Membrane Switch Cutting

Written By Mark Batson Baril

It’s amazing how many things out there involve specialty cutting.

Do you own a Microwave Oven? - a Treadmill for exercising? - a flat faced calculator? - a machine with a pressure sensitive operation switch? If you do, then chances are you own and use a Flat/Tactile Membrane Switch (or several) everyday! These switches can be used for everything from the simplest of on/off switches on a blood pressure reader to a complicated multilevel/multitasking switching/control system for a printing press.

It’s hard to say when the technology came into being because some of the simpler connectors/switches have been cut with dies since the 1950’s. When was electricity invented? Membrane switches really took off in the 1980”s when consumers were demanding lower prices and manufacturers had to push for an alternative to the traditional molded/hard printed circuit boards that were so often used as the base for switches on most machines. Their main attributes are, the relatively low price, their relatively quick turn-around production time, plus they look pretty cool!

Membrane switches are typically made up of six different layers that are all die cut (with Steel Rule Cutting Dies, or laser cut, router cut, matched metal or rotary diecut, etc... depending on the situation) separately and then assembled. The concept is nearly simple in that as with any electrical switch you are trying to create a space between two wires when the circuit is inactive and you are trying to make them touch when you are connecting or making them active.

The basic layers are;

# 1 - Graphic Layer - This layer of thin plastic material is what the user sees and touches. It acts as the guide to show you where to push the switch and it sets the tone for the product and it’s operational instructions via the graphics. As with the other layers of a membrane switch, the graphic layer is silk-screen printed. Sometimes the top/graphic layer is diecut as a final pass once everything has been assembled to it, other times it is cut into it’s shape separately. # 2 - Graphic Adhesive Layer - This layer acts as a two sided glue to bond the graphic layer to the top circuit layer. It’s shape can often times be the most intricate in that there can’t be any adhesive that touches the actual switching area. Each of the areas where there is a button or switch must be cut away. # 3 - Top Circuit Layer - This layer acts as the first half of the electrical connection. Silver Ink is printed on polyester to form the electrical paths. Protection from electrical interference from outside the circuit is stopped by printing conductive ink shields, or applying aluminum foil, metallized mylar or copper foil on the top surface of this top circuit. The feeling of the switch is created in this layer as well. You know that great “Popping” feeling you sometimes get when you press one of these switches? That’s when these switch guys have found your “tactile optimum” a.k.a. “feels good point.” The plastic that this layer is made of is put through a process where a heated mold forms little domes at the areas where you will push. When you push down on this dome you get the feeling that you are actually doing something. I hate those switches when you can’t tell that you have pressed anything! # 4 - Spacer Layer - This is the really ingenious layer! Some designer probably made a fortune on this! This layer creates the space between the two circuit layers. The general shape of the outline is cut as well as holes at the points where you want the switch to activate. When you push the dome/top circuit down it pushes through this spacer layer and makes the connection to the bottom circuit, thus completing the electrical circuit. Some of the feeling of the switch is created in this layer as well. When all of these layers are assembled there is air trapped in the “spaces”. The designers will install more cut-aways, called air-tracks, between the various spacer holes. The movement and resistance of this trapped air, when the dome is pushed by the user, can make it harder or easier to push down depending on how many they plan for and how wide they make them. # 5 - Bottom Circuit Layer - This is where the final electrical connection is passed to from the top circuit. The electrical leads from both the top and the bottom circuit pass through a part of the switch called the “TAIL.” This tail is just an extension of the printed plastics that extends beyond the visible part of the graphic layer and goes to the inner workings of the machine you are controlling. # 6 - Rear Adhesive - This double sided glue layer adheres the completed switch to the surface of the machine/circuit board, or whatever is planned for the tail to go into.

And that’s it! Of course there are about a million variations of how this can go together. Different plastics, metals, rubbers, etc..., can be used to create different electrical properties, feelings for the switch, etc.... . Backlighting can be created, LED’s, resistors, capacitors, even memory chips, can all be added to a switch of this type. Every manufacturer has their own techniques for not only making the switch work but for making it feel like it should for the user, and work for just about any situation.

The concept is fairly simple yet when you see either a set of dies, prints or even cut parts laid out in front of you, it can look like a fairly complicated puzzle.

What’s the future in this type of market? Faster and Cheaper! What else! Many manufacturers are actually producing the cuts for membrane switches with lasers. They can produce one switch or short production runs this way with no die costs and no waiting time for the tools. Diemakers hate to hear that! Digital printers now produce the top/bottom circuit and graphic layers direct from the file without having to produce screens/plates/etc.. .

I’ll be using the membrane switch on my printer now and then switching my computer off to wait for that next inspiring question to hit my desk. Thanks for reading!

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.

Fiberglass Cloth Cutting

Written By Mark Batson Baril

Can woven fiberglass cloth be cut into non-square shapes with a steel rule die?

Fiberglass cloth can be easily cut into shapes with a steel rule die as well as many other types of tooling. In order to make the cut well, with no hanging threads, a sacrificial belt system or an operator with great experience, or both, will have to be involved. The problem comes after the cut in the unraveling of the edges that have been freed during the cut. Like in a slapstick cartoon, a single thread can lead to the entire part falling apart, leaving you exposed to all sorts of problems. If you need just a basic, jagged cut, they can work well. If you need to retain the shape perfectly to pass on to the next operation (usually some type of gluing), you need to make a change to the material.

Add material to the fiberglass to give all the fibers a pre-bond. Either a permeable laminate or a specialty additive work well to give the parts some bond before you make the cut. Your fiberglass supplier should be able to do this for you. Besides adding something to the material to keep it together we have heard of no other way to cut this product and keep it from falling apart. Even a heat sealing type cut is hard to make work because fiberglass is heat resistant. Great question in a very specialty field.

Thanks to Mutual Industries and RP Associates for their technical advice and expertise on this one.

Polycarbonate Cutting

Written By Mark Batson Baril


How would we best cut 1.2mm (.047") polycarbonate (50,000 sheets) using a conventional flatbed - platen style machine? The sheet size is 1,524 x 762 (60" x 30"). The part is a simple rectangular shape with rounded corners, but with 32 keyhole shaped cut outs. These keyholes are 9.52mm x 12.7mm (3/8" x 1/2"). What would be the best type of rule, etc... to use? We are used to cutting paper...

Polycarbonate, very commonly known in the US by its trade name Lexan, is a very diecuttable material. It is used constantly in the nameplate, membrane switch and sign industries due to its toughness, ability to be printed on, electrical non-conductivity, and general availability.

We would make just a few suggestions that may make your life a bit easier going from paper to Polycarbonate.

Feed the sheets and strip the waste the same way you would treat similar shaped paper products.

Use fewer nicks to start with than you normally would and try to get away with just the natural nicks caused by the rule joints. The material will tend to stay with itself even though it has been cut and it can be a real bear to separate if it has not cut all the way through or if too big a nick has been made to get it through the press.

Use 3 point sideface rule with a ground edge. Face the bevel to the waste. Test cut your keyholes with long bevel and sideface before you make them all, especially if their size is critical. A simple one up test die may save you a great deal of time.

Use 3/4" base material (assuming .937" high rule) to support the rule as high as you can. Under the strain of this thickness of this material, the rule will want to move with a thinner base material. Movement will make it more difficult to make-ready and maintain ready. Etch away the front of the board if need be to make way for any feed devices like gripper bars.

Other than that, you shouldn’t have too many problems. It will make one heck of a POP when it cuts compared to paper, but that is normal.

Depending on your quantities you may want to take a look at laser cutting, waterjet cutting and perhaps even routing the parts.