Mold maintenance costs

At our molders, low-volume or special items included pre-colored materials, abrasive compounds, and purchased or consigned components. At the one participant where pre-colored material was an issue, the per-pound material activity cost for pre-colored material was almost triple that for white or black material. We also found that abrasive compounds caused accelerated mold deterioration and higher mold maintenance costs at two of our sites. Finally, purchased components generally required more purchasing and quality control per dollar purchased than compounds and, at one site, the storage and handling of customer-consigned components cost the company close to 30,000 per year. 

FiGURE 5.51 Mold maintenance costs, which should be considered in the parts price... 

If a self-threading screw can be substituted, it will not only appreciably decrease mold maintenance and mold cost but most likely, with proper type selection, also give better holding power. A screw that has a thin thread with relatively deep flights can give high holding power. If the screw or plastic is preheated... 

The crest (tip) of the stud should be designed so that it is slightly larger than a standard size ejector pin if this is not the case, this portion of the mold not only becomes more expensive to produce but also the cost of mold maintenance will increase. Thin ejector pins break fairly easily and frequently, and their replacement is easier and less costly if they do not have to be specially made. 

Use standard mold parts and accessories wherever possible. Many molds, approximately 70%, are now designed around standardized components as this can speed up the drafting process (the standardized components may be held in a computerized system) and, their use can also reduce mold costs - both production costs and, maintenance costs. The range of components now offered by some companies e.g. DME, Hasco, is now very impressive with items such as the following now being standard ... 

For the basic compression, transfer, and injection molding processes, a wide variety of mold types may be considered. Decisions as to the optimum type will often be based on the production volume anticipated and the allowable final part cost, including mold maintenance and amortization costs and hourly cost rates for molding machine and labor. 

There is another method for producing internal threads which are too rigid to be stripped off a mold. That involves a core mechanism which collapses. Such collapsing cores are patented and there is an added cost for this mechanism. Molds utilizing these cores cycle nearly as fast as stripper plate molds and the mechanisms require a moderate amount of additional space. However, these molds are reported to have higher maintenance costs than the other types of molds and are generally thought of as a solution for applications with lower production quantities. 

Maintenance cost It is estimated that the initial cost of mold construction is about 20% of the cost of the mold. Another 40% of the cost is scheduled maintenance, and the other 40% is repair due to breakdowns. 

The surface hardness and the hardness depth determine the wear. If large or vast quantities are to be produced, all forming parts should be hardened. Although an increased effort is put into the production of molds, the maintenance costs can be reduced. This applies equally to the surface quality of the surfaces that are moving against each other. 

From 5% to 30% scrap must be ground, mixed with virgin and recycled—increasing equipment investment and maintenance cost to 15%, also causes a variation in bulk factor in raw material resulting in instability of process. No scrap normally with proper tool and controlled shop efficiency. All bottles are completely finished In mold. Scrap comes from start-up and errors in color mix. Re-run scrap does not affect process materially. 

Another consideration in raising the mold temperature is the longevity of the mold itself It has been dem-onstratedl" that operating the mold at extreme temperatures, even in the absence of thermal degradation of the plastic, affect the mold life and maintenance costs detrimentally. The balance of cycle time reduction and cost increase is unfavorable, especially for resins such as fluoropolymers that require high temperatures. 

Date P. 0. No. No. of Parts Run Description of Repair/Maintenance Cost Mold Shop... 

Table 11.2 shows the mechanical properties of natural (plant) and synthetic fibers [18]. Natural fibers are non abrasive towards mixing and molding equipment. This can contribute to significant equipment maintenance cost reductions. The elementary fibers are bound together by a pectin interphase. This interphase is much stronger than the interphase between the technical fibers [39]. Natural fibers are safe to handle and the working conditions are better when compared to synthetic reinforces, such as glass fibers. 

Cost breakdown of a high production mold or die is approximately as follows Material cost used to about 12 to 20%, design about 5 to 10%, mold building hours about 40 to 60%, and profit at about 5 to 10%. In general they are very expensive with the major cost principally in machine building labor. The proper choice of materials of construction for their different parts is paramount to quality, performance, and longevity of a mold/die. Add good machinability of component metal parts, material which will accept the desired finish (polished, textured, etc.), ability to transfer heat rapidly and evenly, capability of sustained production without constant maintenance, etc. 

As 1n any economic study certain assumptions must be made. It 1s not the Intent of this paper to analyze cost factors 1n fine detail, but rather to examine and compare the major direct cost contributors 1n molding large plastic parts by these major process techniques. These direct cost factors are productivity, raw materials, process energy, tooling, flxturlng, hourly labor and capital. Indirect costs that are based on these direct cost Items are not considered 1n this study. Such Indirect Items Include supervision, maintenance, general plant overhead, Insurance, taxes and building depreciation. 

Many of the organic binders are hot setting and therefore require heating to cure. Hot molds not only add hazards and complicate pollution control problems but add economical problems related to increased use of energy and increased equipment, maintenance and operation costs. 

When compared to the reciprocating-screw IMM, the advantages of the two-stage IMM include (1) consistent melt quality, (2) ram action in the accumulator that provides high injection pressure very fast, (3) very accurate shot-size control, (4) product clarity, and (5) easily molded very thin-walled parts. Its disadvantages include higher equipment cost and increased maintenance. See injection molding, micro-. 

---