^ Horizontal Hydraulic Press for Extrusion of Hot Aluminum – Image Courtesy of Swoolverton at https://en.wikipedia.org/wiki/File:Al_extrusion_machine_with_dies.jpg
A Case for Distributed Application
Anything in excess is harmful. Very septic. Forget about toxins. Consumed in immoderate proportions, even water – the magic element that gives life to us all – can land you in serious medical trouble.
Heat and friction are serious byproducts of any metal forming operation. Friction hinders metal flow needed for imparting the correct shape to the workpiece. It also escalates the forces required for metal forming and can gravely damage the quality of the die as well as of the part.
Operators use metal forming fluids (also called lubricants or oils) to minimize or even eliminate the effects of friction and heat on the part and the die. Fair enough. But for the oil to serve its purpose, you have to distribute it evenly over the entire workpiece before starting operations.
There’s absolutely no point in applying more lubricant than necessary. In fact, over-lubrication is a severe issue in American metal forming shops. And, it is a lose-lose situation.
Because it severely dents the quality of your workpiece and the die. You end up spending more than necessary on the forming fluid, cleaning the oil-puddled floor, and maintaining the die. Not to mention the possible losses due to rejection of parts and a dip in market reputation.
Roller Application Systems
Popular fluid application techniques currently in vogue include spraying oil with nozzles, spreading it with rags, or using the simple drip can method. These however do not guarantee even distribution.
And, there is the risk of incorrect diagnosis. You might hold the forming fluid responsible for an issue when the problem is with its flawed application. Or, you might boost the supply of the oil during the operation. In both cases, you end up losing valuable time and resources.
Spray devices use high pressure to deliver the fluid, some of which is inevitably lost to the air. Some collects on the floor. Result – wastage and unclean ambience. Furthermore, these devices do not deliver the oil uniformly over all parts of the stock.
While designers formulate the stamping fluid meticulously, operators may err in applying it. This is precisely why we should give a serious thought to roller application systems that distribute lubricants evenly over the entire workpiece.
But before you purchase one, ensure you have chosen the correct roller system. Incorrect selection makes many think that roller systems are no better than dripping and spraying mechanisms.
Internally fed rollers come with a perforated roller core enveloped in a wicking membrane and a roller cover. An internal fluid distribution system delivers the lube oil uniformly over the inside of the roller.
With a programmable fluid delivery system, you can deliver a lubricant film of pre-set thickness. The system also feeds the oil at a rate enough to refill the roller and maintain the pre-set film thickness over the part.
As the fluid wicks through the membrane, it saturates the roller and gets applied to the workpiece (sheet metal). The programmed system enables the rollers to consistently deliver an oil film of uniform thickness across the width of the workpiece as well as on its top and bottom faces.
Such is the accuracy and repeatability of roller application systems that they end up using only half as much oil used by conventional spray application systems. Plus the part and die are better protected.
Metal Forming Processes
In metal forming, also called forming, operators impart the required shape to the material through plastic deformation. They do not remove any material and the machine applies a force that exceeds the yield strength of the material.
Plastic deformation is different from elastic deformation in that the object does not regain its original shape even after you remove the force that caused the change of shape.
Humans as far back as 7,000 years ago employed metal forming. This makes it one of mankind’s oldest operations when our ancestors forged utensils, tools, and weapons.
Industrial metal forming processes employ:
- Large Stresses of 50 to 2,500 N/mm2
- Large Capacity Machines
- Economies of Scalee. produce parts in huge quantities in order to minimize the per-unit cost of production
Forming Processes can be:
1.) Compressive Forming uses compressive forces for:
- Rolling: stock is passed between rollers
- Forging: material is shaped by employing local compressive stresses
- Die Forming: job is stamped by a press
- Indenting: tool is inserted into the part
- Extrusion: workpiece is pushed through an opening
- Tensile Forming employs forces of tension for:
- Stretching: extends the length of the workpiece
- Recessing: forms holes or depressions
- Expanding: increases the material’s circumference through tangential loading
2.) Combined Compressive and Tensile Forming involves the use of both tension and compression for:
- Deep Drawing: makes a hollow or concave shape out of sheet metal
- Flange Forming
- Pulling through a Die
- Upset Bulging
3.) Bending forms the metal into angled bends
4.) Shearing cuts the metal utilizing shearing force
Executed at between room temperature and re-crystallization temperature, Warm Working creates complex shapes using lower magnitude forces. These consume lesser power. You don’t need to anneal the part and it does not work-harden.
Cold Working provides superior surface finish, precision, directional properties, strength, and hardness. However, you need to clean the surface post operations and employ larger forces. Strain hardening and ductility restrain the scope of the process.
The Changing Milieu for Metal Forming Fluids
Similar to metal cutting fluids, metal forming fluids serve the basic functions of:
- Corrosion Protection
- Scrap Metal Flushing
Lubrication is the most important function of metal forming fluids because metal forming operations occur under boundary lubrication conditions, or hydrodynamic lubrication conditions, or both. Additives boost any or all of these required characteristics.
In boundary lubrication, the solid surfaces are very close and can come in contact. Hydrodynamic lubrication is when the surfaces in sliding motion are completely separated by the lubricant. Elasto-hydrodynamic lubrication is hydrodynamic lubrication between rolling surfaces.
As mentioned, metal forming generates sizable friction and heat. Unless these fluids slash friction through lubrication i.e. by reducing the contact between the part and the tool, the die-press machine will not produce the expected large number of parts.
This way, you will never make the expected returns from the substantial investment that goes into purchasing and setting up the machine. Recall the point on economies of scale – metal forming operations are financially viable only if one single tool produces large number of parts.
You may need to store completed parts for as long as six months. And storage conditions are far from ideal. This is why forming fluids need to possess corrosion inhibiting properties.
Types of metal forming fluids include:
- Emulsified / Soluble Oils
- Neat Oils
- Semi Synthetic Fluids
- Synthetic Fluids
Metal forming fluids are diverse and so are their applications. Formulating them is therefore a specialized task. The formulator needs to understand the process thoroughly – particularly what happens to the part before and after the process.
Presently, shop operators ask for substitutes to the widely used phosphorous-and-soap-based cold metal forming coatings. Using these fluids is a multi-stage, cumbersome process that leaves behind wastes.
But you cannot change the lubricant in isolation. Changing it entails rectifications in the entire set up – equipment, maintenance, operator training, and a rethink of the pre and post process issues related to the fresh process.
With a view to boost fuel efficiency and strength while lowering energy use and weight, the aerospace, automotive, and energy sectors are increasingly using lighter yet stronger metals such as aluminum, titanium, magnesium, and magnesium alloys.
Such a shifting landscape calls on the formulators to conduct research in close collaboration with original equipment manufacturers, universities, and press and die makers during the development of novel processes, not after.
With globalization spreading at the rate of knots, such research must be international in scope and reach. Plus, formulators will need to understand which fluids do not work – merely understanding which fluids work won’t suffice.
Let us examine a couple of metal forming processes hungry for refined forming fluids:
- Deep Drawing of steel is particularly challenging because the surface area doubles or even triples during operations. In deep drawing, metals are typically drawn to depths greater than the diameter of the punch
Operators normally use emulsifiable fluids and neat oils with high pressure additives for deep drawing of steel. Such additives are redundant for the process uses hydrodynamic lubrication
In order to comply with more stringent regulations and in the interest of better corrosion protection and clean-ability, operators are migrating away from neat oils and chlorinated-paraffin-based forming fluids
The sticking point will be the areas on the die under consistently extreme pressure
- Hot Forging is another area seeking change, to move over from using graphite-based lubricants. Steel is typically hot forged between 1,1500C (2,1000F) and 1,2900C (2,3500C)
Such high temperatures lower the die’s useful life, disturb part dimensions, and spoil surface finish. Graphite is the standard lubricant in hot forging because it is inert at high temperatures and offers excellent friction control
While graphite remains the best lubricant, operators wanting to improve plant hygiene seek non-graphite based lubricants
Testing of Metal Forming fluids
Friction testing of metal forming fluids is a critical step in the evaluation of their efficacy. Formulators study the intricate interactions between the fluid, the workpiece, and the tool. Such tests can be:
- Bench Tests analyze the fundamentals of the entire range of interactions involved in lubrication. These are more useful in that their results are more extendable
Twist Compression Test is one such trial. It measures the torque transmitted between a lubricated sheet and a rotating cylinder, the latter functioning as the tool. You can use diverse combinations of the lubricant, tool, and sheet metal
- Simulation Tests such as the Drawbead Simulator Procedure study process variables. Although you can extend the results to actual operations, these results are process-specific. You cannot apply the test results of one forming operation to another
These days, change management is a buzzword in all walks of life simply because things are changing at breakneck speed. Change is the only certainty. Manufacturers look to continuously cut wastes and use better materials in order to improve production and energy efficiency.
And because all process variables are interwoven into a complex web of relationships, changing one will necessitate changes in others. Formulators of forming fluids have a mountain to climb. Thankfully, we have efficient devices such as lubricant roller application systems.
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