Elements of Plastic Mold Tooling Costs
Besides the time in hours required to build tools for a given plastics part, the items of materials, maintenance and amortization of the tools enter the estimate. Overhead costs for keeping the toolroom also must be included.
The cost of the steel for a mold is not usually very much in proportion to the labor involved. But it should be estimated, usually on a weight basis, although stock parts such as plates, and pins may be purchased machined to size. Especially is it important to look into the steels cost if a new type of mold is contemplated, or is one with which the shop has had no previous experience.
Many times the estimator will be able to use a standard, previously established figure for the material cost of a mold, provided the mold is something like a number of molds which have been produced in his plant. It isn’t necessary to figure the cost of every screw every time a mold or fixture is estimated, but it is necessary to know that the new tooling is nearly the same as tooling previously built and analyzed for material costs.
Estimating Requires Records
Estimating the cost of tool maintenance requires some records and experience. Most molding plants have a procedure for entering costs of maintenance on the books of the accounting department, with costs charged against each tool.
It is often difficult to follow a tool through the books over a period of several months or years to arrive at typical maintenance costs. However, it is good practice for the estimator to select typical tools and follow them carefully and keep track of the nature of the repairs, the hours of actual running time, and the cost in hours for the repairs. In a few months a good basis for maintenance estimating may be established.
These data may then be applied with good judgment to new estimates. If the contract molder in China produces tooling for a plastics part and then charges the cost to his customer, he should not figure tool amortization in the cost of the finished pieces.
However, if he undertakes to sell a finished part for a given price and underwrites the tooling cost, he must include a charge for the tooling upon each piece delivered. Such amortization is usually computed on a basis of expected number of parts during the tool life, or expected total number of parts, whichever is smaller.
If, for example, 100,000 moldings are expected to be ordered from a mold, and the cost of the mold is estimated to be $1000, a charge of $10 per thousand pieces should be added for mold amortization. This amounts to one cent per molding, and this much is important in a piece, for example, which sells for 20 cents.
The mold amortization is 5 percent of the selling price of the molded part. Here it is not difficult to foresee disastrous results if mold amortization charges are ignored. It is not uncommon for orders of 20,000,000 parts to be received for a seasonal item such as an automobile trim part. One mold cavity, of course, would not produce at the required rate. Perhaps 100 cavities would be required, and each one then would be pro-rated 200,000 moldings. Some of the cavities might last long enough to produce twice that number, but probably half of the cavities would not last long enough for 100, 000 moldings. So the mold amortization estimate requires careful study. How many times the mold must be rebuilt during the run must be estimated, and charges must be added accordingly.
Suppose a manufacturer of refrigerators plans to build a special lot of 10,000 units during a season and a molded door handle is required which is intended to be changed when the next season’s models are designed. The mold will not be worn out when the run is finished, but it will have ended its useful life except for service parts production.
The amortization should be computed by absorbing the total mold cost in 10,000 pieces and it might be as high as 10 cents per piece. Usually the portion of overhead costs known as factory expense is computed by the accountants. The various factory departments may incur different portions of the factory expense according to accounting estimates and records of how much it costs to supervise and maintain them. Tool rooms usually average 90 percent to 110 percent factory cost factor. This means that 90 percent of the direct labor cost, for example, should be added to the eestimate of a tool. If the wage schedule calls for $1.50 per hour for the tool maker, and the time estimate is 100 hours, the direct labor cost is $150. The factory expense is 90 percent additional, or $135. Some mold shops charge a flat hourly rate which includes direct labor and factory cost. This is satisfactory if the mold shop is a unit by itself and not a part of a large organization.
The accounting system for the single unit is relatively simple compared with the system which must be devised to care for 20 to 100 departments. The engineering costs of plastics tooling are appreciable. In most systems of cost accounting, the engineering, planning, supervision, and other socalled office departments are considered to be a part of the general burden of the plant. For this reason, the cost of planning the tooling and manufacturing operations is not included directly as such in the estimate. It is satisfactory to cover engineering costs in overhead expense items, if only an ordinary amount of engineering time is required.
Ordinarily 10 to 20 hours of engineering serves to lay out from 100 to 500 hours of tool room work. If the estimator foresees that a certain job will require more than the usual amount of engineering, he may make an allowance for it in the estimate. In some such cases he may lose the job but he may avoid considerable loss at the same time.