Changing technology in the field of grinding, polishing, buffing and deburring for both large and small manufacturing plants continues to upgrade metal finishing operations and facilities. Manual finishing methods are less desirable and highly ineffective as we plan to meet future manufacturing goals and projections. The available labor force typically is not interested in working in “dirty polishing” departments, as there are much more appealing job opportunities. Also, current environmental rules and regulations help to discourage and limit hand grinding and deburring approaches in most U.S. plants. There is a definite trend to minimize hand-finishing operations, as well as to replace many of the older and long established conventional polishing and buffing machines.
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Figure 1: Variety of aluminum wheel
designs
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Another choice is to send this work offshore to the Far East, India, Latin America or Mexico, however this is not a good long-term solution. Problems with extended deliveries and unforeseen delays, excessive inventory of parts, additional shipping costs, quality issues and overall control negatively affect U.S. companies trying to find alternative sources to meet high quality part supplies at controlled costs.
In defining mechanical finishing of specific part types related to various industries, basic categories can be classified under “decorative” and “functional.”
Decorative Parts
Most plants are faced with market pressures to upgrade their products in appearance and performance, as well as reduce their manufacturing cost base to better meet domestic and worldwide competition. Especially on decorative consumer products that are clear coated, painted or plated, significant manufacturing costs are directly related to polishing and buffing operations. Preparation by mechanical surface finishing is important for decorative lock and plumbing hardware, hand tools, cookware and appliances, lamps and lighting fixtures, golf clubs, motorcycles, handguns and rifles, aluminum extruded building products, automotive bumpers and cast aluminum automotive and truck wheels.
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Figure 2: Multiple robotic “detail
finishing” system
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Functional Parts
On functional internal part components that affect product efficiency and performance, deburring and super finishing have become important secondary operations. With extended part warranties, such as in the automotive field, quality control to ensure the integrity of the part components becomes a key cost factor. Specifications for surface finish and geometry of bearing and load surfaces for transmission shafts, gears, yokes, drums, axles, camshafts, crankshafts, connecting rods, pistons and engine blocks are being continually upgraded. Other non-automotive applications requiring better controlled surface finish and tolerances are found on truck and earth moving vehicles, medical prosthesis or implants, pump screws and valves, air compressor and air conditioner components, motor rotor components, aircraft engine compressor discs and blades, aircraft frame components and hydraulic telescopic cylinders.
The examples listed above represent only a portion of the total mechanical surface finishing applications that are being influenced by current market factors. These market factors are causing many changes in the way we control and operate our plants.
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| Figure 3: End-of-arm tooling (EOAT)
configuration |
Market Factors
The following are market factors that affect decision making regarding mechanical surface finishing operations and equipment.
There is a need for greater machine flexibility in finishing a wider range of products on a common system with greater emphasis on rapid machine changeover, simplified tooling and combined finishing operations within the same system.
The quality level continues to rise worldwide. Both cosmetic and functional finishing specifications are better defined and controlled by continuing market pressures. Part geometry, uniformity and consistency relative to surface finish as well as visual specifications are essential as a result of the continued expansion of continuous quality improvement programs in the automotive and non-automotive industries. TQM, ISO 9000 and QS 9000 represent current examples of how we must conduct our businesses today and in the future to maintain our companies as qualified and acceptable suppliers to our customers.
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Figure 4: Single stand-alone robotic
system
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Competitiveness in the marketplace is an ongoing factor. Finishing costs have traditionally been significant, especially on decorative consumer items. Not only have the labor costs been substantial, but also the cost of finishing media (in terms of buffs, abrasive compounds, abrasive belts, wheels and brushes) have been key contributors to the overall cost of the end product. There has been a definite trend to develop more cost-effective ways to finish products. Product development in the areas of buffs, compounds, abrasive belts and wheels, nylon belts, brushes and wheels and micro-polishing rolls has been a challenge to abrasive-media manufacturers. There are many new products and options available today to help maintain higher quality surface finishing standards at controlled costs. A recent example in the field of coated abrasive belts is the development of “structured abrasives.” Coated abrasive belts use a technology known as “microreplication,” which has given them the ability to obtain precisely shaped composite grains bonded to a belt backing. More uniform fine belt finishes can be achieved to reduce sequential belt steps, extend belt life, and ultimately improve final surface quality finishes at reduced operating costs.
Stricter enforcement of laws regarding operator safety, plant working conditions and hazardous waste disposal has created a tremendous burden on our manufacturing plants, to the point where many of the job shops and smaller plants can no longer financially assume the costs incurred in meeting these requirements. OSHA and other environmental regulations continue to be enforced by local, state and federal agencies to help improve plant safety and overall working conditions. Custom-designed machine guards and enclosures are becoming much more common on finishing systems, in order to protect the operator in terms of reduced noise levels, dust and dirt air contamination and overall machine safety and exposure to potential plant hazards.
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| Figure 5: Small abrasive flap wheel
positioned inside window area |
High hidden costs related to carrying in-process inventories, based on traditional batch-type manufacturing operations, have forced most manufacturers to investigate better methods of handling and scheduling production parts throughout the plant. “Kaizen” and lean manufacturing procedures are becoming more common to gain improved manufacturing efficiencies. “Just-In-time” (JIT) manufacturing is one example of improved inventory control being used in U.S. auto plants. Specialized work cells can also combine a number of machining and secondary finishing operations, using common operators to perform multiple tasks within a given work cell. In this case, common part families can be conveniently routed within each line.
Labor shortages of qualified and trained personnel continue to affect most U. S. manufacturers. Local, state and federal training programs are being expanded, but this does not solve the complete problem. There must be other ways to offset the lack of qualified labor pools. Programmable and flexible finishing systems can also help to offset reduced skilled labor availability.
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Figure 6: Dual-spindle robotic
fixture drive arrangement
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Robotic and Programmable Controlled Finishing Systems
As an answer to many market conditions and pressures outlined above, electronic and computer aided hardware and software technology have been developed for grinding, polishing, buffing, deburring and satin finishing. Examples of current applications can help illustrate a variety of computerized and programmable electronic systems that have been integrated into basic mechanical finishing equipment and processes.
These systems address many of the critical market factors, including machine flexibility and rapid changeover, improved part quality and consistency of finish, reduced finishing costs and better use of abrasive media. Operator safety and environmental regulations, and improved parts handling and scheduling procedures to minimize inventory and in-process manufacturing costs, as well as the growing shortage of trained and qualified labor are also factors.
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Figure 7: Double dual spindle robotic
cell configuration
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The industry has been making excellent progress in addressing the market conditions and pressures outlined above. New programmable computer technology using robotic, PLC, CNC- and PC-based devices applied to mechanical finishing systems for grinding, polishing, buffing, deburring, and satin finishing can be integrated into many robotic and programmable controlled finishing systems. Off-line programming simulation methods are becoming another cost-effective tool to allow part manufacturers to expand their systems for new parts and products, without disrupting existing robotic work cells.
The following robotic and programmable controlled finishing systems illustrate and describe a variety of metal finishing applications for aluminum automotive and truck wheels, D.O.M. steel tubes and cold drawn bars, brass and zinc lock hardware, chromium cobalt and zirconium knee and hip orthopedic implants, and chrome-plated and painted motorcycle components.
Case 1: Aluminum Cast and Forged Wheels
The automotive and truck industry has created a growing demand for bright aluminum cast and forged decorative wheels. Figure 1 shows a variety of wheel designs, which are presently automatically polished and buffed to a uniform mirror finish.
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Figure 8: 5-head abrasive belt
centerless bar and tube grinding system
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For high production requirements, Figure 2 illustrates a multiple robotic system designed to perform “detail finishing.” Detail finishing is identified for finishing small areas that restrict the penetration of larger conventional buffing and abrasive wheels. These areas have traditionally been limited to labor intensive off-hand operations using small air tools with abrasive wheels and buffs.
With the integration of custom, constant-force EOAT (end-of-arm tooling) devices, high-speed spindles are used that efficiently combine several required functions. The key to the successful integration of detail finishing goes beyond just processing the part. Compliance for part variation, media wear, and tool/robot motion dynamics all need to be managed to provide constant force finishing processes.
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Figure 9: High production in-line
zinc lever buffing System
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By nature, small detail finishing tools have limited tool life. To compensate for this, the custom EOAT is arranged to efficiently manage and change its own tools as needed. Figure 3 illustrates how the EOAT arrangement is configured. The attending operator performs servicing of the media outside of the work cell. This allows the abrasive tools to be automatically changed without interruption to the process or productivity.
Figures 4 and 5 illustrate how the technology of robot-held tools are used on a single stand-alone system. Again, Figure 2 shows the same technology integrated into multiple robots to allow parallel part processing. The result is a highly efficient cell that produces a finished wheel after each table index.
An alternative wheel-buffing system is a six-axis robotic arm combined with a patent-pending dual-spindle, fixture-drive arrangement (Figures 6 and 7.) A high payload robotic arm is arranged for controlling the cell. The robot provides maximum flexibility for part manipulation and rapid machine changeover. Universal tooling allows the twin-spindle station to be more cost-effective for a variety of automotive-wheel-finishing requirements. The basic twin-spindle arrangement can be set up for “cut” or “color” buffing or wide-wheel “mush” buffing.
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Figure 10: "Smart screen" with
menu-driven software
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Basically, the twin-spindle design provides twice the production output as compared with conventional single-part robotic processing. The patent pending multi-spindle design is also of-fered in a four spindle design, and other multiple spindle systems. The four spindle arrangement allows a single robot arm the ability to produce parts at a rate of approximately four times that of a single-arm robot. The end result is reduced floor space, lower equipment costs, and increased throughput.
Figure 7 illustrates how multiple cells can be integrated together to create efficient work cells. This arrangement allows various manufacturers to efficiently manage their growth by adding automation capacity in manageable economical phases. One operator typically would feed parts to both dual robotic work cells.
Case 2: Five-Head Abrasive Belt Centerless Bar and Tube Grinding System
A five-head fully programmable (CNC) servomotor controlled centerless abrasive belt grinding and polishing system provides high stock removal on telescopic hydraulic cylinder tubes in a “single-pass-through” operation. A 9-axis programmable controlled system is shown in Figure 8.
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Figure 11: Typical medical prosthesis
parts including knee and hip implants
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Approximately 0.02–0.040-inch stock removal can be ground to a controlled finish and precise tolerance standards on thin walled D.O.M. tubing from 2.0–6.0-inches O.D. “Smart Screen” operator controls allow complete machine changeover within 1–5 minutes permitting “Just-In-Time” production part scheduling, in addition to providing high production output on a variety of different part sizes.
The abrasive belt grinding process and automatic tube-handling system help provide a very cost-effective and productive integrated system for high-volume O.D. tube and bar grinding when compared to bonded-wheel centerless grinding and CNC turning and peeling operations.
New coated abrasive belt centerless grinding technology, utilizing ceramic aluminum oxide belts for roughing operations and structured abrasive belts for final finishing, provides an extremely flexible solution to meet high production grinding requirements in the hydraulic cylinder, cold-drawn bar, and automotive-part industries.
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Figure 12: Robotic knee implant
belt grinding operation
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Case 3: Zinc and Brass Lock Hardware
High-production, continuous, in-line and rotary table buffing and satin finishing systems with programmable controls for rapid machine changeover offer maximum flexibility to finish brass and zinc door levers, knobs, and rosettes for a variety of different lock hardware styles. Production rates of 1,000–6,000 parts per hour are typical using this technology on special designed finishing systems.
Figure 9 illustrates an in-line conveyor machine with multiple triple-wheel tangent heads and multiple five-ft wide heads for buffing zinc die cast levers at 2,000–3,000 parts per hour. The heads are controlled by a “Smart Screen” with menu-driven software (Figure 10) for ease of operator control. The buffing heads are equipped with automatic head positioning through a programmable logic controller (PLC) system.
This concept allows the manufacturer to pro-duce at high rates, and still have the ability to changeover quickly to other part styles. Quick-change tooling is also a key factor with rapid machine changeover. This same basic concept can also be provided to belt polish and buff brass cast plumbing handles in various designs with rapid machine changeover.
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| Figure 13: Robotic gas tank and
fender finishing work cell |
Case 4: Robotic Grinding, Polishing, and Buffing of Orthopedic Implants
Another classic benchmark robotic application includes grinding, polishing, and buffing of knee and hip implant prosthesis parts, which in the past had required 15–20 manual polishers to perform the work of one robotic work cell (Figures 11 and 12).
The grinding technology for medical implants has expanded and evolved to a level where robotic grinding and polishing can combine gate removal, contour and tolerance grinding, and mirror finishing of chromium cobalt and zirconium investment cast knee and hip implants. This technology has progressed to a very sophisticated finishing level of achievement and repeatability because of the unique software and hardware evolution over the past 15 years. Part producers with multiple robotic cells are also finding a number of added cost efficiencies gained by the use of new off-line part programming simulation techniques to help free up the production cells to maximize daily production output.
Case 5: Robotic Grinding and Polishing of Motorcycle Gas Tanks and Fenders
Numerous motorcycle parts have traditionally been ground and polished by manual methods. Manual operations have typically proven to be extremely slow and costly, but also dangerous from the operator’s standpoint. A number of very successful robotic finishing work cells have been developed for a variety of both decorative and functional motorcycle part components including:
- Gas Tanks
- Brake Pedals
- Fenders
- Shift Levers
- Guard Rails
- Wheel Rims, Carriers and Pulleys
- Sissy Bars
- Mirror Housings
- Decorative Cast Housings• Brake Calipers
- Valve Covers
- Fork Sliders
Figure 13 shows a robotic work cell for grinding, polishing and brushing gas tanks and fenders. The robot is positioned in an enclosed work cell with fpur force-controlled finishing heads. The parts to be finished are queued on a four-station carousel, allowing the robotic cell to run unattended for approximately 40 minutes. Coated abrasive belts are used to blend the welded areas of the two-piece gas tank, followed by brushing and deburring around the gas intake hole, and final polishing with coated abrasive wheels to prepare the tanks for painting. Operator friendly software has been developed for ease of monitoring and training. Coated abrasive belt and wheel life management screens, machine diagnostics, modem support from outside remote troubleshooting and simplified operator task programming techniques are useful and typically productive software tools to help the operator maximize the output and efficiency of the robotic work cell.
In summary, the domestic and global market factors will continue to push our manufacturing and finishing technology to higher levels of achievement. The advancements in mechanical finishing for decorative and functional part products have been greatly influenced through growing techniques of robotic and computer-controlled finishing processes and systems. Progressive companies must continue to support and encourage these new mechanical finishing technologies to better compete and survive in future world markets. As we move ahead, these ongoing technological changes will continue to expand and advance throughout the U.S. and the world economy.
