Up until the last few years, when writing an article or presenting a seminar about XYZ glass cutting machinery, it was necessary to provide prospective buyers with ways to justify the purchase of a cutting machine. Today, the question has become not "should we," but rather "when" to buy one, or "now that we have one how do we improve its productivity?" If a reader does not feel he can justify an XYZ cutting machine, (and there are some companies who cannot) I will be pleased to furnish a justification list upon request. For this article, I will discuss several issues relating to the purchase of an XYZ glass cutting machine and to maintaining and improving the productivity of an existing machine.
Although it may not seem vital to your production process, safety is a very important topic. Although a glass cutting machine looks like a rather simple, straight-forward designed machine, there are some areas of the machine that can be extremely dangerous to an un-trained or careless operator. Our company publishes a very extensive operators manual which includes references to safe operating procedures, and I assume other manufacturers do the same. Unfortunately, in many cases the operators never have the opportunity to read this manual. Every new operator should read the manual and be trained by a qualified operator.
Good maintenance is another vitally important area to the longevity of a glass cutting machine, and more importantly to the main goal of achieving consistently accurate and clean cut glass. I cant stress enough, that the accuracy and cut quality of the pieces coming off the breakout table is directly related to how well the cutting machine is maintained.
All adjustments, maintenance, and repairs should be performed by qualified personnel who have a thorough knowledge of the machine. Guards, covers and other safety devices should be securely installed before production is resumed. An operators manual should provide recommended maintenance intervals and items to be performed. The first place to look when a problem occurs is the troubleshooting guide in your operators manual. This can save valuable production time and expensive phone calls or unnecessary visits by factory technicians. Sometimes human nature causes us to assume problems are much more serious than they really are. Its best to look for the obvious or simple solutions first.
One very difficult decision, especially for a smaller company that intends to purchase a cutting machine, is the level of maintenance person needed to properly maintain a cutting machine. It is possible to rely completely on the machine manufacturer for assistance and maintenance. However, to avoid expensive service calls and downtime, it is best to have a capable in-house maintenance person. Generally, you will find it is money well spent.
Every cutting machine is designed to cut at a certain maximum speed which should permit it to produce a given number of pieces or square feet in a specified period of time. If the cutting machine is used by itself, without any supporting equipment such as loading devices or breakout tables, the operators will have complete control over the output of the machine. In most cases where this is true, the cutting machine will probably never reach its expected output.
Many XYZ cutting machines, are adaptable to automated loading devices and breakout tables. The following are some suggestions to increase productivity.
Using this technique, a rack of glass is situated adjacent to an air float table, with the bottom edge of the glass level with the table surface. A person peels one lite of glass at a time from the pack and permits it to fall forward and down to the air float table. He then floats the glass from the air float table to the cutting machine table. Several glass racks can be situated around the table if more than one type of glass is used. Smaller size glass packs may be placed on wheeled racks.
An automated free-fall device and system is also available. This automatically peels, tilts, and then causes single lites of glass to free-fall from a vertical glass pack to a horizontal table. The table has an air floatation surface with or without powered belts built into the table surface. After the lite falls onto the table, the glass is floated to the cutting table, or the belts lift and convey the glass lite to the cutting table. The cutting machine surface must also have belts or other type of glass load/offload device to properly automate the system.
Automated free-fall systems that permit access to multiple glass racks in two parallel rows are also available. These can be programmed to operate from the cutting machine program.
When uncut glass larger than 108 inches by 144 inches (2.7m X 3.6 millimeter) is used, some type of mechanical loading device is required. This can be accomplished with vacuum-handling equipment used with an overhead crane and a tilting table, or an automatic stacking unit.
An automatic unstacking unit performs best when the majority of the glass cutting each day is done from one or only a few types and stock sizes of glass. This fully automatic unit removes a lite of glass from a vertical glass rack and positions it on a horizontal conveyor adjacent to the cutting machine. Some stacking machines can also lift lites of glass from a horizontal conveyor, and place (restack) the lites on a vertical rack or case.
A multiple rack, crane loading system is an automated glass selecting and loading system. This system includes the use of an overhead crane dedicated to the loading area, a vacuum cup framework permanently mounted to the overhead crane carriage, a tilting conveyor and a group of permanently located glass racks.
In this situation, the racks are positioned in several rows near the cutting machine, rather than in a long line. The crane and vacuum frame unit is directed to a particular rack by the cutting machine program. A lite of glass is removed from the rack and the unit returns to the tilting conveyor, where it deposits the glass, ready for conveying to the cutting machine. The advantage of this system is that it requires less floor space than a system with two rows of parallel racks mounted in a straight line.
After a stock lite of glass has been completely scored by the cutting machine, the scores must be separated or "broken out." This can be done on the cutting machine table. If room permits, however, this operation should always be performed on an adjacent breakout table. Generally, the breakout area is the greatest bottleneck in the cutting operation. Breakout personnel are extremely important and should be trained to work methodically. For optimum cutting production, breakout persons should not have to stop to remove full racks or find empty ones. Other employees should perform these tasks.
On smaller cutting machines, and glass thickness up to three millimeters, a simple air floatation breakout table, without bars, located adjacent to the cutting machine is normally quite sufficient. The glass is floated or conveyed from the cutting table to the breakout table. An operator separates the scores and places the pieces in racks. Some cutting optimization software programs instruct the operator in what rack and/or slot to place the pieces. This further enhances the breakout process.
For larger XYZ cutting machines and glass from three to 19 millimiters, air float breakout tables have built-in snapper rolls or recessed breaker bars. The glass is floated into position on the table with a cushion of air. The snapper rolls or breaker bars are used to separate the full length scores when the scores are positioned directly over the rolls or bars. Some optimization programs will also enhance the breakout process by placing the main breakout scores to correspond with the breakout bar locations.
The number of tables, the configuration and the number and placement of breaker bars is unlimited. The types and production capability of the cutting machine and the types of glass being cut are the determining factors in choosing the best configuration. To enhance production, a breakout table should always be of sufficient length to accept a full lite from the cutting machine.
Automated breakout equipment is also available. This equipment automatically separates the scores and conveys the glass to off loading areas. This equipment is generally used with high volume X-Y cutters, however it can also be designed to operate with XYZ cut layouts as well. Generally, automatic breakout systems do not reduce the number of operators. They also require significantly more floor space, are very complex and expensive, and are not as "forgiving" as a person is when separating long scores.
Cut-to-size-optimization occurs where factory uncut glass is cut into smaller pieces, in the most appropriate way, to satisfy a set of orders. Computerized, cut-to-size optimization has been designed to reduce waste and inventory carrying costs in all glass cutting operations. Glass waste is reduced because the system has the capability of determining the best way to cut many small sizes out of large sheets. Inventory costs are reduced because the system is able to achieve a high cutting yield using a reduced number of stock lite sizes.
One important fact to remember is your particular glass yield figures, the number of stock sizes you should carry, and their size, will be directly affected by your order mix. Your yields will be low if your orders include a high percentage of large size pieces, with very few small pieces that can be used to fill up areas that would otherwise become waste. However, if you have a good mix of large and small pieces, you will achieve high yields because you can utilize the entire stock lite.
To assist in yield enhancement, some advanced optimization software programs have a low priority feature which permits the automatic insertion of "stock size" pieces in areas of the layout which otherwise would be waste.
This has been a brief overview of suggestions for the purchase, maintenance, and enhancement of a glass cutting system. Some very simple but important factors can either make it a great tool to improve productivity, or become a costly albatross in your factory that does not live up to your initial expectations.
Bob Lang is sales manager at Billco Manufacturing Inc., Zelienople, PA.
The following list includes several very important things to keep in mind when the time comes to purchase a cutting machine.
1. Buy a cutting machine from a supplier whose machine control system is compatible with whatever software you choose.
2. Buy a machine that has the capability to be tied into a future factory wide computer network.
3. Buy a machine that is used widely in the industry and whose company has a good reputation for quality service.
4. Buy a machine that is compatible with any future automated loading equipment that you might add.
5. Buy a machine that will handle all the various cutting requirements (shapes and daily square footage) that you can predict for the next five years.
6. The buyer should understand the various terminology used by the cutting machine industry before beginning to look for a machine. Some of the important terms are:
Computer Numerical Control (CNC) - This designates a method of controlling the drive motors on the cutting machine. A series of binary numerical data is down loaded from the glass optimization software to the CNC control. Using an onboard computer in the control, the numerical data is stored and converted to electrical impulses, and then fed to the drive motors on the machine.
XYZ Cutting - Describes the direction and type of score lines placed on the glass. (see figure above)
Contour (Shape) - Operation of the X and Y axis drive motors simultaneously to produce diagonal or radius cuts. (Note in the above example that in the glass industry "Z" does not refer to a contour cut, but rather an interrupted X or Y cut).
Optimization - This is a technique used for obtaining the best possible yield from the product you are processing. With glass cutting, it means arranging a group of cut sizes on a large sheet of glass in a manner that produces the least waste.
7. One misconception is that maximum cutting speed relates directly to cutting machine thru-put (i.e. faster is better). This is not the case. Thru-put relates more to motivation of the operators, organization of the overall cutting system (i.e. equipment/personnel/software), the efficiency of the breakout area, and the acceleration/deceleration capability of the machine drive system.
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