How to achieve 'balanced' production in your foundry.

Like putting together puzzle pieces, balanced facility planning brings all foundry manufacturing processes together to reveal how to most effectively deliver your net casting requirement.

All foundries today must provide for variable production. While a foundry's capacity might be defined as "low volume," these same metalcasters will undoubtedly be called on to produce large volume runs and/or cast special products at various quantities. This criteria increases the demand to use processes and equipment that not only provide flexibility, but also must accomodate low cost tooling.

A considerable amount of time is necessary to determine the actual needs of each process area. Separating the desires and wants of these areas into the foundry's actual needs is never an easy task.

A net casting requirement should be developed against the foundry's gross capabilities, which is the first step in planning a balanced facility. The basic premise behind a balanced facility is to correlate each foundry process area to produce materials at a commensurate rate with other processes.

To illustrate the objective of such a system, consider the coreroom. Its mission is to only produce cores at a rate needed to meet the mold line, not more and not less. While this may require adding core machines, tooling and/or operators to meet the molding department's needs, it will reduce core inventory and storage, provide less core handling (and thus, less breakage), improve quality due to quick use, and reduce the number of cores that are never used. Under this system, core machines are only operated when molding operates.

This article, based on an AFS Plant Engineering Committee Panel from last spring's Casting Congress, considers the criteria necessary to apply to manufacturing equipment in each of the major foundry production areas. The analysis of production rates and machine capabilities required to produce a net quantity of castings through all foundry processes without bottlenecks and/or unnecessary inventories is necessary.

Basic Criteria

To illustrate how balanced facility planning works in the foundry industry, this article will detail the analysis of a particular modernization on a single gray iron casting at a green sand foundry. The basic criteria to illustrate this procedure (which is used in the flow chart on p. 41) is:

Net good castings                       1,000,000
Net casting weight (lb)                         5
Castings/mold                                   4
Net core weight/casting (lb)                    4
Cores/mold                                      4
Yield (%)                                      60
Sand weight (lb)/mold                   300 (277)
Sand process                           Green Sand
Metal type                              Gray Iron
Hours/year                                   1920
Casting scrap                                  5%
Machine shop scrap                             2%

Balanced facility planning is well described like a financial balance sheet, in which the balance of net worth is calculated bysubtracting liabilities from assets. The foundry facility planning analogy of this concept is: Gross Capabilities - Losses = Net Shipments.

The concept can apply to a new plant, a major expansion program or a departmental capacity increase. The plan should include a process flow chart of the desired changes to the existing plant or a new chart for a new foundry, which may then be used to overlay the desired changes onto the existing capacity network.

This procedure serves to:

* establish and communicate specific project objectives to all involved employees;

* point out and eliminate anyweak links in the present and future expansions;

* provide a useful planning tool for future changes.

Molding

The first production area to consider is molding. The criteria states the requirement of 1,000,000 castings, which provides the molding equipment design criteria. To establish the molding capacity, one must consider all areas of losses - scrap, broken molds, equipment downtime, etc. - to determine the gross number of castings and equipment utilization factors needed to produce and ship a net quantity of 1,000,000 castings.

Allowances for casting losses must include the following:

* machine shop scrap;

* unpoured molds;

* molding line downtime;

* foundry scrap, which must identify all causes, including sand holes, gas porosity, slag, misruns, blows, ranouts, etc.

Allowances of 2% for machine shop scrap, 5% foundry scrap and 1% breakage require the gross production of 1,084,963 castings.

It is necessary to evaluate the patterns to obtain the number of castings per mold. In this scenario, four castings can be produced from each mold.

The total molds required make it necessary to evaluate all of the functions that will interfere with scheduling. These include:

* equipment malfunctions;

* broken molds;

* break time for employees;

* scheduled pattern changes;

* clean-up time at the end of the shift;

* tooling changes.

Reviewing the 2% broken mold allowance and the 85% maximum equipment utilization that can be expected, the foundry needs a minimum mold count of 170 molds/hr to meet the net casting requirement.

Therefore, whether you're using existing molding equipment or purchasing a new molding system, it is necessary to have a capability of 170-175 molds/hr. For ease of calculations in this article, this figure will be rounded to 175 molds/hr.

It is vital that this molding capability be designed into any modernization plan because molding establishes all other capacity requirements for sand, core and cleaning operations. Metal, sand and core demands must maintain the mold rate of 175 molds/hr.

A modernization program often targets one or two major production areas such as melting and molding for the installation of state-of-the-art technology, leaving the core and cleaning operations running below the designed molding process capabilities. Extra labor is needed to produce a quality casting on schedule or these areas fail to deliver to the molding system at the required volumes. This results in loss of molds/castings, which require overtime to produce the net casting requirement.

Sand Volume

The sand volume required to maintain the molding rate with quality, consistent sand is often overlooked. Improper planning in this area results in either undermulled sand or lost molding productivity.

It is necessary to determine the weight of molding sand per mold. The basic design criteria called for a mold weighing 300 lb. This weight represents a solid cake of sand with no deduction for the casting cavity. In this case, 277 lb of molding sand was used to calculate the total amount of sand required per mold.

A 15% allowance for spill sand and a 1% sand loss are recorded into the volume of sand to be mulled per hour. Therefore, 28.8 tons of sand must be delivered to meet molding's requirements of 175 molds/hr. To determine the total operating time (utilization) of the muller, consider the following:

* equipment malfunctions of the total sand handling and mulling system;

* break time for employees;

* clean-up time at the end of the shift;

* scheduled pattern changes;

* equipment downtime of molding and melting system.

A 95% utilization factor was applied to determine that a muller capability of 30.3 tph is needed to supply sand at the 175 molds/hr rate.

Melting Capacity

To determine the melting capability necessary to ship 1,000,000 castings/year, the following evaluations must be considered to establish the minimum melting capacity required. Using the given criteria, the melt capacity is calculated from the following:

While the casting weight/mold is equal to 20 lb, the metal weight per mold factoring a 60% yield is 33.33 lb. Factoring the total metal to molding required for 175 molds plus 3% spill, the total amount of iron needed for molding becomes 3.0 tph (6013 lb).

Factoring this figure with 3% melt losses, 3.1 tph (6189 lb/hr) of charge materials are needed. The utilization of melting equipment must include a design capacity that includes time for the following:

* efficient and accurate charging;

* metal chemistry adjustments;

* metal temperature adjustments;

* skim and slagging procedures;

* tap and pouring;

* refractory repairs.

Therefore, a melting department utilization rate of 90% dictates the need for a melt rate of 3.44 tph (6888 lb/hr).

Coremaking

Many foundries fail to properly plan the capability of their core production facilities. The up-to-date technology available in core machines and processes used in the foundry industry provides the opportunity to produce cores at a different schedule than the molding/melting department.

Producing cores off-schedule of molding reduces the number of core machines required to maintain core production with molding rates. Other problems, however, can result. These include:

* a larger inventory of cores;

* increases in core handling;

* increases in core breakage;

* excessive storage, causing scrap due to moisture pick-up.

With four cores/mold, an initial figure of 700 cores/hr is needed. Factoring in 2% breakage in the drag and 5% in mold core handling, 752 cores/hr are needed.

In core process allowances, another 5% breakage factor is considered for both process handling and at the core machine, thus requiring a production total of 835 cores/hr. An 85% machine utilization will require 983 cores/hr.

In this example of four cores to a mold, a typical blow (cycle time) of 45 sec. can produce 320 cores/hr. Thus, to produce 983 cores/hr, 3.07 core machines are required.

Cleaning

A balanced facility plan for the cleaning room operations must be designed for the maximum number of castings to be produced and delivered to the cleaning room at any given time. The basic criteria establishes a volume of castings at 175 molds to produce 700 castings/hr.

An allowance of 1% for broken castings has been made, however, it may be difficult to determine where that breakage may occur, which makes it necessary to assume it will be possible to receive the full 700 castings at the start of the cleaning process.

The quantity of 700 castings/hr must be used to determine the capacity of all equipment and machines necessary to process the castings and may include:

* casting cooling system;

* shotblast machine;

* automatic/manual grinders;

* automatic/manual definners;

* automatic/manual runner/riser removal;

* automatic/manual quality inspection equipment;

* heat treat furnaces;

* casting handling conveyors;

* painting facilities;

* casting stamping or marking equipment.

The utilization allowance for the total cleaning facility is established at 80%. Therefore, to calculate the capacity for all equipment used to process castings, each operation must be capable of handling 875 castings/hr. To improve that capability to a utilization of 85% or 90%, a good casting handling system with automatic loading/unloading of equipment is needed.

It isn't unusual for finishing operations to correct deficiencies on castings, which result from poor control in other manufacturing areas in the foundry. These added operations increase the manpower requirements and decrease equipment utilizations.

The range of casting volumes entering the cleaning room may vary considerably. In this example, only a single pattern with four castings was considered. In normal operations, several patterns may be used with the number of castings per pattern varying from 1-10.

At 175 molds/hr, castings entering the cleaning room could vary from 175-1750 castings/hr. The process equipment must still have the capability to process 1750 with a designed flexibility to remove manpower on the lower volume production days.

The casting process capability may be established below the maximum volume capabilities of the molding system. When this occurs, castings must be off-loaded and placed back into the cleaning process later. This approach, however, increases casting handling, in-process inventories, floor space and delivery time.

Fitting It Together

Balanced facility planning indicates the necessary equipment capacities that must be designed into each production area to produce the net casting requirements with the necessary allowances (losses) considered in each of those areas.

Since the molding system is the key guide to a production rate, metal, sand and cores must be supplied at the designed molding rate. If this doesn't occur, it is impossible to achieve the average mold rate required to produce the net castings on a scheduled 1920-hr work year. Equipment capabilities are an important consideration when a balanced facility is in the planning stage.

While this article details the balanced facility planning of just one casting, jobbing foundries can apply this procedure to their operations by calculating the net casting requirements of all their current and future customers, and work backward from the balanced facility chart.