injection molding cost sheet
The operations to be applied are determined by the estimator only after he has thoroughly inspected the piece. It is quite helpful if he knows the purpose or application of the item inasmuch as limitations often govern the type of finishing to be used. In the example given, for instance, it might be impractical to sand the flat surface to remove the fin, due to the fact that the depth tolerances given were very close. Under such circumstances the piece would have to be hand filed and hence involve a higher rate of cost. These facts have to be known prior to the submission of a quotation.
Next on the sheet is punching, and this operation is for piercing out two holes in the bottom of the base. A possible alternative in finishing the injection molding plastic would be the use of a kick press. If the quantities warranted it, jigs and punches could be made to remove the side flash and punch the holes in one operation. Any such finishing however would not guarantee the clean cut exterior edge obtained by sanding. Packing might have been included with the final inspecting but where liners or special wrapping is necessary it is poor economy to attempt to combine the two.
Having analyzed the estimated cost plastic molding components and seen how the prime factory cost was obtained; the only remaining features are the addition of percentages for sales and administrative expense, and any profit that can be included. The application of these factors is nothing more than an arithmetical operation once the percentages have become definitely ascertained. We have, then arrived at the selling price and it is this figure which is quoted to the customer. Before taking up the matter of overhead and the other variables let us first make certain observations in need of further explanation. We note for instance that no provision was made in the estimate for the expense of engineering and designing. The cost of transportation does not appear on the sheet, and furthermore the pressing rate does not seem to include fatigue, time out for breakdowns, or any other contingencies.
Moreover, how was the weight of the piece in pounds per thousand obtained? Even though these questions might appear to be somewhat elementary in substance they must be thoroughly understood before proceeding further.
So far as engineering time is concerned, this is usually considered either as part of overhead or administrative expense and therefore requires no separate identification. Transportation costs are very often included as separate charge for each item based on average shipping weights, but as a rule this element of cost is also considered as part of the fixed charges. If prices are quoted as F. O. B. point of origin there becomes no need for inclusion of trucking charges, and if the quotation is given on the basis of F. O. B. destination the cost involved can be appended to the selling price after it has been determined.
In any molding plant provision has to be made for fatigue, breakdowns, accidents, and other contingencies and hence time should include this factor. For instance, in the example given, three minutes were allotted for the cycle time. This means that the job should be done normally in about two and three quarter minutes, leaving fifteen seconds in every three minutes for reserve. While a quarter of a minute should be ample, it is impossible to accurately estimate the exact amount of time. The cost records will give the actual cycle time used after the job has been completed, or if a check-up is made during the run, the information can be obtained prior to acceptance of another order. Therefore, it can be seen that the amount of cycle time given in the estimate should exceed, if anything, the performance expected.
Ordinarily, the pressman operates more than one press at a time, and very often is able to efficiently handle three. Hence the reason for including the proposed press set-up on the estimate sheet. Some concerns enter the total time for the two or three presses and divide by the number used to determine the unit time per press. It is advantageous to have jobs of similar cycle time next to each other for it enables the operator to attain aw efficient stride and leaves 110 waste time while either mold is curing.
The weight given in the estimate was obtained by figuring the volume of the molded plastic part in cubic inches and then converting this to the number of pounds per thousand. Very often a sample is given instead of the print and if so the weight can be obtained directly and converted into the number of pounds per thousand. A good point to remember is that the weight of a piece in grams multiplied by 2.2 will give the desired weight in pounds per thousand.