specimen length i need is 62 mm and dia 10 mm. in dia. should i fabricate die in which a punch presses powder vertically making it a cylindrical part (pressing it parallel to length or should i make die in which punch presses perpendicular to length.
Dear Farhan Shabbir, the Major Problem in pressing parallel to the length axis is that you will see Problems with the densification of the material due to friction in particular since the Diameter is comparably small. From that Point of view it is most advisable to press perpendicular to the length axis.
thanks. is the direction of pressing anything to take from tensile testing of specimen...i mean 500 Mpa pressure wont be enough for good densification if i press it parallel to length. ratio for length to diameter is 7:1 if im right.
Dear Farhan Shabbir, here some more Details which you could also find in text books on PM techniques.
Usually powder compaction is done in a die through the application of high pressures. Typically the tools are held in the vertical orientation with the punch tool forming the bottom of the cavity. The powder is then compacted into a shape and then ejected from the die cavity.
The density of the compacted powder is directly proportional to the amount of pressure applied. Typical pressures range from 80 psi to 1000 psi (0.5 MPa to 7 MPa), pressures from 1000 psi to 1,000,000 psi have been obtained. Pressure of 10 tons/in² to 50 tons/in² (150 MPa to 700 MPa) are commonly used for metal powder compaction. To attain the same compression ratio across a component with more than one level or height, it is necessary to work with multiple lower punches. There are four major classes of tool styles: single-action compaction, used for thin, flat components; opposed double-action with two punch motions, which accommodates thicker components; double-action with floating die; and double action withdrawal die. Double action classes give much better density distribution than single action.
Typical workpiece materials
material Density (grams/cc) Yield strength (psi) Tensile strength (psi) Hardness
Iron 5.2 - 7.0 5.1*103 - 2.3*104 7.3*103 - 2.9*104 40 - 70
Low alloy steel 6.3 - 7.4 1.5*104 - 2.9*104 2.00*104 - 4.4*104 60 - 100
Alloyed steel 6.8 - 7.4 2.6*104 - 8.4*104 2.9*104 - 9.4*104 60 and up
Stainless steel 6.3 - 7.6 3.6*104 - 7.3*104 4.4*104 - 8.7*104 60 and up
Isostatic powder compacting is a mass-conserving shaping process. Fine metal particles are placed into a flexible mould and then high gas or fluid pressure is applied to the mould. The resulting article is then sintered in a furnace which increases the strength of the part by bonding the metal particles. Compacting pressures range from 15,000 psi (100,000 kPa) to 40,000 psi (280,000 kPa) for most metals and approximately 2,000 psi (14,000 kPa) to 10,000 psi (69,000 kPa) for non-metals. The density of isostatic compacted parts is 5% to 10% higher than with other powder metallurgy processes.
Hot isostatic pressing (HIP) compresses and sinters the part simultaneously by applying heat ranging from 900 °F (480 °C) to 2250 °F (1230 °C). Here Argon gas is the most common gas used in HIP because it is an inert gas, thus prevents chemical reactions during the operation.
Dear Farhan,
While choosing an appropriate dimensions of a die for PM routes, please keep in mind that ejection of the green compact (pressed powder) would becomes tricky and you may lose the densification of the compact by un-avoildable vibrations or shocks. which eventually would result in pores or defects. Hot iso-static pressing (HIP) or SPS (spark plasma sintering) encounter these densification problems. However, good choice of lubricants in the steel die for uniaxial or iso-static pressing may result in clean ejection of the samples e.g. Boron nitride solution etc. The die should be designed to prepare the green compacts or press the powders perpendicular to the axis anyway.
Good luck,
Khurram
whats the reason behind pressing powder perpendicular to length axis.. with desired geometry i can make a work piece of 10 mm dia and 65-70 mm length by pressing from top (parallel to axis). i pressing perpendicularly i might waste more material also...
Hi Farhan,
I made a schematic for you. See attached.
Hope it helps.
Khurram
thankyoy very much...i didnot get the design bolts..its a vertical die right??
I wholly agree with the 1st answer from Rüdiger. An aspect ratio of 6:1 height:diameter is extremely difficult to press vertically even with active top and bottom punches (double sided axial pressing), good lubrication, slightly tapered die, best powder properties, etc. You are bound to get a very large density gradient towards the centre of the part. You can press it horizontally and after sintering centreless grind the part. Or you can dry or wet bag CIP (cold isotatically press) the powder then sinter it or HIP (hot isostatic press) directly in a metal can.
thank you everyone...i get the pros and cons for making the required specimen (parallel to length axis). however, now i have decided to make a specimen with 75 mm length and 10 mm height and width each (as per ASTM B-925). In this case i intend to press the material from top(perpendicular to length axis) . i hope after machining i can get the specimen as attached. furthermore im attaching the snap of pressing equipment which i will be using for cold compaction. plz guide me for making the appropriate die. thankz
In my opinion it is much more easier and technically acceptable to manufacture such
parts (with small diameter, too high) by extrusion
The yield strength of die material is critical for the metal powders you want to compact
it is better to make the die with Tungsten carbide up to 7:1 height to dia ratio. so that it can bear loads up to 25 tons. previously i tried with H13 steel, later i found that it can bear only 700MPa (10 mm Dia) for accurate shapes and easy compaction. Zinc stearate along with acetone acts as good lubricant.
Hi dear researcher
There is my recent publication about powder compaction, I hope it will be useful for you.
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