HIMMA P4/TMM

For the process that creates volcanic rock, see Extrusive (geology).

Extruded aluminium with several hollow cavities; slots allow bars to be joined with special connectors.

Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section. The two main advantages of this process over other manufacturing processes are its ability to create very complex cross-sections and work materials that are brittle, because the material only encounters compressive and shear stresses. It also forms finished parts with an excellent surface finish.^[1]
Extrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous (producing many pieces). The extrusion process can be done with the material hot or cold.
Commonly extruded materials include metals, polymers, ceramics, concrete and foodstuffs.
Hollow cavities within extruded material cannot be produced using a simple flat extrusion die, because there would be no way to support the center barrier of the die. Instead, the die assumes the shape of a block with depth, beginning first with a shape profile that supports the center section. The die shape then internally changes along its length into the final shape, with the suspended center pieces supported from the back of the die.

History

In 1797, Joseph Bramah patented the first extrusion process for making lead pipe. It involved preheating the metal and then forcing it through a die via a hand driven plunger. The process wasn't developed until 1820 when Thomas Burr constructed the first hydraulic powered press. At this time the process was called squirting. In 1894, Alexander Dick expanded the extrusion process to copper and brass alloys.^[2]

Process

Extrusion of a round blank through a die.

The process begins by heating the stock material (for hot or warm extrusion). It is then loaded into the container in the press. A dummy block is placed behind it where the ram then presses on the material to push it out of the die. Afterward the extrusion is stretched in order to straighten it. If better properties are required then it may be heat treated or cold worked.^[2]
The extrusion ratio is defined as the starting cross-sectional area divided by the cross-sectional area of the final extrusion. One of the main advantages of the extrusion process is that this ratio can be very large while still producing quality parts.

Hot extrusion

Hot extrusion is a hot working process, which means it is done above the material's recrystallization temperature to keep the material from work hardening and to make it easier to push the material through the die. Most hot extrusions are done on horizontal hydraulic presses that range from 230 to 11,000 metric tons (250 to 12,000 short tons). Pressures range from 30 to 700 MPa (4,400 to 100,000 psi), therefore lubrication is required, which can be oil or graphite for lower temperature extrusions, or glass powder for higher temperature extrusions. The biggest disadvantage of this process is its cost for machinery and its upkeep.^[1]

Hot extrusion temperature for various metals^[1]
Material	Temperature [°C (°F)]
Magnesium	350-450 (650-850)
Aluminium	350-500 (650-900)
Copper	600-1100 (1200-2000)
Steel	1200-1300 (2200–2400)
Titanium	700-1200 (1300-2100)
Nickel	1000-1200 (1900–2200)
Refractory alloys	up to 2000 (4000)

The extrusion process is generally economical when producing between several kilograms (pounds) and many tons, depending on the material being extruded. There is a crossover point where roll forming becomes more economical. For instance, some steels become more economical to roll if producing more than 20,000 kg (50,000 lb).^[2]

Aluminium hot extrusion die
Front side of a four family die. For reference, the die is 228 mm (9.0 in) in diameter.
Close up of the shape cut into the die. Notice that the walls are drafted and that the back wall thickness varies.
Back side of die. The wall thickness of the extrusion is 3 mm (0.12 in).

Cold extrusion

Cold extrusion is done at room temperature or near room temperature. The advantages of this over hot extrusion are the lack of oxidation, higher strength due to cold working, closer tolerances, good surface finish, and fast extrusion speeds if the material is subject to hot shortness.^[1]
Materials that are commonly cold extruded include: lead, tin, aluminum, copper, zirconium, titanium, molybdenum, beryllium, vanadium, niobium, and steel.
Examples of products produced by this process are: collapsible tubes, fire extinguisher cases, shock absorber cylinders, automotive pistons, and gear blanks.

Warm extrusion

Warm extrusion is done above room temperature, but below the recrystallization temperature of the material the temperatures ranges from 800 to 1800 °F (424 to 975 °C). It is usually used to achieve the proper balance of required forces, ductility and final extrusion properties.^[3]

Equipment

A horizontal hydraulic press for hot aluminum extrusion (loose dies and scrap visible in foreground)

There are many different variations of extrusion equipment. They vary by four major characteristics:^[1]

Movement of the extrusion with relation to the ram. If the die is held stationary and the ram moves towards it then its called "direct extrusion". If the ram is held stationary and the die moves towards the ram its called "indirect extrusion".
The position of the press, either vertical or horizontal.
The type of drive, either hydraulic or mechanical.
The type of load applied, either conventional (variable) or hydrostatic.

A single or twin screw auger, powered by an electric motor, or a ram, driven by hydraulic pressure (often used for steel and titanium alloys), oil pressure (for aluminum), or in other specialized processes such as rollers inside a perforated drum for the production of many simultaneous streams of material.
Typical extrusion presses cost more than $100,000, whereas dies can cost up to $2000.

Forming internal cavities

Two-piece aluminum extrusion die set (parts shown separated.) The male part (at right) is for forming the internal cavity in the resulting round tube extrusion.

There are several methods for forming internal cavities in extrusions. One way is to use a hollow billet and then use a fixed or floating mandrel. A fixed mandrel, also known as a German type, means it is integrated into the dummy block and stem. A floating mandrel, also known as a French type, floats in slots in the dummy block and aligns itself in the die when extruding. If a solid billet is used as the feed material then it must first be pierced by the mandrel before extruding through the die. A special press is used in order to control the mandrel independently from the ram.^[1] The solid billet could also be used with a spider die, porthole die or bridge die. All of these types of dies incorporate the mandrel in the die and have "legs" that hold the mandrel in place. During extrusion the metal divides and flows around the legs, leaving weld lines in the final product.^[4]

Direct extrusion

Plot of forces required by various extrusion processes.

Direct extrusion, also known as forward extrusion, is the most common extrusion process. It works by placing the billet in a heavy walled container. The billet is pushed through the die by a ram or screw. There is a reusable dummy block between the ram and the billet to keep them separated. The major disadvantage of this process is that the force required to extrude the billet is greater than that need in the indirect extrusion process because of the frictional forces introduced by the need for the billet to travel the entire length of the container. Because of this the greatest force required is at the beginning of process and slowly decreases as the billet is used up. At the end of the billet the force greatly increases because the billet is thin and the material must flow radially to exit the die. The end of the billet (called the butt end) is not used for this reason.^[5]

Indirect extrusion

In indirect extrusion, also known as backwards extrusion, the billet and container move together while the die is stationary. The die is held in place by a "stem" which has to be longer than the container length. The maximum length of the extrusion is ultimately dictated by the column strength of the stem. Because the billet moves with the container the frictional forces are eliminated. This leads to the following advantages:^[6]

A 25 to 30% reduction of friction, which allows for extruding larger billets, increasing speed, and an increased ability to extrude smaller cross-sections
There is less of a tendency for extrusions to crack because there is no heat formed from friction
The container liner will last longer due to less wear
The billet is used more uniformly so extrusion defects and coarse grained peripherals zones are less likely.

The disadvantages are:^[6]

Impurities and defects on the surface of the billet affect the surface of the extrusion. These defects ruin the piece if it needs to be anodized or the aesthetics are important. In order to get around this the billets may be wire brushed, machined or chemically cleaned before being used.
This process isn't as versatile as direct extrusions because the cross-sectional area is limited by the maximum size of the stem.

Hydrostatic extrusion

In the hydrostatic extrusion process the billet is completely surrounded by a pressurized liquid, except where the billet contacts the die. This process can be done hot, warm, or cold, however the temperature is limited by the stability of the fluid used. The process must be carried out in a sealed cylinder to contain the hydrostatic medium. The fluid can be pressurized two ways:^[6]

Constant-rate extrusion: A ram or plunger is used to pressurize the fluid inside the container.
Constant-pressure extrusion: A pump is used, possibly with a pressure intensifier, to pressurize the fluid, which is then pumped to the container.

The advantages of this process include:^[6]

No friction between the container and the billet reduces force requirements. This ultimately allows for faster speeds, higher reduction ratios, and lower billet temperatures.
Usually the ductility of the material increases when high pressures are applied.
An even flow of material.
Large billets and large cross-sections can be extruded.
No billet residue is left on the container walls.

The disadvantages are:^[6]

The billets must be prepared by tapering one end to match the die entry angle. This is needed to form a seal at the beginning of the cycle. Usually the entire billet needs to be machined to remove any surface defects.
Containing the fluid under high pressures can be difficult.

Drives

Most modern direct or indirect extrusion presses are hydraulically driven, but there are some small mechanical presses still used. Of the hydraulic presses there are two types: direct-drive oil presses and accumulator water drives.
Direct-drive oil presses are the most common because they are reliable and robust. They can deliver over 35 MPa (5000 psi). They supply a constant pressure throughout the whole billet. The disadvantage is that they are slow, between 50 and 200 mm/s (2–8 ips).^[7]
Accumulator water drives are more expensive and larger than direct-drive oil presses, and they lose about 10% of their pressure over the stroke, but they are much faster, up to 380 mm/s (15 ips). Because of this they are used when extruding steel. They are also used on materials that must be heated to very hot temperatures for safety reasons.^[7]
Hydrostatic extrusion presses usually use castor oil at pressure up to 1400 MPa (200 ksi). Castor oil is used because it has good lubricity and high pressure properties.^[8]

Extrusion defects

Surface cracking - When the surface of an extrusion splits. This is often caused by the extrusion temperature, friction, or speed being too high. It can also happen at lower temperatures if the extruded product temporarily sticks to the die.
Pipe - A flow pattern that draws the surface oxides and impurities to the center of the product. Such a pattern is often caused by high friction or cooling of the outer regions of the billet.
Internal cracking - When the center of the extrusion develops cracks or voids. These cracks are attributed to a state of hydrostatic tensile stress at the centerline in the deformation zone in the die. (A similar situation to the necked region in a tensile stress specimen)
Surface lines - When there are lines visible on the surface of the extruded profile. This depends heavily on the quality of the die production and how well the die is maintained, as some residues of the material extruded can stick to the die surface and produce the embossed lines.

Materials

Metal

Metals that are commonly extruded include:^[9]

Aluminium is the most commonly extruded material. Aluminium can be hot or cold extruded. If it is hot extruded it is heated to 575 to 1100 °F (300 to 600 °C). Examples of products include profiles for tracks, frames, rails, mullions, and heat sinks.
Copper (1100 to 1825 °F (600 to 1000 °C)) pipe, wire, rods, bars, tubes, and welding electrodes. Often more than 100 ksi (690 MPa) is required to extrude copper.
Lead and tin (maximum 575 °F (300 °C)) pipes, wire, tubes, and cable sheathing. Molten lead may also be used in place of billets on vertical extrusion presses.
Magnesium (575 to 1100 °F (300 to 600 °C)) aircraft parts and nuclear industry parts. Magnesium is about as extrudable as aluminum.
Zinc (400 to 650 °F (200 to 350 °C)) rods, bar, tubes, hardware components, fitting, and handrails.
Steel (1825 to 2375 °F (1000 to 1300 °C)) rods and tracks. Usually plain carbon steel is extruded, but alloy steel and stainless steel can also be extruded.
Titanium (1100 to 1825 °F (600 to 1000 °C)) aircraft components including seat tracks, engine rings, and other structural parts.

Magnesium and aluminium alloys usually have a 0.75 µm (30 μin) RMS or better surface finish. Titanium and steel can achieve a 3 micrometres (120 μin) RMS.^[1]
In 1950, Ugine Séjournet, of France, invented a process which uses glass as a lubricant for extruding steel.^[10] The Ugine-Sejournet, or Sejournet, process is now used for other materials that have melting temperatures higher than steel or that require a narrow range of temperatures to extrude. The process starts by heating the materials to the extruding temperature and then rolling it in glass powder. The glass melts and forms a thin film, 20 to 30 mils (0.5 to 0.75 mm), in order to separate it from chamber walls and allow it to act as a lubricant. A thick solid glass ring that is 0.25 to 0.75 in (6 to 18 mm) thick is placed in the chamber on the die to lubricate the extrusion as it is forced through the die. A second advantage of this glass ring is its ability to insulate the heat of the billet from the die. The extrusion will have a 1 mil thick layer of glass, which can be easily removed once it cools.^[3]
Another breakthrough in lubrication is the use of phosphate coatings. With this process, in conjunction with glass lubrication, steel can be cold extruded. The phosphate coat absorbs the liquid glass to offer even better lubricating properties.^[3]

Plastic

Sectional view of a plastic extruder showing the components

Main article: Plastics extrusion

Plastics extrusion commonly uses plastic chips or pellets, which are usually dried in a hopper before going to the feed screw. The polymer resin is heated to molten state by a combination of heating elements and shear heating from the extrusion screw. The screw forces the resin through a die, forming the resin into the desired shape. The extrudate is cooled and solidified as it is pulled through the die or water tank. In some cases (such as fibre-reinforced tubes) the extrudate is pulled through a very long die, in a process called pultrusion.
A multitude of polymers are used in the production of plastic tubing, pipes, rods, rails, seals, and sheets or films.

Ceramic

Ceramic can also be formed into shapes via extrusion. Terracotta extrusion is used to produce pipes. Many modern bricks are also manufactured using a brick extrusion process.^[11]

Food

Macaroni is an extruded hollow pasta.

This section requires expansion.

Extrusion has application in food processing. Products such as certain pastas, many breakfast cereals, Fig Newtons, premade cookie dough, Murukku, Sevai, Idiappam, jalebi, some french fries, certain baby foods, dry pet food and ready-to-eat snacks are mostly manufactured by extrusion. In the extrusion process, raw materials are first ground to the correct particle size (usually the consistency of coarse flour). The dry mix is passed through a pre-conditioner, where other ingredients are added (liquid sugar, fats, dyes, meats and water depending on the product being made), steam is injected to start the cooking process. The preconditioned mix is then passed through an extruder, and then forced through a die where it is cut to the desired length. The cooking process takes place within the extruder where the product produces its own friction and heat due to the pressure generated (10–20 bar). The process can induce both protein denaturation and starch gelatinization, depending on inputs and parameters. Extruders using this process have a capacity from 1–25 tonnes per hour depending on design.
As with other forms of cooking, extrusion achieves the following nutritionally:

Inactivation of raw food enzymes
Destruction of certain naturally occurring toxins
Diminishing of microorganisms in the final product
Slight increase of iron-bioavailability
Creation of insulin-desensitizing starches, which are a risk-factor for developing diabetes^[12]^[13]
Loss of the essential amino: lysine, which is essential to developmental growth and nitrogen management^[12]^[13]
Simplification of complex starches, increasing rates of tooth decay^[12]^[13]
Marked increase of processed foods' glycemic indexes^[12]^[13]
Destruction of Vitamin A (beta-carotene)^[12]^[13]

Extrusion is also used to modify starch and to pellet animal feed.

Drug carriers

This section requires expansion.

Extrusion through nano-porous, polymeric filters is being used to manufacture suspensions of lipid vesicles liposomes or Transfersomes for use in pharmaceutical products. The anti-cancer drug Doxorubicin in liposome delivery system is formulated by extrusion, for example.

Biomass briquettes

Main article: Biomass briquettes

The extrusion production technology of fuel briquettes is the process of extrusion screw wastes (straw, sunflower husks, buckwheat, etc.) or finely shredded wood waste (sawdust) under high pressure when heated from 160 to 350 °C. The resulting fuel briquettes do not include any of the binders, but one natural - the lignin contained in the cells of plant wastes. The temperature during compression, causes melting of the surface of bricks, making it more solid, which is important for the transportation of briquettes.

Design

The design of an extrusion profile has a large impact on how readily it can be extruded. The maximum size for an extrusion is determined by finding the smallest circle that will fit around the cross-section, this is called the circumscribing circle. This diameter, in turn, controls the size of the die required, which ultimately determines if the part will fit in a given press. For example, a larger press can handle 60 cm (24 in) diameter circumscribing circles for aluminium and 55 cm (22 in). diameter circles for steel and titanium.^[1]
The complexity of an extruded profile can be roughly quantified by calculating the shape factor, which is the amount of surface area generated per unit mass of extrusion. This affects the cost of tooling as well as the rate of production.^[14]
Thicker sections generally need an increased section size. In order for the material to flow properly legs should not be more than ten times longer than their thickness. If the cross-section is asymmetrical, adjacent sections should be as close to the same size as possible. Sharp corners should be avoided; for aluminium and magnesium the minimum radius should be 0.4 mm (1/64 in) and for steel corners should be 0.75 mm (0.030 in) and fillets should be 3 mm (0.12 in). The following table lists the minimum cross-section and thickness for various materials.^[1]

Material	Minimum cross-section [cm² (sq. in.)]	Minimum thickness [mm (in.)]
Carbon steels	2.5 (0.40)	3.00 (0.120)
Stainless steel	3.0-4.5 (0.45-0.70)	3.00-4.75 (0.120-0.187)
Titanium	3.0 (0.50)	3.80 (0.150)
Aluminium	<2.5 (0.40)	1.00 (0.040)
Magnesium	<2.5 (0.40)	1.00 (0.040)

Tool and die makers are workers in the manufacturing industry who make jigs, fixtures, dies, molds, machine tools, cutting tools (such as milling cutters and form tools), gauges, and other tools used in manufacturing processes.^[1] Depending on which area of concentration a particular person works in, he or she may be called by variations on the name, including tool maker (toolmaker), die maker (diemaker), mold maker (moldmaker), tool fitter (toolfitter), etc.

Tool and die makers are a class of machinists who work primarily in toolroom environments—sometimes literally in one room but more often in an environment with flexible, semipermeable boundaries from production work. They are skilled artisans (craftspeople) who typically learn their trade through a combination of academic coursework and hands-on instruction, with a substantial period of on-the-job training that is functionally an apprenticeship (although usually not nominally today). Art and science (specifically, applied science) are thoroughly intermixed in their work, as they also are in engineering. Mechanical engineers and tool and die makers often work in close consultation. There is often turnover between the careers, as one person may end up working in both at different times of their life, depending on the turns of their particular educational and career path. (In fact, there was no codified difference between them during the 19th century; it was only after World War II that engineering became a profession exclusively defined by a university or college engineering degree.) Both careers require some level of talent in both artistic/artisanal/creative areas and math-and-science areas. Job-shop machinists can be any combination of toolmaker and production machinist. Some work only as machine operators, whereas others switch fluidly between toolroom tasks and production tasks.

Job description

Traditionally, working from engineering drawings, tool makers marked out the design on the raw material (usually metal or wood), then cut it to size and shape using manually controlled machine tools (such as lathes, milling machines, grinding machines, jig borers, and jig grinders) and hand tools (such as files). Many tool makers now use computer-aided design , computer-aided manufacturing and CNC machine tools to perform these tasks.

Tool making

Tool making typically means making tooling used to produce products. Common tools include metal forming rolls, lathe bits, milling cutters, and form tools. Tool making may also include precision fixturing or machine tools used to manufacture, hold, or test products during their fabrication. Due to the unique nature of a tool maker's work, it is often necessary to fabricate custom tools or modify standard tools.

Die making

Main article: die (manufacturing)

Die making is a subgenre of tool making that focuses on making and maintaining dies. This often includes making punches, dies, steel rule dies, and die sets. Precision is key in die making; punches and dies must maintain proper clearance to produce parts accurately, and it is often necessary to have die sets machined with tolerances of less than one thousandth of an inch.

Overlap

One person may be called upon for all of the above activities, and the skills and concepts involved overlap, which is why "tool and die making" is often viewed as one field.

Training

Although the details of training programs vary, many tool and die makers begin an apprenticeship with an employer, possibly including a mix of classroom training and hands-on experience. Some prior qualifications in mathematics, science, engineering or design and technology can be valuable. Many tool and die makers attend a 4- to 5-year apprenticeship program to achieve the status of a journeyman tool and die maker. Today's employment relationships often differ in name and detail from the traditional arrangement of an apprenticeship, and the terms "apprentice" and "journeyman" are not always used, but the idea of a period of years of on-the-job training leading to mastery of the field still applies.

Job outlook

Employment of tool and die makers is expected to decline in some countries due to offshoring and to increased use of automation, including CNC machine tools and computer-aided technologies such as CAD/CAM. On the other hand, tool and die makers play a key role in building and maintaining advanced automated manufacturing equipment. The job market for tool and die workers today tends to look like several other modern job markets, which is part intense competition based on talent and experience and part fateful musical chairs. There is a degree of structural unemployment involved, as employers can't find instantiations of their ideal candidates at the same time that most workers can't find jobs that they qualify for. As elsewhere in IT-rich fields of automated machinery and robotics, there are dualities—on one hand, there is the apparent promise of great need for people to design, build, repair, or maintain highly automated systems including robots; but on the other hand, there are the ideas that it only takes so many human robot builders to make an army of robots (especially as software begins helping to design and build more robots), and that most humans are nowhere close to having the formidable stack of multidisciplinary skills needed to get such jobs, anyway. The few that are will increasingly face global competition, meaning that large differences in standard of living between worker populations will probably undergo rational equilibration in coming decades, like electrical potential differences formerly insulated and now in contact.

Jig maker

A jig maker is another term for a tool and die maker or fixture maker, usually in woodworking or in the metal industries. Actually a jig is what mounts onto a work piece, and a fixture has the work piece placed on it, into, or next to it. The terms are used interchangeably though throughout industry. A jig maker needs to know how to use an assortment of machines to build devices used in automation, robotics, welding, tapping, and mass production operations.

They are often advised by an engineer to do the pre- planned work of building the much needed devices. In a production shop they need to know about an extensive assortment of machines, tools, and materials, and are often the most experienced toolmakers or woodworkers. They are often the ones who create from the original plans, the jigs, the fixtures and devices designed by and with the occasional assistance of the production engineer.

The reason jig makers need to be experienced is so that they can make suggestions for efficient alterations and needed repairs. They sometimes assist and monitor the progress of the jig or the fixture's gauging, locating, and innovative ability. Those who graduate to the level of jig and fixture makers often go on to gain automation skills, and the use of air, and electronic clamping procedures, and automation principles and equipment. They often need to know not only how to use basic machines to cut and machine steel and wood. For the most advanced, they need to be familiar with switches and the use of air supply equipment, various instruments, switches, hydraulic clamps, gauges, and more.

Properly built jigs and fixtures reduces waste, and produce perfect fitting parts, cutting out too much expensive hand work, mistakes and waste. Most are portable, and can be built or even moved throughout a facility. Some jigs and fixtures are as big as a car for placing a whole fender or chassis into them for assembly. It is how every volume shop works. The need for jigs and good gauging is necessary in furniture making for controlling quality and repeatability. A jig maker focuses on building tools in order to avoid placing parts incorrectly.

P4 I 2010

We are young and this is our challenge

Written By P4 polman astra on Kamis, 11 Oktober 2012 | Kamis, Oktober 11, 2012

OUR ACTIVITY IN CAMPUS

Extrusion

Written By P4 polman astra on Selasa, 31 Mei 2011 | Selasa, Mei 31, 2011

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