Considerations for a More Efficient Cleaning Operation.
As limited capital resources are divided, casting cleaning and finishing operations generally have been on the short end of the stick. Despite the availability of up-to-date material handling systems, effective process flow methods and new equipment technologies, the advancement of the cleaning room has lagged behind other areas. As new technologies in melting, molding and core production have outpaced the cleaning and finishing room, the highest labor content in any given foundry remains in the effort to clean, finish and ship castings.
If cleaning and finishing room labor represents 40-50% of a foundry's total labor, it's a good indicator that labor content and in-process inventories are costing the plant far more than is actually necessary.
Casting cleaning operations are those functions necessary to prepare the casting for shipment and are summarized as those tasks that:
* remove molding and core sand and/ or other materials that can adhere to the casting;
* remove runners, gates, risers, flash, vent pins, chaplets and other metal projections from the casting surface that are not a functional part of the casting.
It's also important to remember that cleaning operations add nothing to the physical strength, shape or usefulness of the casting. Cleaning's entire purpose is to present a casting that is acceptable to the customer.
An efficient cleaning operation would clean, finish and prepare the casting for shipment within 24 hr of being produced, with some castings readied for shipment the same day. This article presents ideas for foundries to consider in a cleaning room modernization program, including techniques to reduce labor, inventories and delivery times.
Things to "shoot for" in a casting cleaning operation include a flexible handling system with minimum casting handling, low in-process casting inventories, a straight-through casting process flow, and a clean and pleasant work environment. The key to achieving efficient cleaning is to match your cleaning process rate to that delivered by molding.
Foundries that produce a large variety of casting sizes, weights and configurations require a high degree of process flexibility, a maximum utilization of process equipment and the highest manpower efficiency possible. While a seamless handling and cleaning flow is ideal, it requires a process with the capability of cleaning castings efficiently at high-or low-volume rates.
When several different-size castings are produced at different rates simultaneously in molding, the requirement to design and install cleaning cells or lines to clean and finish these castings simultaneously must be available.
An examination of the major concepts employed for casting cleaning and finishing operations is listed below.
Keep Castings Moving
Casting flow technologies fall into two major methods--batch and continuous processing.
Despite its limitations, batch processing is utilized to provide flexibility in the sequence of operations required for cleaning and finishing the casting. This method typically "schedules" casting cleaning operations from an inventory of castings maintained or stored between molding and cleaning operations. Inventories result from the higher casting production rates of the molding system than the cleaning and finishing department is capable of keeping pace with. Besides the obvious high in-process inventories, some of the disadvantages of this method are that it:
* requires more casting handling and labor content;
* makes the establishment of work times difficult;
* extends the time needed to prepare the casting for shipment;
* makes it difficult to track scrap causes due to the length of time between molding and cleaning the castings;
* can be inconsistent in the sequence of operations;
* requires more floor space.
While this processing type provides greater process flexibility by allowing each batch of castings to be moved freely through any sequence of operations, this concept should be practiced only with lowest volume castings.
On the other hand, continuous casting handling systems transfer all castings directly to a molding shakeout, a casting cooling cycle, into a continuous blastcleaning unit and, finally, into a finishing process flow cell. This method keeps the casting moving through all work stations and equipment without stopping, and provides an effective and efficient system. This scenario requires continuously operating cleaning cells and/or lines, as well as cleaning capacity and scheduling that is commensurate with the rate of molding.
The continuous flow process is more efficient and requires the process to be matched to the needs of the casting. It will:
* reduce casting handling;
* reduce operator fatigue;
* lower the task time at each work station to process the same volume of castings (50% labor reduction possible);
* reduce in-process inventory of castings and eliminate casting batches at each work station;
* establishes a flow pattern (first-in, first-out) to and from each work station and a consistent and predictable work pace;
* allows cellular concepts (square, straight line, circular, rectangle or U-shaped) to be applied;
* significantly reduce casting delivery times.
Cleaning efficiency in medium to highvolume casting production foundries requires a scheduling consideration if cleaning operation efficiencies are to be achieved. When the casting handling system keeps the casting moving into and through the cleaning and finishing operations at a paced rate, the production rate remains high with less cleaning room labor. The surge maintained between molding and cleaning takes the form of high and unnecessary casting inventories waiting to be cleaned and shipped to the customer.
Process Equipment/Work Stations
The selection of process equipment and location of work stations required for cleaning and processing castings should include:
* casting configuration, size and weight;
* type of metal;
* volume of castings to be processed in a given time. The most efficient method is accomplished by balancing casting cleaning schedules to mold production rates;
* sequence of operations required;
* area and configuration of the building available for casting processing;
* labor costs and availability;
* capital investment available for automatic handling and cleaning equipment.
The physical flow of castings in cleaning operations is established by a well-planned sequence of operations. The location of work stations and equipment reduces casting handling, cleaning process time and labor. Good planning eliminates extra handling, backtracking and bottlenecks in the movement of castings, while also providing a cleaner work environment and lower in-process inventories. A variety of castings may require specific cleaning cells/lines to process castings of different sizes, weights and/or configurations.
Some castings may require special handling, especially during shotblasting and transferring in some conveyor systems to prevent damage to the casting during the handling process. Separate process cells/lines with specific equipment for a small variety of castings may be more efficient and can improve casting quality.
Minimal Casting Handling
The movement of castings from molding through shakeout, casting cooling and directly into a cleaning process can be implemented to reduce handling. Effective sand removal of the casting at shakeout is important because the casting will cool faster, excessive sand will not be carried into the shotblast machine and the casting will be cleaner to handle. Sand that must be removed from the casting in the shotblast operation increases wear on the shotblast wheel blades and liners and increases the maintenance cost of the shotblast. Sand remaining on the casting also generates dust in the processing work area. The cleaning process is most effective when the casting is delivered to the first operation in a temperature range of 150F (65C).
The first operation (automatic or manual) should remove all runners, risers, feeders, vent pins and flash, including flash over capped holes to internal cavities. This operation should take place near the entrance of the cleaning room process area. When metal is removed from the casting at different locations in the process, an increase in material handling occurs. At a 50% yield factor, for example, 30 tons of castings shipped will generate 30 tons of return metal that must be transported back to the melt department. The removal of all metal returns from the casting in one location on the cell or line promotes easier and better housekeeping practices.
The second operation usually is shotblasting (in aluminum castings, however, this may be the last operation). Ferrous castings are usually shotblasted as early as possible to provide a casting that is clean to manually handle at each work station. When a continuous shotblast is employed, castings can be automatically loaded and unloaded. This type of operation reduces manual handling compared to a tumble blast or cabinet-designed shotblast machine.
Typically, the third operation is grinding, an operation that typically requires 30-40% of the cleaning room labor. While automatic grinding machines are often considered cost-prohibitive for foundries producing a variety of jobs, the last decade's new grinder designs have provided greater flexibility for foundries with higher volumes, affording them a grinding labor reduction.
In the last decade the use of abrasive belts forgrinding castings has increased.
The advantages include:
* high metal removal rates;
* the wheel diameter does not require adjustment for wheel wear;
* cooler cutting;
* safer operations than abrasive grinding wheels.
Cutoff wheels are the fastest and most economical method of cutting materials in the cleaning room. Unlike most grinding wheels that abrade the metal surface of the casting, cutoff wheels actually cut metallic materials.
In addition to the need for up-to-date process flow to efficiently move and handle castings, effective process control systems are required in all foundry manufacturing areas if casting costs are to be maintained in a competitive market.
Some equipment can be designed for special applications and may generate ideas when planning to upgrade or modernize a future casting cleaning facility. Some of the equipment designed to do repetitive operations, inspection or sorting operations for high-volume or special castings may be installed to reduce manning and improve quality. These include:
* automatic systems for riser, vent pins and flash removal;
* trim presses for automatic flash removal;
* internal cavity-cleaning machines;
* automatic machines with electronic measuring systems (inspection and coordinate measuring) at high production rates;
* machines with high-integrity, computer-vision inspection system;
* robot applications in casting handling, sorting and cell cleaning operations;
* ultra-high-pressure water jet cutting and cleaning applications;
* automatic sonic checking and testing machines.
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|Date:||Jan 1, 2001|
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