Wednesday, June 23, 2010

Cutting Wire Mesh

Written By Mark Batson Baril

This brief and right to the point question came up during the Fall 2000 IADD Association meeting in Vancouver. Should Wire Mesh be die cut or laser cut into unusual shapes?

Well it just so happens that a recent job required an in-depth investigation of this very subject. The answer, as is almost always the case, lies in the details of the job at hand. The main details to consider with this type of cutting project are these:

Type of Material and the Tooling - Wire mesh or screen comes in a large variety of different material types. Everything from hard stainless steel to light duty aluminum are included in the category "wire mesh." Thicknesses can range from a micro-wire of only a few thousandths of an inch to mesh used to screen out rocks for landscaping which can be just about as thick as you can imagine.

When I think of diecutting I automatically think of steel rule dies, forged tools and matched metal tooling. During the research I found that companies are using steel rule dies and forged dies to cut wire mesh, in stainless steel, up to wire diameters of .0625" (1.6mm). This does raise some questions of die-life, or maybe we should call it die-death! Even with some sophisticated coatings, it's tough to find a rule that is much harder than a 60RC and steel rule has the problem that all of it's cutting power is concentrated in the cutting edge. The most common problem with cutting the harder and thicker meshes is not with bending or failing of the rule but is with chipping of the tip of the blade. The steel rule die is great for mesh that is softer than the rule and/or where the quantities are very small. In thicker and harder meshes, no matter the quantity, it really makes no sense at all to use the steel rule or forged die.

Laser cutting or hard tooling is the answer in these more extreme cases. Long run aluminum jobs can run well on steel rule dies but most stainless and other steels are best left for other types of dies or other types of cutting.

Matched Metal tooling is a great way to cut most types of wire mesh. Although the cutting edge of a matched metal tool can experience the same chipping a steel rule die does, there is less of this tendency and the cut edge results of the part will tend to be excellent. Depending on the type of mesh to be cut and the type of press you are cutting with, surprisingly good quality and good running speeds can be achieved with hard tooling. The one disadvantage is the high tooling cost and this may be one good reason to go with laser cutting if the quantity you need is low. If it's a long running job, and the equipment is available, using a matched metal tool will result in far fewer headaches than dealing with a steel rule die or the laser cutter. In some situations wire mesh is being used as screening for a medical device or other high end product and good edge quality far outweighs any other consideration. In this case the sky becomes the limit on the method used, no matter the quantity needed. In most of these cases, the matched metal tool will be the best method.

Quantity to be Cut and Repeat Orders - When we die cut, we are typically dealing with a substantial quantity of parts that need to be produced. The main reason this is true is SPEED. Given a diecuttable product, no other cutting method can beat diecutting for processing speed - and it doesn't matter how many head laser you have! In making the decision on laser vs. die cutting or steel rule die vs. matched metal tool, the total quantity over the course of the life of the project has one heck of a big influence. Laser cutting has the advantage when the material is too thick and/or hard to be cut with a die, and/or the quantity needed is very small - less than 1,000 parts may be a good starting point.

Combine the quantity factor with the type of material factor, and the edge quality factor, and you will be closing in on the perfect cutting method. In the case we were involved with, the parts were produced using a male/female set-up by a company that stocks thousands of different tools specifically made to cut stainless steel mesh/screen. This company also produces the mesh! Once the contact was made the choice became easy as there was no tooling charge and we were able to reach the quantity minimums with no problem even though the run was very small - only 500 parts total. The quality of the cut was perfect and the question of using an alternative method was ruled out. It won't always be so obvious, especially when the shape is a bit on the unusual side or the material is on the edge of being diecuttable. All-in-all this question is a very open ended one with lots of room for discussion of details. This makes it hard to answer with absolute definition, but will make it an interesting and fun job to tackle when it comes into your shop.

Thursday, June 17, 2010

Cutting Punches Defined

Written By Mark Batson Baril

A possible lead-in question may look like this.
As the purchasing agent at medium sized die-cutting house, I am responsible for the purchasing of punches for our dies. It seems that every year our company is purchasing and using more and more punches. It is very important that the punches I purchase are right for our application and are “quality punches”. As there are multiple vendors out there selling punches and there are so many punches available, I would like to know ... what exactly are the most common punches and what makes each a “quality punch”?

You have come to the right place! There ARE many types and qualities of punches available and your specific applications will constitute what types of punches you want to purchase. First, you need to educate yourself as to the most common punches and then what makes each a “quality punch”...

The most common punch is the tubular punch. Tube punches are the most economical of all of the punches and are used for the widest range of applications. Slugs cut by a tube punch do not feed thru the punch, but are left in the product being cut with the help of die ejection. A standard tubular punch by definition is a piece of 16 gauge tubing that has a bevel machined on one end to a specific cut size. Tube punch cut sizes span the decimal chart in both millimeter and inch measurements and can be machined into virtually any custom size. A quality tubular punch should have a chamfer on the bottom on both the inside and outside to aid in ease of insertion into the die board. The base size should have a .000" to +.003" tolerance, the cut edge bevel should be virtually free of tool marks and the cut edge should be razor sharp. Springs are available in tube punches to alleviate the need for die ejection. These springs should protrude approximately 1/16” from the cutting edge. A quality tube punch will also be clean of scale, free of burrs, have a case hardening depth of .003" to .005" and a surface hardness of 58-60 Rockwell.

Similar to the tubular punch is the straight wall punch. Straight wall punches are used for applications with minimum punch space allotment where the base size of a standard tubular punch would be too bog to fit. A straight wall punch has a base size that is only several thousandths of an inch larger than the cut edge. This small difference allows for a slight support bevel for strength. Straight wall punches cause less distortion of cut size in thicker materials. The slugs cut by this punch are left in the product through the use of die ejection or springs and share the tubular punches tolerances and quality guidelines.

Another common punch is the feed thru punch. Most people will confuse a “feed thru” punch with a “side outlet” punch. In a feed thru punch, the slug exits the punch through the bottom rather than the side as in side outlets. Feed thru punches are used when your application calls for the scrap to be removed from your product rather than being hand stripped at a later time in your manufacturing process. Feed thrus must be run on a bolster plate which supports the die while at the same time allowing the slugs to feed thru where they are vacuumed, blown away, or otherwise disposed of. Feed thrus are constructed from thin wall tubing which is spun or sized then re-machined to your specific cut size. This method assures the proper relief for slug ejection. A quality feed thru’s specs and sizes offered are much the same as a tube and straight wall except that the feed thru’s inside chamfer is minimal, the cut edge should have a slight support bevel on the inside for strength and they do not come with springs.

A side outlet punch is a punch who’s waste slug feeds through an exhaust chute machined into the side of the punch. Side outlet punches are used when your application calls for scrap to be ejected - as in a feed thru - but this punch does not require the use of a bolster plate. Other than the location of the exhaust hole for the slugs, differences between the feed thru punch and the side outlet are that the side outlet is machined out of a solid piece of steel and it’s use of a shoulder. A side outlet shoulder is defined as the machined area of the punch from the top of the cut edge to just above the exhaust chute.

The most common type of side outlets are standard and heavy duty. The heavy duty side outlet is used for thicker, heavier, abrasive materials, has an elongated shoulder and often includes a “knurl”. A knurl is a raised portion located at the bottom of a punch - similar in texture to a ratchet handle. It is approximately .005" to .010" larger than the base size of the punch and is .250" wide. The knurl is used to prevent the punch from spinning or becoming misalligned in the routed die board. The standard side outlet is used for easier to cut, medium to thin materials. It has a shorter shoulder than does a heavy duty and does not include a knurl unless specified. Again, a good quality side outlet should be razor sharp, free of tool marks, scale and burrs. It should include a slight support bevel on the inside for strength as well as an undercut which prevents the slug from jamming in the punch before it enters the exhaust chute.

All punches can be made in a variety of heights - the most common being .937" (23.8mm) and each can be altered to meet your specific application. The life of these punches is effected by the material being cut, the application for which the punch was designed and operator skill level. Typically, a punch should last as long - if not greater than - the rule used in the die.

Tubular punches, straight wall punches, feed thrus and side outlets may be the most common punches, but they are far from the only ones offered. Custom punches can be manufactured to virtually any shape or size and can be used to produce everything from high tolerance flex circuits to components used in military aircraft to the gasket in your car. Custom punches ... now THAT is another question altogether!!! I hope that you now have a better understanding of some of the more common punches and what makes each a quality punch.

Sunday, June 13, 2010

Rotary Die Cutting via Matched Metal

In a continuing series of Technical Projects that focus upon rotary diecutting and the tools that go with the processes, we must explore the very exciting method of using the male/female die with a small twist. Actually a very large and fast twist may be a bit closer to the mark as this type of cutting system is designed to turn very quickly and very accurately for a growing number of converted products. There seems to be no specific name that has emerged as the common term for this type of cutting. Some common names for the process include; compression cutting, pressure cutting, male female rotary cutting, and rotary pressure cutting - so for the sake of this writing let's call the method the MMRC or (Matched Metal Rotary Cutting).

Rotary Die Cutting 1

 As a guy with a semi-flat background (careful), I remember seeing one of these tools at the CMM show in Chicago back in the early 1990's. I was amazed. This was probably the most complicated looking monstrosity I had ever seen. It looked to be made in one piece, had to be made to an accuracy that just blew me away, was at least the width of the widest tool I had ever made 60"(1,520mm) and the contraption was round! I mean there were two of them and they were cylinders that matched one another perfectly. Now if I had a hard time getting our flat dies to come up and kiss a flat plate, how in the world could these guys get these things to work. I stood and stared until a salesman explained a little more. Slowly it all began to gel - I was the only sane one in the booth, everyone else had to be nuts! Well, nearly ten years later a good customer of mine has made the decision that this type of MMRC will be the best bet to improve the overall production quality for a particular long run product. I was one of the people that recommended the process to them and in retrospect to that earlier experience in Chicago, the people in that booth were among the savviest converters at the show. The balance of this article will try to explain why.

Rotary Die Cutting 2

 What is a Matched Metal Rotary Cutting System? Instead of using a crushing cut where a knife like cutter rolls against a solid anvil to make the cut, a shear type cut is made by passing two precisely machined blocks or cutters by or through one another without ever touching anything but the material to be cut. The material is actually squeezed or compressed to the point of bursting without the two parts of the tool ever touching. The two cylinders that make up the tool set both rotate at exactly the same rate in order to create a perfect match to one another through the cut. The two can be brought closer, moved apart, and can even be slid parallel to one another in order to maintain the quality of the cut during the run. The fact that the tools and the system that the tools ride in are so accurate and never actually come in contact with one another creates a unique opportunity for perfect quality and long tool life.What type of products can and should be cut on these tools? The tooling that make this type of operation a success can be expensive. They last for a very long time but usually the cost translates into making products that have a large volume and have specific quality requirements that are hard to accommodate with other methods. Material thickness up to .125" (3.175mm) and no less than .007" (.177mm) can be cut. Some typical materials that convert well include paperboard, high-density plastics, corrugated, recycled paperboard, and specialty coated boards. Folding cartons are a very common product followed by gaskets and then specialty items. What is the quality of product difference? When compared to standard crush cut rotary or flatbed cutting the major product quality improvement issues that make a difference include; less dusting, less slivering, less burring, less nicking - both natural and production oriented, and greater accuracy.

 What are the main production advantages?

  • Feed rates are not limited by the cutting operation! Now there's a statement. These tools will spit out finished product as fast as you can push it through the press. Usually another process like in-line printing or part delivery systems will limit the feet per minute speed of the line.
  • Stripping is done at the cutting stage by either a series of fingers, a through the cylinder collection of waste, or other techniques that remove all waste before the part is delivered to the back side of the die. There is no separate stripping stage and parts are delivered waste and web free. "Stream Stripping" is a term used to describe the waste being removed as a continuous stream as it is pulled into a vacuum tube.
  • Tool life is typically measured in millions of revolutions. Depending on the operator, the material being cut, and the method used to manufacture the dies, cases are reported of solid dies lasting up to 350,000,000 *(yes, that's 350 million) revolutions before needing a sharpening. Flexible dies will typically max out earlier than solid tools somewhere in the range of 4 to 5 million revolutions. This long tool life usually translates into less down-time overall and can translate into lower overall tooling costs when compared to other methods.

Rotary Die Cutting 3

What about the tools?

  • The tooling for this type of process is made in both flexible plate and solid machined configurations. The flexible plate tools are usually made via chemical or standard machining or through a combination of the two and are wrapped around a cylinder that stays in the press. The solid machined cylinders are typically made using EDM (Electronic Discharge Machining) or standard direct machining or through a combination of the two.
  • Hardening and finishing techniques for the cutting surfaces can include laser hardening and cladding as well as specialty coatings and platings. All are designed to improve tool life.
  • Web widths can range from 6" to 60" (152.4mm to 1,524mm)
  • Tool diameters can range from 3" to 24" (76.2mm to 610mm)
  • Accuracy is ±.002" (.05mm)
  • Costs for a single matched tool: $1,000.00 to $250,000.00 US That's a huge range and it can vary greatly depending on the image to be cut, the style you choose - flexible or solid, the stripping requirements, the surface finishes, the number of rolls you put in line, etc… Flexible tooling tends to range from $1,000.00 to $3,000.00 US with most narrow web applications falling under the $2,000.00 mark
  • Solid tools can typically be sharpened about five times before they are retired and they can be reworked. Flexible plate tools cannot be sharpened or reworked.
  • Just like male/female cutting in a flat operation, the tolerancing and adjustments made to offsets allow for just about any material to be cut accurately and with ease.
How is a Crease, Emboss or a Perf produced?
The MMRC technique will only cut through material. Just like with a pair of scissors or a steel rule bridger, it's tough to make a kiss cut or a dent with a male/female tool. When a crease or an emboss or a perf need to be produced a crushing operation must be added. A blade like or crease like male is added with a hard anvil counter on the opposite cylinder. Because the upper and lower cylinders are both being machined, reverse scores and reverse cut-scores can be created as easily as the standards. These can be incorporated into the tool that does the perimeter cut or can be incorporated into a second set of die cylinders that fall before the final cut stage. Separating the stages has the advantage of creating a long life tool and a shorter life tool that can be worked on individually.

Are there specialty machines that are needed to run this type of tooling?
There are many companies that make presses to accommodate rotary cutting. This type of tooling and process (MMRC) can be used in many of them. In general the die manufacturers that make this type of tooling will do their best to build a tool that will work in your press.
Finishing Up
Everyone has their own take on techniques used in our industry. What the future will hold for MMRC will most likely be embroiled in what happens to run lengths, corporate consolidations/product consolidations, and mechanization of other attached packaging processes. For the time being this technique has a growing number of markets that it plays very well to. The cheaper flexible and magnetically mounted tooling is being pushed hard right now by a couple of tool manufacturers. Although this type of flexible tooling will never replace the need for the more expensive solid tools it will more than likely allow more converters to use this type of cutting technique on a more regular basis. As more rotary converters discover the benefits, for those special jobs, the technique will flourish. I predict that this will lead to an explosive market over the next twenty years where once again our productivity as converters advances by leaps and bounds.As lessons go, this ten year process of becoming familiar with MMRC has been too slow but has taught me to listen a little longer and a little harder to everyone I meet. I hope you too find a product that can use this process to your full advantage, and that the IADD has once again started you off in the right direction.*At printing of this article the production was closing in on 400,000,000 revolutions (not parts). This solid machined tool was made by Bernal Technologies and is cutting .018" Poly coated SBS. Wow! Not all solid tools will last this long. It all comes down to materials, machines, and operators.

Support for this writing came from several sources including:

    Marc Voorhees - Bermaxx LLC / Bernal TechnologiesMarc Love - Atlas Chem-MillingJim Redd - XynatechRon Brenwall of Maxim InternationalPhotos courtesy of Bermaxx LLC / Bernal Technologies.
Thank-you very much!

Thursday, June 3, 2010

PMC Dies and Diecutting

Written By Mark Batson Baril

PMC Die Cutters and Cutting Tools

The question came to us the other day on whether we worked with companies that dealt in PMC Cutting tools and could we suggest a source. The first part of the question led to the first part of our answer - What the heck is a PMC cutting tool?

Because of my “bag over head” knowledge in this area, and because others may also be in the dark on this one, the mission is clear. So here we go, trying to shed a bit of light on what they are and how they are used.

PMC turned out not to be a type of technology - it turned out to be a brand/manufacturer name. PMC (Printing Machinery Corp.) developed its first hollow die label cutting machine in 1940. The idea was to create a machine that could cut a variety of printed and non-printed materials accurately and quickly. What was developed was a machine that uses a cutting tool that acts as a high speed feed through punch. The machine pushes a large stack of materials up through the tool and the finished parts are ejected out the back of the machine, the tool, and finally the bolster plate. I have found that there are four major players in this type of machinery/cutting system - PMC, BUSCH, BLUMER, and VIJUK.

The machines are designed to feed sheeted materials that have been stacked to a height of up to 4" (102mm). Press bed sizes are usually small, staying in most cases less than 20" x 20" (508mm x 508mm). The machines can cycle up to 20 times per minute. If the part you are cutting is only .005" (.127mm) thick it means you can cut a whole mess of parts in not a whole lot of time. The manufacturers claim that on certain materials on certain machines the cut sheet rate per hour can easily exceed 1,000,000. Yes that’s one million sheets! Just to compare, a fully automatic Bobst Carton cutter on steroids may hit the mid teens (that’s thousands).

So why haven’t some of us been exposed to this type of cutter/tooling in the past? It may be that the machines are primarily used to cut very high volume common products with dies that are not steel rule dies. Plus they are used to cut some fairly usual but specialized products that many of us shy away from.

The list of products and services that work well on this type of machine include the following:
  • Labels
  • Wrappers
  • Envelope Blanks
  • Note Pads
  • Credit Cards
  • Identification Tags
  • Deckle-edge postcards
  • Game Cards
  • Paint Chips
  • Luggage and Price Tags
  • Coasters
  • Placemats
  • 3-way Booklet Trimming
  • Round Cornering

Some of the more common materials that are cut on these machines include:
  • Embossed Paper
  • Unevenly Printed Label papers
  • Plastic
  • Foil
  • Mylar
  • Paperboard

Stacks of material are loaded outside the die cutting area and are automatically jogged and lined up. The stacks are held on all four sides throughout the die cutting operation which makes the possibility of a very accurate cut quite good. There are material shuttles that allow one stack to be automatically loaded while another one is being cut. This creates very little time in which the machine is not actually cutting. Parts do not have to be ejected back out through the front of the die and so the machine can constantly act towards cutting rather than cutting and ejecting. The tooling only makes contact with the cutting plate during the last cut of the stack. This means that tools last longer as the only friction they see is the material they are cutting.

The Tools:
Dies for this type of machine are quite simply feed through specialty punches. They are typically made in two ways. They are forged dies made from pre-ground rule that is bent and formed and then welded at the joint, or they are machined (usually wire cut) dies that are cut from a single block of steel. The height will vary from job to job and machine to machine but usually ranges from 1 1/2" (38mm) to upwards of 4" (102mm). The thickness will vary depending on the application and will have a taper that runs from small at the cutting edge to large at the base. Because the die will feed the finished parts through the center, all the taper will run to the outside of the tool. Support tabs, mounting brackets, and stripping knives are all items that can be built-in to help the operator speed the process and help the tool survive the incredible stress of the impression. Standard bolster plates are used within the machine to create a space for the finished parts to pass through the back of the die. On unusual shapes or large repeat run jobs, a custom bolster plate can be made for a perfect match.

Thanks for all the help from Brian at Stewart Industries (PMC Worldwide) and Lynn at Progressive Service Die Co..