116 Figure 6.2 Schematic of constrained multi-hole extrusion 117 Figure 6.3 Load-displacement curves for free and constrained extrusion. Schematics of single-hole extrusion, multi-hole extrusion, and side extrusion are shown in Figure 1.1 to understand the basics of these processes.
Micro, Meso and Macro Extrusion Process
Extrusion process that provides a product with a diameter of less than 1 mm will be called micro-extrusion, and the extrusion process that provides the parts that have a diameter in the range of 1-10 mm will be called meso-extrusion. The extrusion process that provides the parts with a diameter greater than 10 mm will be called macroextrusion.
Multi-hole Extrusion Processes
Mathematical modeling and finite element analyzes were performed on a multi-hole extrusion process to study the quality of the product and optimize the die design. Multi-hole extrusion process is found to be an important research area to investigate the various aspects of improving product quality and productivity.
Process Parameters in Multi-hole Extrusion Processes
The proposed limited multi-hole extrusion process also eliminates bending of the extruded products. The increased mechanical properties of the extruded product are found with the products of limited multi-hole extrusion process.
Multi-hole Microextrusion Process
In this work, a limited multi-hole extrusion process has been proposed to obtain extruded products of equal length. Many advantages favor the limited multi-hole extrusion process despite the higher extrusion load requirements.
Primary Objectives and Organization of the Thesis
A limited multi-hole extrusion process was developed to produce uniform lengths of extruded products. The mechanical properties of the extruded products of free and constrained multi-hole extrusion are compared and the advantages of the constrained multi-hole extrusion process are highlighted.
Introduction
Typically, multi-hole extrusion is used when the pressure required for extrusion exceeds the capacity of the press. In this chapter, a review of the available literature in the field of multi-hole extrusion process and single-hole extrusion process is presented in different sections.
An Overview of Literature on Multi-hole Extrusion
2009b] studied the mechanical properties of the extruded products obtained by multi-hole extrusion with different dies with different number of holes. This study indicates the possibility of using multi-hole extrusion process for the production of small metal components with improved productivity and quality.
Experimental Studies on Single-hole Extrusion Process
Kim and Ikeda [2000] investigated the influence of some process parameters on the flow behavior of the billet surface layer in the direct extrusion of aluminum in an orifice die. Shahzad and Wagner [2009] studied the effect of extrusion ratio on the mechanical properties of an extruded magnesium alloy.
Experimenral Studies on Multi-hole Extrusion Process
The speeds of the extruded products are sensitive to the die opening positions and the land length of the die. The recrystallized grain size at the surface was found to be smaller than that at the center of the extruded products.
Modeling of Extrusion Process
- Slab Method
- Slip-Line Field Method
- Upper Bound Method
- Visioplasticity Method
- Finite Element Method
- FEM in modeling of multi-hole extrusion
- FEM in modeling of single-hole extrusion
Authors also studied the influence of extrusion ratio on the shape of the dead zone and the extrusion pressure. The effect of the land length on the extrusion pressure increases with increasing complexity of the diameter of the extruded products.
Methods Adapted for Enhancing the Efficiency of the
Optimization of Die Profile
- Slip-line field method
- Upper bound method
- Finite element method
1996] combined the upper limit and finite element method and obtained the optimal die profiles for asymmetric extrusion process. Yang and Lange [1984] obtained the optimal streamlined die length with the upper limit method under different process conditions.
Reduction of Friction
In most research works, the optimal die design is obtained by minimizing the extrusion force. The control of exit velocity of the extruded product is necessary to minimize the deformation of profile.
Use of Vibration in Extrusion Process
The effect of ultrasonic vibrations on the extrusion process was investigated by Akbari Mousavi et al. The average extrusion force decreases by reducing the extrusion speed or increasing the amplitude of the vibration.
Study of Mechanical Properties and Microstructure of Extruded
The effect of extrusion ratio on the hardness property of the extruded aluminum products was studied by Onuh et al. Ajiboye and Adeyemi [2006] studied the effect of die land length on the hardness distribution along the length of the extruded products.
Microextrusion
Measurements of micro-hardness of the extruded micropins were performed by Parasiz et al. It has been observed that the extra hardening of the material occurs as a result of miniaturization.
Challenging Issues
Scope and Objective of the Present Work
Another important goal of this thesis is to perform finite element simulations of the multi-hole extrusion process and compare them with experiments. Multi-hole micro-extrusion: Efficient use of the multi-hole extrusion process for manufacturing micro-products is the final objective of this thesis.
Introduction
In this study, the effects of vibration on the extrusion load and curvature of extruded products in a multi-hole extrusion process are investigated. In a multi-hole extrusion process, controlling the metal flow at the die exit is a challenging task due to complex influencing factors such as product size and shape, number and arrangement of die openings, and die length.
Extrusion Set-up
The die land length of 6.5 mm produced on alternate holes of the peripheral holes as well as on center hole is indicated as Die II. Similarly, the land length of 3 mm produced on alternate holes of the peripheral holes as well as on center hole is designated as The III.
Billet Preparation
The scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) is used to find the material composition. The SEM specifications are provided in Appendix A.
Measurement of Tensile Strength, Hardness and Surface Roughness
The microhardness tests of the extruded products were performed on the extruded products exiting through different holes of 5-hole, 9-hole and 13-hole dies. Vickers Micro Hardness Tester (Make: BUEHLER, Model: MICROMET 2101) was used to determine the microhardness as shown in Figure 3.10.
Measurement of Radius of Curvature
Pocket Surf (Mahr, GMBH) shown in Figure 3.11 was used to measure the surface roughness of the extruded products. For the present study, Image J®, image processing software (Java-based image processing program developed at the National Institute of Health, USA) has been used to measure the radius of curvature of the extruded products.
Fabrication of Die Pockets in Multi-hole Die
The photograph of Die IV with 4 mm deep diaphragm pockets is shown in Figure 3.15 which gives a clear idea about the diaphragm pockets in multi-hole cabins. Extrusion is performed at a speed of 1 mm/min to eliminate the strain rate effect.
Conclusion
Introduction
Ramming forces were measured during the multihole extrusion of lead alloy at different ramming speeds. The effect of die pockets on ram force, length of the extruded products and bending of the extruded products was studied.
Ram Force Obtained for Different Dies in Extrusion of Lead Alloy
Comparison of Ram Forces for Lubricated and Unlubricated
For matrix II and matrix III, there is a decrease in the impact force compared to matrix I. It is observed that in all the cases, when the impact velocity increases, the impact force also increases.
Variation in Radius of Curvature of Extruded Products Obtained
Die length is a more influential parameter compared to lubrication and piston speed to produce a better and large radius of curvature. In experiments, different die lengths were made on alternate holes to observe the flow behavior and curvature of the extruded products.
Variation in Radius of Curvature of Extruded Products Obtained
Interestingly, for the same extrusion ratio condition, the lubrication effect together with the ground length has a great influence on producing a larger radius of curvature of the extruded products. The present experimental results show that the radius of curvature of the extruded product increases with increasing billet length, which agrees with the results obtained by Ajiboye and Adeyemi [2006] for single-hole extrusion.
Multi-hole Extrusion with Imposed Vibrations
Comparison of Ram Force for 20 mm Length Billet Extrusion
Comparison of the radius of curvature of the extruded products from the center hole for a 20 mm billet extrusion. Comparison of radius of curvature of extruded products from peripheral holes for extrusion of 20 mm long billets.
Tensile Strength of the Extruded Lead Alloy Products
Engineering stress-strain curves for center hole lead products with 10 mm ground length (a) unlubricated bulk (b) lubricated bulk. Engineering stress-strain curves for lead products from peripheral holes with 3 mm ground length (a) unlubricated machines (b) lubricated machines.
Micro Hardness of Extruded Lead Products
Hardness value (mean ± standard deviation) for lead products from peripheral holes of unlubricated chairs with 10 mm ground length. Hardness value (mean ± standard deviation) for lead products from peripheral bores of unlubricated chairs with 3 mm ground length.
Micro Hardness of Extruded Aluminum Products
Hardness value (mean ± standard deviation) for lead products from peripheral bores of 3 mm ground length lubricated seats. For diabetes with a ground length of 10 mm, the maximum and minimum hardness values of the extruded products are 45.05 and 39.5 VHN, respectively.
Surface Roughness of Extruded Lead Products
The average value of the surface roughness of products extruded from the central holes of the multi-hole cap with different extrusion ratio. The average value of the surface roughness of the products extruded from the peripheral holes of the multi-hole cap with different extrusion ratio.
Surface Roughness of Extruded Aluminum Products
Effect of Die Pockets in Multi-hole Extrusion Process
Comparison of Extrusion Load Obtained from
Bending of the Extruded Products from the Dies
Radii of curvature of extruded products coming from the central hole (values in parentheses are standard deviations). Radius of curvature of extruded products coming from the peripheral hole (values in parentheses are standard deviations).
Variation in Length of the Extruded Products from
Conclusion
For lead extrusion, extrusion ratio, ground length and lubrication were found to be important factors for surface roughness. Increasing the depth of the cap pockets produces more bent products due to the reduction of soil.
Introduction
Results of Finite Element Simulations of Multihole Extrusion Process. iii) Post processor: It reads the database file from the simulation engine and displays the results graphically, extracts the numerical data and derived quantities such as stress.
Finite Element Simulation of Multi-hole Extrusion Process
Comparison of Extrusion Load Obtained from
From the simulations, it can be observed that the extrusion load is reduced by 15% when the cutting ground length is reduced from 10 mm to zero for 30 mm billet length extrusion. The extrusion load is reduced by 12% when the cutting ground length is reduced from 10mm to zero for 20mm billet length extrusion.
Finite Element Simulations on Bending of Extruded Products
The extrusion load increases with the increase in die land length and bar length for the same extrusion ratio. Higher extrusion load due to the high die land length can be compromised for the better quality of the extruded products.
Finite Element Simulations on Effect of Die Pockets in
Comparison of Extrusion Load Obtained from Experiments
For a particular cap design, the optimum mold pocket depth helps reduce the extrusion load. The depth of the mold pocket can be considered as an important parameter to reduce the extrusion load.
Effective Strain
The 3 and 4 mm die pocket depths provide increased loading compared to the 2 mm pocket depth, although the die length decreases with increasing pocket depth in the current design. It is observed that for dies IV and dies VI (which have a periphery hole closer to the center) the maximum effective strain values decrease with increasing die pocket depth.
Conclusion
It is assumed that the design of the pocket should be based on the location of the holes in order to achieve uniform material flow.
Introduction
Here, a limited multi-hole extrusion process was proposed to obtain equal lengths of the extruded products without bending. A number of experiments were conducted to determine the suitability of the constrained multi-hole extrusion process.
Concept of Constrained Extrusion Process
It was found to be more interesting to have some sort of multi-hole extrusion set up to produce a product of equal length with minimal or no bending. On the other hand, the quality of extruded products in terms of curvature and mechanical properties is much better compared to free extrusion processes with one or more holes.
Experimenrtal Procedure
Tensile tests were carried out for the extruded products on micro tensile tests (Make: DEBEN, Model: MICROTEST, 5 kN capacity). Since the dimensions of the extruded products were small, they could not be used directly to find the mechanical properties.
Results and Discussion
- Load–Displacement Curves
- Length of the Extruded Products from Free Extrusion
- Comparison of Bending of the Extruded Products
- Comparison of Tensile Strength of Extruded Products
- Micro-Hardness of the Extruded Products
Length of extruded products in free extrusion with 5 holes length of extruded products (mm). Length of extruded products in free extrusion with 9-hole cap Length of extruded products (mm).
Conclusion
Surprisingly, the coefficient of variation in hardness value is less for 9-hole die extrusion compared to 5-hole die. This indicates that there may not be a strong correlation between the increase in microhardness and the increase in ultimate tensile strength.
Introduction
1993a), An analysis of the upper limit of back extrusion of tubes of complex internal shapes from round billets, Journal of Materials Processing Technology, 36, pp.157-173. Shah, S.N and Kobayashi, S., (1977), A theory on metal flow in axisymmetric drilling and extraction, Journal of Production Engineering, 1, pp.73.
Experimental Procedure
Fabrication of Container, Punch and Die holder
Components of meso-extrusion set up for extruding 20mm billet to produce 2mm diameter products. Some trial experiments are conducted with the modified setup and both wax and lead alloy products are successfully obtained.
Fabrication of Micro Multi-hole Die
Removing the extruded material from the die land areas of the multi-hole die proved difficult due to the very small holes. An extruded lead microcomponent is shown in Figure 7.11 as an example of the current experiments conducted with the multi-hole micro-die.
Results and Discussion
- Extrusion Load for Wax Extrusion
- Extrusion Load for Lead Alloy Extrusion
- Length of the Extruded Products of Wax and Lead Alloy
- Micro Hardness Test of the Extruded Lead Alloy
- Tensile Test of the Extruded Lead Alloy
More uniform hardness values of the extruded products are observed along the radial direction in the case of 2 mm die length (Figure 7.18 (c)). Tensile tests of the extruded products of lead alloy from the microhole die are performed.
Conclusion
Conclusions
Higher extrusion ratios and die land length help improve the mechanical properties of the extruded products. Removal of extruded products from the matrix land region proved to be a difficult task.
Scope for Future Work
1993b), An analysis of backward extrusion of inner circular tubes from arbitrarily shaped billets by the upper-bound method, Journal of Materials Processing Technology, 36, pp.175–. Wang, J.P., (1997), A slip line approach to visioplasticity in plane strain extrusion by the finite flow line region techniques, Journal of Materials Processing Technology, 70, pp.77−82.
