What are the different methods used to fabricate ACRYLITE® LED sign grade acrylic sheet?

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What are the different methods used to fabricate ACRYLITE® LED sign grade acrylic sheet?

The introduction of ACRYLITE® LED sign grade acrylic sheet marks the development of a modified acrylic sheet designed specifically for use in the sign industry. ACRYLITE® LED sheet was designed as the universal sign product. ACRYLITE® LED sign grade sheet gives the sign fabricator a product with outstanding fabrication ease, excellent weatherability and additional impact strength. The information below provides recommendations to help the fabricator achieve optimum results with this unique product. You may refer to the information prepared for ACRYLITE® extruded (FF) acrylic sheet for additional information.

Cutting with Table and Panel Saws

Generally, straight cuts are made using a conventional table or panel saw. A saw blade specifically designed for acrylic, such as a triple-chip grind, carbide toothed saw blade works best. For a 10-inch saw blade, 80 teeth are recommended. For larger blades, an equivalent tooth spacing can be utilized with good results. On a triple-chip grind saw blade, every other tooth has a beveled cutting edge, which aids in chip removal and reduces heat buildup.

When cutting ACRYLITE® LED sign grade sheet, the blade should protrude ½" to 1" above the surface of the sheet, with optimum results usually obtained using a ¾" blade height. Vibration should be kept to a minimum, either by clamping the sheet to the cutting surface (when operating a vertical saw or panel saw) or providing the proper pressure on a table saw.

Moderate feed rates, in the 15-25 ft/min range, will ensure a proper cut. A chipped edge indicates that the feed rate is too fast, while a melted edge indicates that the feed rate is too slow. It is recommended that the feed rate be decreased at the end of the saw cut, especially on thinner sheets. This will prevent chipping and blowout of the exit edge.

PROBLEM POSSIBLE CAUSE SOLUTION
Chipping Excessive vibration Ensure pieces are properly supported and clamped to working surface.
  Excessive blade run-out Check blade collar, replace if run-out is greater than 0.002".
  Proper blade height Set blade height at ½" to 1" above work pieces.
  Improper blade type For table saw cutting, use a triple-chip blade. (2.5 teeth per inch of circumference)
    For jigsaw cutting use a wavy-set style blade. (8-13 teeth per inch of circumference)
  Feed rate too fast Decrease feed rate
Melting Dull blade Replace or sharpen blade
  Feed rate too slow Increase feed rate
  Improper blade style For jigsaw cutting, use a wavy-style blade with 8 to 13 tpi
    For all-purpose table saw cutting, use a triple-chip, carbide tipped blade, 2.5 teeth per inch of circumference (i.e. 80 teeth for a 10-inch diameter blade).

Jigsaw Cutting

Hand held jigsaws work well with ACRYLITE® Resist sign grade sheet in cutting intricate shapes and letters. Results comparable to those achieved with cell-cast acrylic sheet are possible. For best results, use a wavy-set type blade with 8-13 teeth/inch (tpi). This blade configuration will typically chip cell-cast acrylic, but will work very well with ACRYLITE® Resist sign grade sheet due to the sheet's inherent toughness. Using a blade with a higher number of teeth per inch, 18-24 tpi may result in melting along the cut edge of ACRYLITE® Resist sign grade sheet. It is also important to ensure the blade is sharp — do not use a blade that has already been used for cutting metal or other materials.

In jigsaw cutting, it is important to minimize vibration by clamping the material to a firm surface. Feed rates in the 8-12 ft/min range will yield the best results.

Bandsaw Cutting

Bandsaws are typically used for quick, rough cuts, as well as intricate shapes and letters. As with jigsaw cutting, the quality of the edge is dependent on the type of blade used. Generally, blades in the raker style with teeth in the 18-24 tpi range will produce the best results. Blades with fewer teeth per inch will leave a jagged, rough edge while blades with a higher number of teeth per inch will yield a smoother edge. If blades with more teeth per inch are used, it is recommended to utilize a coolant such as water, compressed air, or a combination of both to reduce melting along the cut edge.

Feed rates in the 10 to 15 ft/min range will yield the best edge.

PROBLEM POSSIBLE CAUSE SOLUTION
Chipping Excessive vibration Ensure pieces are properly supported and clamped to working surface.
  Excessive blade run-out Check blade collar, replace if run-out is greater than 0.002".
  Proper blade height Set blade height at ½" to 1" above work pieces.
  Improper blade type For table saw cutting, use a triple-chip blade. (2.5 teeth per inch of circumference)
    For jigsaw cutting use a wavy-set style blade. (8-13 teeth per inch of circumference)
  Feed rate too fast Decrease feed rate
Melting Dull blade Replace or sharpen blade
  Feed rate too slow Increase feed rate
  Improper blade style For jigsaw cutting, use a wavy-style blade with 8 to 13 tpi

For all-purpose table saw cutting, use a triple-chip, carbide tipped blade, 2.5 teeth per inch of circumference (i.e. 80 teeth for a 10-inch diameter blade).

Scribing and Breaking

ACRYLITE® LED sign grade sheet can be scribed and broken similarly to ACRYLITE® extruded acrylic sheet and ACRYLITE® cast acrylic sheet. Scribing should only be done on the 0.118" (3mm) thickness. With the aid of a straight edge to guide the scribing tool, pull the scribing tool across one side of the sheet surface several times until the tool has penetrated approximately 1/16" through the material. Next, position the sheet so that the scribed line is just beyond the edge of the working surface. While holding the sheet firmly in place on the surface near the scribed line, apply a quick, downward pressure to the end of the sheet overhanging the working surface.

Routing Operations

In general, ACRYLITE® LED sign grade sheet is a more forgiving material to rout than ACRYLITE® extruded sheet or ACRYLITE® cast sheet. Due to its proprietary formulation, ACRYLITE® LED sign grade sheet is less prone to chipping, and permits faster feed rates without sacrificing edge quality.

Handheld and Table Routers

Carbide tipped, ½” diameter bits, with two flutes will yield the best results. In all routing operations, from hand-routing to stationary equipment, minimizing sheet vibration will help to reduce or eliminate chipping. Vibration can be minimized by using sufficient hold-down for stationary routing and a guide when hand routing.

PROBLEM POSSIBLE CAUSE SOLUTION
Bit Breakage Excessive heat buildup in bit due to inadequate chip removal Use compressed air to clear chips.
    Use bit designed to chip removal (twist up).
  Plow routing using fast feed rates Reduce feed rate.
  Dull bit Replace or sharpen bit.
  Excessive load on bit Make multiple passes.
Melting Feed rate too slow Use faster feed rates.
  Dull bit Replace or sharpen bit.
  Inadequate heat removal Use a larger diameter bit.
  Rotational speed too high. Reduce RPM's. May need to be coupled with a faster feed rate.
  Inadequate chip removal Use a twist-up bit.
    Use a slow helix angle rather than a fast helix angle.
    Consider multiple passes.
    Use compressed air to aid in chip removal.
  Incorrect number of flutes on bit. Decrease number of flutes on bit.
Chipping Feed rate too fast Decrease feed rate.
  Vibration Make sure pieces are adequately supported.
  Incorrect number of flutes in bit. Increase the number of flutes on the bit.

Drilling Operations

ACRYLITE® LED sign grade sheet can be easily drilled with the same equipment used for ACRYLITE® extruded or ACRYLITE® cast sheet. It is best to use stationary drilling equipment such as a drill press. The proprietary formulation of ACRYLITE® LED sheet provides excellent resistance to chipping when drilling. In general, it will drill faster and more easily than standard acrylic sheet.

Best results are achieved using high-speed steel “modified-for-plastic” drill bits. Instead of the relatively flat tip angle of 120 degrees present in a standard metal drill bit, a modified for plastic drill bit should be ground to a sharp 60-90 degrees. The sharp angle allows the bit to easily enter and exit the material. The cutting edge should be ground flat to a 0-4 degree positive rake angle, which allows the cutting edge to scrape the material, not gouge it. The surface behind the cutting edge must be ground away to a 12-15 degree clearance angle, which minimizes metal to plastic contact and heat build-up. Rotational speeds in the 500-1000 RPM range, combined with feed rates in the 3-12 in/min range, will produce a clean, low stress drill hole.

Proper backing material such as plywood or another piece of acrylic should be used when drilling ACRYLITE® Resist sign grade sheet. The backing material will help prevent chipping of the bottom surface. When drilling stacks of sheet, it is a good idea to utilize a coolant such as water or kerosene. This will minimize heat buildup and create holes with smooth walls. Slow feed rates should be used when entering and exiting the material to avoid chipping or blowout.

If a “modified-for-plastic” drill bit is not available, a standard metal drill bit can be used to produce satisfactory results. Under these circumstances, it is extremely important to securely clamp the material to the table, to minimize chipping.

PROBLEM POSSIBLE CAUSE SOLUTION
Chipping Feed rate too fast Use feed rates in the 3-12 ft/min range
  Vibration Ensure pieces are properly clamped to work surface
  Incorrect bit For best results, use a "modified-for-plastic" drill bit
Blowout Insufficient back support Use backing material such as plywood or acrylic
Melting Feed rate too slow Use moderate feed rates in 3-12 ft/min range
  Rotational Speed too high Reduce rotational speed. RPM's in the 500-1000 range will yield the best results.
  Inadequate cooling Use air or water mist
  Incorrect bit Use a "modified-for-plastic" drill bits. Smaller bits may require cooling.
  Bit is not true Replace bit

Thermoforming Operations

ACRYLITE® LED sign grade sheet can be thermoformed into a variety of finished parts and sign faces. Its forming temperature range of 270-350°F offers faster cycle times than can be achieved with conventional cell-cast acrylic sheet. This wide range of forming temperatures allows, for greater versatility in thermoforming operations.

In most cases, excellent results can be achieved using forming temperatures of 310-320°F. (Up to a draw ratio of 3:1) Parts that contain more detail or have a deep draw need to be formed at the high end of the forming range, 320-350°F. Parts should be left in the mold after forming until they have reached a temperature of approximately 180’F. It is important to preheat the mold to approximately 160-180°F. If the mold is not preheated, the formed part will cool too quickly, resulting in internal stresses in the thermoformed part. Draft angles of 2-3 degrees will allow for easy part removal.

Due to its method of manufacture, ACRYLITE® LED sign grade sheet will be oriented in the manufacturing direction. Manufacturing direction can be determined by looking at the label or printed masking on the sheet. As you read the label or masking, the manufacturing direction is from top to bottom. The sheet may shrink up to a maximum of 3% in the manufacturing direction when heated. Be sure to allow for shrinkage when cutting blanks for thermoforming.

During the heating cycle, colorless ACRYLITE® LED sign grade sheet will turn a translucent white color. After the sheet is formed and allowed to cool to room temperature, it will regain its high light transmission, losing its milky white appearance.

Forming Cycles

ACRYLITE® LED sign grade sheet can be heated by a variety of methods, including infrared heaters, circulating air ovens, and other conventional heating methods. Generally, when heating ACRYLITE® Resist sign grade sheet in an air-circulating oven, the heating times will be similar to ACRYLITE® extruded sheet. Heating cycles when using infrared heaters tend to be much shorter than oven heating cycles.

The following table illustrates approximate heating times for 0.118" (3mm) ACRYLITE® SG sheet. Testing was done on a thermoformer equipped with ceramic heaters positioned approximately 2.5 to 3 inches above the sheet.

Time Approximate
Temp (°F)
120 seconds 260°
180 seconds 310°
210 seconds 350°

It is important to note that actual times will vary for each individual thermoformer due to various parameters such as the type of heater (convection oven, radiation, etc.), distance from the sheet, and single or dual side heating.

ACRYLITE® Resist sign grade sheet offers outstanding thermoforming definition at reduced cycle times, compared to standard acrylic and polycarbonate sheet. ACRYLITE® SG sheet offers excellent part definitions at temperatures lower than those of conventional cell-cast acrylic sheet.

TROUBLE SHOOTING GUIDE: THERMOFORMING OPERATIONS

Problem Possible Cause Solution Blistering Surface temperature of the sheet is too high Reduce heat time, oven temperature, or increase distance from sheet to heaters.Inadequate part definitionSheet temperature below optimum forming temperatureFor high definition parts, heat to the high end of the forming temperature i.e. 320 - 350°F.

Edge Finishing Operations

The same edge finishing operations that work well with standard acrylic sheet can be used to obtain excellent edge finishes with ACRYLITE® Resist sign grade sheet. However, care must be taken in certain edge finishing operations, such as flame polishing, to ensure the best edge quality. This section will cover proper techniques to ensure an edge finish of the highest quality.

Wet Sanding and Scraping

Wet sanding will yield a smooth, matte-finish edge and is suitable for use prior to flame polishing. Dry sanding is not recommended, as it will lead to a highly stressed and melted edge. To obtain the smoothest edge, start with 240-grit "wet and dry" sandpaper, using plenty of water. The use of water will keep edge stresses to a minimum by acting as a coolant. Finer finishes can be obtained by sanding with 240-grit, then stepping up to 400, 600, and 800 grit, depending on the desired finish.

The use of belt sanders may result in melting and high stress. If using a belt sander, it is important to use light pressure when sanding. Excessive pressure will increase frictional heat buildup, causing the edge to melt and gum.

Hand scraping is an alternative to sanding for preparing the edges of a sheet for polishing. The sheet can be scraped with almost any type of sharp, flat metal edged tool. Holding the scraper vertically, at a 45-degree angle to the edge, scrape the sharp edge of the sheet by drawing the tool across the edge with a firm but steady pressure. A continuous strip should peel as the tool is drawn along the edge. There are tools available that will reduce the sharpness of both edges at the same time. it is important to note that scraping will not provide the smoothness of a sanded or polished edge.

Jointing

Jointing of ACRYLITE® LED sign grade sheet will produce a smooth, machined edge. Knives made from high-speed steel or carbide will work well. Blade height should be set to remove approximately 1/32" from the sheet. The most important aspect of jointing is controlling the feed rate. It is important to use a steady, even feed rate while holding the sheet material firmly to the guide fence. Excessive feed rates will result in a chipped, highly stressed edge.

Edge Finishing Machines

Commercially available edge finishing machines offer a fast method of obtaining smooth edges without sanding or scraping. Finishes will range from smooth, matte-finish to almost polished edges, depending on the design of the machine and cutting tools used. Edge finishing machines are ideal for preparing sheet for subsequent edge finishing steps, such as flame polishing and buffing, or fabrication steps such as cementing. Care should be taken to adjust the feed rate to eliminate chipping and melting of the material. Fast feed rates will result in chipping while slow feed rates will result in melting. In general, faster feed rates can be used for edge finishing ACRYLITE® Resist sign grade sheet than for standard acrylic sheet.

Buffing

Buffing the edges of ACRYLITE® LED sign grade sheet will produce a high luster finish. It is recommended that the edge be scraped, then wet sanded prior to buffing. A stationary buffing wheel or portable polishing head can be used. Loose stitched, bleached muslin wheels, used in combination with a medium to fine buffing compound will provide a high luster edge in a short time.

Flame Polishing

Highly polished edges can be obtained by flame polishing using the same techniques used with standard acrylic with slight modifications. When flame polishing ACRYLITE® LED sign grade sheet, a cooler flame should be used than with standard acrylics. This is best accomplished using MAPP gas.

Another option is to use a hydrogen/oxygen-welding torch. Make sure to reduce the oxygen content to produce a flame that is bright orange/red in color, as opposed to the bluish, almost invisible flame typically used with standard acrylics. ACRYLITE® LED sign grade sheet has a tendency to turn a milky white color when overspray from the flame contacts the surface of the sheet. It is important to minimize this contact by using a quicker feed rate than would normally be used for standard acrylics. Hold the torch at an angle and draw the flame along the edge of the sheet. Practice will help you to estimate the speed and distance. If the first pass does not produce a completely polished edge, allow the piece to cool, then try a second pass. For optimum edge finish, wet sand the edge or pass the sheet through an edge finishing machine or jointer to remove any tooling marks from previous operations prior to flame polishing.

PROBLEM POSSIBLE CAUSE SOLUTION
Dull edge after flame polishing Not enough heat / missed spots Allow piece to cool, then make another, slower pass to cover these areas. Ensure the edge is fully submersed in flame, but with minimum overspray onto the sheet.
Charred edge after flame polishing Too much heat Use MAPP or propane gas rather than Hydrogen/Oxygen mixture. If MAPP gas is unavailable and Hydrogen/Oxygen torch is used, make sure flame is bright red/orange rather than invisible blue.
  Dirt or contamination Make sure edges of sheet are free from dirt or contamination prior to flame polishing.
Blisters on edge after flame polishing Too much heat See above for recommendations.
Rough edge after buffing Improper edge preparation Make sure all tooling marks are removed by wet sanding or edge finishing prior to buffing.
Melting from edge finishing machine Feed rate too slow Increase feed rate
Chipping from edge finishing machine Feed rate too fast Reduced feed rate.

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