Friday, November 28, 2014

Part production with metal atamping

Vortool Manufacturing Ltd. offers practical metal stamping part production solutions to set up part production at your facility or deliver final products to you.

All metal stamping part production solution process developments include planned quality control to have a peace of mind of a consistent product flow, therefore eliminating faulty parts if they do exist and removing them before they reach your customers.

Unit 240 19358-96 Ave.
Surrey, BC V4N 4C1

Call: 604-239-7218

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Wednesday, October 29, 2014

Modular press using multiple punch stations

The modular press using multiple punch station product line by Vortool Manufacturing Ltd. contain a number of individual (portable) presses that are linked together and activated as one.

• For generic or budget oriented projects C frame presses are the most suitable.

• Other models may be used as well as custom solutions that are designed for the specific need of the process.

• Modular presses are excellent to process aluminum extrusions with great lengths and multiple holes, slots, etc. to be punched at once at the full length of the extrusion.

• The process time is minimal, compared to conventional methods where individual holes had to be drilled or punched one at a time. The quality is more predictable and repeatable.

• Multi axis power unit mounts are available to work horizontally or in an angle within the same machine.

• Drilling units can be also used to work along with the cylinders.

• Extrusion positioning and clamping can be automated. The function can be monitored by a PLC to ensure trouble free operation and keep the required quality under control.

• Safety devices may be installed, depending of your company or government requirements.

Unit 240 19358-96 Ave.
Surrey, BC V4N 4C1

Call: 604-239-7218

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Sunday, October 12, 2014

Non marking close space U shape bend with ready bender

Ready Bender - Non Marking Double Bend Part

Non Marking Close Space U Shape Bend with Ready Bender

Ready benders can replace any wipe bending method. The rotary motion is transferred from the press’ vertical motion and allows over bend past 90 degree to compensate material spring back.

This non marking method holds consistent angle tolerances and suitable for high volume production running at 250 spm. Other advantages include reduced tonnage requirements by 50 to 80%. In tooling, adjustments make it superior to wipe tooling. Tool trials and tweaking time is eliminated to a minimum, saving valuable set up time.

Unit 240 19358-96 Ave.
Surrey, BC V4N 4C1

Call: 604-239-7218

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Ball bearing guided high precision progressive metal stamping tool and die for high speed automated production

The picture shows the bottom die set and 
some of its components are being inspected,
aligned and assembled.

Ball Bearing Guided High Precision Progressive Tool for High Speed Automated Production

Stamped metal parts usually require more than one operation in one. This progressive metal stamping tool produces a high volume mounting bracket that pierces holes, blanks out a shape by cutting the strip into separate parts and finally folds the part into an L shape. At each hit a final product falls off at the end of the tool. It is made for a high production automated punch press using coil and an air feeder for continuous operation.

This progressive die design consists all the necessary features that any stamping tool should have from ease of use through high accuracy to reliable operation for a long time. It includes strip feed and guide, stripping, slug separation, and feeder actuation. As an option the tool can be used as a manually operated tool without the air feeder using strips instead of coil.

The cutting components are designed to be made of hardened tool steel that ensures the long usability. Choosing the right alloy for the application and the proper design of the tool can greatly effect the life of the tool. As a result it can operate trouble free for longer, saving on maintenance. It can also reduce or eliminate downtime and minimize costs that are associated with the value of the final product.

The progressive tooling was designed using SolidWorks 3D CAD. Shop drawings, and files generated from the models are seamlessly fit into any machine shop or tool room's profile.

Unit 240 19358-96 Ave.
Surrey, BC V4N 4C1

Call: 604-239-7218

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Metal stamping die design advance documentation with QR code

• QR Codes: Vortool Manufacturing QR codes contain valuable information for manufacturing purposes. The tool room or machine shop may have additional information that could possibly be put on a CAD drawing. The web based pages include images to fully explain how and what is intended to be done, and your input may also be included in the pages.
The QR codes if any, are printed on the actual shop drawings and can be accessed by using e.g. a smart phone with a QR reader. It is a visual and verbal extension of the CAD drawing or its part and or the assemblies.
The sample part drawing has many different holes that the CNC programmer will have difficulties to identify from the drawing. The additional web page has images with colour coded holes to visually identify all holes. The additional information possibilities are endless and can generally answer questions that the machinists are generally looking for.

Bottom Die Shoe Plate Document
Features on drawings, such as holes could be confusing for the programmer using MasterCAM or similar software to generate paths and then NC files to CNC machine the parts. On this example, there is a plate with a number of different holes, like dowel holes, tapped and counter bored holes, etc.
To keep the drawing clutter free yet provide enough information is not always possible. The larger the work piece and or more holes to be processed, mistakes can be easily made. The 3D model’s holes were assigned with different colours, then a web page was created with a color code chart to Identify the holes.
A QR code was generated from the web page and was placed on the drawing. The machinist can scan the code with a smart phone and have an instant answer of the ongoing questions about the type of holes to be made. You may not think it is a big deal but if you know that e.g. MasterCam does not recognize the tapped holes as a feature, than you will find this visual aid invaluable. The designer can have additional images, notes, etc. attached to the web page or pages to have instructions available at hand at all times.
To take a test drive and see how it works, scan the code with a QR code reader (free app for your phone) or download the print and then scan it. Once scanned, the web page automatically opens to view.

Unit 240 19358-96 Ave.
Surrey, BC V4N 4C1

Call: 604-239-7218

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Friday, January 17, 2014

SolidWorks 3D CAD tutoring, Vancouver, BC

Solidworks Training Courses
• Refreshing course for beginners or for experienced users
• Introduction to SolidWorks (for beginners)
• SolidWorks for experienced users

You can generate drawing files and prints that trades people can read and than manufacture actual components.

SolidWorks files are also the base for creating specific program files by others to communicate directly with different type of CNC machines.

It is also the base to generate actual 3D prototype parts or complex assemblies for 3D printers.

Learn more about Solidworks Tutoring.

Unit 240 19358-96 Ave.
Surrey, BC V4N 4C1

Call: 604-239-7218

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A metal (from Greek "μέταλλον" – métallon, "mine, quarry, metal" is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light. In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by de-localized electrons, which are responsible for the conductivity. The solid thus produced is held by electrostatic interactions between the ions and the electron cloud, which are called metallic bonds.

Main article: Metallicity

Metals are sometimes described as an arrangement of positive ions surrounded by a sea of delocalized electrons. Metals occupy the bulk of the periodic table, while non-metallic elements can only be found on its right-hand side. A diagonal line, drawn from boron (B) to polonium (Po), separates the metals from the nonmetals. Most elements on this line are metalloids, sometimes called semiconductors. This is because these elements exhibit electrical propertiescommon to both conductors and insulators. Elements to the lower left of this division line are called metals, while elements to the upper right of the division line are called nonmetals.

An alternative definition of metal refers to the band theory. If one fills the energy bands of a material with available electrons and ends up with a top band partly filled then the material is a metal. This definition opens up the category for metallic polymers and other organic metals. These synthetic materials often have the characteristic silvery gray reflectiveness (luster) of elemental metals.

In the specialized usage of astronomy and astrophysics, the term "metal" is often used to refer collectively to all elements other than hydrogen or helium, including substances as chemically non-metallic as neon, fluorine, and oxygen. Nearly all the hydrogen and helium in the Universe was created in Big Bang nucleosynthesis, whereas all the "metals" were produced by nucleosynthesis in stars or supernovae. The Sun and the Milky Way Galaxy are composed of roughly 74% hydrogen, 24% helium, and 2% "metals" (the rest of the elements; atomic numbers 3–118) by mass.

The concept of a metal in the usual chemical sense is irrelevant in stars, as the chemical bonds that give elements their properties cannot exist at stellar temperatures.

Metals are usually inclined to form cations through electron loss, reacting with oxygen in the air to form oxides over changing timescales (iron rusts over years, while potassium burns in seconds). Examples:4 Na + O2 → 2 Na2O (sodium oxide)2 Ca + O2 → 2 CaO (calcium oxide)4 Al + 3 O2 → 2 Al2O3 (aluminium oxide).

The transition metals (such as iron, copper, zinc, and nickel) take much longer to oxidize. Others, like palladium, platinum and gold, do not react with the atmosphere at all. Some metals form a barrier layer of oxide on their surface which cannot be penetrated by further oxygen molecules and thus retain their shiny appearance and good conductivity for many decades (like aluminium, magnesium, some steels, and titanium). The oxides of metals are generally basic, as opposed to those of nonmetals, which are acidic.

Painting, anodizing or plating metals are good ways to prevent their corrosion. However, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two metals form an electrochemical cell, and if the coating is less reactive than the coatee, the coating actually promotes corrosion.

Gallium crystals
Metals in general have high electrical conductivity which depends on their valency of ions, thermal conductivity, luster and density, and the ability to be deformed under stress without cleaving. While there are several metals that have low density, hardness, and melting points, these (the alkali and alkaline earth metals) are extremely reactive, and are rarely encountered in their elemental, metallic form. Optically speaking, metals are opaque, shiny and lustrous. This is because visible lightwaves are not readily transmitted through the bulk of their microstructure. The large number of mobile electrons in any typical metallic solid (element or alloy) is responsible for the fact that they can never be categorized as transparent materials.

The majority of metals have higher densities than the majority of nonmetals. Nonetheless, there is wide variation in the densities of metals; lithium is the least dense solid element and osmium is the densest. The metals of groups I A and II A are referred to as the light metals because they are exceptions to this generalization. The high density of most metals is due to the tightly packed crystal lattice of the metallic structure. The strength of metallic bonds for different metals reaches a maximum around the center of the transition metal series, as those elements have large amounts of delocalized electrons in tight binding type metallic bonds. However, other factors (such as atomic radius, nuclear charge, number of bonding orbitals, overlap of orbital energies, and crystal form) are involved as well. Most non-ferrous metals can be recycled many times during their life cycle.

The electrical and thermal conductivity of metals originate from the fact that in the metallic bond, the outer electrons of the metal atoms form a gas of nearly free electrons, moving as an electron gas in a background of positive charge formed by the ion cores. Good mathematical predictions for electrical conductivity, as well as the electrons' contribution to the heat capacity and heat conductivity of metals can be calculated from the free electron model, which does not take the detailed structure of the ion lattice into account.

When considering the exact band structure and binding energy of a metal, it is necessary to take into account the positive potential caused by the specific arrangement of the ion cores – which is periodic in crystals. The most important consequence of the periodic potential is the formation of a small band gap at the boundary of the Brillouin zone. Mathematically, the potential of the ion cores can be treated by various models, the simplest being the nearly free electron model.

Mechanical properties of metals include ductility, which is largely due to their inherent capacity for plastic deformation. Reversible elastic deformation in metals can be described by Hooke's Law for restoring forces, where the stress is linearly proportional to the strain. Forces larger than the elastic limit, or heat, may cause a permanent (irreversible) deformation of the object, known as plastic deformation or plasticity. This irreversible change in atomic arrangement may occur as a result of:

The action of an applied force (or work). An applied force may be tensile (pulling) force, compressive (pushing) force, shear, bending or torsion (twisting) forces.

A change in temperature (heat). A temperature change may affect the mobility of the structural defects such as grain boundaries, point vacancies, line and screw dislocations, stacking faults and twins in both crystalline and non-crystalline solids. The movement or displacement of such mobile defects is thermally activated, and thus limited by the rate of atomic diffusion.

Hot metal work from a blacksmith.
Viscous flow near grain boundaries, for example, can give rise to internal slip, creep and fatigue in metals. It can also contribute to significant changes in the microstructure like grain growth and localized densification due to the elimination of intergranular porosity. Screw dislocations may slip in the direction of any lattice plane containing the dislocation, while the principal driving force for "dislocation climb" is the movement or diffusion of vacancies through a crystal lattice.

In addition, the nondirectional nature of metallic bonding is also thought to contribute significantly to the ductility of most metallic solids. When the planes of an ionic bond slide past one another, the resultant change in location shifts ions of the same charge into close proximity, resulting in the cleavage of the crystal; such shift is not observed in covalently bonded crystals where fracture and crystal fragmentation occurs.

An alloy is a mixture of two or more elements in solid solution in which the major component is a metal. Most pure metals are either too soft, brittle or chemically reactive for practical use. Combining different ratios of metals as alloys modifies the properties of pure metals to produce desirable characteristics. The aim of making alloys is generally to make them less brittle, harder, resistant to corrosion, or have a more desirable color and luster. Of all the metallic alloys in use today, the alloys of iron (steel, stainless steel, cast iron, tool steel, alloy steel) make up the largest proportion both by quantity and commercial value. Iron alloyed with various proportions of carbon gives low, mid and high carbon steels, with increasing carbon levels reducing ductility and toughness. The addition of silicon will produce cast irons, while the addition of chromium, nickel and molybdenum to carbon steels (more than 10%) results in stainless steels.

Other significant metallic alloys are those of aluminium, titanium, copper and magnesium. Copper alloys have been known since prehistory—bronze gave the Bronze Age its name—and have many applications today, most importantly in electrical wiring. The alloys of the other three metals have been developed relatively recently; due to their chemical reactivity they require electrolytic extraction processes. The alloys of aluminium, titanium and magnesium are valued for their high strength-to-weight ratios; magnesium can also provide electromagnetic shielding. These materials are ideal for situations where high strength-to-weight ratio is more important than material cost, such as in aerospace and some automotive applications.

Alloys specially designed for highly demanding applications, such as jet engines, may contain more than ten elements.

Zinc, a base metal, reacting with an acid
In chemistry, the term base metal is used informally to refer to a metal that oxidizes or corrodes relatively easily, and reacts variably with dilute hydrochloric acid (HCl) to form hydrogen. Examples include iron, nickel, lead and zinc. Copper is considered a base metal as it oxidizes relatively easily, although it does not react with HCl. It is commonly used in opposition to noble metal.

In alchemy, a base metal was a common and inexpensive metal, as opposed to precious metals, mainly gold and silver. A longtime goal of the alchemists was the transmutation of base metals into precious metals.

In numismatics, coins used to derive their value primarily from the precious metal content. Most modern currencies are fiat currency, allowing the coins to be made of base metal.

The term "ferrous" is derived from the Latin word meaning "containing iron". This can include pure iron, such as wrought iron, or an alloy such as steel. Ferrous metals are often magnetic, but not exclusively.

Noble metals are metals that are resistant to corrosion or oxidation, unlike most base metals. They tend to be precious metals, often due to perceived rarity. Examples include gold, platinum, silver and rhodium.

A gold nugget
Main article: Precious metal
A precious metal is a rare metallic chemical element of high economic value.

Chemically, the precious metals are less reactive than most elements, have high luster and high electrical conductivity. Historically, precious metals were important as currency, but are now regarded mainly as investment and industrial commodities. Gold, silver, platinum and palladium each have an ISO 4217 currency code. The best-known precious metals are gold and silver. While both have industrial uses, they are better known for their uses in art, jewelry, and coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely traded.

The demand for precious metals is driven not only by their practical use, but also by their role as investments and a store of value. Palladium was, as of summer 2006, valued at a little under half the price of gold, and platinum at around twice that of gold. Silver is substantially less expensive than these metals, but is often traditionally considered a precious metal for its role in coinage and jewelry.

Metals are often extracted from the Earth by means of mining, resulting in ores that are relatively rich sources of the requisite elements. Ore is located by prospecting techniques, followed by the exploration and examination of deposits. Mineral sources are generally divided into surface mines, which are mined by excavation using heavy equipment, and subsurface mines.

Once the ore is mined, the metals must be extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometallurgy employs aqueous chemistry for the same purpose. The methods used depend on the metal and their contaminants.

When a metal ore is an ionic compound of that metal and a non-metal, the ore must usually be smelted — heated with a reducing agent — to extract the pure metal. Many common metals, such as iron, are smelted using carbon as a reducing agent. Some metals, such as aluminium and sodium, have no commercially practical reducing agent, and are extracted using electrolysis instead

Sulfide ores are not reduced directly to the metal but are roasted in air to convert them to oxides.

Demand for metals is closely linked to economic growth. During the 20th century, the variety of metals uses in society grew rapidly. Today, the development of major nations, such as China and India, and advances in technologies, are fuelling ever more demand. The result is that mining activities are expanding, and more and more of the world’s metal stocks are above ground in use, rather than below ground as unused reserves. An example is the in-use stock of copper. Between 1932 and 1999, copper in use in the USA rose from 73g to 238g per person.

Metals are inherently recyclable, so in principle, can be used over and over again, minimizing these negative environmental impacts and saving energy at the same time. For example, 95% of the energy used to make aluminium from bauxite ore is saved by using recycled material. However, levels of metals recycling are generally low. In 2010, the International Resource Panel, hosted by the United Nations Environment Programme (UNEP) published reports on metal stocks that exist within society and their recycling rates.

The report authors observed that the metal stocks in society can serve as huge mines above ground. However, they warned that the recycling rates of some rare metals used in applications such as mobile phones, battery packs for hybrid cars and fuel cells are so low that unless future end-of-life recycling rates are dramatically stepped up these critical metals will become unavailable for use in modern technology.

Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys.

Some metals and metal alloys possess high structural strength per unit mass, making them useful materials for carrying large loads or resisting impact damage. Metal alloys can be engineered to have high resistance to shear, torque and deformation. However the same metal can also be vulnerable to fatigue damage through repeated use or from sudden stress failure when a load capacity is exceeded. The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many appliances, tools, pipes, non-illuminated signs and railroad tracks.

The two most commonly used structural metals, iron and aluminium, are also the most abundant metals in the Earth's crust.

Metals are good conductors, making them valuable in electrical appliances and for carrying an electric current over a distance with little energy lost. Electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for the most part, are wired with copper wire for its good conducting properties.

The thermal conductivity of metal is useful for containers to heat materials over a flame. Metal is also used for heat sinks to protect sensitive equipment from overheating.

The high reflectivity of some metals is important in the construction of mirrors, including precision astronomical instruments. This last property can also make metallic jewelry aesthetically appealing.

Some metals have specialized uses; radioactive metals such as uranium and plutonium are used in nuclear power plants to produce energy via nuclear fission. Mercury is a liquid at room temperature and is used in switches to complete a circuit when it flows over the switch contacts. Shape memory alloy is used for applications such as pipes, fasteners and vascular stents.

Article by Wikipedia

EDM Basics

Understanding the Wire EDM Process
An amazing process offers equally amazing benefits

Wire EDM is extremely accurate. Many machines move in increments of 40 millionths of an inch (0.000 04´´), some in 10 millionths of an inch (.000 01´´), and others even in 4 millionths of an inch (.000 004´´).

Wire EDMing produces a smooth finish because the wire electrode goes through the entire part.

Machines can achieve accuracies of ±0.0001´´. Skim cuts are made to obtain such tolerances.

Extremely fine finishes of below 15 RMS can be produced with wire EDM. (Some machines can produce even a mirror finish.) Wire EDM produces an excellent finish even in the so-called "rough cut." Customers are often amazed when shown the fine finish of a single-pass cut.

This fine finish is present even after very large parts are cut. In other cutting operations, such as lasers and abrasive water jet, the larger the part, the rougher the finish. Wire EDM produces a smooth finish because the wire electrode goes through the entire part, and spark erosion occurs along the entire wire electrode.

Wire Path
The wire never contacts the workpiece. The wire electrode cuts by means of spark erosion, leaving a path slightly larger than the wire. A commonly used wire, 0.012´´, usually creates a 0.015´´ to 0.016´´ kerf. Thinner wires have smaller kerfs.

When the wire turns a corner, it can produce a sharp edge on the outside corner, but it will always leave a small radius on the inside corner. The size of this radius is determined by the wire diameter plus the spark gap.

To produce very sharp outside corners, skim cuts are made. Having small corner radii on the outside corners can prevent the need for skim cuts; this also reduces wire EDM costs. In stamping dies, sharp corners usually wear first, so a small outside radius is preferable.

The minimum inside radius for 0.012´´wire is 0.007´´, and the minimum radius for 0.10´´ wire is 0.006´´. Smaller radii are possible with thinner wire; however, most work is done with thicker wires because thinner wire cuts slower.

Skim Cutting
For most jobs, the initial cut is sufficient for both finish and accuracy. However, for precision parts, skim cuts achieve greater accuracy and a finer finish. There are three main reasons for skim cuts:

• barreling effect and wire trail-off,
• metal movement, and
• finishes and accuracy.

There is a 0.001´´ to 0.002´´ gap between the wire and the workpiece. In this gap, a controlled localized eruption takes place. The force of the spark and the gases trying to escape causes a slight barreling. On thick workpieces, this barreling causes the center to be slightly hollow.

When cutting sharp corners, the wire dwells longer by the inside radius, causing a slight overcut; on the outside radius, it speeds, leaving a slight undercut.

A trail-off is produced when the machine cuts a corner. A slight amount of material is left behind for a short distance before the wire returns to its programmed path. For most jobs, this slight undercut is negligible.

The sharper the corner, the greater the overcut and undercut. The accuracy of the part determines the need for skim cutting.

To avoid most of this barreling effect and wire trail-off, some wire EDM machines automatically slow down in corner cutting. Nevertheless, high precision parts still require skim cuts.

Even though metal has been stress relieved, it may move after the part has been cut with wire EDM because the stresses within the metal were not totally removed in stress relieving. If metal has moved due to inherent stresses, and the part requires to be precise, then skim cuts are needed to bring the part into tolerance. The accuracies called for by the print determine the number of skim cuts.

Finishes and Accuracy
First cuts produce a fine finish; however, sometimes a finer finish and greater accuracies are required. To accomplish this, skim cuts are used. (See the chart for a general view of the various finishes that can be produced with wire EDM. Some machines produce different results.)

Skim cutting produces fine finishes because less energy is applied to the wire, thereby creating smaller sparks and thus smaller cavities. These small sparks produce extremely fine finishes, and on some machines a mirror finish.

Tungsten carbide, third in hardness to diamond and boron carbide, is an extremely difficult material to machine. Except for diamond cutting tools and diamond-impregnated grinding wheels, EDM presents the only practical method to machine this hardened material.

To bind tungsten carbide when it is sintered, cobalt is added. The amount of cobalt, from 6% to 15%, determines the hardness and toughness of the carbide. The electrical conductivity of cobalt exceeds that of tungsten, so EDM erodes the cobalt binder in tungsten carbide. The carbide granules fall out of the compound during cutting, so the amount of cobalt binder determines the wire EDM speed, and the energy applied during the cutting determines the depth of binder that is removed.

When cutting carbide on certain wire EDM machines, the initial first cut can cause surface micro-cracks. To eliminate them, skim cuts are used. However, at our company, we have repeatedly cut carbide parts with a single cut. When precision carbide parts are needed, skim cuts are used.

Some older wire EDM machines used capacitors. Since these machines applied more energy into the cut, there was a greater danger for surface micro-cracking. Then DC power supply machines without capacitors were introduced, and this helped in producing less surface damage when cutting carbide.

Today, many machines come equipped with AC power supplies. These machines are especially beneficial when cutting carbide in that they produce smaller heat-affected zones and cause less cobalt depletion than DC power-supplied machines.

To eliminate any danger from micro-cracking and to produce the best surface edge for stamping, it is a good practice to use sufficient skim cuts when EDMing high-precision blanking carbide dies. Studies show that careful skimming greatly improves carbide surface quality. Durability tests prove that an initial fast cut and fast skimming cuts produce very accurate high performance dies.

Polycrystalline Diamond
The introduction of polycrystalline diamond (PCD) on a tungsten carbide substrate has greatly increased cutting efficiency. PCD is a man-made diamond crystal that is sintered with cobalt at very high temperatures and under great pressure. The tungsten substrate provides support for the thin diamond layer.

The cobalt in PCD does not act as a binder, but rather as a catalyst for the diamond crystals. In addition, the electrical conductivity of the cobalt allows PCD to be EDMed. When PCD is EDMed, only the cobalt between the diamonds crystals is being EDMed.

EDMing PCD, like EDMing carbide, is much slower than cutting steel. Cutting speed for PCD depends upon the amount of cobalt that has been sintered with the diamond crystals and the particle size of PCD. Large particles of PCD require very high open voltage for it to be cut. Also, some power supplies cut PCD better than others.

Ceramics are poor conductors of electricity. However, certain ceramics are formulated to be cut with wire EDM.

Flushing is an important factor in cutting efficiently with wire EDM. Flushing pressure is produced from both the top and bottom flushing nozzles. The pressurized deionized fluid aids in spark production and in eroded metal-particle removal.

Sometimes the flushing nozzle may extend beyond the edge of a workpiece. When this occurs, flushing pressure is lost, and this can cause wire breakage and part inaccuracy. To avoid wire breakage in such cases, a lower spark energy is used which slows the machining process. To avoid losing flushing pressure, it is advisable, if possible, to leave at least 3/16´´of material to support the flushing nozzles.

Cutting Speed
Speed is rated by the square inches of material that are cut in one hour. Manufacturers rate their equipment under ideal conditions, usually 2 1/4´´ -thick D2 hardened tool steel under perfect flushing conditions. However, differences in thicknesses, materials, and required accuracies can greatly alter the speeds of EDM machines.

Cutting speed varies according to the conductivity and the melting properties of materials. For example, aluminum, a good conductor with a low melting temperature, cuts much faster than steel.

On the other hand, carbide, a nonconductor, cuts much slower than steel. It is the binder, usually cobalt, that is melted away. When the cobalt is eroded, it causes the carbides to fall out. Various carbides machine at different speeds because of carbide grain size and the binder amount and type.

Generally, impurities cause little difficulty; however, occasionally materials are received with non-conductive impurities. The wire electrode will either stall or pass around small non-conductive impurities, thereby causing possible streaks from raised or indented surfaces.

When welded parts must be EDMed, use caution to make certain there is no slag within the weld. TiG welding is preferred for wire EDM.

Heat-affected Zones
The EDM process uses heat from electrical sparks to cut the material. The sparks create a heat-affected zone that contains a thin layer of recast, also called "white layer." The depth of the heat-affected zone and recast depends upon the power, type of power supply, and the number of skim cuts.

The recast contains a layer of unexpelled molten material. When skim cuts are used, much less energy is applied to the surface, which greatly reduces and practically eliminates the recast layer.

On older wire EDM machines, the heat-affected zones and recast were much more of a problem. Also, the recast and heat-affected zones and recast were much more of a problem. Also, the recast and heat-affected zones of ram EDM are much greater when roughing because more energy can be used than with wire EDM.

Many of today's wire EDM machines have reduced this problem of recast and heat-affected zones. Our company has wire-EDMed thousands of jobs and cut all sorts of materials, including carbide and high alloy steels. We have had practically no negative results from recast and heat-affected zones. Most work is done with just one cut. For precision parts, skim cuts are used.

Our newer machines now come equipped with anti-electrolysis power supplies, also called AC power supplies. These power supplies greatly reduce the recast and heat-affected zones. On some machines, the heat-affected zone for the first cut is 0.0015", on the first skim cut it is 0.0003", and on the second skim cut it is 0.0001".
For years, the recast and heat-affected zones have been a concern for the aerospace and aircraft industry. With the improvement of power supplies, these industries increasingly accept work done with wire EDM.

Power Supplies
Instead of cutting with DC (direct current), some machines cut with AC (alternating current). Cutting with AC allows more heat to be absorbed by the wire instead of the workpiece.

Since AC constantly reverses the polarity of the electrical current, it reduces the heat-affected zone and eliminates electrolysis. Electrolysis is the stray electrical current that occurs when cutting with wire EDM. For most purposes, electrolysis does not have any significant effect on the material. However, the elimination of electrolysis is particularly beneficial when cutting precision carbide dies in that it reduces cobalt depletion.

When Titanium is cut with a DC power supply, there is a blue color along where the material was cut. This blue line is not caused by heat, as some suspect, but by electrolysis. This effect is not generally detrimental to the material. However, AC power supplies eliminates this line.

Like AC power supply, the AE (anti-electrolysis) or EF (electrolysis-free) power supplies improve the surface finish of parts by reducing rust and oxidizing effects of wire EDM. Also, less cobalt binder depletion occurs when cutting carbide, and it eliminates the production of blue lines when cutting Titanium. AC and non-electrolysis power supplies definitely have advantages.

Wire EDM will machine hard or soft steel; however, steel in the hardened condition cuts slightly faster. Materials requiring hardening are commonly heat treated before being cut with wire. By heat treating steel beforehand, it eliminates the distortions that can be created from heat-treating.

Cutting Large Sections
Steels from mills have inherent stresses. Even hardened steel that has been tempered often has stresses remaining. For cutting small sections, the effect is negligible. However, for large sections when there is a danger of metal movement, it is advisable to remove some of the metal. By removing metal, it reduces the possibility of metal movement.

For some parts, provision should be made for clamping.

The better understanding one gains of the wire EDM process, the more benefits one can obtain from the amazing process.

The article above is adapted from a chapter of Carl Sommer's new book, Non-traditional Machining Handbook, and is printed with the permission of Advance Publishing Inc, Houston, TX.

Choosing a CMM

Selecting the System That's Best for You
Today's ever-increasing demands on the manufacturing sector to improve product quality have made coordinate measuring machines the backbone of company quality departments. Surprisingly, many buyers wrongfully believe that all CMMs are the same, and thus find themselves stuck with equipment that fails to meet their inspection needs, much less improve their overall quality. Because of CMMs' growing importance to the entire manufacturing function, extensive thought and planning must go into each purchase.

The basic CMM is comprised of four components: the machine itself, the probing system, the computer system and the measuring software. Most companies know what to look for these days in a computer system, but what important factors should you consider when evaluating CMMs, probes and software? The following information should help you select a system that's right for your company and for your particular application.

CMM Hardware
If you want to invest in a quality product that will stand the test of time, don't skimp on the quality of the machine hardware. Be sure to consider these points when evaluating CMM equipment:

Thermally stable construction materials. Make sure that the primary members of the machine construction consist of materials that are less susceptible to temperature variations. Consider the bridge (the machine X-axis), the bridge supports, the guide rail (the machine Y-axis), the bearings and the machine's Z-axis bar. These parts directly affect the machine's measurements and motions accuracy, and constitute the CMM's backbone components.

Many companies make these components out of aluminum because of its light weight, machinability and relatively low cost. However, materials such as granite or ceramic are much better for CMMs because of their thermal stabilities. In addition to the fact that aluminum expands nearly four times more than granite, granite has superior vibration dampening qualities and can provide an excellent surface finish on which the bearings can travel. Granite has, in fact, been the widely accepted standard for measurement for years.

For CMMs, however, granite has one drawback-it's heavy. The dilemma is to be able, either by hand or by servo, to move a granite CMM around on its axes to take measurements. One organization, The L.S. Starrett Co., has found an interesting solution to this problem: Hollow Granite Technology.

This technology uses solid granite plates and beams that are manufactured and assembled to form hollow structural members. These hollow structures weigh like aluminum while retaining granite's favorable thermal characteristics. Starrett uses this technology for both the bridge and bridge support members. In a similar fashion, they use hollow ceramic for the bridge on the largest CMMs when hollow granite is impractical.

Bearings. Nearly all CMM manufacturers have left the old roller-bearing systems behind, opting for the far-superior air-bearing systems. These systems require no contact between the bearing and the bearing surface during use, resulting in zero wear. Additionally, air bearings have no moving parts and, therefore, no noise or vibrations.

However, air bearings also have their inherent differences. Ideally, look for a system that uses porous graphite as the bearing material instead of aluminum. The graphite in these bearings allows the compressed air to pass directly through the natural porosity inherent in the graphite, resulting in a very evenly dispersed layer of air across the bearing surface. Also, the layer of air that this bearing produces is extremely thin-about 0.0002". Conventional ported aluminum bearings, on the other hand, usually have an air gap between 0.0010" and 0.0030". A small air gap is preferable because it reduces the machine's tendency to bounce on the air cushion and results in a much more rigid, accurate and repeatable machine.

Manual vs. DCC. Determining whether to purchase a manual CMM or an automated one is quite straightforward. If your primary manufacturing environment is production-oriented, then usually a direct computer controlled machine is your best option in the long run, although the initial cost will be higher. Manual CMMs are ideal if they are to be used primarily for first-article inspection work or for reverse engineering. If you do quite a bit of both and don't want to purchase two machines, consider a DCC CMM with disengagable servo drives, allowing manual use when needed.

Drive system. When selecting a DCC CMM, look for a machine with no hysteresis (backlash) in the drive system. Hysteresis adversely affects the machine's positioning accuracy and repeatability. Friction drives use a direct drive shaft with a precision drive band, resulting in zero hysteresis and minimum vibration.

Probing Systems
Once you've found the right CMM, you should select a probing system. Most CMM manufacturers use Renishaw for their probing systems. Renishaw's product quality and accuracy are exceptional in the industry. Selecting a probing system that is most appropriate for your particular application is more involved than simply picking one out of a catalog. You must first have a good understanding of the components that make up a complete system as well as each component's features and benefits. The basic Renishaw probing system consists of three main components: the probe head, the probe and the stylus.

Probe heads. While the probe triggers a measurement point (discussed in greater detail next), the probe head simply holds up the probe. Although this sounds simple enough, the probe head usually costs the most of the three components. Besides the amount of weight that the head will support, basically you should consider two things: articulating vs. nonarticulating, and manual vs. automatic.

Nonarticulating probe heads allow only one probe orientation-straight down. When inspecting cube-shaped parts, you may be able to get by with a nonarticulating probe head if you use a "star" stylus on the probe. This stylus gives you a cluster of up to five styli, pointing forward, back, left, right and down. While you should be able to measure all of the cube's features, keep in mind that this works for only the simplest of part configurations. Nonarticulating probe heads also are used extensively for measuring features machined or stamped into flat sheet metal or on any parts that only need a straight-down probe orientation. They can be used on both manual and DCC machines.

Articulating probe heads enable the operator to point the probe in many different directions. Renishaw uses two angles to control the direction that the probe points-the "A" angle, which is the number of degrees of elevation from the straight-down position, and the "B" angle, which is the direction in the horizontal plane that the probe points. These angles are either in 15-degree or 7.5-degree increments. Probe articulation allows the measurement of features on the back or sides as well as features at oblique angles. Each articulating probe head has a maximum extension length. For example, if you need to reach far down into a bore for a measurement, make sure you purchase a probe head that can support the weight of the required probe extension bar.

Articulating probe heads come in two general varieties: manual and automatic. Just as the name implies, manually articulating probe heads require operator intervention to move the probe to the desired orientation. Although these probes can usually be used on both manual and DCC CMMs, keep in mind that, on a DCC machine, the program will stop at each programmed probe change and wait for the operator to walk back over to the machine and articulate the head.

Automatic articulation allows the probe angles to be changed automatically from within the part program. Thus, very complex part programs utilizing many different probe positions can be run completely unattended. These probe heads are used only on automated CMMs.

If you've already decided to purchase a DCC machine and you need only articulate the probe head occasionally, you're probably better off purchasing a manually articulating probe head. If, on the other hand, you need to articulate the head more than that, you're defeating the purpose of the DCC machine by attaching a manual probe head. An automatic program is of little benefit if an operator must stand there most of the time to change probe orientations.

Probes. As mentioned earlier, the probe triggers the point when the stylus touches the part. There are two considerations here: probe accuracy and stylus interchangeability.

Probe accuracy depends on the triggering system's design. Renishaw primarily uses mechanical triggering mechanisms (used on the TP-2 and TP-20) and strain-gage mechanisms (used on the TP-200). The strain gage-based probe is more accurate than its counterparts, especially when used with longer styli. If, however, the CMM is near a source of strong vibration, consider the TP-2 or TP-20 to avoid false triggers induced by the vibration.

Also consider the system's ability to change the stylus tip automatically within a DCC part program. The TP-2, for example, doesn't have this capability. With this probe, the stylus must be unscrewed from the probe, the new one attached, and the stylus tip recalibrated on the calibration ball.

On the other hand, the TP-20 and TP-200 use stylus modules that are magnetically attached to the probe. These can be removed and replaced, either by hand or by using a module-changing rack, without the need for probe recalibration. Using the module-changing racks allows this entire function to take place automatically within a DCC part program, requiring no operator intervention.

Other probe types such as video, laser and noncontact may also be useful if the application warrants them.

Stylus tips. Styli actually make physical contact with the part. They consist of synthetic spherical rubies mounted on a shaft and are best purchased in kit form. The kits usually contain a wide variety of styli from which to choose.

CMM Software
Because the machine's overall measurement capabilities and ease of use depend almost entirely on the inspection software, don't let your evaluation of this component be limited to how flashy the user interface appears. You may not know the software's true capabilities unless you ask. Also, think about future needs. Buying a system that barely handles your current requirements would be a mistake in this ever-changing industry. At a minimum, make sure you evaluate the following 15 characteristics before you decide which system is right for you:

1. Ease of use. Simple measurement tasks should be easy, obvious and intuitive. Additionally, the software should be easy to navigate, and a good online help system is a must.

2. Nonconventional part alignments. Virtually all CMMs can handle simple part alignments like plane, line and point. But what about more involved alignments like offset datum planes or datum target points on complex surfaces? Though you may not need these features today, a blueprint may come through your shop tomorrow that requires them.
3. Complex surface measuring. CMMs can easily measure simple geometric shapes like circles, lines and cones. Measuring and evaluating complex surface shapes like airfoils, valve heads or bicycle helmets is an entirely different matter. Good CMM software will provide a mechanism to collect data on these features using a CAD surface model of the part. It should also allow you to create section lines on the surface to measure.

4. Automatic feature measurement. This function allows the CMM to automatically move to a defined feature and take the measurement points on it. This can facilitate programming a DCC CMM. Typically, the operator defines the geometric feature by keying in the nominal information or by clicking on the feature in a CAD model. Software without this ability must rely on the operator to program the probe motion and measurement points using only the joysticks.
5. Scanning of unknown geometries. This allows a feature or complex surface to be scanned for data without knowing its nominal definition. On automated machines, the operator typically probes the start and end points for the desired scan and specifies a scanning density, allowing the CMM to "learn" the contour in between.

6. Programming language. Good CMM software uses a powerful yet easy-to-read programming language. While some companies use their own proprietary languages, you can instead acquire inspection software that uses the dimensional measuring interface standard, the industry standard programming code for CMMs. This will allow interchangeability of part programs between different brands of DMIS-based CMMs.

7. Geometric tolerancing. All types of geometric tolerancing should be available in the CMM software, including line and surface profiles.

8. CAD interface. Not only should the CMM software accommodate multiple CAD file types, it should also present that information in a clear and understandable manner on-screen. Ideally, it should allow the user to control the graphical representation (such as wireframe or surface) and to group and hide various features for visual clarity.

9. Offline programming. To get the most throughput from a DCC CMM in high-production situations, the CMM should run part inspections as much as possible. In order for this to happen, there must be a way to write CMM programs without actually utilizing the machine itself. Look for CMM software that enables you to write your programs easily offline using a CAD model. Ideally, you should be able to download a program from an offline workstation into the CMM and have it run with little or no editing.

10. Outstanding reporting capability. All CMMs have some way of printing out inspection results in at least a tabular format. Instead, look for a software with which users can customize the output to their own specifications. The software should also incorporate graphics into the reporting for better understanding of inspection results.

11. Graphical feature analysis. Make sure the CMM software can graphically compare measurement points to the known CAD definition. This helps immensely in visualizing the part's entire dimensional condition.

12. Integrated best fitting. Best fitting mathematically "shakes" the part to find a position where most or all features will come into tolerance. This also allows line and surface profiles to be checked relative to themselves (with no datum reference). Verify that the CMM software allows you to specify any combination of features for inclusion in the best fit and any combination of axes to translate along and rotate about. This is essential to seriously evaluate the entire manufacturing process. Often, best fitting comes only as a third-party package on an offline computer system. Far superior, however, is CMM measuring software that directly integrates best-fitting capabilities.

13. Integrated statistics. As with best fitting, find a system that integrates statistics into the inspection software, eliminating the need to dump data into another system. Ideally, you should be able to incorporate these stats into the inspection report.

14. Reverse engineering. This process creates a CAD definition of an unknown or modified part. To do this, the software must be able to export your measured feature data to a file format that your CAD system can read, such as the initial graphics exchange specification (IGES) format.

15. Support of optional equipment. Verify that the CMM software supports equipment such as stylus-changing racks or rotary tables. You may wish to add this equipment sometime down the road.

A Demanding Industry
Don't forget accuracy when evaluating a CMM. Accuracy requirements depend primarily on the tolerancing of the parts to be measured. Linear accuracy, as the name implies, is an accuracy reading for each axis independently. Remember, however, that each machine axis must be built mutually perpendicular to the other two. Therefore, volumetric accuracy better represents a CMM's true overall accuracy.

Today's manufacturing industry is filled with ever-increasing demands for improving product quality. CMMs, once found in only the largest companies, are now being used by virtually all types and sizes of companies across the entire manufacturing spectrum. Because of the critical role CMMs play, serious thought should go into evaluating the machines before committing to a purchase. After all, the quality of your products depends on it.

Article by by Steve Meredith

Roll Forming

Roll Forming

Roll forming is the most commonly used metal forming method. There are some basic principles that set one system apart from another. There are many other systems as well that incorporate hydro forming or laser forming at some point in the line.

• Flying piercing and cut off stations, where no stock loop is required and the tooling is on the move for a short period of time. Units travel with the same speed as the stock while cutting. This motion emulates a stationary cut where the stock and the press are fixed.

• Stop and go system where the rollers and stock come to a halt for a short time while piercing, notching and the shearing take place. Unfortunately this simple system has a major draw back. The stock gets wavy at the places where the rollers stop.

• Roll form with loop control. This method is generally usable with flexible thinner stock.

This does not require the press and the cut off tooling to be on the move while cutting.

The following article describes the principles of this system.

Feeding stock into a stamping die is necessarily a stop and go operation. A free loop of material between the decoiler and straightner and press feeder is necessary for nearly all coil fed pressworking operations.

Sensing Wires for Loop Control

Figure 1. A simple dual spring-loaded sensing wire device used to start and stop a decoiler.

Purpose of the Material Loop

The material loop serves several purposes that include:

1. The stock loop stores material to permit the stop and go action of the press feeder.

2. The stock loop permits smooth operation of the decoiling and straightening equipment by permitting stock to be fed into the loop in a smooth way.

3. If an effective feedback control system is used in conjunction with variable speed decoiling and/or straightner motors, the loop permits continuous decoiling and straightening action so long as the press is running.
Decoiling and especially roll straightening is most effectively carried out as a continuous process. The roll straightener must flex the metal in a manner that exceeds the yield point. If stop/go operation occurs, the rollers may mark the strip.

Good loop control systems have features that permit continuous decoiling and straightening. System features include:
1. Variable speed drive motors on the decoiler and straightner.

2. Sensing devices to measure the amount of material in the loop and provide an electrical voltage or current signal to vary the speed of the motors feeding material into the loop.

An effective way to assure smooth operation is to control the amount of material in the loop by using sensing devices that provide a feedback signal to vary the motor speed feeding the loop. The feedback control system can be simple in the case of short feed pitches and ample stock loops.

However, in the case of rapid forward feed involving long pitches or progressions of stock, or stable operation, a technique known as feed forward compensation is recommended. This system anticipates the fast forward feed depleting the stock loop and starts feeding material into the loop in advance of the feeding action at the press.

Loop Sensing or Control Devices
Figure 1 illustrates a simple dual spring-loaded sensing wire device used to start and stop a decoiler and/or stock straightner. This is a simple device. One requirement is that the stock conducts electricity. Low voltage and very little current are required. Limiting the voltage and current avoids shock hazards and problems with marking the stock.

How Sense Wire Loop Controllers Work
When the stock contacts the upper sensing wire, the feed motor is started. The stock is fed into the loop until it contacts the lower sense wire, which shuts off the motor. This simple system is satisfactory for many loop control applications.

How to Improve Wire Sensor Loop Control Performance
An improvement in performance can be realized if a variable speed pay out motor is used. When the upper sensing wire is contacted, the motor starts paying out the strip at a rapid rate. Once contact with the upper sensing wire is lost, the motor can be adjusted to run at the speed or slightly faster than the rate at which the loop is depleted by the press working operation.

Once the lower sense wire is contacted, the pay out motor is stopped. This dual speed arrangement has several advantages over a simple on/off controller which include:

1. There is little chance of running the loop out of stock and getting a misfeed because the motor runs at high speed so long as the strip is in contact with the upper sense wire.

2. Long pay out running times are possible by fine tuning the variable speed motor drive controller to run at the same speed or slightly faster than the press depletes the loop.

3. Contacting the bottom wire will stop the pay out motor assuring that excess stock will not be fed out.

4. Die changeover time need not be affected since the controller will provide starting and stopping functions even if not fine-tuned for long running times. The fine-tuning can be accomplished after the new job is running.

Dancer Arm Loop Control Switches
Figure 2 illustrates a decoiler for a thin aluminium stock and stock straightener. A well-designed dancer arm is attached to the exit end of the stock straightener to control the amount of material in the stock loop.

Dancer arms are a popular means of actuating the stock pay out motor on the decoiler and/or straightener. If a position sensing device such as a rheostat, potentiometer or other sensor that will provide a voltage or current in proportion to arm angular position is used in place of an on-off switch proportional operation can be easily achieved provided that the pay out motor and controller provide for variable speed operation.

Dancer Arm Used for Stock Loop Control
Figure 2. A dancer arm with roller is attached to the exit end of the stock straightener to control the amount of material in the stock loop.

Ultrasonic Loop Control Sensors
Ultrasonic sensors are widely used to control stock loops. Most units follow the design principles developed by the Polaroid Camera Corporation for their automatic focusing camera. The sensor head emits pulses of ultrasonic energy above the range of human hearing. The sensing device accurately measures the return echo time and converts this to a distance measurement to control the material in the stock loop.

Ultrasonic Sensors Provide Real Time Distance Measurement
An advantage of ultrasonic distance measuring devices is that they can provide a voltage or current output that varies in proportion to the distance of the sensor from the stock loop. This is an advantage in providing steady operation of the decoiler and stock straightener through proportional control methods. Figure 3 illustrates an ultrasonic loop control sensor. Figure 4 shows how the sensor is placed to control the stock loop.

Figure 3. An ultrasonic sensor loop controller. The sensor head emits pulses of ultrasonic energy above the range of human hearing. The sensing device accurately measures the return echo time and converts this to a distance measurement to control the material in the stock loop. This type of sensor has a number of advantages including the ability to work with non-conductive materials such as plastic sheeting.

Proportional Control and Forward Feed
Compensation Advantages

Proportional control of the stock loop permits the stock decoiler and stock straightner to operate continuously. The stock pay out system, which usually consists of a stock decoiler and stock straightner, must be powered by a variable speed motor drive system. Any loop sensing system that provides a voltage or current output that varies according to the amount of material in the stock loop can be used to control the speed of the stock pay out system.

Figure 4. A progressive die operation using an ultrasonic loop control sensor. The best systems vary the decoiler and stock straightner speed to achieve proportional control. For long feed pitches, forward feed compensation may also be used to advance extra material into the loop before feed advancement.

The most common sensing system that provides this feature is the ultrasonic system. One term for such a system is proportional control since the pay out system can operate continuously so long as the press is running. Material is fed into the loop in proportion to the rate that the press feeder depletes the loop.

By anticipating when the press feeder is going to advance stock into the die, forward feed compensation can also be accomplished. Forward feed compensation advances material into the feed loop rapidly. This is useful for long feed progressions

Other Loop Sensing Systems that can be used for Proportional Control
Not all types of ultrasonic sensors provide a voltage or current output that is proportional to the distance from the stock loop. Some have set points, which provide simple on/off control. The best sensors provide an electrical output that varies according to the distance from the stock loop for proportional control. Some other types include:

1. Radio frequency sensors, one of which is illustrated in Figure 5.

2. Mechanical arms which have a rheostat or potentiometer to provide a variable electrical output.
3. Arrays of multiple photoelectric sensors, which provide variable electrical output.

Figure 5. A radio frequency (RF) loop control device. Note the “V” shaped antenna. The amount of RF energy absorbed by the stock increases when the material loop is higher. This sensing device provides an electrical output that can be used for proportional loop control.

Stock Loop Pits
A stock loop pit is sometimes required to provide enough material for long feed pitches. This should only be done if other measures such as applying forward feed advancement, which is timed to start feeding material into the loop before the feeder is actuated, will not provide enough slack in the loop.

A stock-looping pit is illustrated in Figure 6. Pits should be avoided for several good reasons that include:

1. Pits are expensive to construct.

2. Future plant layout changes are apt to be difficult if a pit location is involved.

3. Pits require guardrails for safety of personnel.

4. Stock loop pits have a magical attraction for debris.

Figure 6. A stock loop pit is sometimes required to provide enough material for long feed pitches. Such pits should be used only if necessary.

Figure 7. An example of placing the press too far from the stock straightner. The usual reason is an erroneous belief that more stock can be accumulated if the distance between the pay out equipment and the press feeder is made longer.

Avoid Excessive Loop Lengths
When conducting plant audits to determine more efficient ways to accomplish stamping operations, it has been the writer’s experience to observe many coil fed operations that have excessive distances between the decoiler and press feeder. The stated reason is usually an erroneous belief that more stock can be accumulated if the distance between the pay out equipment and the press feeder is made longer.

This improper equipment placement is illustrated in Figure 7. In some cases, twenty or more feet (6 or more meters) of stock are on the floor. The main factors that determine the amount of material that can be stored in the stock loop are:

1. The height of the pay out equipment and press feeder above the floor.
2. The permissible bend radius of the stock forming the loop, which determines the optimum distance between the press, and pay out device.

Effect of Stock Loop Contacting the Floor
Figure 6 illustrates a stock loop lying on the floor. There is an erroneous belief in some shops that moving the stock pay out devices as far as possible from the press increases the available amount of stock in the loop. This is incorrect, and has a number of undesirable consequences, which include:

1. Excessive floor space is occupied without providing any benefit.
2. The stock will become contaminated by any dirt on the floor.
3. Persons will almost certainly walk on the stock.
4. Industrial trucks may be driven over the stock.
5. Sometimes felt pads or skate roller conveyor is placed under the stock to keep it off the floor. This adds to cost without addressing the layout problem.

Joining Coils by Welding
Welding equipment specifically designed for joining coil ends at the press is commercially available. This procedure is especially useful for jobs that are difficult to start. A means of cutting the coil ends to provide square edges to weld is required. The joining process must produce a weld that will not damage the die. Depending on the application, any parts containing the weld are discarded although they passed through the die without causing damage and appear to be correctly formed.

Coil end welding has widespread application in the roll forming, tubing and pipe manufacturing operations. The majority of tube and pipe making operations from strip mills utilize welders to join the end of the coiled strip or skelp, an industry term for the some of the steel strip material that is formed into pipe.

Tube, pipe roll formed product production is an excellent application. It is much weld coil ends together than to rethread a processing line. In the Tube and Roll Form Industries the higher speeds use more coils per shift making the coil welding process more easily justified through the reduction of coil related downtime. In the press industry, on the other hand, the reduction in scrap and tooling damage play a big factor in the justification of coil end welding.

Joining coils together is becoming increasingly popular in the press industry. By eliminating rethreading, you will greatly reduce scrap, tooling damage and downtime. Many progressive die operations are difficult to start without the production of scrap and possible die damage. Welding coils together can reduce scrap and die damage. The material savings can be multiplied several times for non-ferrous materials.

Formula for Determining the Loop Radius That Will Deform the Stock
The following formula is based on elementary strength of materials. The greatest uncertainty in using this formula is the actual yield point of the material.


R = −−−−− Equation 1


Where: E = Young’s Modulus

σy = Yield Strength

t = Material Thickness

Applying the Minimum Bend Radius Formula to Stock Loops
The stock in a simple material loop has four bend radii. These occur where the stock emerges from the pay out equipment such as the straightner. The second radius is where the stock bends from a vertical fall and assumes a horizontal plane toward the press. Next, the stock forms a radius as it bends upward toward the feeder and finally there is a radius where the stock enters the feeder.

For the stock to remain flat, it is important not to exceed the minimum bend radius that will exceed the yield point of the stock. This may be calculated from Equation 1.

The normal minimum spacing of the pay out device assuming four radii is four times the minimum bend radius for the stock. To provide a safety factor, base the calculations on the thickest stock and lowest yield point that can be used. In addition, it is a good practice to assume that an error in equipment operation such as excessive stock pay out can occur. Please be aware that some of the values listed in Table 1 are not practical for many operations. This is especially true of low yield point stocks that are very thick.