Posts Categorized : Technical

Considering converting your manual hoist to automatic? Read this first

By implementing an automatic hoist, you are essentially turning the entire line into an automated process line. This would allow you to create process programs that include specifying tank immersion times and possibly tank parameters such as temperature, conductivity, etc. Once these programs are created, your operator will load the work bar, choose the appropriate process program and run it. After processing is complete, the operator will pick up the parts at the other end of the line. It becomes a hands off process for the operator. This can be a good thing or it can be a bad thing. If the automatic line is running well, you can be reasonably assured that you will get a consistent coating. If however things are not running well, the automatic line will not detect those things an experienced operator can. Take part cleaning for example. An automatic hoist cannot see a “clean water break” whereas an experienced operator will know to look for this and continue cleaning until it appears. Also the experienced operator can, to a degree, know the part’s coating thickness based on the color after anodizing. The automatic line cannot. There are a number of benefits from an automatic processing line, but there are also a number of limitations and drawbacks as well.manual hoist

You should also consider what will happen when the process load reaches the anodize tank. If the rectifier is still going to be mmanually operated, the hoist would need some method of waiting for the rectifier to create the coating. After that, it would need some method of resuming when the coating is done. This can certainly be accomplished, but the correct way to implement an automatic hoist is to implement rectifier control as well. With rectifier control implemented in the same control system with the hoist, a seamless process flow is created. When the hoist moves the process load into the anodize tank, the control system runs the rectifiers based on the program chosen by the operator. Although an automatic hoist can be implemented without rectifier control, it would create a bifurcated control system that eventually will have problems.

Whether you implement an automated hoist or not also depends on the type of facility you have and your work loads. Automatic hoists are mainly used in captive shops. These are facilities that typically manufacture and process their own parts or have only one or two customers they process parts for. These shop normally have only 3-4 different parts that are run and the loads sizes and configurations tend to be the same. On the other hand, it is very rare to see an automatic hoist in a job shop that does anodizing work for their customers (who are the manufactures). In job shops, there are just too many different parts, load sizes and load configurations to be supported by automatic processing. Normally automatic lines have a limited number of process programs which limits the line’s flexibility. Also since a job shop may run a specific parts only once, creating and validating the automatic line’s process for the parts become a hindrance.

The cost of converting a manual hoist to automatic line should also be considered. You cannot simply plug your existing push button controls into a PLC and expect it to work. In fact it’s much more likely the hoist mechanicals themselves (chains, gantry, booms, etc), are the only parts that can be reused. Plan on replacing the drive servo motors. Also a servo drive, positioning system, PLC, cabinet, software and a computer for the operator interface will be required. Part cost alone can easily reach 6 figures. Add labor and engineering cost and you could be in the $250,000 range.

For absolute process control, you need absolute consistency. The automatic line affords this. You can be reasonably assured that when the line runs well and your chemistry is maintained, the parts are being processed the same each time. Unfortunately, when the automatic line doesn’t not run well, or if you have under maintained chemistry, there is no operator to provide the all important “reality check” that could save the day and the customer. Couple this with the limitations and cost of implementing an automatic hoist and in some cases, it simply may not be worth it.

Control vs. Quality

In manufacturing process control is key. Without it you may as well spin around 7 times, turn off the lights and play darts. Sometimes you will hit the dart board (and maybe even get a bulls eye), but more likely than not, your dart will be off the board completely. The same can be said in a manufacturing environment that does not have adequate process control. Sometime your quality will be spot on, but more times than not your parts will not be in spec. From this it’s easy to see that process control is not about quality. In fact, process control has just as much to do with quality as fast food has with good flavor. Process control is about consistency, not quality.

Process control systems are created to control process parameter to one extent or another. The control system itself doesn’t care what the process is or how it’s defined, its responsibility is simply to ensure the process parameters are kept within reasonable limits as defined by the process. Again, what those limits are is of no concern to the control system whatsoever. Once the limits are given to the control system, its job is to simply maintain them. And who determines what the process parameters are and what limits should be kept? Someone who knows what the overall quality the control system should maintain.

So what about quality? Quality is simply a subjective measure of the object’s properties, that when taken wholly is determined to be good, bad or somewhere in between. Figuring out how to process something to a certain degree of quality requires setting specific process parameters. This is usually done by trial and error; take a first stab at it based on an educated guess, assess the results, make a change, rinse and repeat. If the control system is working correctly, you should eventually have a process that results in the quality you need. Again, the actual quality is irrelevant. The point is that without the control system functioning properly, you cannot be assured that the change in the part quality was a result of a change in process parameters, and without that, you are playing darts in the dark.

As mentioned, the job of a control system is to maintain process parameters. That is the key. Not necessarily the key to quality, but it is the key to consistency. If the process parameters are not maintained, then the process output will be unpredictable. Why is it that the number one fast food restaurant is so successful? Certainly not because of the great food. It’s because you can get the same consistent food regardless of where and when you visit them. A sign of a great process control system is one that provides the same consistent product all the time. People may argue about the overall quality of the product, but they would generally agree that they are getting the same product. That is what process control brings to the table; consistency, not quality. If you provide a consistent, usable product, the customer will return.

So it always must ┬ábegin with the control system. Once that’s in place, you can make changes to the process parameters and predict how those changes will affect the process output or part quality.