the material necessary for various computations are edited. Also it is possible to define a new material by importing the all material properties. In this paper material properties of Commercially Pure Titanium grade 1 has been studied and imported.

In some applications of Titanium alloy, sheet should have pre-heated for better formability before the hydroforming operation. The specification of die involves various types of dies of different material for SHF. The selection of a particular die profile and the arrangement along with the material depends on the sheet material, size of sheet, and final properties desired of the required products.

VI-2-3. Process Parameter Evaluations:

Corresponding to the above inputs, evaluation of process parameters are carried out. Some of them are calculated directly using the relationship given below or by using an optimization technique. Other process parameters such as average hydro forming pressure, tonnage, cost, etc. are derived using the corresponding primary process parameters such as optimum hydro forming power, etc.

VI-2-4. The Corner radius of the die:

In conventional sheet metal forming, die corner radius

should be between around 3-8 times of sheet thickness 19.

These values in SHF process are around 3 and 7.5 times of sheet thickness for axisymmetric shape and non-symmetric one, respectively.

VI-2-5. Comparison of total force between SHF and conventional cup drawing:

Total stress and forming load (punch force) for SHF cup drawing can be calculated using equation no. 1 and 2 respectively:

(1) P=2π t (2)

Where : Stress in cup wall, P: Punch force, : Angle

between the punch axis and the cup wall, Thickness of

cup wall, The mean radius of the cup at the section

where is determined, : The radius on flange where

bending takes place, : Current outer radius of flange,

Hydrostatic or fluid pressure, Yielding stress,

Factor which has value between 1 and , Die radius.

Also stress in conventional cup drawing can be calculated using equation no.3:

(3)

Where µ: Friction coefficient, : Blank holding force

Forming load (punch force) in conventional cup drawing can be calculated using equation (2). Blank holding force, Area of contact between die and sheet and blank holding pressure can be calculated using equations (4),(5) and (6) respectively[20].

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(5)

=k . (6)

Where : Area of contact between die and sheet, D:

Blank diameter, d : Punch diameter, : Ultimate tensile

strength of sheet material, For non ferrous metals: K=0.005 for t<1mm , k=0.006 for t>1mm

It is illustrated that difference between total force of SHF cup drawing and conventional cup drawing is in second term in equations (1) and (3) due to effect of fluid pressure.

In SHF process effect of fluid pressure can compensate effect of friction in second term of equation (3).

VII. SYSTEM IMPLEMENTATION

The implementation phase deals with the

transformation of analytical design results of concept proposed in previous sections into practice. In case of CAPP, this information is stored in the form of database. The input to process planning is the part design data. Generally, the format of input to the CAPP systems can be either a text inputs or graph input. Text input is the input entered through the key board and graphical input is referred to as inter face input, where the geometrical details of the blank/sheet model are entered from a given drawing details using CAD system such as AutoCAD.

In the present system, both text and graphical types of input have been adapted.

VII-1. Design Selection of sheet/blank material

The following sheet materials are included in the database: Aluminum alloys, copper alloys, steels, zinc alloys, manganese alloys, magnesium alloys, lead alloys and specially Titanium alloys. Some of material properties are given in Table 2. The Table 2 is editable and it can be extended for other materials also.

VII-2. Selection of die parameters

The important die parameters are (i) Type of hydro forming die, (ii) Die material and its life, (iii) Die corner radius and (iv) Die accessories.

VII-3. Die material

The present CAPP system includes the following die material in order of increasing resistance and hardness. 1. Mild steel, 2.High carbon steel, 3.Steel-1045, 4. Hardened die steel, 5.H10, 6.H13, etc.

The selection of die material is based on the shop floor hydro forming practices and depends on the applications (such as mass, batch or job production), normal die pressure and size of the hydro-formed shape. On the basis of these, the proposed system is automatically capable of selecting a die material. For high pressure forming like forging of Titanium alloys, H13 is an appropriate selection as die material due to its high strength while this selection can be even CK45 for SHF process of Ti due to low pressure on die.

VII-4. Selection of lubricant

Lubrication and friction conditions are very important in hydroforming process. Lubricant is used to reduce the sliding friction, prevent sticking to reduce the tool wear. Material is locally stretched to form the final shape. Various types of lubricants are available for hydro forming. They are dry lubricants (solid lubricants), wet lubricants, (solutions and emulsions as well as synthetics) soaps and waxes etc.

Mostly graphite or MoS2 based, polymer based, waxes,

oils and emulsions are used as lubricants. Boron nitride aerosol is one suggestion for Titanium sheet metal forming. Lubricants are easily available and it is well applicable and removable during the operation. A lubricant is selected on the basis of the sheet material Table 3.

VIII. ILLUSTRATION AND PROCESS PLANS

The capability of the present CAPP system is demonstrated for the axisymmetric and non-symmetric shapes in sheet hydroforming simulation with proper boundary conditions and loading paths. Various simulation results can also be used for different parametric studies using the postprocessor of the simulation solver.

Based on the above examples, generative process plans are generated using the proposed CAPP system for the

SHF. Two cases of Axisymmetric and Non-symmetric

shape in sheet hydro forming examples have been taken to demonstrate various results using the proposed CAPP. The CAPP results for the Axisymmetric and Non-symmetric shape in SHF are given as shown in Table 4 and Table 5

respectively. However the most important problem of any

kind of deformation of Titanium alloys is influence of atmosphere elements such as Hydrogen, Nitrogen and specially Oxygen above its recrystalization temperature, and creation the brittle structure, the simulated SHF process of CP Ti is defect free even in microstructure, because process has been done under recrystalization temperature therefore there is no oxidizing in this temperature.

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Also Titanium deformation is very sensitive to strain rate therefore low speed deformation is suggested and speed controller in hydraulic press is very necessary as one of the press accommodations. Above explanation especially in stress and thickness distribution illustrates 100 0C is the best condition as working temperature.

In the absence of CP Titanium grade 1 sheet, previously fabricated setup has been tested for Aluminum, Copper and Brass sheets. Advantage of sheet hydroforming process in comparison to conventional deep drawing has been illustrated using microstructure analysis[26].

Recently, F. Forouhandeh, S. Kumar, S. N. Ojha

(authors) have designed and fabricated a sheet

hydroforming setup as shown in figure 21. A low carbon steel sheet with 0.4mm thickness and 80mm blank diameter has been formed in the setup as shown in figure 22. Total forming load has been measured in experimentation and it is similar to result out of simulation that already has been done[27]. Total forming load 3.46 ton, displacement: 25 mm, blank holding force: 200 MPa, Backward pressure: 600MPa. Result out of simulation has good agreement with the experimentation. Authors will publish details of experimentations in the next report.

Fig1. Schematic of the sheet hydroforming process: (a) blank setting; (b) blank holding; (c) drawing and (d) finishing[9]

Fig2. Limitation in sheet hydroforming[10]

Fig3. Solid modeling of Die for cup shape product (axisymmetric)

Fig4. Blank (0.4mm thickness, 50mm radius) for axisymmetric and non-symmetric

Fig.5 Isometric (a), details (b), geometry of die for non-symmetric product (all dimensions in mm)

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strain rate[18]

Fig. 7 Die filling steps during process for axisymmetric cup shape

Fig.8 Die filling steps during process for non-symmetric shape

Fig9. Area under fluid pressure (green circle) Fig10. Area under blank holding pressure (green area) for both cases

a

b

Fig.11 Effective stress distribution for axisymmetric (a) and non-symmetric (b) shapes

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653 Fig.12 Effective strain distribution for axisymmetric (a) and

non-symmetric (b) shapes

Fig.13 Final Drawn shape (Sliced at the centre)

Fig.14 Final Drawn shape (Sliced along maximum length from centroid)

Fig.15 Effect of contact friction coefficient on thickness variation in final axisymmetric shape

Fig.16 Effect of contact friction coefficient on thickness variation in final non-symmetric shape

Fig.17 Optimum load cycle (a) for axisymmetric shape and (b) for non-symmetric shape

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654 Fig18. Die stress analysis, effective stress of at the end of deformation

(a) for axisymmetric shape and (b) for non-symmetric shape

Fig.19 Damage distribution (a) for axisymmetric shape and (b) for non-symmetric shape

Fig.20 System flow chart for proposed CAPP system of SHF

Fig. 21 Schematic diagram of the sheet hydroforming setup fabricated at IIT (BHU)

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Major CAPP application in manufacturing

Source [15, 16]

ABBREVIATIONS USED

AI: Artificial intelligence based, CAES: computer aided engineering system; CSGtree;

Constructive solid geometry tree, DBO: Design optimization method, DR: Design rules, DTree: Decision tree, RB: Rules based, DXF: Auto CAD DXF file based, FBMS: Feature based management system, GA; Genetic Algorithm based, GT; group technology, IGES: Initial Graphics exchange specification, KBES: Knowledge based expert system, STL: stereo lithography file based ,OOIS: Object oriented intelligent system, PPI: predefined parametric input, RBES: Rule based expert system.

S.No. Application System Developer year Part

Description system Decision logic remark 1 2 3 4 5 6 7 8 9 10 11 12 Machining Sheet metal Unconventional Machining Grinding Forging Wire- Drawing Rolling Deep drawing Injection Molding Extrusion Rapid Prototyping Tube Hydroforming APPAS GARI EXCAP - - - - - - - - FIRMEX - - AGMPO - - - GIFTEP - Wysk Dcscottc & atombc

Zhang et al. Reggenbrass & Reissener Tilley Smith Marcfat ct al. Gu & Zhang Tisza De Gursaran Jain et al. Rao Burman Bariani & Knight

Sevenler et al. Brucker et. al.

Reddy Rey Sassni & Sepehri

Kumar Eshel et al. Sitaraman, ct, al.

Rao

Lowe & Walshe Das Santosh et al. Pande & Kumar

Kumar & Sreenivasulu 1977 1981 1989 1991 1992 1990 1993 1994 1995 1997 1989 1995 1990 1996 1988 1987 1988 1988 1981 1989 1998 1986 1991 1998 1985 1995 2003 2008 2012 GT FBMS RBES GT, RB FBMS FBMS OOIS OOFB KBES FBMS, RB RBES FBES RB FBES KBES FBES ES ES KBES DBO RBES RBES RB, IGES ES RB DXF, RB DXF, RB STL,RB STL,RB DTree AI DTree AI AI AI DTree, AI CSGTree KBS LRES, GA KBS, RS RB AI GA, RB RB, KBS KBS KBS, AI RB KBS, RB RB GA, RB KBS KBS RB - RB RB,AI RB,AI Generative RB,FI,PRIS Generative Generative Generative Semi- Generative Variant Generative Variant Generative Generative Generative Generative Generative Generative Generative Variant Generative Generative Generative Semi- Generative Generative Hybrid (CAES) Generative Variant Generative Generative Generative Generative

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656 Table 2

Material properties of hydro formable material

Material Density X1000 (Kg/m3) E (Gpa) Yield strength (Mpa) % of Elongatio n Passion ratio Tensile strength (Mpa) Thermal conductivity (W/m-k) Hardness (HB) Al alloys Al 1050 Al 2014 Al2024 AA6262 2.6 -2.8 2.8 2.77 2.72 70-80 70-80 70-80 70-80 105 97 76 241 10 20 20 10 0.33 0.33 0.33 0.33 110 185 185 290 231 192 190 170 35 45 55 120 Copper alloys Copper Soft UNS C10200 Brass 8.9 8.8-8.94 8.44 117 117 117 115 69-365 69-497 40 55 20 0.31 0.31 0.34 172-220 221-445 495 391 - - 40-45 - - Steels AISI 1006 AISI 1008 AISI 304 AISI309 7.872 7.871 7.99 8.0 210 190-210 193 -200 200 285 285 215 310 20 20 70 45 0.27-0.33 0.27-0.33 0.33 0.3 330 340 505 620 60 59.5 16.2 15..6 95 95 123 85 Zink alloy Zink alloy Soft 7.1 70 - 65 - 126 112.2 30 Magnesium alloys 1.77 44.8 80-280 5-15 0.35 150-379 - - Titanium alloys CP Ti grade1 Ti-6Al-4V 4.51 4.43 105 113.8 172 827 24 10 0.3 0.34 240 950 16 8.6 120 334 Source [16, 17, 18, 21, 22]

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657 Table 3

Lubricants used in sheet hydro forming

S. No Sheet material Recommended lubricants for sheet hydro forming 1 2 3 4 5 6 7 8 9 Aluminum Copper Magnesium Carbon steel Mild steel Stainless steel Brass Inconel 718 (Nickel alloys) Titanium D, G, MoS2, S S, Wa, MoS2, G D CC+S Cl, P or Wa CC+S, MO, Copper plating MO+F+S+CL GO BNA (CC-18)

Source[21, 23, 24]; Codes used: CC-Conversion coating; D-Dry, Cl-Chlorine additives; F-Fat; G-Graphite; MO-Mineral Oil; MoS2 – Molybdenum Disulphide; P- Polymer; S-Soap; Wa-wax; GO-Gear Oil; B N A-Boron Nitride Aerosol. Friction coefficient is 0.08 and type of friction is coulomb due to all suggestion of Elasto-Plastic material type especially for Titanium alloys [22, 25].

Table 4

Process plan output for Sheet Hydroforming Process – Axisymmetric shape

RT: Room Temperature, minus sign in pressure path is because of fluid pressure from up side to down side.

Process plan output for Sheet Hydro forming Process

Nature of component : Axisymmetric (cup) shape Dome height (mm) : 25

Cup diameter (mm) : 50 Sheet/blank thickness(mm) : 0.4

Sheet Material : C P Titanium grade1 Die corner radius(mm) : 1.2

Maximum Fluid Pressure applied (MPa) : 5, (pressure path: P=(-5/6)t(time) Maximum Blank holding pressure applied (MPa) : 2, (pressure path: P=(-1/3)t(time) Working temperature ( 0C) : 100 (Best condition) Material type : Elasto-Plastic Process Parameter in 100 0C (Best condition) in RT

Maximum effective strain : 1.15 , 2.42 Maximum effective stress(MPa) : 1120 , 1300

Maximum load (KN) : 47 , 86.9 Damage value : 1.31 , 1.41 Strain rate (1/s) : 0.527 , 0.649 Maximum velocity-Total vel (mm/s) : 6.5 , 6.67 Stress-Maximum principle (MPa) : 1070 , 2050 Recommendations

Lubricant suggested: Boron nitride aerosol (cc-18), Friction : 0.08 (coulomb) due to material type

Die : Die type : symmetrical Die cavity shape : Cup Die material : H13, Die Steel

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658 Table 5

Process plan output for Sheet Hydroforming Process – Non-symmetric shape

IX. CONCLUSIONS

Sheet hydro forming process of CP Titanium grade 1 has been modeled for semispherical cup shape and non-symmetric products using FEM package DEFORM-3D. All of the material properties found from different literatures have been successfully implemented in the SHF process. It is a long procedure to get proper deformation without any defects like tearing, wrinkling, surface cracks, incomplete die filling etc.

From various numerical simulations conducted for axisymmetric and non-symmetric shaped products, it can be concluded that, in order to form a part with almost uniform thickness throughout the new geometry while simultaneously maximizing the part deformation, it is quite important to select the optimum blank holding pressure, die radius and suitable contact lubrication conditions.

From the various parameter studies, the thickness and the depth of shape are most sensitive to friction, fluid pressure and blank holding pressure. Maximum effective stress and damage value act at the center of the cup in axisymmetric shape and in bottom corner in non-symmetric one. These regions are considered to be most sensitive for tearing. To decrease this damage a proper loading path and suitable sheet thickness selection is necessary.

Finally generative CAPP system for sheet hydroforming of axisymmetric and non-symmetric shapes was proposed and it was implemented for simulation procedure using C P Titanium as a sheet material.

Acknowledgement

The authorsgratefully acknowledge the help received in

running the simulations at IIT-Kanpur (India).

Process plan output for Sheet Hydro forming Process Nature of component : Non-symmetric (cup) shape Depth (mm) : 10

Maximum length of die cavity (mm) : 50 Sheet/blank thickness(mm) : 0.4

Sheet Material : C P Titanium grade1 Die corner radius(mm) : 3

Maximum Fluid Pressure applied (MP) : 5, (pressure path: P=(-5/6)t(time) Maximum Blank holding pressure applied (MPa) :2, (pressure path:P=(-1/3)t(time) Working temperature ( 0C) : 100 (Best condition) Material type : Elasto-Plastic

Process Parameter

Maximum effective strain : 1.18 Maximum effective stress(MPa) : 300 Maximum load (KN) : 206 Damage value : 1.22 Strain rate (1/s) : 0.00356 Maximum velocity-Total vel (mm/s) : 0.0142 Stress-Maximum principle (MPa) : 299 Recommendations

Lubricant suggested: Boron nitride aerosol (cc-18), Friction : 0.08 (coulomb) due to material type

Die :

Die type : symmetrical Die cavity shape : Non-symmetric Die material : H13, Die Steel

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659

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