Critical Mass: Inspection Efficiency

Courtesy of Rosler Metal Finishing USA

A six-load, centrifugal disc mass-finishing system from Rosler features automatic loading and auto screening.

Mass finishing parts at the machining center offers economic advantages.

There are major economic and scheduling advantages to having a part come off a machining center complete. Most machinists think parts are finished at this point because part dimensions are correct. However, they forget that most parts must be deburred, cleaned, weighed or counted and then packaged before shipping. In most shops, that involves moving the machined parts to another part of the shop, putting them on shelves and eventually having someone perform the final operations prior to shipment.

Done at the Machine

Deburring parts at the machine means that they are truly ready to ship. Joe Gaser, vice president of Osborn International, Cleveland, a manufacturer of industrial brushes and surface finishing tools, noted that manufacturers would obviously like to receive payment for their parts earlier than they do. His solution: “Finish your parts at the machine instead of having them sit for days or weeks waiting to be deburred.”

There are other benefits to finishing parts at a machining center. Shops find and fix problems earlier, better understand the impact of keeping burrs small, prevent mistakes from using the wrong finishing process, do not lose parts, and possibly prevent oils from drying on parts, which makes the oils difficult to remove. In addition, one person is responsible for the completed part.

There are three major ways of producing a burr-free part at the machine: preventing and minimizing burrs, brush deburring during the machine cycle, and cellular manufacturing that includes deburring.

Robotic deburring is the most recognized avenue of cellular deburring, but a lower-cost solution exists: placing small, portable mass-finishing machines at (but not on) the machine tool. These finishing machines have been available for at least 30 years, but have become more popular recently due to lean manufacturing initiatives and the availability of many smaller, lower-cost and faster finishing machines. Shops considering mass finishing must answer several key questions:

• How do I conveniently get machined parts into the finishing unit?
• How much floor space is required?
• How much cleaning do I need? (Mass finishing also cleans.)
• How do I handle waste products?
• How much finishing capacity do I need at any one machine tool?
• How much does an appropriate finishing machine cost?

There are at least 40 suppliers of mass finishing machines operating in the U.S., as well as job shops that specialize in deburring, that can help answer these crucial questions.

Determining how many parts must be finished per hour at each machine is the next question. Knowing part size, edge and finish requirements and production rates allows mass-finishing machine builders to calculate the required capacity and floor space. That information also helps determine the electrical power needed, water usage (if any) and drying requirements.

Courtesy of Rosler Metal Finishing USA

A Rosler automated centrifugal disc system finishes parts, separates them from the media and feeds the parts to final packaging.

Next, determine the method for feeding parts into the mass finishing machine and handling them as they are removed. For many job shops, manual placement and removal of parts is adequate. For higher production and more continuous flow, a direct feed from the machining center or lathe into the finisher is needed. For complex and expensive parts, an overhead load/unload robot might be the answer. The last issue is to calculate equipment payback. Machine builders can help estimate that.

Some shops will choose roll-in finishing machines that can be moved from one machine to another. In most instances, users will want to use overhead power. Water is generally included in tanks under the machine, so a direct water hookup isn’t required. One critical issue is how to treat and dispose of wastewater because it contains metal and fine abrasive particles from the deburring media or plastic particles if plastic media is used.

Typical Machines

James Krier, sales and marketing manager for Burr King, Warsaw, Mo., noted that in the past 2 years he has seen more applications for deburring equipment at lathes and mills. While others provide roll-around units, Burr King offers a small, skid-mounted system that is moved with a floor pallet jack.

For the 1.3-cu.-ft. finishing machines typically found at machine tools, operators either chute the parts straight into the finishing machine, manually place them one at a time or input a batch at a time, depending upon part size. Vibratory machines are available in many sizes. Smaller machines fit well next to a machining center, whereas larger ones, such as a 3-cu.-ft. machine that measures 3 ‘ to 4 ‘ in diameter, are better suited for placement at the end of a cell.

Burr King vibratory machines have a filtration pack that removes fines from the unit’s recirculating 8-gal. water tank. The 2-sq.-ft. footprint of its 1.3-cu.-ft capacity machine is one of the smallest in the market, according to Krier. That system and the company’s 4.5-cu.-ft. machine use 15-amp, 120v power, normally from an overhead drop. Not requiring 220v is a major advantage for many shops because it simplifies moving the deburring machine.

In addition, the machines do not normally use abrasives, eliminating the need to remove abrasive particles from parts. If necessary, users can mount a small ultrasonic cleaner on the machine to provide final parts cleaning. Burr King’s small finishing system sells for around $3,000.

Some of the workpiece material transfers onto the media and into the machine liner, which can then rub off on the next batch of parts, Krier noted. Cross contamination can present corrosion, color and plating problems when machining a variety of materials, such as aluminum, brass and steel. Dedicating small units to specific materials is the easiest solution.

Cellular Arrangements

For quickly finishing parts in a work cell, centrifugal disc machines are available. Steve Alviti, president of Bel-Air Finishing Supply Corp., North Kingston, R.I., noted that centrifugal discs used in cellular manufacturing have typical cycle times of 5 to 30 minutes, with a load/unload time of 2 minutes. The 10G centrifugal force in an open-top centrifugal disc machine allows users to apply very small media, which reaches into small part features. However, this size of media is not effective in vibratory operations because vibratory forces cannot move the media with enough force to deburr.

One Bel-Air cellular system finishes bone screws. The traditional way of making bone screws involved machining, deburring, secondary operations, passivation, inspection and inventorying them in lots of 2,000 parts. When QC at one part manufacturer found even a few rejects, it typically meant the entire lot of 2,000 had to be scrapped. It took 21 days, the process’ cycle time, until the next lot could be produced. By reducing lot size to 200 parts and putting a deburring machine and an ultrasonic cleaner at the machine, the manufacturer’s cycle time fell to 4 days, reject rates decreased dramatically and inventory shrank by 400 to 500 percent.

Courtesy of Bel-Air Finishing Supply