Quality Finishing: Part I: Mechanical Finishing: A Review and New Technologies
One of the most antiquated technologies found in many manufacturing plants today is mechanical (mass) finishing equipment.
One of the most antiquated technologies found in many manufacturing plants today is mechanical (mass) finishing equipment. In some cases, this is so because the old process is still the best for a particular application. In many other cases, the process is simply not updated because it is not understood. Mechanical finishing is often regarded as a “black magic.” As we know, since engineers work with variables not potions, the old process is left alone. It is also regarded as a dirty, noisy process that is operated by the least experienced and trained people in the plant but is often dominated by a single “seasoned” employee who knows the process and what to do to fix it if necessary.
Because of this, one of the best opportunities for savings in the manufacturing process can be found in deburring, radiusing, edge breaking, surface improving, burnishing, polishing or de-flashing processes.
First, are you improving an existing process or are you exploring alternatives for a new part and process?
To upgrade a current process, time must be spent identifying and understanding your process. By using the following parameter list, record the values associated with your current process and determine the cost (per load, hour, day, part). Besides giving you the information you need to start seeking improvements, this exercise will make you familiar with mechanical finishing in general, and you will become more capable of managing this process. As you identify the values for the above parameters, you will also identify variables unique to your plant and process.
Often overlooked is the consistency of the part coming to the mechanical finishing process. The mechanical finishing process is often unfairly expected to “remove a burr,” “refine a surface” or “remove heat treat scale.” This becomes unfair when the burr height or location, value of the surface or amount of scale is not clearly defined. When defining a process with samples that have a 0.002-inch burr height, you should expect this process to effectively address this size burr with a small variance. In too many cases, production produces larger burrs by trying to get more parts out of tooling or various other reasons, and still expects the finishing process to remove the larger burr in the same process time under the same conditions. To make the finishing process repetitive, understanding the condition of the incoming part is critical. If you are trying to determine why parts are not exiting your finishing process as expected, you must first confirm that they are entering the process as expected.
A finishing process will also be easier to maintain if the problems it addresses are minimized as the part is produced. This does not mean you can prevent a process from creating a burr, but you can minimize the burr and make sure it is consistent by controlling the process that creates the burr. This is the single most important consideration in designing an efficient and manageable finishing process. Paying attention to the location of the burr produced will also simplify your quest for the best mechanical finish. This, of course, also applies to operations that produce scale, such as heat treat or welding, or certain surfaces from grinding. All of these processes must be designed so that the problems they produce are consistent and can be handled repetitively by the mechanical finishing process.
To start we must have an understanding of the following:
- The manufacturing problem you are addressing with your mechanical finishing process.
- The parameters that can effect a finishing process.
- Your process parameters and the values of each.
- The technologies are available for your mechanical finishing process.
- Radius/Edge Break
- Surface Improvement (Preparation for another process)
- Pre-polish, pre-plate, painting preparation
- Surface Improvement (Performance)
- Achieve certain surface value, remove defects
Parameters for Mechanical Finishing
A. Part Parameters
- Finish requirement (burr height range, required edge break, R value of surface needed)
- Part dimension
- Part weight
- Production numbers
- Material used to make part
- Special concerns, including but not limited to the following:
-Location of burr (internal burr?)
-Holes, corners, etc., where lodging can occur
-Rust, corrosion, oxidizing
-Surface finish requirements for debur or radiusing processes
B. Process Parameters Equipment
- Type of equipment
- Cost of equipment
- Type of action created
- Energy requirements
- Maintenance and upkeep
- Process time
- Floor to floor time
- Adaptability to handling parts to and from equipment
- Percent of time used for separation and unload
- Requirements of time
- Requirements such as lifting, is height a factor for loading, inspection, etc.
- Cost per pound
- Attrition (% weight per hour)
- Metal removal rate (% weight per hour)
- Cost per gallon
- Concentration requirements and use per hour
- Water use requirements
C. Additional Parameters to Consider
- Waste disposal cost (additional equipment or disposal)
- Pre-process concerns (washing, conveying, queuing)
- Post-operation concerns (inhibiting, washing, drying)
When investigating your alternatives for a new mechanical finishing process, it is best to employ the help of an experienced lab. Most mechanical finishing equipment suppliers have invested in the facilities to test your samples and develop a process. The advantage a lab offers is that it has multiple technologies to investigate and the range of media and compounds needed to test effectively. Also, it has from 15-40 years of experience developing processes for mechanical finishing. There are very few plants that have the variation of machinery, media and compounds in house that are needed to adequately test for the best process to finish a part.
When providing samples to the lab, ensure the following:
- Collect and provide all available parameters. Record the parameters in a spreadsheet and send them with the samples you would like tested.
- Send a sample of the finish you require, when possible.
- Provide prints showing requirements and restrictions.
- Make sure your samples reflect what your production will produce.
When possible, sample testing should be followed by additional tests using estimated production numbers in the equipment recommended. This testing cost is minimal and allows you to address and minimize concerns on the vendors’ floor where problems and improvements can be handled quickly and cost effectively. An experienced operator and maintenance personnel can add value to a visit and reduce the cost of addressing problems and making improvements on your plant floor.