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Elements of automating tool control.

Tool control should be as important as inventory control. Tooling is part of a company's assets; its availability impacts ability to meet production schedules. Unfortunately, tool control doesn't exist in many manufacturing companies.

Companies with diverse products can benefit greatly from planning tool procurement by computer. Justifying an automated system, however, varies by company. Basic considerations include system and tool costs, availability of substitutes and materials for in-plant toolmaking, production deadlines, and lead time to make or buy tools or fixtures.

For companies that already have automated inventory control, the expense of adding tool control usually is minimal. Any of the following can help justify automating tool control:

* When tool control (reorder activity, status checking, etc) requires more than one full-time person.

* When stockouts of certain tools could stop production.

* When certain tools made from unusual or scarce materials are subject to long lead times and unreliable supply.

* When tooling costs are as much as 20 percent of the material cost of the product manufactured, or 20 percent of annual production purchases.

* When unavailable tools continually cause late production starts and less than 95-percent on-time schedule completion.

Costs and benefits

System costs should be weighed against costs of production delays, late deliveries, and lot splitting caused by unavailable tooling. the primary benefits of automated systems are improved tool availability and productivity. If tooling is available when needed, work can begin on time and is more likely tobe produced on schedule.

Tool control can enhance manufacturing performance to a degree unmatched by other techniques. Specifically, better ool planning can reduce inventory, late shipments, overtime, and premiums for rush deliveries. Tool planning also can improve operating efficiency.

Tool control can be accomplished by automated reorder point or MRP systems for control of both noncritical and crictical tooling. In production environments, MRP users have documented benefits of 95-percent on-time schedule performance, 10- to 20-percent reductions in inventory investment, reduced purchase costs, and improved capacity utilization. These benefits also can be realized with tool control.

Dealing with noncritical tooling

Inexpensive, readily available standard tools wih limited life enerally are categorized as noncritical. Most companies include noncritical tooling with operating supplies, along with paper clips, pencils, etc. Control for such tools is typically a card-based inventory system.

If noncritical tool availability creates production problems, an automated tool-control system can help. Recording issue and receipt transactions at a computer terminal is faster than writing on a card, and availability checking can be accomplished in a fraction of the time required to search cards or physically count items.

Reorders are triggered automatically when a transaction reduces inventory to the order point. Using MRP system to control noncritical tool inventories usually isn't practical or cost-effective.

The reorder point system requires basic data that includes inventory status (usually updated daily) and quantities on order (either from a supplier or produced in-house). Figure 1 shows a typical file structure and lists key data elements.

A standard reorder point report format provides tool number, description, balance on hand, quantity on order, and reorder quantity. Many systems also print material requisitions, purchase orders, and tool manufacturing orders when the reorder point is reached. If the master file includes cost data, an inventory valuation report can be generated.

Exploiting MRP

Critical tooling is categorized as capital or perishable tooling. Capital tools are unique, custom-made tools and dies with a significant useful life (e.g., a mold for producing castings). Because capital tools are regarded as a one-time investment for their single application life, theyaren't inventoried or controlled beyond tracking their storage location.

Perishable tooling refers to tools used in continuous operations and replaced frequently during a production run. An automated control system is recommended here. control is critical because of the costs incurred when such tools are unavailable. An automated system must coordinate availability with master production and shop schedules as well as plan requirements.

If tool life for an application tends to be unpredictable, a shrinkage factor to compensate for loss can be applied in determining future requirements. Overall, perishable tooling requires more careful planning and control than is possible with a simple reorder point system. Thus perishable tool control should be intergrated with a plant's MRP system.

To time phase tool planning, the MRP system calculates a projected inventory balance by substracting item demand from on-hand inventory, then adding scheduled receipts. The calculation is made regularly for a given number of future periods (usually weeks). When the projected available balance is negative for a period, the system recommends that an order be placed in an earlier slot to avoid a stockout.

A time-phased tool-control system particularly is useful for planning, scheduling, and reschduling critical tooling to support dynamic production schedules. If tool requirements can be derived from the short-term production schedule, the system can change requirements as the schedule changes, and it can recommend tool schedule changes synchronized with requirements.

A time-phased system requires all the information necessaryfor a reorder point system, plus a product structure or bill of materials (BOM) file. The BOM provides the means to connect the tool and production schedules by defining the relationship of products and the tools used to produce them.

A peg, or requirements, fileis used to store the requirements schedule for each part. These two files enable the system to provide tool "where-used" information and show tool requirements. This integration of tooling into the product structure is preferable toseparate bills or sketchy information included in routing files. Basic system file structure and data elements are shown in Figure 2.

The time-phased MRP system offers extensive query and reporting capabilities; its primary function is generating the requirements planning report.

Master file and requirements file data can be displayed for reference on the same report. Item availabilityis planned for as muchas a year (or more) into the future. Therefore, tool purchases or manufacture can be planned, and requirement for cash, machine capacity, and labor can be projected.

The planning report can be used to simulate proposed production schedule changes. Projections of tool availability for a new production schedule enable the planner to warm management when tooling is a limiting factor in schedule revision.

Handling bum tool orders

Ordinarily, inventory issued to production is treated as a component of a finished product. Unlike raw materials, however, tooling used to make parts can still have useful life after the job is complete. When tools are issued for production, a tool replenishment order may be released. If these tools can be reused, they are returned to inventory, and the new tool order becomes unnecessary.

In one technique, standard MRP logic recommends cancelling or rescheduling such orders. In other planning systems, use of multiple inventory locations avoids this situation. The following example describes a method of preventing invalid planning messages.

Tool requirements are calculated from the production schedule and displayed on the requirements planning report for each tool (see planned requirements column, Figure 3). When an order for production parts is released, tool requirements become an allocation (see allocations column, Figure 4), which is relieved when tooling is issued to the order.

Essentially, demand for the tool is unchanged; the allocations and requirements columns equal the original requirements. Maintaining this balance prevents release of unnecessary tool orders.

When material is issued to begin work on the job, the tool is assigned and transferred to an alternate location of column, Figure 4, shows a quantity of five. Thus, total demand across the planning horizon is unchanged, as is total inventory.

Issued tools that wear out and are discarded are removed from the alternative location's inventory, and MRP reduces the allocation to the work order. No new requirements are added. Demand and inventory are equally reduced at the same time, leaving tool availability status unchanged (see Figure 5), thus preventing invalid planning messages.

When the job is complete, any unissued tools can be returned to the main inventory. Excess allocation quantities from unissued tools are eliminated when the production order is closed. In the situation described, the total on hand and main stock-room quantities are now equal, and allocations and alternate locations columns are blank.

System development

Numerous software packages can perform the tool planning and control functions; however, no commercial system focuses strictly on tool control. Before a software package is selected and tailored for tool control, a company must define minimum data requirements of expected tool inventory size, number of items to be controlled, amount of time and effort (i.e., employee resources) that can be committed, and extent of rescheduling activity required to synchronize production schedules with available capacity.

In most cases, reorder point inventory control is adequate. But, if continual (e.g., weekly) rescheduling is needed to synchronize tool availability with production schedules, or if tool manufacturing must compete for capacity in the work center, MRP is recommended.

The technique determines the required software, which in turn dictates the hardware. Because the reorder point technique uses much simpler file structures and processing logic than MRP, it requires less storage and internal memory.

A microcomputer can easily perform reorder point calculations for a small population of parts (say, up to 3000). Micros, however, aren't always practical for MRP because extensive interaction between system files and large memory capacity often is required.

Hardware and software selection decisions are made easier when a company already has a control system. Most companies use computerized inventory control, thus they already have the fundamental software. An existing order point or MRP system might meet all requirements for tool control without overloading the hardware.

Can CAD help?

Some companies now design tooling with CAD. In many cases, a CAD system can be programmed to produce a tooling item master and product structure. This reduces installation effort for a tool requirements planning system by eliminating manual creation of the database.

An additional CAD enhancement enables direct input of a newly designed tool to the planning system by means of a standard communications protocol.

A time-phased tool planning and control system must be integrated into the overall manufacturing control system. A standalone tool-control system virtually is useless, especially in companies that have implemented closed-loop manufacturing resource planning. Without proper integration into production planning and scheduling, tool control can't be achieved.
COPYRIGHT 1985 Nelson Publishing
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Copyright 1985 Gale, Cengage Learning. All rights reserved.

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Author:Erhorn, Craig R.
Publication:Tooling & Production
Date:Apr 1, 1985
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