Polishing and Bending See-Throughs

Acrylic sheet can be cut, shaped, finished and formed. How well and how efficiently you handle these basics will, in large part, determine your success. We all know our customers are more price and quality conscious than ever before.

Technology is rapidly increasing efficiencies for plastic fabricators. Yet with all the technological gains, the basics remain the same. You can cut more pieces, with tighter tolerances, faster than ever but you must still finish the edges, peel masking, bend and package.

Efficiency gains at the finishing and bending operations will make you more competitive and ultimately add to your bottom line. Ask yourself the following:

• Does your equipment provide the versatility to handle both large and small jobs with minimal setup time?
• Does your bending equipment provide heat from both above and below the work to reduce cycle times?
• Does your edge finishing system polish and produce matte finish bondable edges with the same piece of equipment?
• If you completed the last job in half the time, how would that have affected your profit?

The majority of expenses for any job relate to the time it takes to complete the job. Through automation, efficiency gains may be realized on several fronts. Cost reductions, productivity increases and quality improvements are three that can have an immediate and positive impact to your bottom line. The following outline shows several areas for potential profit improvements.

Efficiency Gains

• One operator can manage multiple units
• Current operator has time for other tasks

• Delay and/or avoid additional Hiring
• Reduce current payroll levels

• Increased production speed
• Operator fatigue no longer a production factor

• Can lead to ability to take on additional business
• Creates customer loyalty

• Scrap reduction
• Manufacturing consistency

Setup/Tool Change Procedures

An often underestimated part of any production environment, and one that when monitored and controlled can produce efficiency gains and add profit, is setup and tool change procedures. Time spent between job setups and scheduled or unscheduled tool changes adds up quickly and associated process costs become a double edged sword. Not only is your process in an idle state at these times but you are expending wage resources during the downtime. This must occur at some point during the process but the time duration is certainly controllable.

Keep spare parts, tools and any necessary measuring instruments as close to their relative machining process as possible.

The savings may not look like much in the short-term but over time if you reduce set up and production times, acquire versatile equipment, hire, train and empower good people you will see a savings.

Consumable Tooling

Saving time and money here is a matter of watchful eyes. Obviously a tool works best and produces superior quality parts when the tool is new or just sharpened. All consumable tools have a fairly finite life expec tancy. In most instances the wear period is predictable. Once you have established the time pattern, remove the tool just before the failure point. Removing the tool from service while it is still fairly sharp will, in the long term, increase the life of the tool. Less material from the tool itself will require removal to bring the cutting edge back to optimum quality.

Different materials will cause your tooling, especially the diamond tooling, to wear at varying time intervals. Harder materials will result in longer tool life. Softer materials will tend to roll over in a cutting process and gum up the edge of a tool resulting in reduced tool life and inferior quality parts.

The manufacture of diamond polishing tools for plastics is still mainly a human driven process. Much of the work is completed by hand, so there will be some variation between tools. The average life expectancy for the diamond polishing tools is approximately 45-60 hours of use between sharpenings and 8-10 sharpenings before the inserts must be replaced.

Tool life for the diamonds is based upon working with clear acrylic material. You will notice a better result with cell cast materials over continuous cast or extruded materials. Tool life will be reduced by one third to one half on colored materials, especially smoke or black and on any of the softer materials like impact modified, polycarbonates, copolymers and PETG. Diamond tools have much the same reaction as your saw and router tooling.

Another factor to consider in your production versus quality equation is to stack or not stack material. Obviously machining multiple pieces of any material simultaneously is preferable to machining them singly; however, you will sacrifice some tool life and edge quality in the process. The loss is due to the many layers of film and or paper masking through which the diamond must pass. Best results are obtained when machining no more than 5 pieces of 1/8” or 3/16” and no more than 4 pieces of 1/4” material. Placing two smaller capacity machines into service can improve both efficiency and quality of your finishing operations. The smaller units will use less valuable floor space and the same operator can easily manage both.

Bending Sheet Materials

After all of your efforts from initial design, cut to size and finishing; you have a great deal of time and money invested in each part. Now you must bend your creation to its final form - this is the point in your process where you clearly want error-free performance.

Enter the variables of ambient temperature fluctuation, relative humidity, process variation and operator differences and your bending operations can present quite the challenge. Of the many options from calrod to quartz, straight nichrome wire will provide the most heat consistency over distance for your process.

Setups with nichrome wire range from over simplification (a length of wire stretched between two ten-penny nails driven into a two by four) to the extremely complex. Generally, an 18-gauge wire set into a 15mm-20mm wide aluminum reflector will provide the best results for materials up to1/4” in thickness. Support along the underside and pressure from above the material adjacent to the heating area will reduce warping and bowing. One of the most important and sometimes least attended to aspects of the bending process is the cooling fixturing. Heating materials in a desired location is ten percent of the battle. The remaining effort is expended designing, building and adjusting cooling jigs. Adding insult to injury, time and money is expended constructing a jig for a particular job that may never come around again. Consequently, the jig is either trashed or thrown on a shelf to forever collect dust.

A universal jig that is designed to accommodate t-stands, shoe risers, photo frames, sign holders and a litany of items is ideal for increasing part quality. (Figure 2). Each new part is placed into the jig, it moves the previous one forward until the parts exit cooled and formed.

For optimum results and efficient cycle times, heat both sides of the material simultaneously. If your current capability allows heating from one side only, it is best to flip the material over during the cycle to ensure even heat distribution through the material.

Worth Mentioning

Bubble free polycarbonate bends: Heat from both sides, lower the wire temperature and be patient! Always be sure your material is fairly dry to prevent blistering.

Thin materials - .010 to .062 vinyl etc.: Use a Teflon®- coated brass insert over the heating wire. You can then place the material directly on the insert surface, heating a narrow (1/16”) area of the material to produce sharp, straight bends.

To reduce and/or eliminate the “dog ear” at the bend point; block off the edges of your parts while they are over the heating area. This will keep the edges a bit cooler than the surface and, when bending the material, will tend to flow toward the center and not out of the edge.

Adding Value

Customers need an education. Teach them about the different processes you can use to ensure a part will look as good on the hundredth day as it did on the first day. Yes, it may cost a bit more but why should we feel the need to apologize for pricing? Products of a superior quality do cost a bit more and they are well worth the extra cost. You know it, I know it, but do your customers know it?