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Numéro
Matériaux & Techniques
Volume 107, Numéro 6, 2019
Numéro d'article 605
Nombre de pages 7
Section Sélection des matériaux et des procédés / Materials and processes selection
DOI https://doi.org/10.1051/mattech/2020009
Publié en ligne 24 mars 2020

© SCF, 2020

1 Introduction

Current trends in materials research for the development in new variety of materials using the powder metallurgy (P/M) process, which has a light weight, corrosion resistance, ductility, high strength, ease of assembly and lower cost. This helps to carry out extensive research in the development of special aluminum compounds. The broadest meaning of a composite material in which two or more numbers of different materials are mixed to form a single composite material with a remarkable interface. The new property found in the compound depends on properties of the constituent materials, and the composite material retains its identity with better mechanical properties compared to a single material. In powder metallurgy (P/M) process, firstly, mixing finely dispersed metal powders and pressing them to the desired shape or form (compaction) within well-designed die. Then, heating the green compact samples inside an atmospheric controlled furnace to bond the grains of the sample. The PM process contains four main steps, such as making a powder, mixing the powder, compacting the powder and sintering, that is, performing at elevated temperature, at atmospheric pressure. The development of dies is one of notable challenge in the powder metallurgy process.

Current research included the re-design and re-manufacture of new sets of dies for the production of cylindrical green compacts as the previous attempts were failed due to its design failure and fracture in die. The new die is designed to satisfy with ASTM B925-08 standard, i.e., standard methods for the production and preparation of PM samples and the die was made from EN 10083: C − 45 round bars steels with taking care of all its design considerations to free from its failure during compaction and ejection of green compacts.

1.1 Composite materials

Basically, a composite material is prepared by adding two or more quantities of materials to one material, which gives different properties. The material group works together to produce a composition of strengthened properties. Composite material provides better properties than the properties of individual components used separately. In addition, the material has various physical, mechanical and chemical properties. The manufacturing interest of the composite material is due to its rigidity, high strength and corrosion, and is also combined with a very low density compared to bulk materials. Various classifications of composite materials are polymer matrix compounds (PMC), metal matrix compounds (MMC) and ceramic matrix compounds (CMC). MMCs have gained great importance due to their potential use in the automotive, aerospace, sports and other industries, due to their excellent materials and mechanical properties, temperature, strength and stability, high specific stiffness, elastic modulus, wear resistance and adequate coefficient of thermal expansion.

1.2 Composite manufacturing

The various composite manufacturing processes are available, such as liquid processing, solids processing, manual coating processing, automatic measurement, spraying, screw winding, injection molding, compression molding, pultrusion processing, resin transfer molding and manual processing. The composite manufacturing is a series of process having complex interactions between people, machines, materials and energy. The process begins with the innovation of each piece and finally is assembled to produce a new product. Each production method uses its own methodology to attain the desired surface finish, shape and accuracy.

1.3 Die manufacturing

The main step in powder metallurgy before producing composite materials is to design a compression die. In general, powder compression is performed on the die by applying high pressure. Typically, the die is held upright and pressure forms the lower side of the cavity. The powdered metals are compressed into a green compact and then discharged from die cavity. The density of compressed powder is equivalent to the amount of applied pressure. The pressure range from 150 to 700 MPa is generally used to compress metal powder by selecting the appropriate dimensions for the PM track die. The die must be prepared to make a green compact or press the powder perpendicular to the axis.

2 Literature review

Several researchers have developed and designed cold compaction dies for preparing aluminum composites and offered many ideas in their research work. The literature review presents some data on the production of composites.

A design criterion of die is one of most vital stage in powder metallurgy process. Since the shape, size and characteristics of the die is directly affecting the final product, so fabrication of the die design should be accompanied by several stages and considerations [1,2]. The development and design of dies depends on compacted green sample. There are several attempts before making and designing dies for the cold compaction used in the P/M process. Dies are designed to ASTM B925 standards with AISI-D3 tooling steel and AISI steel stamping material D2 [36]. Dies should be mapped and designed for cold pressing powder presses. A hydraulically power unit with a lifting capacity of 1.2 tons is designed to lift arrays of P/M components. Design and manufacture of arrays should be considered as more economical [7,8]. The tribological composites characteristics of the product will be improved by addition of SiC and graphite. The subsurface expansion deformation found in composites of Al-SiC-Gr is less than in Al-Sic composites [911]. Copper alloys are suitable for widespread use in the manufacture of highly conductive conductors, bushings and bearings, heat transfer conductors, etc. TiC. The main disadvantages of copper composites are reduced machinability and electrical conductivity [1214]. By studying the hardness and the wear resistance of sintered Al-Cu-Mg alloy products gives the best results [1517]. Von Misses theory indicates the change in hydrostatic pressure on the rigid body [18] gives rise to different stresses. A demonstration of interest in the development of lightweight materials with lower processing costs should create an important view on the aluminum compound in powder metallurgy. The use of separate powder mixture is a unique and important feature of the metal forming process [19]. The addition of Sic to copper revealed an improvement in wear resistance and hardness [20,21]. The characteristics of aluminum with various powder compositions of copper and silicon carbide etc. in the production of alternative materials in mechanical engineering [2225].

3 Powder compaction die design

3.1 Failure die

In the initial phase, several attempts were made to develop a die for cold compaction of AMC products. But due to its failure, the first die could not stand during operation. This was traced to a very high stress in the cavity of the die and relatively low fracture toughness (Fig. 1). In the second die (Fig. 2), the fracture was caused by an increase in cracks in the die cavity and was particularly a fatigue problem. However, defects on the surface of this material could give rise to stress concentration, which increased its fracture strength and ultimately leads to destruction. In this study, the methods were used to successfully manufacture die sets and their designing parameters for the production of AMC sintered products.

thumbnail Fig. 1

Bending die.

thumbnail Fig. 2

Broken die.

3.2 Functional sketch of the die

Before producing composite materials, the major step in powder metallurgy was to design die (Fig. 3) based on technical sketch of the structural part. An exact sketch of the die was being developed. Subsequently, exact dimensions, tolerances and functions for all die members were being established with suitable tool materials to be considered.

The filling depth required for both parts of the die will be calculated according to following ratio: Q = Compact density / filling density = Fill depth / Compact height

The lower and upper punches must be long enough to fully push the compact out of the die.

thumbnail Fig. 3

Parts of die.

3.3 The yield function criterion of die

The die was taking care with yield function criterion with the relationship between the movements of the punch and the location of the neutral zone which may be described by: E = FX / X + Y, where F is the filling depth, X and Y are the distances traveled by the upper and lower punch, respectively, and E is the distance from the neutral zone of the upper punch of the die. If the upper and the lower punch move symmetrically with respect to die the clearance (from 0.005 to 0.010 mm) inside the die depends on the compaction pressure and the powder types are used. In die design, an important factor to be considered is strength. In order to represent the observed behavior in porous compact materials, where, a metallic or plastic mechanical deformation of full strength is obtained. So, according to Von Misses the quality criterion model is specified as: (1)

The first term represents the function of the stress components, which is the equivalent stress of the Von Misses theory, including the change in hydrostatic pressure. The second term refers to the elastic limit in a uniaxial test, whether it is tension or compression.

To obtain a flow function intended to characterize aluminum powders the coordinate axes in Figure 4 reminiscent of the stress for a material element undergoing a closed die compression in terms of compaction pressure and radial presure. The upper punch load transfers axial stress, σaxial to the powder body and the die wall produces radial stress, σradial. These two stresses make it possible to calculate the invariants of stresses.

thumbnail Fig. 4

Analytical stress undergoing compression.

3.4 Radial stress and hoop strain

σradial is calculated from the ring (or tangential) deformation on the external surface of the die wall εθ. Here, the relation εθ = fradial) is called the transduction equation and is obtained as follows in accordance with Figure 5.

The die is thick-walled cylinder. So, the hoop strain is given by: (2) (3)

At, r = b where hoop strain is to be measured, there is a free surface, so σr = 0, then: (4) this may be found for a non-rotating, thick-walled cylinder: (5)where, pi stands for internal pressure and σradial exerted by the loaded specimen. Enforcing r = b and substituting back gives: (6)

Die wall is to be made of EN 10083 steel (E = 200 GPa; ν = 0.3) for radial stress within the specimen which resulting hoop strains for a 30-mm die wall thicknesses.

thumbnail Fig. 5

Closed die cross-section design.

3.5 Volumetric strain

The upper punch displacement δ is proportional to the volume change of the specimen, and a strain can be calculated as: here, H0 is the initial (Fig. 6) fill level height. From source data δ may be of up to 30 mm for H0 of 50 mm on specimen size. This gives a volumetric strain εv = ΔV/V of about 33%. Thus, a logarithmic measure of strain must be considered, yielding: (7)

Relative density is frequently used to characterize the material evolution throughout compaction, and is computed by: (8)

thumbnail Fig. 6

Volumetric strain calculation.

3.6 Dimension calculations

Depending on the current sample size, the thickness and the applied load were considered in the design of the dies. A concept consisting of a statement of ideas showing a product that is usable, marketable, secure, competitive and reliable. In general, these characteristics are taken into account during the design of the die, such as the mechanical properties (Tab. 1) and the chemical composition (Tab. 2) of the selected metal powders, the choice of matrix material, the tension and the maximum load, the size of the green compact and the thickness of the green compact.

As per the ASTM B925 standards the raw materials were purchased from the present market availability. The above-mentioned different chemical and mechanical properties of C45 steel are given in table:

  • die: 50 mm of outer diameter, 20 mm of inner diameter, 130 mm of height and 2357 gm of weight (upper punch, lower punch and container);

  • upper punch: 18 mm of diameter, height of 100 mm and weight of 487 gm;

  • lower punch: 18 mm of diameter, height of 10 mm and weight of 192 gm;

  • green compact: 20 mm of diameter, 7 mm height;

  • working load (F) = 150.0 kN, peak load (F1) = 150.6 kN;

  • peak stress developed in punch due to applied load = 486.08 MPa;

  • area, ;

  • the stress developed on die due to applied load upon punch, 

(Die is also in safe condition). Where, ro, ri are the external and internal radius of die. The ultimate tensile and yield strength of C-45 steel die are 485 and 800 MPa respectively. Therefore, the die can withstand a load of 150 kN which is ease to manufacture.

Table 1

C45 steel round bar mechanical properties (courtesy: supplier’s data).

Table 2

C45 steel round bar chemical composition (courtesy: supplier’s data).

4 Die Machining

EN 10083: C − 45 Round Bar Steel (Fig. 7) was machined by lathe to prepare the specified dimension of die (Figs. 8 and 9) with adopting different machining operations.

thumbnail Fig. 7

C-45 steel bar.

thumbnail Fig. 8

Die with upper.

thumbnail Fig. 9

Die sets and lower punch.

5 Results and discussion

This study is used to solve the previous problem happened in faulty die and carry out an idea to re-manufacture a fresh die for considering the radial stress exerted by the die wall. The design model was introduced to solve the die failure problem during compaction in order to obtain a picture of the radial stress exerted by the material against the die wall. The small elastic strain behavior with a porosity-dependent yield criterion and a Von Mises plasticity recovering at high relative densities reported the elliptical shape of the yield surface for metal compacts. It was an appropriate example of porous bodies at low densities and at complete densities, the material was ductile, so that the von Mises yield surface is correct. The dependent yield criterion and Von Misses plasticity are restored at very high relative densities. This method is successfully solved for the case of powder compaction, and in particular, the maximum value of radial stresses i.e. 553.64 MPa is found at an expected result.

The tensile and yield strength of C-45 steel dies are 485 and 800 MPa, respectively. As a result, the die can withstand a load of 150 kN, which is easy to manufacture. Organic binders were used here to premixes with the powder mixtures for preventing the dust formation and segregation. Due to human concern, the process in powder metallurgy, aluminum powder dusts is a potential safety hazard to environment. The binders added here will burnout completely during sintering and don’t react with metal powders. It is provided lubricity to the die wall and did not interfere with sintering and also, it increases ductility and tensile strength of die.

6 Conclusions

The failure was most likely caused due to the stress concentration and the propagation of cracks but not due to chemical composition of the material. The design of the die was solved by calculating the 50 mm diameter of work piece and up to 300 kN of load. During the process of compacting powdered metals, shape and size, quality of the surface and quality of the samples of the final product depended on the quality of the die. The dies were manufactured and designed according to the safe manufacture for compacting powders with maximum load bearing capacity. A review of the literature made it viable to select the raw materials with various parameters for developing and manufacturing new sets of dies. The concluding remarks are:

  • the type of material used to make the die was: EN 10083: C − 45 round steel bars;

  • the maximum working pressure studied during operation is 553.64 MPa; this working pressure may increased by same material of the die;

  • the property of selected die material helps to easy removal and ejection of the green compact from die due to more ductility and tensile strength of die material (EN 10083 steel), the die does not break during process of compaction. There will be no fracture takes place and the metallic powders get compacted with smooth form of the green compact inside the die.

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Cite this article as: Rajesh Kumar Behera, Birajendu Prasad Samal, Sarat Chandra Panigrahi, Manufacture of die and their designing parameters for sintered AMC product, Matériaux & Techniques 107, 605 (2019)

All Tables

Table 1

C45 steel round bar mechanical properties (courtesy: supplier’s data).

Table 2

C45 steel round bar chemical composition (courtesy: supplier’s data).

All Figures

thumbnail Fig. 1

Bending die.

In the text
thumbnail Fig. 2

Broken die.

In the text
thumbnail Fig. 3

Parts of die.

In the text
thumbnail Fig. 4

Analytical stress undergoing compression.

In the text
thumbnail Fig. 5

Closed die cross-section design.

In the text
thumbnail Fig. 6

Volumetric strain calculation.

In the text
thumbnail Fig. 7

C-45 steel bar.

In the text
thumbnail Fig. 8

Die with upper.

In the text
thumbnail Fig. 9

Die sets and lower punch.

In the text

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