A holistic approach to improved cleaning room efficiency: a holistic approach to improve cleaning room operations means looking at the entire system by starting at casting design and working through to a review of cleaning room equipment.
In addition to being a labor intense operation, cleaning room operations also can be a frequent bottleneck and source of production flow delay. Any increase in efficiency in the cleaning room can improve delivery schedules and profitability through a reduction in material and labor costs.
MODERN CASTING's June 2002 Website Question of the Month asked, "If the foundry industry is to grow instead of shrink, what do you think are the two most important changes that need to occur?" Almost 47% of those responding indicated that foundries must decrease production costs to lower casting prices or rely more on automation in the foundry. Yet when the question was asked "If you could pick one area of your foundry to modernize to improve efficiency significantly, what would you choose?" (February 2002); only 24% selected cleaning and finishing. Many foundries seem to be caught in a dilemma--although improvements in the cleaning room and post-casting process can benefit from on-time delivery and enhance business profitability, it is traditionally neglected in the search to improve efficiency.
A number of top metalcasting operations have already implemented cleaning room upgrades in the last few years through automation, robotics and plant engineering. Although larger foundry operations benefit most from cleaning room improvements due to the volume of casting production, there remains a substantial efficiency and profit improvement within reach for all foundry operations.
Principles Far Improving Efficiency
A common error when looking to improve cleaning room efficiency is to concentrate solely on the equipment and processes in the cleaning room. A more effective analysis takes a holistic approach to cleaning room management, reviewing the entire casting process cycle--beginning with casting design.
Beginning the process in the cleaning room itself is like starting to read a novel in the middle. The source of much of the bottleneck in the cleaning room is the excessive labor put into correcting casting defects and poorly designed and gated castings. The cleaning room becomes responsible for the products of engineering or molding departments.
A holistic approach to improving the cleaning room operations is to begin at the casting design and engineering stage, then move through the core room, molding department, sand control and melting before approaching the cleaning room itself.
Effective Casting Design, Engineering
For maximum cleaning room efficiency, foundries must engineer and gate castings for minimum cleaning room labor. In addition to correct gating for fluid flow and solidification, ease of removal should be part of gating and riser design. Castings should be gated to allow for minimal cleaning room labor, and gated in areas of the casting that allow best access to gating and riser connections. Where possible, minimize the size of gates and design gates and risers to fall off during shakeout to reduce cutting and removal time.
Figure 1 shows an aluminum permanent mold casting (tilt-pour process). The gates connect into a section that will later be machined, so the gate connection does not need to be ground flush to the surface in the cleaning room.
The aluminum casting in Fig. 2 requires band saw cutting through a number of large risers. These risers are located on top of the casting and also must be ground flush to the casting surface after sawing. This casting is an excellent candidate for re-gating. Engineers should determine if this amount of feeding is necessary and eliminate risers, reduce riser size, connect from the side of the casting for easier access and removal, or consider chilling instead of feeding.
Additionally, clearly define customer needs--not only what the customer wants, but also what he can live with. During customer negotiations, foundry sales and engineering personnel may find that the expected level of casting cleanup and finish is not critical. Foundry marketing and sales personnel and engineers working on new casting designs should all work with a view to casting cleaning and finishing. The design and gating is such a critical point in reducing cleaning room labor that in some cases the potential labor savings might offset the cost of repair or re-gating existing patterns.
One foundry was being pressured to reduce casting costs even though their casting processes were already fairly lean. Engineers and management felt that any remaining cost reductions could only be achieved in post-casting production. Foundry engineers designed 'one-point' gating for many of their aluminum permanent mold castings (Fig 3). After fully testing the castings to ensure reliable quality with the unconventional gating, the foundry realized substantial cleaning room labor reductions.
Casting Errors and Defects
After the castings have been designed (or redesigned) for minimal cleaning room labor, the foundry should examine molding and casting production to minimize casting defects and molding errors. This will help reduce the cleaning room time that is devoted to removing excess metal resulting from errors or intentional additions of metal by the foundry to compensate for poor molding practice.
A careful study of scrap and rework castings can help identify and eliminate the root causes. Worn patterns and molds consistently produce castings with excess parting lines and flashing. A change in sand fineness or binder percentage might improve cored surface finish and removal and eliminate internal surface defects. Faulty cores and molds can cause veining, finning and other surface defects that require additional operations in the cleaning room. Excessive metal temperatures can produce rough casting finishes that require extended blast time to correct.
It is particularly helpful to eliminate labor intense operations such as hand-held tools cleaning interior cored surfaces. One foundry was able to increase cleaning room production of iron intake manifolds from 600-800/day to 1400-1800/day (over a five-year period) through improved foundry practice.
Another reason that foundries experience bottlenecks in the cleaning room is because few have engineered the cleaning room for effective workflow. Cleaning operations are often designed as batch operations that are fed with forklifts and containers of castings brought to various bench or stand grinders and cutters. A full evaluation of the cleaning operations should include reorganizing the equipment and processes to restructure workflow improve sequence of operations, reduce handling and minimize storage of work-in-progress.
The goal should be increasing throughput by ensuring a continuous flow and lowering labor costs by reducing the number of times a casting is handled. This should include eliminating inventory-holding areas and reducing movement of products with forklifts through the use of chain or belt conveyors. One option is to use a cell concept rather than the traditional dedicated cleaning room, where cutting, grinding, hand-bench finishing and packaging are moved to the casting station and the casting is complete as it exits the casting cell.
Proper Equipment Operating Efficiently
Only after a holistic' look at the rest of the foundry operations should the foundry begin to look at the cleaning room itself. A review of existing cleaning room equipment is first. The obvious step is to automate repetitive operations, or use robotics to enhance cleaning room efficiency. But outside of capital expenditures to upgrade or replace equipment, cleaning rooms should assure that current equipment is performing at maximum capability.
Grinding machines and band saws should be working at optimum speeds and power. Motors should have adequate horsepower and rpm and belts tightened so that grinding wheels do not stop during heavy grinding. Grinding wheels and abrasive belt backing wheels also must be optimized.
The type and density (hardness) of the wheels for coated abrasive belts can have a significant affect on material removal rates, and should be properly matched to belt weight, abrasive material and grit. Grinding wheels should be properly trued and dressed. Using an improper wheel or running a wheel with uneven wear increases vibration that can increase operator fatigue and machine wear.
Hydraulic pressure fixtures that bring the part to the grinding wheel and apply high pressure can increase the rate of metal removal and speed the grinding process. Blast equipment should use interior parts resistant to wear to reduce down time. Blast equipment should be properly adjusted--misadjusted blast streams can reduce both efficiency and liner life. Infrared target lights added to cutting operations can improve consistency of sawing.
In addition to equipment, there is the cost of energy waste--such as compressed air leaks, loose electrical connections, open doors (summer and winter), and forklifts and other equipment left running when not in use. Preventive and predictive equipment maintenance and energy conservation are critical to cleaning room efficiency.
There is no universal abrasive, and the choice of the proper abrasive material can play a big part in grinding effectiveness. The primary abrasive minerals used in foundry applications--silicon carbide, aluminum oxide, zirconium and man-made ceramics-all react differently with different metals. Each individual cleaning room should do extensive testing to determine the best material for their product mix. The choice of abrasive material is based on several factors:
* the type of material being removed. Abrasive grain minerals react differently with different metals and must be customized for the particular use. In addition to grain minerals, the backing material on abrasive belts and the hardness of abrasive wheels are important and also should be customized for the particular application. Table 1 shows which coated abrasive belts are best choices for grinding different cast metals;
* how much metal must be removed? Is the grinding room removing large riser connections requiring a fast metal removal rate or just light parting-line flash?;
* abrasive material cost. The real issue is cost per casting. A more expensive abrasive material may be a more cost efficient solution;
* the existing cleaning room equipment limits the choice of abrasive materials. For example, ceramic abrasive grinding belts excel at high-pressure applications and can remove a lot of metal quickly. However, they may be cost prohibitive if the current equipment does not apply sufficient pressure to maximize their cutting potential.
Capital Improvements and Improved Processes
Finally, the cleaning room should he evaluated for capital equipment and process improvements. Automation such as robotics and grinding cabinets increase production and reduce labor, but can provide additional benefits as well. Automation improves grinding consistency, accuracy and can hold tighter tolerances that can be hard to achieve in manual operations.
Consistently applied higher force fractures abrasive mineral grains more effectively for shaper abrasives, faster cutting, less loading and reduced heat--creating more efficiency and longer abrasive life. Although typically considered only for high-volume operations, newer equipment includes advanced computer programs useful for a variety of part sizes and configurations that make automation attractive even to jobbing foundries. Several technologies have been used with success in foundry cleaning room applications:
* high volume shotblast equipment including conveyorized cabinet blasts and tumble blast units;
* trim presses. A good choice for high volume casting operations, a trim press can remove gating and parting lines in a single operation, consolidating cutting, grinding and even hand-working functions. Figure 4 shows a ductile iron casting where the gate connection and parting line is removed in a trim press operation. Multi-station trim machines can remove material from a variety of angles and planes;
* cabinet grinding units. Typically, the casting is placed in a fixture and put into an enclosed cabinet where several grinding and cutting units address both the casting's exterior and interior surfaces. Several recent case studies have demonstrated the value of these finishing stations and the considerable efficiency improvements as the units produce more parts with fewer cleaning room personnel;
* robotics. Robotics is used in many material removal operations and excels at repetitive motion applications. Beyond the actual grinding functions, robot applications can include part movements such as loading castings into fixtures for cutting, blasting, grinding or other functions.
As the industry continues to change and profitability becomes increasingly more difficult to maintain, improvements in cleaning room-efficiency, with the attending reduction in labor, material costs and improved casting flow may prove to be vital to the survival of many metalcasting operations.
Table 1 Coated Abrasive Recommendations Abrasive Type Metal Aluminum Oxide Zirconia-Alumina Ceramic-Alumina Cast Iron 3 1 * 2 * Ductile Iron 3 1 * 2 * Carbon Steel 3/2 2 1 Stainless Steel 3 1 2 Specialty Steels 3 2 1 Aluminum 2 * 1 * 2 * Brass/Bronze 2 * 1 * 3 Copper 2 * 1 * 3 1--Most Effective; 2--Good; 3--Not Recommended. * test product
For More In formation
"Considerations for a More Efficient Cleaning Room," N. Luther, MODERN CASTING, January 2001, p.29-31.
"Advances in Coated Abrasives Boost Cleaning Room Options," S. T. Robison and D.C. Cowden, MODERN CASTING, January 1997, p.40-42.
About the Author
Steve Robison is the technical director at AFS, and has been with the department for 7 yrs, dealing mainly with nonferrous casting. Terrance Wilson is the manager of quality assurance for Hickman, Williams & Co., Plymouth, Michigan.
|Printer friendly Cite/link Email Feedback|
|Date:||Jan 1, 2003|
|Previous Article:||U.S. casting shipments expected to increase 6.3% in '03. (Cover Story: AFS 2003 Metalcasting Forecast).|
|Next Article:||What causes electromagnetic pump clogging problems?|