Fine Blanking

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Description Fine blanking is a hybrid metal forming process combining the technologies of stamping and cold extrusion . Triple-action presses combined with specially designed tooling produce parts impossible to make with any other stamping process. Fine blanking is a unique metal forming process that is not widely understood in North America. Developed in Europe in the 1920's, its use is becoming more widespread as engineers discover the value fine blanking can provide in improving costs and improving quality in critical components. Fine blanking, as a process, is a combination of a very specific type of hydraulic press that has three motions and specially designed tooling. The combination of the fine blanking press with fine blanking tooling creates parts with fine blanking's hallmark fully sheared, straight cut edges. It also produces parts with small holes and thin web sections relative to material thickness, parts with excellent flatness, and parts that have very little dimensional variation from the first part through the millionth part and beyond. In short, fine blanking is an extremely precise high volume manufacturing process. Depending on the functional and cosmetic requirements of any given metal component, it may be the most cost effective and/or the most repeatable manufacturing process for that component. Using the fine-blanking process, precise finished components can be produced with inner and outer forms that are cleanly sheared over the total material thickness, while

Transcript of Fine Blanking

Page 1: Fine Blanking

Description

Fine blanking is a hybrid metal forming process combining the technologies of stamping and cold extrusion . Triple-action presses combined with specially designed tooling produce parts impossible to make with any other stamping process.

Fine blanking is a unique metal forming process that is not widely understood in North America. Developed in Europe in the 1920's, its use is becoming more widespread as engineers discover the value fine blanking can provide in improving costs and improving quality in critical components.

Fine blanking, as a process, is a combination of a very specific type of hydraulic press that has three motions and specially designed tooling. The combination of the fine blanking press with fine blanking tooling creates parts with fine blanking's hallmark fully sheared, straight cut edges. It also produces parts with small holes and thin web sections relative to material thickness, parts with excellent flatness, and parts that have very little dimensional variation from the first part through the millionth part and beyond.

In short, fine blanking is an extremely precise high volume manufacturing process. Depending on the functional and cosmetic requirements of any given metal component, it may be the most cost effective and/or the most repeatable manufacturing process for that component.

Using the fine-blanking process, precise finished components can be produced with inner and outer forms that are cleanly sheared over the total material thickness, while achieving superior overall flatness. This process eliminates the need for costly secondary operations such as shaving, milling, reaming, broaching and grinding.

Fine blanking is a specialized form of blanking where there is no fracture zone when shearing. This is achieved by compressing the whole part and then an upper and lower punch extract the blank .This allows the process to hold very tight tolerances, and perhaps eliminate secondary operations.

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History

The fine blanking process was patented for the first time in 1923. In the early 1923, the Fine-Blanking technology was invented by Mr. Schiess in Germany. However, this technology was purely and secretly applied in Watch industry at that time. Until the 1950, the Fine-Blanking press was produced and the technology had been published. In the earlier 1960, the application of the technology was extended from Watch industry to Light industries; also from Western countries to Eastern countries. From the 1970, this technology had been widely applied from Light industries to Heavy industries. In 1980, there were over 2800 sets of the Fine-Blanking Presses in the world.

The original idea was to apply a counter pressure force while blanking to prevent the edges from breaking and causing them to shear over the total thickness of the material. This technology was initially employed mainly in the office machine industry and the watch and clock industry.

During the early years, fine blanking dealt mainly with materials from 1 to 3 mm. Today more than 60% of fine blanked parts are used in the automotive industry with thicknesses of up to 19 mm.

Considerable technological breakthroughs have been made in tooling, presses and materials for fine blanking in recent years. Companies are considering fine blanking at the design stage, taking full advantage of its capabilities.

Today, the fine blanking method of manufacturing has become a necessity in several major industrial sectors. Although first initiated in Europe, fine blanking has taken an important place particularly in the Japanese and North American automotive industry, replacing many of the more expensive manufacturing options.

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Fine Blanking Process Fundamentals

Fine blanking is a cold forming process for high volume production of precision components.

The fine blanking process incorporates three forces, as shown in the adjacent diagram:

Stinger Pressure is applied to the raw material surrounding the area to be fine blanked. An impingement is created in the material, which may be applied to one or both sides of the material, depending on material thickness.

Main Pressure extrudes the part from the material strip. Counter Pressure opposes the Main Pressure to help maintain the shape, flatness

and integrity of the component throughout the fine blank process.

After the part has been formed, the tool is opened and the part and slugs (offal) are ejected from the tool and exit through the back of the die.

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To manufacture parts in fine blanking quality, the following conditions have to be met:

Fine blanking press Fine blanking tool malleable material

Before the material is actually fine blanked, it is firmly clamped, so that it can flow only in cutting direction. On the outside of the component's cutting line, the material is sandwiched by the die and the V-ring plate (stinger), inside by the punch and counter punch.The clearance between punch and die measures only a few 100ths of a mm(1/1000 of an inch) and the cutting speed is relatively slow.

(COMPARISON BETWEEN NORMAL BLANKING & FINE BLANKING)

One of the great advantages of Fine blanking is its ability to produce a straight, clean edge. The final quality of the edge surface is influenced by many factors, the main ones being:

Quality of the Tooling Quality of the Raw Material Type of Raw Material Cutting Lubricant

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How Fineblanking Works:

This represents a simple sliding punch fine blanking tool making a round washer with a hole at its center.

1. The tool closes, pressure embeds impingement ring into stock. This prevents material from flowing away form the punch, ensuring a smooth, extruded edge on the part.

2. Blanking punch advances until part is fully sheared and resting in upper die opening. In the same action, the pierce punch provides a hole in the work piece. Simultaneously, counter punch pressure holds part firmly against face of the advancing blanking punch. This maintains flatness and enhances the sheared edge, eliminating die break or edge fracture.

2. All forces are relaxed, and the tool starts to open. The ram descends by gravity.

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4. Blanking pressure reverses, the punch pulls back and the ejector pin pushes out slug. Simultaneously, raw material advances for the next cycle.

5. Counter pressure is reapplied, pushing part out of the die opening.

6. Air blasts or mechanical sweeps remove part and slug from die area.

7. The system is ready to start the next cycle. And the whole cycle is repeated 4 the next component.

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Fine Blanking Accuracy

The accuracy that can be achieved in fineblanked parts is largely dependent on:

1. The accuracy of the tools and their quality of maintenance2. The quality of the raw material3. The thickness of the material4. The complexity of the component’s shape

Tolerances are generally in the range of a .001 to .005 inches.

The following table should be used as the engineering limit of the Fineblanking process. It assumes perfect tooling, excellent cold rolled mild steel material, and a non-complex part geometry.

In the real world, these values need to be adjusted for high carbon steels, stainless steels, and complex part geometries. A good place to start is two times these values, and you will be very safe at three times these values.

The following tables use the ISO 286 system of tolerancing. If this is unfamiliar to you, there is an excellent treatment at ( under shaft tolerances). If you do any work with fits (slip fit, force fit, etc.) this system will save you a ton of work. But it is not necessary to understand the system to use the tables, but that is where IT7, IT8, etc. come from. Now on to the tables.

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Fine Blanked Edge Quality

One of the great advantages of Fine blanking is its ability to produce a straight, clean edge. In mild steel grades such as 1008/ 1010 Cold Rolled, surface finishes of 16 micro inches are obtainable. As the material gets harder, and therefore less ductile, edge condition will suffer. Use of full spheroidized annealed material is necessary in many applications.

The table below shows how edge finish is related to the die sharpening schedule.

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Tool Manufacturing

Designing and building Fine blanking tooling presents unique challenges. To maintain tolerances of .0004 inches in size and .0002 inches in position requires the utmost in planning and execution. As a result, most components are produced using wire EDM machines. In many cases conventional (sinker) EDM is used to produce punch elements.

Unlike conventional metal stamping dies, Fine blank tooling must withstand heavy tensile stress as well as the normal compressive stress. This forces the die builder to use the best tool steel material available. Depending on the die element CPM 10V, M4, M2, or D2 tool steels are utilized.

As shown above, a completed fine blanking tool is very robust. Note the four-bushing die set needed to maintain tool alignment .Also note the air blast lines shown on the lower left. These lines eject the parts and slugs from the tool, where they are then separated by a vibrating screen.

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Methods of Tool Construction

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Tooling

Fine blanking tooling is unique in its construction. When compared to conventional stamping tooling, there are a few specific features that set fineblanking tools apart. They are:

V-ring (also called impingement ring) Close punch-die clearance Straight (not tapered) die cavity Radiused cutting edges Tooling Construction

V-ring:The V-ring is a raised V-shaped ridge usually on the stinger plate that has the same contour as the blanking punch and is located close to it, roughly a distance equal to 50% of material thickness. In some cases the V-ring is placed on the die plate, sometimes on both the die and the stinger plate, and at times no V-ring is used.

In the initial stage of the fine blanking cycle, the V-ring is pressed into the material to prevent lateral movement of the material in the piercing and blanking operations. The V-ring also ensures that enough material is packed into the die cavity to create fully sheared, straight edges.

Close punch-die clearance:This is another important feature of fine blanking tooling, which enables the unique characteristics of fine blanked parts to be created. Generally the clearance between punch and die is 0.5% of material thickness - per side. In some cases, depending on the material and application, zero clearance between punch and die is used. The minimal punch-die clearance is the key to obtaining the fully sheared edges that fine blanked parts are noted for. This compares with a typical clearance of 10% of material thickness per side for conventional stamping tools.

Straight die-cavity:The die-cavity in a fine blanking tool is straight - not tapered. This helps ensure the cleanly sheared edges and results in cut edges that are tapered approximately only 0.5°. Such a minimal taper enables tight dimensional control through the full thickness of the piece part.

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The straight die cavity also ensures that after the die plate is ground during regular die maintenance, the size of the die cavity does not grow (as it would if the die cavity was tapered). This ensures that the parts produced in every production run will maintain the same nominal dimensions as when the part was first made.

Radiused cutting edges: Fine blanking is as much an extrusion process as a stamping process. The cutting edges of the die cavity are not sharp - they are radiused. This allows the metal to flow into the die cavity.

Tool Construction: Fine blanking tools are compound dies, meaning that the part is ejected out of the die cavity. Most fine blanking dies are single station dies, with all features created at one time with a single stroke of the press. Parts made in a single station tool have extremely consistent relationships between features. The use of progressive fine blanking dies is increasing rapidly, in an effort to provide more and more complex features on parts right out of the tool - eliminating secondary operations and enhancing design possibilities.

Because of the extremely close punch and die clearances and the pressures inherent in the process, fine blanking tools must be produced with very tight fit among all tool components.

There are two types of fine blanking tools: sliding punch and fixed punch. Generally, sliding punch tools are used for smaller and less complex parts, while fixed punch tools are used for larger and more complex parts. Sliding punch tools are less expensive to build, set-up, and maintain, but are not as rigid as fixed punch tools - and cannot be used in every application.

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Tool StandardsA standard tool construction will have the following main component and they are listed below.

1. Top die shoe2. Bottom die shoe3. Guide plate4. Top back-up block5. Bottom back-up block6. Guide pin7. Punch8. Punch retainer with adjusting plate9. V-Ring plate10. Guide bushing11. Adjusting plate12. Punch retainer with adjusting plate13. Ejector14. Die15. Piercing punch retainer16. Guide bushing

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Steel Structures Suitable for Fine blanking

Structure of steel based on carbon percentage

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The raw material for fine blanked components is primarily rolled metal coils, although extruded and rolled strips are also used. In some cases non-metallic materials are fine blanked.

Because fine blanking is as much an extrusion process as a stamping process, the consistent flowing of material into the die cavity is critical. For this reason soft materials and materials with fine grain structure are preferred. When an application requires a hardened component, heat treatable alloys are used.

Here is a partial listing of materials that are commonly fine blanked:

Steels : carbon steels, alloy steels, and stainless steels. Aluminium alloys Copper alloys and brasses

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Tool systems

There are two fine blank tool systems in use: a) tools with a fixed punch (sometimes called "three plate tools") b) tools with a sliding punch (sometimes called "two plate" tools)

Sliding punch tools are easier to design and manufacture so they are cheaper than fixed punch tools. But for some applications, sliding punch design can weaken the tooling elements and shorten die life. Costs for sliding punch tools are in the range of $5000 to $15,000.

Fixed punch tooling has a more robust tool design which makes it the choice for heavy blanking pressures and long runs. However, the cost is prohibitive for short to medium run tools. Costs for fixed punch tools are in the range of $10,000 to $30,000.

As you can see, fine blank tooling is more expensive that conventional stamping tools. This is due to the need for expensive tool steels and extreme accuracy in manufacture.

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V-Rings

Before the actual cutting begins the material is firmly sandwiched between the die and V-Ring plate. This prevents the material from flowing laterally. The material is also held by a so called V-Ringthat is formed into the material along the outside contours of the part.

The die as well as the V-Ring plate are subject to wear and can be re-worked several times. Therefore, the V-Ring is machined into the hardened steel.

Two methods are used to make the V-Ring (stinger):a) by EDM (electrical discharge machining)b) milling with tungsten carbide cutter.

I. milling of the inside

II. milling of the outside

III. milling or grinding of the remaining surface

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Strip Lay-out

A strip lay-out is made to determine the strip width and pitch. The bridge width between the parts and the edge allowance between the part and the edge of the strip have to be selected to meet the following requirements:

a) the V-Ring has to have enough spaceb) arrange for optimum usage of the materialc) the skeleton must have enough strength to allow feeding the strip.

Complex contours or sections that require smooth edges, should be located on the in-feed side of the strip (arrow) because the solid strip is more rigid than the bridge between the parts.

The optimum pitch, i.e. the smallest possible bridge width can be determined in tests. Very often the V-Rings can overlap without a negative effect on the surface quality of the sheared edge.

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Fine Blanking Production Line

The fine blanking press is the heart of an automatic fine blanking production line, which usually consists of the following components:

The rolled strip is fed and straightened using a feeder.The strip after cutting out is deburred .While the strip skelton is cut out using a chopper.

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Fine Blanking Press

The fine blanking press is not a standard stamping press. Fineblanking presses are unique by providing three specific motions:

1) a stinger motion, which brings the stinger plate up and holds the material in place during blanking;

2) a blanking motion, which provides the blanking force to push the part into the die cavity; and

3) a counter pressure motion, which holds the piece against the blank punch during blanking and ejects the piece part from the die cavity after blanking is complete

There are two types of fine blanking presses:

1) Hydraulic presses and

2) Mechanical presses .

Most fine blanking presses are hydraulic presses. Some smaller presses (up to 250 tons) are mechanical and all of the larger presses (over 250 tons) are hydraulic. The mechanical presses use a link system to generate the blanking pressure and hydraulics to create stinger pressure and counter pressure. The hydraulic presses use hydraulic pressure for all three motions.

Fine blanking presses come in a wide range of sizes. The smallest is 40 tons and the largest commercially available is 1400 tons.

The fine blanking presses, 250 tons and below, are mechanical presses. These presses incorporate hydraulic cylinders to control the stinger pressure and counter pressure, but main pressure (blanking force) is applied by mechanical force.

Larger presses, including 250 tons and above, are fully hydraulic presses. In addition to hydraulic cylinders being used to control stinger pressure and counter pressure, the main pressure is also applied by a hydraulic force.

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400 TON FINE BLANKING PRESS

160 TON FINE BLANKING PRESS

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Tolerance comparison

This table shows how Fine blanking fits in with other manufacturing processes. Each part is unique, but in general Fine blanking will hold tolerances of +/- .0005 if necessary.

Advantages

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Excellent dimensional control, accuracy, and repeatability through a production run.

Excellent part flatness is retained. Straight, superior finished edges to other metal stamping processes. Smaller holes possible relative to thickness of material. Little need to machine details. Multiple features can be added simultaneously in 1 operation. More economical for large production runs than traditional operations when

additional machining cost and time are factored in (1000–20000 parts minimum, depending on secondary machining operations)

Disadvantages

Slightly higher tooling cost when compared to traditional punching operations. Slightly slower than traditional punching operations. Tapered edge due to friction with die walls. Rounding of bottom edge.

Applications

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Fine blanking's unique features and cost effectiveness for manufacturing provides value to many industries. Here is a partial listing of the major industries that employ the fine blanking process:

Automotive: seating, safety, power train, brakes, fuel, HVAC ,exhaust, general hardware.

Electronics: disc drives, printers, plotters, heat sinks.

Cutlery: Multi-tool components, knife blades.

Tools/Hardware: lawn and garden equipment, power tools, locks

Reffered from:

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http://www.moriiron.com/english/fb_e.htmlhttp://www.fineblankhubli.com/technology/index.html

http://www.fineblanking.org/process/materials.htmhttp://www.partechfineblanking.com/design_guide/v-rings.htm

http://www.mpi-int.com/process.htmhttp://en.wikipedia.org/wiki/Blanking_%28metalworking%29

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