Experiments on Metal Forming Processes | Metallurgy

Here is a list of experiments on metal forming processes.

1. Experiment on Wire and Tube Drawing:

Wire and tube drawing experiments can be easily conducted on universal testing machine (UTM), because, in these experiments one needs to measure the pull which can be done on UTM. A simple rig shown in Fig. 14.1 may be used.

The die is placed in the recess provided for it in the bottom plate which is connected to top plate by four tie rods. A tube is connected to top plate of rig for hanging it with the machine top gripper. Standard wire drawing dies may be used. Manufacturers of these dies also supply dies with different die angles. One can purchase a carbide die of diameter 6 to 8 mm for wire drawing and a die of diameter 12 to 16 mm for tube drawing.

Wire drawing test specimen may be prepared on lathe. The wire specimen is introduced through the die and is gripped by the bottom gripper of the machine while the apparatus is hanged with the top gripper. Lubricant is applied to the die and wire. The wire is pulled through the die. The load – displacement diagram can be recorded on the machine itself.

The draw bench comprises a bed, a hydraulic cylinder, a direction control valve, a power pack, high pressure hydraulic pipes for connecting the different components, a main bracket for holding die, grippers, load measuring device, a traversing mechanism consisting of two brackets and two guide rods.

Two guide bushes are provided in the main bracket for the guide bars. The die is placed in the main bracket, the wire/tube specimen is passed through the die and is gripped by the gripper on the other side of main bracket. The hydraulic cylinder pushes the traversing mechanism which draws the wire or tube.

The following may be investigated in wire and tube drawing on either of the above two set ups:

(a) Selection of most appropriate lubricant for particular work piece material-die combination. The lubricant which gives minimum drawing force is the best provided the other requirements are fulfilled.

(b) For dry wire drawing the effect of coating thickness with different solid lubricants such as soap powder, soap powder with graphite or grease may be investigated. One may as well test the commercially available lubricants for wire and tube drawing operations.

(c) Effect of reduction and die angle on pull provided you have dies of different die angles.

(d) With split specimen, and with grid scratched or printed on one half, the deformation pattern may be studied.

(e) Dies for polygonal sections and rectangular sections are also available. Study may be carried out on effect of the ratio of circumference/area of cross-section of wire on drawing stress for non-circular wires.

(f) Similar experiments may be carried out for tube drawing.

(g) Study could also be made on change of thickness of tube v/s the ratio of initial thickness/ initial diameter in case of tube sinking. For initial threading through die, the tube may simply be pressed through the die. For tube sinking, the specimen may be made out of commercially available tubes. For study on tubes with different thicknesses, solid bars may be drilled to obtain the specimen.

2. Experiment on Direct and Indirect Extrusion:

The rig may be manufactured in college workshop or one can get it machined from outside as well. This apparatus consists of a base block with central hole for the extrude. The base block has two recesses at the top surface, one for centring the die and the other for centring the cylinder. It also has tapped holes for clamping of top plate to it.

The top plate has six circumferential holes for clamping it with the bottom block with the cylinder and die in between. The bottom block has corresponding tapped holes. The top plate has central hole and guide bush for the piston.

The inside diameter of cylinder may be estimated according to the capacity of the press on which it has to be used. For experiments on lead, a cylinder diameter of 40 mm would require up to 20 ton force for different reductions. For cold extrusion of aluminium, the same dimensions may require a machine of more than 100 ton capacity.

For extrusion you need the required die and a pressure plate. For experiments with lead, pressure plate of aluminium works quite well and it does not score the surface of cylinder bore. For experiments in direct extrusion you need several dies with different die angles, and a set of dies with different bore sizes.

The following studies may be made with the help of this apparatus which is used on universal testing machine:

(a) Determination of co-efficient of friction on cylinder wall from punch displacement – punch load curve which is recorded on the machine.

(b) Determination of constants a and b in the expression p = a + b lnR by finding extrusion pressures for different reductions.

(c) The above experiments may be repeated for different lubricants to find out the most effective lubricant.

(d) In extrusion of section like angles or channels, ensure filling of sections by modifying the approach angles at different sections of die hole.

(e) Study the metal flow in extrusion with different friction conditions. Make a split specimen and mark or scratch grid lines on one half. Study the grid deformation after extrusion.

(f) Repeat the above experiment for extrusion of sections like angles and channels etc. and multi-hole dies with different die angles.

(g) For carrying out similar experiments in indirect extrusion, instead of making several punches, you may make one punch stem and several end plugs. The end plugs of different shapes may be turned for attaching to the punch. Thus study may be made for determining the optimum shape of punch for indirect extrusion.

(h) The above may be repeated with plugs of different sizes to study the effect of reduction in indirect extrusion.

(i) Experiments on direct extrusion of tubes with different sizes of mandrels may be performed. Soft metal may be used as work material. Dies with different approach angles could be made to study its effect on flow of metals into tube.

3. Experiment on Forging:

Many experiments may be performed with a pair of simple flat dies. If you wish to carry out compression of hard materials, the dies should also be hard, better make out of high carbon steel, or still better out of high carbon high chromium alloy steel. It should be hardened, tempered and finished by grinding or lapping. Die sets with different surface roughness should be made to see the effect of surface roughness on effectiveness of lubricant. Measure the hardness and surface roughness of the dies before carrying out experiments.

The experiments you can do with these dies are as follows:

(a) Effectiveness of different lubricants with dies of different surface roughness.

(b) Determination of effectiveness of different lubricants by compressing ring specimen made out of different materials. Compare the values with those available in literature. Always mention the temperature, surface roughness, lay of surface, lubricant etc. with the values you get. Thoroughly clean the die surfaces before applying a new lubricant.

(c) Study of metal flow in compression of non-circular discs.

(d) Experiments on study of die loads in compression of non-circular discs may be performed. Compare the load values with those for circular discs of same area.

(e) Study of metal flow and loads in fullering operation with dies of different curvatures may be performed.

(f) Make dies for coining operations and study the press load v/s height of engraved shapes on dies with and without lubricants and surface preparations. Other die sets may be made to simulate the upsetting of bolts, rivets and many other shapes.

4. Experiment on Roller Dies:

This is simple but a very versatile piece of equipment and can be easy fabricated in a college workshop.

It has four rolls which may be flat or each with quarter circle shape so that four together make a circular hole between them. If the design is rigid enough it can be used for reducing tube diameter by pulling through the rolls. The rig can be mounted on a universal testing machine. The pull is recorded by the machine.

For measuring force on the rolls, one of the rolls is mounted on a beam on which strain gauges are fixed, or the deflection of beam may be measured with the help of a sensitive dial gauge. On this equipment gear could be rolled on a lead blank. Though the equipment cannot roll gear in steel, nevertheless, the many technical problems could be studied and sorted out.

Besides it may be used for the following experimental studies:

(a) For drawing circular wires and tubes.

(b) For drawing wires and tubes of square cross section.

(c) For rolling shapes on a strip.

(d) For rolling of gear with single rack.

(e) For rolling of splines on a shaft.

5. Experiment on Sheet Metals:

The experiments on sheet metal may also be performed on Universal Testing Machine if press is not available. If you have a mechanical press the range of experiments may be extended. A simple constant gap type die may be fabricated in the college workshop.

It consists of a bottom plate which has recess to centre the die and a ring which centres the specimen as well as provides a constant gap between the blank holding plate and the die. In fact a set of centring rings is required for experimenting with blanks of different diameters. The gap is equal to the thickness of centring ring. The thickness of ring may be slightly more (0.1-0.2 mm) than the sheet thickness. This ensures very little blank holding force.

The following may be studied on this die:

(a) Drawability of sheet metal.

(b) Effect of punch profile radius and die profile radius on drawability.

(c) Effect of roughness at punch profile radius on drawability.

(d) Change of sheet thickness during cup drawing.

(e) Effect of sheet anisotropy ratio on drawability.

(f) Effect of planer anisotropy on ears produced on cup rim.

(g) Besides cups could be made for using them in redrawing experiments.

One of the problems is to get circular blanks. If the blanking die and press is available, the blanks may be made on press. For making them of different sizes, groups of them may be turned on lathe. If the above equipment is not there, sheet blanks may be cut to approximate shape and finally turned (in packs) on lathe for circularity and size.

For experiments on effect of blank holding pressure on drawability, you need a press with double cylinder-one for blank holding and other for cup drawing which is a costly machine. An experimental die of the design shown in Fig. 14.9 may be constructed.

The problem with this type of set up is that experiment takes more time. Setting the blank in the die is time consuming process. The figure is self-explanatory. The different blank holding pressure may be obtained by tightening the springs to different heights. The force exerted by springs may be calibrated.